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3. nervous system part 1

The nervous system has three main functions: sensory, integration, and motor. It is divided into the central nervous system (CNS; brain and spinal cord) and peripheral nervous system (PNS). The CNS contains neurons and neuroglia. Neuroglia provide support and protection for neurons. There are two types of neurons - sensory neurons transmit sensory information to the CNS, and motor neurons transmit signals from the CNS to effectors like muscles. Neurons communicate via electrical or chemical synapses using neurotransmitters like acetylcholine, GABA, glutamate, and catecholamines.

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11 ChapterChapter :8:8 NervousNervous SystemSystem PartPart :1:1 Presented by: Prof.Mirza Anwar BaigPresented by: Prof.Mirza Anwar Baig Anjuman-I-Islam's Kalsekar Technical CampusAnjuman-I-Islam's Kalsekar Technical Campus School of Pharmacy,New Pavel,NaviSchool of Pharmacy,New Pavel,Navi Mumbai,MaharashtraMumbai,Maharashtra 11
2 The Nervous system has three major functions:  Sensory – monitors internal & external environment through presence of receptors  Integration – interpretation of sensory information (information processing); complex (higher order) functions  Motor – response to information processed through stimulation of effectors  muscle contraction  glandular secretion
3 Basic Organization • Sensory Input triggered by stimuli – conduction of signals to processing center • Integration – interpretation of sensory signals within processing centers • Motor output – conduction of signals to effector cells (i.e. muscles, gland cells) sensory receptor (sensory input)  integration  (motor output)  effector
4 • Brain WHAT PARTS DO YOU KNOW THAT ARE IN THE NERVOUS SYSTEM? • Spinal Cord • Peripheral Nerves
5 Two Anatomical Divisions  Central nervous system (CNS)  Brain  Spinal cord  Peripheral nervous system (PNS)  All the neural tissue outside CNS  Afferent division (sensory input)  Efferent division (motor output)  Somatic nervous system  Autonomic nervous system General Organization of the nervous system
6 General Organization of the nervous system Brain & spinal cord
7 Histology of neural tissue Two types of neural cells in the nervous system:  Neurons - For processing, transfer, and storage of information  Neuroglia – For support, regulation & protection of neurons
8 Neuroglia (glial cells) CNS neuroglia: Astrocytes: Induces blood-brain barrier Oligodendrocytes: Produce myelin Microglia : Phagocytes in CNS Ependymal cells : Line brain ventricles and central canal of spinal cord also part of structure that makes CSF PNS neuroglia: Schwann cells : Produce myelin Satellite cells : Support neurons in PNS
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12 Astrocytes • create supportive framework for neurons • create “blood-brain barrier” • monitor & regulate interstitial fluid surrounding neurons • secrete chemicals for embryological neuron formation • stimulate the formation of scar tissue secondary to CNS injury
13 Oligodendrocytes • create myelin sheath around axons of neurons in the CNS. Myelinated axons transmit impulses faster than unmyelinated axons Microglia • “brain macrophages” • phagocytize cellular wastes & pathogens
14 Ependymal cells • line ventricles of brain & central canal of spinal cord • produce, monitor & help circulate CSF (cerebrospinal fluid)
15 Schwann cells • surround all axons of neurons in the PNS creating a neurilemma around them. Neurilemma allows for potential regeneration of damaged axons • creates myelin sheath around most axons of PNS Satellite cells • support groups of cell bodies of neurons within ganglia of the PNS
16 Neuron structure
17 •Most axons of the nervous system are surrounded by a myelin sheath (myelinated axons) •The presence of myelin speeds up the transmission of action potentials along the axon •Myelin will get laid down in segments (internodes) along the axon, leaving unmyelinated gaps known as “nodes of Ranvier” •Regions of the nervous system containing groupings of myelinated axons make up the “white matter” •“gray matter” is mainly comprised of groups of neuron cell bodies, dendrites & synapses (connections between neurons) of Ranvier
18 Classification of neurons 1. Structural classification based on number of processes coming off of the cell body:
19 Anaxonic neurons • no anatomical clues to determine axons from dendrites • functions unknown Multipolar neuron multiple dendrites & single axon most common type
20 Bipolar neuron • two processes coming off cell body – one dendrite & one axon • only found in eye, ear & nose Unipolar (pseudounipolar) neuron • single process coming off cell body, giving rise to dendrites (at one end) & axon (making up rest of process)
21 2. Functional classification based on type of information & direction of information transmission: Sensory (afferent) neurons – •transmit sensory information from receptors of PNS towards the CNS •most sensory neurons are unipolar, a few are bipolar Motor (efferent) neurons – transmit motor information from the CNS to effectors (muscles/glands/adipose tissue) in the periphery of the body all are multipolar Association (interneurons) – transmit information between neurons within the CNS; analyze inputs, coordinate outputs are the most common type of neuron (20 billion) are all multipolar
22 Conduction across synapses Most synapses within the nervous system are chemical synapses, & involve the release of a neurotransmitter In order for neural control to occur, “information” must not only be conducted along nerve cells, but must also be transferred from one nerve cell to another across a synapse.
23 Neuronal Pools
24 Anatomical organization of neurons Neurons of the nervous system tend to group together into organized bundles The axons of neurons are bundled together to form nerves in the PNS & tracts/pathways in the CNS. Most axons are myelinated so these structures will be part of “white matter” The cell bodies of neurons are clustered together into ganglia in the PNS & nuclei/centers in the CNS. These are unmyelinated structures and will be part of “gray matter”
25 Anatomical structure of Nerves Fig. 14.6
26 Generation - Conduction of Neural Impulses • Dependent on concentration gradients of Na+ & K+ – Na+ 14x greater outside – K+ 28x greater inside • Membrane permeability – lipid bilayer bars passage of K+ & Na+ ions – protein channels and pumps regulate passage of K+ & Na+ • at rest more K+ move out than Na+ move in • K+ ions diffuse out leave behind excess negative charge • Sodium-potassium pump – Na+ out - K+ in (more Na+ out than K+ in – contributes to loss of (+)
27 Overview of Neural Impulse
28 • Maintenance of negative charge within neuron – resting membrane potential about -70 millivolts • Dissolved organic molecules [negative charge] kept inside • Na+ - K+ balance
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30 Neurotransmissions:
31 • Stimulus causes opening of Na+ gates & closing of K+ gates - • Threshold [~ +30 mV] – all - or - nothing response • Action potential localized electrical event • Changes permeability of region immediately ahead – changes in K+ & Na+ gates – domino effect – propagation of signal • Intensity of stimuli (i.e. pinch vs. punch) = number of neurons firing • Speed on impulse based on diameter of axon & amount of myelination
32 Neurons Communicate at Synapses Electrical [no synapse] – common in heart & digestive tract - maintains steady, rhythmic contraction – All cells in effector contain receptor proteins for neurotransmitters Chemical - skeletal muscles & CNS – presence of gap (SYNAPTIC CLEFT) which prevents action potential from moving directly to receiving neuron – ACTION POTENTIAL (electrical) converted to CHEMICAL SIGNAL at synapse (molecules of neurotransmitter) then generate ACTION POTENTIAL (electrical) in receiving neuron
33 Overview of Transmission of Nerve Impulse Action potential 1.synaptic knob 2.opening of Ca+ channels 3.neurotransmitter vesicles fuse with membrane 4.release of neurotransmitter into synaptic cleft 5.binding of neurotransmitter to protein receptor molecules on receiving neuron membrane 6.opening of ion channels 7.triggering of new action potential • Neurotransmitter is broken down by enzymes & ion channels close -- effect brief and precise
34 Nerve Impulse • Presynaptic neuron • Vesicles • [Calcium channels] • Synaptic cleft • Postsynaptic neuron • Neurotransmitter receptor
35 Nerve Impulse • Action potential 1.synaptic knob 2. opening of Ca+ channels 3.neurotransmitter vesicles fuse with membrane 4.release of neurotransmitter into synaptic cleft Ca2+
36 Nerve Impulse • Action potential neurotransmitter vesicles fuse with membrane release of neurotransmitter into synaptic cleft
37 • Action potential binding of neurotransmitter to protein receptor molecules on receiving neuron membrane opening of sodium channels triggering of new action potential
38 Classification of Nerve Fibers • Axons can be classified into three major groups based on the amount of myelination, their diameters, and their propagation speeds: 1. A fibers : The largest-diameter axons (5 – 20 mm) and are myelinated. A fibers have a brief absolute refractory period. and conduct nerve impulses (action potentials) at speeds of 12 to 130 m/sec (27–280 mi/hr). Example: axons of sensory neurons for touch ,pressure etc 2. B fibers: having axons with diameters of 2 – 3 mm. Like A fibers,B fibers are myelinated and exhibit saltatory conduction at speeds up to 15 m/sec (32 mi/hr). B fibers have a somewhat longer absolute refractory period than A fibers. B fibers con- duct sensory nerve impulses from the viscera to the brain and spinal cord. 3. C fibres: Smallest-diameter axons (0.5–1.5 mm) and unmyelinated. Nerve impulse propagation 0.5 to 2 m/sec (1 – 4 mi/hr),longest absolute refractory periods. These unmyeli- nated axons conduct some sensory impulses for pain, touch,pressure, heat, and cold from the skin, and pain impulses from the viscera.
39 Neurotransmitters • Catecholamine Neurotransmitters – Derived from amino acid tyrosine • Dopamine [Parkinson’s], norepinephrine, epinephrine • Amine Neurotransmitters – acetylcholine, histamine, serotonin • Amino Acids – aspartic acid, GABA, glutamic acid, glycine • Polypeptides – Include many which also function as hormones – endorphins
40 Neurotransmitters: • About 100 substances are either known or suspected neurotrans-mitters. • Some neurotransmitters bind to their receptors and act quickly ,Others act more slowly via second-messenger systems to influence chemical reactions inside cells. • The result of either process can be excitation or inhibition of postsynaptic neurons. Many neuro- transmitters are also hormones released into the bloodstream by endocrine cells in organs throughout the body. • Within the brain, certain neurons, called neurosecretory cells, also secrete hormones. • Neurotransmitters can be divided into two classes based on size: small-molecule neurotransmitters and neuropeptides • The small-molecule neurotransmitters include acetylcholine, amino acids, biogenic amines, ATP and other purines, and nitric oxide.
41 Ion channels for neurotransmitters
42 1. Acetylcholine: • The acetylcholine (ACh) is released by many PNS neurons and by some CNS neu-rons. • ACh is an excitatory neurotransmitter at some synapses,such as the neuromuscular junction, where the binding of ACh to ionotropic receptors opens cation channels. • It is also an inhibitory neurotransmitter at other synapses, where it binds to metabotropic receptors coupled to G proteins that open K channels. • For example, ACh slows heart rate at inhibitory synapses made by parasympathetic neu-rons of the vagus (X) nerve. • The enzyme acetylcholinesterase (AChE) inactivates ACh by splitting it into acetate and choline fragments.
43 2. Amino Acids: • These neurotransmitters are present in the CNS. • Glutamate (glutamic acid) and aspartate (aspartic acid) have powerful excitatory effects. • Most excitatory neurons in the CNS and perhaps half of the synapses in the brain communicate via glutamate. • At some glutamate synapses, binding of the neuro- transmitter to ionotropic receptors opens cation channels. • The consequent inflow of cations (mainly Na ions) produces an EPSP. Inactivation of glutamate occurs via reuptake. • Glutamate transporters actively transport glutamate back into the synaptic end bulbs and neighboring neuroglia
44 Excitotoxicity: • A high level of glutamate in the interstitial fluid of the CNS causes excitotoxicity—destruction of neurons through prolonged activation of excitatory synaptic transmission. • The most common cause of excitotoxicity is oxygen deprivation of the brain due to ischemia (inadequate blood flow), as happens during a stroke. • Lack of oxygen causes the glu-tamate transporters to fail, and glutamate accumulates in the interstitial spaces between neurons and glia, literally stimulating the neurons to death. • Clinical trials are underway to see if antiglutamate drugs administered after a stroke can offer some protection from excitotoxicity.
45 Gamma aminobutyric acid: • GABA and glycine are important inhibitory neurotransmitters. • At many synapses, the binding of GABA to ionotropic receptors opens Cl ion channels. • GABA is found only in the CNS, where it is the most common inhibitory neurotransmitter. • As many as one-third of all brain synapses use GABA. • Antianxiety drugs such as diazepam enhance the action of GABA. • Like GABA, the binding of glycine to ionotropic receptors opens Cl channels. • About half of the inhibitory synapses in the spinal cord use the amino acid glycine; the rest use GABA.
46 3. Catecholeamine (Biogenic Amines) • Norepinephrine, dopamine, and epinephrine are classified Catecholamines, are synthesized from the amino acid tyrosine. • Inactivation of catecholamines occurs via reuptake into synaptic end bulbs. • Then they are either recycled back into the synaptic vesicles or destroyed by the enzymes. • The two enzymes that break down catecholamines are catechol- O-methyltrans- ferase or COMT, and monoamine oxidase or MAO.
47 • Certain amino acids are modified and decarboxylated to produce biogenic amines. • Those that are prevalent in the nervous system include norepinephrine, epineph-rine, dopamine, and serotonin. • Most biogenic amines bind to metabotropic receptors • Biogenic amines may cause either excitation or inhibition. a. Norepinephrine (NE) : NE plays roles in arousal (awakening from deep sleep), dreaming, and regulating mood. • A smaller number of neurons in the brain use epinephrine as a neurotransmitter. • Both epinephrine and norepinephrine also serve as hormones. • Cells of the adrenal medulla, the inner portion of the adrenal gland, release them into the blood.
48 b. Dopamine: • Brain neurons containing the neurotransmitter dopamine (DA) are active during emotional responses, addictive behaviors, and pleasurable experiences. • In addition, dopamine-releasing neurons help regulate skeletal muscle tone and some aspects of movement due to contraction of skeletal muscles. • The muscular stiffness that occurs in Parkinson disease is due to degeneration of neurons that release dopamine. One form of schizophrenia is due to accumulation of excess dopamine. c.Serotonin: • Also known as 5-hydroxytryptamine (5-HT). • Concentrated in the neurons in a part of the brain called the raphe nucleus. • It is thought to be involved in sensory perception,temperature regulation, control of mood, appetite, and the induc-tion of sleep.
49 ATP and Other Purines: • It is an excitatory neurotransmitter in both the CNS and the PNS. • Most of the synaptic vesicles that contain ATP also contain another neurotransmitter. • In the PNS, ATP and norepinephrine are released together from some sympathetic neurons; some parasympathetic neurons release ATP and acetyl-choline in the same vesicles. Nitric Oxide: • The simple gas nitric oxide (NO) is an important neurotransmitter that has widespread effects throughout the body. • NO contains a single nitrogen atom, in contrast to nitrous oxide (N 2 O), or laughing gas, which has two nitrogen atoms. • N 2 O is sometimes used as an anesthetic during dental procedures.
50 Neuropeptides: • Neurotransmitters consisting of 3 to 40 amino acids linked by peptide bonds called neuropeptides , are numerous and widespread in both the CNS and the PNS. • Neuropeptides bind to metabotropic receptors and have excita-tory or inhibitory actions, depending on the type of metabotropic receptor at the synapse. • Neuropeptides are formed in the neuron cell body, packaged into vesicles, and transported to axon terminals. • Besides their role as neurotransmitters, many neuropeptides serve as hormones that regulate physiological responses.
51 Role of Neuropeptides:
52 Modifying the effect of neurotransmitters: Substances naturally present in the body as well as drugs and toxins can modify the effects of neurotransmitters in several ways: 1. Neurotransmitter synthesis can be stimulated or inhibited. For in-stance, many patients with Parkinson disease receive benefit from the drug L -dopa because it is a precursor of dopamine. It boosts dopamine production in affected brain areas. 2. Neurotransmitter release can be enhanced or blocked. Amphetamines promote release of dopamine and norepinephrine. & Botulinum toxin causes paralysis by blocking release of acetylcholine from somatic motor neurons. 3. The neurotransmitter receptors can be activated or blocked. Isoproterenol (Isuprel ® ) is a powerful agonist of epinephrine and norepinephrine.
53 Regeneration & repair of nervous tissue: Throughout your life, nervous system exhibits plasticity. At the level of individual neurons, the changes that can occur include the germination of new dendrites, synthesis of new proteins, and changes in synaptic contacts with other neurons. Despite plasticity, mammalian neurons have very limited powers of regeneration, the capability to replicate or repair themselves. In the PNS, damage to dendrites and myelinated axons may be repaired if the cell body remains intact and if the Schwann cells that produce myelination remain active. In the CNS, little or no repair of damage to neurons occurs. Even when the cell body remains intact, a severed axon cannot be repaired or regrown.
54 Neurogenesis in CNS: • Neurogenesis—the birth of new neurons from undifferenti- • ated stem cells—occurs regularly in some animals. For example, new neurons appear and disappear every year in some songbirds. Until recently, the dogma in humans and other primates was “no new neurons” in the adult brain. • Epidermal growth factor (EGF) stimulated cells taken from the brains of adult mice to proliferate into both neurons and astrocytes. • In 1998, scientists dis-covered that significant numbers of new neurons do arise in the adult human hippocampus only , an area of the brain that is crucial for learning .
55 Reasons for lack of regenration of neurons in CNS: Factors responsible for lack of regenration: 1) inhibitory influences from neuroglia, particularly oligoden- drocytes. 2) absence of growth-stimulating signals during fetal development. 3) Axons in the CNS are myeli-nated by oligodendrocytes rather than Schwann cells, and this CNS myelin is one of the factors inhibiting regeneration of neurons. 4) Also, after axonal damage, nearby astrocytes proliferate rapidly, forming a type of scar tissue that acts as a physical barrier to regeneration. Thus, injury of the brain or spinal cord usually is permanent.
56 ANATOMY OF CENTRAL NERVOUS SYSTEM
57 Parts of Brain: 1. Cerebrum-largest part of brain. responsible for reasoning, thought, memory, speech, sensation, etc. • Divided into two halves. • Further divided into lobes; occipital, parietal, temporal and frontal.
58 2. Cerebellum- responsible for muscle coordination 3. Brain stem- most basic functions; respiration, swallowing, blood pressure. 4.Lower part (medulla oblongata) is continuous with spinal cord
59 5. Spinal cord- begins at foramen magnum and ends at second lumbar vertebrae Contains both afferent (to the brain) and efferent (motor neurons- away from the brain)
60 Coverings: Both the brain and spinal cord are covered by a membrane system called the meninges,lying between the skull and the brain and between the vertebrae and the spinal cord. • Named from outside inwards they are: 1)Dura mater 2)Arachnoid mater 3)Pia mater The dura and arachnoid maters are separated by a potential space, the subdural space. The arachnoid and pia maters are separated by the subarachnoid space, containing cerebrospinal fluid.
61 Coverings and Blood Brain Barrier:
62 Cerebrospinal fluid (CSF) • Ependymal cells form cerebrospinal fluid from blood plasma by filtration and secretion. • Secreted into each ventricle of the brain by choroid plexuses (vascular areas where there is a proliferation of blood vessels surrounded by ependymal cells in the lining of ventricle walls.) • CSF is a clear, slightly alkaline fluid with a specific gravity of 1.005, consisting of: – water – mineral salts – glucose – plasma proteins: small amounts of albumin and globulin – creatinine – urea – a few leukocytes.
63 Formation of CSF:
64 Flow of CSF:
65 Ventricles 1.Filled with CSF (cerebrospinal fluid) 2.Lined by ependymal cells (these cells lining the choroid plexus make the CSF) 3.Continuous with each other and central canal of spinal cord
66 Functions of cerebrospinal fluid 1. It supports and protects the brain and spinal cord. 2. It maintains a uniform pressure around these delicate structures. 3. It acts as a cushion and shock absorber between the brain and the cranial bones. 4. It keeps the brain and spinal cord moist and there may be interchange of substances between CSF and nerve cells, such as nutrients and waste products.
67 Peripheral nervous system • Somatic system – 12 pairs cranial nerves – 31 pairs spinal nerves • Autonomic – Sympathetic • Fight or flight – Parasympathetic
68 Brain: The brain constitutes about one- fiftieth of the body weight and lies within the cranial cavity. The parts are 1. cerebrum 2. midbrain 3. pons 4. medulla oblongata 5. cerebellum. 6. the brain stem
69 Blood supply to the brain: • The circulus arteriosus and its contributing arteries play a vital role in maintaining a constant supply of oxygen and glucose. • The brain receives about 15% of the cardiac output, approx 750 ml of blood/minute. • Autoregulation maintain blood flow to the brain constant by adjusting the diameter (about 65-140 mmHg) with changes occurring only outside these limits.
70 Cerebrum This is the largest part of the brain and it occupies the anterior and middle cranial fossae. It is divided by a deep cleft, the longitudinal cerebral fis-sure, into right and left cerebral hemispheres, each containing one of the lateral ventricles. Deep within the brain the hemispheres are connected by a mass of white matter (nerve fibres) called the corpus callosum. The superficial (peripheral) part of the cerebrum is composed of nerve cell bodies or grey matter, forming the cerebral cortex, and the deeper layers consist of nerve fibres or white matter.
71 Surface anatomy Gyri (plural of gyrus) Elevated ridges Entire surface Grooves separate gyri A sulcus is a shallow groove (plural, sulci) Deeper grooves are fissures
72 Gyri (plural of gyrus) Elevated ridges Entire surface Grooves separate gyri A sulcus is a shallow groove (plural, sulci) Deeper grooves are fissures
73  Lateral sulcus separates temporal lobe from parietal lobe  Parieto-occipital sulcus divides occipital and parietal lobes (not seen from outside)  Transverse cerebral fissure separates cerebral hemispheres from cerebellum
74 Cerberal cortex: The cerebral cortex shows many infoldings or furrows of varying depth. The exposed areas of the folds are the gyri or convolutions and these are separated by sulci or fissures. These convolutions greatly increase the surface area of the cerebrum. For descriptive purposes each hemisphere of the cerebrum is divided into lobes which take the names of the bones of the cranium under which they lie: frontal, parietal,temporal and occipital. The boundaries of the lobes are marked by deep sulci (fissures). These are the central, lateral and parieto-occipital sulci .
75 Interior of the cerebrum: The surface of the cerebral cortex is composed of grey matter (nerve cell bodies). Within the cerebrum the lobes are connected by masses of nerve fibres, or tracts, which make up the white matter of the brain. The afferent and efferent fibres linking the different parts of the brain and spinal cord are as follows. • Association (arcuate) fibres • Commissural fibres • Projection fibres
76 Afferent and efferent fibres: • Association (arcuate) fibres connect different parts of a cerebral hemisphere by extending from one gyrus to another, some of which are adjacent and some distant. • Commissural fibres connect corresponding areas of the two cerebral hemispheres; the largest and most important commissure is the corpus callosum. • Projection fibres connect the cerebral cortex with grey matter of lower parts of the brain and with the spinal cord, e.g. the internal capsule ( lies deep within the brain between the basal nuclei (ganglia) and the thalamus. Many nerve impulses passing to and from the cerebral cerebral cortex are carried by fibres that form the internal capsule. Motor fibres within the internal capsule form the pyramidal tracts (corticospinal tracts) that cross over (decussate) at the medulla oblongata.
77 Functions of cerbrum (simplified) Back of brain: perception Top of brain: movement Front of brain: thinking
78 Functional areas of the cerebrum 1. Motor areas of the cerebrum a.The premotor area. This lies in the frontal lobe immediately anterior to the motor area. Motor speech (Broca's) area which controls the movements necessary for speech. It is dominant in the left hemisphere in right-handed people and vice versa. b.The frontal area. This extends anteriorly from the premotor area to include the remainder of the frontal lobe.
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80 Sensory areas of the cerebrum The postcentral (sensory) area. Ø This is the area behind the central sulcus. Ø Sensations of pain, temperature, pressure and touch, knowledge of muscular movement and the position of joints are perceived. The sensory area of the right hemisphere receives impulses from the left side of the body and vice versa.
81 The auditory (hearing) area. This lies immediately below the lateral sulcus within the temporal lobe. (8th cranial nerves). The olfactory (smell) area. This lies deep within the temporal lobe where impulses from the nose via the olfactory nerves (1st cranial nerves) are received and interpreted. The taste area. This is thought to lie just above the lateral sulcus in the deep layers of the sensory area. (8th cranial nerves) The visual area. This lies behind the parieto-occipital sulcus and includes the greater part of the occipital lobe. (2nd cranial nerves)
82 Association Areas  Tie together different kinds of sensory input  Associate new input with memories  Is to be renamed “higher-order processing“ areas Different areas 1. Premotor area: 2. Prefrontal area: 3. Wernicke’s area (speech area): 4. Pareito-occipital temporal area:
83 Motor areas of cerebrum
84 Other areas of the cerebrum Deep within the cerebral hemispheres there are groups of cell bodies called nuclei (called ganglia) which act as relay stations where impulses are passed from one neurone to the next in a chain. Important masses of grey matter include: • basal nuclei • thalamus • hypothalamus.
85 Basal nuclei. These are areas of grey matter, lying deep within the cerebral hemispheres, with connections to the cerebral cortex and thalamus. The basal nuclei form part of the extrapyramidal tracts and are thought to be involved in initiating muscle tone in slow and coordi-nated activities. If control is inadequate or absent, move-ments are jerky, clumsy and uncoordinated.
86 Thalamus. The thalamus consists of two masses of nerve cells and fibres situated within the cerebral hemispheres just below the corpus callosum, one on each side of the third ventricle. Sensory input from the skin, viscera and special sense organs is transmitted to the thalamus before redistribution to the cerebrum. Hypothalamus. • The hypothalamus is composed of a number of groups of nerve cells. It is situated below and in front of the thalamus, immediately above the pituitary gland. • The hypothalamus is linked to the posterior lobe of the pituitary gland by nerve fibres and to the anterior lobe by a complex system of blood vessels. • Through these connections, the hypothalamus controls the output of hormones from both lobes of the gland.
87 Other functions of hypothalamus: autonomic nervous system appetite and satiety thirst and water balance body temperature emotional reactions, e.g. pleasure, fear, rage sexual behaviour including mating and child rearing biological clocks or circadian rhythms, e.g. sleeping and waking cycles, body temperature and secretion of some hormones.
88 Brain stem 1. Midbrain: The midbrain is the area of the brain situated around the cerebral aqueduct between the cerebrum above and the pons below. It consists of groups of cell bodies and nerve fibres (tracts) which connect the cerebrum with lower parts of the brain and with the spinal cord. The cell bod-ies act as relay stations for the ascending and descending nerve fibres.
89 2. Pons The pons is situated in front of the cerebellum, below the midbrain and above the medulla oblongata. It consists mainly of nerve fibres which form a bridge between the two hemispheres of the cerebellum, and of fibres passing between the higher levels of the brain and the spinal cord. There are groups of cells within the pons which act as relay stations and some of these are associated with the cranial nerves. The anatomical structure of the pons differs from that of the cerebrum in that the cell bodies (grey matter) lie deeply and the nerve fibres are on the surface.
90 3.Medulla oblongata The medulla oblongata extends from the pons above and is continuous with the spinal cord below. It is about 2.5 cm long and it lies just within the cranium above the foramen magnum. Its anterior and posterior surfaces are marked by central fissures. The outer aspect is composed of white matter which passes between the brain and the spinal cord, and grey matter lies centrally. Some cells con-stitute relay stations for sensory nerves passing from the spinal cord to the cerebrum. The vital centres, consisting of groups of cells associated with autonomic reflex activity, lie in its deeper structure. These are the: cardiac centre respiratory centre vasomotor centre reflex centres of vomiting, coughing, sneezing and swallowing.
91 Other functions of medulla oblongata: 1. Decussation (crossing) of the pyramids. In the medulla motor nerves descending from the motor area in the cerebrum to the spinal cord in the pyramidal (corticospinal) tracts cross from one side to the other. These tracts are the main pathway for impulses to skeletal (voluntary) muscles. 2. Sensory decussation. Some of the sensory nerves ascending to the cerebrum from the spinal cord cross from one side to the other in the medulla. 3. Others decussate at lower levels, i.e. in the spinal cord.
92 4. The cardiovascular centre : controls the rate and force of cardiac contraction. sympathetic and parasympathetic nerve fibres originating in the medulla pass to the heart. Sympathetic stimulation increases the rate and force of the heartbeat and parasympathetic stimulation has the opposite effect. 5. The respiratory centre: controls the rate and depth of respiration. From this centre, nerve impulses pass to the phrenic and intercostal nerves which stimulate contraction of the diaphragm and intercostal muscles,thus initiating inspiration. The respiratory centre is stimulated by excess carbon dioxide and, to a lesser extent, by deficiency of oxygen in its blood supply and by nerve impulses
93 6. The vasomotor centre: It controls the diameter of the blood vessels, especially the small arteries and arterioles which have a large proportion of smooth muscle fibres in their walls. Vasomotor impulses reach the blood vessels through the autonomic nervous system. Stimulation may cause either constriction or dilatation of blood vessels depending on the site. The sources of stimulation of the vasomotor centre are the arterial baroreceptors, body temperature and emotions such as sexual excitement and anger. Pain usually causes vasoconstriction although severe pain may cause vasodilatation, a fall in blood pressure and fainting.
94 7. Reflex centres: • When irritating substances are present in the stomach or respiratory tract, nerve impulses pass to the medulla oblongata, stimulating the reflex centres which initiate the reflex actions of vomiting, coughing and sneezing to expel the irritant.
95 Reticular formation: The reticular formation is involved in: Coordination of skeletal muscle activity associated with voluntary motor movement and the maintenance of balance Coordination of activity controlled by the autonomic nervous system, e.g. cardiovascular, respiratory and gastrointestinal activity. Selective awareness that functions through the reticular activating system (RAS) which selectively blocks or passes sensory information to the cerebral cortex, e.g. the slight sound made by a sick child moving in bed may arouse his mother but the noise of regularly passing trains may be suppressed.
96 Cerebellum: • The cerebellum is situated behind the pons and immediately below the posterior portion of the cerebrum occupying the posterior cranial fossa. • It is ovoid in shape and has two hemispheres, separated by a narrow median strip called the vermis. • Grey matter forms the surface of the cerebellum, and the white matter lies deeply.
97 CerebellumTwo major hemispheres: three lobes each Anterior Posterior Floculonodular Vermis: midline lobe connecting hemispheres Outer cortex of gray Inner branching white matter, called “arbor vitae” Separated from brain stem by 4th ventricle
98 Functions: • The cerebellum is concerned with the coordination of voluntary muscular movement, posture and balance. • Cerebellar activities are not under voluntary control. • The sensory input for these functions is derived from the muscles and joints, the eyes and the ears. • Proprioceptor impulses from the muscles and joints indicate their position in relation to the body as a whole and those impulses from the eyes and the semicircular canals in the ears provide information about the position of the head in space. • Impulses from the cerebellum influence the contraction of skeletal muscle so that balance and posture are maintained. • Damage to the cerebellum results in clumsy uncoordinated muscular movement, staggering gait and inability to carry out smooth, steady, precise movements.
99 SPINAL CODE:
100 SPINAL CORD: It is the elongated, almost cylindrical part of the central nervous system, which is suspended in the vertebral canal surrounded by the meninges and cerebrospinal fluid. It is continuous above with the medulla oblongata and extends from the upper border of the atlas to the lower border of the 1st lumbar vertebra. It is approximately 45 cm long in an adult Caucasian male, and is about the thickness of the little finger. When a specimen of cerebrospinal fluid is required it is taken from a point below the end of the cord, i.e. below the level of the 2nd lumbar vertebra (lumbar puncture). Nerves conveying impulses from the brain to the various organs and tissues descend through the spinal cord.
101 Some activities of the spinal cord are independent of the brain, i.e. spinal reflexes (through extensive neurone connections between sensory and motor neurones ). The spinal cord is incompletely divided into two equal parts, anteriorly by a short, shallow median fissure and posteriorly by a deep narrow septum, the posterior median septum. A cross-section of the spinal cord shows that it is composed of grey matter in the centre surrounded by white matter supported by neuroglia.
102 Grey matter: • The arrangement of grey matter in the spinal cord resembles the shape of the letter H, having two posterior, two anterior and two lateral columns. • The area of grey matter lying transversely is the transverse commissure and it is pierced by the central canal, an extension from the fourth ventricle, containing cerebrospinal fluid. • The cell bodies may be: • Sensory cells: which receive impulses from the periphery of the body • Lower motor neurones: which transmit impulses to the skeletal muscles •Connector neurones: linking sensory and motor neurones, at the same or different levels, which form spinal reflex arcs. • At each point where nerve impulses are passed from one neurone to another there is a synaptic cleft and a neurotransmitter
103 Posterior columns of grey matter: These are composed of cell bodies which are stimulated by sensory impulses from the periphery of the body. The nerve fibres of these cells contribute to the formation of the white matter of the cord and transmit the sensory impulses upwards to the brain. Anterior columns of grey matter These are composed of the cell bodies of the lower motor neurones which are stimulated by the axons of the upper motor neurones or by the cell bodies of connector neurones linking the anterior and posterior columns to form reflex arcs. The posterior root (spinal) ganglia are composed of cell bodies which lie just outside the spinal cord on the pathway of the sensory nerves. • All sensory nerve fibres pass through these ganglia. The only function of the cells is to promote the onward movement of nerve impulses.
104 White matter: It is arranged in three columns or tracts 1. anterior 2.posterior 3.lateral. These tracts are formed by sensory nerve fibres ascending to the brain, motor nerve fibres descending from the brain and fibres of connector neurones. Tracts are often named according to their points of origin and destination, e.g. spinothalamic, corticospinal.
105 Sensory nerve tracts (afferent or ascending) & motor nerve tracts (efferent or descending) in the spinal cord
106 Reflex arc:
107 The Stretch Reflex • A stretch reflex causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle. • This type of reflex occurs via a monosynaptic reflex arc. The reflex can occur by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron.
108 Tendon refelx:
109 Functions 1.Sensory and motor innervation of entire body inferior to the head through the spinal nerves 2.Two-way conduction pathway between the body and the brain 3.Major center for reflexes

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3. nervous system part 1

  • 1.
    11 ChapterChapter :8:8 NervousNervous SystemSystem PartPart:1:1 Presented by: Prof.Mirza Anwar BaigPresented by: Prof.Mirza Anwar Baig Anjuman-I-Islam's Kalsekar Technical CampusAnjuman-I-Islam's Kalsekar Technical Campus School of Pharmacy,New Pavel,NaviSchool of Pharmacy,New Pavel,Navi Mumbai,MaharashtraMumbai,Maharashtra 11
  • 2.
    2 The Nervous systemhas three major functions:  Sensory – monitors internal & external environment through presence of receptors  Integration – interpretation of sensory information (information processing); complex (higher order) functions  Motor – response to information processed through stimulation of effectors  muscle contraction  glandular secretion
  • 3.
    3 Basic Organization • SensoryInput triggered by stimuli – conduction of signals to processing center • Integration – interpretation of sensory signals within processing centers • Motor output – conduction of signals to effector cells (i.e. muscles, gland cells) sensory receptor (sensory input)  integration  (motor output)  effector
  • 4.
    4 • Brain WHAT PARTSDO YOU KNOW THAT ARE IN THE NERVOUS SYSTEM? • Spinal Cord • Peripheral Nerves
  • 5.
    5 Two Anatomical Divisions Central nervous system (CNS)  Brain  Spinal cord  Peripheral nervous system (PNS)  All the neural tissue outside CNS  Afferent division (sensory input)  Efferent division (motor output)  Somatic nervous system  Autonomic nervous system General Organization of the nervous system
  • 6.
    6 General Organization ofthe nervous system Brain & spinal cord
  • 7.
    7 Histology of neuraltissue Two types of neural cells in the nervous system:  Neurons - For processing, transfer, and storage of information  Neuroglia – For support, regulation & protection of neurons
  • 8.
    8 Neuroglia (glial cells) CNSneuroglia: Astrocytes: Induces blood-brain barrier Oligodendrocytes: Produce myelin Microglia : Phagocytes in CNS Ependymal cells : Line brain ventricles and central canal of spinal cord also part of structure that makes CSF PNS neuroglia: Schwann cells : Produce myelin Satellite cells : Support neurons in PNS
  • 9.
  • 10.
  • 11.
  • 12.
    12 Astrocytes • create supportive frameworkfor neurons • create “blood-brain barrier” • monitor & regulate interstitial fluid surrounding neurons • secrete chemicals for embryological neuron formation • stimulate the formation of scar tissue secondary to CNS injury
  • 13.
    13 Oligodendrocytes • create myelinsheath around axons of neurons in the CNS. Myelinated axons transmit impulses faster than unmyelinated axons Microglia • “brain macrophages” • phagocytize cellular wastes & pathogens
  • 14.
    14 Ependymal cells • lineventricles of brain & central canal of spinal cord • produce, monitor & help circulate CSF (cerebrospinal fluid)
  • 15.
    15 Schwann cells • surroundall axons of neurons in the PNS creating a neurilemma around them. Neurilemma allows for potential regeneration of damaged axons • creates myelin sheath around most axons of PNS Satellite cells • support groups of cell bodies of neurons within ganglia of the PNS
  • 16.
  • 17.
    17 •Most axons ofthe nervous system are surrounded by a myelin sheath (myelinated axons) •The presence of myelin speeds up the transmission of action potentials along the axon •Myelin will get laid down in segments (internodes) along the axon, leaving unmyelinated gaps known as “nodes of Ranvier” •Regions of the nervous system containing groupings of myelinated axons make up the “white matter” •“gray matter” is mainly comprised of groups of neuron cell bodies, dendrites & synapses (connections between neurons) of Ranvier
  • 18.
    18 Classification of neurons 1.Structural classification based on number of processes coming off of the cell body:
  • 19.
    19 Anaxonic neurons • noanatomical clues to determine axons from dendrites • functions unknown Multipolar neuron multiple dendrites & single axon most common type
  • 20.
    20 Bipolar neuron • twoprocesses coming off cell body – one dendrite & one axon • only found in eye, ear & nose Unipolar (pseudounipolar) neuron • single process coming off cell body, giving rise to dendrites (at one end) & axon (making up rest of process)
  • 21.
    21 2. Functional classificationbased on type of information & direction of information transmission: Sensory (afferent) neurons – •transmit sensory information from receptors of PNS towards the CNS •most sensory neurons are unipolar, a few are bipolar Motor (efferent) neurons – transmit motor information from the CNS to effectors (muscles/glands/adipose tissue) in the periphery of the body all are multipolar Association (interneurons) – transmit information between neurons within the CNS; analyze inputs, coordinate outputs are the most common type of neuron (20 billion) are all multipolar
  • 22.
    22 Conduction across synapses Mostsynapses within the nervous system are chemical synapses, & involve the release of a neurotransmitter In order for neural control to occur, “information” must not only be conducted along nerve cells, but must also be transferred from one nerve cell to another across a synapse.
  • 23.
  • 24.
    24 Anatomical organization ofneurons Neurons of the nervous system tend to group together into organized bundles The axons of neurons are bundled together to form nerves in the PNS & tracts/pathways in the CNS. Most axons are myelinated so these structures will be part of “white matter” The cell bodies of neurons are clustered together into ganglia in the PNS & nuclei/centers in the CNS. These are unmyelinated structures and will be part of “gray matter”
  • 25.
  • 26.
    26 Generation - Conductionof Neural Impulses • Dependent on concentration gradients of Na+ & K+ – Na+ 14x greater outside – K+ 28x greater inside • Membrane permeability – lipid bilayer bars passage of K+ & Na+ ions – protein channels and pumps regulate passage of K+ & Na+ • at rest more K+ move out than Na+ move in • K+ ions diffuse out leave behind excess negative charge • Sodium-potassium pump – Na+ out - K+ in (more Na+ out than K+ in – contributes to loss of (+)
  • 27.
  • 28.
    28 • Maintenance ofnegative charge within neuron – resting membrane potential about -70 millivolts • Dissolved organic molecules [negative charge] kept inside • Na+ - K+ balance
  • 29.
  • 30.
  • 31.
    31 • Stimulus causesopening of Na+ gates & closing of K+ gates - • Threshold [~ +30 mV] – all - or - nothing response • Action potential localized electrical event • Changes permeability of region immediately ahead – changes in K+ & Na+ gates – domino effect – propagation of signal • Intensity of stimuli (i.e. pinch vs. punch) = number of neurons firing • Speed on impulse based on diameter of axon & amount of myelination
  • 32.
    32 Neurons Communicate atSynapses Electrical [no synapse] – common in heart & digestive tract - maintains steady, rhythmic contraction – All cells in effector contain receptor proteins for neurotransmitters Chemical - skeletal muscles & CNS – presence of gap (SYNAPTIC CLEFT) which prevents action potential from moving directly to receiving neuron – ACTION POTENTIAL (electrical) converted to CHEMICAL SIGNAL at synapse (molecules of neurotransmitter) then generate ACTION POTENTIAL (electrical) in receiving neuron
  • 33.
    33 Overview of Transmissionof Nerve Impulse Action potential 1.synaptic knob 2.opening of Ca+ channels 3.neurotransmitter vesicles fuse with membrane 4.release of neurotransmitter into synaptic cleft 5.binding of neurotransmitter to protein receptor molecules on receiving neuron membrane 6.opening of ion channels 7.triggering of new action potential • Neurotransmitter is broken down by enzymes & ion channels close -- effect brief and precise
  • 34.
    34 Nerve Impulse • Presynapticneuron • Vesicles • [Calcium channels] • Synaptic cleft • Postsynaptic neuron • Neurotransmitter receptor
  • 35.
    35 Nerve Impulse • Actionpotential 1.synaptic knob 2. opening of Ca+ channels 3.neurotransmitter vesicles fuse with membrane 4.release of neurotransmitter into synaptic cleft Ca2+
  • 36.
    36 Nerve Impulse • Actionpotential neurotransmitter vesicles fuse with membrane release of neurotransmitter into synaptic cleft
  • 37.
    37 • Action potential bindingof neurotransmitter to protein receptor molecules on receiving neuron membrane opening of sodium channels triggering of new action potential
  • 38.
    38 Classification of NerveFibers • Axons can be classified into three major groups based on the amount of myelination, their diameters, and their propagation speeds: 1. A fibers : The largest-diameter axons (5 – 20 mm) and are myelinated. A fibers have a brief absolute refractory period. and conduct nerve impulses (action potentials) at speeds of 12 to 130 m/sec (27–280 mi/hr). Example: axons of sensory neurons for touch ,pressure etc 2. B fibers: having axons with diameters of 2 – 3 mm. Like A fibers,B fibers are myelinated and exhibit saltatory conduction at speeds up to 15 m/sec (32 mi/hr). B fibers have a somewhat longer absolute refractory period than A fibers. B fibers con- duct sensory nerve impulses from the viscera to the brain and spinal cord. 3. C fibres: Smallest-diameter axons (0.5–1.5 mm) and unmyelinated. Nerve impulse propagation 0.5 to 2 m/sec (1 – 4 mi/hr),longest absolute refractory periods. These unmyeli- nated axons conduct some sensory impulses for pain, touch,pressure, heat, and cold from the skin, and pain impulses from the viscera.
  • 39.
    39 Neurotransmitters • Catecholamine Neurotransmitters –Derived from amino acid tyrosine • Dopamine [Parkinson’s], norepinephrine, epinephrine • Amine Neurotransmitters – acetylcholine, histamine, serotonin • Amino Acids – aspartic acid, GABA, glutamic acid, glycine • Polypeptides – Include many which also function as hormones – endorphins
  • 40.
    40 Neurotransmitters: • About 100substances are either known or suspected neurotrans-mitters. • Some neurotransmitters bind to their receptors and act quickly ,Others act more slowly via second-messenger systems to influence chemical reactions inside cells. • The result of either process can be excitation or inhibition of postsynaptic neurons. Many neuro- transmitters are also hormones released into the bloodstream by endocrine cells in organs throughout the body. • Within the brain, certain neurons, called neurosecretory cells, also secrete hormones. • Neurotransmitters can be divided into two classes based on size: small-molecule neurotransmitters and neuropeptides • The small-molecule neurotransmitters include acetylcholine, amino acids, biogenic amines, ATP and other purines, and nitric oxide.
  • 41.
    41 Ion channels forneurotransmitters
  • 42.
    42 1. Acetylcholine: • Theacetylcholine (ACh) is released by many PNS neurons and by some CNS neu-rons. • ACh is an excitatory neurotransmitter at some synapses,such as the neuromuscular junction, where the binding of ACh to ionotropic receptors opens cation channels. • It is also an inhibitory neurotransmitter at other synapses, where it binds to metabotropic receptors coupled to G proteins that open K channels. • For example, ACh slows heart rate at inhibitory synapses made by parasympathetic neu-rons of the vagus (X) nerve. • The enzyme acetylcholinesterase (AChE) inactivates ACh by splitting it into acetate and choline fragments.
  • 43.
    43 2. Amino Acids: •These neurotransmitters are present in the CNS. • Glutamate (glutamic acid) and aspartate (aspartic acid) have powerful excitatory effects. • Most excitatory neurons in the CNS and perhaps half of the synapses in the brain communicate via glutamate. • At some glutamate synapses, binding of the neuro- transmitter to ionotropic receptors opens cation channels. • The consequent inflow of cations (mainly Na ions) produces an EPSP. Inactivation of glutamate occurs via reuptake. • Glutamate transporters actively transport glutamate back into the synaptic end bulbs and neighboring neuroglia
  • 44.
    44 Excitotoxicity: • A highlevel of glutamate in the interstitial fluid of the CNS causes excitotoxicity—destruction of neurons through prolonged activation of excitatory synaptic transmission. • The most common cause of excitotoxicity is oxygen deprivation of the brain due to ischemia (inadequate blood flow), as happens during a stroke. • Lack of oxygen causes the glu-tamate transporters to fail, and glutamate accumulates in the interstitial spaces between neurons and glia, literally stimulating the neurons to death. • Clinical trials are underway to see if antiglutamate drugs administered after a stroke can offer some protection from excitotoxicity.
  • 45.
    45 Gamma aminobutyric acid: •GABA and glycine are important inhibitory neurotransmitters. • At many synapses, the binding of GABA to ionotropic receptors opens Cl ion channels. • GABA is found only in the CNS, where it is the most common inhibitory neurotransmitter. • As many as one-third of all brain synapses use GABA. • Antianxiety drugs such as diazepam enhance the action of GABA. • Like GABA, the binding of glycine to ionotropic receptors opens Cl channels. • About half of the inhibitory synapses in the spinal cord use the amino acid glycine; the rest use GABA.
  • 46.
    46 3. Catecholeamine (BiogenicAmines) • Norepinephrine, dopamine, and epinephrine are classified Catecholamines, are synthesized from the amino acid tyrosine. • Inactivation of catecholamines occurs via reuptake into synaptic end bulbs. • Then they are either recycled back into the synaptic vesicles or destroyed by the enzymes. • The two enzymes that break down catecholamines are catechol- O-methyltrans- ferase or COMT, and monoamine oxidase or MAO.
  • 47.
    47 • Certain aminoacids are modified and decarboxylated to produce biogenic amines. • Those that are prevalent in the nervous system include norepinephrine, epineph-rine, dopamine, and serotonin. • Most biogenic amines bind to metabotropic receptors • Biogenic amines may cause either excitation or inhibition. a. Norepinephrine (NE) : NE plays roles in arousal (awakening from deep sleep), dreaming, and regulating mood. • A smaller number of neurons in the brain use epinephrine as a neurotransmitter. • Both epinephrine and norepinephrine also serve as hormones. • Cells of the adrenal medulla, the inner portion of the adrenal gland, release them into the blood.
  • 48.
    48 b. Dopamine: • Brainneurons containing the neurotransmitter dopamine (DA) are active during emotional responses, addictive behaviors, and pleasurable experiences. • In addition, dopamine-releasing neurons help regulate skeletal muscle tone and some aspects of movement due to contraction of skeletal muscles. • The muscular stiffness that occurs in Parkinson disease is due to degeneration of neurons that release dopamine. One form of schizophrenia is due to accumulation of excess dopamine. c.Serotonin: • Also known as 5-hydroxytryptamine (5-HT). • Concentrated in the neurons in a part of the brain called the raphe nucleus. • It is thought to be involved in sensory perception,temperature regulation, control of mood, appetite, and the induc-tion of sleep.
  • 49.
    49 ATP and OtherPurines: • It is an excitatory neurotransmitter in both the CNS and the PNS. • Most of the synaptic vesicles that contain ATP also contain another neurotransmitter. • In the PNS, ATP and norepinephrine are released together from some sympathetic neurons; some parasympathetic neurons release ATP and acetyl-choline in the same vesicles. Nitric Oxide: • The simple gas nitric oxide (NO) is an important neurotransmitter that has widespread effects throughout the body. • NO contains a single nitrogen atom, in contrast to nitrous oxide (N 2 O), or laughing gas, which has two nitrogen atoms. • N 2 O is sometimes used as an anesthetic during dental procedures.
  • 50.
    50 Neuropeptides: • Neurotransmitters consistingof 3 to 40 amino acids linked by peptide bonds called neuropeptides , are numerous and widespread in both the CNS and the PNS. • Neuropeptides bind to metabotropic receptors and have excita-tory or inhibitory actions, depending on the type of metabotropic receptor at the synapse. • Neuropeptides are formed in the neuron cell body, packaged into vesicles, and transported to axon terminals. • Besides their role as neurotransmitters, many neuropeptides serve as hormones that regulate physiological responses.
  • 51.
  • 52.
    52 Modifying the effectof neurotransmitters: Substances naturally present in the body as well as drugs and toxins can modify the effects of neurotransmitters in several ways: 1. Neurotransmitter synthesis can be stimulated or inhibited. For in-stance, many patients with Parkinson disease receive benefit from the drug L -dopa because it is a precursor of dopamine. It boosts dopamine production in affected brain areas. 2. Neurotransmitter release can be enhanced or blocked. Amphetamines promote release of dopamine and norepinephrine. & Botulinum toxin causes paralysis by blocking release of acetylcholine from somatic motor neurons. 3. The neurotransmitter receptors can be activated or blocked. Isoproterenol (Isuprel ® ) is a powerful agonist of epinephrine and norepinephrine.
  • 53.
    53 Regeneration & repairof nervous tissue: Throughout your life, nervous system exhibits plasticity. At the level of individual neurons, the changes that can occur include the germination of new dendrites, synthesis of new proteins, and changes in synaptic contacts with other neurons. Despite plasticity, mammalian neurons have very limited powers of regeneration, the capability to replicate or repair themselves. In the PNS, damage to dendrites and myelinated axons may be repaired if the cell body remains intact and if the Schwann cells that produce myelination remain active. In the CNS, little or no repair of damage to neurons occurs. Even when the cell body remains intact, a severed axon cannot be repaired or regrown.
  • 54.
    54 Neurogenesis in CNS: •Neurogenesis—the birth of new neurons from undifferenti- • ated stem cells—occurs regularly in some animals. For example, new neurons appear and disappear every year in some songbirds. Until recently, the dogma in humans and other primates was “no new neurons” in the adult brain. • Epidermal growth factor (EGF) stimulated cells taken from the brains of adult mice to proliferate into both neurons and astrocytes. • In 1998, scientists dis-covered that significant numbers of new neurons do arise in the adult human hippocampus only , an area of the brain that is crucial for learning .
  • 55.
    55 Reasons for lackof regenration of neurons in CNS: Factors responsible for lack of regenration: 1) inhibitory influences from neuroglia, particularly oligoden- drocytes. 2) absence of growth-stimulating signals during fetal development. 3) Axons in the CNS are myeli-nated by oligodendrocytes rather than Schwann cells, and this CNS myelin is one of the factors inhibiting regeneration of neurons. 4) Also, after axonal damage, nearby astrocytes proliferate rapidly, forming a type of scar tissue that acts as a physical barrier to regeneration. Thus, injury of the brain or spinal cord usually is permanent.
  • 56.
  • 57.
    57 Parts of Brain: 1.Cerebrum-largest part of brain. responsible for reasoning, thought, memory, speech, sensation, etc. • Divided into two halves. • Further divided into lobes; occipital, parietal, temporal and frontal.
  • 58.
    58 2. Cerebellum- responsible for musclecoordination 3. Brain stem- most basic functions; respiration, swallowing, blood pressure. 4.Lower part (medulla oblongata) is continuous with spinal cord
  • 59.
    59 5. Spinal cord- beginsat foramen magnum and ends at second lumbar vertebrae Contains both afferent (to the brain) and efferent (motor neurons- away from the brain)
  • 60.
    60 Coverings: Both the brainand spinal cord are covered by a membrane system called the meninges,lying between the skull and the brain and between the vertebrae and the spinal cord. • Named from outside inwards they are: 1)Dura mater 2)Arachnoid mater 3)Pia mater The dura and arachnoid maters are separated by a potential space, the subdural space. The arachnoid and pia maters are separated by the subarachnoid space, containing cerebrospinal fluid.
  • 61.
    61 Coverings and BloodBrain Barrier:
  • 62.
    62 Cerebrospinal fluid (CSF) •Ependymal cells form cerebrospinal fluid from blood plasma by filtration and secretion. • Secreted into each ventricle of the brain by choroid plexuses (vascular areas where there is a proliferation of blood vessels surrounded by ependymal cells in the lining of ventricle walls.) • CSF is a clear, slightly alkaline fluid with a specific gravity of 1.005, consisting of: – water – mineral salts – glucose – plasma proteins: small amounts of albumin and globulin – creatinine – urea – a few leukocytes.
  • 63.
  • 64.
  • 65.
    65 Ventricles 1.Filled with CSF(cerebrospinal fluid) 2.Lined by ependymal cells (these cells lining the choroid plexus make the CSF) 3.Continuous with each other and central canal of spinal cord
  • 66.
    66 Functions of cerebrospinalfluid 1. It supports and protects the brain and spinal cord. 2. It maintains a uniform pressure around these delicate structures. 3. It acts as a cushion and shock absorber between the brain and the cranial bones. 4. It keeps the brain and spinal cord moist and there may be interchange of substances between CSF and nerve cells, such as nutrients and waste products.
  • 67.
    67 Peripheral nervous system •Somatic system – 12 pairs cranial nerves – 31 pairs spinal nerves • Autonomic – Sympathetic • Fight or flight – Parasympathetic
  • 68.
    68 Brain: The brain constitutesabout one- fiftieth of the body weight and lies within the cranial cavity. The parts are 1. cerebrum 2. midbrain 3. pons 4. medulla oblongata 5. cerebellum. 6. the brain stem
  • 69.
    69 Blood supply tothe brain: • The circulus arteriosus and its contributing arteries play a vital role in maintaining a constant supply of oxygen and glucose. • The brain receives about 15% of the cardiac output, approx 750 ml of blood/minute. • Autoregulation maintain blood flow to the brain constant by adjusting the diameter (about 65-140 mmHg) with changes occurring only outside these limits.
  • 70.
    70 Cerebrum This is thelargest part of the brain and it occupies the anterior and middle cranial fossae. It is divided by a deep cleft, the longitudinal cerebral fis-sure, into right and left cerebral hemispheres, each containing one of the lateral ventricles. Deep within the brain the hemispheres are connected by a mass of white matter (nerve fibres) called the corpus callosum. The superficial (peripheral) part of the cerebrum is composed of nerve cell bodies or grey matter, forming the cerebral cortex, and the deeper layers consist of nerve fibres or white matter.
  • 71.
    71 Surface anatomy Gyri (pluralof gyrus) Elevated ridges Entire surface Grooves separate gyri A sulcus is a shallow groove (plural, sulci) Deeper grooves are fissures
  • 72.
    72 Gyri (plural ofgyrus) Elevated ridges Entire surface Grooves separate gyri A sulcus is a shallow groove (plural, sulci) Deeper grooves are fissures
  • 73.
    73  Lateral sulcusseparates temporal lobe from parietal lobe  Parieto-occipital sulcus divides occipital and parietal lobes (not seen from outside)  Transverse cerebral fissure separates cerebral hemispheres from cerebellum
  • 74.
    74 Cerberal cortex: The cerebralcortex shows many infoldings or furrows of varying depth. The exposed areas of the folds are the gyri or convolutions and these are separated by sulci or fissures. These convolutions greatly increase the surface area of the cerebrum. For descriptive purposes each hemisphere of the cerebrum is divided into lobes which take the names of the bones of the cranium under which they lie: frontal, parietal,temporal and occipital. The boundaries of the lobes are marked by deep sulci (fissures). These are the central, lateral and parieto-occipital sulci .
  • 75.
    75 Interior of thecerebrum: The surface of the cerebral cortex is composed of grey matter (nerve cell bodies). Within the cerebrum the lobes are connected by masses of nerve fibres, or tracts, which make up the white matter of the brain. The afferent and efferent fibres linking the different parts of the brain and spinal cord are as follows. • Association (arcuate) fibres • Commissural fibres • Projection fibres
  • 76.
    76 Afferent and efferentfibres: • Association (arcuate) fibres connect different parts of a cerebral hemisphere by extending from one gyrus to another, some of which are adjacent and some distant. • Commissural fibres connect corresponding areas of the two cerebral hemispheres; the largest and most important commissure is the corpus callosum. • Projection fibres connect the cerebral cortex with grey matter of lower parts of the brain and with the spinal cord, e.g. the internal capsule ( lies deep within the brain between the basal nuclei (ganglia) and the thalamus. Many nerve impulses passing to and from the cerebral cerebral cortex are carried by fibres that form the internal capsule. Motor fibres within the internal capsule form the pyramidal tracts (corticospinal tracts) that cross over (decussate) at the medulla oblongata.
  • 77.
    77 Functions of cerbrum(simplified) Back of brain: perception Top of brain: movement Front of brain: thinking
  • 78.
    78 Functional areas ofthe cerebrum 1. Motor areas of the cerebrum a.The premotor area. This lies in the frontal lobe immediately anterior to the motor area. Motor speech (Broca's) area which controls the movements necessary for speech. It is dominant in the left hemisphere in right-handed people and vice versa. b.The frontal area. This extends anteriorly from the premotor area to include the remainder of the frontal lobe.
  • 79.
  • 80.
    80 Sensory areas ofthe cerebrum The postcentral (sensory) area. Ø This is the area behind the central sulcus. Ø Sensations of pain, temperature, pressure and touch, knowledge of muscular movement and the position of joints are perceived. The sensory area of the right hemisphere receives impulses from the left side of the body and vice versa.
  • 81.
    81 The auditory (hearing)area. This lies immediately below the lateral sulcus within the temporal lobe. (8th cranial nerves). The olfactory (smell) area. This lies deep within the temporal lobe where impulses from the nose via the olfactory nerves (1st cranial nerves) are received and interpreted. The taste area. This is thought to lie just above the lateral sulcus in the deep layers of the sensory area. (8th cranial nerves) The visual area. This lies behind the parieto-occipital sulcus and includes the greater part of the occipital lobe. (2nd cranial nerves)
  • 82.
    82 Association Areas  Tietogether different kinds of sensory input  Associate new input with memories  Is to be renamed “higher-order processing“ areas Different areas 1. Premotor area: 2. Prefrontal area: 3. Wernicke’s area (speech area): 4. Pareito-occipital temporal area:
  • 83.
  • 84.
    84 Other areas ofthe cerebrum Deep within the cerebral hemispheres there are groups of cell bodies called nuclei (called ganglia) which act as relay stations where impulses are passed from one neurone to the next in a chain. Important masses of grey matter include: • basal nuclei • thalamus • hypothalamus.
  • 85.
    85 Basal nuclei. These areareas of grey matter, lying deep within the cerebral hemispheres, with connections to the cerebral cortex and thalamus. The basal nuclei form part of the extrapyramidal tracts and are thought to be involved in initiating muscle tone in slow and coordi-nated activities. If control is inadequate or absent, move-ments are jerky, clumsy and uncoordinated.
  • 86.
    86 Thalamus. The thalamus consistsof two masses of nerve cells and fibres situated within the cerebral hemispheres just below the corpus callosum, one on each side of the third ventricle. Sensory input from the skin, viscera and special sense organs is transmitted to the thalamus before redistribution to the cerebrum. Hypothalamus. • The hypothalamus is composed of a number of groups of nerve cells. It is situated below and in front of the thalamus, immediately above the pituitary gland. • The hypothalamus is linked to the posterior lobe of the pituitary gland by nerve fibres and to the anterior lobe by a complex system of blood vessels. • Through these connections, the hypothalamus controls the output of hormones from both lobes of the gland.
  • 87.
    87 Other functions ofhypothalamus: autonomic nervous system appetite and satiety thirst and water balance body temperature emotional reactions, e.g. pleasure, fear, rage sexual behaviour including mating and child rearing biological clocks or circadian rhythms, e.g. sleeping and waking cycles, body temperature and secretion of some hormones.
  • 88.
    88 Brain stem 1. Midbrain: Themidbrain is the area of the brain situated around the cerebral aqueduct between the cerebrum above and the pons below. It consists of groups of cell bodies and nerve fibres (tracts) which connect the cerebrum with lower parts of the brain and with the spinal cord. The cell bod-ies act as relay stations for the ascending and descending nerve fibres.
  • 89.
    89 2. Pons The ponsis situated in front of the cerebellum, below the midbrain and above the medulla oblongata. It consists mainly of nerve fibres which form a bridge between the two hemispheres of the cerebellum, and of fibres passing between the higher levels of the brain and the spinal cord. There are groups of cells within the pons which act as relay stations and some of these are associated with the cranial nerves. The anatomical structure of the pons differs from that of the cerebrum in that the cell bodies (grey matter) lie deeply and the nerve fibres are on the surface.
  • 90.
    90 3.Medulla oblongata The medullaoblongata extends from the pons above and is continuous with the spinal cord below. It is about 2.5 cm long and it lies just within the cranium above the foramen magnum. Its anterior and posterior surfaces are marked by central fissures. The outer aspect is composed of white matter which passes between the brain and the spinal cord, and grey matter lies centrally. Some cells con-stitute relay stations for sensory nerves passing from the spinal cord to the cerebrum. The vital centres, consisting of groups of cells associated with autonomic reflex activity, lie in its deeper structure. These are the: cardiac centre respiratory centre vasomotor centre reflex centres of vomiting, coughing, sneezing and swallowing.
  • 91.
    91 Other functions ofmedulla oblongata: 1. Decussation (crossing) of the pyramids. In the medulla motor nerves descending from the motor area in the cerebrum to the spinal cord in the pyramidal (corticospinal) tracts cross from one side to the other. These tracts are the main pathway for impulses to skeletal (voluntary) muscles. 2. Sensory decussation. Some of the sensory nerves ascending to the cerebrum from the spinal cord cross from one side to the other in the medulla. 3. Others decussate at lower levels, i.e. in the spinal cord.
  • 92.
    92 4. The cardiovascularcentre : controls the rate and force of cardiac contraction. sympathetic and parasympathetic nerve fibres originating in the medulla pass to the heart. Sympathetic stimulation increases the rate and force of the heartbeat and parasympathetic stimulation has the opposite effect. 5. The respiratory centre: controls the rate and depth of respiration. From this centre, nerve impulses pass to the phrenic and intercostal nerves which stimulate contraction of the diaphragm and intercostal muscles,thus initiating inspiration. The respiratory centre is stimulated by excess carbon dioxide and, to a lesser extent, by deficiency of oxygen in its blood supply and by nerve impulses
  • 93.
    93 6. The vasomotorcentre: It controls the diameter of the blood vessels, especially the small arteries and arterioles which have a large proportion of smooth muscle fibres in their walls. Vasomotor impulses reach the blood vessels through the autonomic nervous system. Stimulation may cause either constriction or dilatation of blood vessels depending on the site. The sources of stimulation of the vasomotor centre are the arterial baroreceptors, body temperature and emotions such as sexual excitement and anger. Pain usually causes vasoconstriction although severe pain may cause vasodilatation, a fall in blood pressure and fainting.
  • 94.
    94 7. Reflex centres: •When irritating substances are present in the stomach or respiratory tract, nerve impulses pass to the medulla oblongata, stimulating the reflex centres which initiate the reflex actions of vomiting, coughing and sneezing to expel the irritant.
  • 95.
    95 Reticular formation: The reticularformation is involved in: Coordination of skeletal muscle activity associated with voluntary motor movement and the maintenance of balance Coordination of activity controlled by the autonomic nervous system, e.g. cardiovascular, respiratory and gastrointestinal activity. Selective awareness that functions through the reticular activating system (RAS) which selectively blocks or passes sensory information to the cerebral cortex, e.g. the slight sound made by a sick child moving in bed may arouse his mother but the noise of regularly passing trains may be suppressed.
  • 96.
    96 Cerebellum: • The cerebellumis situated behind the pons and immediately below the posterior portion of the cerebrum occupying the posterior cranial fossa. • It is ovoid in shape and has two hemispheres, separated by a narrow median strip called the vermis. • Grey matter forms the surface of the cerebellum, and the white matter lies deeply.
  • 97.
    97 CerebellumTwo major hemispheres:three lobes each Anterior Posterior Floculonodular Vermis: midline lobe connecting hemispheres Outer cortex of gray Inner branching white matter, called “arbor vitae” Separated from brain stem by 4th ventricle
  • 98.
    98 Functions: • The cerebellumis concerned with the coordination of voluntary muscular movement, posture and balance. • Cerebellar activities are not under voluntary control. • The sensory input for these functions is derived from the muscles and joints, the eyes and the ears. • Proprioceptor impulses from the muscles and joints indicate their position in relation to the body as a whole and those impulses from the eyes and the semicircular canals in the ears provide information about the position of the head in space. • Impulses from the cerebellum influence the contraction of skeletal muscle so that balance and posture are maintained. • Damage to the cerebellum results in clumsy uncoordinated muscular movement, staggering gait and inability to carry out smooth, steady, precise movements.
  • 99.
  • 100.
    100 SPINAL CORD: It isthe elongated, almost cylindrical part of the central nervous system, which is suspended in the vertebral canal surrounded by the meninges and cerebrospinal fluid. It is continuous above with the medulla oblongata and extends from the upper border of the atlas to the lower border of the 1st lumbar vertebra. It is approximately 45 cm long in an adult Caucasian male, and is about the thickness of the little finger. When a specimen of cerebrospinal fluid is required it is taken from a point below the end of the cord, i.e. below the level of the 2nd lumbar vertebra (lumbar puncture). Nerves conveying impulses from the brain to the various organs and tissues descend through the spinal cord.
  • 101.
    101 Some activities ofthe spinal cord are independent of the brain, i.e. spinal reflexes (through extensive neurone connections between sensory and motor neurones ). The spinal cord is incompletely divided into two equal parts, anteriorly by a short, shallow median fissure and posteriorly by a deep narrow septum, the posterior median septum. A cross-section of the spinal cord shows that it is composed of grey matter in the centre surrounded by white matter supported by neuroglia.
  • 102.
    102 Grey matter: • Thearrangement of grey matter in the spinal cord resembles the shape of the letter H, having two posterior, two anterior and two lateral columns. • The area of grey matter lying transversely is the transverse commissure and it is pierced by the central canal, an extension from the fourth ventricle, containing cerebrospinal fluid. • The cell bodies may be: • Sensory cells: which receive impulses from the periphery of the body • Lower motor neurones: which transmit impulses to the skeletal muscles •Connector neurones: linking sensory and motor neurones, at the same or different levels, which form spinal reflex arcs. • At each point where nerve impulses are passed from one neurone to another there is a synaptic cleft and a neurotransmitter
  • 103.
    103 Posterior columns ofgrey matter: These are composed of cell bodies which are stimulated by sensory impulses from the periphery of the body. The nerve fibres of these cells contribute to the formation of the white matter of the cord and transmit the sensory impulses upwards to the brain. Anterior columns of grey matter These are composed of the cell bodies of the lower motor neurones which are stimulated by the axons of the upper motor neurones or by the cell bodies of connector neurones linking the anterior and posterior columns to form reflex arcs. The posterior root (spinal) ganglia are composed of cell bodies which lie just outside the spinal cord on the pathway of the sensory nerves. • All sensory nerve fibres pass through these ganglia. The only function of the cells is to promote the onward movement of nerve impulses.
  • 104.
    104 White matter: It isarranged in three columns or tracts 1. anterior 2.posterior 3.lateral. These tracts are formed by sensory nerve fibres ascending to the brain, motor nerve fibres descending from the brain and fibres of connector neurones. Tracts are often named according to their points of origin and destination, e.g. spinothalamic, corticospinal.
  • 105.
    105 Sensory nerve tracts(afferent or ascending) & motor nerve tracts (efferent or descending) in the spinal cord
  • 106.
  • 107.
    107 The Stretch Reflex •A stretch reflex causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle. • This type of reflex occurs via a monosynaptic reflex arc. The reflex can occur by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron.
  • 108.
  • 109.
    109 Functions 1.Sensory and motorinnervation of entire body inferior to the head through the spinal nerves 2.Two-way conduction pathway between the body and the brain 3.Major center for reflexes