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The nervous system is divided into the central nervous system (CNS; brain and spinal cord) and peripheral nervous system (PNS). The CNS is organized into the forebrain, brainstem, and cerebellum. It contains neurons and glial cells. The PNS connects the CNS to the body and is divided into somatic and autonomic divisions. It transmits signals between the CNS and peripheral organs.

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NERVOUS SYSTEM Overview and anatomical consideration
Organisation  The central nervous system  Brain and spinal cord  The peripheral nervous system (PNS)- nerve fibers that carry information between the CNS and other parts of the body (periphery)  Afferent division- carries information to the CNS, apprising it of the external environment and providing status reports on internal activities.  Efferent division- Instructions from the CNS are transmitted to effector organs- the muscles or glands  Enteric nervous system
Central nervous system  The adult human brain weighs between 1,200 to 1,500 g.  Occupies a volume of about 1400 cc  The adult spinal cord is approximately 40 to 50 cm long and occupies about 150 cc  The human nervous system is estimated to consist of roughly 360 billion non-neural glial cells and 90 billion nerve cells
 Morphology:  Grey matter- nerve cell bodies  Superficial in- cerebral cortex & cerebellum  Central in- brain stem and spinal cord  White matter- nerve fibers  Collection of cell bodies in white matter- nuclei Central nervous system
Central nervous system • The brain and the spinal cord arise in early development from the neural tube, which expands to form the three primary brain divisions: – The Prosencephalon, – The Mesencephalon and – The Rhombencephalon
Central nervous system  These three vesicles further differentiate into five subdivisions:  Prosencephalon-  Telencephalon & Diencephalon  Mesencephalon,  Rhombencephalon-  Metencephalon and the myelencephalon  The mesencephalon, metencephalon, and the myelencephalon comprise the brain stem.
Central nervous system
The Brain  Although no part of the brain acts in isolation, the neurons that work together to accomplish a given function are organized within a discrete location. The parts of the brain can be grouped into-  Forebrain-  Cerebral hemisphere- Cerebral cortex & Basal nuclei  Diencephalon- Thalamus & Hypothalamus  Brain stem- Mid brain, Pons, Medulla  Cerebellum
Cerebral hemispheres  Largest portion of the Brain  Consists of two symmetrical halves separated by median longitudinal fissure  The surface is highly convoluted with alternate gyri & sulci  Divided into four lobes- frontal, parietal, temporal & occipital  Function:  Finer aspects of sensory and motor functions  Seat of higher functions
Central sulcus Fissure of Sylvius or Lateral fissure
Cerebral hemispheres  Ventricles- hollow cavities within the cerebral hemispheres  Lateral ventricles- two long cavities  These communicate with the third ventricle in the midline between two halves of Diencephalon  Limbic system- lies in the deeper parts  Mainly concerned with emotion
The Diencephalon  Thalamus  Paired, present on either side of third ventricle  Important relay station. Most ascending sensory tracts relay in the Thalamus  Laterally related to Basal Ganglia (subcortical nuclear masses)- have important motor functions  Hypothalamus- lies deep to the Thalamus  Forms floor & part of lateral wall of third ventricle  Important functions- control autonomic function, endocrine control of pituitary, regulation of thirst, appetite and body temperature etc.
The Brain Stem  Midbrain- contains the cerebral aqueduct in center which link the third and fourth ventricle  Contains nuclei of Oculomotor and Trochlear nerves  Pons & Medulla  Contains many important nuclei including nuclei of many cranial nerves  Contains cardiorespiratory centers  Dorsal aspect forms the floor of the fourth ventricle
Cerebellum  Globular structure lying below the posterior Part of cerebral hemispheres and on the posterior aspect of brain stem  Four nuclei are present within the white matter- fastigial, globose, emboliform & dentate  Surface is densely fissured  Connected to the brain stem with three pairs of cerebellar peduncles.
Spinal cord  Downward continuation of the medulla oblongata  Extend down into the vertebral canal up to the first lumbar vertebra.  Has central canal surrounded by a mass of gray matter which is divided into anterior, lateral & posterior horns.  White matter surrounds the gray matter
The peripheral nervous system (PNS)  Consisting of nerve fibers that carry information between the CNS and other parts of the body. These include-  Cranial nerves- 12 pairs  Spinal nerves- 31 pairs  The paravertibral sympathetic chain  Preganglionic and postganglionic autonomic nerves
The peripheral nervous system (PNS)  Afferent division- carries information to the CNS,  Sensory stimuli- apprising it of the external environment and  Visceral stimuli- providing status reports on internal activities  Efferent division- transmit instructions from the CNS to effector organs i.e. the muscles or glands  The somatic nervous system- The fibers of the motor neurons that supply the skeletal muscles; and  The autonomic nervous system- The fibers that innervate smooth muscle, cardiac muscle, and glands.
The peripheral nervous system (PNS)  The enteric nervous system  An extensive nerve network in the wall of the digestive tract.  Controls digestive activities along with the autonomic nervous system and hormones.  The enteric nervous system can act independently of the rest of the nervous system but is also influenced by autonomic fibers that terminate on the enteric neurons.
Cranial nerves  Arise from nuclei situated in the brain stem except first two cranial nerves  Olfactory  Optic  Oculomotor- arise from upper half of midbrain  Innervate extrinsic muscles of the eyeball  Supplies parasympathetic fibers arising from Edinger- Westphal nucleus to ciliary muscles and constrictor pupillae  Trochlear- arise from lower half of midbrain  Supplies superior oblique muscle
Cranial nerves  Abducent (sixth nerve)- arise from its nucleus from pons and emerges from dorsal aspect of midbrain.  Supplies lateral rectus  Trigeminal- mixed nerve. Carries sensory impulses from the face to-  Spinal nucleus (long sensory nucleus), mainly receives pain sensation  Principal sensory nucleus, especially concerned with touch  Motor nucleus lies in the pons. Innervate the muscles of mastication.
 Facial nerve- mixed nerve  Motor fibers- supply the muscles of face and scalp  Sensory fibers- carry taste sensation from anterior two thirds of the tongue  Secretomotor fibers (parasympathetic)- Submandibular and Sublingual salivary glands and Lacrimal and palatal glands Cranial nerves
 Vestibulocochlear nerve  Vesibular division- receives sensory information from vestibular apparatus (otolith organs & semicircular canal)- maintains equilibrium  Cochlear division- hearing  Glossopharyngeal nerve- mixed nerve  Motor fiber from nucleus ambiguus to stylopharyngeus muscle  Secretomotor fibers to Parotid gland Cranial nerves
 Glossopharyngeal nerve  Sensory fibers-  Taste sensation from posterior 1/3rd of tongue,  General sensation- posterior 1/3rd of tongue, oropharynx, tonsils etc  Innervates the baroreceptors in carotid sinus & chemoreceptors in carotid body. Cranial nerves
 Vagus nerve- longest cranial nerve  Parasympathetic component supplies the heart, lungs & most of the abdominal viscera  Motor to laryngeal & pharyngeal muscles  Sensory- visceral sensation from thoracic and abdominal organs via parasympathetic afferents  Supplies the baroreceptors in the aortic arch & chemoreceptors in the aortic body. Cranial nerves
 Accessory nerve- eleventh nerve  Spinal accessory- motor to trapezius & sternocleidomastoid  Cranial part- supplies laryngeal & pharyngeal muscles along with vagus  Hypoglossal nerve- motor nerve supplying the muscles of the tongue Cranial nerves
Spinal nerves  Arise from spinal cord by two roots-  Ventral (anterior)- motor fibers and  Dorsal (posterior)- sensory fibers  The somatic motor fibers in the anterior root also carry-  Sympathetic efferent- T1- L2  Parasympathetic efferent- S2 – S4  Bell-Magendies law- the sensory fibers enter through the posterior root & the motor fibers emerge through anterior root in the spinal cord.
Cellular components of CNS  Glial cells (neuroglia)-  Serve as connective tissue of the CNS and so support the neurons both physically & metabolically  Maintain homeostasis of fluids that bathe the neurons  Actively modulate synaptic function & are considered nearly as important as neurons to learning and memory.  Neuroglias constitute about 90% of the cells in CNS but occupy only 50% the volume.  Neurons- transmit impulses in the form of action potentials
Neuroglia  Four major types of glial cells in the CNS:  Astrocytes,  Oligodendrocytes,  Microglia, and  Ependymal cell  Astrocytes- star shaped. Processes of astrocytes surround the neurons and often terminate on the wall of blood vessels.
Neuroglia  Functions Astrocytes  Physically support neurons in proper spatial relationships  Serve as a scaffold during fetal brain development  Induce formation of blood–brain barrier  Help transfer nutrients from blood to neurons  Important in the repair of brain injuries and form neural scar tissue  Take up and degrade released neurotransmitters (Glutamate & GABA)  Take up excess K+ to help maintain proper brain-ECF ion concentration and normal neural excitability
Neuroglia  Functions Astrocytes:  Enhance synapse formation and strengthen synaptic transmission via chemical signaling (thrombospondin) with neurons  Communicate by chemical means with neurons and among themselves  Oligodendrocytes-  Forms the myelin sheath around axons in the brain and spinal cord.  Unlike Schwann cells they can myelinate several nerve cells simultaneously
 Microglia-  Derived from bone marrow & behave like macrophages  Release low levels of nerve growth factor, which help neurons and other glial cells survive and thrive  Ependymal cells  Line the surfaces of the brains ventricles and central canal of the spinal cord  Posses cilia beating of which contribute to CSF movement  Contribute to formation of cerebrospinal fluid  Serve as neural stem cells with the potential to form new neurons and glial cells Neuroglia
Types of Neuroglia  Unlike neurons, glial cells do not lose the ability to undergo cell division, so most brain tumors of neural origin consist of glial cells (gliomas)
Protection and nourishment of the brain
Protection of the brain  Four major features help protect the CNS from injury-  It is enclosed by hard, bony structures. The cranium (skull) encases the brain, and the vertebral column surrounds the spinal cord.  Three protective and nourishing membranes, the meninges, lie between the bony covering and the nervous tissue.  The brain “floats” in a special cushioning fluid, the cerebrospinal fluid (CSF).  A highly selective blood-brain barrier limits access of blood borne materials into the vulnerable brain tissue
The meninges  Duramater- tough, inelastic covering that consists of two layers, endosteal and meningeal layers- dural & venous sinuses lies between these two layers  Venous blood draining from the brain empties into these sinuses  Cerebrospinal fluid also re-enters the blood at one of these sinus sites
The meninges  Arachnoidmater- richly vascularized layer with a cobwebby appearance  Arachnoid villi, penetrate through gaps in the overlying dura and project into the dural sinuses  Subarachnoid space- between arachnoidmater & piamater- contains CSF  Piamater- most fragile and highly vascular. Closely adheres to the surfaces of the brain and spinal cord
 Ventricles- CSF filled spaces inside the brain  Lateral ventricles- within the cerebral hemispheres  Connects with the third ventricle between the thalami through foramina of Monroe  The third ventricle communicates with fourth ventricle by the aqueduct of Sylvious- runs through the mid brain  The fourth ventricl communicates with the subarachnoid space through the foramina of Magendie (midline) & two foramina of Luschka (laterally)  Below fourth ventricle is continuous with central The meninges
 Surrounds and cushions the brain and spinal cord.  The CSF has about the same density as the brain itself, so it essentially floats or is suspended in this fluid environment  Functions:  Serve as a shock-absorbing fluid to prevent the brain from bumping against the interior of the hard skull when the head is subjected to sudden, jarring movements.  Plays an important role in the exchange of materials between the neural cells and the interstitial fluid surrounding the brain. Cerebrospinal fluid
 Functions:  The composition of the brain interstitial fluid is influenced more by changes in the composition of the CSF than by alterations in the blood.  Materials are exchanged fairly freely between the CSF and brain interstitial fluid, whereas only limited exchange occurs between the blood and brain interstitial fluid. Cerebrospinal fluid
 Formed primarily by the choroid plexuses found in particular regions of the ventricles.  Choroid plexuses consist of richly vascularized, cauliflower-like masses of pia mater tissue that dip into pockets formed by ependymal cells.  Cerebrospinal fluid forms as a result of selective transport mechanisms across the membranes of the choroid plexuses.  The composition of CSF differs from that of blood. For example, CSF is lower in K+ and slightly higher in Na+  The biggest difference is the presence of plasma proteins in the blood but almost no protein is normally present in the CSF. Cerebrospinal fluid
Cerebrospinal fluid  Circulation of CSF Lateral ventricles Third ventricle Fourth ventricle Suarachnoid space Foramen of Monro Aqueduct of Sylvius Formina of Luschka & Magendie Central canal of spinal canal
Absorption of CSF  CSF in the subarachnoid space is absorbed in the dural venous sinuses by way of arachnoid villi which project into the superior sagittal sinus between the layers of duramater  The membrane contains pores which allow absorption of CSF into venous sinuses when CSF pressure is high  When venous pressure is higher back flow is prevented by collapse of the pores.  Much higher osmolality of venous blood draws CSF into it
Composition of CSF  Clear fluid with-  Normal cell conunt- 0-5/cu-mm  Glucose- 50-80 mg/100 ml  Protein- 20-90 mg/100 ml  Chloride- 720-750 mg/100 ml  Na+, K+, Ca+, bicarbonate & urea in trace amounts
Cerebrospinal Fluid- Applied  Lumbar puncture- hollow needle is inserted into the spinal canal between the third and fourth lumbar vertebra. Collected CSF is examined for  Subarachnoid hemmorrhage- blood in CSF  Pyogenic meningitis- turbid with high cell count & plenty neutrophils. Low glucose & high protein content  Tubercular meningitis-clear & may show fine clot. Contains lymphocytes, high protein but low glucose & Cl+  Viral encephalitis- raised protein, lymphocyte may also be high
 Hydrcephalus- excessive accumulation of CSF with dilatation of ventricles (normal CSF pressure- 70-180 mm CSF)  Two types-  External or communicating- obstruction outside the ventricular system. There may be decrease in reabsorption.  Internal or noncommunicating- there is block within the ventricles or at the foramina of Magendie & Luschka. Cerebrospinal Fluid- Applied
 The resulting increase in CSF pressure can lead to brain damage and mental retardation if untreated.  Treatment consists of surgically shunting the excess CSF to veins elsewhere in the body. Cerebrospinal Fluid- Applied
Blood Brain Barrier  The brain is carefully shielded from harmful changes in the blood by a highly selective blood-brain barrier (BBB)  Unlike the free exchange across capillaries elsewhere, only selected, carefully regulated exchanges can be made across the BBB (between the blood and interstitial fluid)  Features  In brain capillaries, the cells are joined by tight junctions which completely seal the capillary wall
Blood Brain Barrier  Features  The only possible exchanges are through the capillary cells themselves  Lipid-soluble substances such as O2, CO2, alcohol, and steroid hormones penetrate these cells easily by dissolving in their lipid plasma membrane  Small water molecules also diffuse through readily by passing between the phospholipid molecules of the plasma membrane or through aquaporins
Blood Brain Barrier  Features  All other substances exchanged between the blood and brain interstitial fluid, including such essential materials as glucose, amino acids, and ions, are transported by highly selective membrane-bound carriers  Thus it protects the delicate brain from  Chemical fluctuations in the blood and  Minimizes the possibility that potentially harmful blood-borne substances might reach the central neural tissue  Prevents certain circulating hormones that could also act as neurotransmitters from reaching the brain
Blood Brain Barrier  The negative side-  It limits the use of drugs for the treatment of brain and spinal cord disorders because many drugs are unable to penetrate this barrier  Astrocytes play two roles in the BBB:  They signal the cells forming the brain capillaries to “get tight.” Capillary cells do not have an inherent ability to form tight junctions;  They participate in the cross-cellular transport of some substances, such as K+ .  Certain areas of the brain, most notably a portion of the hypothalamus, are not subject to the BBB.
Sensory system- receptors  Most activities of the nervous system are initiated by sensory experiences that excite sensory receptors  Sensory experience can either cause  immediate reaction from the brain or  memory of the experience can be stored in the brain for minutes, weeks or years and determine bodily reactions at some future date
Sensory system  This information enters the central nervous system through peripheral nerves and is conducted immediately to multiple sensory areas in-  The spinal cord at all levels;  The reticular substance of the medulla, pons, and mesencephalon of the brain;  The cerebellum;  The thalamus; and  Areas of the cerebral cortex.
Sensory system
Motor system- effectors  Controls  Contraction of appropriate skeletal muscles throughout the body,  Contraction of smooth muscle in the internal organs, and  Secretion of active chemical substances by both exocrine and endocrine glands in many parts of the body  The muscles and glands are called effectors.
Motor system
Processing of Information- Integrative Function  One of the most important functions of the nervous system is to process incoming information  Necessary for appropriate mental and motor responses.  More than 99 percent of all sensory information is discarded by the brain as irrelevant and unimportant.  Important sensory information's excite the mind & is channelled into proper integrative and motor regions of the brain to cause
Role of Synapses in Processing Information  Synapse is the junction point from one neuron to the next  Synapses determine the directions of spread of nervous signals through the nervous system  facilitatory and inhibitory signals from other areas in the nervous system can control synaptic transmission  some postsynaptic neurons respond with large numbers of output impulses, and others respond with only a few.  Thus, the synapses perform a selective action
Storage of Information- Memory  The process of storage of information is called memory- a function of the synapses  After the sensory signals have passed through the synapses a large number of times, they become more capable of transmitting the same type of signal the next time- facilitation  Most storage occurs in the cerebral cortex, but some can occur in basal regions of the brain and the spinal cord  They become part of the brain processing mechanism for future “thinking.”  That is, the thinking processes of the brain compare new sensory experiences with stored memories
MAJOR LEVELS OF CNS FUNCTION •The spinal cord level •The lower brain or subcortical level, and •The higher brain or cortical level
The spinal cord level  Neuronal circuits in the cord can cause  walking movements,  Reflexes that withdraw portions of the body from painful objects,  Reflexes that stiffen the legs to support the body against gravity, and  Reflexes that control local blood vessels, gastrointestinal movements, or urinary excretion.  The upper levels of the nervous system often operate not by sending signals directly to the periphery of the body but by simply “commanding” the cord centers to perform their functions.
The lower brain or subcortical level  Many subconscious activities of the body are controlled in the lower areas of the brain- the medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, and basal ganglia  The medulla & Pons- subconscious control of arterial pressure and respiration  Control of equilibrium- combined function of the cerebellum and the reticular substance of the medulla, pons, and mesencephalon  Feeding reflexes, such as salivation and licking of the lips in response to the taste of food- controlled by areas in the medulla, pons, mesencephalon, amygdala, and hypothalamus  Many emotional patterns, such as anger, excitement, sexual response, reaction to pain, and reaction to pleasure, can still occur after destruction of much of the
The higher brain or cortical level  The cortex never functions alone but always in association with lower centers of the nervous system  Without the cerebral cortex, the functions of the lower brain centers are often imprecise  The cerebral cortex is essential for most of our thought processes, but it cannot function by itself.  It is the lower brain centers, not the cortex, that initiate wakefulness in the cerebral cortex
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Overview ns

  • 1.
    NERVOUS SYSTEM Overview andanatomical consideration
  • 2.
    Organisation  The centralnervous system  Brain and spinal cord  The peripheral nervous system (PNS)- nerve fibers that carry information between the CNS and other parts of the body (periphery)  Afferent division- carries information to the CNS, apprising it of the external environment and providing status reports on internal activities.  Efferent division- Instructions from the CNS are transmitted to effector organs- the muscles or glands  Enteric nervous system
  • 4.
    Central nervous system The adult human brain weighs between 1,200 to 1,500 g.  Occupies a volume of about 1400 cc  The adult spinal cord is approximately 40 to 50 cm long and occupies about 150 cc  The human nervous system is estimated to consist of roughly 360 billion non-neural glial cells and 90 billion nerve cells
  • 5.
     Morphology:  Greymatter- nerve cell bodies  Superficial in- cerebral cortex & cerebellum  Central in- brain stem and spinal cord  White matter- nerve fibers  Collection of cell bodies in white matter- nuclei Central nervous system
  • 6.
    Central nervous system •The brain and the spinal cord arise in early development from the neural tube, which expands to form the three primary brain divisions: – The Prosencephalon, – The Mesencephalon and – The Rhombencephalon
  • 8.
    Central nervous system These three vesicles further differentiate into five subdivisions:  Prosencephalon-  Telencephalon & Diencephalon  Mesencephalon,  Rhombencephalon-  Metencephalon and the myelencephalon  The mesencephalon, metencephalon, and the myelencephalon comprise the brain stem.
  • 9.
  • 10.
    The Brain  Althoughno part of the brain acts in isolation, the neurons that work together to accomplish a given function are organized within a discrete location. The parts of the brain can be grouped into-  Forebrain-  Cerebral hemisphere- Cerebral cortex & Basal nuclei  Diencephalon- Thalamus & Hypothalamus  Brain stem- Mid brain, Pons, Medulla  Cerebellum
  • 11.
    Cerebral hemispheres  Largestportion of the Brain  Consists of two symmetrical halves separated by median longitudinal fissure  The surface is highly convoluted with alternate gyri & sulci  Divided into four lobes- frontal, parietal, temporal & occipital  Function:  Finer aspects of sensory and motor functions  Seat of higher functions
  • 12.
    Central sulcus Fissure ofSylvius or Lateral fissure
  • 13.
    Cerebral hemispheres  Ventricles-hollow cavities within the cerebral hemispheres  Lateral ventricles- two long cavities  These communicate with the third ventricle in the midline between two halves of Diencephalon  Limbic system- lies in the deeper parts  Mainly concerned with emotion
  • 16.
    The Diencephalon  Thalamus Paired, present on either side of third ventricle  Important relay station. Most ascending sensory tracts relay in the Thalamus  Laterally related to Basal Ganglia (subcortical nuclear masses)- have important motor functions  Hypothalamus- lies deep to the Thalamus  Forms floor & part of lateral wall of third ventricle  Important functions- control autonomic function, endocrine control of pituitary, regulation of thirst, appetite and body temperature etc.
  • 18.
    The Brain Stem Midbrain- contains the cerebral aqueduct in center which link the third and fourth ventricle  Contains nuclei of Oculomotor and Trochlear nerves  Pons & Medulla  Contains many important nuclei including nuclei of many cranial nerves  Contains cardiorespiratory centers  Dorsal aspect forms the floor of the fourth ventricle
  • 19.
    Cerebellum  Globular structurelying below the posterior Part of cerebral hemispheres and on the posterior aspect of brain stem  Four nuclei are present within the white matter- fastigial, globose, emboliform & dentate  Surface is densely fissured  Connected to the brain stem with three pairs of cerebellar peduncles.
  • 20.
    Spinal cord  Downwardcontinuation of the medulla oblongata  Extend down into the vertebral canal up to the first lumbar vertebra.  Has central canal surrounded by a mass of gray matter which is divided into anterior, lateral & posterior horns.  White matter surrounds the gray matter
  • 22.
    The peripheral nervoussystem (PNS)  Consisting of nerve fibers that carry information between the CNS and other parts of the body. These include-  Cranial nerves- 12 pairs  Spinal nerves- 31 pairs  The paravertibral sympathetic chain  Preganglionic and postganglionic autonomic nerves
  • 23.
    The peripheral nervoussystem (PNS)  Afferent division- carries information to the CNS,  Sensory stimuli- apprising it of the external environment and  Visceral stimuli- providing status reports on internal activities  Efferent division- transmit instructions from the CNS to effector organs i.e. the muscles or glands  The somatic nervous system- The fibers of the motor neurons that supply the skeletal muscles; and  The autonomic nervous system- The fibers that innervate smooth muscle, cardiac muscle, and glands.
  • 24.
    The peripheral nervoussystem (PNS)  The enteric nervous system  An extensive nerve network in the wall of the digestive tract.  Controls digestive activities along with the autonomic nervous system and hormones.  The enteric nervous system can act independently of the rest of the nervous system but is also influenced by autonomic fibers that terminate on the enteric neurons.
  • 25.
    Cranial nerves  Arisefrom nuclei situated in the brain stem except first two cranial nerves  Olfactory  Optic  Oculomotor- arise from upper half of midbrain  Innervate extrinsic muscles of the eyeball  Supplies parasympathetic fibers arising from Edinger- Westphal nucleus to ciliary muscles and constrictor pupillae  Trochlear- arise from lower half of midbrain  Supplies superior oblique muscle
  • 26.
    Cranial nerves  Abducent(sixth nerve)- arise from its nucleus from pons and emerges from dorsal aspect of midbrain.  Supplies lateral rectus  Trigeminal- mixed nerve. Carries sensory impulses from the face to-  Spinal nucleus (long sensory nucleus), mainly receives pain sensation  Principal sensory nucleus, especially concerned with touch  Motor nucleus lies in the pons. Innervate the muscles of mastication.
  • 27.
     Facial nerve-mixed nerve  Motor fibers- supply the muscles of face and scalp  Sensory fibers- carry taste sensation from anterior two thirds of the tongue  Secretomotor fibers (parasympathetic)- Submandibular and Sublingual salivary glands and Lacrimal and palatal glands Cranial nerves
  • 28.
     Vestibulocochlear nerve Vesibular division- receives sensory information from vestibular apparatus (otolith organs & semicircular canal)- maintains equilibrium  Cochlear division- hearing  Glossopharyngeal nerve- mixed nerve  Motor fiber from nucleus ambiguus to stylopharyngeus muscle  Secretomotor fibers to Parotid gland Cranial nerves
  • 29.
     Glossopharyngeal nerve Sensory fibers-  Taste sensation from posterior 1/3rd of tongue,  General sensation- posterior 1/3rd of tongue, oropharynx, tonsils etc  Innervates the baroreceptors in carotid sinus & chemoreceptors in carotid body. Cranial nerves
  • 30.
     Vagus nerve-longest cranial nerve  Parasympathetic component supplies the heart, lungs & most of the abdominal viscera  Motor to laryngeal & pharyngeal muscles  Sensory- visceral sensation from thoracic and abdominal organs via parasympathetic afferents  Supplies the baroreceptors in the aortic arch & chemoreceptors in the aortic body. Cranial nerves
  • 31.
     Accessory nerve-eleventh nerve  Spinal accessory- motor to trapezius & sternocleidomastoid  Cranial part- supplies laryngeal & pharyngeal muscles along with vagus  Hypoglossal nerve- motor nerve supplying the muscles of the tongue Cranial nerves
  • 32.
    Spinal nerves  Arisefrom spinal cord by two roots-  Ventral (anterior)- motor fibers and  Dorsal (posterior)- sensory fibers  The somatic motor fibers in the anterior root also carry-  Sympathetic efferent- T1- L2  Parasympathetic efferent- S2 – S4  Bell-Magendies law- the sensory fibers enter through the posterior root & the motor fibers emerge through anterior root in the spinal cord.
  • 34.
    Cellular components ofCNS  Glial cells (neuroglia)-  Serve as connective tissue of the CNS and so support the neurons both physically & metabolically  Maintain homeostasis of fluids that bathe the neurons  Actively modulate synaptic function & are considered nearly as important as neurons to learning and memory.  Neuroglias constitute about 90% of the cells in CNS but occupy only 50% the volume.  Neurons- transmit impulses in the form of action potentials
  • 35.
    Neuroglia  Four majortypes of glial cells in the CNS:  Astrocytes,  Oligodendrocytes,  Microglia, and  Ependymal cell  Astrocytes- star shaped. Processes of astrocytes surround the neurons and often terminate on the wall of blood vessels.
  • 36.
    Neuroglia  Functions Astrocytes Physically support neurons in proper spatial relationships  Serve as a scaffold during fetal brain development  Induce formation of blood–brain barrier  Help transfer nutrients from blood to neurons  Important in the repair of brain injuries and form neural scar tissue  Take up and degrade released neurotransmitters (Glutamate & GABA)  Take up excess K+ to help maintain proper brain-ECF ion concentration and normal neural excitability
  • 37.
    Neuroglia  Functions Astrocytes: Enhance synapse formation and strengthen synaptic transmission via chemical signaling (thrombospondin) with neurons  Communicate by chemical means with neurons and among themselves  Oligodendrocytes-  Forms the myelin sheath around axons in the brain and spinal cord.  Unlike Schwann cells they can myelinate several nerve cells simultaneously
  • 38.
     Microglia-  Derivedfrom bone marrow & behave like macrophages  Release low levels of nerve growth factor, which help neurons and other glial cells survive and thrive  Ependymal cells  Line the surfaces of the brains ventricles and central canal of the spinal cord  Posses cilia beating of which contribute to CSF movement  Contribute to formation of cerebrospinal fluid  Serve as neural stem cells with the potential to form new neurons and glial cells Neuroglia
  • 39.
    Types of Neuroglia Unlike neurons, glial cells do not lose the ability to undergo cell division, so most brain tumors of neural origin consist of glial cells (gliomas)
  • 41.
  • 42.
    Protection of thebrain  Four major features help protect the CNS from injury-  It is enclosed by hard, bony structures. The cranium (skull) encases the brain, and the vertebral column surrounds the spinal cord.  Three protective and nourishing membranes, the meninges, lie between the bony covering and the nervous tissue.  The brain “floats” in a special cushioning fluid, the cerebrospinal fluid (CSF).  A highly selective blood-brain barrier limits access of blood borne materials into the vulnerable brain tissue
  • 43.
    The meninges  Duramater-tough, inelastic covering that consists of two layers, endosteal and meningeal layers- dural & venous sinuses lies between these two layers  Venous blood draining from the brain empties into these sinuses  Cerebrospinal fluid also re-enters the blood at one of these sinus sites
  • 44.
    The meninges  Arachnoidmater-richly vascularized layer with a cobwebby appearance  Arachnoid villi, penetrate through gaps in the overlying dura and project into the dural sinuses  Subarachnoid space- between arachnoidmater & piamater- contains CSF  Piamater- most fragile and highly vascular. Closely adheres to the surfaces of the brain and spinal cord
  • 45.
     Ventricles- CSFfilled spaces inside the brain  Lateral ventricles- within the cerebral hemispheres  Connects with the third ventricle between the thalami through foramina of Monroe  The third ventricle communicates with fourth ventricle by the aqueduct of Sylvious- runs through the mid brain  The fourth ventricl communicates with the subarachnoid space through the foramina of Magendie (midline) & two foramina of Luschka (laterally)  Below fourth ventricle is continuous with central The meninges
  • 46.
     Surrounds andcushions the brain and spinal cord.  The CSF has about the same density as the brain itself, so it essentially floats or is suspended in this fluid environment  Functions:  Serve as a shock-absorbing fluid to prevent the brain from bumping against the interior of the hard skull when the head is subjected to sudden, jarring movements.  Plays an important role in the exchange of materials between the neural cells and the interstitial fluid surrounding the brain. Cerebrospinal fluid
  • 47.
     Functions:  Thecomposition of the brain interstitial fluid is influenced more by changes in the composition of the CSF than by alterations in the blood.  Materials are exchanged fairly freely between the CSF and brain interstitial fluid, whereas only limited exchange occurs between the blood and brain interstitial fluid. Cerebrospinal fluid
  • 48.
     Formed primarilyby the choroid plexuses found in particular regions of the ventricles.  Choroid plexuses consist of richly vascularized, cauliflower-like masses of pia mater tissue that dip into pockets formed by ependymal cells.  Cerebrospinal fluid forms as a result of selective transport mechanisms across the membranes of the choroid plexuses.  The composition of CSF differs from that of blood. For example, CSF is lower in K+ and slightly higher in Na+  The biggest difference is the presence of plasma proteins in the blood but almost no protein is normally present in the CSF. Cerebrospinal fluid
  • 49.
    Cerebrospinal fluid  Circulationof CSF Lateral ventricles Third ventricle Fourth ventricle Suarachnoid space Foramen of Monro Aqueduct of Sylvius Formina of Luschka & Magendie Central canal of spinal canal
  • 52.
    Absorption of CSF CSF in the subarachnoid space is absorbed in the dural venous sinuses by way of arachnoid villi which project into the superior sagittal sinus between the layers of duramater  The membrane contains pores which allow absorption of CSF into venous sinuses when CSF pressure is high  When venous pressure is higher back flow is prevented by collapse of the pores.  Much higher osmolality of venous blood draws CSF into it
  • 54.
    Composition of CSF Clear fluid with-  Normal cell conunt- 0-5/cu-mm  Glucose- 50-80 mg/100 ml  Protein- 20-90 mg/100 ml  Chloride- 720-750 mg/100 ml  Na+, K+, Ca+, bicarbonate & urea in trace amounts
  • 55.
    Cerebrospinal Fluid- Applied Lumbar puncture- hollow needle is inserted into the spinal canal between the third and fourth lumbar vertebra. Collected CSF is examined for  Subarachnoid hemmorrhage- blood in CSF  Pyogenic meningitis- turbid with high cell count & plenty neutrophils. Low glucose & high protein content  Tubercular meningitis-clear & may show fine clot. Contains lymphocytes, high protein but low glucose & Cl+  Viral encephalitis- raised protein, lymphocyte may also be high
  • 56.
     Hydrcephalus- excessiveaccumulation of CSF with dilatation of ventricles (normal CSF pressure- 70-180 mm CSF)  Two types-  External or communicating- obstruction outside the ventricular system. There may be decrease in reabsorption.  Internal or noncommunicating- there is block within the ventricles or at the foramina of Magendie & Luschka. Cerebrospinal Fluid- Applied
  • 57.
     The resultingincrease in CSF pressure can lead to brain damage and mental retardation if untreated.  Treatment consists of surgically shunting the excess CSF to veins elsewhere in the body. Cerebrospinal Fluid- Applied
  • 58.
    Blood Brain Barrier The brain is carefully shielded from harmful changes in the blood by a highly selective blood-brain barrier (BBB)  Unlike the free exchange across capillaries elsewhere, only selected, carefully regulated exchanges can be made across the BBB (between the blood and interstitial fluid)  Features  In brain capillaries, the cells are joined by tight junctions which completely seal the capillary wall
  • 59.
    Blood Brain Barrier Features  The only possible exchanges are through the capillary cells themselves  Lipid-soluble substances such as O2, CO2, alcohol, and steroid hormones penetrate these cells easily by dissolving in their lipid plasma membrane  Small water molecules also diffuse through readily by passing between the phospholipid molecules of the plasma membrane or through aquaporins
  • 60.
    Blood Brain Barrier Features  All other substances exchanged between the blood and brain interstitial fluid, including such essential materials as glucose, amino acids, and ions, are transported by highly selective membrane-bound carriers  Thus it protects the delicate brain from  Chemical fluctuations in the blood and  Minimizes the possibility that potentially harmful blood-borne substances might reach the central neural tissue  Prevents certain circulating hormones that could also act as neurotransmitters from reaching the brain
  • 61.
    Blood Brain Barrier The negative side-  It limits the use of drugs for the treatment of brain and spinal cord disorders because many drugs are unable to penetrate this barrier  Astrocytes play two roles in the BBB:  They signal the cells forming the brain capillaries to “get tight.” Capillary cells do not have an inherent ability to form tight junctions;  They participate in the cross-cellular transport of some substances, such as K+ .  Certain areas of the brain, most notably a portion of the hypothalamus, are not subject to the BBB.
  • 63.
    Sensory system- receptors Most activities of the nervous system are initiated by sensory experiences that excite sensory receptors  Sensory experience can either cause  immediate reaction from the brain or  memory of the experience can be stored in the brain for minutes, weeks or years and determine bodily reactions at some future date
  • 64.
    Sensory system  Thisinformation enters the central nervous system through peripheral nerves and is conducted immediately to multiple sensory areas in-  The spinal cord at all levels;  The reticular substance of the medulla, pons, and mesencephalon of the brain;  The cerebellum;  The thalamus; and  Areas of the cerebral cortex.
  • 65.
  • 66.
    Motor system- effectors Controls  Contraction of appropriate skeletal muscles throughout the body,  Contraction of smooth muscle in the internal organs, and  Secretion of active chemical substances by both exocrine and endocrine glands in many parts of the body  The muscles and glands are called effectors.
  • 67.
  • 68.
    Processing of Information- IntegrativeFunction  One of the most important functions of the nervous system is to process incoming information  Necessary for appropriate mental and motor responses.  More than 99 percent of all sensory information is discarded by the brain as irrelevant and unimportant.  Important sensory information's excite the mind & is channelled into proper integrative and motor regions of the brain to cause
  • 69.
    Role of Synapsesin Processing Information  Synapse is the junction point from one neuron to the next  Synapses determine the directions of spread of nervous signals through the nervous system  facilitatory and inhibitory signals from other areas in the nervous system can control synaptic transmission  some postsynaptic neurons respond with large numbers of output impulses, and others respond with only a few.  Thus, the synapses perform a selective action
  • 70.
    Storage of Information-Memory  The process of storage of information is called memory- a function of the synapses  After the sensory signals have passed through the synapses a large number of times, they become more capable of transmitting the same type of signal the next time- facilitation  Most storage occurs in the cerebral cortex, but some can occur in basal regions of the brain and the spinal cord  They become part of the brain processing mechanism for future “thinking.”  That is, the thinking processes of the brain compare new sensory experiences with stored memories
  • 71.
    MAJOR LEVELS OF CNSFUNCTION •The spinal cord level •The lower brain or subcortical level, and •The higher brain or cortical level
  • 72.
    The spinal cordlevel  Neuronal circuits in the cord can cause  walking movements,  Reflexes that withdraw portions of the body from painful objects,  Reflexes that stiffen the legs to support the body against gravity, and  Reflexes that control local blood vessels, gastrointestinal movements, or urinary excretion.  The upper levels of the nervous system often operate not by sending signals directly to the periphery of the body but by simply “commanding” the cord centers to perform their functions.
  • 73.
    The lower brainor subcortical level  Many subconscious activities of the body are controlled in the lower areas of the brain- the medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, and basal ganglia  The medulla & Pons- subconscious control of arterial pressure and respiration  Control of equilibrium- combined function of the cerebellum and the reticular substance of the medulla, pons, and mesencephalon  Feeding reflexes, such as salivation and licking of the lips in response to the taste of food- controlled by areas in the medulla, pons, mesencephalon, amygdala, and hypothalamus  Many emotional patterns, such as anger, excitement, sexual response, reaction to pain, and reaction to pleasure, can still occur after destruction of much of the
  • 74.
    The higher brainor cortical level  The cortex never functions alone but always in association with lower centers of the nervous system  Without the cerebral cortex, the functions of the lower brain centers are often imprecise  The cerebral cortex is essential for most of our thought processes, but it cannot function by itself.  It is the lower brain centers, not the cortex, that initiate wakefulness in the cerebral cortex
  • 75.