Brain Anatomy & Physiology

NEUROPHYSIOLOGY Dr. Steven Resnick, D.O. Neurology Resident Jackson Memorial Hospital

LECTURE OUTLINE I INTRO - OVERVIEW OF THE NERVOUS SYSTEM II NEURON III ACTION POTENTIAL IV SYNAPSE V BRAIN VI SPINAL CORD VII AUTONOMIC NERVOUS SYSTEM VIII CRANIAL NERVES IX CONCLUSION

Basic Functions of the Nervous System Sensory Function Detection of both internal and external stimuli Interpretive Function Analyzes, stores, and makes decisions based on sensory information Motor Function (Response) Response to interpretive data

Nervous System Afferent (sensory) Neurons – Carry impulses toward the CNS Efferent (Motor) Neurons – Carry impulses from the CNS Interneurons – conduct impulses within the spinal cord (between afferent and efferent) (Syn. Association, Internuncial) Ganglia are small masses of nervous tissue located outside the brain and spinal cord.

Fine Anatomy of the Nervous System Three kinds of neurons: Sensory Motor Interneurons 1) Sensory: Sensory organs to CNS “ Receptors” 2) Motor: CNS to muscles and organs “ Effectors” 3) Interneurons: Connections within CNS “ Processors” Neurons Sensory Motor Interneurons

Sensory Neurons INPUT From sensory organs to the brain and spinal cord. Somatosensory neuron - spinal Vision, hearing, taste and smell - cranial Spinal Cord Brain Sensory Neuron Touch receptors in skin

Motor Neurons OUTPUT From the brain and spinal cord to muscles and glands Motor neurons in spinal cord Spinal Cord Brain Motor Neuron

Interneurons PROCESSING Relay information between other neurons Spinal Cord Brain Inter- Neurons Interneurons in brain

General Organisation of the Nervous System The Nervous System Central Nervous System Peripheral Nervous System Brain Spinal Cord Somatic Autonomic Sensory Motor Parasympathetic Sympathetic

The Nervous System Two subsystems Central nervous system (CNS) Brain and Spinal Cord Integrate, correlate, and respond to many different kinds of sensory information Source of thoughts, emotions, and memories Peripheral nervous system (PNS) Includes all nervous tissue outside of the CNS Cranial nerves, spinal nerves, etc.

Divisions of the PNS Somatic Nervous System (SNS) Sensory neurons that convey information from sensory receptors in the head, body wall and limbs to the CNS Motor neurons from the CNS that conduct impulses to the skeletal (voluntary) muscles only.

Divisions of the PNS Autonomic Nervous System (ANS) The motor portion of the ANS consists of two divisions Sympathetic (thoracolumbar region) Fight/flight (prepares the body to cope with stressful situations) Parasympathetic (craniosacral region) Rest/Repose (generally an opposite response to the sympathetic nervous system)

Divisions of the PNS Autonomic Nervous System (ANS) Sensory neurons convey information from receptors in the viscera (internal organs), to the CNS. Motor neurons then convey information from the CNS to smooth muscle, cardiac muscle, glands, etc. Motor functions in the ANS are not normally under conscious control; they are involuntary .

Major Divisions of the Nervous System { sensory motor autonomic nervous system { somatic nervous system { somatic nervous system { brain spinal cord { afferent nerves efferent nerves { parasympathetic nervous system sympathetic nervous system peripheral nervous system (PNS) nervous system central nervous system (CNS)

Peripheral Nervous System: Afferent and Efferent Neurons

Neurons “Functional unit” of nervous system Several Types Conduct nerve impulses Electrical excitability Structures Cell body Axon Dendrites

The Nerve Cell Body An enlarged part of the nerve cell containing abundant cytoplasm and cell organelles. It is sometimes called the soma. Receives information from dendrites and sends messages out through the axon. The primary site for maintaining the life of the nerve cell which support the dendrites and axon.

Nervous Tissue Cell body Nucleus surrounded by cytoplasm Contain organelles such as lysosomes, mitochondria, Golgi complexes, and rough ER (Nissl bodies) for protein production. No mitotic apparatus

The Dendrite An incoming nerve cell process that can act as a receptor or connect to separate specialized receptors. Conducts stimulus information to the nerve cell body. Produces voltage changes in response to various stimuli and assists in nerve impulse formation.

Nervous Tissue Dendrites (little trees) Receiving end of the neuron Conduct impulses toward the cell body Short and highly branched Also contain organelles

The Axon Hillock The junction site between the nerve cell body and the axon. Processes voltage changes , or generator potentials (GP’s) from the cell body and dendrites, and assists the formation of a transmittable nerve impulse.

The Axon Conducts nerve impulses away from the nerve cell to the axon terminals. Is very small in diameter, but can be very long (e.g. the length of a leg). Each nerve cell has only one axon. If an axon is cut, the distal portion degenerates due a disruption of the cytoplasm extending from the cell body.

Axon Conducts impulses away from the cell body toward another neuron, muscle fiber or gland cell. Also contains organelles “ Axon hillock – where the axon joins the cell body. The “initial segment” is the beginning of the axon. The “trigger zone” is the junction between the axon hillock and the initial segment.

Axon Terminals Axon terminals are bulbous distal endings of the many branches that extend from the end of an axon. These bulb-like structures can also be called synaptic knobs, boutons or even “end feet”. The axon terminal serves as a secretory component that releases neurotransmitters in response to nerve impulses.

Nervous Tissue Axon Terminals Site of communication between two neurons or between a neuron and an effector cell.

Representative neuron in out Soma “ cell body”

Neuron that Delivers signal To the synapse Region where an Axon termimal Meets its target Cell The cell that Receives the signal

Nervous Tissue (2 Types) Neuroglia = “glue” Smaller than neurons but more numerous Do not generate or conduct nerve impulses Support neurons Form myelin sheath Participate in phagocytosis

Neuroglia CNS Astrocytes-maintain chemical environment (Ca & K) - Blood Brain Barrier Oligodendrocytes-produce myelin in CNS Microglia-participate in phagocytosis Epedymal cells-form and circulate CSF PNS Schwann cells-produces myelin in PNS Satellite cells-support neurons in PNS

Astrocytes: Nutrient Take up K+ And Neuro- Transmitters From ECF GLIAL CELLS OF THE CNS

GLIAL CELLS OF THE CNS Ependymal Cells: Epithelial Cells Create Selectively Permeable Barrier Between Compartments Of the Brain

GLIAL CELLS OF THE CNS Oligodendrocytes: Support and Insulate axons By creating myelin In CNS, one Oligodentrocyte Forms myelin Around portions of Several Axons

Glial Cells Peripheral nervous system: Schwann cells: produce myelin sheath of peripheral nerve fibers; wrap around the axon **spaces between adjacent sections of myelin where the axon’s plasma membrane is exposed to extracellular frluid are the Nodes of Ranvier . Each Schwann cell associates with a single axon. Satellite cells: nonmyelinating Schwann cell: Form supportive capsules around nerve cell bodies that are located in the ganglia, outside the CNS

The Schwann Cell A specialized cell that supports and maintains the fibers (axons and dendrites) of nerve cells in the peripheral nervous system (PNS). Contains myelin material. Assists the in repair and regeneration of fibers. Wraps around a section of a nerve fiber and creates a protective myelin sheath.

Nodes of Ranvier A Node of Ranvier is a space or gap found on a nerve cell process (axon or dendrite) and is located between the myelin sheaths formed by cells such as the Schwann Cell. The exposed cell membrane located in the node can facilitate the formation and transmission of nerve impulses.

The Myelin Sheath The Schwann Cell wraps around a section of nerve cell fiber in “jellyroll”fashion resulting in a tight coil of concentric membranes called the Myelin Sheath. The whitish, fatty myelin material acts as an excellent insulator and protector of the nerve cell fiber.

Myelin Sheath Cover for a nerve fiber Lipid (white matter) and Protein Insulates and increases impulse speed Formed by Schwann cell membranes (PNS) Oligodendrocytes (CNS) Multiple Sclerosis Autoimmune destruction of myelin sheaths

The Neurilemma The most external portion of the plasma or cell membrane of the Schwann Cell. This specialized membrane surrounds the myelin sheath. The neurilemma is sometimes called the sheath of the Schwann Cell or a neuron “husk”.

Myelination 1 mm in length Up to 100 layers Neurolemma (sheath of Schwann) assists with regeneration of damaged neurons

Nerve Tissue Regeneration At birth, the cell bodies of neurons lose their mitotic features (Can not be replaced by daughter cells) To regenerate, neurons must: Be myelinated Have intact cell body Have functional Schwann cells

Regeneration Wallerian Degeneration is anterograde degeneration characterized by the disappearance of axons and myelin sheaths and secondary proliferation of Schwann cells (occurs in CNS and PNS) Chromatolysis- the result of retrograde degeneratin in the neurons of the CNS and PNS.

Regeneration CNS- Effective regeneration does not occur in the CNS. For examaple, there is no regeneration of the optic nerve or no basement membrane/endoneural surrounding the axons of the CNS PNS- Regeneration does not occur in the PNS. The proximal tip of a severed axon grows into the endoneural tube which consists of Schwann basement membrane and endonerium.

Nerve Tissue Regeneration The axons sprout grows at the rate of 3 mm/day

Nerve Tissue Regeneration Axons in the CNS do not form neurilemmas, so they do not survive axonal damage. Damaged Neurons in the CNS are also rapidly converted to scar tissue (proliferation of astrocytes)

ACTION POTENTIAL Nerve signals are transmitted by action potentials that are abrupt, pulse-like changes in the membrane potential that last a few ten thousandths of a second. Action potentials can be divided into three phases: the resting or polarized state, depolarization, and repolarization The amplitude of an action potential is nearly constant and is not related to the size of the stimulus, so action potentials are all-or-nothing events.

ACTION POTENTIAL Cell membranes of excitable tissue, including neurons, contain ion channels that are responsible for generating action potentials These membrane channels are guarded by voltage-dependent gates that open and close with change in the membrane potential There are separate voltage-gated channels for the sodium., potassium, and calcium channels.

Membrane potential 2 factors influence membrane potential: 1.) Concentration gradients of different ions across the membrane 2.) The permeability of the membrane to these ions

Ionic Concentration Gradients Cell Membrane in resting state K+ Na+ Cl- K+ A- Outside of Cell Inside of Cell Na + Cl- 0 mV

RESTING MEMBRANE POTENTIAL Approximately -70mV, cell negative is the result of the high resting conductance to K+, which drives the membrane potential toward the K+ equilibrium potential At rest, the Na+, channels are closed and Na+ conductance is low

The Resting Potential: Ionic Gradients & a Semi-Permeable Membrane Cell Membrane at rest Na+ Cl- K+ Na+ Cl- K+ A- Outside of Cell Inside of Cell Potassium (K+) can pass through open channels to equilibrate its concentration Sodium and Chlorine cannot pass through Result - inside is negative relative to outside - 70 mV

ACTION POTENTIAL • K + is high inside so increased K + permeability causes more K + to leave cell (inside becomes negative). Na + is high outside so increased Na + permeability causes more Na + to enter cell (inside becomes positive). Membrane potential is a compromise based on which ion is more permanent

UPSTROKE OF A.P. 1) Inward current depolarizes the membrane potential to threshold 2) Depolarization causes rapid opening of the activation gates of the Na channel, and the Na+ conductance of the membrane promptly increases. 3) The Na+ conductance becomes higher than the K conductance and so the membrane potential is driven toward the Na+ equilibrium potential of +65 mV ** The rapid depolarization during the upstroke is caused by an inward NA+ current

REPOLARIZATION OF A.P. Depolarization also closes the inactivation gates of the Na+ channel (more slowly than it opens the activation gates). Closure of the inactivation gates means that the Na+ channels close, and so Na+ conductance returns toward zero Depolarization slowly opens K+ channels and increases K+ conductance to even higher levels that at rest. The combined effect of closing the Na channels and greater opening of the K channels makes the K conductance higher than the Na conductance and the membrane potential is repolarized. ** Repolarization is caused by an outward K current

Action potential initiation S.I.Z.

Action potential termination Think “votes”

Positive feedback loop Na+ enters (depolarization) V-gate Na+ channels open graded Na+ potential Reach “ threshold”? If YES, then...

Absolute Refractory Period. Is the period during which another action potential cannot be elicited no matter how large the stimulus coincides with almost the entire duration of the action potential Explanation: the inactivation gates of the Na channel are closed and will remain closed until repolarization occurs. No action potential can occur until the inactivation gates open.

Relative refractory period Begins at the end of the absolute refractory period and continues until the membrane potential returns to the resting level An action potential can be elicited during this period if a stronger than usual current is provided Explanation: The K+ conductance is higher than at rest, the membrane potential is closer to the K equilibrium potential and farther away for threshold; more current is required to bring the membrane to threshold.

Saltatory Conduction Propagation of action potentials occurs by spread of local currents to adjacent areas of membrane, which are then depolarized to threshold and generate action potentials. Conduction velocity is increased by: 1) increasing diameter of a verve fiber resuts in decreased internal resistance and so conduction velocity down the nerve is faster 2) Myelination. Myelin acts as an insulator around nerve axons and increases conduction velocity. Myelinated nerve exhibits saltatory conduction because action potentials can be generated only at the nodes of Ranvier, where there are gaps in the myelin sheath.

Terminology Synapse Region at which neurons come nearly together to communicate. (neuron or effector organ) Synaptic Cleft Gap between neurons (at a synapse) Impulses can not propagate across a cleft Synaptic Vesicle Packets of neurotransmitter in presynaptic neuron

Terminology Presynaptic Neuron Neuron sending a signal (before the synapse) Postsynaptic Neuron Neuron receiving a signal (after the synapse) Neurotransmitter Substance that tends to cause excitement Required to transmit impulses across a synaptic cleft

Direction of chemical synapse One Direction Synaptic vesicles are only located in the pre-synaptic nerve ending. Only the post-synaptic neuron contains receptors for the neurotransmitters

Chemical Synapses An action potential in the presynaptic cell causes depolarization of the presynaptic terminal As a result of the depolarization, Ca enters the presynaptic terminal Ca entry causes release of neurotransmitter in the presynaptic cleft Neurotransmitter diffuse across the synaptic cleft and combines with receptors on the postsynaptic cell membrane, causing a change in its permeablilty to ions and its membrane potential.

Locks and Keys Neurotransmitter molecules have specific shapes positive ions (NA+ ) depolarize the neuron negative ions (CL-) hyperpolarize When NT binds to receptor, ions enter Receptor molecules have binding sites

Synaptic transmission Excitatory postsynaptic potentials(EPSP)/ Inhibitory postsynaptic potentials (IPSP) are inputs that depolarize/heperpolarize the postsynaptic cell bringing it closer/away from firing an action potential EPSP are cause by opening of channels that are permeable to Na and K Neurotransmitters :Ach, NE, Epinephrine, dopamine, serotonin IPSP are cause by opening Cl channels Neurotransmitters: GABA and glycine

Postsynaptic Inhibition IPSP EPSP

Types of Neurotransmitters Acetylcholine Serotonin Norepinephrine Dopamine Endorphins GABA Glutamate

Acetylcholine Found at neuro-muscular junction Involved in muscle movements (nicotine, curare) In CNS: recticular activating system Slow excitation of cerebral neurons (muscarine, atropine) Memory

Neuromuscular Junction Is the synapse between axons of motorneurons and skeletal muscle. The neurotransmitter released from the presynaptic terminal Ach, and the receptor on the postsynaptic membrane is nicotinic

Neuromuscular Junction and Ach 1. Synthesis and storage of Ach in the presynpatic terminal choline acetylransferase catalyzes the formation from acetyl coA and choline in the presynaptic terminal. 2. Depolarization of the presynaptic terminal and Ca uptake 3. Calcium uptake causes release of Ach into the synaptic cleft 4. Diffusion of Ach to the poststnaptic membrane (muscle end-plate) and binding to specific receptors 5. depolarization of adjacent membrane to threshold 6. Degradation of Ach to acetyl CoA and choline by acetylcholinesterase (acheE) on the muscle end plate

Myasthenia gravis Is characterized by skeletal muscle weakness and fatigability resulting from a reduced number of Ach receptors on the muscle end plate ( due to autoimmune antibodies against acetylcholine receptors at the neuromusclar juntion Diagnosis and treatment involves Acetylchlinesterase inhibitors (neostigmine)- prolong the action of Ach at the muscle end plate.

Curare - ACh antagonist paralysis Nicotine - ACh agonist stimulates skeletal muscles, trembling movements Nerve gases/Black Widow spider venom -release of ACh Severe muscle spasms and death Atropine - ACh antagonist Stupefying agent - delirium & coma Disorders of Cholinergic Transmission

Synaptic Function - Drug Effects 1) Release Inhibitors - ex: Botulinum toxin (in botulism) 2) Acetylcholinesterase Inhibitors - ex: Nerve Gas 3) Postsynaptic Blockers - ex: Curare and most Snake venoms 4) Sodium Channel Blockers - ex: Pufferfish venom and red tide toxins

Serotonin Involved in mood, depression Prozac works by blocking reuptake Ecstasy (MDMA) kills 5-HT terminals in forebrain, releasing massive amounts Pain regulation (descending brainstem) Involved in regulation of cortical activity (sleep?)

Dopamine Involved in movement, attention, learning, motivation, reward Overactive dopamine: Schizophrenia Underactive (loss of) dopamine: Parkinson’s Disease

Loss of dopamine neurons in the substantia nigra Symptoms: difficulty starting/stopping voluntary movements tremors at rest stooped posture rigidity poor balance Parkinson’s Disease

Main inhibitory neurotransmitter in CNS Benzodiazepines (Valium) and alcohol agonise GABA receptor complexes Also some anti-epileptic drugs Gamma-Aminobutyric Acid (GABA)

Huntington’s Chorea Involves loss of neurons in striatum that utilize GABA Symptoms: jerky involuntary movements mental deterioration

Central Nervous System Cerebral ganglia (brain) Spinal Cord

Basic Directions dorsal caudal or posterior rostral or anterior ventral dorsal neuraxis dorsal ventral lateral medial medial lateral dorsal lateral medial medial lateral ventral caudal or posterior caudal or posterior dorsal ventral rostral or anterior neuraxis

Basic Directions FIGURES 4.3 & 4.4 on pgs. 90-91 X dorsal ventral

This is Your Brain 1.5kg of water, lipids and protein contained in your cranium The most important and complex organ in your body 100 billion neurons 100 million billion connections between neurons Top Bottom Side Middle

6 Major Regions of the Brain 1.) Cerebrum 2.) Diencephalon 3.) Midbrain 4.) Pons 5.) Cerebellum 6.) Medulla Oblongata

Brain White matter Mostly axons Myelin sheaths Bundles of axons that connect different regions of the CNS are TRACTS Gray Matter: Unmyelinated Dendrites, Axon terminals

Ascending tracts= carry sensory information from cord to the brain Descending tracts = carry efferent (motor) signals from brain to cord

Functions of Brain Structures Sulcus ----------- A depression or groove in the surface of the cerebrum that helps increase surface area of the cerebrum. Gyrus ------------ An elevated ridge that projects upwards between the sulci of the cerebrum and also helps increase surface area of the cerebrum.. Central Sulcus ------- a deep groove that serves as a dividing line between the frontal and parietal lobe.

Functions of Brain Structures Continued: Frontal Lobe ----- controls conscious muscle action, planning for movements, motor memory, voluntary eye movements. Parietal Lobe ----- Controls conscious interpretation of sensation from muscles, tongue and cutaneous areas. Temporal Lobe --- conscious interpretation of auditory and olfactory sensations. Memory of sounds and smells. Occipital Lobe ------- the most posterior lobe of the cerebrum which deals with conscious seeing, eye focus and integrating visual memory with other sensations.

Lobes of the Cerebrum Frontal Lobe -voluntary and involuntary control of skeletal muscles, speaking & writing Parietal Lobe -general sensations Temporal Lobe -sound and smell Occipital lobe -sight All Lobes- Memory, emotions, reasoning, and intelligence

Function of Brain Structures Continued Cerebral Cortex ----- the outer layer of the cerebrum that consists of gray matter which deals with conscious motor action, sensation, memory, communication, reasoning, emotions, intelligence Sensory Area of the Cerebral Cortex -- Located in areas posterior to the central sulcus. Receives and interprets conscious sensory impulses. The postcentral gyrus of the parietal lobe is a key ridge of gray matter that allows a person to judge the source of sensory stimuli. Motor Area of the Cerebral Cortex --- Located in areas anterior to the central sulcus. Plans and initiates impulses for conscious motor movements. The precentral gyrus of the frontal lobe is a another key ridge of gray matter that allows a person to operate specific areas of the body.

Brain Parts Cerebrum Left and Right cerebral Hemispheres Connected at the Corpus Callosum

Cerebrum Corpus Callosum Transverse fibers of white matter that connects the cerebral hemispheres

Cerebral Cortex Thick blanket of neural cortex Covers the cerebrum Outer surface: Series of elevated ridges or gyri separated by shallow depressions called sulci , or deeper grooves called fissures

Cerebrum Cortex Superficial layer of gray matter (6 layers)

Cerebrum Gyrus (gyri) (Convolutions) Out-folds or ridges in the gray matter Gray matter grows faster that white during development

Cerebrum Sulcus Shallow grooves in gray matter Fissure Deep grooves The “longitudinal fissure” separates left and right hemispheres (halves) Transverse fissure separates the cerebrum from the cerebellum

Hemispheric Lateralization (split-brain) The two hemispheres of the brain share performance of many functions but they also specialize in performing certain unique functions. Left hemisphere Language, numerical and scientific skills, reasoning, control of right-side skeletal muscles Right hemisphere Musical and artistic awareness, perception, recognition, emotional content of language, mental imaging from sound, touch, taste, smell, and control of left-side skeletal muscles

Cerebral Lateralization Language/Verbal = left Dominant for Right handed people Spatial Skills = Right Right hemisphere = synthesis E.G., drawing, map reading, perception, recognition

Damage to Cerebral Cortex Damage to primary somatic sensory cortex = reduced sensitivity of the skin on the opposite side of the body Damage to primary motor cortices= frontal lobes = skeletal muscle and voluntary movement Example: Stroke Paralysis of the opposite side occurs

Cerebrum Interior of cerebrum contains 3 clusters of cell bodies: 1.) Basal ganglia = corpus striatum Control of movement 2.) Amygdala = emotion and memory 3.) Hippocampus = learning and memory

Basal Ganglia (Cerebral Nuclei) Masses of gray matter located mainly in each hemisphere that control gross, unconscious movements of skeletal muscles. (swing arms while walking, talking with your hands, etc.)

Thalamus The thalamus functions a relay station for all sensory impulses (except smell-hypothalamus) to the cerebral cortex. The thalamus also functions as a center for impulses such as pain, temperature, and crude touch and pressure.

Limbic System Region of the cerebrum that surrounds the brain stem Includes several groups of neurons- limbic cortex-cingulate gyrus, parahippocampal gyrus, uncus and associated subcortical strucures- thalamus, hypothalamus, amygdala

Limbic System Also includes centers within the hypothalamus responsible for: 1.) emotional states—rage, fear, and sexual arousal 2.) control of reflexes that can be consciously activated like chewing, licking, and swallowing

Brain Parts Cerebellum “ Little Brain” Inferior to cerebrum Posterior to brain stem Separated from the cerebrum by the transverse fissure

Cerebellum Subconscious level Adjusts postural muscles, maintains balance and equilibrium Coordinates complex movements

Similarities of the Cerebellum and Cerebrum Two hemispheres Lobes Sulci, fissures, and convolutions (folia) Gray matter cortex White matter (cerebellar nuclei)

Functions of the Cerebellum Coordination Posture Proprioception Awareness of movement, equilibrium and position Balance

Brain Parts Brain Stem (3 parts) Superior to the spinal cord Midbrain Pons Medulla Oblongta (medulla)

Brain Stem Contains important processing centers and relay stations for information passing from or to cerebrum or cerebellum and controls vital functions such as breathing and digestive activities

Functions of Brain Structures Continued Medulla Oblongata ------ The most inferior part of the brain stem which relays information between the spinal cord, the pons and cerebellum. The medulla also contains control centers for regulating “ vital signs” such heart rate, blood pressure and primary respiration rate. Pons -------------- A part of the brain stem that serves as a relay between the medulla oblongata, cerebellum and the midbrain. The pons also contains the pneumotaxic and apneustic center for secondary control of breathing. Midbrain ------------------- A central section in the brain interior that is located between the pons and thalamus. This brain region is the most superior part of the brain stem and contains visual reflex centers, auditory reflex centers and motor control centers (e.g. substantia nigra

Medulla Medulla has two external bulges called the pyramids.The pyramids are formed by the largest motor tracts. Axons from the left pyramid cross over to the right and axons on the right cross over to the left. (Decussation of Pyramids) Left hemisphere of brain controls right side muscles; right hemisphere controls left side. Lateral to each pyramid is an oval-shaped swelling called an “olive”. The swelling is caused by the “inferior olivary nucleus”. They carry signals from proprioceptors in muscles to the cerebellum.

Medulla Contains reflex centers that function in regulating Heartbeat, force of cardiac contraction, diameter of blood vessels (Cardiovascular center) , rhythm of breathing, and reflex centers for vomiting, coughing, and sneezing. Controls input and output of 5 of 12 cranial nerves (VIII, IX, X, XI, XII)

Pons Lies directly above the medulla and anterior to the cerebellum (2.5 cm). Bridge connecting the spinal cord with the brain and parts of the brain with each other. Together with the medulla, areas in the pons help control breathing. Origin of 4 cranial nerves (V, VI, VII, VIII) Chewing, head and face sensations, certain eyeball movements, taste, salivation, facial expression, and equilibrium

Midbrain Extends from the pons to the diencephalon (2.5 cm). The cerebral aqueduct passes through the midbrain thereby connecting the third and fourth ventricles. Reflex center for eyes, head, and neck Origin of 2 cranial nerves (III, IV)

Oxygen And Glucose Requirements Of The Brain The brain is very active and uses about 20% of the total oxygen supply in the body. The primary nutrient of the brain is glucose. Glucose is broken down aerobically in presence of the abundant brain oxygen supply in order to yield large quantities of ATP.

External Support For Nervous Tissue BONE Casing: Skull or cranium –brain Vertebral column – spinal cord

Brain Structure Functions Continued Gray Matter ---------- Dark tissue of the brain made up of cell bodies and nuclei. White Matter --------- Light tissue of the brain made up of myelinated nerve cell processes (dendrites and axons). Dura Mater ------------ The tough, outermost meningeal membrane that covers and protects the surface of the brain and spinal cord (“the tough mother membrane”). Arachnoid Mater ------ The middle meningeal membrane that contains web-like spaces for storing and circulating CSF (“the spider web membrane”).

Brain Structure Functions Continued Pia Mater -------------- The innermost meningeal membrane that covers the surface of the brain and spinal cord in a very close, protective fashion (“the gentle mother membrane”). Association Areas ----- Regions of the cerebral cortex that analyze, recognize and act on sensory input and communicate with the motor areas. Examples include the visual and auditory association areas.

External Support For Nervous Tissue Between bones and tissue of the CNS: three layers of connective tissue membrane: meninges 1.) dura mater: forms the outermost covering of the CNS. Inner and outer layers are separated by an area of loose connective tissue that contains tissue fluids and blood vessels

External Support for Nervous Tissue 2.) Arachnoid membrane: Spidery web of collagen and elastic fibers that fills the underlying subarachnoid space. The subarachnoid space is filled with cerebrospinal fluid.

External Support for Nervous Tissue 3.) pia mater: below the subarachnoid space is the innermost meningeal layer. This layer is firmly attached to the neural tissue of the CNS, supports the blood vessels serving the brain, and spinal cord.

Brain Structure Functions Continued Ventricles ----------------------- Hollow spaces in the brain which store cerebral spinal fluid ( CSF ) for support, protection and circulation of extracellular fluid (ECF). Cerebral Spinal Fluid ( CSF ) - A specialized extracellular fluid produced by choroid plexi which bathes, supports and protects the interior of the brain and spinal cord. Choroid Plexus ------------------ A cluster of specialized capillaries enclosed by specialized cells that line the brain ventricles. These circulatory bodies produce cerebral spinal fluid ( CSF ).

External Support for Nervous Tissue Cerebrospinal Fluid (CSF) Salty solution continuously secreted into ventricles (hollow cavities) of the brain

CSF 1.) Physical protection 2.) Regulate extracellular fluid environment: Concenctrations of K + , Ca + , HCO3 - , and glucose are lower, and H + is higher in CSF as compared to plasma CSF contains very little protein, and no blood cells

Composition of CSF vs Plasma Substance Plasma CSF Protein mg/dl 7500 20 Na (Meq/L) 145 141 Cl- 101 124 K+ 4.5 2.9 HCO3 25 24 pH 7.4 7.32 Glucose (mg/dl) 92.0 61.0

Ventricles Fluid filled cavities within the brain

2 lateral ventricles, one in each cerebral Hemisphere; no direct connection between The 2, but both open into the third ventricle of The diencephalon Midbrain has a slender canal known as the cerebral Aqueduct which connects the third ventricle with the Fourth ventricle of the pons and superior portion Of the medulla oblongata

Within the medulla oblongata the fourth ventricle Narrows and joins the central canal of the spinal cord

Choroid Plexus Choroid plexus: specialized tissue found on the walls of the ventricles Secretes CSF Consists of capillaries and transporting epithelium: Ependyma Ependyma actively pump Na and other solutes into the ventricles, creating an osmotic gradient that draws water into the ventricles

CNS - Flow of CSF in CNS 1) Choroid Plexus makes CSF in Lateral Ventricle 2) CSF moves around fornix 3) Joins fluids from choroid plexus in 3rd Ventricle 4) Down cerebral aqueduct 5) Joins 4th Ventricle fluids from choroid plexus 6) Leaves aperatures or goes down central canal in spine 7) Circulates in arachnoid 8) Reabsorbed into blood of dural sinus by arachnoid villi

Arachnoid Villi CSF is gradually reabsorbed into the blood through the arachnoid villi (finger-like projections that project into the dural sinuses) example: superior sagital sinus 20 mL/hr reabsorption rate Pressure remains constant because reabsorption and formation rates are the same.

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