Nervous System

NERVOUS SYSTEM Terminologies: Please memorize the following terms for your sake. * Afferent

- conveying toward the center; sensory

* Axon - central core which forms the essential part of a nerve fiber. It transmits impulses to the other neurons(away from the cell body0, or to muscle fiber and grand cells. *Dendrite - A branched and tree-shaped protoplasmic process from a neuron. It transmits impulse towards the cell body. *Effector - a nerve end organ which serves to distribute impulses which activate muscle contraction and gland secretion. *Efferent

- conveying away from the center; motor.

*Fissure - any cleft or groove; a deep fold in the cerebral cortex which involves the entire thickness of the brain wall. *Ganglion

- Collection or mass of nerve cell bodies outside the CNS

*Gyrus - a convoluted ridge; tortuous elevations of the surface of the brain caused by unfolding of the cortex *Intemuncial neuron - a nerve cell that transmit impulses from one part of the brain or spinal cord to another. *Nucleus/ei

- group of neurons serving a common function located in the CNS

*Neuroglia

- supporting structure unit of the nervous tissue

*Neuron

- anatomical or basic structure unit of the nervous system

*Plexus

- a network of nerves

*Preganglionic fiber - axon of neurons whose cell bodies are in the brain or spinal cord. Fiber that transmit impulse from the CNS to the autonomic ganglia. *Postganglionic fibers - transmit impulse from cell bodies in the autonomic ganglia to visceral effectors *Ramus

- a branch of a nerve

*Receptor

- sensory nerve terminal which respond to stimuli

*Reflex - it is an involuntary response to stimuli; physiological or functional unit in the nervous system * Reflex arc - the structural basis of reflex action * Stimulus

- any agent, act or influence producing a reaction in a receptor

*Sulcus- a groove, trench or furrow; a depression on the surface on the brain The gyri/gyrus *Synapse - region of contact between processes of two adjacent neurons, forming a place at which nerve impulse is transmitting from one neuron to anothe *Tract - A collection or bundle of nerve fibers having the same origin, function and termination. *Meninges

- protective covering of the Brain and Spinal Cord.

Nervous System -

concerned with the reception, transmission, interpretation, integration of these sensations which arise from the internal and external environment Pathway and processing system of impulses

2 Main Division 1. CNS - brain and spinal cord 2. PNS - cranial, spinal nerves, autonomic nerves NEURON OR NERVE CELL -

3Unit of the nervous system

Part of the Neuron 1. Dendrites - receptive surface for the neuron. 2. Axon - arises from an elevation on the nerve cell body (axon hillock). Transmit impulse away from the cell body. 3. Cell body - contains the organelles and is responsible for metabolic processes.

Components of Nerves Nerve fibers (surrounded by Endoneurium) -- Fascicles/Nerve bundle (surrounded by Perineurium) –Nerve (surrounded by Epineurium) *Myelin Sheath – contains cholesterol, cerebroside and phospholipids - it serves as an insulator for faster nerve conduction/transmission of impulses - it covers the axon of the myelinated nerves - produced by the Schwann Cells (PNS) and Oligodendrocytes (CNS) *Nodes of Ranvier - these are areas in the axon of myelinated fibers devoid of myelin -

responsible for SALTATORY CONDUCTION

Classification of Neurons 1. UNIPOLAR - has short processes has only one main process leaving the cell body E.g. Cerebrospinal ganglia 2. BIPOLAR - it has 2 main processes leaving the cell body E.g. retina, spinal and vestibular ganglion of the inner ear, olfactory mucous membrane 3. MULTIPOLA - if it has only one axon and many dentrites E.g. CNS, Penpheral Autonomic ganglia Note; All Unipolar and Bipolar neurons are sensory or afferent in function. B. According to Function 1. Afferent 2. Efferent a. Somatic efferent – carry impulses that cause contraction of skeletal muscles b. Secretory efferent - carry impulse that lead to secretion of glands c. Augmentor efferent - strengthen the force of contraction d. Accelerator neurons - increase the force and rate of contraction e. Inhibiting neuron – decrease the force and rate of contraction of smooth and cardiac muscle 3. Associational (Intemuncial) - transmits impulses form one part of the brain or spinal cord to another and their processes do not leave the CNS NEUROGLIA - supporting cells of the nervous system

3 Types of Neuroglia 1. Astrocytes - star shaped that participates in brain development and metabolism of neurothransmitter, helps from the blood brain barrier maintain proper balance of K a. Protoplasmic astrocytes - attained to the blood vessels to the pia mater by means of pedicles and are found chiefly in the gray matter b. Fibrous astrocyles - attached to blood vessels by means of their processes and are found chieftly in the white matter 2. Oligodendrocytes/Oligodendroglia - produce myelin sheath in the Brain and Spinal Cord 3. Microglia – brain macrophages SYNAPSE - site of transmission of nerve impulse from one neuron to another - permits transmission of impulse in one direction only Types of Synapse 1. Axodendritic 2. Axosomatic 3. Axoaxonic *Syanptic Vesicle – found in sypnatic endings - contains the neurotransmitters for facilitation of transmission of impulses *Synaptic Cleft – separates the presynaptic and postsymatic membrance Note: Transmission of activity from one neuron to another is chemical in nature. It involves the release of an excitatory neurotransmitter (Ach) by the synaptic vesicle across the synaptic cleft. Termination of transmission is made by the release of the Acetylcholinesterase which stops the action of the Acetylcholine. Characteristics of Nervous Tissue A. All or None Law – nerve fibers respond to a threshold stimulus (stimulus strong enough to cause a response) maximally or not at all. B. Absolute Refractory Period – period when the nerve fibers will not respond to any maximal stimulus. This gives the fiber a forced rest, thus making the nerve indefatigable. C. Relative Refractory Period - only a stimulus stronger than the first that produced an action potential, will result in the transmission of a nerve impulse

D. Super Normal Phase – the nerve become more excitable than before it can be excited by a subthreshold stimulus in reference to the first stimulus which excited the nerve. E. Self-Propagation – the impulse does not die before it gets to its destination. It gets a boost at each node of Ranvier to furnish it with enough energy to get it to the node. Action Potential - a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolanization) and then restore it to the resting state (repolarization) Gray Matter - contains either neuron cell bodies, dendrite, and axon terminals or bundle of unmyelinated axons and neuroglia. - no myelin sheath White Matter - aggregations of myelinated processes from mayneurons. - there is myelin sheath Directions of White Matter 1. Project Fibers – connects cerebral cortex with subcortical centers 2. Association Fibers – connects cerebral cortex of one area which another area on the same side. 3. Commissural Fibers – transverse fiber which connect one side of the brain to the other. Brain -

is a hollow organ which contain a system of spaces (Ventrides) 2% of total body weight Contains billions of neurons and glial cells Well developed, involved in many aspect of higher learning such a memory, behavior and learning language

Ventricles of the Brain - 5 cavities within the brain lined with ependyma - filled with CSF - 2 lateral ventricles, 3rd Ventricle, Cerebral Aqueduct/Aqueduct of Sylvius/Iter, 4th Ventricle Cerebrospinal Fluid - entire nervous system contains abut 80-150 ml of CSF - 400-500 ml produced and reabsorbed daily - Source of nourishment of the brain Functions of the CSF: 1. Mechanical Support to the Brain

2. Controls brain excitability – regulates ionic composition/balances the electrolytes 3. protection from pressure changes *Choroid Plexus – produces the CSF CSP Flow: Choroid Plexus - Lateral Ventricle – Foramen of Monroe – 3rd Ventricle --Iter --- 4th Ventricle --- Foramen of Magendie (Medial)/Foramen of Luschka (Lateral) --- Subarachnoid space --- Cerebral Convexities --- Arachnoid Villi --Venous Circulation Division of the Brain 1. Forebrain (Prosencephalon) a. Cerebral Hemisphere (Telencephalon) with each hemisphere composed of 1. Cerebral Cortex 2. Basal Ganglia 3. Rhinenception b. Diencephalon 1. Doral portion (Thalamus and Epithalamus) 2. Ventral portion (hypothalamus and subthalamus) 2. Midbrain or (Mesencephalon) - this connects, the forebrain with the hindbrain and surrounds cerebral aqueduct of Sylvius. a. Ventral portion - cerebral peduncle b. Dorsal portion - superior and inferior colliculi 3. Hindbrain or (Rhombencephalon) a. Metencephalon - cerebellum, pons b. Myelencephalon - Medulla Oblongata 1. Forebain - largest division of the brain - consists of cerebral hemispheres and diencephalons Cerebral Hemisphere - extend posteriorly overlap the portion of the brain - median longitudinal fissure separates the 2 hemisphere - corpus callosum connects the 2 hemispheres - has 5 lobes frontal, parietal, occipital, temporal and insula *Central Sulcu/Fissure of Rolando - separates the frontal lobe and parietal lobe

*Lateral Cerebral Fissure/Sylvian Fissure – separates the fronto-pariental lobes from the temporal lobes. *Parieto-Occipital Fissure – separates the occipital lobe from the parietal and temporal lobe A. Cerebral Cortex - convoluted layer of gray matter upon the surface of each cerebral hemisphere Functions of the Cerebral Cortex 1. It is the organ of sensation and is concerned with sensory discrimination. 2. All the activities of the body regulated through visceral afferent or efferent or autonomic nerves are influenced by impulses from cerebral cortex. 3. Its project fibers transmit impulses to the basal ganglia and influence the spinal cord motor neurons by way of the extrapyramidal tracts. 4. It is the center for a. reflexes b. hearing (temporal lobe) c. speech d. sleep e. vision f. mental process like intelligence, memory, judgment, imagination, creativity and conscious thought 5.It forms conditioned reflexes 6. It is the location of the sensory areas 7. It is the location of association areas Brodmann’s Area of the Brain Area 4 - Pre-central gyrus - primary motor area - in charge with all the movements in the body - Flaccidity Area 5 - Pre-motor area - Spasticity Area 3, 1, 2 – Post-Central gyrus - primary sensory area - in charge with all the sensory function of the body Area 7 - Sensory Association Area

Area 41 - Superior Temporal Gyrus - Primary Auditor Cortex - In charge with hearing Area 43 – Primary Gustatory Area Area 17 - Occipital Lobe - Primary Visual Area - Also known as Striate Cortex Area 18, 19 – Visual Association Area Area 44, 45 – Broca’s Area - motor speech - in charge with talking Area 22 – Wernicke’s Area - Speech comprehension - Anterior 1/3 of superior temporal gyrus Limbic System - composed of the cingulated and parahippocampal gyri - visceral brain - concerned with emotion and visceral activity of the individual Note: Destruction of the limbic system in men is followed by loss of fear and rage reactions, compulsion to examine objects, increased sexual activity with homosexual tendencies, and excessive food intake. This is known as the Kluve-Bucy syndrome. Basal Ganglia - dark masses of gray matter located deep within the cerebral hemisphere - composed of the Caudate nucleus, Putamen, Globus Pallidus - aid in the activity of the motor area and are concerned with the modifying and coordinating voluntary muscle movement. - CN and Putamen are the major input of the Basal ganglia - Globus Pallidus major outflow of the Basa Ganglia - Parkinson’s Disease Rhinencephalon - olfactory portion of the cerebral hemisphere Functions: 1. Receives and integrates olfactory impulse 2. Establishes reflex connections with visceral activities by way of the hypothalamus and medulla oblongata

3. established cortical connections in the hippocampus which send out commissural and projection fibers B. Diencephalon 1. Hypothalamus - forms the floor and part of the wall of the 3rd ventricle and extends from the optic chiasm to the caudal boundary of the mamillary bodies, ventrally it is connected with neurohypophysis (posterior pituitary gland) Functions: 1. Chief subcortical center for regulation of visceral activities 2. temperature regulating center 3. water balance center – osmoreceptors in the hypothalamus are sensitive to the osmotic pressure of blood and the amount of water in the body. 4. center for regulation of food intake 5. regulates gastric secretion 6. regulates activities of the adenohypophysis by secreting hormone releasing factors 7. active during emotional expression. 2. Thalamus - located at the dorsal portion of the diencephalons - important relay center for sensory fibers - sensory integrating center, relay station for visceral response, regulates and maintains state of consciousness, alertness, attention, expression of emotions. II . Midbrain - otherwise known as mesencephalon - cerebral peduncles on the central and the superior and inferior colliculi on the roof of the midbrain Functions: 1. concerned with ocular reflexes and relaying of auditory and visual impulses 2. it is the conduction pathway for impulse to and from numerous structures of the central nervous system 3. It contains motor nuclei of CN III and CN IV 4. it is the location of the Edinger-Westphal nuclei which give rise to visceral efferent supplying the smooth muscles of the eye. 5. center involved in postural or attitudinal reflex (tonic neck and labyrinthine reflexes) 6. center for righting reflexes, concerned with orientation of the head in space.

III. Hindbrain - rhombencephalon (metencephalon and myelencephalon) 1. Metencephalon - further divided into the pons and cerebellum Cerebellum - Also know as the little Brain - Largest part o the hindbrain - Overlaps the pons and medulla oblongata and is overlapped by the occipital lobe - Attached to the midbrain by the cerebellar peducles Functions: 1. coordinates voluntary muscular activity 2. regulates tone in extension muscles 3. maintains equilibrium/balance 4. regulates essential excitatory and inhibitory impulses for agonists, antagonists, and synergists in various muscles movements Pons -

Means bridge Extends from the medulla oblongata to the midbrain Motor an sensory nuclei of CNV, VI, VII an VIII Pathway for ascending sensory and descending motor fibers

2. Myelencephalon - also called the Medulla Oblongata - expanded continuation of the spinal cord - extends from the foramen magnum to the caudal border of the pons - CN IX, X, XI, and XII Functions: 1. serves as the conduction pathway between the higher and lower parts of the central nervous system 2. contains vital centers important in the control of the heart, blood pressure, respiration, and swallowing, vomiting and coughing reflex Reticular Formation - of the medulla oblongata replaces the gray matte of the spinal cord - composed of cell bodies or neurons of various sizes, types and shapes - extends forward from the medulla through the pons, midbrain, and into the thalamus in the diencephalons - receives nerve fibers from the second order neurons that are on their way to the thalamus from the spinal cord, cerebellum, hypothalamus, and the orbitofrontal region of the cerebral cortex

Functions: 1. the Inhibiting center located at the centromedial portion. Stimulation of this area results in inhibition of voluntary movements induced by the stimulation of the cerebral cortex, reflexes, muscle tone, depression of respiration, and blood pressure. 2. the Facilitating center extends throughout the length of the reticular formation from the medulla oblongata to the diencephalon. Stimulation of this area will have the opposite effects of the stimulation of the inhibiting center.

SPINAL CORD - lies within the vertebral canal - Extends from the foramen magnum to the lower border of the first lumbar vertebra. - 42 – 45 cm long *Conus Medullaries - cone shaped end of the spinal cord *Filum Terminale – extends through the end of the dural sac at the level of the 2nd sacral vertebra to attach to the back of the 1st segment of the coccyx Cross Section of the Spinal Cord: *Gray Matter – butterfly shaped located centrally in the spinal cord - it has 2 ventral/ anterior horns which has motor function - it has 2 dorsal/posterior horn which has sensory functions - it has 2 lateral horns (thoraco-lumba area only) which contains the preganglionic fibers of the sympathetic nervous system *White Matter - composed of myelinated nerve fibers - fibers are arranged in tracts which are bundles of nerve fibers with the same origin, termination and function. Functions of the Spinal Cord 1.Reflex Center *Reflex - it is an involuntary response to a stimulus Component of the Reflex Arc a. Receptor – sensory nerve termina which receives a stimulus b. Afferent Neuron - transmits impulses from the receptor to the CNS c. Center or Internuncial Neuron - area where impulse pass from an afferent neuron across one or more synapses d. Efferent Neuron- transmit impulses from the CNS to the effector organ e. Effector Neuron - nerve end organ which serves to distribute impulses to activate muscle contraction and gland secretion

2. Conduction Pathway - composed of fibers that transmit impulse to (ascending tracts) and from (descending tracts) the CNS. Ascending Tracts: 1. Posterior Funiculi (Fasciculus Gracilis and Fasciculus Cuneatus) -

impulses coming from the extremities and are concerned with proprioception and kinesthesia (position and movement sense) receptors are located in the muscles, tendons, joints Fasciculus Gracilis - subserves the LE Fasciculus Cuneatus - subserves the UE

2, Spinocereballar Tracts -

transmit impulses from muscles, tendons and joint from all parts of the body and the information given to the cerebellum involved in the limb movements and maintenance of the posture

3. Spinothalamic Tracts -

has 2 types o Anterior Spinothalamic – concerned with transmission of impulses concerned with light touch and pressure o Lateral Spinothalamic – concerned with the transmission of impulses concerned with paid and temperature

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from muscles, skin tendons, joints, viscera sensation of fullness of the Urinary Bladder, pain from ureter, urinary bladder, urethra and sexual sensations.

Descending Tracts 1. Corticospinal and Pyramidal Tract -

these tracts transmit impulses concerned with volitional movements

2. Extrapyramidal Tracts -

these are short tracts that integrate activities of the spinal cord impulses from the various parts of the brain to exert influence on the neurons of the spinal cord.

3. Descending Autonomic Tracts -

excitatory and inhibitory influences of the spinal reflex arc