Chapter 9 - Nervous System PDF

Preview

Summary

An organized list of all terms covered in chapter 9...

Description

VET 112 Chapter 9 Terms ❏ Neurology - study of the nervous system ❏ Neur/o - nervous system ❏ Afferent - moving towards ❏ Efferent - moving away Nervous System ❏ Composed of the central nervous system ( CNS - brain and spinal cord) and the peripheral nerves (PNS - nerves that link spinal cord to rest of body) ❏ Functions: ● Sensory - ie: smell, touch, taste, hearing, etc. ● Motor functions - ie: movement ● Integrating functions - ie: avoiding being burned ❏ .Afferent nerves - conduct impulses towards the CNS. ● Also called sensory nerves ❏ Efferent nerves - conduct impulses away from the CNS. ● Also called motor nerves ❏ Somatic nervous system handles actions under conscious or voluntary control. ❏ Autonomic nervous system controls and coordinates automatic function. (ie. decreasing heart rate in response to increased blood pressure) Neurons ❏ Basic functional units of the nervous system ❏ High requirement for oxygen ❏ Cannot reproduces but can regenerate cell processes if the cell body remains intact ❏ Glial cells/neuroglia provide structural and functional support and protection to neurons. ● Glial cells that are found in the brain and spinal cord are called oligodendrocytes. ● Glial cells that are found outside the brain and spinal cord are called schwann cells. ❏ Neuron Structure: ● Central cell body - soma or perikaryon ● Dendrites - numerous afferent, short, multibranched cell process that receive stimuli and conducted the stimuli to the cell body. (ie: heat, cold, touch, stretch) ● Axons - single efferent, long cell process that conducts nerve impulses away and may be covered with myelin. ○ Tissue containing myelinated axons are called white matter ○ Myelinated axons conduct impulses faster due to depolarization not needing to take place where myelin is found (saltatory conduction) ● Myelin - helps the axon conduct the impulse faster. ○ Composed of the cell membrane of a glial cell that is tightly wrapped around the axon. ○ Nodes of Ranvier - gaps between adjacent glial cells. ○ Only location for depolarization on the axon when myelin is present ❏ When a neuron is in resting state, the neuron is not being stimulated. ❏ The resting state is maintained by a specialized molecule and sodium-potassium pumps ● At resting state (Kᐩ ) is found at higher concentrations inside of the neuron ● Sodium potassium pump: ○ pumps (Naᐩ ) from inside of neuron to the outside ○ pumps (Kᐩ ) from outside of neuron to the inside Neuron conduction: ❏ Resting membrane potential is the difference in electrical charge across neuronal membrane resulting

VET 112 from the differences in distribution of positive and negative charges from sodium, potassium, proteins and other charged ions. ❏ Action potential - during depolarization, inside of the neuron changes from negatively charged resting membrane potential to a net positive charge due to inflow of (Naᐩ ) creating a large change in electrical charge from negative to positive. ❏ Threshold stimulus - the point that determines if a stimulus is sufficient enough to make the neuron respond and cause complete depolarization, for a neuron depolarizes to its max strength or not at all. ❏ Conduction of the action potential - spreading wave of opening sodium channels (depolarization/nerve impulse) in sufficient numbers to allow sodium influx and depolarization. ❏ Depolarization process: 1. Neuron receives external stimulus 2. Sodium channel opens on neuron cell membrane 3. (Naᐩ ) flow into cell by passive diffusion 4. Net charge of the cell is changed from (-) to (+) ❏ Repolarization process: 5. Sodium channels close and potassium channels open 6. (Kᐩ ) diffuses out of the cell 7. Potassium inside cell restores the charge to (-) 8. Sodium-potassium pumps restore (Naᐩ ) and (Kᐩ ) back to original sides 9. Resting state restored ❏ Refractory period: ● Time period during which a neuron is insensitive to additional stimuli due to still being in depolarization/early repolarization ● Absolute refractory period - during sodium influx and early potassium outflow (step 6) ● Relative refractory period - during end of repolarization period (step 8) ○ May be possible to stimulate another depolarization if stimulus is very large ❏ Saltatory conduction - rapid means of conducting an action potential by depolarization only taking place at the nodes of ranvier Synaptic Transmission ❏ Synapse - junction between two neurons or a neuron and a target cell ❏ Synaptic cleft - gap between adjacent neurons ❏ Presynaptic neuron - neuron bringing the depolarization wave to the synapse resulting in the releasing of the neurotransmitter ❏ Postsynaptic neuron - contains receptors for neurotransmitter ❏ Telodendron - branched structure on presynaptic neuron ● Terminal bouton - slightly enlarged bulb on each end of telodendron (synaptic end bulb.synaptic knob) ● Vesicle in the knob contain the neurotransmitter and release it via exocytosis ❏ Once released neurotransmitters diffuse across synaptic cleft to the postsynaptic membrane where receptors on the postsynaptic membrane bind with the neurotransmitter. Neurotransmitters: ❏ Excitatory neurotransmitters - usually cause an influx of sodium causing the postsynaptic membrane to move toward threshold ❏ Inhibitory neurotransmitters - move the charge within the postsynaptic cell farther away from the threshold. ❏ Examples of neurotransmitters: ● Acetylcholine - excitatory or inhibitory depending on location in body ○ Primary neurotransmitter of parasympathetic ○ Released by cholinergic neurons

VET 112 ○

Nicotinic acetylcholine receptors - on postganglionic neurons of sympathetic and parasympathetic systems and between neurons and muscle ○ Muscarinic acetylcholine receptors - on target organs and tissues supplied by the postganglionic neuron of the parasympathetic nervous system ● Catecholamines - main two are norepinephrine and epinephrine which are associated with “fight or flight” reactions of the sympathetic nervous system ○ Dopamine - a catecholamine that is found in the brain, involved with autonomic functions and muscle control. ○ Norepinephrine - released by adrenergic neurons and is the primary neurotransmitter of sympathetic nervous system ■ Can also be released from adrenal medulla ● Gamma-aminobutyric acid (GABA) - inhibitory neurotransmitter found in the brain ● Glycine - inhibitory neurotransmitter found in the spinal cord ❏ Recycling neurotransmitters: breaks down neurotransmitters to aid the body in meeting the requirements ● Acetylcholinesterase - found on postsynaptic membrane, breaks down acetylcholine ● Monoamine oxidase (MAO) - breaks down norepinephrine after resorption into the cell ● Catechol-o-methyl transferase (COMT) - breaks down norepinephrine that is not reabsorbed and is still in the synapse ❏ Blood vessels in skin, GI tract and skeletal muscles have adrenergic (catecholamine) receptors to epinephrine or norepinephrine ● Alpha₁ - (adrenergic receptors) cause vasoconstriction of the skin, GI tract, and kidney ● Beta₁ - (adrenergic receptors) increase heart rate and force of contraction ● Beta₂ - (adrenergic receptors) cause bronchodilation Central Nervous System (CNS) ❏ Cerebrum - area of the brain responsible for higher - order behaviors (ie. learning, intelligence, awareness) ● Cerebral cortex - outer layer of the brain composed of grey matter (no myelin) ● White matter - myelinated fibers beneath the cerebral cortex and corpus callosum ○ Corpus callosum - portion of fibers that connect the two hemispheres of the cerebral cortex ● Gyri/Gyrus - folds in cerebral hemispheres ● Sulci/Sulcus - shallow grooves separating gyri that divides the cerebral hemispheres into lobes ● Fissures - deep grooves separating the gyri ○ Longitudinal fissure - prominent groove that divides the cerebrum in right and left hemispheres ● Blood-brain barrier - a specialized protection around blood vessels in the brain to prevent substances and chemicals from entering the brain. ❏ Cerebellum - area of the brain responsible for coordinated movement, balance, posture and complex reflexes ● Located just caudal to the cerebrum

❏ Diencephalon - passageway between brainstem and cerebrum composed of: ● Thalamus - acts as a relay station for regulating sensory inputs to the cerebrum ● Hypothalamus - interface between the nervous system and the endocrine system ○ Plays a major role in temperature regulation, hunger, thirst, rage/anger responses ● Pituitary - endocrine “master gland” ❏ Brain Stem - connection between the rest of the brain and spinal cord

VET 112 ● ●

❏

❏

❏

❏

❏

Composed of the medulla oblongata, pons, and midbrain Area of the brain responsible for maintaining basic support functions of the body (ie. heart, respiration, blood vessel diameter, swallowing and vomiting) ● Many of the cranial nerves originate from this area of the brain ● Damage to brain stem will likely result in death Spinal Cord ● Medulla - central part of the spinal cord composed of grey matter ● Central canal - center of medulla containing cerebrospinal fluid ● Cortex - outer part of spinal cord composed of white matter ● Dorsal and ventral nerve roots emerge between each pair of adjacent vertebrae ○ Dorsal nerve roots contain sensory fibers ○ Ventral nerve roots contain motor fibers ● Dorsal horns - neurons in grey matter that forward sensory nerve impulses to brain or other parts of the spinal cord ● Ventral horns - neurons in grey matter that forward motor nerve impulses to spinal nerves Meninges - connective tissue layers that surround brain and spinal cord ● Contain blood vessels, fluid, and fat that supply nutrients and oxygen to the superficial tissues of the brain and spinal cord ● Provide some cushioning and distribution of nutrients for CNS ● Composed of three layers: ○ Dura mater - tough fibrous ○ Arachnoid - delicate spider web-like above subarachnoid space ○ Pia mater - very thin, lies directly on surface of brain and spinal cord Cerebrospinal fluid ● Fluid between layers of the meninges and in canals and ventricles inside the brain and central canal of spinal cord ● Provides cushioning and may play a role in regulation of autonomic functions (ie. respiration and vomiting) Blood-brain barrier ● Separates the capillaries in the brain from the nervous tissue ● Capillary walls in the brain have no fenestrations (small holes allowing certain substances/particles to pass in/out), and covered by cell membranes of glial cells ● Prevents many drugs, proteins, ions, and other molecules from readily passing from the blood into the brain Nerve II - Optic Nerve ● Runs from the back of the eye to the brain, and the only cranial nerve that is part of the CNS and not PNS ● Optic chiasm - where the optic nerves cross and relay info to the opposite hemispheres ● Transfers visual information from the retina to the vision centers of the brain

Peripheral Nervous System (PNS) ❏ 12 Cranial Nerve pairs: I. Olfactory II. Optic III. Oculomotor IV. Trochlear V. Trigeminal VI. Abducens

VII. VIII. IX. X. XI. XII.

Facial Vestibulocochlear Glossopharyngeal Vagus Spinal accessory Hypoglossal

VET 112 ● Each nerve may contain axons of motor neurons, sensory neurons, or combinations of both ❏ Nerve VII - Facial ● Controls facial muscles and relays sensations from taste buds, carries nerve fibers to tear and salivary ducts ● Paralysis causes drooping of facial muscles on the affected side ❏ Nerve X (cranial) - Vagus nerve ● Travels from the brainstem to the colon, found in next running net to the carotid artery and jugular vein ● Supplies motor impulses to the pharynx, larynx, trachea, lungs, heart, esophagus, and digestive tract. ● Brings sensory impulses from ear, tongue, pharynx, and larynx to the brain ❏ Brachial Plexus ● Musculocutaneous nerve - innervates the biceps brachii and brachialis ○ Supplies cutaneous innervation to the medial side of forelimb ○ Thin nerve found in the cranial portion of the brachial plexus ● Radial nerve - primary nerve of support for the limb. ○ Motor nerve to all the extensors of the elbow, carpus, and digits ○ Large nerve found slightly deep to to ulnar and median nerves ● Median nerve - supplies all of the flexor muscles of the carpus and digits ○ Supplies sensation to the medial side of the paw ○ Cranial branch of the brachial plexus ● Ulnar nerve - supplies all of the flexor muscles of the carpus and digits ○ Supplies sensation to the lateral side of the paw ○ Caudal branch of the brachial plexus, runs along the olecranon. ❏ Femoral Nerve ● Runs alongside the femoral artery and vein ● Supplies motor function to the muscles of the cranial thigh ● Carries sensory impulses from the skin of the hip, thigh, leg and knee ❏ Sciatic nerve ● Divides into the peroneal and tibial nerves ● Carries motor impulses to all the muscles of the distal hind limb Autonomic Nervous System ❏ Controls automatic functions at the subconscious level ❏ Efferent motor nerves are composed of a sequence of two neurons: ● Preganglionic neuron - cell body in the brain or spinal cord and axon extended out to an autonomic ganglion ● Postganglionic neuron - one or more additional neurons that are then connected to the target organ ❏ Sympathetic ganglion chain - series of autonomic ganglia outside thoracolumbar area of spinal column ❏ Sympathetic nervous system - nerves emerge from the thoracic and lumbar vertebral regions (thoracolumbar system) ● Sympathetic preganglionic neuron may: ○ synapse with a neuron within the ganglion chain ○ Pass through the ganglionic chain and synapse with a neuron located beyond the sympathetic chain ○ Usually synapses with many postganglionic neurons in the sympathetic chain or ganglions outside the sympathetic chain ○ Sympathetic postganglionic neuron is much longer than its corresponding preganglionic

VET 112 neuron ● Increases: ○ Heart rate ○ Diameter of bronchioles ○ Diameter of pupil ○ Diameter of muscle blood vessels ● Decreases: ○ Diameter of skin blood vessels ○ Gut function ○ Salivary glands (except cats) ❏ Parasympathetic nervous system - nerves emerge from the brain and sacral vertebral regions (cranialsacral) ● Parasympathetic preganglionic neuron travels directly from the CNS to its target organ ○ Synapses with a short postganglionic neuron in the target organ ○ Parasympathetic preganglionic neuron is relatively long compared with the very short postganglionic neuron ● Decreases to normal: ○ Heart rate ○ Diameter of bronchioles ○ Diameter of pupil ○ Diameter of muscle blood vessels ● Increases to normal: ○ Diameter of skin blood vessels ○ Gut function ○ Salivary glands Reflexes ❏ Somatic reflexes - involve contraction of skeletal muscle ❏ Autonomic reflexes - regulate smooth muscle, cardiac muscle, and endocrine glands ❏ Contralateral reflex - starts on one side of body and travels to opposite side ❏ Ipsilateral reflex - stimulus and response are on the same side of the body (ie. stretch reflex) ❏ CNS moderation of reflexes: ● Upper CNS normally produces an inhibitory effect on the reflex arcs ● With injury, intact reflex arcs caudal to the spinal cord trauma become hyperreflexive ● Trauma where reflex arc enters or leaves the spinal cord, or damage to the sensory nerve/motor nerve of the reflex, results in either hyporeflexive or absent reflex arcs

❏ Reflex arc: 1. Sensory receptor sends an action potential along the sensory neuron to the grey matter of the spinal cord or brain stem 2. Sensory neuron synapses with other neurons 3. Integrated neurons takes incoming sensory impulse integrated with other impulses from other sensory neurons 4. Integrated response of the reflex is sent out by the motor neuron, which ends at the target organ. ❏ Reflex arcs: ● Stretch Reflex(Monosynaptic reflex arc): ○ Involves a sensory neuron located on a muscle spindle and a motor neuron located on a muscle fiber

VET 112

●

●

●

●

○ Only one synapse between them without any interneurons ○ Results in stretched muscle to rapidly contract and the antagonistic muscle to relax Withdraw Reflex(flexor reflex) ○ Sensory receptor(s) receive stimulus and several interneuron synapses carry out response ○ Results in contraction or flexing of muscles Crossed Extensor Reflex ○ contralateral reflex ○ If withdrawal reflex initiated, afferent sensory neuron synapse with interneurons ○ Causes contraction of opposite extensor muscles Palpebral reflex arc ○ Light tap on the medial canthus of the eye produces a blink of the eyelids ○ Used to test cranial nerve damage Pupillary light reflex (PLR) ○ Normal response to shining a light in the eye of an animal is for the iris in both eyes to constrict...