Nervous System

1. Nervous System • Spinal Cord & Peripheral Nerves

2. Spinal Cord • Continuation of the brain stem • Tube-like structure w/i spinal cavity • Diameter similar to width of the thumb • Extends from foramen magnum of the occipital bone to the level of the first lumbar vertebrae – • Lumbar Puncture – this arrangement is the basis for sampling/withdrawing CSF fluid from the subarachnoid space between L3/L4 for evaluation: blood, pathogens, abnormal signs… • Well protected by vertebrae, meninges, CSF, blood-brain barreier

3. Herniated Disc • What Happens with a herniated disc? • Spinal disc (cartilaginous disc) becomes less elastic – can rupture! • A portion of the spinal disc pushes outside it’s normal boundary = herniation. • Spinal nerves/spinal cord can be pinched/compressed. • May occur suddenly in an vent such as fall/accident – or gradually w/ repetitive straining of the spine. Typically patients already have spinal stenosis (narrowing of space around spinal cord/nerves) • Spinal cord/nerve compression alters the function – either abnormal signals are passed or none at all.

4. Symptoms of Disc Herniation • Electric Shock PainPressure on the nerve can cause abnormal sensations, commonly experienced as electric shock pains. • EX. When the compression occurs in the cervical (neck) region, the shocks go down your arms, when the compression is in the lumbar (low back) region, the shocks go down your legs. • Tingling & NumbnessPatients often have abnormal sensations such as tingling, numbness, or pins and needles. These symptoms may be experienced in the same region as painful electric shock sensations. • Muscle WeaknessBecause of the nerve irritation, signals from the brain may be interrupted causing muscle weakness. Nerve irritation can also be tested by examining reflexes. • Bowel or Bladder ProblemsThese symptoms are important because it may be a sign of cauda equina syndrome, a possible condition resulting from a herniated disc. This is a medical emergency,

5. Gray Matter and White Matter • Gray Matter • Center of spinal cord – butterfly shaped • Consists of cell bodies and interneurons • 2 projections – dorsal horn (posterior horn) • ventral horn (anterior horn) • Central canal – opening in the center of gray matter that extends the length of the spinal cord • Open to the ventricular system in the brain and subarachnoid space – CSF circulates throughout the subarachnoid space

6. White Matter • Outer layer of spinal cord • Composed primarily of axons • Neuronal axon are clumped together = nerve tracts • Sensory Tracts – ascending tracts • Carry information from the periphery up the spinal cord to the brain • Spinothalmic – temperature, pressure pain, light touch • Dorsal column – proprioception, deep pressure, vibration • Spinocerebellar - proprioception • Motor Tracts – descending tracts • Carry information from the brain, down the spinal cord toward the periphery • Pyramidal - skeletal muscle tone, voluntary muscle movement • Extrapyramidal – skeletal muscle activity, balance/posture

8. Decussation: • Most nerve tracts cross over from one side to another • EX. Corticospinal tract originates in the Lt – frontal lobe – descends to the medulla oblongata – fibers then decussate and descend down the Rt – side of the spinal cord – innervate the Lt side of the body. • Most sensory tracts decussate in the spinal cord

10. Injury? • Neurons of the brain and spinal cord do not regenerate • If spinal cord can be severed – w/ neck/back injuries. • Quadriplegia – when cord is severed at neck region (cervical)… trunk and all four extremities are paralyzed • Paraplegia – when injury occurs to lower (lumbar) spinal cord and paralysis is from waist down – still having use of upper extremities

11. Spinal Nerves • Spinal nerves attach to the spinal cord • Each nerve is attached to the cord by 2 roots • Dorsal root – contains sensory nerve fibers that come together to form a dorsal root ganglion • Ventral root – contains motor fibers – distributed to the muscles/glands • Dorsal/Ventral roots are packaged together to form a spinal nerve (mixed nerve) – contains both sensory/motor nerves

12. Spinal Nerves

13. Spinal Cord Functions: • Sensory Pathway – spinal cord provides a pathway for sensory information traveling from the periphery to the brain • Information ascends the spinal cord through the dorsal root ganglion – dorsal root – into spinal cord. • Motor Pathway – spinal cord provides a pathway for information descending from the brain to the periphery out the ventral root of spinal cord to motor neurons • Reflex Center – spinal cord acts a reflex center • Ex. When you stick your finger on a tack – you quickly/automatically withdraw your finger - the spinal cord, not the brain performs this function

14. Reflexes: • Reflex = an involuntary response to a stimulus • Many activities we engage in everyday occur very rapidly and w/o conscious control – happens reflexively. • Ex. When you touch a hot surface – your hand is removed very quickly – hand is safe long before you consciously say “This is hot!” (withdrawal reflex) • Reflex Arc – nerve pathway involved in a reflex • 4 components: • Receptor – receives stimulus • Afferent (sensory neuron) – nerve impulse is carried by the sensory neuron to the spinal cord • Efferent (motor neuron) – nerve impulse in carried by a motor neuron the muscle • Effector organ – responds to the impulse

15. Patellar reflex (knee-jerk reflex) • Receptor – by tapping the tendon, the mallet stimulates sensory receptors in the thigh muscles. • Afferent – nerve impulse is carried is carried by the sensory neuron to the spinal cord • Efferent – nerve impulse is carried by a motor nerve to the muscles of the thigh • Effector organ – the muscles of the thigh, specifically the quadriceps femoris, is an effector organ. In response to the nerv impulse, the muscles contract and move the leg in an upward movement.

16. Patellar Reflex:

17. Many, Many Reflexes! • Organ Reflexes – help regulate organ function • Physiologic functions: • Pupillary reflex - regulates the amount of light that enters the eye • Baroreceptor reflex – when BP changes, this reflex causes the heart and blood vessels to respond in a way that restores BP to normal • Diagnostic – to asses nerve function, abnormal findings may indicate CNS lesions, tumors, or neurological diseases • Abdominal reflex - • Babinski reflex – • Patellar (knee-jerk reflex)

18. Peripheral Nervous SystemNerves and ganglia outside the CNS • Nerve vs Neruon • Neuron is a single nerve cell • Nerve contains many neuron bundled together w/ blood vessels – wrapped in connective tissue • Nerves are outside the CNS – within the CNS they are called tracts • Sensory Nerve – composed of only sensory neurons • Motor Nerve – composed only of motor neurons • Mixed nerves – both sensory and motor neuron, most nerves are mixed, all spinal nerves are mixed!

19. Classification of Peripheral NervesCranial Nerves & Spinal Nerves(based on origin of the fiber) • Cranial Nerves • 12 Pairs – numbered in order the nerves exit the brain from front to back • Name – associated w/ the anatomical area served by the nerve. • Cranial nerves primarily serve the head, face, neck ****except for the vagus nerve which extends throughout the thoracic/abdominal cavity. • Functions of Cranial Nerves: • Sensory information special senses: taste, smell, vision, hearing • Sensory information general senses: touch, pressure, pain, temperature, vibration • Motor information that results in contraction of skeletal muscles • Motor information that results in the secretion of glands and the contraction of cardiac/smooth muscle

20. Cranial Nerves • I Olfactory (S) sense of smell • II Optic (S) sense of sight • III Oculomotor (MX) eyeball/eyelid movement,pupil size • IV Trochlear (MX) movement of eyeball • V Trigeminal (MX) chewing,sensations of face,cornea • VI Abducens (MX) movement of eyeball • VII Facial (MX) facial expressions, saliva/tears,taste • VIII Vestibulocochlear (S) hearing/balance • IX Glossopharyngeal (MXD) swallowing/saliva/gag/BP • X Vaugus (MXD) Visceral muscle/sensations, BP, digestive system • XI Accessory (MXD) swallowing, head/shoulder movement/speaking • XII Hypogloassal (MXD) speech, swallowing

22. Cranial Nerve Assessment • I – Olfactory – smell and identify odor • II – Optic – opthalmoscope, eye chart, peripheral vision • III – Oculomotor – eye movement, pupil constriction, size, shape, equality • IV – Trochlear – ability for eyes to follow moving object • V – Trigeminal– sensations tested (sharp/dull), corneal reflex, motor fxn of jaw • VI – Abducens – ability of eye to follow moving object • VII – Facial – taste, facial motor fxn(smile,close eyes, whistle) • VIII – Vestibulocochlear – hearing (w/ tuning fork) • IX – Glossopharangeal – gag/swallow reflex, speak, cough • X – Vagus – similar to above – both innervate throat • XI – Accessory – rotate head side/side, shrug shoulders • XII – Hypoglossal – stick tongue out – note deviations

23. Spinal Nerves • 31 pairs emerge from spinal cord • Each pair numbered according to level it arises from spinal cord • 8 pairs – cervical nerves • 12 pairs of thoracic nerves • 5 pairs of lumbar nerves • 5 pairs of sacral nerves • 1 pair of coccygeal nerves • Cauda Equina – include the lumbar and sacral nerves – extend from spinal cord through the spinal cavity before exiting through tiny holes in the vertebrae (foramina) • Spinal nerve plexus – when nerve fibers converge after exiting the vertebral column to form a network (plexus) • Cervical Plexus (C1-C4) – skin, muscles of the neck shoulder:diaphragm • Brachial Plexus (C5-C8,T1) – skin, muscles of the upper extremeties • Lumbosacral plexus (T12, L1-L5, S1-S4) skin, muscles of lower extremeities

24. Plexuses • Cervical Plexus – fibers supply the muscles and skin of the neck. • Motor fibers pass into the phrenic nerve (stimulates the contraction of the diaphragm – major breathing muscle) • EX. Injury below C5 level – the person is paralyzed but can still breath on their own. If the injury is higher (C2) the motor impulses to the diaphragm are interrupted –can’t breathe w/o assistance • Brachial Plexus – nerves that emerge from this plexus supply muscles and skin of the shoulder, arm, forearm, wrist, hand. • EX Axillary nerve in the shoulder suseptible to damage when a person is using crutches – weight of the body can damage the axillary nerve = crutch palsey • Lumbosacral Plexus - gives rise to nerves that supply the muscles and skin of the lower abdominal wall, external genitalia, buttocks, and lower extremities • Ex. Sciatic Nerve, the longest nerve in the body arises from this plexus – it supplies the entire musculature of the leg and foot – it can become inflamed and cause pain in the buttock and posterior thigh region – common cause is a ruptured/herniated vertebral disc.

25. Dermatome… • Dermatome is where each spinal nerve innervates a particular area of the skin • Each dermatome is named for the particular nerve that serves it ( C4 dermatome is innervated by the C4 nerve) • Clinically useful – EX. If the skin of the shoulder region is stimulated w/ a pin and the person doesn’t feel it – there is reason to believe that the C4 nerve is impaired

27. Functional Classification of the Peripheral Nervous System: • This type of classification explains where the nerves go and what they do. • Somatic Afferent nerves: • Bring sensory information from the different parts of the body (skin, muscles) to the CNS • Somatic Efferent nerves: • Bring motor information from the CNS to the skeletal muscles throughout the body • Autonomic nervous system (ANS): • Composed of nerves that supply the organs (viscera) and glands