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Nervous System Subdivisions

Nervous System Subdivisions. Peripheral Nervous System. Peripheral Nervous System. Cranial nerves arising from brain Somatic fibers connecting to skin & skeletal muscles Autonomic fibers connecting to viscera Spinal nerves arising from spinal cord

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Nervous System Subdivisions

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  1. Nervous System Subdivisions Peripheral Nervous System

  2. Peripheral Nervous System • Cranial nerves arising from brain • Somatic fibers connecting to skin & skeletal muscles • Autonomic fibers connecting to viscera • Spinal nerves arising from spinal cord • Somatic fibers connecting to skin & skeletal muscle • Autonomic fibers connecting to viscera

  3. Characteristics of Spinal Cord • 17” long; ¾” thick • 2-way conduction pathway ; to and from brain • Major reflex center • Extends from foramen magnum to L1 • Posterior to L1 is “cauda equina”

  4. Meninges of Spinal Cord

  5. Gray Matter Looks like an “H” in cross section Contains: Posterior (dorsal) horn – axons of sensory neurons and association neurons Anterior (ventral) horn - cell bodies of somatic motor neurons

  6. Amount of gray matter reflects amount of skeletal muscle innervated at that level Dorsal horn Ventral horn

  7. Nerve Roots Dorsal nerve root – carries incoming messages (sensory) Ventral nerve root – carries outgoing messages (motor)

  8. Dorsal and ventral roots join to form 31 “spinal nerves” Area of skin innervated by each spinal nerve = “dermatome” Muscle group innervated by each spinal nerve = “myotome”

  9. White Matter Contain “nerve tracts” of myelinated and unmyelinated fibers; run in 3 directions: Up (ascending; sensory) Down (descending; motor) Side to side

  10. Structure of Spinal Cord

  11. Functions of Spinal Cord Conduit of nerve impulses to and from brain & brainstem Center for spinal reflexes

  12. Reflex Arcs • Reflexes are automatic, involuntary responses to stimuli • Simple reflex arc • Sensory – motor • Most common reflex arc • Sensory – association - motor

  13. Reflex Arcs

  14. General Components of Spinal Reflex

  15. Reflex Behavior Knee-jerk reflex Simple monosynaptic reflex Helps maintain upright posture

  16. Reflex Behavior Withdrawal reflex Prevents/limits tissue damage

  17. Reflex Arc Crossed Extensor reflex Crossing of sensory reflexes impulses within the reflex center to produce an opposite effect

  18. Uses of Reflexes Used to determine neurological status/dmg Plantar reflex – flexes foot Babinski reflex – abnormal; dorsiflexion of great toe Biceps-jerk reflex – tap on inside of elbow causes flexing Plantar reflex Babinski reflex

  19. Uses of Reflexes Triceps-jerk reflex – tapping short tendon of triceps close to insertion near tip of elbow; extends elbow Abdominal reflexes – stroking skin of abdomen causes contraction of abdominal muscles & umbilicus moves twd stimulated area

  20. Uses of Reflexes Ankle-jerk reflex – tapping calcaneous tendon above insertion on calcaneous = plantar flexion

  21. Tracts of Spinal Cord Ascending tracts conduct sensory impulses to brain Descending tracts conduct motor impulses to motor neurons reaching muscles & glands

  22. Spinal Cord Injuries 1st few days of spinal injury: vertebrae are compressed/may break = action potentials in neurons which kills them Dying neurons rls calcium ions; activates tissue-degrading enzymes Inflammation Axons tear, myelin coatings are stripped off; vital connections bt nerves/muscles cut Tissue is unable to regenerate

  23. Spinal Injuries Injuring nerve pathways = depressed cord reflex activity (spinal shock) – normal reflex activity may rtn Severed nerve fibers = permanent loss of fxn Blow, whiplash, rupture of vertebral disc = pain, weakness, muscular atrophy

  24. Pathology Paralysis – loss of motor function Parathesias – loss of sensation Paraplegia – loss of lower limb function Quadraplegia – loss of all limb function

  25. Hemiplegia – brain disorder resulting in loss of function on one side Flaccid paralysis – loss of muscle tone due to damage of ventral horn or root Spastic paralysis – damage to brain neurons; muscles are stimulated by spinal nerves

  26. Poliomyelitis – “gray matter inflammation” – viral disease which destroys the ventral horn of the spinal cord; virus is contracted through contaminated water; Salk and Sabin vaccines prevent infection

  27. Regeneration – stems cells in rodents: regain some ability to walk Spinal Injury - Treatments

  28. Structure of a Peripheral Nerve

  29. Nerve & Nerve Fiber Classification • Sensory Nerves • Conduct impulses into brain or spinal cord

  30. Nerve & Nerve Fiber Classification • Motor Nerves • Conduct impulses to muscles or glands

  31. Nerve & Nerve Fiber Classification • Mixed (both sensory & motor) nerves • Contain both sensory nerve fibers & motor nerve fibers • Most nerves are mixed nerves • ALL spinal nerves are mixed nerves (except 1st pair)

  32. Cranial Nerves O-O-O-T-T-A-F-V-G-V-A-H (structural)

  33. Cranial Nerves • Designated: ‘CN’ • Given Roman numerals: I – XII • “Oh-Oh-Oh-To-Touch-And-Feel-Very-Good-Velvet-AH!” - structural • “Some say marry money but my brother says bad business marry money” – sensory, motor or both

  34. Cranial Nerve I • Olfactory Nerve (CN I) • Sensory nerve • Fibers transmit impulses associated with smell

  35. Cranial Nerve II • Optic Nerve (CN II) • Sensory nerve • Fibers transmit impulses associated with vision

  36. Oculomotor nerve (CN III) Primarily motor nerve Motor impulses to muscles that: Raise eyelids Move the eyes Focus the lens Adjust light entering eye Some sensory Proprioceptors – chgs in muscles & tendons such as at joints Cranial Nerve III

  37. Cranial Nerve IV • Trochlear Nerve (CN IV) • Primarily motor nerve • Motor impulses to muscles that move eyes • Some sensory • proprioceptors

  38. Trigeminal nerve (CN V) Mixed nerve “3 Sisters”: (1) Opthalmic division Sensory from sfc of eyes, tear glands, scalp, forehead, & upper lids Cranial Nerve V

  39. Cranial Nerve V • (2) Maxillary division • Sensory from upper teeth, upper gum, upper lip, palate, & skin of face • (3) Mandibular division • Sensory from scalp, skin of jaw, lower teeth, lower gum, & lower lip • Motor to muscles of mastication & muscles in lower floor of mouth

  40. Cranial Nerve VI • Abducens nerve (CN VI) • Primarily motor nerve • Motor impulses to muscles that move eye • Some sensory • proprioceptors

  41. Cranial Nerve VII • Facial Nerve (CN VII) • Mixed nerve • Sensory from taste receptors • Motor to muscles of facial expression, tear glands, and salivary glands

  42. Cranial Nerve VII – Facial Nerve

  43. Cranial Nerve VIII • Vestibulocochlear nerve (CN VIII) • Aka acoustic & auditory nerve • Sensory nerve

  44. Cranial Nerve VIII • 2 branches: • Vestibular branch • Sensory from equilibrium receptors of ear • Cochlear branch • Sensory from hearing receptors

  45. Cranial Nerve IX • Glossopharyngeal nerve (CN IX) • Mixed nerve • Sensory from pharynx, tonsils, tongue, & carotid arteries • Motor to salivary glands & muscles of pharynx

  46. Cranial Nerve X • Vagus nerve (CN X) • Mixed nerve • Somatic motor to muscles of speech & swallowing

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