The Spinal Cord & Spinal Nerves Together with brain forms the CNS Functions spinal cord reflexes integration (summation of inhibitory and excitatory) nerve impulses highway for upward and downward travel of sensory and motor information

Spinal Cord Protection By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.

Structures Covering the Spinal Cord Vertebrae Epidural space filled with fat Dura mater dense irregular CT tube Subdural space filled with interstitial fluid Arachnoid = spider web of collagen fibers Subarachnoid space = CSF Pia mater

External Anatomy of Spinal Cord Flattened cylinder 16-18 Inches long & 3/4 inch diameter In adult ends at L2 In newborn ends at L4 Growth of cord stops at age 5 Cervical enlargement upper limbs Lumbar enlargement lower limbs

Inferior End of Spinal Cord Conus medullaris cone-shaped end of spinal cord Caudae equinae (horse’s tail) dorsal & ventral roots of lowest spinal nerves

Spinal Cord & Spinal Nerves Spinal nerves begin as roots Dorsal or posterior root is incoming sensory fibers dorsal root ganglion (swelling) = cell bodies of sensory nerves Ventral or anterior root is outgoing motor fibers

Spinal tap or Lumbar Puncture Technique long needle into subarachnoid space safe from L3 to L5 Purpose sampling CSF for diagnosis injection of antibiotics, anesthetics or chemotherapy measurement of CSF pressure

Spinal Reflexes Automatic response to change in environment Integration center for spinal reflexes is gray matter of spinal cord Examples somatic reflexes result in skeletal muscle contraction autonomic (visceral) reflexes involve smooth & cardiac muscle and glands. heart rate, respiration, digestion, urination, etc Note: cranial reflexes involve cranial nerves

Reflex Arc Specific nerve impulse pathway 5 components of reflex arc receptor sensory neuron integrating center motor neuron effector

Stretch Reflex (patellar reflex) Monosynaptic,ipsilateral reflex arc Prevents injury from over stretching because muscle contracts when it is stretched Events of stretch reflex muscle spindle signals stretch of muscle motor neuron activated & muscle contracts Brain sets muscle spindle sensitivity as it sets muscle tone (degree of muscle contraction at rest) Reciprocal innervation (polysynaptic- interneuron) antagonistic muscles relax as part of reflex

Illustration of the Stretch Reflex

Flexor (withdrawal) Reflex Step on tack (pain fibers send signal to spinal cord Interneurons branch to different spinal cord segments Motor fibers in several segments are activated More than one muscle group activated to lift foot off of tack

Clinical Considerations Checking a patient’s reflexes may help to detect disorders/injury Plantar flexion reflex -- stroke the lateral margin of the sole normal response is curling under the toes abnormal response or response of children under 18 months is called Babinski sign (upward fanning of toes due to incomplete myelination in child)

Spinal Nerves 31 Pairs of spinal nerves Named & numbered by the cord level of their origin 8 pairs of cervical nerves (C1 to C8) 12 pairs of thoracic nerves (T1 to T12) 5 pairs of lumbar nerves (L1 to L5) 5 pairs of sacral nerves (S1 to S5) 1 pair of coccygeal nerves Mixed sensory & motor nerves

Dermatomes & Myotomes Each spinal nerve contains both sensory & motor nerve fibers Dermatome area of skin supplied by one spinal nerve overlap prevents loss of sensation if one damaged sensory anesthesia requires 3 spinal nerves to be blocked Skin on face supplied by Cranial Nerve V

Dermatomes Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region Spinal cord transection injury that severs the cord loss of sensation & motor control below the injury

Disorders Neuritis Shingles Poliomyelitis inflammation of nerves caused by injury, vitamin deficiency or poison Shingles infection of peripheral nerve by chicken pox virus causes pain, skin discoloration, line of skin blisters Poliomyelitis viral infection causing motor neuron death and possible death from cardiac failure or respiratory arrest