Chapter 13 The Spinal Cord Spinal Nerves

1. 1 Chapter 13The 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

2. 2 Spinal Cord Protection

3. 3 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

4. 4 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

5. 5 Inferior End of Spinal Cord Conus medullaris cone-shaped end of spinal cord Filum terminale thread-like extension of pia mater stabilizes spinal cord in canal Caudae equinae (horse’s tail) dorsal & ventral roots of lowest spinal nerves Spinal segment area of cord from which each pair of spinal nerves arises

6. 6 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

7. 7 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

8. 8 Gray Matter of the Spinal Cord Gray matter is shaped like the letter H or a butterfly contains neuron cell bodies, unmyelinated axons & dendrites paired dorsal and ventral gray horns lateral horns only present in thoracic spinal cord

9. 9 White Matter of the Spinal Cord White matter covers gray matter

10. 10 Tracts of the Spinal Cord Function of tracts highway for sensory & motor information sensory tracts ascend motor tracts descend Naming of tracts indicates position & direction of signal example = anterior spinothalamic tract impulses travel from spinal cord towards brain (thalamus) found in anterior part of spinal cord

11. 11 Location of Tracts inside Cord Motor tracts Sensory tracts pyramidal tract (corticospinal) ---spinothalamic tract extrapyramidal tract ---posterior column

12. 12 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

13. 13 Reflex Arc Specific nerve impulse pathway 5 components of reflex arc receptor sensory neuron integrating center motor neuron effector 4 important somatic spinal reflexes stretch, tendon, flexor(withdrawal) & crossed extensor reflexes

14. 14 Stretch Reflex (patellar reflex) 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)

15. 15 Illustration of the Stretch Reflex

16. 16 Tendon Reflex Controls muscle tension by causing muscle relaxation that prevents tendon damage Both tendon & muscle are protected

17. 17 Illustration of Tendon Reflex

18. 18 Flexor (withdrawal) Reflex Step on tack (pain fibers send signal to spinal cord More than one muscle group activated to lift foot off of tack

19. 19 Crossed Extensor Reflex Lifting left foot requires extension of right leg to maintain one’s balance Pain signals cross to opposite spinal cord

20. 20 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)

21. 21 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

22. 22 Branching of Spinal Nerve Spinal nerves formed from dorsal & ventral roots Spinal nerves branch into dorsal & ventral rami

23. 23 A Nerve Plexus Joining of ventral rami of spinal nerves to form nerve networks or plexuses Found in neck, arm, low back & sacral regions No plexus in thoracic region

24. 24 Cervical Plexus Ventral rami of spinal nerves (C1 to C5) Supplies parts of head, neck & shoulders Phrenic nerve (C3-C5) keeps diaphragm alive Damage to cord above C3 causes respiratory arrest

25. 25 Brachial Plexus Ventral rami from C5 to T1 Supplies shoulder & upper limb Passes superior to 1st rib & under clavicle Axillary n. = deltoid & teres m. Musculocutaneous n. = elbow flexors Radial n. = shoulder & elbow extensors Median & ulnar nn. = flexors of wrist & hand

26. 26 Clinical Correlations Erb-Duchene palsy waiter’s tip position fall on shoulder Radial nerve injury improper deltoid injectionor tight cast wrist drop Median nerve injury numb palm & fingers; inability to pronate & flex fingers Ulnar nerve injury (clawhand) inability to adduct/abduct fingers,

27. 27 Lumbar Plexus Ventral rami of L1 to L4 Supplies abdominal wall, external genitals & anterior/medial thigh Injury to femoral nerve causes inability to extend leg & loss of sensation in thigh Injury to obturator nerve causes paralysis of thigh adductors

28. 28 Sacral Plexus Ventral rami of L4-L5 & S1-S4 Anterior to the sacrum Supplies buttocks, perineum & part of lower limb Sciatic nerve = L4 to S3 supplies post thigh & all below knee Peroneal nerve injury produces foot drop or numbness Tibial nerve injury produces calcaneovalgus (loss of function on anterior leg & dorsum of foot)

29. 29 Sciatic Nerve Branches Notice: Common Peroneal nerve and Tibial nerve behind the knee Notice: Sciatica pain extends from the buttock down the leg to the foot may be sign of herniated disc

30. 30 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

31. 31 Dermatomes Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region Infusing local anesthetics or cutting roots must be done over 3 adjacent spinal nerves. Spinal cord transection injury that severs the cord loss of sensation& motor control below the injury

32. 32 Disorders Neuritis 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