1. 13-1 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

2. 13-2 Spinal Cord Protection By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.

3. 13-3 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 –thin layer covers BV –denticulate ligs hold in place

4. 13-4 Spinal Cord Figure 13–3 The Spinal Cord and Spinal Meninges

5. 13-5 External Anatomy of Spinal Cord Flattened cylinder 16-18 Inches long & 3/4 inch diameter In adult ends at L1/L2 In newborn ends at L4 Growth of cord stops at age 5

6. 13-6 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

7. 13-7 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

8. 13-8 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

9. 13-9 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 –gray commissure crosses the midline Central canal continuous with 4th ventricle of brain Note: colors in reverse due to staining of tissue

10. 13-10 White Matter of the Spinal Cord White matter covers gray matter Anterior median fissure deeper than Posterior median sulcus Anterior, Lateral and Posterior White Columns contain axons that form ascending & descending tracts

11. 13-11 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

12. 13-12 Location of Tracts inside Cord Motor tractsSensory tracts –pyramidal tract (corticospinal)---spinothalamic tract –extrapyramidal tract---posterior column – ---spinocerebellar

13. 13-13 Function of Spinal Tracts Spinothalamic tract –pain, temperature, deep pressure & crude touch Posterior columns –proprioception, discriminative touch, two-point discrimination, pressure and vibration Direct pathways (corticospinal & corticobulbar) –precise, voluntary movements Indirect pathways (rubrospinal, vestibulospinal) –programming automatic movements, posture & muscle tone, equilibrium & coordination of visual reflexes

14. 13-14 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

15. 13-15 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

16. 13-16 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 Reciprocal innervation (polysynaptic- interneuron) –antagonistic muscles relax as part of reflex

17. 13-17 Illustration of the Stretch Reflex

18. 13-18 Tendon Reflex Controls muscle tension by causing muscle relaxation that prevents tendon damage Golgi tendon organs in tendon –activated by stretching of tendon –inhibitory neuron is stimulated (polysynaptic) –motor neuron is hyperpolarized and muscle relaxes Both tendon & muscle are protected Reciprocal innervation (polysynaptic) –causes contraction of ipsilateral muscle group

19. 13-19 Illustration of Tendon Reflex

20. 13-20 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

21. 13-21 Crossed Extensor Reflex Lifting left foot requires extension of right leg to maintain one’s balance Pain signals cross to opposite spinal cord Contralateral extensor muscles are stimulated by interneurons to hold up the body weight Reciprocal innervation - when extensors contract flexors relax, etc

22. 13-22 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)

23. 13-23 The Brain Can Alter Spinal Reflexes The Babinski Reflexes –Normal in infants –May indicate CNS damage in adults

24. 13-24 The Brain Can Alter Spinal Reflexes Figure 13–21 The Babinski Reflexes.

25. 13-25 Lecture 2 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

26. 13-26 Connective Tissue Coverings Endoneurium = wrapping of each nerve fibers Perineurium = surrounds group of nerve fibers forming a fascicle Epineurium = covering of entire nerve –dura mater blends into it at intervertebral foramen

27. 13-27 Endoneurium Perineurium Epineurium

28. 13-28 Branching of Spinal Nerve Spinal nerves formed from dorsal & ventral roots Spinal nerves branch into dorsal & ventral rami –dorsal rami supply skin & muscles of back –ventral rami form plexus supply anterior trunk & limbs –meningeal branches supply meninges, vertebrae & BV

29. 13-29 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 –intercostal nn. innervate intercostal spaces

30. 13-30 Spinal Nerves and Plexuses Figure 13–10 Peripheral Nerves and Nerve Plexuses.

31. 13-31 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

32. 13-32 Phrenic Nerve

33. 13-33 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

34. 13-34 Branches off Brachial Plexus

35. 13-35 Clinical Correlations Radial nerve injury –improper deltoid injection or tight cast –wrist drop Median nerve injury –numb palm & fingers; inability to pronate & flex fingers Ulnar nerve injury (clawhand) –inability to adduct/abduct fingers, atrophy of interosseus Long thoracic nerve injury (winged scapula) –paralysis of serratus anterior, can’t abduct above horizontal

36. 13-36 Spinal Nerves and Plexuses Figure 13–12b The Brachial Plexus.

37. 13-37 Spinal Nerves and Plexuses Figure 13–10 Peripheral Nerves and Nerve Plexuses.

38. 13-38 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

39. 13-39 Branches of Lumbar Plexus Notice: Femoral and Obturator nerves Found anterior and medial to hip joint

40. 13-40 Sacral Plexus Ventral rami of L4-L5 & S1-S4 Anterior to the sacrum Supplies buttocks, perineum & part of lower limb Sciatic nerve = L4 to S4 supplies post thigh & all below knee –Peroneal nerve injury produces foot drop or numbness

41. 13-41 Spinal Nerves and Plexuses Figure 13–13b The Lumbar and Sacral Plexuses.

42. 13-42 Branches of Sacral Plexus Notice: Sciatic nerve origins

43. 13-43 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, Spinal Subluxations, piriformis syndrome, tilted pelvis

44. 13-44 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 Skin on face supplied by Cranial Nerve V

45. 13-45 Spinal Nerves and Plexuses Figure 13–8 Dermatomes.

46. 13-46 Spinal Nerves and Plexuses Figure 13–9 Shingles.

47. 13-47 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

48. 13-48 Sciatica Irritation of the sciatic nerve by a subluxated vertebrae, arthritis of the spine, disc bulge or herniations, tilted pelvis, piriformis muscle, scoliosis, military spine, hyperlordosis, pes planus ( flat feet )

49. 13-49 Carpal Tunnel syndrome -Median nerve, 3 ½ fingers, tinels sign, phalens test, Needle EMG, Carpal bones(floor) Flexor retinaculum (roof), transverse carpal ligament) Thoracic outlet Syndrome – Lower end of brachial plexus and/or subclavian artery compression by: scalene muscles and/or pec minor muscle. Adson’s test, Wrights test. Numbness down the medial aspect of the forearm and the ½ of the 4 th and 5 th digit, diminished pulse and cold fingers.