Lucky Chapter 13. Spinal Cord and Spinal Nerves

1. Lucky Chapter 13.Spinal Cord and Spinal Nerves Biology 315. Anatomy and Physiology I.

2. What structures protect the spinal cord? Bones (vertebral column) Meninges, in layers Epidural space Dura mater Subdural space Arachnoid mater Subarachnoid space (contains CSF) Pia mater -- very vascular

3. The meninges

4. Another view of the meninges

6. Cervical enlargement C4-T1

7. Segmentation of the Spinal Cord C1-C8 T1-T12 L1-L5 S1-S5 Note differential growth of vertebral column such that adult spinal cord ends at L1-L2 interspace.

8. Spinal Cord Schematic

10. Spinal cord: horns and columns

12. Quiz…

13. Spinal cord tracts…. Ascending tracts = sensory Spino-thalamic Descending tracts = motor *Cortico-spinal

14. Sensory tracts…examples Anterior and lateral spinothalamic tracts Pain Temperature Itching Tickling Deep pressure Crude touch

15. Anterior and lateral spinothalamic tracts

16. Sensory tracts: example Posterior column system Proprioception Discriminative touch 2-point discrimination Light pressure Vibration

17. Motor tracts: Descending… Direct pathways: “Pyramidal” Lateral corticospinal tract Anterior corticospinal tract Corticobulbar tract These carry motor impulses that originate from the cerebral cortex and result in precise, voluntary movements of skeletal muscle.

18. Motor tracts: descending Indirect pathways (Extrapyramidal) Rubrospinal Tectospinal Vestibulospinal These carry impulses from brain stem, coordinate movements with visual stimuli Regulate muscle tone Maintain contraction of postural muscles Equilibrium

19. Motor tracts……….

20. What is a reflex? A fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus. Somatic: contraction of skeletal muscles Autonomic (visceral):urination, gastrocolic… (easy one to test: pupillary light reflex) Consider Newtons 3rd law: For every action there is an equal and opposite reaction.

21. What makes up a reflex?: 5 components Sensory receptor Sensory neuron Integrating center (multisynaptic or monosynaptic; spinal cord or brain stem) Motor neuron Effector (skeletal muscle, smooth muscle, cardiac muscle, glands)

22. The Stretch Reflex:  monosynaptic, ipsilateral Receptor: muscle spindle,monitors stretch Sensory nerve: from receptor through posterior root Integrating center: spinal cord; sensory neuron synapses with Motor neuron in the anterior gray horn Motor axon travels out anterior root to PNS to muscle

23. Reciprocal innervation: If the agonist muscle contracts, the Antagonist muscle must _____________ If not, the two muscle groups are in conflict and the appropriate movement can’t occur.

24. The Tendon Reflex: also protective Receptor: Golgi tendon organ detects increased muscle tension Nerve impulse carried through posterior root into posterior horn Integrating center: spinal cord, inhibitory neuron synapses with a motor neuron , which is hyperpolarized (inhibited) Effector muscle of that tendon relaxes and relieves excess tension.

26. Flexor-Crossed Extensor Reflex I. Receptor: pain receptors Sensory neuron to spinal cord Integrating center: spinal cord, various segments (intersegmental) ,multiple neurons Motor neurons send impulses to Neuromuscular junctions– ACh : flexors contract; others inhibited. You pull your foot back…..

27. Flexor-Crossed Extensor Reflex II. In spinal cord interneurons synapse with motor neurons on the opposite side of the spinal cord ( contralateral) Motor neurons carry nerve impulse to nerve ending, Effector: contraction of extensor muscles of the opposite side

28. Why do reflex testing? If a given reflex “works,” all the parts of that reflex must be intact. (receptor; sensory neuron; integrative center; motor neuron; effector). Various reflexes test specific spinal cord levels E.g. patellar reflex: L2-L4 Achilles: lumbosacral levels

29. The True Blue Spinal Nerves Terms to review Anterior root Posterior root Spinal nerve Ramus Plexus

30. Structure of a peripheral nerve

31. Structure of a peripheral nerve

32. The generic, but True Blue, spinal nerve

33. The generic, but True Blue, spinal nerve

34. The generic, but True Blue, spinal nerve

35. Distribution of Spinal Nerves Dorsal ramus: supplies muscles and skin of back Ventral ramus: extremities, lateral and ventral trunk (the big one) Ventral rami of T2-T12 = intercostal nerves Ramus (pl. rami) communicantes: part of ANS

36. What is a plexus ? Ventral rami of spinal nerves branch and form networks Cervical plexus = C1-C4 Innervates skin, muscles of neck, head,shoulder region plus diaphragm. Connects with XI (spinal accessory) and XII (Hypoglossal) THE NERVE to know = Phrenic: C3,C4,C5

37. What is a plexus ? Ventral rami of spinal nerves branch and form networks Brachial = C5-T1 Upper extremity Some neck/ shoulder areas Complicated structure (trunks/ divisions/cords) THE NERVES to know

38. The Brachial Plexus …… 6 nerves to know Axillary nerve: deltoid, teres major Musculocutaneous nerve: flexors of arm and forearm Radial nerve: muscles of posterior arm and forearm Damage to radial nerve: “wrist drop”

39. The Brachial Plexus ……Part Deux Median Nerve: muscles of anterior forearm and palm thumb Damage = numbness, tingling pain in fingers, weak thumb movements, inability to pronate forearm Ulnar nerve : anteromedial muscles of forearm and fingers Damage: difficulty holding/picking up piece of paper; inability to flex and adduct the wrist Long thoracic nerve: serratus anterior Damage: “winged” scapula

40. The Lumbar Plexus: L1-L4 Femoral nerve: flexors of the thigh and extensors of the legs (quads; iliopsoas; sartorius);skin over anterior and medial aspect of thigh and medial side of leg and foot Know that these nerves are part of the lumbar plexus: Iliohypogastric Ilioinguinal Genitofemoral Lateral cutaneous nerve of the thigh Obturator nerve

41. The Sacral Plexus: L4-S4 Buttocks, perineum, lower extremity Sciatic nerve : largest nerve; composed of tibial and common fibular/peroneal nerve Tibial nerve: posterior compartment muscles; medial and lateral plantar nerves Common Fibular/Peroneal nerve : anterior compartment, lateral compartment of leg Pudendal nerve = muscles of perineum, skin over external genitalia, vagina Damage: “foot drop”

42. Dermatome: skin supplied by the dorsal root of a spinal nerve

43. Dermatome: skin supplied by the dorsal root of a spinal nerve

45. Notes on dermatomes: related to development Helpful for determining general level of injury or anesthesia Herpes zoster follows the dermatomes Same organization for MYOTOMES Try to memorize a few…. Shoulder C3-C4 Nipple T4 Umbilicus T10

46. Transection of the spinal cord 1. Permanent loss of sensation in dermatomes distal to the injury 2. Permanent loss of voluntary muscle contraction distal to the injury

47. A few last terms…. Polio Meningitis Nerve block Epidural block Neuralgia Neuritis Paresthesia Shingles