Spinal Cord and Spinal Nerves

Question 1

1. Define spinal nerve and cauda equina.

Answer 1

1. Part of peripheral nervous system taking messages to and from spinal cord. They are mixed carrying both sensory and motor info. The caudal-most spinal nerves pass caudally together resembling a horse’s tail before exiting the appropriate intervertebral foramen.

Question 2

2. Describe the overall functions of the spinal cord.

Answer 2

2. Carry messages to and from brain and spinal reflexes.

Question 3

3. Describe the location of the spinal cord.

Answer 3

3. Vertebral foramen/canal. It runs from foramen magnum to about L2.

Question 4

4. Describe the significance of the two spinal cord enlargements.

Answer 4

4. Arms & legs nerves entering & exiting spinal cord

Question 5

5. Name the protective coverings of the CNS (general & specific).

Answer 5

5. General is meninges specific is dura mater (outermost) arachnoid then pia mater.

Question 6

6. Describe the location of the cerebrospinal fluid (CSF).

Answer 6

6. Subarachnoid space

Question 7

7. Name the space and location where anesthetics are given.

Answer 7

7. Epidurals are given outside of the dura mater. L2 or below would be a safe place to administer the anesthetic without hitting the spinal cord.

Question 8

8. Describe the parts of the gray matter of the spinal cord.

Answer 8

8. The dorsal gray horns receive sensory information and the ventral gray horns transmit motor information. Since it is gray it would contain neuron cell bodies and unmyelinated neurons.

Question 9

9. Describe the parts of the white matter of the spinal cord.

Answer 9

9. The lateral dorsal (posterior) and ventral (anterior) columns.

Question 10

10. Describe the function of the ascending and descending tracts.

Answer 10

10. Within the white columns are the ascending tracts carrying sensory information toward the brain and the descending tracts carrying motor information away from the brain.

Question 11

11. Define reflex spinal reflex somatic reflex and autonomic reflex.

Answer 11

11. Reflex is a fast repetitive response to a stimulus. It is involuntary i.e. not at the conscious level. If it involves the spinal cord it is a spinal reflex. A somatic reflex terminates in skeletal muscle the autonomic reflex terminates in smooth muscle cardiac muscle and glands.

Question 12

12. Describe the pathway of a generalized reflex arc.

Answer 12

12. Stimulus - Receptor - ascending sensory neuron - CNS (spinal cord) - descending motor neuron - effector (such as a skeletal muscle)

Question 13

13. Contrast monosynaptic polysynaptic ipsilateral and contralateral reflexes. Describe the pathway for the patellar reflex the withdrawal (flexor) reflex and the crossed-extensor reflex.

Answer 13

13. One synapse in the spinal cord is monosynaptic reflex and would be very fast. The patellar reflex is monosynaptic and ipsilateral. A polysynaptic reflex has more than one synpase in the spinal cord - thus synapsing on interneurons or association neurons before synapsing on the motor neuron. These are slower reflexes and if they stay ipsilateral may describe the withdrawal reflex and if they go contralateral may describe the crossed extensor reflex. If you hit the patellar tendon you stretch the quad. muscle and stimulate the stretch receptor. It is an ipsilateral monosynaptic reflex ending with the quad. muscle contracting thus extending the knee. If you step on the nail the pathway is the withdrawal reflex resulting in an ipsilateral contraction of your flexors so that you pull away from the nail and a compensatory extension of the contralateral leg so that you can support your weight (crossed extensor reflex).

Question 14

14. Describe a spinal nerve; include the roots and which roots carry motor/sensory impulses. Define ramus.

Answer 14

14. Spinal nerves described under one. It has a dorsal root carrying sensory info into the dorsal gray horn and a ventral root carrying motor info exiting the ventral gray horn. After the mixed spinal nerve leaves the vertebra it branches into a dorsal ramus (branch) going toward your back and a ventral ramus going everywhere else in your body including limbs and viscera. The rami are mixed.

Question 15

15. Define plexus.

Answer 15

15. Network of successive spinal nerves.

Question 16

16. Name and locate the 4 main plexuses.

Answer 16

16. Cervical (about C1-4); Brachial (about C5-T1) Lumbar (about L1-4) and Sacral (about L4-S4)

Question 17

17. Name the plexus of origin and the general structures or areas innervated by the radial ulnar musculocutaneous median femoral sciatic and phrenic nerves.

Answer 17

17. Radial nerve - Brachial plexus innervates pectoral limb extensors Ulnar nerve - Brachial plexus innervates distal medial flexors (e.g. flexor carpi ulnaris) Musculocutaneous nerve - Brachial plexus innervates elbow flexors (e.g. biceps brachii) Median nerve - Brachial plexus innervates distal lateral flexors (e.g. flexor carpi radialis) Femoral nerve - Lumbar plexus innervates hip flexors and knee extensors (e.g. quadriceps) Sciatic nerve - Sacral plexus innervates knee flexors (hamstrings) as well as all distal to your knee. Phrenic nerve - Cervical plexus innervates your diaphragm and needed to breathe!