DSA12 Shi Spinal Cord Physiology

Question 1

Type I muscle fibers

Answer 1

Oxidative, slow velocity of shortening

Question 2

Type IIa muscle fibers

Answer 2

Fast-oxidative-glycolytic

Question 3

Type IIb muscle fibers

Answer 3

Fast-glycolytic

Question 4

Describe the symptoms of muscle denervation syndrome.

Answer 4

Atrophy, fasciculations and fibrillations.

Question 5

Type Ia/II sensory fibers

Answer 5

In parallel with extrafusal fibers; sense changes in length/stretch

Question 6

Type Ib sensory fibers

Answer 6

In series with extrafusal fibers (Golgi tendon organ); sense changes in force/tension.

Question 7

stretch/myotatic reflex

Answer 7

Stretch receptors (type Ia/II) directly activate alpha motor neurons (monosynaptic). Also triggers reciprocal inhibition via interneurons.

Question 8

skin receptors - reflex arc

Answer 8

Receptor sends signal to cell in dorsal horn which integrates signals and activates motor neurons in ventral horn to act on effectors. Reciprocal inhibition.

Question 9

flexor reflex

Answer 9

Nociceptors enter the spinal gray and synapse on: ascending neurons (conscious perception), excitatory interneurons (flexors), and inhibitory interneurons (extensors).

Question 10

crossed extension

Answer 10

Adding to the flexor reflex, nociceptors also activate interneurons that decussate and activate excitatory (extensors) and inhibitory (flexors) interneurons.

Question 11

tendon organ reflex

Answer 11

Given excessive stretch, autogenic inhibition of the muscle will occur via the Golgi tendon organ neurons, which activate inhibitory (extensors) and excitatory (flexors) interneurons. Prevents the excessive action of the myotatic reflex.

Question 12

rubrospinal tract

Answer 12

CARRIES: goal-directed motor movements

Question 13

tectospinal tract

Answer 13

CARRIES: reflex head movement

Question 14

Which is the only tract that decussates in the spinal cord?

Answer 14

Spinothalamic tract

Question 15

plantar flexion reflex

Answer 15

Response to scratching surface of foot

Question 16

Babinski sign

Answer 16

Dorsiflexion in response to scratching surface of foot. Indicates UMN damage.

Question 17

abdominal reflex

Answer 17

Stroking skin below umbilicus produces contraction of abdominal muscles. Absent in UMN damage.

Question 18

What are the signs of LMN damage?

Answer 18

Flaccid paralysis, decreased DTR, atrophy, fasciculations & fibrillations. No Babinski’s sign.

Question 19

What are the signs of UMN damage?

Answer 19

Spastic paralysis, increased or unaffected DTR, Babinski’s sign. Atrophy can be present if due to long-term disuse. No fasciculations or fibrillations.

Question 20

What tissue is affected in poliomyelitis?

Answer 20

Alpha motor neurons of spinal cord.

Question 21

S/Sx of Tabes Dorsalis

Answer 21

Damage to dorsal columns and spinocerebellar tracts (due to neurosyphilis) leads to sensory ataxia (aka Friedreich ataxia or cerebellar ataxia); ROMBERG’S SIGN.

Question 22

Romberg’s sign

Answer 22

The inability to maintatin steady posture with feet close together when eyes are closed because of loss of proprioceptive input. Demonstrative of degeneration of dorsal columns/spinocerebellar tracts, as in neurosyphilis/tabes dorsalis.

Question 23

amyotrophic lateral sclerosis

Answer 23

Bilateral degeneration of both corticospinal tracts (UMNs) and motor neurons in cranial nuclei and ventral horns (LMNs), so patient has signs of both.

Question 24

Brown-Sequard syndrome

Answer 24

Complete or partial hemisection; usually due to trauma.

Question 25

syringomyelia

Answer 25

Progressive cavitation of central canal. Damages decussation of spinothalamic tract (thoracocervical area, so arms/hands/shoulders). Variable symptoms depending on the spread.

Question 26

spinal shock

Answer 26

An initial reaction to interruption of cord reflexes immediately following SC transection (loss of tonic input throws reflexes off). Flaccid paralysis (may also have spastic paralysis), areflexia (resolves in 2 weeks-several months, but may be hyperexcitable; Babinski shows up), BP drop (resolves within a few days) and retention of urine & feces(usually return in a few weeks).