Spinal cord (Chapter 10)

Question 1

The spinal cord has _____ major segments, divided into ____ major segments.

Answer 1

31; 5

Question 2

What part of the spinal cord innervates the head, neck, and arms?

Answer 2

Cervical

Question 3

What part of the spinal cord innervates the trunk?

Answer 3

Thoracic

Question 4

What part of the spinal cord innervates the legs?

Answer 4

Lumbar

Question 5

What part of the spinal cord innervates the pelvic area?

Answer 5

Sacral

Question 6

What part of the spinal cord innervates the tailbone?

Answer 6

Coccygeal

Question 7

What is the cauda equina?

Answer 7

Fibers (dorsal and ventral roots) arising from lumbar and sacral regions that fan out, travelling to their sites of exit along the vertebral canal.

Question 8

Where do most motor tracts synapse in a spinal cord segment?

Answer 8

Anterior horn (contains alpha motor neurons that supply skeletal muscle)

Question 9

Where do most afferent fibers synapse in a spinal cord segment?

Answer 9

Posterior horn

Question 10

What is the function of the intermediate gray?

Answer 10

Contains autonomic neurons. Plays a modulatory role (more interneurons here). Some characteristics of both anterior and posterior horns.

Question 11

The posterior horn has two distinct regions present at all spinal levels, the ____________ (function?) and ____________ (function?).

Answer 11

Substantia gelatinosa (pain and temperature)
Body (somatic and visceral sensory info)

Question 12

What is the spinal accessory nucleus and where is it found?

Answer 12

It is one of the columns of motor neurons in the cervical anterior horn (caudal medulla-C5). It innervates the neck and shoulders, forming the accessory nerve.

Question 13

What is the phrenic nucleus and where is it found?

Answer 13

It is located in the medial anterior horn in segments C3-C5. It contains motor neurons that control the diaphragm, so damage results in inability to breathe.

Question 14

What is Clarke’s nucleus (nucleus dorsalis; posterior thoracic nucleus) and where is it found?

Answer 14

Found in the posterior horn from T1-L2. Clarke’s nucleus is an important relay nucleus for transmission of info to cerebellum (i.e., spinocerebellar tract) and has a role in sensory processing, so considered part of the posterior horn.

Question 15

Name the three major ascending/descending pathways.

Answer 15

Posterior column-medial lemniscus, spinothalamic, spinocerebellar.

Question 16

What is the major function of the posterior column-medial lemniscus?

Answer 16

The ML conveys information about touch and limb position.

Question 17

What is the major function of the spinothalamic tract?

Answer 17

The spinothalamic tract carries pain and temperature information.

Question 18

What is the major function of the spinocerebellar tract?

Answer 18

The spinocerebellar tract conveys proprioceptive information (incl. attempted movement in space).

Question 19

How is somatotopic organization maintained in the spinal cord?

Answer 19

Somatotopic organization is maintained in the spinal cord because at each successive spinal level, fibers entering the posterior column add on laterally to those already present (i.e., lamination). This means that sacral levels are represented in the medial-most layers and cervical areas are represented in the lateral-most levels.

Question 20

Where do posterior column fibers synapse in the brainstem?

Answer 20

Posterior column fibers synapse in the nucleus gracilis or nucleus cuneatus in the caudal medulla. (They then cross the midline to form the ML.)

Question 21

Why does damage to the posterior column-medial lemniscus system cause impairment but NOT total loss of tactile and proprioceptive sensations?

Answer 21

Because of redundant pathways - sensory info can reach cortex via other ascending pathways.

Question 22

When there is damage to the PC-ML system, _______ sensory discrimination tasks are less severely affected than _______ sensory discrimination tasks.

Answer 22

Simple; complex

Question 23

Name the three ways that serotonergic projections from the raphe nuclei can decrease pain sensitivity.

Answer 23

1. They can inhibit nocioceptive primary afferents directly.
2. They can inhibit spinothalamic tract neurons directly.
3. They can make excitatory synapses on inhibitory interneurons in the substantia gelatinosa.

Question 24

What are the consequences of damage to the spinothalamic tract?

Answer 24

Not too many, a great deal of tactile info is carried by the posterior column system. However, sensations like itch, pressure sensations from bladder and bowel, and sexual sensations are subserved primarily by the ST tract. However, most of this information is carried bilaterally (except itch) so unilateral damage generally results in little dysfunction.

Question 25

What type of information do the spinocerebellar/cuneocerebellar tracts carry, and where does it go?

Answer 25

They carry proprioceptive and mechanoreceptive afferents, and ascend to the ipsilateral cerebellar cortex.

Question 26

The _______ corticospinal tract(s) runs contralateral, while the _______ runs ipsilateral.

Answer 26

Anterior; posterior & cuneocerebellar.

Question 27

Damage to the _______ motor neurons results in flaccid paralysis, while damage to the _______ motor neurons results in spasticity/loss of coordination.

Answer 27

Lower; upper

Question 28

The _______ corticospinal tract(s) run(s) contralateral, while the _______ tract(s) run(s) ipsilateral.

Answer 28

Anterior; posterior and cuneocerebellar.

Question 29

What is the major function of the corticospinal tract?

Answer 29

The corticospinal tract mediates voluntary movement.

Question 30

In the spinal cord, ventral = [anterior/posterior?] and dorsal = [anterior/posterior?]

Answer 30

In the spinal cord, ventral = anterior and dorsal = posterior.

Question 31

What is a reflex?

Answer 31

A reflex is an involuntary, stereotyped response to sensory input.

Question 32

Muscle _______ leads to excitation of motor neurons.

Answer 32

Stretch

Question 33

What is reciprocal inhibition?

Answer 33

Reciprocal inhibition occurs when a stimulus elicits a stretch reflex (i.e., excites ipsilateral synergist motor neurons) and causes inhibition of motor neurons to the ipsilateral antagonist. For example, patellar tendon reflex: hamstring is inhibited (i.e., relaxes) while quadricep contracts. This facilitates the shortening of a stretched muscle.

Question 34

What are crossed effects in reflex actions?

Answer 34

Simultaneous and opposite pattern of activity in contralateral limb (i.e., in flexor reflex, as left leg flexes and withdraws, right leg extends so that you don’t fall over).