Module 3

Question 1

What sensory modalities are carried by the PCML pathway?

Answer 1

Proprioception, vibration, light touch

Question 2

What sensory modalities are carried by the AL pathway?

Answer 2

Crude touch, pressure, pain/temperature

Question 3

What is a dermatome?

Answer 3

A peripheral sensory area of the body that is innervated by sensory fibers of a single nerve root.

Question 4

What are the clinically relevant cervical dermatomes?

Answer 4

C5: lateral deltoids (upper half of the arms)
C6: upper half of the lower arm
C6, C7, C8: regions of the hand

Question 5

What are the clinically relevant thoracic dermatomes?

Answer 5

T1: lower half of the arm containing the elbow
T4: chest area going through the nipples
T10: area through the belly button

Question 6

What are the clinically relevant lumbar and sacral dermatomes?

Answer 6

L2: upper thigh
L3: knees
L4: medial aspect of lower leg
L5: lateral aspect of lower leg
S1: Achilles tendon and base of foot

Question 7

Describe the general path of PCML neurons.

Answer 7

Primary sensory neurons enter in the dorsal horn of the spinal cord.

Primary sensory neurons synapse onto nucleus gracilis/cuneatus into the medulla and become second order neurons. They cross the midline at the medulla and ascend to the contralateral thalamus. As they cross the midline, the 2nd order neurons are called internal arcuate fibers.

Second order sensory neurons become third order neurons when they synapse on thalamic nuclei, and then they project to the somatosensory cortex.

Question 8

How do lower body PCML neurons travel?

Answer 8

Via the fasciculus gracilis, the medial part of the posterior column, and primary neurons synapse on the nucleus gracilis. This encompasses spinal segments T6 and below.

Question 9

How do upper body PCML neurons travel?

Answer 9

Via the fasciculus cuneatus, the lateral part of the posterior column, and primary neurons synapse on the nucleus cuneatus. This encompasses spinal segments above T6.

Question 10

What are the 3 tracts the AL pathway is composed of?

Answer 10

Spino-thalamic tract: going to the thalamus, regulates pain and temperature

Spino-reticular tract: goes to the reticular formation in the central brainstem, is responsible for the emotional and arousal aspects of pain

Spino-mesencephalic tract: goes to the periaqueductal gray area in the midbrain, which modulates feelings of pain

Question 11

Describe the general path of AL neurons.

Answer 11

Primary sensory neurons are found in the dorsal horn, terminate on the ipsilateral side, and synapse on 2nd order neurons in the dorsal horn.

2nd order neurons cross the midline via the anterior commissure in the SC, and ascend in a ramp formation across 2-3 spinal levels.

2nd order neurons ascend to the thalamus, and become 3rd order neurons when they synapse onto thalamic nuclei. 3rd order neurons project onto the somatosensory cortex.

Question 12

What is the somatotopic organization of the AL pathway?

Answer 12

Opposite to the PCML pathway - upper body is medial while lower body is lateral.

Question 13

Where is the somatosensory cortex?

Answer 13

In the post-central gyrus.

Question 14

What are Negative Symptoms?

Answer 14

A subtraction or removal of sensation.

Question 15

What is astereognosis?

Answer 15

The inability to recognize objects by touch.

Question 16

What is sensory ataxia?

Answer 16

Unsteady balance and gait and poorly coordinated movements - both are worse w/o vision.

Question 17

What is tabetic gait?

Answer 17

Consists of…

High stepping: no awareness of where legs are, so this is to avoid tripping.

Foot flapping: heels touch first, then toes slap down - a ‘double tap’

Unsteady gait: wide, and legs cross over each other

Question 18

What are some negative symptoms to primary sensory neurons?

Answer 18

Hyporeflexia - a loss of deep tendon reflexes.

Question 19

What are negative symptoms to the AL pathway?

Answer 19

Loss of pain and temperature sensations, and reduced crude touch sensation.

Question 20

What are positive symptoms?

Answer 20

An addition of an abnormal sensation that is not normally there.

Question 21

What is paresthesia?

Answer 21

An abnormal sensation that is not painful, related to PCML damage.

Question 22

What is hyperpathia?

Answer 22

An excessively painful response to something that is normally painful.

Question 23

What is allodynia?

Answer 23

A pain sensation to a stimulus that is not normally painful.

Question 24

What are positive symptoms to primary sensory neurons?

Answer 24

Radicular pain: radiating pain down through the nerve and dermatome, numbness and tingling throughout the dermatome

Question 25

Describe the path of sensory input for the face.

Answer 25

Trigeminal nerve (CN V) exits the brainstem through the pons, and goes to Meckel's cave. Meckel's cave contains cell bodies and the trigeminal ganglion. From the trigeminal ganglion, the nerve splits into 3, innervating different regions of the face (V1, V2, V3). The trigeminal nerve then goes to synapse on the trigeminal nuclei, crosses the midline, goes to the contralateral thalamus, and relays information to the facial region of the somatosensory cortex.

Question 26

What is the location and function of the chief trigeminal nucleus?

Answer 26

It is located in the rostral, medial pons. It carries information for light touch on the face (PCML pathway). Neurons immediately cross the midline and ascend to the contralateral thalamus.

Question 27

What is the location and function of the spinal trigeminal nucleus?

Answer 27

It is located from the lower medulla to the rostral SC. It carries information for crude touch, pain, and temperature (AL pathway). Neurons immediately cross the midline and ascend to the contralateral thalamus.

Question 28

Where will symptoms appear if there are lesions to the trigeminal pathway?

Answer 28

If lesions are to the cortex or thalamus, symptoms will be on the contralateral side. If lesions are to the nuclei, then symptoms will be on the ipsilateral side.

Question 29

Describe the symptoms of a transverse cord lesion.

Answer 29

Motor function: - LMN symptoms at the level of injury bilaterally - UMN symptoms below the level of injury bilaterally PCML: - Bilateral loss of vibration, proprioception and light touch at the level of injury and below AL: - Bilateral loss of pain, temperature, and crude touch at the level of injury and below

Question 30

Describe the symptoms of a central cord lesion.

Answer 30

Only affects the anterior commissure at the spinal level, which carries 2nd order neurons from 1 segment below. Symptoms: - Bilateral loss of pain, temperature, and crude touch at the dermatome one level below the lesion.

Question 31

Describe the symptoms of posterior cord syndrome.

Answer 31

Bilateral damage to the levels below the level of injury, possibly to the level itself as well. Loss of vibration, light touch, and proprioception (PCML symptoms only). Key cause: vitamin B-12 deficiency and tabes dorsalis.

Question 32

Describe the symptoms of anterior cord syndrome.

Answer 32

Motor: - LMN symptoms at the level of injury bilaterally - UMN symptoms below the level of injury bilaterally AL: - Bilateral loss of pain, temperature, and crude touch one level below the injury + all levels below that *Preserved sensation at the level of injury, and preserved PCML function.

Question 33

Describe the symptoms of a hemi-cord lesion.

Answer 33

Motor: - Ipsilateral LMN symptoms at the level of injury - Ipsilateral UMN symptoms below the level of injury PCML: - Ipsilateral loss of proprioception, vibration, and light touch at the level of injury and below AL: - Ipsilateral strip of pain and temperature loss at the level of injury + one level below - Contralateral loss of pain and temperature 1 segment below the injury + all segments below that