3.2

Question 1

Function of ALS

Answer 1

Carry sensory signals to the cerebral cortex
- neurons travel by the direct or the indirect path

Question 2

Direct path of ALS carries…

Answer 2

Carries pain, temperature, and crude touch to the thalamus
Spinothalamic

Question 3

Indirect path of the ALS

Answer 3

Carries pain to other structures before they reach the thalamus
- reticular formation
- hypothalamus
- superior colliculus
- brainstem
Spinoreticular

Question 4

Three neurons of the ALS

Answer 4

First order neuron: carries signals from the receptor to the dorsal horn; cell body in dorsal root ganglion
Second order neuron: carries signals from the dorsal horn to the thalamus; cell body in dorsal horn
Third order neuron: carries signals from the thalamus to the cerebral cortex; cell body in the thalamus

Question 5

First order neuron of the ALS

Answer 5

Pain receptors are free nerve endings of the 1st order neurons.
Collaterals go up and down 1-3 levels to synapse on second order neuron cell bodies.
Carries signals from the receptor to the dorsal horn; cell body in dorsal root ganglion

Question 6

Second order neuron of the ALS

Answer 6

Cell bodies in dorsal horn
Decussate to travel up the ALS tract
Direct path: directly to the thalamus
Indirect path: reticular system and other structures then the thalamus

Question 7

Second order neuron: function of indirect path

Answer 7

Contributes to maintaining consciousness (reticular activation system)
Pain-inhibiting pathway: modulates the delivery of pain signals
Turn head and eyes toward the painful stimulus
Mediates autonomic and reflex responses
Send projections to the cerebellum

Question 8

Third order neuron of the ALS

Answer 8

Cell bodies in the thalamus
Axons travel through the corona radiata and internal capsule to the postcentral gyrus (primary somatosensory cortex)
The fibers terminate in primary and secondary somatosensory cortices.

Question 9

Columns of the DCML

Answer 9

Fasciculus gracillis: on either side of the midline, carries LE signals
Fasciculus cuneatus: lateral to fasciculus gracilis, carries UE signals

Question 10

Three neurons of the DCML

Answer 10

First order neuron: carries signals from the receptor to the medulla; cell body in dorsal root ganglion
Second order neuron: carries signals from the dorsal horn to the thalamus; cell body in the dorsal column nuclei of the medulla
Third order neuron; carries signals from the thalamus to the cerebral cortex; cell body in the thalamus

Question 11

First order neuron of the DCML

Answer 11

Remains ipsilateral
The peripheral processes terminate in:
- unencapsulated receptors
- encapsulated receptors
- proprioceptive receptors
Collaterals go up and down to synapse with interneurons and motor neurons (direct, muscle stretch)

Question 12

First order neuron of DCML below T6

Answer 12

Central processes of first order neurons carry signals from the lower extremities and trunk.
Travel in the fasciculus gracilis.
Terminate in the nucleus gracilis of the medulla.

Question 13

First order neuron of DCML above T6

Answer 13

Central processes of first order neurons carry signals from the upper thoracic and cervical levels.
Travel in the fasciculus cuneatus.
Terminate in the nucleus cuneatus of the medulla.

Question 14

Second order neuron of the DCML

Answer 14

The fasciculus gracilis synapses with cell bodies in the nucleus gracilis of the medulla.
The fasciculus cuneatus synapses with cell bodies in the nucleus cuneatus of the medulla.
- The axons decussate and ascend to the thalamus via the medial lemniscus.

Question 15

Third order neurons of the DCMLS

Answer 15

Cell bodies in the thalamus.
Axons travel through the corona radiata and internal capsule to the postcentral gyrus.
The fibers terminate in the primary and secondary somatosensory cortices.

Question 16

Symptoms of dorsal root and spinal nerve lesions

Answer 16

Segmental deficits
May be difficult to trace sensory deficits because of collaterals
Pain/parasthesia

Question 17

Brown Sequard syndrome

Answer 17

Ipsilateral motor
- LMN paralysis at level of lesion
- UMN signs after first few days below level of injury followed by spastic paralysis
Sensory at and below level of lesion
- loss of pain, temp, and crude touch
- loss of sensory info from contralateral side of body

Question 18

What modalities are carried in the ALS?

Answer 18

Nociceptive, thermal, itch, and nondiscriminatory (crude) touch

Question 19

What modalities are carried in the DCML?

Answer 19

Discriminative (fine) touch, flutter-vibratory sense, proprioception

Question 20

Two point touch

Answer 20

The ability to distinguish between two distinct points applied to the skin surface simultaneously

Question 21

Stereognosis

Answer 21

The recognition of the 3D shape of an object by the sense of touch

Question 22

Static proprioception

Answer 22

The awareness of the position of a motionless body part

Question 23

Dynamic proprioception

Answer 23

The awareness of movement of a body part and balance

Question 24

What are the sensory deficits noted after a lesion to a dorsal root or spinal nerve?

Answer 24

segmental distribution

Question 25

Motor effects of Brown Sequard Syndrom

Answer 25

○ When the spinal cord is hemisected (only the right or left half is severed), all of the tracts (both ascending and descending) coursing through the level of the lesion are severed, and the following will be observed:
1. The lower motoneurons ipsilateral to and at the level of the lesion will be damaged, leading to ipsilateral lower motoneuron paralysis at the level of the lesion.
2. Since the corticospinal tract (upper motoneurons) will be severed, the individual will exhibit an ipsilateral loss of motor function below the level of the lesion, followed by spastic paralysis

Question 26

Sensory effects of Brown Sequard Syndrome

Answer 26

In this lesion, the anterolateral system (which includes the spinothalamic, spinoreticular, spinomesencephalic, spinotectal, spinoolivary, and spinohypothalamic fibers) has been severed.
- The fibers that relay pain, temperature, and crude touch sensation to consciousness cross in the spinal cord before joining the spinothalamic tract
- The spinothalamic tract located in the anterolateral aspect of the spinal cord is a crossed tract whose fibers carry sensory information from the opposite side of the body.
- At the spinal cord level, the anterolateral system (ALS) consists of both Aδ (fast-conducting fibers, relaying sharp, well-localized pain) and C (slow-conducting fibers, relaying dull, poorly- localized pain). Thus with a lesion at the spinal cord level, there will be:
● Complete loss of pain and temperature sensation beginning one to three segments below the level of the lesion, contralaterally.
● A diminution of non-discriminative (crude) touch sensation beginning one to three segments below the level of the lesion, contralaterally