Session 4 - Group work 2

Question 1

What is A?

Answer 1

Lateral corticospinal tract

Question 2

What is the function of lateral corticospinal tract?

Answer 2

Voluntary control of skeletal muscle (precision movement especially)

Question 3

Where does lateral corticospinal tract decussate

Answer 3

Medula

Question 4

What is B?

Answer 4

Vestibulospinal tract

Question 5

What is the function of vestibulospinal tract?

Answer 5

Involuntary control of skeletal muscle (balance)

Question 6

What is the site of decussation of vestibulospinal tract?

Answer 6

Uncrossed

Question 7

WHat is C?

Answer 7

Ventral corticospinal tract

Question 8

What is the function of the ventral corticospinal tract?

Answer 8

Voluntary control of skeletal muscle

Question 9

Where does ventral corticospinal tract decussate?

Answer 9

Segmental level

Question 10

What is tract D?

Answer 10

Rubrospinal tract

Question 11

What is the function of the rubrospinal tract?

Answer 11

Voluntary control of skeletal muscle (flexor tone)

Question 12

Where is the site of decussation of rubrospinal tract?

Answer 12

Midbrain

Question 13

What is the strict definition of a reflex?

Answer 13

An automatic, unlearned, repeatable response to a specific stimulus that does not require the brain to be intact

Question 14

What are the five anatomical components of a reflex pathway?

Answer 14

Receptor, 2) Afferent Neurone, 3) Integration Centre (Synapse), 4) Efferent Neurone, 5) Effector Organ

Question 15

What do you understand by the term reflex movement?

Answer 15

Unlearned, automatic displacement of a limb in response to a specific stimulus applied to some part of the body

Question 16

Why is it important to distinguish between voluntary movements and reflex movements when examining patients

Answer 16

In the process of examining a patient, a doctor can ask a patient to make certain movements voluntarily or by testing limb tendon reflexes. The central nervous system uses different and separate neural circuits to produce these two classes of movements. As such, a neurological examination of the motor system will seek to distinguish the integrity each of these neural 4 - 3 circuits, independently. Thus, when a patient makes a movement, a doctor will need to be clear in his/her mind as to what class of movement that was. Patients who are brain dead but whose circulation and breathing are assisted artificially may still be reflexive if their spinal cords are intact and perfused normally with blood. Thus, reflex movements do not tell us much about the integrity of the brain movement bathways. In contrast, voluntary movements can only be evoked in patients with a functioning brain ( though the quality of this may be debatable). Q4-5 Give an example of a common class of limb motor reflexes routinely examined as part

Question 17

Give an example of a common class of limb motor reflexes routinely examined as part of a medical examination

Answer 17

Deep Tendon Reflexes

Question 18

What is the distinction between a monosynaptic stretch reflex and a muscle stretch reflex

Answer 18

The monosynaptic stretch reflex is the simplest reflex circuit, having just one synapse between the afferent and efferent neurone. Monosynaptic stretch reflex can be made into a disynaptic stretch reflex by adding an interneurone between afferent and efferent neurones and so forth. n. That the term muscle stretch reflex (MSR) is an umbrella term that covers the various versions of the reflex circuits built upon the monosynaptic stretch reflex. In a healthy individual, only the monosynaptic stretch reflex can easily be elicited by tapping tendons. Multi-synaptic reflexes tend to be seen in diseased central nervous systems.

Question 19

The term “muscle stretch reflex” is an umbrella term for a series of motor reflexes that can be evoked following stretch of a muscle. Identify the various sub-types of stretch reflexes.

Answer 19

The monosynaptic stretch reflex The disynaptic stretch reflex The oligosynaptic or multisynaptic stretch reflex

Question 20

When testing for tendon jerk reflexes in a healthy individual exhibiting normal responses, which of the sub-types above (Q 4-6) of the muscle stretch reflex is most likely elicited?

Answer 20

The Monosynpatic stretch reflex is the most likely to be elicited because this mode of excitation of the reflex recruits only a subset of muscle spindle afferents. The di- and multi-synaptic limbs of the stretch reflex are unlikely to be elicited because their spindle afferents would not have been recruited by deep tendon reflex testing whilst at the same time, the spinal cord motor nucleus will be under tonic descending inhibition. (This inhibition will be more pronounced on the di- and multi-synaptic pathways as they are doubly or multiply inhibited whilst the monosynaptic pathways is relatively mildly affected at its single central synapse)

Question 21

Apart from the muscle stretch reflex sub-type just identified in Q4-6 above, what is the explanation then for the failure to evoke the other sub-types of muscle stretch reflexes when testing for limb reflexes in a relaxed healthy individual exhibiting normal responses?

Answer 21

Apart from the muscle stretch reflex sub-type just identified in Q4-6 above, what is the explanation then for the failure to evoke the other sub-types of muscle stretch reflexes when testing for limb reflexes in a relaxed healthy individual exhibiting normal responses?

Question 22

It is to be expected that when testing muscle stretch reflexes in some relaxed healthy individuals, they may be found to be areflexic. What is the explanation for this otherwise normal feature in such individuals?

Answer 22

Although descending inhibition is tonic/constant, its severity is variable, meaning that the nervous system can be heavily inhibited at some points in time whilst less so in others. When testing to evoke limb reflexes in patients, this can sometimes be difficult owing to the constant and heavy descending inhibition. In other cases, a patient who has a depressed central nervous system as is the case during sleep, when taking certain formulations of medication or when intoxicated with alcohol may be found to be a reflexic.