FUNCTIONAL ANATOMY - Motor Control

Question 1

Which four higher brain systems are involved in voluntary motor control?

Answer 1

Limbic system
Basal ganglia
Cerebellum
Motor cortex

Question 2

Describe briefly the hierarchy of motor control

Answer 2

The hierarchy of motor control involves the processing of sensory information by the limbic system, then basal ganglia, followed by the cerebellum and the motor cortex which sends motor signals down descending pathways to the spinal cord and eventually the muscles

Question 3

What is the function of the basal ganglia?

Answer 3

The basal ganglia contributes to coordinated and smooth voluntary movements through balancing the initiation and inhibition of motor movements

Question 4

What are the three structural components of the basal ganglia?

Answer 4

Caudate nucleus
Putamen
Globus pallidus

Question 5

What is the collective name for the caudate nucleus and the putamen?

Answer 5

Striatum

Question 6

What are the two main pathways used by the basal ganglia to initiate and inhibit motor movement?

Answer 6

Direct (excitatory) pathway
Indirect (inhibitory) pathway

Question 7

What is the main neurotransmitter involved in the direct (excitatory) pathway?

Answer 7

Glutamate

Question 8

What is the main neurotransmitter involved in the indirect (inhibitory) pathway?

Answer 8

GABA

Question 9

Describe the direct (excitatory) pathway of the basal ganglia

Answer 9

The striatum receives excitatory input from the cerebral cortex about a desired movement, then, the striatum sends inhibitory signals to the internal globus pallidus. The internal globus pallidus would normally inhibit the thalamus, however, when the inhibitory activity of the internal globus pallidus is inhibited, this allows the thalamus to send excitatory signals to the motor cortex to stimulate voluntary movements

Question 10

Describe the indirect (inhibitory) pathway of the basal ganglia

Answer 10

The striatum receives excitatory input from the cerebral cortex about a desired movement, then, the striatum sends inhibitory signals to the external globus pallidus. The external globus pallidus would normally inhibit the subthalamic nucleus, however, when the inhibitory activity of the external globus pallidus is inhibited, this allows the sub thalamus nucleus to send excitatory signals to the internal globus pallidus which then send inhibitory signals to the thalamus, preventing the thalamus from sending excitatory signals to the motor cortex and consequently inhibiting voluntary movements

Question 11

Which structure in the mesencephalon (midbrain) does the basal ganglia receive input from?

Answer 11

Substantia nigra

Question 12

Which neurotransmitter is released from the substantia nigra and acts on the basal ganglia?

Answer 12

Dopamine

Question 13

How does dopamine modulate the direct (excitatory) pathway of the basal ganglia?

Answer 13

Dopamine binds to D1 (excitatory) receptors expressed by the striatal cells projecting to the internal globus pallidus, activating the direct (excitatory) pathway and reinforcing desired voluntary movements

Question 14

How does dopamine modulate the indirect (inhibitory) pathway of the basal ganglia?

Answer 14

Dopamine binds to D2 (inhibitory) receptors expressed by the striatal cells projecting to the external globus pallidus, inhibiting the indirect (inhibitory) pathways, preventing the inhibition of unwanted voluntary movement

Question 15

What are the two main descending pathways in control of motor responses?

Answer 15

Pyramidal tract
Extrapyramidal tract

Question 16

What are the two main divisions of the pyramidal tract?

Answer 16

Corticospinal tract
Corticobulbar tract

Question 17

Describe the pathway of the corticospinal tract

Answer 17

The upper motor neurones of the corticospinal tract originate in the motor cortex and travel to the level of the medulla oblongata where the tract splits to form the lateral and anterior corticospinal tracts which travel through the spinal cord and synapse with lower motor neurones in the ventral gray matter horn of the spinal cord

Question 18

Which muscles are controlled by the lateral corticospinal tract?

Answer 18

The muscles of the limbs are controlled by the lateral corticospinal tract

Question 19

Which muscles are controlled by the anterior corticospinal tract?

Answer 19

The muscles of the trunk are controlled by the anterior corticospinal tract

Question 20

Describe the pathway of the corticobulbar tract

Answer 20

The upper motor neurones of the corticobulbar tract originate in the motor cortex and travel to the level of the pons and the medulla oblongata where they synapse with the lower motor neurones located at the cranial nerve nuclei

Question 21

Describe the structural composition of the extrapyramidal tract

Answer 21

The extrapyramidal tract is composed of upper motor neurones originating in the brainstem nuclei and indirectly innervate and inhibit lower motor neurones through interneurones

Question 22

What are the four divisions of the extrapyramidal tract?

Answer 22

Reticulospinal tract
Rubrospinal tract
Vestibulospinal tract
Tectospinal tract

Question 23

What are the functions of the reticulospinal tract?

Answer 23

Initiation of locomotion and posture

Question 24

What is the function of the rubrospinal tract?

Answer 24

Mainly postural control and acts on flexor muscles

Question 25

What are the functions of the vestibulospinal tract?

Answer 25

Mainly postural control and acts on extensor muscles

Question 26

What are the functions of the tectospinal tract?

Answer 26

Coordinates head movements in response to auditory and visual stimuli

Question 27

How do lesions in the pyramidal tract present?

Answer 27

Spasticity
Paralysis

Question 28

How do lesions in the extrapyramidal tract present?

Answer 28

Involuntary movement
Muscle rigidity
Impaired balance and coordination