L12 Motor Systems

Question 1

What is the primary motor cortex?

Answer 1

M1.

An area found in the frontal lobe anterior to the central sulcus, executes muscle control.

Question 2

What is the primary sensory cortex?

Answer 2

S1.

An area behind the central sulcus, recieves sensation from skin, muscles and viscera.

Question 3

What is the primary visual cortex?

Answer 3

V1.

Found in the occipital lobe, recieves visual info from the retina.

Question 4

What is the primary auditory cortex?

Answer 4

The area of the brain on the superior surface of the temporal lobe which recieves auditory info.

Question 5

What are upper and lower motor neurons?

Answer 5

The motor system is a 2-neuron relay:

• Upper motor neurons: found in M1, PMA or SMA, axons project through internal capsule, midbrain, medulla or pons and synapse with lower motor neurons
• Lower motor neurons: found in the ventral horn of the spinal cord, control muscle contraction of axial muscles of trunk and appendicular muscles
• Lower motor neurons in cranial nerve nuclei are also innervated by upper motor neurons, these project to muscles of the face, neck, tongue, larynx and pharynx

Question 6

Describe the somatosensory map of the primary motor cortex.

Answer 6

• Mapped in the same way that the sensory cortex is mapped

- Motor neurons for muscles of the hand, mastication and facial expression very high

Question 7

What is the function of the primary motor cortex?

Answer 7

Controls generation of muscular force and allows higher level of control of limb trajectories and specific muscle activation.

Question 8

How is information sent to the primary motor cortex?

Answer 8

• M1 recieves most of its input from the sensory association cortex
• Primary sensory cortex and visual cortex send info to sensory association cortex
• There is also a direct stream of some info from primary sensory cortex to the primary motor cortex

Question 9

What are the accessory motor areas?

Answer 9

• PMA: premotor area
• SMA: supplementary motor area

Both found just anterior to the primary motor cortex.

Question 10

What is the function of the PMA?

Answer 10

• Some info from the sensory association cortex is sent to the PMA
• PMA computes the info and relays it back to M1
• PMA also has axons which project directly to the spinal cord lower motor neurons

Question 11

What is the function of the SMA?

Answer 11

• Does not recieve any sensory input
• SMA has a role in initiating memorised movements, sends info to primary motor cortex or directly outputs to spinal cord lower motor neurons

Question 12

Which motor pathway is only present in recent primates?

Answer 12

Pyramidal motor pathway

Question 13

What 2 fibre tracts is the pyramidal motor pathway comprised of?

Answer 13

• Cortico-bulbar tract

- Cortico-spinal tract

Question 14

What is the role of the pyramidal motor pathways?

Answer 14

Meidates conscious control of motor activity.

Question 15

Where does the pyramidal motor pathway arise from?

Answer 15

Arises from upper motor neurons of M1, PMA and SMA

Question 16

Describe the corticobulbar fibres of the pyramidal motor pathway.

Answer 16

• Decussate at the level of cranial nerve nuclei
• These nerves control the muscles of the face and neck
• Decussate at midbrain: oculomotor and trochlear nerves
• Decussate at pons: trigeminal, abducens and facial nerve
• Decussate at medulla: hypoglossal nerve and lower motor neurons which innervate the muscles of the larynx and pharynx

Question 17

Describe the corticospinal fibres of the pyramidal motor pathway.

Answer 17

• Emerge through medulla in pyramidal shape
• Decussate at the spinal cord at the level of the lower motor neurons which control axial muscles
• These nerves carry info from the cerebral cortex to the spinal cord

Question 18

What is the difference between the lateral and ventral corticospinal tracts?

Answer 18

90% of the corticospinal fibres decussate to form the lateral corticospinal tract: innervate lower motor neurons that control limb muscles

The 10% which don’t decussate form the ventral/medial corticospinal tract and decussate at the level of the lowor motor neurons which control axial muscles.

Question 19

Which motor pathways are present in all vertebrates (evolutionary ancient pathways)?

Answer 19

Extra-pyramidal motor pathways.

Question 20

What is the funciton of the extra-pyramidal motor system?

Answer 20

Mediates the unconscious control of motor activity e.g. posture, balance and reflexes.

Question 21

What is the role of the cerebellum in the extra-pyramidal motor pathways?

Answer 21

Compares the movement that takes place with the intention.

Recieves ascending sensory input and descneding motor input.

Question 22

What is the role of the basal ganglia in the extra-pyramidal motor pathways?

Answer 22

Co-ordinates motor subroutines needed for some unconscious movements, important role in the execution of movement.

Question 23

What is the role of the thalamus in the extra-pyramidal motor pathways?

Answer 23

Relays between the basal ganglia and cortex.

Question 24

What is the role of the midbrain tectum in the extra-pyramidal motor pathways?

Answer 24

Role in visual and auditory reflexes.

Question 25

What is the role of the reticular formation in the extra-pyramidal motor pathways?

Answer 25

Series of motor nuclei which run through the midbrain, pons and medulla.

Question 26

Name 4 extra-pyramidal motor pathways.

Answer 26

- The reticulospinal tract - The tectospinal tract - The vestibulospinal tract - The rubrospinal tract

Question 27

What is the reticulospinal tract?

Answer 27

- Tract running from the reticular nuclei within the pons and medulla to the spinal cord - Input to the nuclei neurons is predominantly from the primary motor cortex via the corticopontine tract and the vestibular nucleus - Reticulospinal tract axons then project to lower motor neurons which innervate the trunk, head/neck and proximal limb muscles Controls muscle tone, posture, balance.

Question 28

What is the tectospinal tract?

Answer 28

- Tract running from the neurons within the superior colliculus of the midbrain tectum to the spinal cord - Afferent input to superior colliculus is from the retina and visual cortex, and the auditory cortex - Axons project to the lower motor neurons in the cervical spinal cord which innervate neck and upper back muscles Coordinates reflex head movement towards auditory or visual stimuli e.g. looking in direction of loud noise or bright light.

Question 29

What is the vestibulospinal tract?

Answer 29

- Tract from vestibular nuclei to the spinal cord - Input to these nuclei neurons is from the inner ear and cerebellum - The ascending medial longitudinal fasciculus carries VST axons to cranial nerve motor nuclei which innervate extrinsic eye muscle - The descending medial longitudinal fasciculus carries VST axons to lower motor neurons to control upper back and neck muscles Plays a role in coordinating balance and keeping eyes horizontal whilst the body is moving.

Question 30

What is the rubrospinal tract?

Answer 30

- Tract from the red nucleus in the midbrain tegmentum to the spinal cord - Recieves input from M1 - Axons from red nucleus decussate in the pons and innervate lower motor neurons at all levels of the spinal cord Appears to modulate lateral corticospinal tract induced motor activity.

Question 31

Where is the reticulospinal tract found?

Answer 31

2 components; 1 found in the reticular nuclei in the medulla, 1 found in the reticular nuclei in the pons.

Question 32

Where is the tectospinal tract found?

Answer 32

Found between the vestibulospinal and medio-cortical spinal tracts, in the ventral region of the white matter in the spinal cord.

Question 33

Where is the vestibulospinal tract found?

Answer 33

In the ventral region of the white matter of the spinal cord.

Question 34

Where is the rubrospinal tract found?

Answer 34

Embedded in the lateral corticospinal tract.