motor systems

Question 1

draw and label the primary sensory and motor areas of cortex

Answer 1

Question 2

draw and label the locations of the upper and lower motor neurons

Answer 2

upper motor neurons -> lower motor neurons -> effector

Question 3

how is the primary motor cortex mapped?

Answer 3

in the same way as the sensory cortex

• columnar organisation of cortical layer V pyramidal neurons
• Different regions of M1 contain upper motor neurons that control the movement of specific muscles
• The somatotopic motor map is also distorted like the sensory map

Question 4

what are the functions of the primary motor cortex?

Answer 4

1. controls muscular force generated
2. Higher level control control of limb trajectories and task specific muscle activation (e.g. precision vs power grip)

Question 5

where do layer V upper motor neurons project to?

what roles does this have?

Answer 5

Spinal cord

• Lower motor neurons that regulate trunk axial muscles and appendicular muscles

Cranial nerve motor nuclei

• Lower motor nuclei that regulate muscles of the head and neck

Question 6

which neurons project to the spinal cord and the cranial nerve motor nuclei?

Answer 6

layer V upper motor neurons from the primary motor cortex

Question 7

where does the primary motor cortex receive most of its input from?

Answer 7

sensory association areas

Question 8

what are the accessory motor areas?

where do they receive input from? where do they give input to?

Answer 8

premotor cortex (PMA)

supplementary motor cortex (SMA)

Question 9

what are the pyramidal motor pathways?

what tracts does it comprise of?

Answer 9

The pyramidal motor pathway is evolutionarily recent (primates)

The pathway comprises the cortico bulbar and cortico spinal tracts

It arises from upper motor neurons of the primary motor cortex, PMA and SMA

The pyramidal pathway mediates the conscious control of motor activity

Question 10

what are the extra-pyramidal motor pathways?

role?

Answer 10

1. reticulospinal tract
2. tectospinal tract
3. vestibulospinal tract
4. rubrospinal tract

The extra-pyramidal motor system mediates the unconscious control of motor activity:

• Posture
• Balance
• reflexes

The pyramidal and extra-pyramidal motor systems do not work in isolation, they work closely together to coordinate posture reflexes and voluntary movement

Question 11

what are the components of the extra-pyramidal motor system

Answer 11

• cerebellum
• vestibular system
• basal ganglia
• thalamus
• reticular formation nuclei
• midbrain nuclei
• cortex

Question 12

describe the reticulospinal tract

Answer 12

• emanates from neurons within the pontine and medullary reticular nuclei
• input to the reticular nuclei neurons is from the cortex via the corticopontine tract and from the vestibular nucleus
  
  • (input to vestibular nucleus is from cerebellum + inner ear)
• reticulospinal tract axons project to lower motor neurons that innervate trunk, head/neck and proximal limb muscles.
• The reticulospinal tract controls muscle tone, posture and simple stereotyped movements.
• basal ganglia, thalamus and cortex exchange information to coordinate motor output/execution

Question 13

describe the tectospinal tract

Answer 13

• the tract emerges from neurons within the superior colliculus (SC) of the midbrain tectum
  
  • afferent input to the SC is mainly from retina, visual cortex, inferior colliculus and auditory cortex
• axons from tectospinal tract project to cervical spinal cord lower motor neurons that innervate neck and upper back muscles
• This tract coordinates reflex head movement towards auditory or visual stimuli.

Question 14

describe the vestibulospinal tract

Answer 14

• tract arises from neurons within superior, lateral and medial vestibular nuclei
  
  • afferent input to these vestibular nuclei neurons is from the inner ear (via vestibular ganglion neurons) and cerebellum.
• the VST axons project in the ascending medial longitudinal fasciculus to cranial nerve motor nuclei containing lower motor neurons that innervate the extrinsic eye muscles (III, IV, VI)
• the descending medial longitudinal fasciculus carries VST axons that innervate lower motor neurons that control upper back and neck muscles
• The VST also projects to lower motor neurons innervating proximal leg muscles
• The VST plays a role in coordinating balance and keeping the head balanced and eyes horizontal when the body is moving

Question 15

describe the rubrospinal tract

Answer 15

• tract arises from neurons within the red nucleus of the midbrain tegmentum
  
  • red nucleus receives direct input from motor cortex
  • axons arising from red nucleus decussate in the pons and innervate lower motor neurons at all levels of spinal cord
• this tract has similar function to lateral corticospinal tract in mammals and modulates lateral corticospinal tract induced motor activity in humans