Motor systems overview week 6

Question 1

The control of movement can be grouped into what 3 functions?

Answer 1

1. reflexes
2. posture
3. voluntary movement

Question 2

What are the sensory influences of posture?

Answer 2

NEURAL CONTROL OF POSTURE: automatic maintenance of static posture and postural adjustments during voluntary movements (anticipation of and adapting to them)

Normal muscle tone and posture is dependent on several inputs that modulate the spinal reflex circuits.

Sensory influences

1. Muscle receptors and proprioceptors
2. Vestibular
3. Visual

Question 3

What is the function of the reticulospinal tract? Where does it originate?

What does role does this tract play in sleep?

Where is this tract located in the spinal cord?

Answer 3

Reticulospinal

1. Medial reticulospinal tract originates in the pontine reticular formation facilitates axial muscles and limb extensors
2. Lateral reticulospinal tract originates in the medullary reticular formation inhibits neck and axial activity, mixed effects on extensors and flexors, tends to add to extensor bias

We do not have to know the differences btwn the medial and lateral reticulospinal tracts. Just know that together they are excitatory to extensor tone. The reticulospinal tract shuts off motor pathways during sleep. If there are issues with this pathway, can physically act out dreams

This tract is located in the anterior spinal cord.

Question 4

Where does the vestibulospinal tract originate? Where is it located in the spinal cord?

What is the function of the vestibulospinal tract?

What inhibits this tract?

Answer 4

Vestibulospinal influences.

1. Lateral vestibulospinal tract: originates in the vestibular nuclei. anteriorly located in the spinal cord
   a. excitatory to arm and leg extensors
   b. inhibited by the cerebellum

The vestibulospinal tract constantly maintains some level of tone for balance, particularly in legs. if someone has stroke, may be able to stand because this system is intact even if they cannot walk

Question 5

Where does the rubrospinal tract originate?

What is the function of the rubrospinal tract?

What tract is near the rubrospinal tract causing them to often be lesioned together?

Answer 5

Rubrospinal tract

• Facilitates motor neurons to arm flexors

​​This tract is the reason why the contralateral arm is contracted individuals who suffered a stroke. Rubrospinal tract tonically stimulates arm flexors. Does not affect leg tone (only goes to thoracic level in spinal cord). Is very near corticospinal tract in spinal cord so when lesion one typically lesion the other

Question 6

What are the 2 indirect inputs to motor neurons? (just list)

Answer 6

Cerebellar and basal ganglia influences

Question 7

What relationship does the anterior lobe of the cerebellum have with vestibular nucleus? What else does it connect with to influence movement?

How does the basal ganglia influence movement?

Answer 7

Cerebellar influences

• The anterior lobe of the cerebellum inhibits the lateral vestibular nucleus and has bidirectional connections with the cortex

Basal Ganglia influences

• This important input to postural adjustments is exerted indirectly through the thalamus and the cortex

Question 8

A lesion where in the brain produces decerebrate rigidity?

Explain why.

Answer 8

A bilateral lesion in the brainstem between the red nucleus and the vestibular nuclei produces decerebrate rigidity. (Damage to the red nucleus and the corticospinal tract in the midbrain has a similar effect).

The corticospinal and rubrospinal pathways are damaged in this lesion. This means there is no input from the corticospinal and rubrospinal pathways to the vestibulospinal and reticulospinal pathways-extremities are tonically extended.

The appearance of decerebrate posturing is particularly ominous because it indicates widespread dysfunction affecting the brainstem, putting at risk vital structures for respiration (and consciousness) and thus survival. It requires immediate attention and intensive care.

attached is pg 256 of course notes, slide 7 of PP

Question 9

A lesion where in the brain causes decorticate rigidity?

Explain why.

Answer 9

Lesion in: - motor cortex OR

• internal capsule (posterior limb) (above the red nucleus)

Produces:

Decorticate rigidity: tonically extended leg, flexed arm

This type of lesion causes loss of corticospinal tract input to the rubrospinal and vestibulospinal tracts in addition to flexor motor neurons. These tracts can then stimulate flexion of the arms (rubrospinal) and extension of the legs (vestibulospinal).

Question 10

What kind of motor neurons does the reticulospinal tract innervate? What is the function of these motor neurons?

Answer 10

Reticulospinal tracts input mostly to gamma motor neurons. Gamma motor neurons innervate intrafusal fibers which firee action potentials during muscle contraction so as to maintain the sensitivity of the muscle spindle. When activated by reticulospinal input, changes the tone of intrafusal fiber. This is required so one can move. Reflexes are designed to hold same tension in muscle all the time. Need this input to change sensitivity of receptor so can move voluntarily

Question 11

What is the function of the premotor cortex?

What can damage to the premotor cortex cause?

Answer 11

Premotor cortex:

a. Stimulation produces movements involving multiple muscles in contralateral limbs
b. Damage impairs the ability to develop an appropriate strategy for movement: apraxia. Apraxia: inability to carry out skilled movements, despite intact muscle strength i.e. brushing teeth, combing hair

Question 12

What is the function of the supplementary motor cortex?

What results from damage to this area?

Where is it located?

Answer 12

Supplementary motor cortex. Located just anterior to the primary motor cortex

• Stimulation produces bilateral movements involving multiple limbs. This area involves coordination of movement btwn body parts so they can be moved together
• Damage produces:
  
  • Transient movement impairment
  • sometimes transient mutism (with left sided damage)

Question 13

The primary motor cortex receives strong input from premotor and supplementary motor cortex, areas active before the primary motor cortex. Thus, the primary motor cortex cannot be considered the sole source or originator of movement, but rather, one of several ways stations that send signals to the motorneuron pools in the brainstem and spinal cord, that are the “final common pathway” to the muscles.

Electrical potentials recorded from the cortex suggest a sequence of activation starting in the prefrontal cortex, projecting to the premotor cortex and then to the primary motor cortex. Subcortical sites in the basal ganglia also contribute importantly to the initiation of movements.