L9 - Motor Control

Question 1

How is the motor system arranged?

Answer 1

Hierarchically

Question 2

What is the order of the hierarchy of the motor system?

Answer 2

Highest - primary motor cortex
Middle - brainstem
Lowest - spinal cord

Question 3

What does the primary motor cortex control?

Answer 3

Projects directly to spinal cord via corticospinal tract

Regulates motor tracts that originate in brainstem

Question 4

What does the brainstem control?

Answer 4

Lateral descending system that controls distal limbs

Important for goal-directed movements of hand and arm

Question 5

What does the spinal cord control?

Answer 5

Contains neuronal circuits that mediate reflexes automatisms – e.g. walking
Simplest reflex - monosynaptic-sensory neurone and motor neurone
Most reflexes are polysynaptic with interneurons

Question 6

Where does the basal ganglia and cerebellum receive information from?

Answer 6

Many areas of the cortex

Question 7

Where does the basal ganglia and cerebellum project to?

Answer 7

Motor cortex via the thalamus

Question 8

Where does the basal ganglia feed back to?

Answer 8

Only feeds back to motor cortex - subcortical loop

Question 9

Where does the cerebellum feed back to?

Answer 9

Mainly feeds back to motor cortex

In an emergency it can by-pass the motor cortex and send signals down the brainstem, spinal cord and onto muscles

Question 10

What is the important of the basal ganglia and cerebellum being aware of the situation the person is in?

Answer 10

Monitor commands going down to the muscles to ensure they are appropriate for situation
If commands are not appropriate they calculate correction signals
Sent back to the motor cortex for approval before the signal is sent to the muscles

Question 11

How was the motor cortex discovered?

Answer 11

1870 - electrical stimulus to areas of frontal lobe produced movements on opposite side of body
Mid 20th Century - electrical stimulation used to identify specific motor effects of discrete sites in frontal lobe in different species

Question 12

What else was produced to aid in the discovery of the motor cortex?

Answer 12

Motor Maps produced and correlated with anatomical and clinical observations on effects of lesions

Question 13

What is Brodmanns area 4?

Answer 13

Area in which lowest intensity stimulation elicited movement - Primary Motor Cortex
Located just before the central sulcus
Sometimes called precentral gyrus to highlight its position

Question 14

Motor cortex map

Answer 14

Showed orderly arrangement along the gyrus of control area for leg, trunk, hand

Question 15

Lesions to specific area of motor cortex lead to?

Answer 15

Degeneration in associated spinal cord area

Question 16

What was the issue of the motor cortex map for the fingers, hand and face?

Answer 16

Fingers, hand and face had disproportionately large representation for fine movement
Large areas of brain required to control these areas

Question 17

What causes simple, voluntary movements?

Answer 17

Electrical stimulation of motor cortex does not produce complex or learned movements

• Twitches in individual muscles
• Speech is only simple vowels

Question 18

What are motor cortex first neurons?

Answer 18

Called upper motor neurones

Carry motor commands down through the brain, brainstem and to the spinal cord

Question 19

What is the output to upper motor neurons?

Answer 19

Output to lower motor neurons via interneurones

Question 20

What is the function of upper motor neurons?

Answer 20

Involved in planning, initiating and directing movements

Question 21

What are some example of other upper motor neurons?

Answer 21

Originate in phylogenetically ancient motor centres of brainstem
Red and vestibular nuclei
Superior colliculus
Reticular formation

Question 22

What do upper motor neurones regulate?

Answer 22

Muscle tone
Postural muscle
Balance
Head orientation

Question 23

What are the two upper motor neuron pathways?

Answer 23

Direct and indirect
Both pathways govern production of action potentials in lower motor neuron - final common pathway
- Leads to muscle contraction and movement

Question 24

What is the indirect motor pathway?

Answer 24

Input to lower motor neurones from motor centres in brainstem

Question 25

What is the direct motor pathway?

Answer 25

Input to lower motor neurones from axons extending directly from cerebral cortex

Question 26

What does the basal ganglia contain?

Answer 26

Caudate Putamen Substantia nigra Subthalamic nuclei

Question 27

What is the function of the basal ganglia?

Answer 27

Provide input to upper motor neurons and connects with motor cortex Helps initiate and terminate movement Suppresses unwanted movements Establishes normal level of tone

Question 28

What is Tourette's syndrome?

Answer 28

Damage to basal ganglia so people do not have this level of control

Question 29

What is the function of the cerebellum?

Answer 29

Control activity of upper motor neurons and connect to cortex via thalamus and to brainstem Monitors movements for differences in intended and actual movements - If any discrepancies, sends an error signal and tries to reduce discrepancy

Question 30

What does proprioception allow?

Answer 30

Allows you to know the orientation of limbs without visual input Muscle spindles tell the brain about how long the muscle is to work out orientation Muscle spindle fibres are intrafusal – inside capsule

Question 31

What do muscle spindles contain?

Answer 31

Bag fibres – nuclei gather in one place | Chain fibres – nuclei all in a straight line

Question 32

What do Bag and Chain fibred contain?

Answer 32

Sensory fibres – group Ia | Motor fibres – group II

Question 33

Group Ia fibres

Answer 33

Anulospiral endings Wrap around equator of bag and nuclear chain fibres Pulling apart of these coils initiates action potentials in axon

Question 34

Group II fibres

Answer 34

Endings have a flower spray terminal ending embedded in equatorial region of bag fibres Anulospiral endings wrap around equator of nuclear chain fibres

Question 35

What do group Ia fibres relay?

Answer 35

Sensory endings relay information on the dynamic phase of muscle stretch E.g. as stretch is occurring

Question 36

What do group II fibres relay?

Answer 36

Sensory endings relay information on the static phase of muscle stretch E.g. its final length

Question 37

When are muscle spindles useful?

Answer 37

When under tension

Question 38

What happens when extrafusal muscles contracts and shorten around the muscle spindle?

Answer 38

Muscle spindles unload and loses tension as intrafusal fibres aren’t doing anything If no tension - no stretch information going to brain

Question 39

To solve the problem of a lack of tension of muscle spindles what happens?

Answer 39

As extrafusal muscles contract gamma-motoneurones are co-activated with alpha-motoneurones - Contract intrafusal fibres - Spindle shortens in register - Allows brain to continue to get information from group II and group Ia

Question 40

What is the effect of noradrenaline of gamma motor neuron activity?

Answer 40

Decreases activity By inhibiting the γ-motoneurones - intrafusal fibres can be made more elastic Elastic materials don’t transmit stretches well

Question 41

What is the effect of 5HT of gamma motor neuron activity?

Answer 41

Increases activity By stimulating the γ-motoneurone - intrafusal fibres can be made slightly stiffer Stiffer materials transmit stretches with greater fidelity

Question 42

What are the 3 synaptic relays in the proprioceptive pathway?

Answer 42

1. Central processes of DRG cells synapse on neurones in gracile and cuneate nuclei in lower medulla 2. Axons from these nuclei synapse on neurones in ventral posterior lateral nucleus of thalamus 3. Axons sent to primary somatosensory cortex

Question 43

Where are somatosensory cortices found?

Answer 43

Primary and secondary somatosensory cortices are in the anterior parietal lobe and the posterior parietal cortex

Question 44

Where is SII found?

Answer 44

Deep within lateral sulcus

Question 45

Lesioning S1 does?

Answer 45

Produced proprioceptive deficits

Question 46

What is the structure of S1?

Answer 46

Divided into four distinct regions cytoarchitectonic regions