L23 - neurophysiology of motor control

Question 1

Why are movement injuries common?

Answer 1

Because a large portion of the brain is devoted to voluntary movement.

Question 2

What is a reflex movement?

Answer 2

Rapid, reproducible, sterotypical, autonomic motor response to an external stimulus

Question 3

What kind of circuit in a refex movement?

Answer 3

Simple neural circuit of spinal cord and peripheral nerves (sensory stimulus here –> info sent to SC locally and motor output from SC)

Question 4

What is a voluntary movement?

Answer 4

Wide variety of movements of varying speed, duration and complexity

Question 5

What kind of circuit in a voluntary movement?

Answer 5

Complex patterns of sensory and motor processing, centres involved in control is in the circuit i.e parts of the brain is required

Question 6

What is a stretch reflex? Monosynapse at the SC

Answer 6

Stimulate a receptor (tendon) –> pull muscles i.e LENGTHENING stretch receptors present in muscle spindles –> opens mechanically gated ion channels leads to AP (receptor potential type of local potential - localised change in potential in the SENSORY APPARATUS of sensory nerve cell) –> info passed to posterior root ganglion unipolar cell body if AP occurs–>info processed in SC –> activation of motor neuron (sensory synapses with a motor neuron in the LATERAL horn - EXITATORY connection) –> ventral root –> changes length of muscle and muscle contraction in response to stretch

Question 7

Which receptors give a sense of position?

Answer 7

Proprioceptors

Question 8

Withdrawal reflex pathway (polysynaptic)

Answer 8

sensory receptor (Thermal - nociceptors in skin - free nerve endings) –> mechanically gated ion channels –> AP to dorsal root ganglion –> SC –> interneuron in dorsal horn to inhibit and excite motor neurons –> motor neuron in ventral horn

Also info sent through dorsal column pathway so brain is aware of sensation

Question 9

What does the brain need to know

Answer 9

Position of muscles needed for an action so it uses proprioceptors eg muscle spindles to do that

Question 10

What happens when there is movement of the joints and muscles

Answer 10

The proprioceptors are still at work so that brain knows the correct action is being carried out

Question 11

What is the brainstem and SC responsible for?

Answer 11

*Simple cranial and spinal reflexes
*Group of neurons called central pattern generators control autonomic activity such as breathing and chewing so that thalamus is not overwhelmed with info input i.e rhythmic patterns

Question 12

What is the Pons and Medulla Oblongata responsible for?

Answer 12

Balance replexes and more complex respiratory reflexes

Question 13

What is the Hypothalamus responsible for?

Answer 13

Reflex motor patterns related to eating, drinking (osmotic pressure of ECM changes) , sexual activity, modifies respiratory reflexes

Question 14

What is the Basal nuclei responsible for?

Answer 14

Basal ganglia modify motor and reflexive patterns at subconcious level, inititiation of voluntary movements
*Adjust output along corticospinal tract by altering pyrimydal cells sensitivity
*Change ex/in output of medial/lateral pathways

Question 15

What is the motor cortex responsible for?

Answer 15

Initiates voluntary motor movement

Question 16

What is the Thalamus and midbrain responsible for?

Answer 16

controls reflexes in response to auditory or visual stimuli

Question 17

What is the Cerebellum responsible for?

Answer 17

complex motor patterns through feedback loops

Question 18

What is the prefrontal cortex responsible for?

Answer 18

Making a decision of an action that is socially acceptable based on proprioception, memory

*emotion and personality
*Co-ordinates with basal ganglia and premotor cortex to carry out an action in their right order

Question 19

What does the primary motor cortex form?

Answer 19

Latin for a small body homunculus

Question 20

What do areas of the motor cortex mean?

Answer 20

Related to the complexity of the movement i.e more complex movements of the face have more neurons in the brain

Question 21

Cerebellum

Answer 21

*motor programs - organises complex movements without having to “practice” everytime i.e a learned behaviour
*intergrates sensory info into planned events so voluntary movements can be modified
*Organises timing of of muscle contraction and comparing planned with actual movement with the pathways of the primary motor cortex –> correction mechanism
*Modify the output pathway and makes sure intentended action is carried out
*disorders of the cerebellum results in ataxia i.e movement disorders

Question 22

Pathway of voluntary action

Answer 22

Prefrontal cortex –> premotor cortex –> basal nuclei and cerebellum to activate neurons that initiate movemnt and which sense the position of the required body parts and send info to the cortex? premotor cortex neurons activate appropriate neurons in primary motor cortex are picked and AP carried out to lower motor neurons –> change in position detected by sensory neurons and fed back to the cerebellum which then modifies pathways for the pri motor cortex and basal ganglia so that correct action is carried out i.e original plan

Question 23

What kind of neuron is the unipolar cell body?

Answer 23

Somatic sensory neuron

Question 24

Channels at the input end of the unipolar somatic sensory neuron

Answer 24

Mech GIC

Question 25

What is a receptor potential

Answer 25

Localised change in voltage in the sensory apparatus of a sensory nerve cell

Question 26

synapse between sensory and motor neuron is an?

Answer 26

Excitatory connection

Question 27

The stretch synapse is what kind of neural circuit?

Answer 27

Monosynaptic, requires MGIC

Question 28

What kind of neural circuit is the withdrawal reflex?

Answer 28

Polysynaptic

Question 29

What is an interneuron?

Answer 29

Receives info from a neuron and gives out info to another neuron

Question 30

What other neuron does the interneuron interact with?

Answer 30

The inhibitory interneuron

Motor activates the flexors and inhibitory removes excitation of the extensors eg triceps must not be active
*Inhibit neuron that would excite the muscle i.e IPSP (one muscle active at one)

Question 31

Central pattern generators

Answer 31

Initiate response, take feedback and keep those activities going

Question 32

What does the thalamus do

Answer 32

Major relay centre for sensory info to required parts of the brain

Question 33

Frontal lobe

Answer 33

*Executive functions –> decision making on position of the body, memory on past experiences i.e is it risky

Question 34

Desire to initiate a movement arises in?

Answer 34

Prefrontal cortex

Question 35

Ataxia

Answer 35

*Slow feedback through circuit because correction mechanism not activating

Question 36

Cerebellar disease

Answer 36

*Speech impediment
*Ataxia
*Tremor
*Dismetria - misjudge distances (a learned behaviour)