Motor control and reflexes

Question 1

Where is the sensory input to alpha motor neurons from?

Answer 1

From muscle spindles – feedback from ipsi- and contralateral muscles

Question 2

What initiates and controls voluntary movement in alpha motor neurons?

Answer 2

Upper motor neurons from the motor cortex and brain stem

Question 3

What is the functions of interneurons in the spinal cord in alpha motor neurons?

Answer 3

Circuitry that generates spinal motor programs

Question 4

What do muscles contain within them (sensory feedback)

Answer 4

Muscle spindles/stretch receptors (intrafusal fibres)

Question 5

What are muscles innervated by at distal ends?

Answer 5

Gamma motor neurons

Question 6

What wraps around centre and synapse on alpha motor neurons that innervate the muscle in the spinal cord?

Answer 6

1a sensory axons

Question 7

What is the function of group I and II afferent axons?

Answer 7

Sensory - carry info to CNS

Question 8

What occurs when muscle starts to stretch and muscle spindles are stretched?

Answer 8

Depolarisation of 1a sensory axons

Question 9

What does depolarisation of 1a sensory axons occur via?

Answer 9

Via mechanosensitive ion channels

Question 10

What occurs when 1a sensory axons deporarise?

Answer 10

Increases APs generated and synapse on alpha motor neurons thus increasing their AP frequency and causing muscle to contract to resist this change

Question 11

What are the steps of the stretch reflex?

Answer 11

1. Increased afferent to spinal cord
2. Increased efferent output through alpha motor neurons
3. Muscle contracts
4. Firing rate of afferent sensory neuron decreases (negative feedback)

Question 12

What do gamma motor neurons innervate?

Answer 12

Both ends of the muscle spindle

Question 13

What do gamma motors neurons operate to do as muscle contracts?

Answer 13

To stimulate contractile portions of spindle to contract

Question 14

What are the steps in muscle spindle innervation?

Answer 14

1. Afferent input from sensory endings of muscle spindle fibre
2. Alpha motor neuron output to regular skeletal muscle fibre
3. Stretch reflex pathway
4. Gamma motor neuron output to contractile end portions of spindle fibre
5. Descending pathways coactivating alpha and gamma motor neurons

Question 15

Unstretched muscle (action potentials)

Answer 15

Action potentials are generated at a constant rate in the associated sensory fibre.

Question 16

Stretched muscle (action potentials)

Answer 16

Stretching activates the muscle spindle, increasing the rate of APs.

Question 17

What does contraction of muscle cause? (muscle spindle)

Answer 17

Causes muscle spindle to slacken

Question 18

What does activation of gamma-motor neurons

cause?

Answer 18

Causes contractile distal ends of spindle to contract

Question 19

What do gamma-motor neurons ensure?

Answer 19

Ensures central ‘sensory’ portion remains taut

Question 20

What would happen if only alpha motor neurons were activated?

Answer 20

Only the extrafusal muscle fibres contract. The muscle spindle becomes slack and no APs are fired. It is unable to signal further length changes.

Question 21

What occurs when alpha-gamma coactivation occurs?

Answer 21

Both extrafusal and intrafusal muscle fibres contract. Tension is maintained in the muscle spindle and it can still signal changes in length.

Question 22

What is the increase in AP frequency is proportional to?

Answer 22

Rate of stretch - detect velocity of muscle stretch

Question 23

What is the resting discharge rate of firing of AP?

Answer 23

~10 / sec

Question 24

What happens to AP when muscle spindle is stretched?

Answer 24

An increase in AP discharge

Question 25

During very rapid stretch, how high can AP frequency rise?

Answer 25

As high as 500/sec

Question 26

What can phasic receptors do?

Answer 26

Can rapidly adapt in response to stretch of muscle and muscle spindle

Question 27

What are tonic receptors? (adaptation)

Answer 27

Only slow adaption in response to stretch of muscle and muscle spindle

Question 28

What do secondary endings detect?

Answer 28

Detect absolute of muscle length

Question 29

Why is proprioception from the Golgi tendon organs important?

Answer 29

For information on whole muscle tension – conscious level

Question 30

How are muscle spindles physically related to muscle fibres?

Answer 30

Muscles spindles are parallel to muscle fibres

Question 31

How are golgi tendon organs organised?

Answer 31

In series with muscle fibres

Question 32

Where is the synapse with 1b sensory axons ?

Answer 32

On interneurons of ventral horn

Question 33

What is the GTO primarily a sensor system for?

Answer 33

Tension

Question 34

What type of fibres are golgi tendon organs? (and where)

Answer 34

Afferent (type 1b) fibres lying within the tendons

Question 35

What do Golgi tendon organs respond to?

Answer 35

To alterations in muscle tension

Question 36

What does muscle tension cause in tendon?

Answer 36

Causes tendon tightening and uplift to joint

Question 37

What does increased tension in the tendon cause?

Answer 37

It stretches Golgi tendon organs

Question 38

What does stretch intensity increase?

Answer 38

AP frequency

Question 39

How are afferent signals delivered and interpreted?

Answer 39

centrally and interpreted consciously

Question 40

What muscle spindles fire when muscle is stretched?

Answer 40

(1a) and GTO (1b) fire (GTO to a lesser extent)

Question 41

What happens to muscle spindle activity during active contraction?

Answer 41

It decreases

Question 42

Why does GTO become more active?

Answer 42

Due to tension created at either end of contracting muscle

Question 43

What tendon involved knee jerk reflex?

Answer 43

Patellar Tendon

Question 44

What does passive stretching of extensor, which stretches muscle spindles induce?

Answer 44

Induces contraction of extensor and inhibition of flexor

Question 45

Extensor muscles -> (full)

Answer 45

Axon of sensory neuron (peripheral process) - ce;; body of sensory neuron - interneuron - cells bodies of motor neurons - axons of motor neurons - flexor muscles

Question 46

What do alpha motor neurons receive input from?

Answer 46

1. Primary sensory axons, 2. Descending axons from brain 3. Collaterals of lower motor neuron axons.

Question 47

What does the arrangement of alpha motor neurons allow?

Answer 47

Allow coordinated motor programs to be generated in response to many inputs

Question 48

Where do collaterals of 1a sensory axons from muscles spindles synapse?

Answer 48

Via inhibitory interneurons on alpha motor neurons of antagonist muscle

Question 49

Where do nociceptive axons terminate?

Answer 49

On excitatory or inhibitory interneurons in spinal cord

Question 50

What is the function of ipsilateral side?

Answer 50

1. Inhibits activity of extensor muscle | 2. Stimulates contraction of flexor muscle

Question 51

Why do nociceptor fibres stimulate extensors and cause relaxation of flexors?

Answer 51

- To withdraw limb on ipsilateral side - To stabilise limb on contralateral side and ensure weight-bearing - To ensure stabilisation of organism

Question 52

What is the function of nociceptor fibres?

Answer 52

To stimulate extensors and cause relaxation of flexors

Question 53

What does planning of movement require?

Answer 53

Input about current body position, visual and somatosensory information

Question 54

Where is the motor cortex located?

Answer 54

On the frontal lobe, anterior to the central sulcus

Question 55

What are the areas that are believed to be important in planning of movement?

Answer 55

Pre and supplementary motor areas

Question 56

What are the areas of central control of movement?

Answer 56

- Cortex and basal ganglia (forebrain) - Motor cortex and cerebellum - Brain stem and spinal cord

Question 57

What are the principal descending pathways?

Answer 57

- Corticospinal (pyramidal) | - Brainstem

Question 58

return 29

Answer 58

rip

Question 59

What are the three motor control systems?

Answer 59

1. Spinal reflexes 2. Corticospinal pyramidal motor system 3. Extrapyramidal system

Question 60

What is the role of spinal reflexes?

Answer 60

Posture adjustment, withdrawal reflexes

Question 61

What is the role of the corticospinal pyramidal motor system

Answer 61

Fine, discrete voluntary movement

Question 62

What is the role of the extrapyramidal system

Answer 62

Overall posture, involuntary maintenance

Question 63

What is the effect of motor neuron damage?

Answer 63

Flaccid paralysis, no reflexes

Question 64

What is the effect of cerebellum/basal nuclei damage?

Answer 64

Uncoordinated voluntary movement

Question 65

What is the effect of damage to higher cortical command centres?

Answer 65

Inertia, inability to translate voluntary planning into motor activity

Question 66

What does sensory information do?

Answer 66

It informs central input

Question 67

What does central input do?

Answer 67

It varies

Question 68

What does the motor unit output pattern affect?

Answer 68

Skeletal Muscle Activity

Question 69

What does skeletal muscle activity determine?

Answer 69

Observable motor responses

Question 70

What would alpha motor neuron activation alone cause?

Answer 70

A decrease in 1a sensory activity as muscle spindle would be slack; contraction would cease as muscle spindle would be flaccid

Question 71

What would gamma motor neuron activation alone cause?

Answer 71

An increase in 1a sensory activity as muscle spindle (centre) is stretched; induces contraction of muscle

Question 72

What is required to maintain muscle tone.

Answer 72

A balance between alpha and gamma motor neuron activation.

Question 73

What does layer V of the brain surface receive input from?

Answer 73

From other cortical areas and thalamus

Question 74

What do layer V of the brain surface send and where?

Answer 74

Send axon collaterals to subcortical sites involved in sensorimotor processing (brain stem)

Question 75

What do layer V pyramidal cells project to?

Answer 75

To spinal cord

Question 76

What is subcortical input from?

Answer 76

Basal ganglia

Question 77

Where does basal ganglia receive input from?

Answer 77

Cerebral, prefrontal and parietal cortex

Question 78

What does input from basal gangle initiate?

Answer 78

Activity of motor cortex in initiating movement

Question 79

What is the basal ganglia composed of?

Answer 79

Caudate nucleus, putamen, globus pallidus, subthalamic nucleus and substantia nigra

Question 80

When does initiation of movement begin?

Answer 80

When activation of SMA is boosted beyond some threshold