Motor System

Question 1

What neurones innervate skeletal muscle

Answer 1

Alpha motor neurones

• cell bodies in Ventral root
• motor axons exit ventral root

Question 2

What is a motor unit

Answer 2

Alpha motor neurone + all innervated muscle fibres

• each muscle fibre receives input from one motor neurone
• each motor neurone innervates several muscle fibres

Question 3

What controls voluntary movement

Answer 3

1. Descending motor controls
2. Controlled by higher motor areas
3. Upper&lower motor neurones

Question 4

What controls involuntary movement

Answer 4

1. Response evoked from peripheral stimulation
2. Coupling sensory input to motor output
3. Spinal reflexes

Question 5

Describe Cutaneous reflexes

Answer 5

Flexion withdrawal reflex

1. Cutaneous receptors detect noxious stimuli
2. Primary afferent activated
3. Synergistic activation and inhibition of muscles

Rapidly removes limb from harmful stimuli

Question 6

Describe the Myotatic reflex

Answer 6

Prevents over-stretching the muscle

1. One synapse
2. Stimuli stretches attached muscle
3. Subsequent contraction of same muscle restores muscle length

Question 7

Describe how a muscle detects stretch

Answer 7

1. Muscle spindles (proprioceptors)
2. Sensory neurones in spindle encode information of muscle length
3. Ia and II afferents monitor extent of stretch and synapse with motor neurones in the spinal cord

Question 8

Describe the polysynaptic reflex

Answer 8

1. Two or more synapses
2. Stimulus is muscle stretch
3. Inhibitory interneurones synapse alpha motor neurones

Question 9

Role of Gamma motor neurones

Answer 9

1. Innervates intrafusal fibres
2. Adjusts sensitivity of muscle spindle
3. Increased range of function

Question 10

What are the three types of interneurones involved in motor system

Answer 10

A. Inhibitory interneurones
B. Excitatory interneurones
C. Renshaw cells

Question 11

Role of inhibitory interneurones

Answer 11

• activated by PANs
• inhibits alpha motor neuron
• inhibits contraction of associated muscle

Question 12

Role of excitatory interneurones

Answer 12

• activate Y motor neurone
• synapse onto intrafusal muscle fibre
• increased sensitivity of spindle

Question 13

Role of Renshaw cells

Answer 13

• inhibitory interneurones
• activated by alpha motor neurone
• also inhibits alpha neurones (andromic inhibition)
• inhibits interneurones and y motor neurones

Question 14

Describe the 3 types of spinal cord organisation

Answer 14

1. Segmental
   - basic circuits and connections at each level
   - basic spinal reflexes mediate these
2. Prospinal system
   - connecting different levels of SC
   - enables coordination
3. Descending motor tracts
   - controls muscle tone

Question 15

Describe the crossed extensor reflex

Answer 15

Maintains balance

• flexion withdrawal removes ipsilateral limb
• simultaneous extension of contralateral limb

Question 16

Law of reciprocal innervation

Answer 16

When contraction of a muscle is stimulated, there is a simultaneous inhibition of its antagonist
- essential for coordinated movement

Question 17

What circuits are required to generate rhythmic movements

Answer 17

Only Spinal cord intrinsic circuits

- although modified and initiated by descending commands and sensory feedback

Question 18

Define a Central pattern generator

Answer 18

Biological neural network that produces rhythmic patterned outputs without sensory feedback

Question 19

Describe the half-centre hypothesis

Answer 19

Generation of alt activity involves two neuronal centres with mutual reciprocal inhibition

• two groups of spinal cord neurones
• mutually inhibiting each other
• capable of producing basic rhythm when coupled to each other

Question 20

Describe half-centre oscillator theory

Answer 20

1. Segmental pathways activated by high-threshold flexor reflex afferents (FRA)
2. Excitation of flexors (by ipsilateral FRA) and of extensors (contralateral side)
3. Reciprocally inhibitory interactions

TRANSMISSION IN ONE PREVENTS SIMULTANEOUS TRANSMISSION IN THE OTHER

Question 21

Describe pacemaker neurones/ concept

Answer 21

Pacemaker neurone directing continuous rhythmic movement

Question 22

What are the two types of motor system organisation

Answer 22

Parallel: each level issues commands that act directly on the lowest level

Okay hierarchical: motor system organised into a series of functional levels- higher command lower

Question 23

What are the four major components of the motor system

Answer 23

1. Pre-motor cortex
2. Primary motor cortex
3. Brainstem
4. Spinal cord
   Both parallel and hierarchical organisation

Question 24

Describe the differences between higher and lower level damage

Answer 24

Lower: obvious specific deficit

Higher: higher commands lose ability to coordinate lower levels resulting in new patterns of activity

Question 25

Difference between upper and lower motor neurones

Answer 25

Upper: from cerebrum or brainstem with connections to spinal cord Lower: in cranial nerve nuclei in brainstem or spinal cord with connections to muscle/ periphery

Question 26

Why is the Babinski sign (toes curl upwards) a sign of high motor neurone damage

Answer 26

Lesions to higher control frees lower centres from their normal functioning

Question 27

Describe lesion at level of C1

Answer 27

1. Spinal cord divided from CNS 2. Lower motorneuones spared 3. Flaccid paralysis (loss of voluntary muscle control and muscle tone)

Question 28

Describe lesions at level of colliculi

Answer 28

1. Dividing upper and lower brainstem 2. Extensor muscles contract leading general stiffness 3. Higher centres disconnected thus releasing lower levels of control

Question 29

Name 3 organisational features of motor system

Answer 29

1. Body maps - distal branch of ventral horn controls distal muscles 2. Sensory feedback - each level receives sensory feedback to correct movement 3. Descending motor control - higher levels modulate levels of sensory input into motor system

Question 30

Name two side loops of the motor system

Answer 30

1. Basal ganglia | 2. Cerebellum

Question 31

What are the three types of stroke

Answer 31

Ischaemic- due to closure of blood vessel by blood clot Haemorrhagic- blood vessel rupture and bleeding Transient ischaemic attach (TIA)- temporary blockage of blood flow

Question 32

What is an insufficient blood supply called | What is permanent brain damage called

Answer 32

Ischaemia Infraction

Question 33

Describe the corticospinal pathway

Answer 33

From motor area of cortex to spinal cord, synapsids in brainstem nuclei With rubrispinal pathway Known as the lateral descending motor pathway

Question 34

Describe the corticobulbar pathway

Answer 34

From brainstem nuclei to spinal cord Medial white matter tract

Question 35

What does the lateral descending motor pathway control

Answer 35

Distal musculature Fine movement