Hierarchy of motor control

Question 1

What is the difference between lower and upper motor neurones ?

Answer 1

Lower: Nerves that directly innervate muscles
Upper: Neurones in the brain that alter the activity of alpha moto rneurones

Question 2

What horn of the spinal cord houses alpha motor neurones?

Answer 2

Ventral horn

Question 3

What higher brain centres are involved in motor control?

Answer 3

Cerebral cortex
Basal Ganglia
Cerebellum

Question 4

What tracts carry the descending input for the higher order reflexes?

Answer 4

Vestibulospinal tract

reticulospinal tract

Question 5

What is a segmental reflex?

Answer 5

The sensory input is detected at the level of the spinal cord. Alpha motor neurones stimulated from this level without going ‘higher’

Question 6

What is a higher order reflex?

Answer 6

Sensory input is detected by the brainstem nuclei. Reaction is carried to the spinal cord by the vestibulospinal and reticulospinal tracts.

Question 7

What does the corticospinal tract do?

Answer 7

Transmits impulses from the brain straight to the spinal cord, bypassing the brainstem. Associated with voluntary movement.

Question 8

What detects sensory input in the spinal cord?

Answer 8

proprioceptors

Question 9

what detects sensory input in the brainstem?

Answer 9

The vestibular system i.e. balance and positional awareness

Question 10

Is the stretch reflex a segmental or a higher-order reflex

Answer 10

Segmental

Question 11

What is the main function of gamma motorneurones?

Answer 11

Keeping muscle spindles taught

Question 12

How can the stretch reflex be influenced by higher centres?

Answer 12

Direct inhibtion of the alpha motor neurones.
Acting on inter neurones to change the balance between agonist and antagonist
Acting on gamma motor neurones and changing the spindle sensitivity

Question 13

What is alpha gamma coactivation?

Answer 13

As alpha neurones induce movement, the gamma must also activate to maintain the same spindle tension, as this tension is what feeds back to the brain.

Question 14

What is a reflex test used to test for?

Answer 14

Detects spinal cord damage at specific vertebral levels.

Question 15

What vertebral level is likely to be damaged if the bicep jerk reflex is impaired?

Answer 15

C6

Question 16

What vertebral level innervates the triceps jerk reflex?

Answer 16

C7

Question 17

What reflex is mediated by vertebral level L4?

Answer 17

Patellar tendon relfex

Question 18

With damage to the spinal cord at S1 level, which reflex is likely to be missing or impaired?

Answer 18

Achilles tendon reflex

Question 19

As well as cord damage, what other things could cause an impaired reflex?

Answer 19

Nerve damage, example being in diabetes, where the ankle jerk reflex is commonly impaired.

Question 20

Why is it sometimes necessary to distract a patient during an examination of the reflexes?

Answer 20

Voluntary tensing or other influencing of the muscles will spoil the findings

Question 21

In the withdrawal reflex, what happens?

Answer 21

Stimulus on one side - extensors inhibited, flexors contract - move away from stimulus.
Simulatneously, the opposite happens on the contralateral side to maintain balance.

Question 22

What is the Babinski sign?

Answer 22

Extension of toe occurs when the dorsum of the foot is stroked. In healthy individuals there should be curling downwards.

Question 23

In what case is the Babinski sign not a sign of CS damage?

Answer 23

In children under 1 year old, as the motor system isn’t fully developed. Also after epileptic fits as the motor system is temporarily disturbed.

Question 24

What is spinal shock, and how long does it usually last?

Answer 24

Period of around 2-6 weeks following spinal transection in which no reflexes can be evoked.

Question 25

What can sometimes be noticed a while after the spinal shock?

Answer 25

Reflexes can become very exaggerated, so that a light touch can evoke a whole limb contraction.

Question 26

What is a possible theory for the hypersensitivity of reflexes following spinal shock?

Answer 26

Collateral sprouting - when outgrowths appear on existing axons, increasing sensitivity to excitatory neurotransmitters

Question 27

Explain the process of collateral sprouting

Answer 27

Spindle and CNS inputs usually cover the post synaptic membrane. The CNS ones die leaving a lot of space on the alpha neurone. The spindles and remaining inputs (all segmental) send collaterals to fill the remaining space. This leads to increased efficacy of the segmental resposnses.

Question 28

What is the main motor area in the cerebral cortex?

Answer 28

precentral gyrus (broadmans area 4)

Question 29

What cells give rise to the Corticospinal projections?

Answer 29

Cortical cells

Question 30

What makes up most of the human cerebral cortex?

Answer 30

Association cortex, involved in complex processing

Question 31

What area does the precentral gyrus have close connections to?

Answer 31

S1, the primary somatosensory cortex.

Question 32

How many Corticospinal tract neurones make direct contact?

Answer 32

10%, the rest end on interneurones.

Question 33

What percentage of CS tract axons are myelinated?

Answer 33

50%

Question 34

Does the CS cross over in the brainstem?

Answer 34

yes, left controls right and v.v.

Question 35

What is the motor homunculus?

Answer 35

Essentially a map of the areas of the brain and their corresponding areas of motor control.

Question 36

At what point do 80% of CS tract fibres cross over?

Answer 36

The pyramids in the medulla oblongata

Question 37

What is the difference between the lateral and the anterior CS tract?

Answer 37

Lateral contains the fibres that have crossed over (80%), the anterior contains fibres on the side that they started.

Question 38

What type of body region had the biggest representation on the motor homunculus?

Answer 38

Hands and face, due to the amount of precision required to operate them effectively. the trunk moves a lot less dextrously.

Question 39

What would be noticed if the motor cortex or CS tract was damaged?

Answer 39

Clumsiness and general lack of dexterity, primarily distally.

Question 40

What starts the first electrical activity before any movement?

Answer 40

The process of considering an action evokes electrical activity in all parts of the cortex, and some sub cortical ones, this is called the READINESS POTENTIAL and reduces the amount of time taken to perform an action

Question 41

What are the two main subdivisions of the Association cortex?

Answer 41

Premotor cortex | Supplementary motor area

Question 42

What is the function of the Premotor cortex?

Answer 42

Identifying goals and choosing a course of action

Question 43

What is the function of the Supplementary motor area?

Answer 43

Programming voluntary movements (muscle memory)

Question 44

What area of the brain deals with processing information for attention

Answer 44

Parietal cortex, particularly the posterior parietal cortex.

Question 45

What conditions could arise due to a lesion in the posterior parietal cortex?

Answer 45

Neglect syndrome, inability to respond to stimuli on the contralateral side of the body.