40 - Initiation of Movement

Question 1

Rough cortical map of motor control, from medial to lateral

Answer 1

Leg, hand, digits, neck, face, tongue

Question 2

Effect of stimulating premotor areas with an electrode

Answer 2

Requires more current to elicit a response than motor cortex, but results in more complex movements, EG multi-joint, bilateral.

Question 3

Artery supplying motor cortex representing lower limbs

Answer 3

Anterior cerebral artery

Question 4

Broad functional difference between motor and motor association cortices

Answer 4

Motor cortex involved in simple movements.
Motor association cortex (aka premotor), with the motor cortex is involved in more complex movements, EG compiling several movements temporally and carrying them out.

By itself, the motor association cortex is involved in mental rehearsal of complex movement

Question 5

Parts of the cortex around the central sulcus

Answer 5

Anterior to central sulcus is motor cortex.

Posterior to central sulcus is somatosensory cortex

Question 6

What is now thought to be mapped on the motor cortex?

Answer 6

A single patch of cortex being activated (in a monkey) by an electrode brings hand to the face, no matter where the hand was previously.
Might be that a particular part of the motor cortex maps to the endpoint of a movement, EG hand touching face.

Question 7

Two very broad movement endpoints mapped on the motor cortex, w/r/t the hands

Answer 7

Bring to mouth (eat) or chest (to observe)

Question 8

Role of upper motor neurons in grip strength

Answer 8

Particular upper motor neurons involved in producing a precision grip.
Different upper motor neurons involved in power grip.

Question 9

Mirror motor neurons

Answer 9

Visually-guided motor neurons.
Same neuron activated in performing a task as in observing the same task.

Neurons respond to performing movement without seeing it, showing that it doesn’t need visual input.

Perhaps involved in learning.

Question 10

Inputs to premotor cortex

Answer 10

Inputs from sensory cortices.

Inputs from preforntal cortex (concepts of value, planning, purpose of movement).

Question 11

Visual cortex inputs into premotor cortex.

Answer 11

Dorsal and ventral streams map quite well onto different parts of premotor cortex.

Dorsal (‘where’) stream controls reaching (EG forearm reaching)

Ventral (‘what’) controls grasping with the hand.

Question 12

Functions of basal ganglia 
1
2
3
4

Answer 12

1) Allow the selection of complex patterns of voluntary movements
2) Evaluating the success of actions in achieving the goals
of those actions
3) Initiating movements
4) Also involved in modulating how entire cortex works. Not just movement.

Question 13

Layout of basal ganglia

Answer 13

Five nuclei

Caudate around lateral ventricles
Putamen 
Globus pallidus
Subthalamic nucleus
Substantia nigra

Question 14

Name for Parkinsonian gait

Answer 14

Hypokinesia

Question 15

Huntington’s gait

Answer 15

Chorea
Wobbles from side to side.
Arms don’t swing, often held outwards to balance
Irregular stride (sudden impositions on movement, unplanned movements inserted into gait)

Question 16

Broad role of indirect pathway

Answer 16

Inhibit movements that aren’t wanted, that might be similar to those that are desired.

Question 17

Broad role of direct pathway

Answer 17

Select movements that are desired

Question 18

Functions of the cerebellum
1
2
3
4
5

Answer 18

1) Coordinating the timing and sequence
of muscle actions and movements
2) The maintenance of muscle tone
3) Motor learning
4) Planning sequences of muscle
activation for complex movements
5) Similar to basal ganglia, but maybe operates on a shorter timescale.

Question 19

Cerebellar gross anatomy

Answer 19

Gross structure: tightly folded, three main divisions (lobes), the cerebellar
peduncles that attach the cerebellum to the brainstem are fibres connection
with medulla, pons and midbrain

Question 20

Histological anatomy of cerebellum

Answer 20

Histology: cortex, sub-cortical white matter, sub-cortical grey matter (the
deep nuclei), massively iterated canonical neural circuit

Question 21

Basic functional layout of cerebellum

Answer 21

Functional organisation: approximately medial to lateral (some fragmented somatotopy)

Question 22

Effect of cerebellar defect

Answer 22

Deficits: The inability to appropriately integrate / coordinate movement is called ataxia.
Effects of a unilateral lesion are generally ipsilateral

Question 23

Anterior lobe syndrome of cerebellum
1
2
3
4

Answer 23

Affects lower limbs more

1) Ataxic gait (“drunken sailor”)
2) Loss of inter-limb coordination (slide heel down opposite shin)
3) With chronic ethanol toxicity, anterior Purkinje cells are preferentially lost.
4) Progression posteriorly involves upper limbs and facial muscle dys-coordination
(ataxic speech).

Question 24

Posterior lobe syndrome of cerebellum
1
2
3

Answer 24

More effects upper limbs

1) Dysmetria (overshoot in precision reach)
2) Dysdiadochokinesia (inability to rapidly alternate movements)
3) Speech abnormality (loss of natural rhythm, slurring across syllables, over compensation by explosive speech)

Question 25

Flocconodular syndrome

Answer 25

Affects trunk

Truncal Ataxia (difficulty walking, even standing or sitting in severe cases)

Question 26

What do lateral parts of cerebellum control?

Answer 26

Contralateral motor cortex.

Motor cortex also crosses over, so cerebellar defects tend to affect ipsilateral parts of body