Motor Pathways

Question 1

What are the broad principles of motor control?

Answer 1

Functional segregation - Motor system organised in a number of different areas that control different aspects of movement
Hierarchical - high order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity)
Lower level areas of hierarchy perform lower level tasks (execution of movement) See slides

Question 2

Where and what is the primary motor cortex?

Answer 2

M1 is located in the precentral gyrus. Its function is control of fine, discrete, precise voluntary movement. And it provides descending signals to execute movement. See slide on the somatotopic organisation

Note: anteriolaterally is supplementary motor cortex and inferiolaterally premotor cortex. See diagram

Question 3

Where is the primary sensory cortex located?

Answer 3

Somatosensory - located in the postcentral gyrus

Question 4

Describe the two descending motor pathways

Answer 4

See diagram, slides and kenhub

Question 5

What are the symptoms of upper motor neurone lesion?

Answer 5

Loss of function:
Muscle weakness - Paresis
Paralysis (plegia) - complete loss of muscle activty
No fasiculations

Decreased motor control: increased abnormal motor function due to loss of inhibitory descending inputs
Increased tone - Spasticity
Exaggerated and sometimes repeating deep tendon reflexes = hyperreflexia = clonus
Babinski sign - normal condition when you rub a sharp object on the base of the foot the toes flex and point downwards. However you get extension of the toes in UMN syndrome = +ve babinski reflex

Question 6

What are the symptoms of lower motor neurone syndrome?

Answer 6

Muscle weakness
Decreased tone - hypotonia
Muscle atrophy (wasting)
Fasiculations - damage motor units produce spontaneous action potentials, resulting in a visible twitch
Reduced deep tendon reflexes = hyporeflexia
Fibrillations - spontaneous twitching of individual muscle fibres; recorded during needle electromyography

Question 7

Describe the corticobulbar pathway

Answer 7

See notes

Question 8

What is the premotor cortex?

Answer 8

It is the frontal lobe anterior to M1

Involved in planning of movements and regulates externally cued movements. See slides

Question 9

What is the supplementary motor cortex?

Answer 9

It is the frontal lobe anterior to M1, medially
Planing complex movements; programming sequencing of movements (one movement after the other to pick up an apple)
Regulates internally driven movements (e.g speech)
SMC becomes active when thinking about movement before executing movement.

Question 10

What is the association cortex?

Answer 10

These are brain areas are not strictly motor areas as their activity does not correlate with motor output however they do affect movement.

Posterior parietal cortex - ensures movements are targeted accurately to objects in external space

Prefrontal cortex - involved in selection of appropriate movements for a particular course of action

Question 11

Define lower motor neurone

Answer 11

Spinal cord, brainstem. (a-motor neurones)

Question 12

Define upper motor neurone

Answer 12

Corticospinal, corticobulbar

Question 13

What is apraxia?

Answer 13

A disorder of skilled movement. Not paretic but have lost information about how to perform skilled movements

Question 14

What can cause apraxia?

Answer 14

Lesion of the premotor cortex and/or supplementary motor cortex. Lesion of the inferior parietal lobe and/or the frontal lobe.
Stroke and dementia

Question 15

What is motor neurone disease?

Answer 15

Progressive neurodegenerative disorder or the motor system
Spectrum of disorders
Amyotrophic Lateral Sclerosis (ALS)
Usually progresses in a caudal rostral way. People lose control of their respiratory muscles then die.

Question 16

What are the signs of MND?

Answer 16

Affects both the upper and lower motor neurones

Upper motor neurone signs:

1) Increased muscle tone (spasticity of limbs and tongue)
2) Brisk limbs and jaw
3) Babinski’s sgn
4) Loss of dexterity
5) Dysarthria (problems with speaking)
6) Dysphagia (problems with swallowing)

Lower motor neurone signs:

1) Weakness
2) Muscle wasting
3) Tongue fasciculations and wasting
4) Nasal speech
5) Dysphagia

Question 17

Describe the basal ganglia

Answer 17

It is extrapyramidal - meaning its not part of the descending tract
It includes:
Caudate nucleus
Lentiform nucleus (putamen + globus pallidus)
Subthalamic nucleus
Substantia nigra
Amygdala

Ventral pallidum, claustrum, nucleus accumbens, nucleus basalis of Meynert

Striatum = lentiform nucleus + caudate

See the cross sections on the brain on the slides

Question 18

What lies between the two lateral ventricles?

Answer 18

Septum pellucidum.

Note the lateral wall of the lateral ventricle is made up by the caudate nucleus

Question 19

What are the functions of the basal ganglia?

Answer 19

Elaborating associated movements (e.g swinging arms when walking or changing facial expression to match emotion)
Moderating and coordinating movement (suppressing unwanted movements)
Performing movements in order

Question 20

Draw the basal ganglia circuitry

Answer 20

See lecture

Question 21

Describe parkinsons disease?

Answer 21

See lecture slides.
Loss of dopamingeric neurones going to the striatum in the substantia nigra (nigro-striatal projections). This is the classical primary pathology. The black colour of the substantia nigra is caused by neuromelanin

Question 22

What are the main motor signs of Parkinson’s disease?

Answer 22

Bradykinesia
Hypomimic face - expressionless ace
Akinesia - difficulty in the initiation of movements because cannot initiate movements internally
Rigidity - muscle tone increase, causing resistance to externally imposed joint movements (e.g doctor moving the joints)
Tremor at rest (pill-rolling tremor) - 4-7Hz starts at one hand spreads to other parts of the body

Parkinsons symptoms are almost always unilateral to begin with.

Question 23

Describe huntingtons disease?

Answer 23

Genetic neurogenerative disorders.
Chromosome 4 autosomal dominant
CAG repeats

Results in degeneration of GABAergic neurones (generally inhibitor neurones - think about the effect of loss of inhibition) in the striatum, caudate and then putamen.

Question 24

Motor signs of huntingtons disease?

Answer 24

Choreic movements (chorea) - rapid jerky involuntary movements of the body; hands and face affected first; then legs and the rest of the body
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages, cognitive decline and dementia

Question 25

Describe the structure of the cerebellum

Answer 25

3 layers of grey matter:
Molecular layer - few neurones mainly cell processes
Piriform layer - purkinje cell layer: main processing cell
Granular layer - small neurones, closely pact

The inferior olivary nucleus projects to the purkinje cells by the climbing fibres. They synapse on the dendritic trees of the purkinje cells.

All other input to granule cells via mossy fibres and then onwards via parallel fibres

All output comes from Purkinje cells via deep nuclei
See notes/slides

This is the modulation of fine movement and motor learning of the output of the primary motor system.

Question 26

What are the divisions of the cerebellum?

Answer 26

Vestibulocerebellum - regulation of gait, posture and equilibrium. Coordination of head movements with eye movements - linked to superior collicolus.
Spinocerebellum - Coordination of speech. Adjustment of muscle tone. Coordination of limb movements.
Cerebrocerebellum - coordination of skilled movements. Cognitive function, attention, processing of language. Emotional control

The cerebellum is connected to the medulla and spinal cord the inferior cerebellar peduncle.

Question 27

Describe the symptoms associated with the damage of all the divisions of the cerebellum?

Answer 27

Vestibulocerebellar Syndrome
Damage (tumor) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)

Spinocerebellar syndrome
Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)

Cerebrocerebellar or Lateral Cerebellar Syndrome
Damage affects mainly arms/skilled coordinated movements (tremor) and speech

Question 28

What are the main signs of cerebellar dysfunctions apparent only upon movement?

Answer 28

Ataxia - General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Dysmetria - Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor - Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dysdiadochokinesia - Inability to perform rapidly alternating movements, (rapidly pronating and supinating hands and forearms)
Scanning speech - Staccato, due to impaired coordination of speech muscles