Motor pathways Flashcards
What is volition?
When motor systems produce movements that are adaptive and accomplish a certain goal
What is proprioception?
Information on the starting point of an action, length of muscles and forces needed
What does functional segregation mean?
Motor system is organised into different areas which control different functions
What does hierarchical organisation mean?
High order areas are involved in complex functions (programme and decide on movement, coordinate muscle activity) and lower order ares carry out simple functions (execution of movement)
What is the motor system hierarchy?
Level 1: Spinal cord (basic- movement)
Level 2: Brainstem- centre of integration of different inputs coming from the vestibular system, the vision system and auditory system
Level 3: Motor cortex- primary motor cortex, premotor cortex and supplementary motor area (movements are coordinated)
Level 4: Association cortex- contains parietal and frontal cortex (involved in planning and execution of movements)
In terms of motor system organisation, what are the two main parts of the pyramidal (descending) system?
Corticobulbar tract and corticospinal tract
What is the corticobulbar tract?
Starts in cortex, then exits and innervates the muscles in the face
What is the corticospinal tract?
Starts in the cortex and innervates the muscles of the arms and legs
Where do the two side loops of the descending pathway go to and what happens at these locations?
Basal ganglia and cerebellum, information gets checked and approved
Which 3 parts of the motor cortex are found in the frontal lobe?
Primary motor cortex (M1)- Broadmann’s area 4
Premotor cortex- Broadmann’s area 6
Supplementary motor area- Broadmann’s area 6
They are anterior to the central sulcus
What does the central sulcus separate?
Frontal and parietal lobes
Which cells are the most important in the primary motor cortex?
Betz cells (pyramidal cells)
Why are Betz cells important?
Corticospinal tracts originate from them
What route does the corticospinal tracts follow?
They start in the primary motor cortex, descend and go through the brainstem all the way down. They cross over to the other side at the medulla oblongata at the pyramidal decussation. They then continue all the way down the spinal cord and synapse with a lower motor neurone and exit into a peripheral nerve to reach the skeletal muscle.
What route does the corticolbulbar tracts follow?
They start in the primary motor cortex, descend and go down into the brainstem and they synapse with a second motor neurone and send innervation to muscles of the face
What two groups are the descending pathways split into based on function?
Lateral and medial pathways
Which pathways are in the lateral group and what is their function?
Lateral corticospinal and rubrospinal
They control proximal and distal muscles
They’re involved in voluntary movements of arms and legs
Which pathways are in the medial group and what is their function?
Vestibulospinal, reticulospinal, tectospinal and anterior corticospinal tract
They control axial muscles
They’re involved in balance and posture
What percentage of corticospinal tract axons cross over at the pyramidal decussation and what do they form?
90% and they form the lateral corticospinal tract, the others are in the anterior corticospinal tract
Where does the rubrospinal tract originate?
In the red nucleus of the midbrain
Why is the rubrospinal tract important?
It is an alternative by which voluntary motor commands can be sent to the spinal cord. So if there is a lesion to the primary motor cortex, the body can still compensate and other descending tracts get activated.
It has a role in movement velocity
What would a lesion in the rubrospinal tract cause?
Movements to be much slower as it has a role in movement velocity
Where do the lateral and medial vestibulospinal tracts originate?
Lateral originate in the lateral vestibular nucleus (brainstem) and medial originate in the medial vestibular nucleus
What do lateral and medial vestibulospinal tracts mediate?
Postural adjustments and head and eye movements
What are tracts names based on?
Where they originate and where they travel- e.g. corticospinal - originate in the cortex and travel through the spinal cord
Where do the pontine and medullary reticulospinal tracts originate?
Brainstem’s reticular formation
What are the pontine and medullary reticulospinal tracts involved in?
Orienting, stretching and maintaining a complex posture
Where does the tectospinal tract originate?
Superior colliculus
What is the tectospinal tract involved in?
Unknown but most likely involved in reflexive turning of head to orient to visual stimuli
Where does the anterior corticospinal tract originate?
Motor cortex
What does the anterior corticospinal tract control?
Proximal musculature
Where is the premotor cortex in relation to the primary motor cortex?
It is anterior to the primary motor cortex in the frontal lobe
What does the premotor cortex do?
It plans movement and is involved in assembling movements into coordinated actions
What is the function of the supplementary motor area?
Planning complex internally driven movements e.g. speech
Also when thinking about movement before movement
What is association cortex?
Brain areas that aren’t really motor areas because their activity doesn’t correlate with motor output- they don’t have any upper motor neurones
What are the two main components of association cortex?
Posterior parietal cortex and prefrontal cortex
What does posterior parietal cortex do?
Ensures movements are targeted accurately to objects in external space
What does the prefrontal cortex do?
It is involved in the selection of appropriate movements for a particular course of action
What is the first effect of an upper motor neurone lesion?
Loss of function which leads to paresis and paralysis
What is paresis?
Graded weakness of movement
What happens in an upper motor neurone lesion after a few weeks?
Increased abnormal motor function- loss of inhibitory descending inputs. This results in spasticity, hyperreflexia and clonus
What is clonus?
Abnormal oscillatory muscle contraction
What is Babinski’s sign?
Very important sign of an upper motor lesion. If you stroke the plantar side of the foot, the toes will flex down including the big toe but after upper motor neurone lesion, toes will fan and big toe will go up
What is apraxia?
A disorder in skilled movement not caused by weakness, abnormal tone or posture or movement disorders. They have lost information about how to perform skilled movements
When does apraxia occur?
Lesions of the inferior parietal lobe and frontal lobe- stroke and dementia are most common causes
What does a lower motor neurone lesion affect?
The second motor neurone (starts in the grey matter of spinal cord and exits to form peripheral nerve)
What are the signs of a lower motor neurone lesion?
Weakness, hyporeflexia, hypotonia, muscle atrophy, fasciculations and fibrillations
What are fasciculations?
When damaged motor units produce spontaneous action potentials, resulting in a visible twitch
What are fibrillations?
Twitches of individual muscle fibres- aren’t visible to the naked eye but can be recorded if the patients have needle electromyography
What is amyotrophic lateral sclerosis (ALS)?
Motor neurone disease that affects both upper and lower motor neurones
Why is ALS difficult to diagnose?
Because it is a combination of upper and lower motor lesions which have opposite signs
