Principles of Neuroscience Lecture 13 The Upper Motor Neuron Flashcards
Do upper motor neurons directly stimulate muscle?
No, the transmission must go through lower motor neurons first
Define upper motor Neurons
Neurons that convey signals to lower motor neurons about movement
Carry information down to the final common pathway
What is the organisation of lower motor neurons in the spinal cord?
Medial white matter
Lateral white matter
Describe the function of axons in the Lateral White Matter
Innervate distal muscles; fine motor control
Describe the function of axons in the medial white matter
Innervate axial muscle and proximal muscles.
Maintenance of posture
Describe the path of neurons from the cortex to the medial white matter
Cortex to the brain stem via the corticobulbar tract
Through brainstem via one of the three pathways
Corticobulbar fibres leave brain stem at appropriate level to synapse onto Lower Motor Neurons
Lower Motor Neurons travel down Medial White Matter in spinal cord
What are the different pathways descending from the brainstem to the spinal cord?
To which area of the spinal cord to these neurons go?
Corticobulbar: cortex -> brainstem -> spinal cord (medial white matter)
Corticospinal: cortex -> spinal cord (lateral white matter)
What is the role of the vestibular nuclei?
Where are they?
Balance, angular and linear acceleration of the head
What is the function of the reticular formation?
Where is it?
Give two examples of movements that require this area
Pre-emptive postural maintenance, feed forward information
- Pulling on a bar
- Reaching out
What is the function of the colliculospinal tract?
Where is it?
Integration of sensory information from eyes, ears and mechanoreceptors
Describe the bar pulling experiment, outline which areas are important
The reticulospinal tract
How is feed forward information used to maintain posture?
When we are about to perform an action that will shift our centre of gravity, the reticular formation sends information to axial muscles to readjust our posture before we do the movement. This way, we don’t overbalance
What are the direct and indirect pathways from the motor cortex to the lower motor neurons?
Direct: cortex -> spinal cord (lateral white matter and medial white matter)
Indirect: cortex -> brainstem via one of the three tracts
Which are the main areas in the frontal lobe responsible for movement?
Where are these areas located
The primary motor cortex, pre central gyrus
Motor association areas, frontal cortex
What is the term Brodmann used for the Primary motor cortex?
Area 4
Describe the cytoarchitecture of the primary motor cortex
6 layers of neurons
Beta cells in layer 5
What is the name of the upper motor neurons in the 5th layer of the primary motor cortex?
What is the structure of these cells?
What is the function of these cells?
Betz cells
These are extremely thick and long
These are the neurons that directly project down to the brain stem and spinal cord
Describe the topography of the primary motor cortex
Much coarser than the primary somatosensory cortex.
Regions such as: face, upper and lower extremities, trunk
Describe the relationship between neurons and muscle in the primary motor cortex
Simple connections
Describe the relationship between neurons and muscle in the motor association areas
More complicated relationship
What are the pathways from the motor cortex to the brain stem?
Corticobulbar
What does the pyramidal tract refer to?
The corticobulbar and corticospinal tracts
What is the path that the corticospinal tract takes?
What is it made up of?
Motor cortex -> spinal cord (Decussation), lateral and ventral tracts
Made up of axons origination from the motor cortex
Describe the path that the corticobulbar tract takes
Motor cortex -> brainstem -> Decussation
Where does the corticospinal tract originate?
The cerebral cortex
What is the Decussation?
What do the two groups go on to form?
This is when 90% of axons in the corticobulbar tract cross over to the other side of the brain stem and form the lateral corticospinal tract
Describe the experiment wherein monkeys experienced micro stimulation of specific areas of the brain
Micro stimulation of specific brain areas when the arms are in various areas.
The stimulation resulted in the hand being brought to quite specific regions eg. Face, stomach
What does the monkey experiment tell us about motor maps in the brain?
That the motor mapping is of different types of movement that are important to the animal
What sort of movements are the motor association areas responsible for?
Complex movement that requires many muscles.
Eg. Unplugging a cord
Where are mirror motor neurons found?
In the motor association areas
Describe the activity of mirror motor neurons
Explain the main experiment
When a monkeys sees a task being performed, the exact same neuron fires as when the monkey performs the task himself.
What is the test for the Babinski sign?
Scrape along the bottom of the foot.
Normal: no Babinski sign; there is plantar flexion and toes go downwards
Babinski: dorso flexion and toes go upwards
What represents a normal response from the Babinski test?
What is a positive result for the Babinski sign?
Dorso flexion and toes going down
Positive result: Babinski sign : dorso flexion, toes go up
What does a positive Babinski sign mean about the brain and spinal cord?
There is so,e damage to the connection between the brain and the lower motor neurons in the spinal cord
What are the signs and symptoms of upper motor neuronal lesions?
Weakness Increased muscle tone Muscle spasticity Babinski sign Loss of fine movements Clonus Increased reflexes
What are the signs and symptoms of lower motor neuronal lesions?
Weakness and paralysis
Decreased muscle tone, atrophy
Fibrillations
Decreased reflexes
What is the general role of the upper motor neurons in respect to the spinal cord?
Inhibiting the action of the spinal cord
Way are the two tracts that make up the corticospinal tract?
Ventral and lateral
