Medsci L4: The motor systems of the brain

Question 1

what is the function of pyramidal tract?

Answer 1

initiating, controlling and stopping voluntary movement

Question 2

Corticospinal tract( pyramidal tract)

Answer 2

Arm fibre(from homuncular region)->internal capsule-> through midbrain & pons down into medulla( motor fibres are in the front of the brain stem)-> 85% of neurons cross over at Pyramidal decussation & go into the lateral Corticospinal tract, 10-30% of neurons remain on the same side as they arose in the brain, go in the anterior corticospinal tract and cross over down at the spinal segmental lvl.-> the 85% crossed over fibres enter the area of the motor columns in the lateral funiculus-> go to lower motor neuron pool(area 8 &9) Where the motor neurons terminate-> another neuron(lower motor neuron) goes out the ventral root & innervates muscle.

Question 3

What paralysis does damage to the lower motor neuron result in?

Answer 3

Flaccid paralysis

Question 4

What type of paralysis does damage to the upper motor neuron result in?

Answer 4

Spastic paralysis

Question 5

Symptoms of flaccid paralysis

Answer 5

no nervous control of the limb

decreased muscle activation-> decreased muscle tone

Question 6

Symptoms of spastic paralysis

Answer 6

increased muscle activation-> more tone

jerky movements

Question 7

What is the function of cerebellum?

Answer 7

• direct output to the spinal cord
• adjusts movement to account for the discrepancy between planned and actual movements
• coordinates, maps, terminates movement, and works with unconscious movement( e.g swinging arms while walking)

Question 8

What are the functions of basal ganglia?

Answer 8

• initiation of movement
• no direct output/input to the spinal cord
• conveying mood through movement
• modifies movement after practice to be smoother, more precise

Question 9

Lesion in the left side of the cerebellum would affect what type of movements on what part of the body?

Answer 9

-Movements would be uncoordinated on the left side of the body
Same side as the damage

Question 10

Lesion/damage in the left side of basal ganglia would result in what type of movement on what side of the body?

Answer 10

-Unrefined movement on the right side of the body( the opposite side to the lesion)

Question 11

Damage to the lower motor neuron on the right side results in flaccid paralysis on which side of the body?

Answer 11

Right (the same side as the damage and the neurons at this point have already decussated and are now operating on one side of the body)

Question 12

Damage to the arm area on the right side of the motor cortex results in:

Answer 12

The left side of the body is affected( the opposite side as upper motor neurons decussate into the opposite side of the body)
the left arm will exhibit spastic paralysis, loss of voluntary control of the limb

Question 13

Characteristic motor symptoms of Parkinson’s disease

Answer 13

• bradykinesia/ hypokinesia
• rigidity
• tremor at rest

Question 14

Basal ganglia circuit

Answer 14

• A neuron fiber housed in the planning part( premotor cortex) is sent down to the striatum. It uses glutamate(excitatory neurotransmitter). Activates the basal ganglia circuit.
• In the striatum : 3 locations where the main striatal neurons project to Globus Pallidus external segment, Substantia Nigra, Globus pallidus internal segment. All these 3 neurons use GABA( Gamma amino butyric acid) inhibitory. When these 3 neurons fire it dampens down the response in the neurons they are connected to.
• Another set of neurons goes from Globus Pallidus internal segment and goes up to the VA-VL region of the thalamus. This neuron is also inhibitory( uses GABA)
• Neuron within the thalamus goes up to the premotor cortex->motor cortex( uses excitatory neurotransmitter)
• Pyramidal cell is activated-> goes down corticospinal tract-> lower motor neuron in the spinal cord-> muscle is activated.

Question 15

what are the 3 locations where the main striatal nerve projects to?

Answer 15

Globus Pallidus external and internal segments

Substantia nigra

Question 16

What is the function of Substantia nigra in the basal ganglia circuit?

Answer 16

A lot of fibers from Substantia nigra, synapse on the 3 types of neurons in the Striatum. These neurons use dopamine. Dopamine can be inhibitory or excitatory depending on the type of receptor on the receiving cell. These dopamine neurons keep the 3 neurons in the striatum primed & ready to fire. So little glutamate is needed to activate these neurons.

Presensitize the neurons in the basal ganglia

Question 17

What is striatum?

Answer 17

Putamen+ caudate nucleus

Question 18

What are the 5 nuclei in the basal ganglia

Answer 18

the caudate nucleus,
putamen
globus pallidus ( external & internal segment)
Subthalamic nucleus
Substantia nigra

Question 19

What portion of dopamine is produced in substantia nigra?

Answer 19

85-90%

Question 20

what allows the 1st order neurons in the discriminative sensation pathway to decussate ?

Answer 20

Internal arcuate fibres

Question 21

where does the primary neuron in the spinothalamic pathway terminates?

Answer 21

Area 1+2

Question 22

Where does the 1st order neuron in the dorsal column medial lemniscal pathway terminate?

Answer 22

Gracile( lower body) and cuneate( upper body) nuclei

Question 23

What part of the spinal cord does the 2nd order neuron go through in the pain/temp pathway?

Answer 23

Ventral Funiculus

Question 24

What part of the dorsal columns receives discriminatory information from upper and lower body?

Answer 24

upper body- cuneate fasciculus

lower body- gracile fasciculus

Question 25

Pallidotomy

Answer 25

lesion done surgically to the internal segment of the globus pallidus, which wipes out the overactive inhibitory cells going from the internal segment of globus pallidus to the thalamus, allowing the upper glutamate pathway to behave more normally in people with Parkinson’s

Question 26

Thalamotomy

Answer 26

lesion done surgically to the thalamus to remove inhibitory cells to treat Parkinson’s