Motor Systems L4 Flashcards
What are the basal ganglia?
5 Gray matter nuclei which help to control and coordinate movement
What is the motor pathway taken to control movement?
Called the corticospinal tract (pyramidal tract)
UMNs start out in the primary motor cortex.
Run down the internal capsule, down through the pyramidal tract in the pons and down to the medulla
85% decussate here, and from both sides this looks like a pyramid hatching shape
Run down the lateral corticospinal tract
end in the lateral white matter, synapse with a LMN
LMN exits the spinal cord via anterior root
15 % do not decussate in the medulla
Run down the ventral corticospinal tract
Decussate at the individual spinal level
Synapses with (interneuron) LMN
LMN exits the spinal cord via the anterior root
What are the 5 basal ganglia and their relative positions?
Caudate Nucleius: Most superior and anterior
Putamen: Most lateral and inferior to caudate nucleius
Globus Pallidus: medial to the putamen. External is lateral to internal segment
Sub- thalamic nucleus: Inferior to thalamus. Medial
Sibstantia Nigra: Pars compacta and reticulata. Inferior to sub thalamic nucleus.
What is the connective pathway between the cerebral cortex and the striatum? (Inc. neurotransmitters involved)
Neuron from cerebral cortex planning area talks to the striatum to clarify what movements are needed. Uses GLUT
Neurons between striatum to GP ex and GP int.
Neuron from GP int. to VA-VL area of thalamus. Uses GABA. This is inhibitory and suppresses successive nerves from firing. If suppressed, it allows nerves to fire uninhibited- a balance is required.
Neuron from VA-VL to cerebral cortex, where is uses GLUT to activate an UMN
What are the functions of the basal ganglia?
- Mood expression through movement- ability to display our mood
- Initiation of movement
- Fine motor control
What is the pathway between the cerebellum and the UMNs?
Neuron from Cerebellum to VA-VL using glutamate to stimulate the following neuron
Neuron from VA-VL to the UMN of the cerebral cortex
What are the functions of the cerebellum?
- Coordination of movement
- Unconscious movements
Balance - Ballistic movement
- Termination of movement
What are the functions of basal ganglia?
initiation of movement
no direct output/input to the spinal cord
conveying mood through movement
modifies movement after practice to be smoother, more precise
Lesion in the left side of the cerebellum would affect what type of movements on what part of the body?
- Movements would be uncoordinated on the left side of the body
Same side as the damage
Lesion/damage in the left side of basal ganglia would result in what type of movement on what side of the body?
-Unrefined movement on the right side of the body( the opposite side to the lesion)
Damage to the lower motor neuron on the right side results in flaccid paralysis on which side of the body?
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)
Damage to the arm area on the right side of the motor cortex results in:
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
Characteristic motor symptoms of Parkinson’s disease
- bradykinesia/ hypokinesia
- rigidity
- tremor at rest
Basal ganglia circuit
- 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.
What are the 3 locations where the main striatal nerve projects to?
- Globus Pallidus external and internal segments
- Substantia nigra
What is the function of Substantia nigra in the basal ganglia circuit?
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
What is striatum?
Putamen+ caudate nucleus
What are the 5 nuclei in the basal ganglia?
The caudate nucleus,
putamen
globus pallidus ( external & internal segment)
Subthalamic nucleus
Substantia nigra
What portion of dopamine is produced in substantia nigra?
85-90%
What allows the 1st order neurons in the discriminative sensation pathway to decussate ?
Internal arcuate fibres
Where does the primary neuron in the spinothalamic pathway terminates?
Area 1+2
Where does the 1st order neuron in the dorsal column medial lemniscal pathway terminate?
Gracile( lower body) and cuneate( upper body) nuclei
What part of the spinal cord does the 2nd order neuron go through in the pain/temp pathway?
Ventral Funiculus
Pallidotomy
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
Thalamotomy
Lesion done surgically to the thalamus to remove inhibitory cells to treat Parkinson’s
What is the effect of a lesion in the basal ganglia?
Difficulty initiating movement- brady/hypokinesia.
Impairment of fine motor movements, inability to display mood through movement all on the opposite side of the body as the lesion. Poor mood, catatonic or psychotic state.
What is the effect of a lesion in the cerebellum?
Overshooting of movement, loss of balance and coordination, poor ballistic and unconscious movement on the same side of the body as the lesion
What is the effect of a lesion in a LMN?
Inability to move the body’s innervated part on the same side as the lesion (flaccid paralysis)
What is the effect of a lesion in an UMN?
Spastic paralysis - increase in corresponding muscles’ tone and tension as control over LMNs is lost and they are not prevented from firing. Depending on where the lesion and the decussation for a UMN is, it may be the same or opposite side of the body
What is the effect of a lesion in the spinal cord?
Dissociative sensory loss: discriminatory sensation lost on the same side of the corresponding body part as the lesion, while non-discriminatory sensation is lost on the opposite side to the lesion in the corresponding body part
What is the effect of a lesion in the brainstem?
Associative sensory loss: discriminatory and non-discriminatory sensation both lost on the corresponding part of the body on the opposite side to the lesion
What is the effect of a lesion in the arcuate fasciculus?
Understand language (eg. can read), but cannot say what they mean, even though they can physically make sounds
What is the effect of a lesion in AGLA?
Issues writing
What is the effect of a lesion in SMAGLA?
Issues reading
What is the effect of a lesion in the primary auditory cortex?
Loss of ability to hear in opposite ear
What is the effect of a lesion in the postcentral gyrus?
Loss of sensation on the corresponding body part on the opposite side
What is the effect of a lesion in the precentral gyrus?
Loss of ability to move the corresponding body part on the opposite side
What is DBS?
Deep brain stimulation involves connecting electrodes to the GPi or sub-thalamic nucleii in order to turn the inhibitory neurons on or off as needed. It is preferable to the other surgeries as it is reversible, and can be adjusted to different degrees.
However, it is expensive and has the most benefits for the most serious patients, so less serious cases may not benefit so much.
What is the function of substansia nigra?
Make and send dopamine to the forebrain
What does dopamine do in the forebrain?
Smoothes movement and controls mindstate
How does dopamine reach the striatum?
It is released as a neurotransmitter from a lightly myelinated neuron
What is the pathway between the Substansia nigra and the striatum?
A neuron runs between the pars compacta and the striatum, using dopamine as a neurotransmitter
This pathway innervates the cells in the putamen which stretch to the GP. It holds them in a ready to fire position.
What about the striatum means that it is very sensitive to GLUT?
It is tonically active- the presence of dopamine ensures that it is always on the brink of releasing an AP, so can be easily tipped over the edge by GLUT.
What is the underlying cause of parkinson’s disease?
The SN pars compacta stops producing dopamine. This may be due to O2 depletion as this area is very sensitive to the concentration of oxygen
What does the inability of the SN PC to produce dopamine mean for the rest of the pathway?
The striatum is not held at an almost-firing position by the dopamine, so when GLUT arrives no AP is generated
As a result, there is no conduction from Putamen to GPe and none from GPe to GPi. Consequently, the inhibitory pathway from GPi to the thalamus is allowed to fire unchecked, and inhibits movement as the UMN is no longer able to be activated.
Hypokinesia (reduction in cortical excitation) results.
What do the two halves of the putamen do?
Upper: Movement
Lower: connected to the frontal lobe and limbic system. (mood)
What does low/high dopamine mean psychologically?
Low: Poor movement, catatonia
High: Wild movements and in extreme cases, psychosis
What are the current treatments for parkinsons disease?
Dopamine replacement drugs (L-Dopa)
Pallidotomy of GPi
Thalamotomy of VA-VL
Deep brain stimulation
Why and how does L-Dopa work?
It replaces the dopamine the SN is no longer producing. Simple dopamine was used originally, but could not be digested or cross the blood/brain barrier.
However, it causes extreme swings- in mood as well as movement ability. Also, it only works for 8 years after the commencement of treatment
Discriminative Touch and Pressure Pathway:
This pathway, also known as the dorsal column-medial lemniscus pathway, carries sensations of fine touch, pressure, vibration, and proprioception.
It involves neurons that ascend ipsilaterally (on the same side) through the spinal cord to the medulla, where they cross to the opposite side of the brain.
Lesion on the Right Side of the Spinal Cord:
Touch and Pressure: Because the fibers for discriminative touch and pressure ascend ipsilaterally until they reach the brainstem, a lesion on the right side of the spinal cord will affect these sensations on the right side of the body.
Lesion on the Right Side of the Brainstem:
Touch and Pressure: Since the fibers have already crossed over, a lesion on the right side of the brainstem will affect these sensations on the left side of the body.
Pain and Temperature Pathway:
This pathway, known as the spinothalamic tract, carries sensations of pain and temperature.
The neurons in this pathway cross to the opposite side of the spinal cord soon after entering it and then ascend contralaterally (on the opposite side) to the brain.
Pain and Temperature: Since the fibers for pain and temperature cross over to the opposite side of the spinal cord shortly after entering, a lesion on the right side will affect these sensations on the left side of the body.
Pain and Temperature: Similarly, since these fibers also crossed over, a lesion on the right side of the brainstem will affect these sensations on the left side of the body.
