Motor control and movement disorders Flashcards
Acetylcholine
Contraction of skeletal muscles results from the release of the this neurotransmitter from the terminals of motor neurons.
Where can we find cell bodies of motor neurons?
Spinal cord, which are controlled by a variety of descending neurons from the brain and some ascending neurons in the cord itself.
Brain-spinal cord pathways
Neurons in cortex do not make direct contact with muscles, but Fritsch and Hitzig found that electrical stimulation of the brain can rapidly induce movement.
There are 4 major tracts from the brain:
- the corticospinal tract
- the corticobulbar pathway
- The ventromedial pathway
- The rubrospinal pathway
The corticospinal tract
Consist of neurons whose cell bodies are found in the cortex (primary motors trip, M1), which is the most posterior gyrus of the frontal lobes and immediately forward of the primary somatosensory cortex.
M1 is highly topographically organized.
The axons descend within the brain to the MEDULLA, where they cross to the opposite side before continuing into the spinal cord to synapse with motor neurons.
The pathway consist of two tracts:
- The lateral tract: control distal muscles contralaterally.
- The ventral tract: controls medial muscles on both sides.
The corticobulbar pathway
Origin in primary motor strip, but the axons only descend to the pons where they innervate some of the cranial nerves to control facial, mouth, and tongue muscles.
The ventromedial pathway
Origins in the brainstem or midbrain rather than cortex and projections terminate in proximal muscles in the trunk, shoulders and neck.
The rubrospinal pathway
Origins in the red nucleus of the midbrain, which receives inputs from both the motor cortex and the cerebellum.
It projects mainly to distal limb parts and the primary function is thought to be the movement of limbs independent of movements of trunk.
ipsilateral
to the same side of the body; opposite of contralateral.
Cerebellum
fundamentally involved in the modulation of motor coordination and the acquisition of motor skills, because of its reciprocal connections between the cortex and parts of the cerebellum.
The cerebellum influence motor control on the IPSILATERAL side of the body, so right side damage affects movement on the right side of the body.
Cerebellar structure
size of two walnuts, the structure is bilateral symmetrical.
The cerebellum contains four different types of neurons:
- innermost: vermis (receives somatosensory and kinesthetic information from the spinal cord) affect balance.
- the next: reciprocal information from the red nucleus. intentional tremor.
- The lateral zones (left and right outer sections): receives information from motor and association cortex. affect movement of limbs.
Bilateral
affecting both sides
Three anatomically separate regions of cerebellum
Can be distinguished in terms of inputs and outputs as well.
- Medial region: modulate and smooth out movement
- Lateral regions: coordinate skill movement enacted “in time”.
Damage to the cerebellum does not eliminate movement per se, rather it seems that tasks that were once effortless become a struggle after cerebellar damage.
The basal ganglia
A group of subcritical structure that connect with each other and the cortex in a series of five parallel “closed loops”. Each of the loops originates from, and returns output to, a particular region of cortex.
- Motor loop
- Oculomotor loop
- Dorsolateral prefrontal loop
- Orbitolateral loop
- Limbic loop
Motor loop
Mainfunction: the initiation, maintenance and switching of actions
Oculomotor loop
Main function: the direction of voluntary eye movements
Dorsolateral prefrontal loop
Main function: maintenance of spatiale working memory and other executive functions, shifting sets.
Orbitolateral loop
Main function: switching/inhibiting behaviors, perhaps including the inhibition of inappropriate behaviors in relation to social settings. Possibly also empathy and imitation.
Limbic loop
Main function: remain vague but likely to involve selection of emotional expression or tone, and motivated behavior.
Components of basal ganglia
Caudate, putamen and ventral striatum, the internal and external segments of the globus pallid us, the subthalamic nucleus, and the substantial nigra.
D1 receptors
a class of dopamine receptor found particularly in the frontal lobes and striatum
D2 receptors
Another class of dopamine receptor found particularly in the striatum and pituitary.
Direct and indirect routes
For each oft he major parallel loops, two competing paths through the basal ganglia.
Direct route: path from the striatum > internal regions of the globus pallid us > thalamus > back to cortex.
Basal ganglia functions
Damage to basal ganglia sometimes have writhing-like movements or other postural disturbances, they also sometimes have difficulties in starting movements but are OK once they start.
The motor strip
Predominantly contralateral control.
in cases where the entire left or right primary motor cortex is damages = contralateral hemiplegia.
Hemiplegia
paralysis of one side of the body.
When the entire left or right primary motor cortex is damaged.
what control the activity of pyramidal cells?
Supplementary motor area and premotor cortex. its hierarchical.
Damage to this area: have fine motor control fingers but are impaired on tasks that require the coordination of two hands.
