Exam 3: MOTOR CONTROL Flashcards
What regions of the CNS are important for voluntary control of movement?
The corticospinal tract and others motor tracts, are responsible for taking motor plans from the cerebral cortex and sending them to the spinal cord or brainstem, after which a motor command can be sent to muscle—voluntary motor movement
What are the pathways for voluntary movement?
The general descending motor pathway from the cerebral cortex to the spinal cord (or brainstem) is:
Upper motor neurons from the cerebral cortex carry motor system outputs to the lower motor neurons in the spinal cord and brainstem. These lower motor neurons then project to muscles in the periphery
1. primary motor cortex to spinal cord to muscle
What occurs when those regions responsible for movement are damaged?
- Damage to the motor pathways has different effects based on where the damage occurred and how extensive the damage was
- Because the lower motor neurons have local circuits (reflexes), it is possible with upper motor neuron damage to still have reflexive movement
- Damage to the upper motor neurons would prevent non-reflexive muscle activation whereas damage to the lower motor neuron could result in complete paralysis because there would be no way to generate movement, reflexive or voluntary
primary motor cortex (pathway)
- Where are the neurons in the first part of this pathway located? Primarily in the primary motor cortex. This region is located within the precentral gyrus in the frontal lobe
- The primary motor cortex contains betz cells, which are large diameter neurons, and normal non-Betz pyramidal neuron
- These neurons form the upper motor neurons and project down to the lower motor neurons to control movement
- Recording from primary motor cortex neurons demonstrates that groups of neurons fire based on movement type and not necessarily muscle
- Additionally, recording from the primary motor cortex of a monkey brain while the monkey moves a joystick in a specific direction demonstrates the movement specific firing of neurons within the primary motor cortex
basal ganglia
- The basil ganglia are a collections of neuronal cell bodies in the cortex and brainstem that connect to one another
1. Caudate
2. Putamen
3. Striatum
4. Globus pallidus
5. Substantia niagra - The substantia niagra and globus pallidus are the output regions of the basal ganglia. The striatum is the main input region, receiving input from all over the cortex from primary and secondary sensory areas
cerebellum
A. The cerebellum, like the basal ganglia, controls/regulates action of the upper motor neurons
B. The primary function of the cerebellum is to detect the motor error between the intended movement and actual movement
C. The cerebellum sends output to the premotor cortex and the primary motor cortex. The cerebellum receives input from the spinal cord and indirectly via the frontal/parietal lobes
what are mirror neurons
- Mirror neurons are present in the premotor cortex and they fire in response to an internally generated goal directed behavior as well as when a monkey views someone performing that same movement
- There is no neuronal firing of these neurons when a tool is used to perform the same behavior, indicating the region is likely involved in selecting and recognize appropriate behavioral plans
- Many think mirror neurons underlie our ability to work cooperatively and have empathy (i.e. recognize emotions in others even if we ourselves are not affected)
- These neurons will synapse with primary motor cortex neurons to influence motor execution.
What part of the motor pathway does Parkinsons damage?
In Parkinson’s disease, dopamine-containing neurons in the substantia nigra pars compacta (SNc) degenerate, which are a part of the nigrostriatal pathway
1. Loss of dopamine leads to net inhibition of the thalamus through both direct and indirect pathways as seen in Parkinson’s.
The symptoms of Parkinson’s are:
1. Bradykinesia - slowness of movements, with difficulty initiating movement, resting tremor, rigidity, postural instability
What are the two types of motor neurons?
There are two types of motor neurons: gamma (𝛾) and alpha (⍶)
The alpha motor neuron is the one that directly synapses onto the muscle fiber for movement
What is the role of each motor neuron?
A single alpha motor neuron sends its axon to one muscle, with its axon terminal each innervating a single muscle fiber within that muscle
Key motor areas in the cerebral cortex are:
association areas: - supplementary motor cortex - premotor cortex primary area: - primary motor cortex
Association areas
Association areas –higher order motor planning, both areas project to the primary motor cortex
a. Supplementary motor cortex
b. Premotor cortex
- Functions include:
anticipation of movement,
prepares primary motor
cortex for planned
movement, and is where
mirror neurons are
located
- Influences motor behavior
by innervating the
primary motor cortex
(indirect) and sending
axons to descending
pathways (direct)Primary Area
Primary area – send motor executions commands to spinal cord/brainstem
a. Primary motor cortex
Primary Area: Primary motor cortex
- Separated from the somatosensory cortex by the central sulcus
- Controls individual or sequences of movements that require the activity of multiple muscle groups
- Neurons in this region encode the following aspects of movement:
Force, direction, extent,
speed - Can be distinguished from other motor areas by: Cytoarchitecture and physiology: low intensity of current necessary to elicit movements by electrical stimulation
Somatotopic Organization
Within the primary motor cortex, adjacent regions on the cortex roughly correspond to adjacent areas on the body surface, which is called somatotopic organization
spinal cord and gray and white matter
- The spinal cord consists of a butterfly shaped central gray matter, which contains cell bodies, and a surrounding white matter that consists of the ascending and descending axonal pathways
- Upper levels of the spinal cord have more white matter because all of the ascending (sensory) fibers have already entered the cord and the descending motor pathways have not left yet
spinal cord and ventral components
- Motor axons that will leave the spinal cord have their cell bodies located on the ventral side, in a region called the ventral horn
- The motor axons that leave the spinal cord are called ventral nerve roots
ALCOHOL AND THE CEREBELLUM
The cerebellum is particularly susceptible to alcohol. Why?
Alcohol acts on GABA receptors, and the cerebellum is tightly controlled/regulated by GABAergic neurons (dense population).
During excessive drinking, you will notice errors in movement where individuals loose balance, cannot accurately make/fix motor movements (i.e. DUI tests walking in a line/touching your nose)
