Descending Motor Systems Quiz

Study Notes

The brain and spinal cord are responsible for voluntary movement.
Two neurones are required for voluntary movement to occur: upper motor neurones (UMNS) and lower motor neurones (LMNs).
UMNs are responsible for sending signals to the LMNs which control muscle movements.

Descending fibres travel from the brain to the spinal cord.
The descending motor system includes the pyramidal and extrapyramidal tracts.
The pyramidal tracts include the corticospinal and corticobulbar tract.
The extrapyramidal tracts include the rubrospinal, reticulospinal, vestibulospinal and tectospinal tracts.

UMNs: cell bodies are located in brain and brain stem; axons constitute descending motor pathways.
LMNs: cell bodies are located in the spinal ventral horn or cranial motor nuclei.
LMNs include alpha and gamma neurones.
Axons proceed through peripheral somatic nerves to innervate skeletal muscle.

Originates in the cerebral cortex.
It passes through the pyramid of the medulla.
This is why it is called the pyramidal tract.
It is responsible for initiating and controlling voluntary movements, especially fine motor skills.
It controls the movements of limbs and trunk.
97% of the fibres in the corticospinal tract are small and conduct background tonic signals to the spinal cord.
Only 3% of the fibres are large, originate from giant Betz cells located in the primary motor cortex, and are responsible for the fine control of movement.

Originates in the cerebral cortex.
It descends to the brainstem to control the muscles of the face, head, and neck.
This tract is responsible for voluntary movements of the head and face, such as chewing, swallowing, facial expressions, and speech.

The corticospinal tracts are responsible for most of the voluntary movements we make.
They are involved in planning, initiating, and controlling complex sequences of movements.
They are also responsible for the accuracy and precision of our movements.
The corticospinal tracts are divided into two main tracts: the lateral corticospinal tract and the anterior corticospinal tract.
The lateral corticospinal tract is responsible for controlling the movement of the limbs.
The anterior corticospinal tract is responsible for controlling the muscles of the trunk.

Found in the primary motor cortex.
Only about 34,000 Betz cells in each corticospinal tract.
The axons from Betz cells send short collateral back to the cortex itself to monitor activity.
These cells transmit the majority of the corticospinal tract.
The cell bodies are very large, often larger than 100 micrometers in diameter.
They are responsible for sending signals to the spinal cord, controlling the movement of the limbs and trunk.

The majority of the corticospinal tract originates in the primary motor cortex (M1)
The M1 is located in the precentral gyrus, which is the anterior portion of the frontal lobe.
30% of the corticospinal tract originates in the primary motor cortex,
30% of the corticospinal tract comes from the premotor and supplementary motor areas.
40% originates from the parietal cortex (somatosensory cortex).

An area located in the frontal lobe of the brain that plays a role in planning, sequencing, and coordinating movements.
This area (6) is concerned with planning, programming motor sequences and bimanual activity.

Located in the frontal lobe of the brain.
Plays a role in preparing the body for movement, such as setting the body in a certain posture to perform a specific task.
The premotor area receives input from the parietal and prefrontal cortex and projects to the primary motor cortex.
It sends signals to the spinal cord for the execution of movements.

The parietal cortex is responsible for processing sensory information, including touch, temperature, and pain.
It helps to coordinate movements by providing feedback about the position of the body in space.