Module 4: Motor Systems Flashcards
Where does motor information leave the spinal cord?
Through the anterior roots
Motor information leaves the spinal cord through the anterior roots, and lower motor neurons are located where?
In the anterior horn at each spinal level
What are the two kinds of rootlets in the spinal cord?
motor (anterior)
sensory (posterior)
In the spinal cord, rootlets are either motor (anterior) or sensory (posterior), but what happens when they leave the spinal cord?
They combine outside the vertebral canal into spinal nerves that are mixed, ie. both sensory and motor
On this image of the spinal cord, identify:
- a spinal nerve (mixed)
- a posterior root (sensory)
- an anterior root (motor)
On this image of the spinal cord, identify:
- a spinal nerve (mixed)
- a posterior root (sensory)
- an anterior root (motor)
- spinal ganglion
On this micrograph of the spinal cord, where is the anterior corticospinal tract located? What is it implicated in?
The anterior corticospinal tract is implicated in motor to ipsi- and contra-lateral ventral horn; mostly axial musclature
On this micrograph of the spinal cord, where is the spinothalamic tract located? What is it implicated in?
Pain and temperature from the contralateral side of the body
On this micrograph of the spinal cord, where is the lateral corticospinal tract located? What is it implicated in?
motor to the ipsilateral ventral horn; mostly limb musculature
On this micrograph of the spinal cord, where is the spinocerebellar tract located? What is it implicated in?
Proprioception from the limbs to the cerebellum
On this micrograph of the spinal cord, where is the fasciculus gracilis located? What is it implicated in?
sensory (fine touch and proprioception) from ipsilateral lower limb
On this micrograph of the spinal cord, where is the fasciculus cuneatus located? What is it implicated in?
Sensory (fine touch, proprioception) from ipsilateral upper limb
The corticospinal tract can be divided into what two components?
lateral corticospinal tract
anterior corticospinal tract
What is the function of the descending lateral corticospinal tract?
Skilled movement of the extremities
What is the function of the descending anterior corticospinal tract?
Postural adjustment
A descending motor tract, corticospinal fibers transmit information controlling what?
voluntary, discrete, skilled movements
The corticospinal tract is organized somatotopically, describe.
Fibers from the lower levels of the cord are found laterally within the tract, while fibers from higher levels are found medially within the tract.
Where does the corticospinal tract originate?
In the motor cortex
The corticospinal tract travels through the posterior limb of the [blank], exhibiting a somatotopic arrangement
internal capsule
Where do corticospinal fibers descend on this micrograph of the midbrain?
ipsilaterally through the middle 3/5 of the cerebral peduncles (crus cerebri) in the anterior part of the midbrain
What happens to corticospinal fibers as they descend through the pons?
They are broken up into many bundles
How does the corticospinal tract descend through the medulla
As the pyramids in the anterior part of the medulla
What happens to corticospinal fibers at the caudal medulla (the junction of the medulla and the spinal cord)?
most (85-90%) of fibers cross the midline in the decussation of the pyramids. These crossed fibers go on to form the lateral corticospinal tract. Uncrossed fibers (10-15%) descend as the anterior corticospinal tract.
Which tract is organized in parallel with the corticospinal system?
The corticobulbar tract
What is the function of the corticobulbar tract?
Innervating several cranial nerves
Where does the corticobulbar tract arise? What is its descending pathway?
arises in areas of the motor cortex related to the head and face
descends through the corona radiata. Fibers converge in the genu of the internal capsule, and then descend with corticospinal fibers
What is the corticopontine (corticopontocerebellar tract) implicated in?
Planning, initiation, timing and coordination of voluntary movement.
It is organized partially in parallel with the corticospinal system.
Aside from the corticospinal and corticobulbar tracts, there are three other main pathways that influence lower motor neurons, and therefore play a role in modulating motor activity. What are they?
- vestibulospinal tracts
- reticulospinal tracts
- rubrospinal tracts
What is the role of vestibulospinal tracts?
Important mediators of postural adjustment and head movements
What is the role of reticulospinal tracts?
They influence muscle tone
What is the role of the rubrospinal tract?
It is quite small in humans, but probably plays a minor role in fluencing voluntary movement
The vestibulospinal tracts originate in the caudal pons and rostral medulla. On this micrograph of the caudal pons, locate the vestibular nuclei
The vestibulospinal tracts originate in the caudal pons and rostral medulla. On this micrograph of the rostral medulla, locate the vestibular nuclei
The reticulospinal tracts influence voluntary movement and muscle tone, where do they originate?
In scattered reticular formation nuclei in the tegmentum of the pons and the medulla
The rubrospinal tract facilitates flexor and inhibits extensor muscle activity. Where does it originate?
It originates in the red nucleus in the tegmentum of the midbrain
The cortical motor system is a network of cortical areas. What does it include?
Where does the tectospinal tract originate?
What is it implicated in?
The superior colliculus of the midbrain
This tract is responsible for orienting the head and neck during eye movements.
The control centers that fine tune the signals to both the lower motor neurons (LMNs) and the (UMNs) come from two distinct systems, what are they?
- the basal ganglia (projects to the cortex only)
- the cerebellum (projects to all levels of the motor system)
What is the function of the basal ganglia?
The basal ganglia are the main integrators of cortical and limbic input to the motor system. The basal ganglia ensure that movements are planned and executed precisely. They encode for the decision to move, the direction of movement, the amplitude of movement, and motor expression of emotions.
What is the function of the cerebellum, with respect to motor control?
The cerebellum ensures smooth coordinated movements of voluntary muscles. It receives information concerning the position of the body (proprioceptive information from spinocerebellar and cuneocerebellar tracts), muscle tone and activity of spinal reflex arcs (spinocerebellar and cuneocerebellar tracts), position of the head (vestibular information), cortical activity (sensory, motor, and association areas), and the environment (visual and acoustic).
