Motor Systems and Reflexes - Friedman Flashcards
Every level of the NS can generate ___.
movement
The primary motor cortex, as you can see is a target of the ___ ____, and the ___. It gives input to the brainstem from the spinal cord and generates downward commands to everything.
The primary motor cortex, as you can see is a target of the basal ganglia, and the cerebellum. It gives input to the brainstem from the spinal cord and generates downward commands to everything.
Sensory inputs guide movement. Sensory inputs in the spinal cord help to control alpha motor neurons. Sensory inputs in the cerebellum help keep us coordinated. Sensory inputs in the basal ganglia help us decide which movements to make. Sensory and motor are inseparable to each other, although we separate them conceptually all the time.
The _____ tract is what conveys axial and motor control. This is the pathway that lets the brain control the movement of muscles.
This pathway begins in the ____ gyrus (the primary motor cortex).
Our journey begins with two neurons. One will ultimately innervate the axial muscles, and the other will innervate the limb muscles. They leave the cortex by descending through the internal capsule and into the brain stem.
As the pathway descends ino the medulla, __% to ___% of the fibers decussate in the pyramids. The ___ fibers do not decussate though.
After leaving the brainstem, the fibers run down the two corticospinal tracts (the ___ __ tract, and the __ __tracts).
When they get to their target level, the fibers of the anterior corticospinal tract finally decussate through the __ __ __ before synapsing to a neuron in the ventromedial ventral horn of the grey matter.
Conversely, the fibers of the lateral corticopspinal tract have already decussated at the level of the pyramids. As such when the fibers of the lateral corticospinal tract get to the appropriate level, They just synapse onto a neuron in the dorsolateral ventral horn and intermediate zone.
It is worth noting that the neurons in the cortex are known as ___ __ ___ and a lesion any where in these fibers (from the cortex all the way down to the dorsolateral ventral horn and intermediate zone) are known as __ __ __ lesions. These neurons in the ventral horn (ventral horn cells) then project to the limb muscles and to the axial muscles. These neurons are known as __ ___neurons and as such, a lesion between the anterior horn and the muscle are known as ___ lesions.
In summary, the ___ tract is a two neuron pathway. There is an upper motor neuron which arises in the cortex, and a lower motor neuron, which arises in the anterior horn. The limb pathway decussate at the pyrimids in the medulla and the axial pathway decussates through the anterior white commissure in the spinal cord.
The corticospinal tract is what conveys axial and motor control. This is the pathway that lets the brain control the movement of muscles.
This pathway begins in the pre-central gyrus (the primary motor cortex).
Our journey begins with two neurons. One will ultimately innervate the axial muscles, and the other will innervate the limb muscles. They leave the cortex by descending through the internal capsule and into the brain stem.
As the pathway descends ino the medulla, 75% to 90% of the fibers decussate in the pyramids. The axial fibers do not decussate though.
After leaving the brainstem, the fibers run down the two corticospinal tracts (the lateral corticospinal tract, and the anterior corticospinal tracts).
When they get to their target level, the fibers of the anterior corticospinal tract finally decussate through the anterior white commissure before synapsing to a neuron in the ventromedial ventral horn of the grey matter.
Conversely, the fibers of the lateral corticopspinal tract have already decussated at the level of the pyramids. As such when the fibers of the lateral corticospinal tract get to the appropriate level, They just synapse onto a neuron in the dorsolateral ventral horn and intermediate zone.
It is worth noting that the neurons in the cortex are known as upper motor neurons, and a lesion any where in these fibers (from the cortex all the way down to the dorsolateral ventral horn and intermediate zone) are known as UMN lesions. These neurons in the ventral horn (ventral horn cells) then project to the limb muscles and to the axial muscles. These neurons are known as LM neurons and as such, a lesion between the anterior horn and the muscle are known as LMN lesions
In summary, the corticospinal tract is a two neuron pathway. There is an upper motor neuron which arises in the cortex, and a lower motor neuron, which arises in the anterior horn. The limb pathway decussate at the pyrimids in the medulla and the axial pathway decussates through the anterior white commissure in the spinal cord.
The lateral system of the corticospinal tract:
__ musculature
Terminates only ___
Focused terminations
Terminate on motor neurons and interneurons.
The medial system of the corticospinal tract:
__ and __ muscles
Terminates ___
Terminates widely
Terminates only on ___.
The lateral system of the corticospinal tract:
Distal musculature
Terminates only contralaterally
Focused terminations
Terminate on motor neurons and interneurons.
The medial system of the corticospinal tract:
Axial and proximal muscles
Terminates bilaterally
Terminates widely
Terminates only on interneurons
There are tons of inerneurons in the ___ zone of the spinal cord, in between the dorsal and ventral horn. They project into these alpha motor neurons aka ___.They are cholinergic (they use the NT, acetocholine, to get their messges through).
There are tons of inerneurons in the intermediate zone of the spinal cord, in between the dorsal and ventral horn. They project into these alpha motor neurons aka LMNs.They are cholinergic (they use the NT, acetocholine, to get their messages through).
___ damage produces characteristic syndromes:
Paralysis or paresis (weakness)
Loss of muscle tone
Hyporeflexia or loss of reflexes
Fasciculation and fibrillation (muscle fibers start to fire on their own)
Muscle atrophy (why?)
LMN damage produces characteristic syndromes:
Paralysis or paresis
Loss of muscle tone
Hyporeflexia or loss of reflexes
Fasciculation and fibrillation (muscle fibers start to fire on their own)
Muscle atrophy (Why?)
–> It turns out that LMN not only activates muscles by releasing ACh, but they release trophic factors that the muscles need to be healthy. If you remove the trophic factors the muscles will atrophy.
What four brainstem pathways contribute to their medial system? What are they and what do they do?
Medieval Art of Van Gogue
Medial ART-V
- Tectospinal - responsible for visually tracking moving objects. It arises in the superior colliculus. The fibers decussate immediately, and travel down the ventral columns to the upper level of the spinal cord (mainly for neck and upper body muscles).
- Reticulospinal - originates in the pons and medulla. It has an ipsilateral course and controls automatic posture and gait-related movements.
- Vestibulospinal tracts - receives input from vestibular nerve and from cerebellum. Descending projections help control postural adjustment. Ascending projections modulate eye movement. The descending projections keeps us upright and keeps our head oriented to gravity and earth.
- Anterior corticospinal tract - (10% of fibers in pyrmids. Decussate with other corticospinal fibers. Travel in anterior columns. Bilateral terminations. Originates from primary motor cortex and supplementary motor area. It controls bilateral axial and girdle muscles.
Motor cortex is the main contributor to the __ __ tract. This tract, although most of the contribution comes from the motor cortex, there is some cotribution from the somatosensory cortex. So the motor corticospinal neurons terminate in ventral horn and the comoponent that tract S1 terminates in dorsal horn where they control afferent input from muscle spindles
corticospinal tract
A stroke in the pons causes ___ ___ syndrome.
Locked-in syndrome. You can destroy the entire descendnig corticospinal system and leave a person unable to move except for some eye blinks and eye movement. They are conscious and alert and cognitively capable but completely paralyzed.
The corticospinal tract passes through the __ ___. The head portion or face portion of the corticospinal tract is through the __ of the internal capsule. The arms, trunks and legs pass through the __ __ of the internal capsule. You can get strokes there and you can get very weird syndromes such as complete paralysis of the lower body but not the head.
From the internal capsule, they pass into the __ __ and then into the ventral pons, where they are kind of spread out into big fasicles. They then coalesce in the medulla and go into the __ where they decussate. After the pyramids they go into the lateral corticospinal tract.
Again, the reason to know the pathway is because different kinds of strokes will involve different portions of the corticospinal tract, and the symptoms are diagnostic. There are strokes in the pons that causes a thing called “___-____ syndrome, where you can destroy the entire descending corticospinal system and leave a person unable to move except for eye movements and blnkings. In this syndrome, they are conscious and alert but completely paralyzed.
The corticospinal tract passes through the internal capsule. The head portion or face portion of the corticospinal tract is through the genu of the internal capsule. The arms, trunks and legs pass through the posterior horn of the internal capsule. You can get strokes there and you can get very weird syndromes such as complete paralysis of the lower body but not the head.
From the internal capsule, they pass into the cerebral peduncles and then into the ventral pons, where they spread out into big fasicles. They then coalesce in the medulla and go into the pyramids where they decussate. After the pyramids they go into the lateral corticospinal tract. Again, the reason to know the pathway is because different kinds of strokes will involve different portions of the corticospinal tract, and the symptoms are diagnostic. There are strokes in the pons that causes a thing called “locked-in” syndrome, where you can destroy the entire descending corticospinal system and leave a person unable to move except for eye movements and blnkings. In this syndrome, they are conscious and alert but completely paralyzed.
___ tract - these are the fibers that are going to the cranial nerves. They travel the same route: through the internal capsule and then the cerebral peduncles, but they start dropping off as they get to the midbrain. There are fibers that go to different cranial nerves. These fibers are called ___ fibers.
Corticobulbar tract - these are the fibers that are going to the cranial nerves. They travel the same route: through the internal capsule and then the cerebral peduncles, but they start dropping off as they get to the midbrain. There are fibers that go to different cranial nerves. These fibers are called corticobulbar fibers.
If you get a lesion of the corticospinal system, you get ___ syndromes. You get the loss of fine movements, and eventually (unlike LMN syndrome), UMN syndrome will evolve into __ (increase in muscle tone, ___ and a ___ sign). Remember, UMN lesions, everything goes UP!
If you get a lesion of the corticospinal system, you get UMN syndromes. You get the loss of fine movements, and eventually (unlike LMN syndrome), UMN syndrome will evolve into spasticity (increase in muscle tone, hyperreflexia and a babinski sign). Remember, UMN lesions, everything goes UP!
If you get a __ lesion, everything goes DOWN.
Paralysis or paresis
Loss of muscle tone
Hyporeflexia or loss of reflexes
Fascinculation and fibrilation
Muscle atrophy
LMN
Spasticity is the ultimate result of __ damage
It causes increased tone in leg extensors and arm flexors (decorticate rigidity)
It causes increased resistance to ___ movements (varies with speed of movement). If you try to move a spastic limb, it won’t move.
It causes increased __ __ reflex. You get this thing called a __ ___ reflex and __ (you tap a tendon and the response keeps going). So the initial response from tapping the tendon is the stretch reflex. ___ seems to be responding to the stretch reflex
Spasticity is the ultimate result of corticospinal tract damage
It causes increased tone in leg extensors and arm flexors (decorticate rigidity)
It causes increased resistance to passive movements (varies with speed of movement). If you try to move a spastic limb, it won’t move.
It causes increased deep tendon reflex. You get this thing called a clasp knife reflex and clonus (you tap a tendon and the response keeps going). So the initial response from tapping the tendon is the stretch reflex. Clonus seems to be responding to the stretch reflex.
When there is serious damage to the brain, the patient does not just lie flaccidly. They lie with different types of postures. One of them is called the __ (__) posture. You see this posture when there is damage in the brain ____ the midbrain. The midbrain is intact but the structures ____ the midbrain have been damaged. It causes the___ to be flexed and __ to be extended.
We believe that this posture with the arms has to do with the fact that the ___ ___ is still in tact. The __ __ has got the arms flexing and the more caudal reticulo and vestibularspinal tract excite leg extensors so the legs are extended.
When there is serious damage to the brain, they do not just lie their flaccidly. They lie with different types of postures. One of them is called the decorticate (flexor) posture. You see this when there is damage in the brain ABOVE the midbrain. The midbrain is intact but the structures above the midbrain have been damaged. It causes the arms to be flexed and legs to be extended.
We believe it has to do with the fact that the red nucleus is still intact. The red nucleus has got the arms flexing and the more caudal reticulo and vestibularspinal tract excite leg extensors so the legs are extended.
Decerebrate (extensor) posturing occurs when there is a lesion __ the midbrain. In this scenario, arms and legs are ___ (in response to painful stimulus). Release of reticulo- and vestibulospinal that excite both upper and lower limb extensors.
Decerebrate (extensor) posturing occurs when there is a lesion below the midbrain. In this scenario, arms and legs are extended (in response to painful stimulus). Release of reticulospinal and vestibulospinal that excite both upper and lower limb extensors.
The red nucleus is located in the __ midbrain. The ___ tract originates from here. In decorticate (flexor) posturing, what is the cause of the arms to be in the decortico position?
–> Since the lesion is above the midbrain, the __ nucleus is still intact, so the patient’s arms are bent because the __ __ is responsible for exciting the upper limb flexors.
Decerebrate posturing occurs by damage of the __ __. The damage is __ the midbrain. This causes arms to be ___ by the patient’s sides, wrist __ back and pushed against side. The legs are also ___ because the __ __ are still intact (these are responsible for exciting both the upper and lower limb extensors)
The red nucleus is located in the rostral midbrain. The rubrospinal tract originates from here. In decorticate (flexor) posturing, what is the cause of the arms to be in the decortico position?
–> Since the lesion is above the midbrain, the red nucleus is still intact so the patients arms are bent because the red nucleus is responsible for exciting the upper limb flexors.
Decerebrate posturing occurs by damage of the red nucleus. The damage is below the midbrain. This causes arms to be extended by the patient’s sides, wrist flexed back and pushed against side. The legs are also extended because the vestibulo and reticulospintal tracts are still intact (these are responsible for exciting both the upper and lower limb extensors).
The motor nuclei of the thalamus are also in the ventral group. The ventral anterior nucleus receives inputs from the __ __ and __ __. It is the relay from the __ __. The ventrolateral nucleus has two parts. The most rostral part projects to pre-motor supplementory cortex. the more caudal part projects to primary motor cortex, receiving its input from the cerebellum. The cerebellum has a direct connection to the motor cortex.
The motor nuclei of the thalamus are also in the ventral group. The ventral anterior nucleus receives inputs from the substantia niagra and globus pallidus. It is the relay from the motor cortex. The ventrolateral nucleus has two parts. The most rostral part projects to pre-motor supplementory cortex. The more caudal part projects to primary motor cortex, receiving its input from the cerebellum. The cerebellum has a direct connection to the motor cortex.
