Motor Pathways of the body Flashcards
Where does voluntary movement begin?
Has input from many places – there is no true starting point for movement so we are choosing motor cortex.
Upper Motor Neuron in the Anterior Paracentral Gyrus (a.k.a. Precentral gyrus - Primary Motor Cortex)
All motor synapses occur where?
Ventral horn of the spinal cord
There is ____ Lower Motor Neuron pathway that exits the spinal cord and forms the peripheral motor nerves.
only ONE
What percentage of motor neurons are in each of the 3 types of motor pathways?
- Unilateral movement that decussates in the medulla (90%)
- Unilateral movement that decussates at the spinal cord level (10%)
- Bilateral movement (Extremely small)
Motor Homunculus vs Sensory Homonculus
Very similar BUT motor will adapt based on use of type of body parts.
Ex: Maddie G plays violin, likely has a much larger hand homonculus portion than most people.
Medial: Legs/Feet; Anterior Cerebral A supplies here
Lateral: Hands/Face; Middle Cerebral A supplies here
Most Lateral: Gut
If someone has a stroke of in the middle cerbral artery what portions of the brain are affected?
Lateral portion of the brain. Will effect hands/face/gut
If someone has a stroke with the anterior cerebral artery what portion of the brain will be affected?
Legs/Feet
Motor Planning - Intention to Move
- Primary Motor Cortex – Voluntary movement control of individual motor units
Activate “Motor Unit 1” within Tibialis anterior. - Unimodal Motor Association Cortex – Coordinate complex interactions of muscle units
Assist in generation of gait pattern - Heteromodal Motor Association Cortex –Coordinate motions with intended outcomes
Walk across the room
Primary Unilateral Movement Pathway
- Primary Motor Pathway (precentral gyrus) -> Posterior Limb of internal capsule -> cerebral pedicules in midbrain
- Descends to caudal aspect of medulla and decussates -> descends as lateral corticospinal tract
- Synapse occurs in the ventral horn of spinal cord to exit -> leaves spinal cord through ventral root and travel to the target muscle.
Note: Does not go through thalamus
Secondary Unilateral Movement Pattern
- Primary Motor Pathway (precentral gyrus) -> Posterior Limb of internal capsule -> cerebral pedicules in midbrain
- Descends on ipsilateral side as ventral corticospinal tract to spinal level
- Decussation occurs -> Synapse occurs in the ventral horn of spinal cord to exit -> leaves spinal cord through ventral root and travel to the target muscle.
Bilateral Movement
- Primary Motor Pathway (precentral gyrus) -> Posterior Limb of internal capsule -> cerebral pedicules in midbrain
- Descends on ipsilateral side as ventral corticospinal tract to spinal level
- Half decussate AND half stays ipsilateral once at spinal level -> Synapse occurs in the ventral horn of spinal cord to exit -> leaves spinal cord through ventral root and travel to the target muscle.
What is so special about the bilateral movement pathway?
A partial SCI will not stop it from working for the trunk muscle due to bilateral innervation! Only a complete spinal cord injury will effect it!
Trunk muscles are innervated by what pathway?
Bilateral pathway (General) BUT also primary unilateral pathway (lateral corticospinal) for lateral flexion.
UMN vs LMN Presentations
UMN
* Hyperreflexia
* Hypertonia
* Muscle Weakness
* Spasticity (Combines all three presentations above)
LMN
* Hyporeflexia
* Hypotonia
* Muscle Weakness
Theory of why UMN cause hyper active symptoms?
- UMN are both excitatory and inhibitory; most are inhibitory
- Damage to UMN leads to less inhibitory signals making it closer to threshold for an action potential.
- LMN now will be more responsive to a lesser stimulus.
