Motor Pathways I Flashcards
What is the difference between alpha neurons and gamma neurons?
Alpha motor neurons execute the movement by contracting the main muscle fibers.
Gamma motor neurons regulate muscle spindle sensitivity to maintain proprioceptive feedback.
What can sometimes be between a UMN and a LMN?
interneuron
Are UMN gamma or alpha?
alpha
Are LMN gamma or alpha?
can be both
Pyramidal vs Extrapyramidal
Pyramidal Pathway: Direct, controls voluntary movement.
Extrapyramidal Pathway: Indirect, controls involuntary movement
Describe the pyramidal pathway
Decision: This begins with a decision-making process in the brain.
Motor Cortex: Sends direct signals to initiate voluntary movement.
Thalamus: Acts as a relay station, transmitting signals from the motor cortex to the spinal cord.
Spinal Cord: Receives signals for conscious movement (voluntary movement) and processes conscious proprioception (awareness of body position in space).
The pyramidal system is primarily responsible for voluntary movement and conscious proprioception.
Describe the extrapyramidal pathway
Basal Ganglia: Coordinates movement patterns and provides input to the spinal cord via the reticulospinal tract, which helps control posture and muscle tone.
Cerebellum: Integrates sensory input to fine-tune movements and coordinates unconscious proprioception (balance and posture).
Pons: Supports the cerebellum and basal ganglia for coordinated, smooth movement.
The extrapyramidal system is involved in unconscious movement control, such as balance, posture, and coordination of involuntary movements.
Where do axons leave the cortex in the corticospinal tract?
primary motor cortex
supplementary motor area/cortex
pre-motor area/cortex
Some motor responses leave from the sensory cortex, why?
The sensory cortex processes proprioceptive signals to inform and refine motor commands, ensuring that movements are smooth, coordinated, and appropriately adjusted based on body position and movement.
What does the lateral corticospinal tract do?
controls fine motor movements
What does the anterior corticospinal tract do?
controls posture and balance
What is the path of the corticospinal tract?
lateral and anterior
- Both tracts (UMN) originate from the primary motor cortex
- Axons descend through the corona radiata, which is a fan-shaped arrangement of nerve fibers.
They continue through the posterior limb of the internal capsule, where they compactly pass down through the forebrain. - Pyramidal Decussation
Lateral Corticospinal Tract:
Approximately 85% of the fibers decussate at the medulla pyramidal decussation.
After decussation, these fibers descend into the lateral column of the spinal cord, forming the lateral corticospinal tract, primarily controlling limb muscles.
Anterior Corticospinal Tract:
The remaining 15% of fibers continue down the same side without crossing. These fibers enter the spinal cord and descend in the anterior column.
Some of these fibers eventually decussate at the spinal cord level (to synapse with motor neurons. - Synapsing with Lower Motor Neurons
In the spinal cord, both tracts synapse with lower motor neurons located in the ventral horn: - Motor Neuron Exit
The lower motor neurons exit the spinal cord via the ventral roots and travel to their target muscles.
What body parts do the lateral and anterior tracts innervate?
Lateral Corticospinal Tract: Primarily innervates the distal muscles (e.g., hands and fingers) for precise movements. (lateral for limbs)
Anterior Corticospinal Tract: Primarily innervates proximal muscles (e.g., trunk and shoulder) for posture and gross movements. (anterior for axial)
A lesion affecting corticospinal fibres in the left side of the ventral pons impairs voluntary movement of the arm and the leg on which side?
RIGHT SIDE (contralateral) Hemiplegia or Paresis
affects lateral corticospinal tract
A lesion affecting the cervical spinal cord on the left side impairs voluntary movement of the limbs on which side?
LEFT SIDE (ipsilateral) Hemiplegia or Paresis
lateral corticospinal
If the lesion is below the crossing point, as in the cervical spinal cord, impairments occur on the same side.
