Week 4 Flashcards
Main functions of the motor cortex?
Initiates and controls voluntary movement
Corticospinal Tract originates from the motor cortex, contributing significantly to precise motor control.
Somatotopy organizes specific regions of the cortex to correspond to different body parts, as illustrated by the homunculus.
Evidence for somatotopy?
Jacksonian March:
Observed in patients with focal epilepsy where seizures spread sequentially across body parts (e.g., hand to arm to neck).
Demonstrates the spatial organization of motor control within the motor cortex.
Movements of motor cortex cells?
Kinematics:
Motor cortex cells encode the direction and trajectory of movement (movement direction).
Kinetics:
Cells also encode the force required for movement (movement force).
Directional Tuning:
Neurons exhibit a “preferred direction,” and the summation of activity across many neurons aligns closely with actual movement direction.
Population Coding:
Movement is represented by the collective activity of neuron populations, predicting movement direction and force.
Basic Principles of Transcranial Magnetic Stimulation (TMS)?
Technique:
TMS applies magnetic pulses to stimulate the motor cortex non-invasively.
Applications:
Used to map motor cortical regions and assess the integrity of corticospinal pathways.
Insights:
Helps measure cortical excitability and plasticity, contributing to understanding motor function and rehabilitation strategies.
Effect of practice in motor cortex?
Repetitive practice of a task can produce changes/plasticity in the motor cortex
representation of different muscles
Role of the spinal cord ?
The spinal cord α-motor neuron is the final
common pathway of motor control by receiving input from local circuit neurons within
the spinal cord (interneurons) and directly
from the brainstem and motor cortex
What modulates motor output?
Cerebellum - Ensures posture and movement coordination by detecting errors.
Basal ganglia - Initiates and terminates movements.
Thalamus
Role: Acts as a relay station for sensory and motor signals to the cerebral cortex.
Motor Function: Integrates inputs from the cerebellum and basal ganglia to modulate motor activity.
Connectivity: 2 parts
Relays sensory information (except smell) to appropriate cortical areas.
Facilitates communication between motor control centers (e.g., motor cortex, basal ganglia).
Key Function: Ensures coordinated motor output by processing and transmitting essential information to the cortex.
What are the descending tracts of the spinal cord?
Corticospinal Tract
Rubrospinal Tract
Reticulospinal Tract
Vestibulospinal tract
Corticospinal Tract ?
Largest descending tract, critical for voluntary movement.
Lateral tract (90%) crosses at the medullary pyramids and controls distal muscles.
Ventral tract (10%) remains uncrossed and controls trunk and proximal muscles.
Rubrospinal Tract?
Originates in the red nucleus of the midbrain.
Primary function is voluntary control of muscle as stimulation of red nucleus produces contralateral flexion and inhibition of extension therefore controliing flexor motor neurons
Also Provides compensation for corticospinal damage.
Reticulospinal Tract?
Originates from the reticular formation.
Medial (Pontine): Facilitates extensor spinal reflexes. Projects ipsilaterally to entire spinal cord
Lateral (Medullary): Suppresses extensor activity. Projects bilaterally to entire spinal cord
Involved in posture, autonomic functions(heart/kidneys), and respiratory control(somatic).
Vestibulospinal Tract?
Originates in vestibular nuclei in the pons-medulla junction and maintains balance and posture.
Medial tract: Controls neck muscles.
Lateral tract: Controls body posture and muscle tone.
Functional and Clinical Insights of the Motor Cortex?
Somatotopy:
Motor neurons are arranged to correspond spatially to body parts (proximal to distal).
Plasticity and Adaptation:
Tracts like the rubrospinal system demonstrate compensatory mechanisms after injury.
Corticospinal Tract Specialization:
Direct connections to motor neurons in humans enable high dexterity but limit recovery after injury.
Babinski Sign:
A clinical indicator of corticospinal tract damage, showing abnormal plantar reflex
Where are cell bodies of a-motor neurones stored?
ventral spinal cord
