Neurophysiology Lecture: Motor Function and Reflexes

Introduction

• Lecturer discussed motor and neuromuscular topics.
• Emphasis on spinal control of muscles and reflex pathways.
• Questions encouraged as the next lecture will be pre-recorded.

Spinal Control of Motor Function

Overview

• Sensory fibers from skeletal muscles connect to motor neurons sent to muscles.
• Communication occurs through the anterior aspect of the spinal cord.
• Gray matter of the spinal cord integrates sensory input and CNS signals, determining output.

Sensory and Motor Pathways

• Sensory signals enter via the posterior/dorsal root.
• Some signals branch to higher nervous centers; others terminate in the gray matter for reflexive actions.
• Reflexes allow for instantaneous muscle responses without brain involvement.

Interneurons

• Communication intermediaries between sensory nerves and motor neurons.
• Provide modulatory functions for overall signal before reaching motor neurons.

Renshaw Cells & Lateral Inhibition

• Renshaw cells enable lateral inhibition, increasing fine motor control by focusing signal.
• Propriospinal fibers allow communication between different cord segments.

Muscle Spindle and Golgi Tendon Organs

Function and Role

• Muscle spindle detects muscle stretch and contributes to muscle tone and reflexes.
• Golgi tendon organs located in tendons sense stretch and help prevent excess tension, thus vetoing contraction.

Motor Neurons

• Alpha motor neurons: stimulate muscle contraction at motor end plate.
• Gamma motor neurons: control muscle spindle tone, allowing for muscle tone regulation.

Key Reflexes

• Dynamic vs. static responses described.
• Reflex actions oppose sudden muscle length changes.
• Coactivation of alpha and gamma motor neurons helps stabilize muscle movements under load.

Brainstem and Cortical Control

Brainstem Functions

• Brainstem areas like the medulla, pons, and mesencephalon control involuntary functions (cardiovascular, GI, equilibrium, etc.).

Sensory Feedback

• Feedback from muscle spindles and Golgi tendons integrated for motor control.

Red Nucleus

• A pathway for detailed control of specific muscles (hands, fingers).

Cerebellum and Basal Ganglia

Cerebellum Functions

• Coordinates sequential movements and corrects motor errors.
• Subdivided into the vermis, intermediate zone, and lateral zone for trunk and limb movement coordination.

Basal Ganglia Functions

• Manages complex motor activities (e.g., writing, hammering).
• Involves circuits like the putamen and caudate nucleus.

Parkinson's Disease

• Associated with basal ganglia dysfunction, particularly the loss of dopamine-producing neurons in the substantia nigra.
• Symptoms include rigidity, tremors, and difficulty initiating movement.

Vestibular Apparatus and Equilibrium

Function and Structure

• Semicircular canals detect rotational acceleration.
• Utricle and saccule detect linear acceleration (horizontal and vertical).
• Otoliths in utricle and saccule aid motion detection.

Signal Transmission

• Sensory hair cells in semicircular canals convert endolymphatic fluid movement into nerve signals.
• Vestibular nerve transmits signals to brain areas for equilibrium control.

Motion Sickness and Vertigo

• Mismatch between vestibular and visual inputs can cause vertigo and nausea.
• Example: seasickness, becoming disoriented with VR headsets.

Summary

• The lecture highlighted spinal and brainstem roles in motor function and reflexes.
• Described muscle spindles and Golgi tendon organs' role in muscle control.
• Introduced vestibular apparatus for maintaining balance and equilibrium.
• Emphasized the cerebellum and basal ganglia in coordinated movement.

Questions and Review

• Encouraged students to ask questions or review difficult topics with examples.
• Provided summaries and engaged in interactive Q&A to clarify concepts.