Chapter 16- Lower Motor Neurons

Lower Motor Neurons (LMNs)

Neurons in the ventral horn of the spinal cord or cranial motor nuclei that project directly to skeletal muscle.

Alpha (α) Motor Neurons

Innervate extrafusal muscle fibers responsible for generating muscle force.

Gamma (γ) Motor Neurons

Innervate intrafusal fibers within muscle spindles to regulate spindle sensitivity.

Motor Unit

A single α motor neuron and all the muscle fibers it innervates.

Motor Unit Recruitment

Process of activating more motor units to increase muscle force.

Motor Pool

All the motor neurons that innervate a single muscle.

Muscle Spindle

A sensory receptor within muscle that detects stretch and contributes to the stretch reflex.

Golgi Tendon Organ

A sensory receptor in tendons that detects tension, helping regulate force output.

Reflex Arc

Neural pathway that mediates a reflex, including sensory input, integration, and motor output.

Monosynaptic Reflex

Reflex involving a direct synapse between sensory and motor neurons (e.g., knee-jerk).

Local Circuit Neuron

Spinal interneurons that coordinate activity between different motor neurons for smooth movement.

Central Pattern Generators (CPGs)

Neural circuits that produce rhythmic motor patterns like walking or swimming, even without sensory input.

Proprioception

Sense of body position and movement from muscle spindles and joint receptors

Lower Motor Neuron Syndrome

Weakness, decreased tone, and loss of reflexes due to LMN damage.

Amyotrophic Lateral Sclerosis (ALS)

A progressive disease that degenerates both upper and lower motor neurons, causing paralysis.