Muscles & Spinal Control of Movement and Brain Control of Movement

A set of flashcards covering key terms and concepts related to muscle physiology, spinal cord function, and brain control of movement.

Sarcoplasmic Reticulum

Specialized smooth ER in muscle fibers that stores and releases Ca²⁺ for contraction.

T-tubules

Carry action potentials deep into muscle fibers to trigger Ca²⁺ release from SR.

Z lines (Z disks)

Boundaries of a sarcomere where actin filaments are anchored.

Muscle Spindle

Senses muscle length and rate of stretch.

Golgi Tendon Organ

Senses muscle tension/force.

Ia Sensory Axons

From muscle spindles; detect muscle length and stretch velocity.

Ib Sensory Axons

From Golgi tendon organs; detect muscle tension.

Alpha Motor Neurons

Innervate extrafusal muscle fibers; generate force.

Gamma Motor Neurons

Innervate intrafusal muscle fibers; adjust spindle sensitivity.

Intrafusal Muscle Fibers

Sensory fibers within muscle spindles.

Extrafusal Muscle Fibers

Force-producing muscle fibers.

Why activate alpha and gamma motor neurons simultaneously?

Maintains muscle spindle sensitivity during contraction

Reciprocal Inhibition

Activation of agonist muscle inhibits antagonist muscle.

Crossed-Extensor Reflex

Withdrawal of one limb with extension of the opposite limb for balance.

Excitation Phase of Excitation-Contraction Coupling

Motor neuron AP → ACh release → muscle fiber depolarization.

Coupling Phase of excitation

contraction coupling AP down T-tubules → Ca²⁺ released from SR

Contraction phase of excitation

contraction coupling Ca²⁺ binds troponin → myosin-actin cross-bridge cycling

Inputs to alpha motor neurons

Sensory afferents, descending motor pathways, spinal interneurons

Location of alpha motor neurons

Ventral horn of spinal cord

Why are there cervical and lumbar enlargements in the spinal cord?

Increased motor neurons for limb control

Three levels of the central motor system

Strategy, tactics, execution

Strategy level of motor control

Association cortex, basal ganglia, cerebellum

Execution Level of Motor Control

Spinal cord motor neurons.

Lateral Descending Pathways

Function in voluntary distal limb movement.

Ventromedial descending pathways function

Posture, balance, axial muscles

Corticospinal Tract

Function in fine voluntary movements, especially hands and fingers.

Rubrospinal tract function

Assists upper limb flexor movements

Vestibulospinal tract function

Balance and head position

Tectospinal tract function

Head and eye movements toward stimuli

Pontine reticulospinal tract function

Facilitates extensor tone and posture

Medullary reticulospinal tract function

Inhibits extensor tone; enables voluntary movement

Area 4

function Execution of voluntary movement

Area 6

Motor planning

Primary motor cortex (M1)

Area 4

Premotor area (PMA) function

Movements guided by external cues

Supplementary motor area (SMA) function

Internally generated movement sequences

Basal ganglia motor loop

Cortex → basal ganglia → thalamus → motor cortex

Immediate effect of unilateral motor cortex lesion

Contralateral flaccid paralysis

Motor loop through lateral cerebellum

Cortex → pons → cerebellum → thalamus → motor cortex

Effects of Cerebellar Damage

Ataxia, intention tremor, dysmetria, poor coordination.

Mirror neurons

Neurons that fire during both action execution and observation

Babinski Sign in Adults

Abnormal; indicates upper motor neuron damage.

Main Pathology of Parkinson’s Disease

Loss of dopamine neurons in substantia nigra pars compacta.

Babinski sign in children

Normal due to immature corticospinal tract

Basal ganglia effect in Parkinson’s disease

Excessive inhibition of the thalamus

Basal ganglia effect in Huntington’s disease

Reduced inhibition of the thalamus