Lesson 8: Muscle Tissue and Contraction

Vocabulary and key concepts regarding skeletal, cardiac, and smooth muscle tissues, anatomy, and the mechanisms of contraction and relaxation.

Properties of Muscle Tissue

Excitability, Contractility, Elasticity, and Externability.

Cardiac Muscle

Found in the heart (myocardium), it is shaped with intercalated discs, can be uninucleate or binucleate, and is striated, auto-rythmic, and involuntary.

Smooth Muscle

Found in the walls of visceral organs, it has a fusiform shape, is uninucleate, has no striations, and is involuntary and fatigue resistant.

Skeletal Muscle

Large cylindrical shape, multinucleate (formed from fusion of myoblasts), striated, voluntary, vascular, and innervated at the neuromuscular junction.

Functions of Skeletal Muscle

Movement, maintaining posture, temperature regulation, storing and moving materials, supporting abdominal organs, and joint stabilization.

Endomysium

Connective tissue that wraps around individual muscle fibers.

Perimysium

Connective tissue that wraps around muscle fascicles.

Epimysium

Connective tissue that wraps the entire muscle.

Deep Fascia

Connective tissue that wraps a muscle group.

Aponeurosis

A flat tendon, such as the external oblique.

Sarcomere

Long chains that make up myofibrils; during contraction, the distance between its Z discs decreases.

Sarcolemma

The plasma membrane of a muscle fiber.

Sarcoplasm

The cytoplasm of a muscle fiber.

Sarcoplasmic Reticulum

An internal membrane system that stores calcium; its gates shut during muscle relaxation.

T-tubule

Transverse tubules along which the action potential travels into the muscle fiber.

Triad

A structure formed by a T-tubule and terminal cisternae.

Sliding Filament Mechanism

The process where sarcomeres shorten and thin filaments slide past thick filaments toward the M line.

Muscle Contraction Step 2

$ACh$ is released and binds to receptors, opening sodium ion channels and creating an action potential in the sarcolemma.

Muscle Contraction Step 5

Calcium floods the sarcoplasm and binds to troponin, shifting blocking proteins out of the way.

Cross Bridge

The connection formed when myosin heads (thick filaments) bind to actin.

$$AChE$$

An enzyme that cleans up $ACh$ during muscle relaxation to shut down the signal on the sarcolemma.

ATP in Relaxation

Reabsorption of calcium back into the sarcoplasmic reticulum requires $ATP$ to actively drain and reset the system.

Tropomyosin

The protein that slides back to block binding sites on the actin filament during relaxation.