Muscular System: Key Concepts, Vocabulary, and Microscopic Anatomy

Origin

The muscle attachment that is not movable or is less movable than the insertion.

Insertion

The movable attachment of a muscle as opposed to its origin.

Epimysium

A connective tissue that wraps around the entire muscle.

Perimysium

The connective tissue that surrounds individual fascicles within a muscle.

Endomysium

The connective tissue that surrounds each muscle fiber.

Fascicle

A bundle of muscle fibers surrounded by perimysium.

Tendon

A cord of dense fibrous tissue attaching a muscle to bone.

Aponeurosis

A fibrous or membranous sheet connecting a muscle and the part it moves.

Myofibrils

Complex organelles composed of bundles of myofilaments within a muscle fiber.

Sarcolemma

The plasma membrane surrounding a muscle fiber.

Sarcomere

The basic contractile unit of muscle tissue, composed of actin and myosin.

Myofilament

The filaments of myofibrils, composed of proteins, primarily actin and myosin.

Actin

A thin myofilament that plays a crucial role in muscle contraction.

Myosin

A thick myofilament that interacts with actin to produce muscle contraction.

Sarcoplasmic reticulum

A specialized smooth endoplasmic reticulum that stores and releases calcium for muscle contraction.

Neurotransmitter

A chemical messenger, such as acetylcholine, that transmits signals across a synapse.

Neuromuscular junction

The synapse or junction between a motor neuron and a skeletal muscle fiber.

Axon

The part of a neuron that carries impulses away from the nerve cell body.

Synaptic cleft

The gap between the axon terminal of a neuron and the sarcolemma of a muscle fiber.

Action potential

A rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane.

Motor unit

A motor neuron and all the muscle fibers it stimulates.

Acetylcholine

A neurotransmitter that sends signals for muscle contraction.

Sliding filament theory

The theory that explains muscle contraction as the sliding of actin filaments over myosin filaments.

Calcium binds to troponin, ATP binds to myosin head to provide energy

Flexion

A movement that brings two bones closer together.

Extension

A movement that brings two bones further apart.

Abduction

A movement that moves a limb away from the midline of the body.

Adduction

A movement that moves a limb toward the midline of the body.

Circumduction

A circular movement of a limb, where the distal end moves in a circle.

Dorsiflexion

A movement that brings the toes toward the head.

Plantar flexion

A movement that points the toes away from the head.

Opposition

The movement of the thumb to touch the fingers on the same hand.

Cardiac, skeletal, smooth

Name three types of muscle tissue

Branching, uninucleated, chains of cells, striations, intercalated disks

Cardiac Muscle Tissue Hallmarks

Single, tapered, uninucleate, no striations

Smooth Muscle Tissue Hallmarks

Long, cylindrical, multinucleated, striations

Skeletal Muscle Tissue Hallmarks

Produce movement, posture & position, stabilize joints, generate heat

What are the 4 functions of Skeletal Muscle?

Cross at least one joint, bulk of skeletal muscle proximal to joint crossed, 2 attachments: origin and insertion, only pulls, during contraction muscle insertion moves toward origin

What are the 5 golden rules of skeletal muscle activity?

turn sole medially

Inversion

turn sole laterally

Eversion

Palms turn face up

Supination

Palms turn face down

Pronation

Irritability, contractibility, extensibility, elasticity

What are the four special properties of skeletal muscle fibers?

Step 1

AcH is released into the neuromuscular junction by the axonal terminal

Step 2

AcH diffuses across the neuromuscular junction and binds to receptors on the sarcolemma

Step 3

Depolarization occurs, and the action potential is generated

Step 4

The action potential carried deep into the cell causes the sarcoplasmic reticulum to release calcium

Step 5

Calcium ion concentration at the myofilaments increases, myofilaments slide past one another and the cell shortens

Step 6

As calcium is actively reabsorbed into the sarcoplasmic reticulum its concentration at the myofilament decreases