Muscle Tissue Types, Structure, and Function in Human Anatomy

Types of Muscle Tissue

Skeletal, Smooth, Cardiac

Myology

Study of structure, function, & diseases of muscle tissues

Skeletal Tissue

Moves skeletal bones; striated; primarily voluntary control

Cardiac Tissue

Only in the heart; striated; involuntary control; intrinsic rhythm acts as natural pacemaker

Smooth Tissue

In walls of hollow structures; not striated; usually involuntary

Functions of Muscular Tissues

Produce body movements, stabilize body positions, store & move substances, produce heat

Electric Excitability

Ability to respond to stimuli from electrical signals

Contractility

Ability to contract when stimulated by action potential

Extensibility

Ability to stretch without being damaged & take on new length

Elasticity

Ability to stretch & return to original length

Muscle Fibers

Structure that make up the skeletal muscle system

Muscle Belly

Body of the muscle; vascularized

Tendons

Connects muscles to bone; white dense connective tissue

Endomysium

Binds together muscle fibers

Fascicle

Muscle fiber bundle

Perimysium

Surrounds muscle fiber bundles

Epimysium

Surrounds each muscle

Fascia

Surrounds every muscle, nerve & blood vessel

Neurovascular Bundle

Nerves & blood vessels that typically enter the muscle together

Motor Fibers

Initiate contractile function of muscle cells

Sarcolemma

The plasma membrane of a muscle fiber

Transverse Tubules

Tunnel in from the surface toward the center of each muscle fiber

Sarcoplasm

The cytoplasm of a muscle fiber

Myofibril

Small structures that are the contractile elements of skeletal muscle

Sarcoplasmic Reticulum

Fluid-filled system of membranous sacs that encircle each myofibril

Actin Filaments

Thin filaments that extend from anchoring points within the Z discs

Myosin Filaments

Thick filaments; main component of thick filaments

Sarcomere

Basic functional unit of myofibril; separated by Z discs

Z Discs

Narrow, plate-shaped regions of dense protein material that separate one sarcomere from the next

A Band

Dark, middle part of the sarcomere that extends the entire length of the thick filaments

I Band

Lighter, less dense area of sarcomere; contains the rest of the thin filaments but no thick filaments

H Zone

A narrow region in the center of each A band; contains thick filaments but no thin filaments

M Line

A region in the center of the H zone; contains proteins that hold the thick filaments together at the center of the sarcomere

Contractile Proteins

Proteins that generate force during contraction

Regulatory Proteins

Proteins that help switch the contraction process on and off

Structural Proteins

Proteins that keep the thick & thin filaments in the proper alignment

Neuromuscular Junction

Location where muscle action potential arises

Synapse

Region where communication occurs between two neurons

Neurotransmitter

Chemical messenger

Muscular System

Voluntarily controlled muscles of your body comprise the muscular system.

Muscle Function

Produce movements by exerting force on tendons.

Muscle Attachment

Muscles are attached to bones by tendons at their origin & insertion.

Origin

The attachment of a muscle's tendon to the stationary bone.

Insertion

The attachment of the muscle's other tendon to the movable bone.

Rule of Thumb for Origin and Insertion

The origin is usually proximal & the insertion distal, especially true in the limbs.

Belly of Muscle

Fleshy portion of the muscle.

Muscle Action

Main movements that occur when the muscle contracts.

Reverse Muscle Action (RMA)

Certain muscles are also capable of reverse muscle action, also called closed kinetic chain (CKC) exercises.

Levers

Rigid structure that can move around a fixed point (fulcrum).

Effort (E)

Force exerted by muscular contraction.

Load

Weight of the body part or some resistance that the moving body part is trying to overcome.

Mechanical Advantage

If load is closer to the fulcrum, the effort farther from the fulcrum; only a relatively small effort is required to move a large load over a small distance.

Mechanical Disadvantage

If load is farther from the fulcrum, the effort is applied closer to the fulcrum; a relatively large effort is required to move a small load (but at greater speed).

First Class Lever

Fulcrum is between the effort & the load; can produce either a mechanical advantage or mechanical disadvantage.

Example of First Class Lever in Body

Skull resting on the vertebral column; effort is contraction of the posterior neck muscles.

Second Class Lever

Load is between the fulcrum & the effort; operates like a wheelbarrow.

Third Class Lever

Effort is between the fulcrum & the load.

Example of Lever in Body

Biceps brachii flexing the forearm at the elbow as an object is lifted.

Fulcrum

The fixed point around which a lever moves.

Second Class Lever in Body

Example in body: standing up on your toes (plantarflexing)

Fulcrum in Second Class Lever

Fulcrum (F)= ball of the foot

Load in Second Class Lever

Load (L)= weight of the body

Effort in Second Class Lever

Effort (E)= contraction of the muscles of the calf, which raise the heel off the ground

Example of Third Class Lever

Example: Pair of forceps (tweezers)

Third Class Lever in Body

Example: elbow flexion (biceps)

Effort in Third Class Lever

Effort (E)= biceps brachii muscle contracting

Load in Third Class Lever

Load (L)= weight of the arm or something held in hand

Fulcrum in Third Class Lever

Fulcrum (F)= elbow joint

Fascicles

Bundles of skeletal muscle fibers (cells)

Muscle Fiber Arrangement

All muscle fibers are parallel to one another

Muscle Fascicle Patterns

May form one of 5 patterns with respect to the tendons: Parallel, Fusiform, Circular, Triangular, Pennate

Concentric Contraction

Shortening

Eccentric Contraction

Lengthening

Prime Movers

Contracts to cause an action while the other muscle (follower) stretches & yields to prime mover

Antagonist

Stretches and yields to the prime mover

Example of Prime Mover and Antagonist

Flexing forearm at elbow: Biceps brachii (prime mover) and Triceps brachii (antagonist)

Naming Skeletal Muscles

Contain combinations of the word roots of their distinctive features: Pattern, Size, Shape, Action, Number of origins, Location, Sites of origin and insertion