Chapter 5 : The Muscular System

Function of Muscles

Produce movement,

Maintain posture

Stabilize joints

Generate heat

Types of Muscles

Skeletal muscle, Cardiac muscle, Smooth muscle

Function of Muscles

Produce movement,

Maintain posture

Stabilize joints

Generate heat

Types of Muscles

Skeletal muscle, Cardiac muscle, Smooth muscle

Prefix myo and mys

Refers to muscle

Prefix sarco

Refers to flesh

Skeletal Muscle Characteristics

- Cells are multinucleate,

- Striated - have visible banding,

- Voluntary control,

- Cells surrounded and bundled by connective tissue

Connective tissue for muscle

Endomysium

Perimysium

Epimysium

Fascia

Endomysium

Surrounds individual muscle fibers

Perimysium

Surrounds fascicles

Epimysium

Covers the entire skeletal muscle

Fasciae

On the outside of the epimysium

Tendon

Cord-like structure that links skeletal muscles to bones

Aponeuroses

Sheet-like structure for muscle attachment

Smooth Muscle Characteristics

Has no striations

Spindle-shaped cells

Single nucleus

Involuntary - no conscious control

Found mainly in the walls of hollow organs

Cardiac Muscle Characteristics

Has striations,

Usually has a single nucleus,

Joined to another muscle cell at an intercalated disc

Involuntary

Found only in the heart

Origin

Attachment to bone that does NOT move

Insertion

Attachment to bone that MOVES

Sarcoplasmic reticulum

Specialized smooth endoplasmic reticulum in muscle cells. Used for the storage of calcium in muscle cells.

Myofibril

Bundles of myofilaments that are aligned to give distinct bands.

I band

Light band in muscle fibers.

A band

Dark band in muscle fibers.

Sarcomere

Contractile unit of a muscle fiber.

Thick filaments

Myosin filaments composed of the protein myosin.

Thin filaments

Actin filaments composed of the protein actin.

Myosin heads

Extensions or cross bridges of myosin filaments.

Irritability of muscle

Ability to receive and respond to a stimulus.

Contractility

Ability to shorten when an adequate stimulus is received.

Motor unit

One neuron and muscle cells stimulated by that neuron.

Neuromuscular junctions

Association site of nerve and muscle.

Acetylcholine

Principal neurotransmitter at the vertebrate neuromuscular junction.

Synaptic cleft

Gap between nerve and muscle filled with interstitial fluid.

Action potential

Generated by sodium rushing into the cell.

Sliding Filament Theory

Activation by nerve causes myosin heads to attach to binding sites on the thin filament.

Agonist

Muscle that causes a movement.

Antagonist

Muscle that opposes the action of another muscle.

Muscle Fiber Types

Two general categories: fast twitch & slow twitch.

Type I Muscle Fiber

Called slow twitch or slow oxidative fibers, containing large amounts of myoglobin, many mitochondria, and huge blood capillaries.

Type II Muscle Fiber: 2 A

Fast twitch or fast oxidative fibers that contain very large amounts of myoglobin and have a fast contraction velocity.

Type II Muscle Fiber: 2 B

Fast twitch or fast glycolytic fibers that contain a low content of myoglobin and generate ATP by anaerobic metabolic processes.

Concentric Contractions

When a muscle is activated and required to lift a load, generating intramuscular tension and shortening the muscle.

Eccentric Contractions

Occurs when a force applied to the muscle exceeds the momentary force produced by the muscle, resulting in forced lengthening.

Isometric Contraction

A contraction where the muscle is activated but held at a constant length without lengthening or shortening.

Passive Stretch

A type of muscle contraction where the muscle is lengthened while in a passive state, not being stimulated to contract.

Fast Twitch Muscle Fibers

Muscle fibers that generate ATP quickly and are resistant to fatigue.

Slow Twitch Muscle Fibers

Muscle fibers that generate ATP slowly and are very resistant to fatigue.

Contractile Properties of Muscle

Contractile properties refer to how muscles generate force and change length.

Fatigue Resistance in Muscle Fibers

Type I fibers are very resistant to fatigue, while Type II B fibers fatigue easily.

ATP Generation in Muscle Fibers

Type I fibers generate ATP by oxidative metabolic processes, while Type II B fibers generate ATP by anaerobic processes.