BIO-2050: Chapter 10 - Muscle pt. 1

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What is muscle?

Specialized tissue converting chemical energy into mechanical motion, enabling body movement and organ function.

Types of Muscle

Skeletal, Smooth, and Cardiac muscle.

Skeletal Muscle

Attached to the skeleton for movement, generates heat, maintains posture; striated, multinucleated, voluntary.

Cardiac Muscle

Found in the heart, pumps blood continuously; striated, single nucleus, involuntary.

Smooth Muscle

Located in G.I. tract, blood vessels, etc.; involved in peristalsis, blood pressure, pupil size, etc.; non-striated, single nucleus, involuntary.

Functions of Muscle

Movement, peristalsis, heartbeat, sound production, facial expression, support, childbirth, heat production, acts as sphincter, flexibility.

Additional Functions of Muscle

Stabilizes body, maintains posture; stores nutrients; protects organs and supports pelvic organs.

Irritability (Responsiveness)

Ability to respond to stimulation.

Contractility

Ability to shorten when stimulated.

Extensibility

Ability to stretch beyond resting length (protective).

Elasticity

Ability to return to resting length after stretching (protective).

Characteristics of Muscle

Responsiveness to signals, conductivity of electrical changes, contractility, extensibility, elasticity.

Endomysium

Around single muscle fiber.

Perimysium

Around a fascicle (bundle) of fibers.

Epimysium

Covers the entire skeletal muscle.

Fascia

On the outside of the epimysium.

Contractile Proteins

Actin (thin) and Myosin (thick).

Regulatory Proteins

Tropomyosin and Troponin.

Attachment Proteins

Titin, nebulin, alpha actinin, dystrophin.

Sarcomere

Repeating unit of muscle between Z discs; contains thick and thin filaments.

Types of Skeletal Muscle Fibers

Slow Oxidative (SO), Fast Oxidative-Glycolytic (FOG), Fast Glycolytic (FG).

Motor Unit

Motor neuron and all muscle fibers it stimulates.

Motor Neuron

Nerve cells carrying action potentials to skeletal muscle fibers.

Neuromuscular Junction

Site where neuron and muscle come together.

Nerve vs. Muscle Action Potential Speed

Fast in nerves, slow in muscles.

Motor Unit Definition

Includes a motor neuron and all muscle fibers it controls.

Neuromuscular Junction Components

Presynaptic membrane (nerve terminal), synaptic cleft, postsynaptic membrane (motor end plate).

Phases of Muscle Contraction and Relaxation

Excitation, excitation-contraction coupling, contraction, relaxation.

Excitation-Contraction Coupling

Converting an electrical stimulus to a mechanical response.

SERCA

SERCA stands for Sarcoplasmic Endoplasmic Reticulum Calcium ATPASE

Fast Twitch Fibers

Anaerobic, pale, low blood supply, fatigue rapidly, low capillaries/mitochondria.

Slow Twitch Muscle Fiber

Oxidative phosphorylation, fatigue resistance, red color.

Fast Twitch Muscle Fiber

Glycolysis, fatigue easily, white/pale color.

Types of Muscle Contraction

Concentric, Eccentric, Isometric

Concentric Contraction

Shortening of muscle while contracting (lifting book)

Eccentric Contraction

Lengthening of muscle while contracting (lowering book)

Isometric Contraction

Muscle tenses but does not shorten (holding book steady)

Aerobic Activity

Requires oxygen, primarily works type I fibers; increases endurance.

Anaerobic Activity

Does not require oxygen, works type II fibers; increases size and strength.

Steps of Cross Bridge Cycling

Initiation, Actin-myosin complex formation, power stroke, detachment, reactivation.

Causes of Muscle Fatigue

Ion imbalance, nervous fatigue, metabolic fatigue, exercise/aging, lactic acid accumulation.