Muscle Tissue: Types and Functions

Muscle Overview

• Muscle tissue is specialized for movement, consisting of skeletal, cardiac, and smooth types.

Key Muscle Differences

• Structure: Skeletal muscles have long, striated fibres; cardiac muscles have branched, striated fibres; smooth muscles have spindle-shaped, non-striated fibres.
• Location: Skeletal muscles are attached to bones, cardiac muscle is in the heart, and smooth muscle is in the walls of organs and vessels.
• Function: Skeletal muscles enable locomotion, cardiac muscle pumps blood, and smooth muscle propels substances and maintains pressure.
• Activation: Skeletal muscle is voluntary/somatic nervous system, cardiac muscle is involuntary/pacemaker/autonomic, and smooth muscle is involuntary/autonomic/chemicals.
• Mnemonic: "SCS - Skeletal, Cardiac, Smooth”, helps to differentiate the unique traits of each muscle type.
• Each muscle type's function is tailored to its role; skeletal moves you, cardiac keeps you alive, and smooth manages internal flow.

Muscle Similarities

• Skeletal and smooth muscle cells are elongated and called muscle fibers; cardiac is branched (less emphasized)
• All muscle cells are striated.
• Contraction depends on two myofilaments: actin (thin) and myosin (thick).

Muscle Terminology:

• Sarcolemma refers to the muscle cell plasma membrane.
• Sarcoplasm refers to the muscle cell cytoplasm.
• Prefixes: Myo-, mys-, sarco- all pertain to muscle (e.g., myofibril, sarcoplasmic reticulum).
• Mnemonic: "FAM - Fibers, Actin/Myosin, Muscle terms (Sarcolemma, Sarcoplasm)” is a helpful tool.
• Muscle fibers are elongated for force generation; actin/myosin slide for contraction, and terminology ties it all to muscle identity.
• Describe the roles of actin and myosin in muscle contraction.
• These filaments slide past each other, causing the muscle fiber to shorten and contract

Functional Characteristics of Muscle Tissue

• Excitability (Irritability): Ability to receive and respond to stimuli (e.g., nerve signals, hormones).
• Contractility: Ability to shorten forcibly (movement or tension).
• Extensibility: Ability to be stretched/extended (beyond resting length).
• Elasticity: Ability to recoil and resume original resting length.
• Mnemonic: "ECE - Excitability, Contractility, Extensibility, Elasticity” is useful.
• These traits allow muscles to work—excitability triggers, contractility acts, extensibility adapts, elasticity resets.

Muscle Function

• Skeletal muscle is responsible for all locomotion (e.g., walking, lifting).
• Cardiac muscle courses blood through the body (heart pumping).
• Smooth muscle maintains blood pressure and propels substances through organs (e.g., food in the gut, feces in colon).
• Additional Roles: Muscles maintain posture (e.g., standing), stabilize joints (e.g., shoulder support), and generate heat (e.g., shivering).
• Mnemonic: "LPH – Locomotion (Skeletal), Pumping (Cardiac), propel/Pressure/Heat (Smooth)”
• Each muscle type has a primary role, but all contribute to stability and heat.

Skeletal Muscle: Nerve and Blood Supply

• Each muscle has one nerve, one artery, and one or more veins.
• Nerve Role: Each fiber has a nerve ending controlling contraction (motor neuron).
• Blood Role: Arteries deliver oxygen/nutrients continuously; veins remove wastes.
• Mnemonic: "NAV - Nerve, Artery, Veins” is a lifeline trio for skeletal muscle.
• Nerve signals trigger contraction, blood fuels it and cleans up.