Overview of Muscle Tissue Types and Functions

Smooth Muscle

Oldest muscle tissue, involuntary, non-striated.

Cardiac Muscle

Striated, involuntary muscle found in the heart.

Skeletal Muscle

Voluntary, striated muscle attached to bones.

Excitability

Ability to respond to stimuli.

Contractility

Ability to shorten when stimulated.

Extensibility

Ability to be stretched.

Elasticity

Ability to recoil to resting length.

Epimysium

Dense tissue surrounding entire muscle.

Perimysium

Tissue surrounding muscle fiber groups (fascicles).

Endomysium

Fine tissue surrounding each muscle fiber.

Multinucleated

Muscle fibers have multiple peripheral nuclei.

Sarcoplasm

Cytoplasm of a muscle cell.

Mitochondria

Organelles for ATP production in muscle cells.

Glycosomes

Storage of glycogen in muscle fibers.

Myoglobin

Oxygen storage protein in muscle cells.

Sarcoplasmic Reticulum

Storage and release of Ca2+ in muscle.

Sarcolemma

Plasma membrane of muscle fibers.

T-Tubules

Extensions carrying action potentials into muscle.

Myofibril

Contractile unit of a muscle fiber.

Z Disc

Anchors thin filaments in myofibrils.

Thick Filaments

Composed of myosin, run entire A band.

Thin Filaments

Composed of actin, run into A band.

Skeletal Muscle

Type of muscle responsible for voluntary movements.

Muscle Cell (Fiber)

Basic unit of skeletal muscle tissue.

Sarcomere

Smallest functional unit of a muscle fiber.

Fascicle

Bundle of muscle fibers within a muscle.

Myofibril

Long, thread-like structures within muscle fibers.

Actin

Thin filament protein involved in muscle contraction.

Myosin

Thick filament protein that interacts with actin.

M-line

Middle line of the sarcomere, anchoring myosin.

I-Band

Region of sarcomere containing only actin filaments.

A-Band

Region of sarcomere containing both actin and myosin.

H-Zone

Area within the A-band where actin does not overlap.

Z-Disc

Boundary of a sarcomere, anchoring actin filaments.

Tropomyosin

Regulatory protein blocking myosin binding sites on actin.

Troponin

Protein that binds calcium, causing tropomyosin to move.

Calcium ions (Ca2+)

Trigger muscle contraction by binding to troponin.

Excitation-contraction coupling

Process linking neural stimulation to muscle contraction.

Neuromuscular junction

Connection between motor neuron and muscle fiber.

Acetylcholine (ACh)

Neurotransmitter released at the neuromuscular junction.

Action potential

Electrical signal triggering muscle fiber contraction.

Synaptic cleft

Gap between axon terminal and muscle fiber.

Motor unit

Single motor neuron and the muscle fibers it controls.

End plate potential

Local depolarization at the neuromuscular junction.

End Plate Potential

Initial depolarization at the neuromuscular junction.

Voltage-gated Na+ Channels

Channels that open in response to membrane depolarization.

Na+ Influx

Sodium ions entering the cell, decreasing voltage.

Critical Threshold

Membrane voltage level needed to generate action potential.

Local Depolarization Wave

Spread of depolarization across the sarcolemma.

Repolarization

Restoration of resting membrane potential after depolarization.

K+ Efflux

Potassium ions exiting the cell during repolarization.

Refractory Period

Time during which fiber cannot be stimulated.

Na+-K+ Pump

Restores ionic conditions of resting state post-action potential.

Calcium Ion Release

Calcium ions released from sarcoplasmic reticulum during contraction.

T Tubules

Transverse tubules that propagate action potentials into muscle fibers.

Troponin

Protein that binds calcium and moves tropomyosin.

Tropomyosin

Protein that blocks actin active sites at low Ca2+.

Cross Bridge Cycle

Series of events for muscle contraction involving myosin and actin.

Power Stroke

Myosin head pivots, pulling actin filament toward M line.

Cross Bridge Formation

Attachment of myosin heads to actin binding sites.

Cross Bridge Detachment

Release of myosin from actin due to ATP binding.

Cocking of Myosin Head

Myosin head returns to high-energy state using ATP.

Active Sites Exposed

Condition allowing myosin to bind to actin.

Sarcoplasmic Reticulum (SR)

Organelle that stores calcium ions in muscle cells.

Sarcomere Shortening

Decrease in length of sarcomere during muscle contraction.

Calcium Signal

Presence of calcium ions necessary for muscle contraction.

Ca2+

Calcium ion crucial for muscle contraction.

Myosin head

Part of myosin that binds to actin.

Thick filament

Composed mainly of myosin proteins.

Thin filament

Composed mainly of actin proteins.

ADP

Adenosine diphosphate, energy currency in cells.

P i

Inorganic phosphate, released during ATP hydrolysis.

ATP hydrolysis

Process releasing energy for muscle contraction.

Skeletal Muscle

Type of muscle responsible for voluntary movement.

Muscle Contraction

Process of muscle fibers shortening to produce movement.

Sliding Filament Model

Theory explaining muscle contraction via filament sliding.

Muscle Tone

Slight contraction state of muscles at rest.

Isometric Contraction

Muscle tension without changing length.

Isotonic Contraction

Muscle changes length while moving a load.

Concentric Contraction

Muscle shortens while performing work.

Eccentric Contraction

Muscle lengthens while under tension.

Muscle Metabolism

Chemical processes providing energy for muscle activity.

Direct Phosphorylation

ATP regeneration via creatine phosphate transfer.

Anaerobic Pathway

ATP production without oxygen, leads to lactic acid.

Aerobic Pathway

ATP production using oxygen, yields high energy.

Oxygen Deficit

Extra oxygen needed post-exercise for recovery.

Muscle Fiber Types

Classified by contraction speed and metabolic pathways.

Slow Oxidative Fibers

High fatigue resistance, use aerobic metabolism.

Fast Glycolytic Fibers

Low myoglobin, rely on anaerobic glycolysis.

Effects of Endurance Exercise

Increases capillaries, mitochondria, and endurance.

Resistance Exercise

Promotes muscle hypertrophy and strength gains.

Overload Principle

Muscles must be challenged for growth.