Chapter $$11$$ Muscle Tissue – Condensed Exam Notes

Flashcards for muscle tissue lecture review.

Movement

Fundamental characteristic of all living organisms.

Three types of muscular tissue

Skeletal, cardiac, and smooth muscle.

Functions of Skeletal Muscles

Heat production, Support the body, Create movement, Help maintain a constant body temperature, Assists movement in cardiac and lymphatic vessels, Protection.

Excitability (responsiveness)

To chemical signals, stretch, and electrical changes across the membrane.

Conductivity

Local electrical change triggers a wave of excitation that travels along the muscle fiber.

Contractility

Shortens when stimulated.

Extensibility

Capable of being stretched between contractions.

Elasticity

Returns to its original rest length after being stretched.

Skeletal Muscle

Voluntary, striated muscle usually attached to bones.

Striations

Alternating light and dark transverse bands.

Voluntary

Usually subject to conscious control.

Muscle fiber (myofiber)

Muscle cell; as long as 30 cm.

Tendons

Attachments between muscle and bone.

Endomysium

Connective tissue around muscle cell.

Perimysium

Connective tissue around muscle fascicle.

Epimysium

Connective tissue surrounding entire muscle.

Sarcolemma

Plasma membrane of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber.

Myofibrils

Long protein cords occupying most of sarcoplasm.

Glycogen

Carbohydrate stored to provide energy for exercise.

Myoglobin

Red pigment; provides some oxygen needed for muscle activity.

Myoblasts

Stem cells that fused to form each muscle fiber early in development.

Satellite cells

Unspecialized myoblasts remaining between the muscle fiber and endomysium.

Sarcoplasmic reticulum (SR)

Smooth ER that forms a network around each myofibril.

Terminal cisternae

Dilated end-sacs of SR which cross the muscle fiber from one side to the other.

T tubules

Tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side.

Triad

A T tubule and two terminal cisternae associated with it.

Myofibril

Bundle of parallel protein microfilaments called myofilaments.

Contractile proteins

Contractile proteins that do the work of shortening the muscle fiber.

Thick filaments

15nm in diameter made up of hundreds of proteins called myosin.

Thin filaments

7nm in diameter and made of intertwined strands of protein called F actin.

Thin filaments

Made up of a string of subunits called G actin that has an active site that binds the head of myosin.

Thick filaments

Made of several hundred myosin molecules.

Fibrous (F) actin:

Two intertwined strands.

Troponin molecule:

Small, calcium-binding protein on each tropomyosin molecule

Regulatory proteins

Switches to determine when the fiber contracts.

Elastic filaments

Run through core of thin filament and anchor it to Z disc and M line.

Regulatory proteins

Act like a switch that determines when fiber can (and cannot) contract.

Sarcomere

Segment from Z disc to Z disc.

Sarcomere

Functional contractile unit of muscle fiber.

Striations

Alternating A-bands (dark; thick myosin and actin overlap) and I-bands (light; thin actin).

Myofibrils

Cylindrical units of the cytoskeleton made up of microfilaments (myofilaments).

Sarcomeres

Repeating, overlapping pattern of thin and thick filaments in the myofibril.

Tropomyosin

A strand of protein that blocks actin’s active sites (prevents actin from binding with myosin).

Troponin

A protein (glob) that holds tropomyosin in its blocking position.

Motor unit

One nerve fiber and all the muscle fibers innervated by it.

Neuromuscular junction (NMJ)

The point where a nerve fiber meets a muscle fiber.

Denervation atrophy

Shrinkage of paralyzed muscle when nerve remains disconnected.

Somatic motor neurons

Nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles.

Somatic motor fibers

Their axons that lead to the skeletal muscle.

Synapse

Point where a nerve fiber meets its target cell.

Neuromuscular junction (NMJ)

When target cell is a muscle fiber.

Synaptic knob

Swollen end of nerve fiber.

Synaptic cleft

Gap between synaptic knob and sarcolemma.

Schwann cell

Envelops and isolates NMJ.

Basal lamina

Thin layer of collagen and glycoprotein separating Schwann cell and muscle cell from surrounding tissues.

Acetylcholinesterase (AChE)

Breaks down Ach, allowing for relaxation.

Voltage (electrical potential)

A difference in electrical charge from one point to another.

Resting membrane potential

About −90 mV in skeletal muscle cells.

Depolarization and repolarization

A quick up-and-down voltage shift is called an action potential.

Spastic paralysis

A state of continual contraction of the muscles; possible suffocation.

Tetanus (lockjaw)

A form of spastic paralysis caused by toxin Clostridium tetani.

Flaccid paralysis

A state in which the muscles are limp and cannot contract.

Excitation

Process in which nerve action potentials lead to muscle action potentials.

Excitation–contraction coupling

Events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract.

Contraction

Step in which the muscle fiber develops tension and may shorten.

Relaxation

When stimulation ends, a muscle fiber relaxes and returns to its resting length.

Length–tension relationship

The amount of tension generated by a muscle depends on how stretched or shortened it was before it was stimulated.

Rigor mortis

Hardening of muscles and stiffening of body beginning 3 to 4 hours after death.

Recruitment

Increasing tension is produced by slowly increasing size or number of motor neurons stimulated.

Isotonic muscle contraction

Muscle changes in length with no change in tension.

Concentric contraction

Muscle shortens as it maintains tension.

Eccentric contraction

Muscle lengthens as it maintains tension.

Isometric muscle contraction

Muscle produces internal tension but external resistance causes it to stay the same length.

Anaerobic fermentation

Enables cells to produce ATP in the absence of oxygen.

Aerobic respiration

Produces far more ATP.

Phosphagen system

The combination of ATP and CP which provides nearly all energy for short bursts of activity.

Glycogen–lactic acid system

The pathway from glycogen to lactic acid.

Muscle fatigue

Progressive weakness from prolonged use of muscles.

Slow-twitch, slow oxidative (SO), red or type I fibers

Well adapted for endurance; resist fatigue by oxidative (aerobic) ATP production.

Fast-twitch, fast glycolytic (FG), white, or type IIb fibers

Fibers are well adapted for quick responses.

Myocytes

Not as long and fibrous as skeletal muscles; they have one nucleus.

Cardiac muscle

Contracts with regular rhythm.

Cardiac muscle cells

Striated like skeletal muscle, but myocytes (cardiocytes) are shorter and thicker; branched.

Myocyte

Joined at its ends to other myocytes by intercalated discs.

Autorhythmic

Able to contract rhythmically and independently.

Smooth muscle

Named for its lack of striations.

Smooth Muscle Myocyte Structure

Myocytes have a fusiform shape.

Multiunit smooth muscle

Occurs in some of the largest arteries and air passages, in piloerector muscles, and in iris of the eye.

Single-unit smooth muscle

Occurs in most blood vessels, in digestive, respiratory, urinary, and reproductive tracts.

Autonomic activity

Parasympathetic nerves secrete acetylcholine stimulating GI tract smooth muscle.

Peristalsis

Waves of contraction brought about by food distending the esophagus or feces distending the colon.

Stress–relaxation response

Helps hollow organs gradually fill (urinary bladder).

Plasticity

The ability to adjust its tension to the degree of stretch.

Muscular dystrophy

Group of hereditary diseases in which skeletal muscles degenerate and weaken, and are replaced with fat and fibrous scar tissue.

Myasthenia Gravis

Autoimmune disease in which antibodies attack neuromuscular junctions and bind ACh receptors together in clusters.