Anatomy Exam 2

Muscle is the primary tissue in the

Heart (cardiac muscle tissue) and walls of hollow organs (smooth muscle tissue)

Skeletal muscle make up nearly

½ of the body’s mass

Properties of muscle tissue

Contractibility, excitability, extensibility, and elasticity

Contractibility

Myofilaments (actin or myosin) are responsible for shortening muscle cells

Excitability

Nerve signals excite muscle cells, causing electrical impulses to travel along the cell’s plasma membrane

Extensibility

Contraction of a skeletal muscle stretches the opposing muscle

Smooth muscle tissue is stretched by

Substances in that hollow organ (food in stomach, urine in bladder, etc.)

Elasticity

Recoils after stretching, resumes resting length

Myo- and mys- mean

Muscle

Sacro means

Flesh

Sarcolemma

Plasma membrane of muscle cells

Sacrcoplasm

Cytoplasm of muscle cells

Functions of muscle tissue

Produce movement, open and close body passageways, maintain posture and stabilize joints, heat generation

Skeletal muscle tissue produces movement

Attached to skeleton, move body by moving bones

Smooth muscle tissue produces movement

Squeeze fluids and substances through hollow organs

Sphincter muscles

Function as valves, relax to let passage, contract to close

Maintain posture and stabilize joints

Remain sitting or standing, stabilize synovial joints

Heat generation of muscle

Muscle contractions product heat, help maintain a normal body temperature

Skeletal muscle tissue

Discrete organs that attach to and move skeleton, packaged into skeletal muscles, striated cells, innervated by voluntary division of the nervous system and is conscious control

Cardiac muscle tissue

Walls of the heart, branched, striated cells, involuntary movement

Smooth muscle tissue

Walls of hollow organs, no striations, innervated by involuntary division of the nervous system

Visceral muscle

Cardiac and smooth muscle tissues (involuntary control, in visceral organs)

Skeletal muscle is attached to

Bone, tendon, or fascia

Skeletal muscle is

An organ

Skeletal muscle consists of

Skeletal muscle tissue, connective tissue, blood vessels, and nerves

Myofiber

Single, elongated, multinucleated skeletal muscle cell

Connective tissue and fasicles

Sheaths of connective tissue bind skeletal muscle and its fibers together

Epimysium

Dense irregular connective tissue surrounding and entire muscle

Perimysium

Fibrous connective tissue that surrounds each fascicle (group of muscle fibers)

Endomysium

Fine sheath of connective tissue wrapping each muscle cell

Connective tissue sheaths are

continuous with tendons

When muscle fibers contract

Pull is exerted in all layers of connective tissue and tendon

Sheaths provide

Elasticity and carry blood vessels and nerves

Muscles are supplied by

One nerve, one artery, and one or more veins

Nerves and vessels

branch repeatedly

Smallest branches of nerves and vessels

Serve individual muscle fibers

Muscle attachments

From one bone to another

Orgin

Less movable attachment (proximal on limbs)

Insertion

More movable attachment (distal on limbs)

Direct (fleshy) attachment

CT fibers are short and appear to attach directly to the bone

Indirect attachment

Tendon (cordlike) or aponeurosis (flat sheet) formed by CT

Tendon

Cordlike attachment of muscle to bone

Aponeurosis

Flat sheet of CT attaching muscle to bone

Indirect attachments can also

Attach to skin, cartilage, fascia, or raphes

Biarticular

Muscles span 2 joints

Skeletal muscle fibers

Long and cylindrical, huge cells, very long

Skeletal muscle fibers are formed by

Fusion of embryonic cells

Skeletal muscle fibers nuclei

Multinucleated, nuclei are peripherally located

Straiations formed from

Internal structure of myofibrils

Myofibrils

Long rods within cytoplasm, 80% of cytoplasm, Specialized contractile organelle in muscle tissue

Myofibrils are made up of

Long rows of repeating segments called sarcomeres

Sarcomeres

Functional unit of skeletal muscle tissue, unit of contraction

Z disc

Boundaries of each sacromere

Thin (actin) filamanet

Extend from Z disc towards center of sarcomere

Thin filament contains

Regulatory proteins troponin and tropomyosin

Thick (myosin) filament

At center of sarcomere, overlap thin filament, contain ATPase enzymes

A bands

Full length of thick filaments and inner ends of thin filaments

H zone

Center of A band where there’s no thin filament

A bands are

Anisotropic

I bands are

Isotropic

M line

Center of H zone, contain tiny rods that hold myosin together

I band

Region with only thin filament, part of 2 adjacent sarcomeres

Titin

Springlike molecule that resists overstretching

Where is titin

Extends from Z disc to thick filaments to M line

Titin functions

Hold thick filament in place, unfold when muscle is stretched

Sarcoplasmic reticulum

Specialized smooth ER, interconnecting tubules surround each myofibril

Terminal cisterns

Tubules form cross-channels at A-I junction

Cisterns occur

In pairs on either side of a T tubule

Sarcoplasmic reticulum

Contain calcium ions that are released when muscle is stimulated to contract

T tubules

Deep invaginations of sarcolemma

Triad

T tubules flanked by 2 terminal cisterns

Concentric contraction

Muscles shorten to do work

Eccentric contraction

Muscle generates force as it lengthens, controlled movement & gravity resistance

Sliding filament contraction

Myosin head attach to actin at both ends of sarcomere and pull actin towards the center

Contraction on Z discs, sarcomeres, I band, H zone, and A band

Z discs move closer together, sarcomeres shorten, I bands shorten, H zone disappears, A band stays the same

Muscle extension

Stretched by movement opposite of normal

Greatest force produced when

Fiber starts partially stretched

What innervated skeletal muscle tissue

Motor neurons

Neuromuscular junction

Where nerve ending and muscle fiber meet

Terminal boutons (axon terminals)

At ends of axons, store neurotransmitters (acetylcholine)

Synaptic cleft

Space between axon terminal and sarcolemma

Step one of innervation

Nerve impulse stimulates release of the neurotransmitter acetylcholine into synaptic cleft

Step 2 of innervation

ACh stimulates changes in the sarcolemma that excite the muscle fiber stimulus carried to T tubules to initiate fiber contraction

Step 3 of innervation

Enzymes in synaptic cleft break down ACh and limit action to single muscle twitch

Motor unit

A motor neuron and all the muscle fibers it innervates

Recruitment

Addition of motor units to accomplish a movement

Oxidative fibers

Produce ATP aerobically

Glycolic fibers

Produce ATP anaerobically by glycolysis

Slow oxidative fibers

Red due to myoglobin and capillaries, contract slowly and resist fatigue, small in diameter, marathon runner

Fast glycolytic fibers

White, fast, little myoglobin and few mitochondria, double diameter of slow oxidative, more myofilaments and generate more power, contract rapidly and tire quickly, sprinters

Fast oxidative fibers

Intermediate diameter, contract quickly, oxygen dependent, middle distance runner

Muscle fascicles

Bundle of muscle fibers = myofibrils = skeletal muscle cells

Fascia

Wrap muscles or muscle groups

Skeletal muscle infection

Very resistant

Muscular dystrophy

Group of inherited muscle destroying diseases, affected muscles enlarge with fat and connective tissue, muscles degenerate

Duchenne muscular dystrophy

Huge gene, no cure, active children become clumsy, rarely live past 30 (die of respiratory infection or failure), lack protein dystrophin so the sarcolemma weakens and tears

Satellite cells

Surround skeletal muscle fibers, undifferentiated myoblasts, fuse into existing muscle fibers to help them grow

Males have more muscle due to

Androgens

Increased age

Increased amount of connective tissue, decreased amount of muscle fibers, decreased 50% of muscle strength by 80

Sarcopenia

Muscle wasting