Human Anatomy Exam 3

Skeletal muscle

Found attached to the bones of the body, voluntary, and striated

Cardiac muscle

Found in the heart, involuntary, striated

Smooth muscle

Found in the walls of hollow organs, involuntary, not striated

Contractility

Ability of a muscle to shorten

Excitability

Ability of a muscle to respond to a stimulus

Stimulus

Impulse from the nervous system indicating the muscle needs to do something

Neuron

A cell that can carry an impulse to and from the nervous system

Motor unit

One motor neuron and the muscle fibers that it innervates

All or none law

Individual muscle fibers contract as hard as they can or there is no contraction

Extensibility

Ability of a muscle to lengthen

Elasticity

Ability of a muscle to return to its resting length

Properties of muscle tissue

• Contractibility

• Excitability

• Extensibility

• Elasticity

Functions of muscle tissue

• Movement

• Opening and closing passageways

• Maintaining posture and stabilizing joints

• Heat generation - when muscles contract, heat is generated

Epimysium

Perimysium

Fascicles

Endomysium

Anatomy of a skeletal muscle

Fascicle

Bundle of muscle fibers/cells

Joint

Skeletal muscles cross a moveable _______

Origin

The point of attachment, where the muscle attaches to the bone that remains stationary

Insertion

The portion of the muscle that attaches to the bone that moves during contraction

Toward

Upon contraction, insertion is pulled (toward/away from) the origin

Myo-

Mys-

Sarco-

Prefixes that refer to muscle

Myofibrils

• Where the contraction actually occurs

• Contractile elements of muscle fiber

• Bundles of thick and thin filaments (contractile proteins)

• Myofibril displays alternating dark (A bands) and light (I bands)

Sarcomere

Basic unit of contraction

Titin

Spring-like structure that is attached to the thick filament to prevent over stretching of the muscle

Actin

Thin filament

Myosin

Thick filament

A band

Any portion of the sarcomere where there is myosin or thick filament present

H zone/band

At the center of the A band where there is only thick filament present

M line

Line in the center of the sarcomere and H zone

I band

Where there are lighter striations and only thin filament

Thick filament

• Main protein component = myosin

• Heads form cross bridges between thick and thin filaments

Myosin heads

• Actin binding site

• ATP binding site

Thin filaments

• Actin = contractile protein

• Each actin molecule has special binding site for attachment with myosin cross bridge

• Two other regulatory proteins (tropomyosin and troponin)

Tropomyosin and troponin

Regulatory proteins

Tropomyosin

• Lies along groove of actin

• Resting, covers myosin binding sites blocking interaction

Troponin

• Binds to tropomyosin

• Binds to actin

• Binds with Ca2+

Isometric contraction

The muscle is contracting, but is not shortening

Concentric contraction

When a muscle does work as it shortens

Eccentric contraction

When a muscle does work as it lengthens

ATP

Calcium

O2

Acetylcholine

Chemicals needed for contraction

ATP

Gives energy

Calcium

Allows actin and myosin to slide over each other

O2

Allows for cellular respiration for ATP production

Acetylcholine

• Neurotransmitter

• Leaves the neuron and enters the cleft (space) between the neuron and the muscle fiber and the neuromuscular junction

• The stimulus causes calcium to be released from the sarcoplasmic reticulum (ER of muscle fiber)

Step 1 of sliding filament theory

Troponin molecules hold the actin and myosin in place (muscle is relaxed)

Step 2 of sliding filament theory

A nerve impulse (action potential) travels down a motor neuron to the muscle causing the release of acetylcholine into the space between the neuron and the muscle fiber

Step 3 of sliding filament theory

Acetylcholine stimulates receptors on the muscle fiber, which initiates an impulse that travels along the sarcolemma (muscle cell membrane) to the sarcoplasmic reticulum

Step 4 of sliding filament theory

Calcium is released from sarcoplasmic reticulum into the sarcoplasm (cytoplasm of a muscle cell)

Step 5 of sliding filament theory

Calcium binds with troponin on the actin

Step 6 of sliding filament theory

Binding causes tropomyosin to change shape, moving it away from blocking position - uncovers binding sites on actin for myosin cross bridges

Step 7 of sliding filament theory

Myosin cross bridges attach to actin on the exposed binding site

Step 8 of sliding filament theory

Binding causes cross bridge to bend, resulting in power stroke - fueled by ATP

Step 9 of sliding filament theory

Following power stroke, cross bridge unbinds. If calcium still present, returns to step 7

Step 10 of sliding filament theory

When AP's stop, calcium is taken up by the SR. Tropomyosin returns to its resting position, blocking myosin binding sites on actin. Contraction stops. Thin and thick filaments slide back to their resting locations/lengths

Oxygen debt

When oxygen cannot be supplied fast enough

Prime mover

The primary muscle that produces a certain movement in a joint

Synergists

An assisting muscle that also produces the same movement

Antagonists

The muscle that has the opposite movement of the prime mover (always on opposite sides of the joint)

Ways to make a muscle contract harder

• Each muscle fiber contracts more often

• More muscle fibers contract at the same time

Tetany

A maximal sustained contraction

Fibromyalgia

• Unexplainable chronic muscle pain

• Treatment: antidepressants, exercise, pain relievers

Muscular dystrophy

• Inherited disease characterized by progressive deterioration of muscle tissue

• Characteristics: winged scapulae, scoliosis

• Results in atrophy of the the affected muscle

• Muscle fibers are replaced by connective and fatty tissue

Botulism

• Poisoning caused by eating contaminated food

• Bacteria in food produce a neurotoxin

• Toxin prevents release of acetylcholine necessary for muscle contraction

• Symptoms: dropping eyes, double vision, dry mouth, difficulty swallowing

• Condition may result in paralysis if not properly treated (antitoxin) and death may occur

ALS (Amyotrophic lateral sclerosis)

• Neurodegenerative disease affecting various motor neurons

• Loss of function leads to muscle weakness, atrophy, and spastic paralysis

• Death usually occurs due to respiratory failure within 5 years of diagnosis