08 Muscular System

Axial Division

Axial muscles support and position axial skeleton

-head, neck, trunk

appendicular division

Appendicular muscles support, move, and brace the limbs

-upper and lower extremities

Tendon

Attaches muscle to specific point on a bone

Aponeurosis

strong sheet of tissue that acts as a tendon to attach muscles to bone

-broad flat tendon

Myofibril (muscle fiber)

Cylindrical structures arranged parallel inside muscle fiber; run length of muscle fiber

Endomysium

Thin layer of areolar connective tissue around each muscle fiber

Collagen & elastic fibers, blood vessels, nerves

muscle fascicle

Bundle of muscle fibers/cells & surrounding endomysium

Perimysium

Fibrous layer dividing fascicles

Muscle

tissue composed of fibers that can contract, causing movement of an organ or part of the body

Epimysium

Dense sheath of collagen fibers around muscle

Separates muscle from other tissues/organs

Connected to deep fascia

Sarcolemma

plasma membrane of a muscle fiber

Sarcoplasm

Cytoplasm

Transverse Tubule

Continuous with sarcolemma and extend into sarcoplasm

Form passageways through muscle fiber and encircle sarcomere

Allows events at cell surface to penetrate "into" the cell

sarcoplasmic reticulum

Similar to smooth endoplasmic reticulum of other cells

Makes contact with T-tubule

Surrounds each muscle cell

Stores calcium ions (actively pumped in from cytosol) Major role in muscle contraction

Myofilament

Bundles of protein filaments inside myofibrils

thin filaments

mostly composed of actin

thick filments

mostly composed of myosin

Actin

A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

Myosin

A protein present in muscle fibers that aids in contraction and makes up the majority of muscle fiber

Sarcomere

Repeating functional units of skeletal muscle fiber

Overlapping sections of thick & thin filaments

~10,000 sarcomeres/myofibril, each ~2 µm resting length

Z line

Junction of adjacent sarcomeres

I band

Lighter band with only thin filaments (l-I-ght)

A band

Dark/dense region containing thick filaments (d-A-rk)

M line

Center of A band where adjacent thick filaments connect

H band

Region on each side of M line with only thick filaments

zone of overlap

Within A band; overlapping thick/thin filaments

F-actin

A fibrous protein made of a long chain of G actin molecules twisted into a helix; main protein of the thin myofilament

G-actin

a globular subunit of F actin with an active site for binding a myosin head

Nebulin

Holds F-actin strands together

Tropomyosin

A protein of muscle that forms a complex with troponin regulating the interaction of actin and myosin in muscular contraction

Tropinin

Part of the thin actin filament that has a binding site for calcium ions

myosin tail

(Twisted golf club handles); points toward the M line in the center of the sarcomere; tails of neighboring myosin molecules lie parallel to one another, forming the shaft of the thick filament.

myosin heads

Bind to specific sites on actin molecules to form cross bridges

resting membrane potential

the electrical charge of a neuron when it is not active

-70mV

action potential

a neural impulse; a brief electrical charge that travels down an axon

Change in membrane potential due to ion movement

Depolarization

Change of membrane potential to positive

Repolarization

Membrane potential returns to polarized state

refractory period

Time when firing an AP is impossible or difficult

Acetylcholine

A neurotransmitter that enables learning and memory and also triggers muscle contraction

Neurotransmitter

chemical messengers that cross the synaptic gaps between neurons

motor end plate

Portion of muscle fiber that receives nerve signal

Has ACh receptors able to bind ACh

Junctional folds (creases) increase # of ACh receptors

synaptic cleft

space between axon terminal and motor end plate

-Contains acetylcholinesterase (AChE)

-Breaks down ACh

Acetylcholinesterase

the enzyme that breaks down acetylcholine in the synaptic cleft

Cross bridge

The connection of a mosin head group to an actin filament during muscle contraction (the sliding filament theory).

Power stroke

action of myosin pulling actin inward (toward the M line)

motor unit

A motor neuron and all of the muscle fibers it innervates

One motor neuron for multiple muscle fibers

muscle twitch

Single stimulus-contraction-relaxation sequence in a muscle fiber

Duration varies by muscle type, location, environmental factors

Fasciculation

involuntary "muscle twitch" under skin

myogram

Shows development of muscle tension

latent period

Action potential stimulates sarcolemma

Calcium released from sarcoplasmic reticulum

No tension yet

contraction phase (of a muscle twitch)

Calcium binds to troponin

Cross-bridge cycling

Start of tension development to peak tension

relaxation phase

Calcium drops; cross-bridges detach; active sites covered

Tension returns to resting levels

From peak tension to end of twitch (about 25 msec)

Treppe

stepwise increase in contraction tension

wave summation

this occurs when a second stimulus is received before the muscle fiber has relaxed, creating a second contraction that is stronger than the first

incomplete tetanus

muscle fibers partially relax between contraction

Tetanus

a sustained muscular contraction resulting from a rapid series of nerve impulses

asynchronous motor unit summation

motor units activated on a rotating basis to maintain a sustained contraction

muscle tone

Resting tension in a skeletal muscle

-uses energy

isotonic contraction

muscle shortens because muscle tension exceeds load

isometric contraction

Muscle contracts but there is no movement, muscle stays the same length

concentric contraction

muscle shortens as it maintains tension

eccentric contraction

muscle lengthens as it maintains tension

origin

attachment of a muscle that remains relatively fixed during muscular contraction

Insertion

The attachment of a muscle tendon to a moveable bone or the end opposite the origin

action

Specific movement produced by a skeletal muscle

Agonist

muscle whose contraction is mostly responsible for producing the movement

Example: biceps brachii - elbow flexion

Antagonist

Muscle whose action opposes a particular agonist

Example: triceps brachii for elbow flexion

Antagonist to biceps brachii

Agonist for elbow extension

Synergist

Muscle that helps a larger agonist work efficiently

May provide additional pull or stabilize origin

Example: brachioradialis for elbow flexion

Fixator

Synergists that assist by preventing movement at another joint

creatine phosphate

Reforms ATP (ADP + Pi ATP)

Up to 15s of energy

muscle fatigue

-Muscle can no longer perform at required level

-Decreased pH

-Decreases calcium/troponin binding

-Alters enzyme activities

recovery period

Time needed to return to pre-fatigue conditions

Activity decreases

Oxygen now available

The cell resets the system Lactate converted back to pyruvate Pyruvate makes ATP (aerobic) or recycled to glucose/glycogen

Cori Cycle

Shuttling of lactate to liver, glucose back to muscles

oxygen debt

Amount of oxygen required to restore normal, pre-exertion conditions

In muscles Restore ATP, creatine phosphate, and glycogen levels

In liver Produce ATP to convert excess lactate to glucose

Slow fibers (Type I)

Contractions

-Take 3× longer than fast fibers

-Longer sustained

-Slow to fatigue

Energy

-Mostly aerobic ATP production

-Use more oxygen

-Extensive capillary network

-Myoglobin pigment (binds O2)

Appearance

-Half the diameter of fast fibers

-Appear dark red(myoglobin/blood)

Fast fibers (type IIx)

Contractions

-Reach peak tension in

Intermediate fibers (type IIa)

More closely resemble fast fibers (little myoglobin; pale color)

More capillaries and more fatigue-resistant than fast fibers

hypertrophy

increase in muscle size

atrophy

(n.) the wasting away of a body organ or tissue; any progressive decline or failure; (v.) to waste away

An isotonic contraction causes changes in a muscles

length

Muscle tone refers to

the amount of tension present in a resting muscle

Which part of the myofibril is myosin attached to?

M-line

The H-band contains which of the following?

Myosin only

When two Z-lines come closer together, what has occurred?

Concentric isotonic contraction

What change would turn an incomplete tetanus into a complete tetanus?

Increased action potential frequency

Which muscle tissue moves bones?

Skeletal Muscle

Which muscle tissue moves the digestive system, blood vessels, and other internal organs?

Smooth Muscle

A thick myofilament is made of what protein structure?

Actin

______ tension is produced when fewer motor units are recruited in a contraction

less

During a muscle shortening, the Z-line

does not change size

Which region of a myofibril contains myosin and actin?

A-band

During a muscle lengthening, which regions of a myofibril become shorter?

Zone of overlap only

Which muscle tissue has striations?

Skeletal and cardiac muscle

An isometric contraction causes changes in a muscles _______

tone

Unequal distribution of ______ create a membrane potential

ions

What is a muscles insertion?

The muscle connection that moves when the musce is activated

What is a muscle's origin?

The muscle connection that does not move when the muscle is activated

During a muscle shortening which regions of a myofibril become shorter?

H- and I- bands

During a specific body movement, a muscle that functions to limit other secondary movement is called the_______

fixator

What type of activity would anaerobic metabolism be a good use for?

A one-minute sprint