Muscular System

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Excitability

ability to receive/respond to electrical stimulus

Contractility

generate force when sufficient stimulus is received

Extensibility

can contract when stretched

Elasticity

resume resting length after being stretched

Functions of Muscle

Motion, Posture Maintenance, Generate Heat, Stabilizes joints

Types of Muscle Tissue

Smooth, Skeletal, Cardiac

Skeletal Muscle

long, cylindrical, striations, voluntary control

Skeletal Muscle

this muscle type has rapid contractions and tires easily

Cardiac Muscle

intercalated disc, striated, gap junctions, involuntary

Cardiac Muscle

this muscle type has a steady rate of contraction and is the internal pacemaker

Smooth Muscle

spindle shaped, no striations, gap junctions, involuntary

Smooth Muscle

this muscle type is found in the walls of organs thus maintaining the internal environment with slow sustained contractions

Endomysium

CT around each muscle cell

Perimysium

CT around fascicles

Epimysium

CT around entire muscle

Fascicle

muscle fiber bundles

Indirect Attachment to Bone

CT wrappings extend beyond the muscle as a tendon or aponeurosis

Direct Attachment to Bone

epimysium fuses to periosteum of a bone

Sarcolema

plasma membrane of muscle

Sarcoplasm

surrounds myofibrils and stores calcium

Myoglobin

binds oxygen

T Tubules

invaginations toward center of cell

Terminal Cisterns

enlarged cross channels at the end portions of the SR that release calcium

Triad

T-tubules + 2 terminal cisterns of SR

Triad

Located at A/I band junction and zipped together via integral proteins

Myofibrils

Proteins that run length of muscle fiber

Myofilaments

overlap of thick and thin types

Sarcomere

basic contractile unit of muscle

I Band

thin filaments only

H Zone

thick filaments only

Myosin

thick filament

Actin

thin filament

Head of Mysoin

associated with ATPase, bonding site for ATP, interacts with actin, forms cross bridges

Crossbridges

Link actin and myosin during contraction

Z Disc

anchor actin

Contractile Proteins/Myofilaments

Actin, Myosin

Regulatory proteins

Tropomyosin, Troponin

Tropomyosin

blocks myosin binding site, loosely attached to actin

Troponin

3 polypeptide subunits

Troponin I

which subunit binds to actin

Troponin C

which subunit binds to calcium

Troponin T

which subunit binds to tropomyosin

Titin

elastic structural protein that stabilizes thick filaments

Shortens During Muscle Contraction

H Zone and sarcomere

To Contract A Muscle

Stimulate neuron, Increase calcium, propagate electrical current along sarcolemma

Neuromuscular Junction

Axonal endings contain sacs (synaptic vesicles) of special chemicals

Motor End Plate

part of the sarcolemma that helps form the NMJ

Synaptic Cleft

Space between axonal ends and muscle fibers

Depolarization

inside of membrane becomes less negative than RMP

Repolarization

membrane returns to RMP

Hyperpolarization

inside of membrane becomes more negative than RMP

Depolarization

Na+ gates are opened; K+ gates are closed

Repolarization

Na+ gates close, K+ gates open: K+ exits cell

Hyperpolarization

K+ still open: excessive efflux of K+

High-Energy Configuration

energy from hydrolysis of ATP cocks the myosin head

Power Stroke

myosin head pivots and pulls actin filament toward center of the sarcomere

Roles of ATP During Contraction

energy, release crossbridges, brings intracellular calcium back into the sarcoplasmic reticulum

Ways to Stop Contraction

No nerve impulses, Ach-ase, remove calcium, block myosin binding site, ATP binds to myosin head, ATPase inhibition

All-or-None Principle

Individual muscle fibers contract completely or not at all

Motor Unit

Motor neuron and all the muscle fibers it stimulates

Small Motor Unit

Muscles with precise movements, fine control, fewer fibers per neuron

Large Motor Unit

Gross movements, less precise, many fibers per neuron

Twitch

Response of a muscle to a single, brief threshold stimulus

Phases of Muscle Twitch

Latent, Contraction, Relaxation

Latent Period

period where you would find excitation contraction coupling & Release of calcium in response to nerve stimulation

Contraction Period

period of cross bridge activity & Increase in muscle tension, muscle shortening

Relaxation Period

period when calcium is returned to SR & Muscle tension decreases

Refractory Period

period of temporary lost of excitability where muscle can't respond to stimulus

Complete Tetanus

no relaxation (additive effects of calcium), Maximum frequency reached, no more increase in tension

Incomplete Tetanus

Increase frequency of stimulation more

Heart

this organ cannot achieve tetanus

Temporal Summation

stimuli from one source, 2nd stimulus arrives after refractory period, before end of relaxation; 2nd contraction is greater than 1st (more calcium)

Spatial Summation

stimuli from many sources which occur at same time from different motor units

Recruitment Pattern

recruit small to large

Types of Contraction

Isotonic, Isometric

Isotonic

muscle shortens during contraction, muscle tension is greater than load thus there is movement

Isometric

tension increases but muscle doesn't shorten; load is greater than muscle thus there is no movement

Ways to Generate More ATP

creatine phosphate, glycolysis, oxidative phosphorylation (aerobic respiration)

Aerobic Endurance

length of time a muscle can continue to contract

Anaerobic Threshold

point where muscle metabolism converts to anerobic glycolysis

Muscle Fatigue

inability to contract

Muscle Contraction Force Factors

increase calcium, recruitment, relative muscle size, muscle length

Sarcoplasmic Reticulum

store and release calcium

Agonist

prime mover

Antagonist

opposes movement

Synergist

add/reduces force

Fixators

stabilize muscles`

Aponeuroses

muscles attach to each other or directly to bone

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