Slides power point

Excitability (responsiveness)

to chemical signals, stretch, and electrical changes across the plasma membrane

Conductivity

local electrical excitation sets off 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; results from arrangement of internal contractile proteins

Voluntary

usually subject to conscious control ( the other muscle types are involuntary)

What can skeletal muscles also be called?

muscle fibers or myofibers

What kind of tissue does skeletal muscle contain?

fibrous connective

Endomysium

surrounds each muscle fiber

Perimysium

bundles muscle fibers into fascicles

fascicles

surrounded by perimysium

epimysium

surrounds entire muscle

Collagen is somewhat…

extensible and elastic

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

Where is myofibrils, glycogen, and myoglobin?

in the sarcoplasm

Sarcoplasmic reticulum

smooth ER that forms a network around each myofibril

Terminal cisterns

dilated end-sacs of sarcoplasmic reticulum which cross the muscle fiber from one side to another

Terminal cisterns are reservoirs for what?

calcium

Within cisterns, calcium is bound to what protein?

calsequestrin

Transverse tubules

tubular infolding of the sarcolemma which penetrate through the cell and emerge on the other side

Components of t tubules

two terminal cisterns associated with it on either side

Triad

A T tubule and two terminal cisterns

Myoblasts

stem cells that fused to form each muscle fiber early in development, each contributing one nucleus

Satellite cells

unspecialzed myoblasts remaining between the muscle fiber and endomysium

What do Satellite cells play a role in?

regeneration of damaged skeletal muscle tissue

Three kinds of filaments

thin, thick, and elastic

Thin filaments

made of several hundred myosin molecules

What is myosin?

A motor protein

What are thick filaments shaped like?

golf clubs

Thin filaments

composed of three different protein types

Thin filaments protein types

fibrous actin, tropomyosin, and troponin

Fibrous actin

two intertwined strands of globular (G) actin subunits, each with an active site that can bind to head of myosin molecule

Tropomyosin

each blocks six or seven active sites on G actin subunits

Troponin

small, calcium-binding protein on each tropomyosin molecule

Elastic filaments

made of hinge spongy protein called titan

What does titin do?

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

What do tropomyosin and troponin act as?

regulatory proteins

A bands

dark band

H band

not as dark; middle of A band; thick filaments only

M line

dark, transverse protein in middle of H band

I band

light band

Z disc

protein complex that provides anchorage for thin filaments and elastic filaments

Sarcomere

segment from Z disc to Z disc; functional contractile unit of muscle fiber

Skeletal muscles cannot contact…

Unless stimulated by a nerve

Denervation atrophy

shrinkage of paralyzed muscle when nerve remains disconnected

Motor Unit

one nerve fiber and all the muscle fibers innervated by it; they behave as a functional unit

Small motor units

provide a fine degree of control (ex. eyes and hands)

Large motor units

provide more strength than control

Synapse

point where a nerve fiber meets its target cell

What is it called when a target cell is a muscle fiber, a synapse

neuromuscular junction or motor end plate

Axon terminal

swollen end of nerve fiber

Synaptic cleft

narrow gap between axon terminal and sarcolemma

Postsynaptic membrane folds…

of sarcolemma increase surface area, maximize number of ACh receptors

What is NMJ enclosed in?

basal lamina

Basal lamina

thin layer of collagen and glycoprotein separating muscle fiber and nerve ending from surrounding connective tissue

What do sarcolemma and laminate with synaptic cleft contain?

acetylcholinesterase

Electrophysiology

the study of the electrical activity of cells

membrane is polarized

contains a net negative charge

ICF has what

more potassium ions

ECF has what

more sodium ions

Synaptic paralysis

a state of continual contraction of the muscles; possible suffocations

Tetanus

is a form of spastic paralysis caused by toxin Clostridium tetani

Flaccid paralysis

a state in which the muscles are limp and cannot contract

Curare

competes with ACh for receptor sites, but does not stimulate the muscles

Botulism

type of food poisoning caused by a neuromuscular toxin secreted by the bacterium Clostridium botulinum

Excitation

action potentials in motor nerve fiber lead to AP in the muscle fiber

Excitation-contraction coupling

events that link the AP on the sarcolemma to activation of myofilaments, thereby preparing them to contract

Contraction

the 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

Anaerobic threshold

point at which lactate becomes detectable in the blood

Glycogen lactate system

the pathway from glycogen to lactate

Short term energy

anaerobic threshold and glycogen lactate system

In long term energy aerobic respiration produces…

more ATP per glucose than glycolysis does

Myocytes

not as long and fibrous as skeletal muscles

Intercalated discs

cardiomyocytes branch and join to other cells at connections

What does smooth muscles form?

layers within walls of hallow organs

Myocyte structure

fusiform shape, single nucleus, thick and thin filaments present

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 kind ACh receptors together in clusters