Muscle A and P (1)

Movement

is a fundamental characteristic of all living organisms

Skeletal, Cardiac, Smooth muscle

What are the three types of muscular tissue

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

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Muscle, Fascicle, Muscle Fiber, Myofibril, Sacromere, Myofilaments

What is the Structural Hierarchy of Skeletal Muscle

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

Endomysium

connective tissue around muscle cell

Perimysium

connective tissue around muscle fascicle

Epimysium

connective tissue surrounding entire muscle

Sarcolemma

(Muscle fiber)

plasma membrane of a muscle fiber

Sarcoplasm

(Muscle Fiber)

cytoplasm of a muscle fiber

Myofibrils

(Muscle Fiber)

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

Myoblasts (muscle fiber)

stem cells that fused to form each muscle fiber early in development

Satellite cells

(muscle fiber)

unspecialized myoblasts remaining between the muscle fiber and endomysium

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\-Play a role in regeneration of damaged skeletal muscle tissue

Mitochondria

packed into spaces between myofibrils

Multiple nuclei

flattened nuclei pressed against the inside of the sarcolemma

Sarcoplasmic reticulum (SR)

smooth ER that forms a network around each myofibril:

Terminal cisterns

dilated end-sacs of SR which cross the muscle fiber from one side to the other

\- Acts as a calcium reservoir; it releases calcium through channels to activate contraction

T tubules

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

Triad

a T tubule and two terminal cisterns associated with it

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Sarcomere

segment from Z disc to Z disc

Sarcomere

\-Functional contractile unit of muscle fiber

- Muscle cells shorten because their individual sarcomeres shorten

-Z disc (Z lines) are pulled closer together as thick and thin filaments slide past each other

Sarcomere

Neither thick nor thin filaments change length during shortening

\-Only the amount of overlap changes

During shortening of Sarcomere

\-dystrophin and linking proteins also pull on extracellular proteins

Transfers pull to extracellular tissue

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Myofilaments

Thick filaments—made of several hundred myosin molecules

Myofilaments

\-Two chains intertwined

\- Double globular head

\-Heads on one half of the thick filament angle to the left, while heads on other half angle to the right

\- Bare zone

(Thin Filament)- Myofilament

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Fibrous (F) actin

\-two intertwined strands

\-String of globular (G) actin subunits each with an active site that can bind to head of myosin molecule

(Thin Filament)-Myofilament

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Tropomyosin molecules

\-Each blocking six or seven active sites on G actin subunits

(Thin Filament)- Myofilament

Troponin molecule

small, calcium-binding protein on each tropomyosin molecule

(Elastic Filament)- Myofilament

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Titin

huge, springy protein

\-Run through core of thin filament and anchor it to Z disc and M line

\- Help stabilize and position the thick filament

\- Prevent overstretching and provide recoil

(Myofilament)

Contractile proteins

myosin and actin do the work of contraction

(Myofilament)

Regulatory proteins

tropomyosin and troponin - Act like a switch that determines when fiber can (and cannot) contract

Contraction activated by:

\-release of calcium into sarcoplasm and its binding to troponin

-Troponin changes shape and moves tropomyosin off the active sites on actin

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Contracted

Rest length

Stretched

(Myofilament)

Dystrophin

clinically important protein

(Myofilament)

Dystrophin

\- Links actin in outermost myofilaments to membrane proteins that link to endomysium

-Transfers forces of muscle contraction to connective tissue ultimately leading to tendon

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Striations

result from the precise organization of myosin and actin in cardiac and skeletal muscle cells

Z disc

provides anchorage for thin filaments and elastic filaments

YES

Does a Skeletal muscle cannot contract unless stimulated by a nerve

Denervation atrophy

shrinkage of paralyzed muscle when nerve remains disconnected

Somatic motor neurons

Nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles

Somatic motor fibers

their axons that lead to the skeletal muscle

YES

Is Each muscle fiber is supplied by only one motor neuron

Motor unit

one nerve fiber and all the muscle fibers innervated by it

Muscle fibers of one motor unit:

\-Provide ability to sustain long-term contraction as motor units take turns contracting

\-Dispersed throughout muscle

\-Effective contraction usually requires contraction of several motor units at once

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200

How many muscle fibers does the average motor unit contain

Small motor units

fine degree of control

\- Three to six muscle fibers per neuron - Eye and hand muscles

Large motor units

more strength than control

\-Powerful contractions supplied by large motor units with hundreds of fibers - Quadriceps femoris and gastrocnemius have 1,000 muscle fibers per neuron

Synapse

point where a nerve fiber meets its target cell

Neuromuscular junction (NMJ)

when target cell is a muscle fiber

Axon terminal

swollen end of nerve fiber

-Contains synaptic vesicles with acetylcholine (ACh)

Synaptic cleft

gap between axon terminal and sarcolemma

Schwann cells

envelope and isolate NMJ

YES

Does the Nerve impulse causes synaptic vesicles to undergo exocytosis releasing Ach (acetylcholine) into synaptic cleft

YES

Does the muscle cells have millions of ACh receptors

Basal lamina

thin layer of collagen and glycoprotein separating Schwann cell and muscle cell from surrounding tissues

YES

Are muscle fibers and neurons are excitability excitable

YES

Does the Their membranes exhibit voltage changes in response to stimulation

Voltage (electrical potential)

a difference in electrical charge from one point to another

Resting membrane potential

\-about −90 mV in skeletal muscle cells -Maintained by sodium–potassium pump

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In an unstimulated (resting) cell

There are more anions (negatively charged particles) on the inside of the membrane than on the outside

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\-These anions make the inside of the
plasma membrane negatively charged
by comparison to its outer surface

In an unstimulated (resting) cell

The plasma membrane is electrically polarized (charged) with a negative resting membrane potential (RMP)

In an unstimulated (resting) cell

There are excess sodium ions (Na+) in the extracellular fluid (ECF)

In an unstimulated (resting) cell

There are excess potassium ions (K+) \n in the intracellular fluid (ICF

In a stimulated (active) muscle fiber or nerve cell

1. Na+ ion gates open in the plasma
membrane
2. Na+ flows into cell down its electrochemical
gradient

In a stimulated (active) muscle fiber or nerve cel

3. These cations override the negative
charges in the ICF
4. Depolarization: inside of plasma membrane
becomes positive

In a stimulated (active) muscle fiber or nerve cell

5. Immediately, Na+ gates close and K+ gates
open
6. K+ rushes out of cell partly repelled by
positive sodium charge and partly because
of its concentration gradient
7. Loss of positive potassium ions turns the
membrane negative again (repolarization

A resting membrane potential

s seen in a waiting excitable cell,

action potential

is a quick event seen in a stimulated excitable cell

An action potential

perpetuates itself down the length of a cell’s membrane

Toxins

interfering with synaptic function can paralyze muscles

pesticides

contain cholinesterase inhibitors

pesticides

Bind to acetylcholinesterase and prevent it from degrading ACh

Spastic paralysis

a state of continual contraction of the muscles; possible suffocation

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Tetanus

(lockjaw) is a form of spastic paralysis caused by toxin Clostridium tetani

Tetanus

Does the Glycine in the spinal cord normally stops motor neurons from producing unwanted muscle contractions

YES

Does Tetanus toxin blocks glycine release in the spinal cord and causes overstimulation and spastic paralysis of the muscles

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

a process in which nerve action potentials lead to muscle action potentials

Excitation–contraction coupling

events that link the action potentials on the sarcolemma to activation of the 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

The Length–Tension Relationship and Muscle Tone

the amount of tension generated by a muscle depends on how stretched or shortened it was before it was stimulated

If overly shortened before stimulated

a weak contraction results, as thick filaments just butt against Z discs

If too stretched before stimulated,

a weak contraction results, as minimal overlap between thick and thin filaments results in minimal cross-bridge formation

Optimum resting length

produces greatest force when muscle contracts

Rigor mortis

hardening of muscles and stiffening of
body beginning 3–4 hr after death


1. Deteriorating sarcoplasmic reticulum releases Ca+2
and deteriorating sarcolemma allows Ca+2 to enter
cytosol
2. Ca+2 activates myosin–actin cross-bridging
3. Muscle contracts, but cannot relax