Muscle Tissue

Which muscle have the largest mitochondria

Cardiac muscles have the largest

Exposure to clostridium tetani causes continuous release of ACh, what is the effect on smooth muscle

The continuous release of ACh has no effect of this muscle after the introduction of Clostridium Tetani

Competitive weight lifters work to increase the

average number of myofibrils/muscle fibers

In treppe, twitches become progressively ________ because

Twitches become progressively stronger calcium accumulates in the sarcoplasm faster than the sarcoplasmic reticulum can reabsorb it

Sarcolemma of a resting muscle fiber is most permeable to

potassium

Why does cardiac muscle have very little capacity for regenerating

Because it lacks satellite discs

When does skeletal muscle generate the greatest tension?

Skeletal muscle generates the greatest tension when it is partially stretched before being stimulated

What is the function of creatine kinase?

It catalyzes transfer from phosphate from CP to ADP

Deficiency in ACh receptors leads to

muscle paralysis in myasthenia gravis

What is incomplete tetanus?

Incomplete tetanus is if one nerve stimulus arrives at a muscle fiber so soon that the fiber has only partially relaxed from the previous twitch

What is an isotonic contraction?

Shortening of a muscle while maintaining constant tension

In a relaxed muscle fiber, the active sites of the actin are blocked by _______

Tropomyosin

What is the purpose of a triad?

A triad allows for calcium release when the muscle is excited

One somatic neuron is stimulated by ____ muscle fibers?

One somatic neuron is stimulated by zero muscle fibers

A myofilament that connects a thick filament and anchors it into a z disc called an ______ _______

elastic filament

Skeletal muscles depend solely on

the sarcoplasmic reticulum and its calcium source

Smooth muscle contracts and relaxes _____ ______ than skeletal muscle

more slowly

Varicosities release

norepinephrine

What would happen if ACh was inhibited at the synapse?

Tetanus

Collagen is

elastic

What is the smooth ER of a muscle fiber?

Sarcoplasmic reticulum

What are intercalated discs of cardiac muscle?

Numerous gap junctions in muscular tissue

What makes a triad?

two terminal cisternau and one t-tubule make a

The deltoid muscle is

extrinsic

Calcium channel blockers

prevent calcium from entering the smooth muscle, allowing smooth muscle to relax

as a result, blood pressure decreases because the arteries vasodilate

During an isometric contraction, what happens to muscle length?

The muscle length does not change.

The minimum stimulus needed to cause muscle contraction is called

the threshold

The contraction strength of smooth muscle is relatively independent of its resting length partly because

it does not have Z discs.

Muscle fibers are arranged in bundles called

fascicles

Loss of muscle mass from lack of activity is termed

atrophy

Release of ACh

increases permeability of the sarcolemma.

Which muscle(s) can contract without the need for nervous stimulation?

cardiac and smooth muscles can contract without the need for nervous stimulation

Which of the following would be caused by contraction of smooth muscle?

goose bumps

The protein that acts as a calcium receptor in skeletal muscle is

troponin

Where are single-unit smooth muscles found?

most blood vessels and viscera as circular and longitudinal muscles

Periosteum is

NOT a muscle tissue

The ability of the muscle cell to stretch under tension is known as

extensibility

T-tubules are extensions of the _____ in skeletal muscle.

sarcolemma (plasma membrane)

One motor neuron can stimulate up to _____ muscle fiber(s).

1000

Fatigue can be caused by all of the following except

Low acetylcholine supplies
pH imbalance
Excess of myoglobin
Excess of lactic acid
Reduced ATP concentration

excess myoglobin

Myoglobin supplies oxygen for a limited amount of aerobic respiration at onset; it is rapidly depleted

What are the contractile proteins?

Actin
Myosin

Muscle fibers are grouped in bundles called fascicles by which layer of connective tissue?

perimysium

A brief activity using maximum muscular effort (weight-lifting) is fueled best by the

glycogen-lactic acid system (anaerobic)

Smooth muscles lack..

T-tubules

What is the major purpose of the muscular system?

Converting the chemical energy in ATP into the mechanical energy of motion

This connective tissue of the muscle separates neighboring muscles or muscle groups from each other and the subcutaneous tissue

This tissue is made of dense regular connective tissue

Fascia

This layer of connective tissue of muscle forms a fibrous sheath around the entire muscle, is made of denser regular connective tissue

Epimysium; its outer surface grades into the fascia

This layer of connective tissue surround fascicles (bundles of muscle fibers), and carry larger nerves and blood vessels and stretch receptors

Perimysium

This layer of connective tissue of muscle is a thin sleeve of loose connective tissue that surrounds each muscle fiber (cell)
it allows room for capillaries and nerve fibers to reach each muscle fiber

Endomysium

List the layers of connective tissue of muscle from superficial to deep

Fascia
Epimysium
Perimysium
Endomysium

Deep Fascia are found between

adjacent muscles

Superficial fascia, AKA _________ are found between ________________________ and contain _________________

between skin and muscles and contain adipose tissue

Characteristics of tendons

Attachments between muscle and bone
Dense-regular connective tissue composed of collagen fibers
The epimysium surrounding the entire muscle is continuous with collagen fibers of tendons
Which in turn, are continuous with connective tissue (periosteum) of bone

Collagen is somewhat

extensible and elastic

Characteristics of collagen

Collagen stretches slightly under tension and recoils when released
-resists excessive stretching and protects muscle from injury
-returns muscle to its resting length
-contribute to power output and muscle efficiency

What determines the strength of a muscle and the direction of its pull?

Shape and orientation of its fascicles

Fusiform muscles are

thick in the middle and tapered at the ends

Triangular (convergent) muscles are

broad at origin and tapering to a narrower insertion

Parallel muscles have ______ fascicles and ______________________________

parallel fascicles; can span longer distances than other shapes

Circular muscles

are skeletal muscles that act as sphincters, and ring around the body opening

Pennate muscles

fascicles insert obliquely on a tendon (feather shaped)

Tendons attach _____ to ______

muscle to bone

Aponeurosis

tendon is a broad, flat sheet

Which skeletal muscles do not insert on bone, but in dermis of the skin

muscles of facial expression

This type of muscle modifies the direction of movement, stabilizes the nearby joints and aids the prime mover

synergist

This type of muscle prevents excessive movement and injury, relaxes to give the prime mover control over an action

antagonist- also opposes the prime mover

This type of muscle prevents movement of bone

fixator

Intrinsic muscles

contained within a region, both of its origin and insertion are in the same region (phalanges)

Extrinsic muscles

act on a designated region but have orgins elsewhere

Responsiveness (exciteability)

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

Conductivity

local electrical change triggers 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 resting length after being stretched

This muscles is

voluntary
striated
and attached to one or more bones

Skeletal muscle

What are striations a result of?

Overlapping of internal contractile proteins

What is a skeletal muscle made of

muscle cells, called muscle fibers or myofibers

How long are muscle fibers or myofibers of a skeletal muscle?

30 cm long

Myofibers are muscle cells composed of _________ which are composed of _________

myofibrils; myofilaments

Myofibrils are

long protein bundles that occupies the main portion of the interior of a muscle fiber.

They make up myofibers

Myofibrils are composed of myofilaments

Myofilaments make up ______ which make up __________; they are

myofibrils which make up myofibers; they are a protein microfilament responsible for muscle cell contraction

Myofilaments are composed of ______ or ______ proteins

myosin or actin proteins

Sarcolemma

plasma membrane of a muscle fiber

Sarcoplasma

cytoplasm of a muscle fiber

Mitochondria

packed in spaces between myofibrils

Terminal Cisternae

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

T tubule

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

What are the two internal proteins of myofibers?

Glycogen and Myoglobin

Glycogen, an internal protein of myofibers, are

stored in abundance to provide energy with heightened exercise

Myoglobin, an internal protein of myofibers, are

red pigment that stores oxygen needed for muscle activity

Glycogen and myoglobin are long protein bundles that occupy the main portion of the sarcoplasm, AKA ______ that make up ______

internal proteins that make up myofibers

How do myofibers repair?

by fibrosis rather than regeneration of functional muscle

Myofibers are made up of multiple nuclei that are pressed against the inside of the sarcolemma, as well as stem cells that fuse to form each muscle fiber called ______ and unspecializd myoblasts remaining between the muscle fiber and endomysium called _________ ________

myoblasts are stem cells that fuse to form each muscle fiber

satellite cells are unspecialized myoblasts remaining between the muscle fiber and endomysium

The three kinds of myofilaments found in a myofibril are called

Thin, thick and elastic filaments

These are stem cells that fuse to form each muscle fiber

Myoblasts

These are unspecialized myoblasts remaining between the muscle fiber and endomysium

Satellite cells

Thin filaments are found in myofibrils that are made of

myosin protein

Thick filaments are found in myofibrils that are made of

primarily actin proteins

Elastic filaments are found in myofibrils that are made of

titin (connectin) proteins

Thick myofilaments are made of several hundred _________ molecules. Their heads are directed ______ in a helical array around the bundle.

myosin; outward

Thin myofilaments are made of three things:

Fibrous (F) actin
Tropomyosin
and
Troponin complex

Fibrous (F) actin, found in ______ ______, are

found in thin myofilaments, are two intertwined strands, a string of globular (G) actin subunits each with an active site that can bind to head of myosin molecule

Tropomyosin, found in ____ _____________,

thin myofilaments, each block 6 or 7 active sites on G actin subunits

The troponin complex of ______ ________ are

thin myofilaments, are small, calcium-binding proteins on each tropomyosin molecule

Elastic Myofilaments are made of _______ (______)

titin (connectin)

titin (connectin) make up _____ ________ and are characterized as

elastic myofilaments and are characterized by huge springy protein, they flank each thick filament and anchor it to the Z disc, help the cell recoil to its resting length (elastiity), keep thick and thin filaments aligned (help stabilize the thick filament and center it between the thin filaments), and prevent overstretching

The regulatory proteins, _____ and ______, act

tropomyosin and troponin, act like a switch that states and stops contraction

How i contraction activated?

By the release of calcium into sarcoplasm and its binding to troponin

What happens after calcium enters the sarcoplasm and binds to troponin?

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

What are the function of accessory proteins

Accessory proteins of thick and thin filaments act to anchor the myofilaments, regulate length of myofilaments, and align myofilaments for optimal effectiveness

What is the most clinically important accessory protein? What is its function?

Dystrophin – most clinically important
links actin in outermost myofilaments to transmembrane proteins and eventually to fibrous endomysium surrounding the entire muscle cell
transfers forces of muscle contraction to connective tissue around myofiber
genetic defects in dystrophin produce disabling disease muscular dystrophy

Group of hereditary diseases in which skeletal muscles degenerate & are replaced with scar tissue and adipose tissue

Muscular Dystrophy

Fascioscapulohumeral MD is

facial & shoulder muscle only
affects both sexes equally

Myostatin is a protein that limits muscle growth. Some mutations in the gene coding for myostatin can lead to the production of non-functional protein. What would be the phenotypic result of this mutation in a baby?

Baby is abnormally muscular

What is the function of myosin and actin

function in cellular motility, mitosis, transport of intracellular material

A band

– dark – A stands for anisotropic
part of A band where thick and thin filaments overlap is especially dark
H band in the middle of A band – just thick filaments
M is in the middle of the H band

H band

middle of A band- just thick filaments

I band

alternating lighter band-
I= isotropic

Z disc

– provides anchorage for thin filaments and elastic filaments
bisects I band

M is the middle of the

H band

A sarcomere is a

segment of the myofibril from one z disc to the next

functional contractile unit of the muscle fiber

Sarcomere

Muscles shorten when

individual sarcomeres shorten and pull z discs closer to eachother as thick and thin filaments slide past eachother

Segment from Z disc to Z disc

Sarcomere

During muscle contraction, what happens the the thick and thin filaments?

Neither change length during shortening, only the amount of overlap changes

Skeletal muscle must be stimulated by a ______ or it will not contract

nerve

What happens if nerve connections are severed or poisoned, a muscle is _________

paralyzed

Denervation atrophy is

shrinkage of paralyzed muscle when connection not restored

Somatic motor neurons

stimulate skeletal muscle
cell bodies are located in the brainstem and spinal cord

Somatic motor fibers

– axons of somatic motor neurons
lead to the skeletal muscle
each nerve fiber branches out to a number of muscle fibers
200 myofibers on average are controlled by a single somatic motor neuron
each myofiber is supplied by only one motor neuron
one nerve fiber and all the muscle fibers innervated by it is a motor unit

Motor unit=

one nerve fiber and all the muscle fibers innervated by it

Myofibers of one motor unit

dispersed throughout the muscle
contract in unison
produce weak contraction over wide area
provides ability to sustain long-term contraction as motor units take turns contracting
postural control
effective contraction usually requires the contraction of several motor units at once

Average motor unit

200 muscle fibers/neuron

Small motor units

fine degree of control
3-6 muscle fibers per neuron
eye and hand muscles

Where are small motor units found?

Eye and hand muscles

Large motor units have more _______ then _______

strength than control

Large motor units

powerful contractions supplied by large motor units
many muscle fibers per motor unit
gastrocnemius – 1000 myofibers per neuron

Synapse

point where a nerve fiber meets its target cell

Neuromuscular junction (NMJ)

- when target cell is a muscle fiber
each terminal branch of the nerve fiber within the NMJ forms separate synapse with the muscle fiber
one nerve fiber stimulates the muscle fiber at several points within the NMJ

Synaptic knob

swollen end of a nerve fiber

The synaptic knob contains ______ _______ filled with _________

synaptic vesicles filled with acetylcholine (ACh)

Synaptic vesicles undergo _______ releasing ACh into synaptic cleft

exocytosis

Synaptic cleft

- tiny gap between synaptic knob and muscle sarcolemma

Schwann cell

envelops & isolates all of the NMJ from surrounding tissue fluid

How many Ach receptors– proteins are incorporated into muscle cell plasma membrane

50 million

ACh receptors are

junctional folds of sarcolemma
increases surface area holding ACh receptors

The lack of ACh receptors can lead to

paralysis

Basal lamina

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

contains acetylcholinesterase (AChE)

What is acetylcholinesterase (AChE)? Where is it found?

breaks down ACh after contraction causing relaxation, found in the basal lamina

cholinesterase inhibitors

bind to acetylcholinesterase and prevent it from degrading ACh
which leads to spastic paralysis - - a state of continual contraction of the muscles
possible suffocation

Tetanus

(lockjaw) is a form of spastic paralysis caused by toxin of Clostridium tetani
glycine (inhibitory neurotransmitter) in the spinal cord normally stops motor neurons from producing unwanted muscle contractions
tetanus toxin blocks glycine release in the spinal cord and causes overstimulation and spastic paralysis of the muscles

tetanus toxin blocks ____________ release in the spinal cord and causes overstimulation and spastic paralysis of the muscles

glycine

Flaccid paralysis

a state in which the muscles are limp and cannot contract

Curare is an example of

flaccid paralysis; curare – plant poison used by South American natives to poison blowgun darts

In __________ _________, compete with ACh for receptor sites, but do not stimulate the muscles

flaccid paralysis

Botulism occurs wen a bacterium releases a neurotoxin that prevent motor neurons from releaseing Ach. Now which of te following is not an effect of botulism flaccid paralysis

Tetany- muscle gets contracted and cant relax

______ ______ and _______ are electrically excitable cells

muscle fibers and neurons

Electrophysiology

- the study of the electrical activity of cells

In an unstimulated (resting) cell

there are more anions (negative ions) on the inside of the plasma membrane than on the outside
the plasma membrane is electrically polarized(charged)
there are excess sodium ions (Na+) in the extracellular fluid (ECF)
there are excess potassium ions (K+) in the intracellular fluid (ICF)
also in the ICF, there are anions such as proteins, nucleic acids, and phosphates that cannot penetrate the plasma membrane
The inside of the plasma membrane is negatively charged by comparison to its outer surface

Voltage (electrical potential)

a difference in electrical charge from one point to another

Resting membrane potential (RMP) of a myofiber is about _____ ____ and is maintained by

90 mV

maintained by sodium-potassium pump

Slide 10

Muscles part 2

4 major phases of contraction and relaxation

Excitation
Excitation- contraction coupling
Contraction
Relaxation

Excitation

the 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

step in which the muscle fiber develops tension and may shorten

Relaxation

when its work is done, a muscle fiber relaxes and returns to its resting length

Excitation (steps 1 and 2)

Nerve signal opens voltage-gated calcium channels in synaptic knob
Calcium stimulates exocytosis of ACh from synaptic vesicles
ACh released into synaptic cleft

Excitation (steps 3 and 4)

2 ACh molecules bind to each receptor protein, opening Na+ and K+ channels.
Na+ enters shifting RMP goes from -90mV to +75mV, then K+ exits and RMP returns to -90mV
quick voltage shift is called an end-plate potential (EPP)

Excitation (step 5)

Voltage change (EPP) in end-plate region opens nearby voltage-gated channels producing an action potential that spreads over muscle surface

Excitation-Contraction Coupling (steps 6 and 7)

Action potential spreads down into T tubules
Opens voltage-gated ion channels in T tubules and Ca+2 channels in SR
Ca+2 enters the cytosol

Excitation-Contraction Coupling (steps 8 and 9)

Calcium binds to troponin in thin filaments
Troponin-tropomyosin complex changes shape and exposes active sites on actin

Contraction (steps 10 and 11)

Myosin ATPase enzyme in myosin head hydrolyzes an ATP molecule

Activates the head “cocking” it in an extended position
ADP + Pi remain attached

Head binds to actin active site forming a myosin - actin cross-bridge

Contraction (steps 12 and 13)

Myosin head releasesADP and Pi, flexes pullingthin filament past thick - power stroke

Upon binding more ATP, myosin releases actin and process is repeated
each head performs 5 power strokes per second
each stroke utilizes one molecule of ATP

Relaxation (steps 14 and 15)

Nerve stimulation & ACh release stop
AChE breaks down ACh & fragments reabsorbed into synaptic knob
Stimulation by ACh stops

Relaxation (step 16)

Ca+2 pumped back into SR by active transport. Ca+2 binds to calsequestrin while in storage in SR
ATP is needed for muscle relaxation as well as muscle contraction

Relaxation (steps 17 and 18)

Ca+2 removed from troponin is pumped back into SR

Tropomyosin reblocks the active sites

Muscle fiber ceases to produce or maintain tension

Muscle fiber returns to its resting length
due to recoil of elastic components & contraction of antagonistic muscles

Rigor Mortis

hardening of muscles and stiffening of body beginning 3 to 4 hours after death
deteriorating sarcoplasmic reticulum releases Ca+2
deteriorating sarcolemma allows Ca+2 to enter cytosol
Ca+2 activates myosin-actin cross-bridging
muscle contracts, but can not relax

Rigor mortis peaks about ____ hours after death, then diminishes over the next ____ to ____ hours

12; 48-60 hours

What causes no contraction

If signal doesn’t go down neuron
If Ach not present or not released
If Ach cant bind to receptors
If SR doesn’t release Calcium

Length-Tension Relationship

the amount of tension generated by a muscle and the force of contraction depends on how stretched or contracted it was before it was stimulated

Overly contracted

contracted at rest, a weak contraction results
thick filaments too close to Z discs and can’t slide

Too stretched

before stimulated, a weak contraction results
little overlap of thin and thick does not allow for many cross bridges to form

Optimum resting length

produces greatest force when muscle contracts

CNS continually monitors & adjusts length of the resting muscle
maintains a state of partial contraction – muscle tone (tonus)
maintains optimum length and makes the muscles ideally ready for action

Myogram

chart of timing & strength of a muscle contraction

A weak, subthreshold, electrical stimulus causes

no contraction

Threshold

the minimum voltage necessary to generate an action potential in the muscle fiber and produce a contraction

Twitch

a quick cycle of contraction when stimulus is at threshold or higher

Phases of a twitch contraction

latent period
contraction phase
relaxation phase

Latent period

2 msec delay between the onset of stimulus and onset of twitch response
time required for excitation, excitation-contraction coupling and tensing of elastic components of the muscle

internal tension

– force generated during latent period and no shortening of the muscle occurs

Contraction phase

phase in which filaments slide and the muscle shortens

once elastic components are taut, muscle begins to produce external tension – in muscle that moves a load
short-lived phase

Relaxation

last phase of twitch contraction

SR quickly reabsorbs Ca+2, myosin releases the thin filaments and tension declines
muscle returns to resting length
entire twitch lasts from 7 to 100 msec

Subthreshold stimulus

– no contraction at all

Threshold intensity and above

a twitch is produced
twitches caused by increased voltage are no stronger than those at threshold

Muscle Tissue Part 2

Slides 30-36

Myoglobin

supplies oxygen for a limited amount of aerobic respiration at onset
rapidly depleted

Muscles meet most of ATP demand by borrowing ______________ from other molecules and transferring them to ___

phosphate groups; ADP

2 enzyme systems control these phosphate transfers

myokinase
creatinekinase

myokinase

transfers Pi from one ADP to another converting the latter to ATP

creatinekinase

obtains Pi from a phosphate-storage molecule creatine phosphate (CP)
fast-acting system that helps maintain the ATP level while other ATP-generating mechanisms are being activated

Posphagen system

ATP and CP collectively
provides nearly all energy used for short bursts of intense activity
one minute of brisk walking
6 seconds of sprinting or fast swimming
important in activities requiring brief but maximum effort
football, baseball, and weight lifting

As the posphagen system is exhausted..

Muscles shift to ___________ ________________

anaerobic fermentation

During anaerobic fermentation

muscles obtain glucose from blood and their own stored glycogen
in the absence of oxygen, glycolysis can generate a net gain of 2 ATP for every glucose molecule consumed
converts glucose to lactic acid

Glycogen-lactic acid system

the pathway from glycogen to lactic acid
produces enough ATP for 30 – 40 seconds of maximum activity

After ~40 sec

the respiratory and cardiovascular systems “catch up” and deliver oxygen to the muscles fast enough for aerobic respiration to meet most of the ATP demands

During aerobic respiration
___ to ______ ATP/glucose are produce

36 to 38

During aerobic respiration

efficient means of meeting the ATP demands of prolonged exercise
one’s rate of oxygen consumption rises for 3 to 4 minutes and levels off to a steady state in which aerobic ATP production keeps pace with demand
little lactic acid accumulates under steady state conditions
depletion of glycogen and blood glucose, together with the loss of fluid and electrolytes through sweating, set limits on endurance and performance

Muscle fatigue

progressive weakness and loss of contractility from prolonged use of the muscles

Causes of muscle fatigue

ATP synthesis declines as glycogen is consumed
ATP shortage slows down the Na+ - K + pumps
compromises their ability to maintain the resting membrane potential and excitability of the muscle fibers
Lactic acid lowers pH of sarcoplasm
inhibits enzymes involved in contraction, ATP synthesis, and other aspects of muscle function
Release of K+ with each action potential causes the accumulation of extracellular K+
hyperpolarizes the cell and makes the muscle fiber less excitable
Motor nerve fibers use up their ACh
less capable of stimulating muscle fibers – junctional fatigue
Central nervous system fatigues by unknown processes
less signal output to the skeletal muscles

Endurance

the ability to maintain high-intensity exercise for more than 4 to 5 minutes

What determines endurance

determined in large part by one’s maximum O2 uptake(VO2max)

maximum oxygen uptake

the point at which the rate of oxygen consumption reaches a plateau and does not increase further with an added workload

Maximum oxygen uptake characteristics

proportional to body size
peaks at around age 20
usually greater in males than females
can be twice as great in trained endurance athletes as in untrained person
results in twice the ATP production

Oxygen Debt

Heavy breathing continues after strenuous exercise

excess post-exercise oxygen consumption (EPOC)

the difference between the resting rate of oxygen consumption and the elevated rate following exercise

Oxygen Debt is needed

replace oxygen reserves that were depleted in the first minute of exercise

replenishing the phosphagen system

oxidizing lactic acid

serving the elevated metabolic rate

Oral creatine supplement

increases level of creatine phosphate in muscle tissue and increases speed of ATP regeneration

useful in burst type exercises – weight-lifting

Carbohydrate loading

dietary regimen
packs extra glycogen into muscle cells
extra glycogen is hydrophilic and adds 2.7 g water/ g glycogen
some athletes feel sense of heaviness outweighs benefits of extra available glycogen

Fatigue can be caused by all of the following except

Low acetylcholine supplies
pH imbalance
Excess of myoglobin
Excess of lactic acid
Reduced ATP concentration

excess myoglobin

Slow oxidative (SO), slow-twitch, red, or type I fibers

“dark meat”
abundant mitochondria, myoglobin and capillaries - deep red color
adapted for aerobic respiration and fatigue resistance
relative long twitch lasting about 100 msec
soleus of calf and postural muscles of the back

Fast glycolytic (FG), fast-twitch, white, or type II fibers

“white meat”
fibers are well adapted for quick responses, but not for fatigue resistance
rich in enzymes of phosphagen and glycogen-lactic acid systems
generate lactic acid causing fatigue
less mitochondria, myoglobin, and blood capillaries which gives paler appearance
SR releases & reabsorbs Ca+2 quickly so contractions are quicker
(7.5 msec/twitch)
extrinsic eye muscles, gastrocnemius and biceps brachii

You would expect a body-builder to have more _______ muscle fibers than a marathon runner. Slow oxidative fibersFast glycolytic fibers

Fast- glycolytic fibers

A single muscle has both

FG and SO muscle fibers but differ in ratio

Ratio of different fiber types have

genetic predisposition

gastrocnemius is predominantly
___ for quick movements

FG

soleus is predominantly _____ used for endurance (jogging)

SO

Muscular strength depends primarily on

muscle size

fascicle arrangement
vs
strength

pennate are stronger than parallel, and parallel stronger than circular

Size of motor units

vs strength

larger the motor unit the stronger the contraction

multiple motor unit summation – recruitment

vs strength

when stronger contraction is required, the nervous system activates more motor units

temporal summation

nerve impulses usually arrive at a muscle in a series of closely spaced action potentials
the greater the stimulation frequency, the more strongly a muscle contracts

length – tension relationship

a muscle resting at optimal length is prepared to contract more forcefully than a muscle that is excessively contracted or stretched

Resistance training (weight lifting)

contraction of a muscles against a load that resist movement
a few minutes of resistance exercise a few times a week is enough to stimulate muscle growth
growth is from cellular enlargement
muscle fibers synthesize more myofilaments and myofibrils and grow thicker

Endurance training (aerobic exercise)

improves fatigue resistant muscles
slow twitch fibers produce more mitochondria, glycogen, and acquire a greater density of blood capillaries
improves skeletal strength
increases the red blood cell count and oxygen transport capacity of the blood
enhances the function of the cardiovascular, respiratory, and nervous systems

Required properties of cardiac muscle

contraction with regular rhythm

muscle cells of each chamber must contract in unison

contractions must last long enough to expel blood

must work in sleep or wakefulness, with out fail, and without conscious attention

must be highly resistant to fatigue

Characteristics of cardiac muscle cells

Striated (like skeletal muscle)
Myocytes (cardiocytes or cardiomyocytes) are shorter and thicker

Each myocyte is joined to several others at the uneven, notched linkages – intercalated discs
appear as thick dark lines in stained tissue sections
electrical gap junctions allow each myocyte to directly stimulate its neighbors
mechanical junctions that keep the myocytes from pulling apart

Sarcoplasmic reticulum less developed, but T tubules are larger and admit supplemental Ca2+ from the extracellular fluid

Damaged cardiac muscle cells repair by fibrosis
a little mitosis observed following heart attacks
not in significant amounts to regenerate functional muscle

_________ stimulation
contains a built-in __________ that rhythmically sets off a wave of electrical excitation
wave travels through the muscle and triggers ___________ of heart chambers
___________ – because of its ability to contract rhythmically and independently

Can contract without need for nervous stimulation
contains a built-in pacemaker that rhythmically sets off a wave of electrical excitation
wave travels through the muscle and triggers contraction of heart chambers
autorhythmic – because of its ability to contract rhythmically and independently

Autonomic nervous system (ANS) does send ______fibers to the heart
can increase or decrease heart rate and contraction strength

nerve

Smooth muscle twitches are

Very slow twitches - does not exhibit quick twitches like skeletal muscle
maintains tension for about 200 to 250 msec
gives the heart time to expel blood

Cardiac muscle uses __________ respiration

aerobic respiration almost exclusively

rich in myoglobin and glycogen
has especially large mitochondria
25% of volume of cardiac muscle cell
2% of skeletal muscle cell with smaller mitochondria

Cardiac muscle

Very adaptable with respect to fuel used

Very vulnerable to interruptions of __________ ____________

Highly ________ resistant

Very adaptable with respect to fuel used

Very vulnerable to interruptions of oxygen supply

Highly fatigue resistant

Smooth muscle

Composed of ________ that have a ________ shape

myocytes, fusiform

if injured smooth muscle

Smooth muscle

Capable of mitosis and hyperplasia

regenerates well

Some smooth muscles lack ______ ________, while others receive ________ fibers, not ________ motor fibers as in skeletal muscle

Some smooth muscles lack nerve supply, while others receive autonomic fibers, not somatic motor fibers as in skeletal muscle

________ needed for muscle contraction comes from the _______ by way of ____________ channels in the sarcolemma

calcium; ECF; calcium

Sarcoplasmic reticulum of smooth muscle have no

T tubules

Intermediate filaments in the cytoplasm of smooth muscle provide

mechanical linkages between the thin myofilaments and the plasma membrane

In smooth muscle, Z discs

are absent and replaced by protein plaques well ordered array of protein masses in cytoplasm
dense bodies on the inner face of the plasma membrane

Smooth muscle,
are named smooth muscle because

reason for the name ‘smooth muscle’
thick and thin filaments are present, but not aligned with each other

Multiunit smooth muscle

occurs in

some of the largest arteries and pulmonary air passages, in piloerector muscles of hair follicle, and in the iris of the eye

Multiunit smooth muscle have a autonomic innervation

similar to skeletal muscle
terminal branches of a nerve fiber synapse with individual myocytes and form a motor unit
each motor unit contracts independently of the others

Single-unit smooth muscle
are more widespread, and occur in

most blood vessels, in the digestive, respiratory, urinary, and reproductive tracts – also called visceral muscle
often in two layers
inner circular
outer longitudinal

Single-unit smooth muscle

myocytes of this cell type are electrically coupled to each other by

gap junctions

Single-unit smooth muscle

directly stimulate each other

and a large number of cells contract as a single unit

Smooth muscle is involuntary and can contract without __________ ____________

nervous stimulation

Most smooth muscle is innervated by

autonomic nerve fibers

stimulate smooth muscle with either _______ or _________

stimulate smooth muscle with either acetylcholine or norepinephrine

In single unit smooth, each autonomic nerve fibers has up to 20,000 beadlike swelling called ________________

In single unit smooth, each autonomic nerve fibers has up to 20,000 beadlike swelling called varicosities

Each varicosity of smooth muscle contains

each contains synaptic vesicles and a few mitochondria
nerve fiber passes amid several myocytes and stimulates all of them at once when it releases its neurotransmitter
diffuse junctions – no motor end plates; receptors scattered throughout surface
no one-to-one relationship between nerve fiber and myocyte

Contraction is triggered by

Contraction is triggered by Ca+2, energized by ATP, and achieved by sliding thin past thick filaments

During contraction and relaxation Calcium binds to __________ on thick filaments

Calcium binds to calmodulin on thick filaments

Calcium binds to calmodulin on thick filaments, myosin light-chain kinase is activated
adds phosphate to regulatory protein on myosin head
activates myosin ________ - hydrolyzes ATP
enables myosin similar power and recovery strokes like skeletal muscle

Calcium binds to calmodulin on thick filaments, myosin light-chain kinase is activated
adds phosphate to regulatory protein on myosin head
activates myosin ATPase - hydrolyzes ATP
enables myosin similar power and recovery strokes like skeletal muscle
thick filaments pull on thin ones, thin ones pull on dense bodies and membrane plaques
force is transferred to plasma membrane and entire cell shortens
puckers and twists like someone wringing out a wet towel

Contraction and relaxation of smooth muscle are very different in comparison to skeletal muscle

latent period in skeletal 2 msec, smooth muscle __ - ___ msec
tension peaks at about ___ msec (0.5 sec)
declines over a period of _____-_____seconds
slows myosin ATPase enzyme and slow pumps that remove Ca+2
Ca+2 binds to calmodulin instead of __________
activates kinases and ATPases that hydrolyze ATP

latent period in skeletal 2 msec, smooth muscle 50 - 100 msec
tension peaks at about 500 msec (0.5 sec)
declines over a period of 1 – 2 seconds
slows myosin ATPase enzyme and slow pumps that remove Ca+2
Ca+2 binds to calmodulin instead of troponin
activates kinases and ATPases that hydrolyze ATP

latch-bridge mechanism

latch-bridge mechanism is resistant to fatigue
heads of myosin molecules do not detach from actin immediately
do not consume any more ATP
maintains tetanus tonic contraction (smooth muscle tone)
arteries – vasomotor tone; intestinal tone; bladder tone
makes most of its ATP aerobically

Stretching smooth muscle

can open mechanically-gated calcium channels in the sarcolemma causing contraction

peristalsis

waves of contraction brought about by food distending the esophagus or feces distending the colon
propels contents along the organ

Stress-relaxation response

(receptive relaxation) -helps hollow organs gradually fill (urinary bladder)
when stretched, tissue briefly contracts then relaxes – helps prevent emptying while filling

Skeletal muscle cannot contract forcefully if ________________

Skeletal muscle cannot contract forcefully if overstretched

Smooth muscle contracts forcefully ____________________________ this
allows hollow organs such as the stomach and bladder to fill and then expel their contents efficiently

Smooth muscle contracts forcefully even when greatly stretched
allows hollow organs such as the stomach and bladder to fill and then expel their contents efficiently

Smooth muscle can be anywhere from _________ to __________ its resting length and still contract powerfully

Smooth muscle can be anywhere from half to twice its resting length and still contract powerfully

Smooth muscle can be anywhere from half to twice its resting length and still contract powerfully

3 reasons:
there are no _____ _______, so thick filaments cannot butt against them and stop contraction
since the thick and thin filaments are not arranged in orderly sarcomeres, stretching does not cause a situation where there is too little overlap for cross-bridges to form
the thick filaments of smooth muscle have myosin heads along their entire length, so cross-bridges can form anywhere

Smooth muscle contracts forcefully even when greatly stretched
allows hollow organs such as the stomach and bladder to fill and then expel their contents efficiently

Smooth muscle can be anywhere from half to twice its resting length and still contract powerfully

3 reasons:
there are no z discs, so thick filaments cannot butt against them and stop contraction
since the thick and thin filaments are not arranged in orderly sarcomeres, stretching does not cause a situation where there is too little overlap for cross-bridges to form
the thick filaments of smooth muscle have myosin heads along their entire length, so cross-bridges can form anywhere

plasticity

the ability to adjust its tension to the degree of stretch
a hollow organ such as the bladder can be greatly stretched yet not become flabby when it is empty

Myasthenia GravisAutoimmune disease in which antibodies attack neuromuscular junctions and bind ACh receptors together in clusters
disease mainly of women between 20 and 40
muscle fibers then remove the clusters of receptors from the sarcolemma by endocytosis
fiber becomes less and less sensitive to ACh
effects usually first appear in facial muscles
drooping eyelids and double vision, difficulty swallowing, and weakness of the limbs

Myasthenia Gravis

Strabismus

inability to fixate on the same point with both eyes

Which of the following would NOT occur as a result of living in near zer-gravty conditions?
Bone loss
Cardiac muscle atrophy
Joint luxation
Skeletal muscle atrophy

Joint luxation (dislocation)

- zero gravity does not take much effort for your muscles to do work, they don’t have stress on them, they instead are not being stressed and bone loss results from inactivity, the heart does not work as hard either and the heart muscle weakens

Treatments for myasthenia gravis

cholinesterase inhibitors retard breakdown of ACh allowing it to stimulate the muscle longer
Immunosuppressive agents suppress the production of antibodies that destroy ACh receptors
thymus removal (tymectomy) – helps to dampen the overactive immune response that causes myasthenia gravis
plasmapheresis –technique to remove harmful antibodies from blood plasma

cholinesterase inhibitors

retard breakdown of ACh allowing it to stimulate the muscle longer

Immunosuppressive agents

suppress the production of antibodies that destroy ACh receptors

thymus removal (tymectomy)

helps to dampen the overactive immune response that causes myasthenia gravis

plasmapheresis

technique to remove harmful antibodies from blood plasma

You would expect a body-builder to have more _______ muscle fibers than a marathon runner. Slow oxidative fibersFast glycolytic fibers

Fast- glycolytic fibers