chapter 10

J

"A" band

G

"I" band

Mitochondrial activity in skeletal muscle cells are usually efficient, but can have limited

ATP production if there is limited O2 availability

C

Axon collateral

Skeletal muscle is

voluntarily controlled.

Aponeurosis is a

wide and flat tendon.

G

Nucleus

C

Epimysium

E

Fascicle

I

Filaments

I

H zone

c

Incomplete tetanus (unfused tetanus)

D

M line

When cross-bridges bind to the active site of actin thin filaments (myosin binding site), the thick filaments pivot toward the

M line.

B

Mitochondrion

D

Muscle fiber or muscle cell

F

Muscle fiber or muscle cell

A

Myofibril

G

Myofibrils

The protein of M line is

Myomesin.

B

Perimysium

F

SR

H

Sarcolemma

L

Sarcolemma

F

Sarcomere

J

Sarcomere

K

Sarcoplasm

E

Skeletal muscle fiber

D

Somatic motor neuron

A

Tendon

E

Terminal cistern

Cori cycle is

a cycle in the liver in which the lactic acid is converted to pyruvic acid and glucose.

An action potential or a (depolarization) or a (nerve impulse) is required for the SR releases Ca2+ into sarcoplasm because when an action potential travels along the T. Tubule to open the voltage-gated Ca2+ channel allows

a large amount of calcium flow out of the SR.

Endomysium is the delicate connective tissue that surrounds the individual muscle fiber and contains

a large capillary network.

Incomplete tetanus (unfused tetanus):

a muscle producing peak tension with rapid cycles of contraction and relaxation.

Complete tetanus (fused tetanus):

a muscle that is stimulated so frequently that the relaxation phase is completely eliminated

Each thin filament consists of

a pair of protein actin strands wound together into a helix.

The refractory period is

a period that the muscle fiber loses its excitability and cannot response to a second stimulus.

A myogram is

a record of muscle contraction.

Treppe is the increased strength of a contraction that occurs when

a second stimulus arrives after the muscle fiber has relaxed completely following the previous stimulus.

Twitch is a brief contraction of all muscle fibers in a motor unit in response to

a single action potential moving down the somatic motor neuron.

Each skeletal muscle fiber is controlled by a neuron at

a single neuromuscular junction.

Muscle tone is

a small amount of tension in the muscle at rest due to weak, involuntary contractions of its motor units.

Motor unit is a term that describes

a somatic motor neuron and all the skeletal muscle fibers it stimulates.

Flaccid is

a state of limpness in which muscle tone is lost.

A T-tubule and two terminal cisterns on either side form

a triad.

In summary, in order to form crossbridges:

a. ATP must be broken down by enzyme ATPase b. Calcium ions must be present in the sarcoplasm c. Myosin binding sites (actin active site) must be exposed

Major functions of smooth muscle:

a. Altering the diameter of the respiratory passageways b. Moving food materials along the digestive tract c. Moving sperms in the male reproductive tract and oocytes in the uterine tract d. Expelling fetus by contraction of the wall of the uterus e. Acting as a sphincter

Four properties of muscle tissues are

a. Electrical excitability b. Contractility c. Extensibility [property of muscle gives it the ability to stretch without damage] d. Elasticity [property of muscle gives it the ability to recoil]

The factors that lead to muscle fatigue include:

a. Inadequate release of calcium ions from the SR b. Depletion of creatine phosphate c. Insufficient oxygen d. Depletion of glycogen and other nutrients e. Buildup lactic acid f. Failure of action potentials in the motor neurons to release enough Ach

Fast fibers: Fast glycolytic fibers (FG)

a. Large diameter b. Produces powerful contraction c. Less resistant to fatigue d. Glycolytic fiber: fast fibers have fewer mitochondria and large of glycogen reserves and that why it uses anaerobic respiration e. low concentration of myoglobin (White meat)

Activities during aerobic endurance:

a. Most of the muscle's energy is produced in mitochondria b. Krebs cycle is a main source of ATP (36 ATPs) c. No oxygen debt d. Oxygen is required e. Dependent on slow oxidative fibers f. Fatigue resistant (sustained contraction for hours)

Muscle has three ways to produce ATP:

a. Producing ATP from creatine phosphate by direct phosphorylation b. Producing ATP from anaerobic glycolysis c. Producing aerobic respiration

Major functions of skeletal muscle include

a. Producing body movement and storing nutrients as glycogen, proteins b. Maintaining posture (upright position) c. Generating heat d. Controlling entrance and exit

Slow fibers: Slow oxidative fiber (SO)

a. Small diameter b. MOST resistant to fatigue c. Oxidative fibers have many mitochondria. That is a reason why they use aerobic respiration. d. high concentration of myoglobin (Red meat) e. Produce slow contraction

Major characteristics of smooth muscle cells:

a. Smooth muscle cells are uninucleate b. Smooth muscles lack sarcomeres c. Thin filaments are attached to dense bodies d. Transmitting the contractile forces from cell to cell throughout the muscle tissue. e. Involuntary control (pacesetter cells)

The contraction cycle includes:

a. Step 1: Myosin head hydrolyses ATP and become energized and oriented b. Step 2: Myosin head binds to actin , forming the cross bridge c. Step 3: Myosin head pivots, pulling the thin filament past the thick filament toward center of the sarcomere (power stroke) d. Step 4 : Another ATP binds attches to the cross bridge, myosin head detaches from actin. Then the cycle repeats

Myasthenia Gravis is

an autoimmune disorder that targets the ACh receptors at the NMJ and ultimately reduces the number of available receptors. Treat the patient with a drug that inhibits the activity of acetylcholinesterase will increase contraction.

Creatine phosphate acts as

an energy reserves in muscle tissue.

Spasticity is

an increased muscle tone associated with an increase in tendon reflexes.

Rigidity is

an increased muscle tone in which tendon reflexes are not affected (tetanus).

Skeletal muscle cells that have more than one nucleus

are large and run parallel to each other.

A

axon terminal

In skeletal muscles, the combined amounts of creatine phosphate and ATP provide enough energy for the muscle to

contract maximally for approximately 15 seconds.

H

Thick filaments

C

Thick myosin filament

B

Thin actin filament

I

Thin filament

Actin and myosin are

contractile proteins of the muscle fiber.

E

Titin

D

Transcerse tubule

a

Treppe

C

Triad

b

Wave summation

Hypotonia refers to

decreased or lost muscle tone.

Nebulin is a long, non-elastic protein wrapped around the entire length of

each thin filament.

The sequence of events that links excitation (generation an action potential) to the contraction is called

excitation-contraction coupling.

The ratio of motor neurons to muscle fiber is the greatest in muscles that control the

eye and the tongue.

In sarcomere, thick and thin filaments are linked laterally by

filaments of the M line.

Cardiac muscle cells also are connected to each other via

gap junctions.

Like cardiac muscle cells, some smooth muscle cells communicate via

gap junctions.

Sarcoplasm stores

glycogen and myoglobin, a red-colored protein that binds O2.

After the fusion of myoblasts, the muscle fiber loses its ability to

go through mitosis

Hypertonia refers to

increased muscle tone.

Recruitment is the increase in muscle tension that is produced by

increasing the number of active motor units.

Both cardiac and smooth muscle tissue are

involuntary and auto-rhythmic.

During the refractory period, additional oxygen is required to

metabolize the lactic acid produced during exercise.

Myosin is the main component of the thick filament and functions as a

motor protein of muscle tissue.

There are approximately 40 million receptors for Ach that are found in the

motor-end -plate.

Receptors for acetylcholine are located on the

motor-end plate (the region of the sarcolemma opposite the synaptic end)

Myofibrils are contractile organelles of

muscle cell.

When energy reserves in a muscle are exhausted and lactic acid levels increase,

muscle fatigue occurs.

Sarcolemma is plasma membrane of a

muscle fiber (muscle cell)

Myoblast is embryonic cell (stem cell) that forms

muscle fiber.

Sarcoplasm is the cytoplasm of a

muscle fiber.

Transverse tubules or T tubules are tunnels in from the surface toward the center of each

muscle fiber.

Rigor mortis is a condition in which

muscles are in a state of rigidity 3-4 hour after death and last about 24 hours.

Aerobic respiration supplies enough ATP for

muscles during periods of rest or moderate exercises (running, jogging, swimming, and walking)

Anaerobic glycolysis supplies enough ATP for

muscles for two minutes of maximal activity.

Sarcomere is the basic functional unit of a

myofibril of a skeletal muscle fiber.

Sarcoplasmic reticulum (SR) is the series of membraneous channels that surround each

myofibril.

Microfilaments are smaller proteins within

myofibrils.

The part of the titin that extends from the Z disc is very elastic. Thus, titin accounts for much of the elasticity and extensibility of

myofibrils.

ATP hydrolysis reaction energizes the

myosin head.

Active sites on the actin thin filament become available (exposed) for binding when calcium ion binds to troponin subunit. Once calcium ion binds to troponin, troponin then moves tropomyosin away from the

myosin-binding sites of thin filament.

Somatic motor neurons (voluntary control) provide

nerve impulses that stimulate skeletal muscle to contract.

Perimysium is a fibrous connective tissue that covers each fascicle of muscle and contains

nerves and blood vessels that service the muscle fibers

To generate an action potential, acetylcholine (Ach), a neurotransmitter must be released at the

neuromuscular junction (NMJ)

Synaptic cleft is the narrow space between the

neuron and the muscle fiber.

The cytoplasm of the synaptic terminal at NMJ contains mitochondria and vesicles filled with

neurotransmitter acetylcholine

In single-unit smooth muscle tissue, action potentials are initiated in response to

neurotransmitters, hormones, or an auto-rhythmic signal. The action potential spreads throughout the tissue by moving through gap junctions that connect all the muscle cells together within the tissue.

Cardiac muscle cells usually have

only one, sometimes two, centrally located nuclei and are branched.

At peak levels of exertion, mitochondria can provide

only one-third (33%) of the ATP needed. The remainder comes from glycolysis.

Tetanus is due to a toxin that makes the muscle cell membrane more permeable to calcium ions (Ca2+), causing

powerful tetanic contraction.

Rigor mortis disappears as

proteolytic enzymes from lysosomes digest the cross-bridges)

Tropomyosin and troponin are

regulatory proteins of the muscle fibers.

The epimysium, perimysium, and endomysium are all continuous with the connective tissue to form a

rope like tendon that attaches a muscle to the periosteum of the bone.

Thin and thick filaments do not extend the entire length of muscle fiber. Instead, they are arranged in compartment called

sarcomere.

Terminal cisterns are dilated end sac of the

sarcoplasmic reticulum.

Z line or Z disk is narrow, plate-shaped region of dense protein material that

separates one sarcomere from another.

There are two types of smooth muscle

single-unit visceral smooth muscle and multi-unit smooth muscle.

Individual who lifts weights builds larger muscles because

skeletal muscles increase number of myofibrils but not number of cells.

When acetylcholine binds to receptors at the motor-end plate, the muscle membrane becomes more permeable to

sodium ions ( Voltage-gated Na+ channel opens to allow Na+ ions entering inside the sarcolemma)

Both cardiac and skeletal muscle tissues are

striated and smooth muscle is not.

The overlapping of thick and thin filaments and the prominent striations of the myofibrils make the entire skeletal muscle fiber appear

striated.

Titin, myomesin, nebulin, α-Actinin, and dystrophin are

structural proteins of the muscle fibers.

Fascia lines the body wall and limbs that

surround and support muscles.

B

synaptic end bulb

Dystrophin is protein used to reinforce the sarcolemma and help transmit the tension generated by the sarcomeres to the

tendons.

Titin is the largest size protein in the muscle fiber that extends from

the Z disk to M line.

Thin filaments at either end of sarcomere are attached to

the Z line (Z disc).

Epimysium is the dense irregular connective tissue that surrounds

the entire muscle.

Muscle fibers have many nuclei in order to produce large amounts of

the enzymes and structural proteins needed for contraction.

Wave summation is

the increased strength of a contraction that occurs when a second stimulus arrives before the muscle fiber has relaxed completely.

A myogram of twitch contraction includes

the latent period, the contraction period, and the relaxation period.

A muscle fiber develops its greatest tension when there is an optimal zone of overlap (sarcomere length is 2.0-2.4 μm) between thick and thin filament. This dependency is

the length-tension relationship.

Eccentric isotonic contraction

the muscle fiber lengthens. (object is dropped)

Concentric isotonic contraction

the muscle fiber shortens. (object is lifted)

Isometric contraction is the type of contraction in which

the muscle fibers produce tension but do not shorten nor lengthen. (Object cannot be moved)

Isotonic contraction is the type of contraction in which

the muscle fibers produce tension while muscle length is changed.

Cramp occurs because

the relaxation phase of a muscle contraction is often prolonged in a fatigued muscle, raising the likelihood of fused summation of action potentials causing painful disturbances to a skeletal muscle.

Single-unit smooth muscle is found in

the skin and in tubular arrangements that form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder.

Muscle tissue is capable of undergoing

the stress-relaxation response when stretched is single-unit smooth muscle fibers.

NMJ is the synapse between

the terminal end of a somatic motor (axon terminal) neuron and a portion sarcolemma (called Motor-End-Plate) of a skeletal muscle fiber.

Actin is the main protein of

the thin filament.

Multi-unit smooth muscle is found in

the walls of large arteries, in airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye.

In multi-unit smooth muscle tissue, muscle cells have few gap junctions with neighboring cells and thus must be excited by

their own motor neuron terminal.

A band: the darker middle area of sarcomere that contains

thick & thin filament.

H zone: the narrow area in the center of the A band that contains

thick filament only.

Smooth muscle cells are small but form

thick layers of hollow organs.

The zone of overlap is a dark region where

thin and thick filaments lie side by side.

There are two types of microfilaments:

thin and thick filaments.

I band: the light area of the sarcomere that contains

thin filament only.

Action potentials are conducted into a skeletal muscle fiber by

transverse tubules (T-tubules).

At rest, active sites of actin (myosin-binding site) thin filament are blocked (covered) by

tropomyosin molecules.

At rest, the tropomyosin molecule is held in place by

troponin.

A

Z disc

H

Zone of overlap

d

Complete tetanus (fused tetanus)

Plasticity is

an ability of the smooth muscle to function over a wide range of lengths.

The SR (sarcoplasmic reticulum) releases calcium in response to

an arrival of action potential.

When a muscle fiber is relaxed, the concentration of Ca2+in the sarcoplasm is very slow, but the concentration of Ca2+ in the sarcoplasm reticulum (SR) is very high. As a result, to trigger muscle contraction

Ca2+ must be released from SR.

The order of steps in generating an action potential

a. Step 1: The arrival of a nerve impulse at a motor neuron opens voltage-gated calcium Ca2+ channel in the sarcolemma, allowing Ca2+ enter to the synaptic terminal to trigger the releasing of acetylcholine. b. Step 2: Ach diffuses across the synaptic cleft by exocytosis and binds to receptors in the motor-end-plate. The binding opens voltage-gated sodium Na+ channel in the sarcolemma, allowing Na+ enters to the sarcoplasm. c. Step 3: The influx of Na+ produces a depolarization of the sarcolemma called "muscle action potential" d. Step 4: The muscle action potential that propagates along the T. Tubules triggers the opening of voltage-gated Ca channel in the sarcoplasmic reticulum (SR). SR releases Ca into sarcoplasm e. Step 5: Termination of Ach by enzyme Acetylcholinesterase (AChE) f. Step 6: Ca2+ binds to troponin on the thin filament, exposing the active site or myosin-binding site of actin. g. Step 7: Crossbridges are formed and contraction cycle begins.h. Step 8: When the generation of action potential ends, Ca2+ is pumped back to the SR by an active transport.

A Troponin molecule consists three globular subunits:

a. Unit 1 binds to tropomyosin b. Unit 2 binds to G-actin c. Unit 3 binds to calcium ions.

When a skeletal muscle fiber contracts in the sliding filament mechanism:

a. Z line (Z disk) moves closer together b. The H zones and I bands get smaller c. The width of the A band remains constant d. The zone of overlap gets larger (more zone of overlaps between thin & thick filament)

Cross bridges :

a. are portions of thick filament (myosin head) b. act as (an enzymes) ATPase during the contraction cycle of muscle c. generate force

After prolonged strenuous exercise has stopped, heavy breathing will often continue for several minutes in order to provide the oxygen needed to

a. convert the lactic acid produced during exercise back into glycogen b. resynthesize creatine phosphate c. replace oxygen displaced from muscle myoglobin

Sarcoplasmic reticulum stores

calcium ions (Ca2+)

Smooth muscle contracts when

calcium ions Ca2+ interact with calmodulin which activate the enzyme myosin light chain kinase, enabling myosin heads to attach to actin.

The mechanisms of rigor mortis is due to

calcium ions leak out of the SR (allowing myosin heads to bind to actin) and muscle fibers run out of ATP (causing the cross-bridges cannot detach from actin).

Contraction of myofibrils within a muscle fiber begins when

calciumion is released from the terminal cistern of sarcoplasmic reticulum.