muscular system - human anatomy and physiology · muscular system bmls ii-e (2012) human anatomy...

Muscular System

BMLS II-E (2012) Human Anatomy and Physiology 1

UNDERSTANDING WORDS

Calat - something inserted e.g. interalated disc—membranous band that

connects cardiac muscle cells Erg – work

e.g. synergist – muscle that works with a prime mover to produce a movement

Fasc – bundles e.g. fasciculus – bundles of muscle of fibers

Gram – something written e.g. myogram – recording of a muscular

contraction Hyper – over, more

e.g. muscle hypertrophy – enlargement of muscle fibers

Inter – between e.g. intercalated disc – membranous band that

connects cardiac muscle cells Iso – equal

e.g. isotonic contraction – contraction during which the tension in a muscle remains unchanged

Laten – hidden e.g. latent period – period between a stimulus

and the beginning of a muscle contraction Myo – muscle

e.g. myofibril – contractile fiber of a muscle cell Reticul – a net

e.g. sarcoplasmic reticulum – network of membranous channels within a muscle fiber

Sarco – flesh e.g. sarcoplasm – substance (cytoplasm) within

a muscle fiber Syn – together

e.g. synergist – muscle that works with a prime mover to produce a movement

Tetan – stiff e.g. titanic contraction – sustained muscular

contraction Tonic – stretched

e.g. isotonic contraction – contraction during which the tension of a muscle remains unchanged

Troph – well fed

e.g. muscular hypertrophy – enlargement of muscle fibers

Voluntar – of one’s free will e.g. voluntary muscle – muscle that can be

controlled by conscious effort STRUCTURE OF A SKELETAL MUSCLE

- it is composed primarily of skeletal muscle tissue, nervous tissue, blood and connective tissue

- CONNECTIVE TISSUE COVERINGS

- An individual skeletal muscle is separated from

adjacent muscles and held in position by layers

of dense connective tissue called fascia. This

connective tissue surrounds each muscle and

may project beyond the ends of its muscle

fibers to form a cord-like tendon. Fibers in a

tendon may intertwine with those in the

periosteum of a bone, attaching the muscle to

the bone or the connective tissue associated

with a muscle from broad, fibrous sheets called

aponeuroses which may attach to bone or the

coverings of adjacent muscles

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- The layer of connective tissue that closely

surrounds a skeletal muscle is called the

epimysium. Another layer of connective tissue

called the perimysium, extends inward form the

epimysoum and separates the muscle tissue

into small sections. These sections contain

bundles of skeletal muscle fibers called

fascicles. Each muscle fiber within a fascicle lies

within a layer of connective tissue in the form

of a thin covering called endomysium.

DEEP FASCIA

- The portion of the network that surrounds and

penetrates the muscles

SUBCUTANEOUS FASCIA

- Deep fascia is continuous with this

- It lies just beneath the skin, forming the

subcutaneous layer.

SUBSEROUS FASCIA

- Subcutaneous fascia is also continuous with this

that forms the connective tissue layer of the

serous membranes covering organs in various

body cavities and lining those cavities

SKELETAL MUSCLE FIBERS

Myofibrils

- The sarcoplasm also has abundant, parallel,

thread-like structures called myofibrils

- Play a fundamental role in the muscle

contraction mechanism

MYOSIN (thick filaments) – composed of protein

ACTIN (thin filaments) composed primarily of

the protein actin

Sarcomeres

- Striations form a repeating pattern of units

STRIATION PATTERN

I Bands (light bands)

Composed of thin actin filaments held by

direct attachments to structures called Z

line

Z line – appear in the center of the I bands

A Bands (dark bands)

Composed of thick myosin filaments

overlapping thin actin filaments

H zone – slightly lighter cental region of A

band

It includes a thickening known as M line

M line – consists of proteins that help hold

the thick filaments in place

* TTIN – large protein

Cross-bridges

- Two twisted protein strands with globular parts

that project outward along their lengths

TWO OTHER TYPES OF PROTEIN

Troponin

Have 3 protein subunits and are attached to

actin

Tropomyosin

Are rod-shaped and occupy the longitudinal

grooves of the actin helix

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Troponin-tropomyosin complex

- This is form when each tropomyosin is held in

place by a troponin molecule

Sarcoplamic Reticulum

- Within the sarcoplasm of a muscle fiber is a

network of membranous channels that

surrounds each myobfibril and runs parallel to

it. This membranous form the sarcoplasmic

reticulum

- Corresponds to the endoplasmic reticulum of

other cells

Transverse tubule (T-tubules)

- A set of membranous channels

- It extends into the sarcoplasm as an

invaginations continuous with the sarcolemma

and contains extracellular fluid

Cisternae

- transverse tubule lies between two enlarges

portions of the sarcoplasmic reticulum

Triad

- formed by the 3 structures (sarcoplasmic

reticulum, T-tubules, cisternae) near the region

where the actin and myosin filaments overlap

SKELETAL MUSCLE CONTRACTION

- A muscle fiber contraction is a complex

interaction of several cellular and chemical

constituents. The final result is a movement

within the myofibrils in which the filaments of

actin and myosin slide past one another,

shortening the sarcomeres. When this happens,

the muscle fiber shortens and pulls on its

attachments

NEUROMUSCULAR JUNCTION

Motor Neurons

- Neurons that control effectors, including

skeletal muscle

Synapse

- It is a space through which information can pass

Neurotransmitters

- Neurons communicate with the cells that they

control by releasing these chemicals

Neuromuscular Junction

- The site where an axon and a muscle fiber meet

Motor end plate

- Muscle fiber membrane is specialized to form

this where nuclei and mitochondria are

abundant and the sarcolemma is extensively

folded

* together, a motor neuron and the muscle fibers it

controls constitute a motor unit

Synaptic Cleft

- A small gap that separates the membrane of the

neuron and the membrane of the muscle fiber

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STIMULUS FOR CONTRACTION

Acetylcholine

- Is the neurotransmitter that motor neurons use

to control skeletal muscle contraction

- It is synthesized in the cytoplasm of the motor

neuron and is stored in synaptic vesicle near the

distal end of its axon

- Acetylcholine diffuses rapidly across the

synaptic cleft, combines with Ach receptors on

the motor endplate, and stimulates the muscle

fiber, the response is muscle impulse

Muscle Impulse

- Is an electrical signal that is very much like a

nerve impulse

- It changes the muscle cell membrane in a way

that transmits the impulse in all directions along

and around the muscle cell into the T-tubules,

into the sarcoplasm and ultimately to the

sarcoplasmic reticulum and the cisternae.

EXCITATION CONTRACTION COUPLING

THE SLIDING FILAMENT

Model of Muscle Contraction

- when sarcomeres shorten, the thick and thin

filaments do not change length. They slide past

one another with the thin filaments moving

toward the center of the sarcomere form both

ends. As this occurs, the H zone and the I bands

narrow, the regions of overlap widen and Z lines

move closer together, shortening the sarcomere

Major events of muscle fiber contraction

- a nerve impulse travels down a motor neuron

axon

- the motor neuron terminal releases the

neurotransmitter acetylcholine (Ach)

- Ach binds to Ach receptors

- The sarcolemma is stimulated and a muscle

impulse travels over the surface of the muscle

fiber and deep into the fiber through the

transverse tubules

- The muscle impulse reaches the sarcoplasmic

reticulum and calcium channels open

- Calcium ion diffuse from the sarcoplasmic

reticulum into the sarcoplasm and bind to

troponin molecules

- Tropomyosin molecules move and expose

specific sites on actin

- Actin and myosin form linkages

- Thin (actin) filaments are pulled toward the

center of the sarcomere by myosin cross-

bridges

- The muscle fiber shortens and contracts

Cross-Bridge Cycling

- the force that shortens the sarcomeres comes

from cross-bridges pulling on the thin filaments.

A myosin cross bridge can attach to an actin

binding site and bend slightly, pulling on the

actin filament. Then the head can release,

straighten, combine with another binding site

further down the actin filament and pull again.

- Myosin cross-bridges contain the enzyme

ATPase, which catalyzes the breakdown of ATP

to ADP and phosphate

Relaxation

- When nerve impulses cease, two events relax

the muscle fiber.

- Acetylcholinesterase rapidly decomposes any

acetylcholine remaining in the synapse. This

enzyme prevents a single nerve impulse from

continuous stimulating a muscle fiber.

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Major events of muscle fiber relaxation

- Acetylcholinesterase decomposes acetylcholine

and the muscle fiber membrane is no longer

stimulated

- Calcium ions are actively transported into the

sarcoplasmic reticulum

- ATP breaks linkages between actin and myosin

fiaments without breakdown of the ATP itself

- Breakdown of ATP “cocks” the cross-bridges

- Troponin and tropomyosin molecules inhibit the

interaction between myosin and actin filaments

- Muscle fiber remains relaxed, yet ready until

stimulated again

ENERGY SOURCES FOR CONTRACTION

Creatine Phosphate

- The initial source of energy available to

regenerate ATP from ADP and phosphate

- Includes a high-energy phosphate bond

- Is 4 to 6 times more abundant in muscle fibers

than ATP

- Cannot directly supply energy to a cell

- It stores energy released from mitochondria

OXYGEN SUPPLY AND CELLULAR RESPIRATION

Anaerobic

- Early phase of cellular respiration, occurs in the

cytoplasm is anaerobic

- Only partially breaks down energy-supplying

glucose and releases only a few ATP molevules

Aerobic

- Complete breakdown of glucose occurs in the

mitochondria and is aerobic

- Includes the complex series of reactions of the

citric acid cycle and electron transport chain

Myoglobin

- A pigment and is synthesized in muscle cells and

imparts the reddish brown color of skeletal

muscle tissue.

- Can loosely bind oxygen and has greater

attraction for oxygen than does hemoglobin

- Can temporarily store oxygen in muscle tissue

which reduces a muscle’s requirement for a

continuous blood supply during contraction

OXYGEN DEBT

Lactic acid threshold

- Shift in metabolism

- Anaerobic threshold

OXYGEN DEBT

- When lactic acid accumulates, a person

develops an oxygen debt

- The amount of oxygen debt roughly equals the

amount of oxygen liver cells require to use the

accumulated lactic acid to produce glucose, plus

the amount the muscle cells require to

resynthesize ATP and creatine phosphate and

restore their original concentrations

MUSCLE FATIGUE

- A condition when a muscle exercised

persistently for a prolonged period may lose its

ability to contract

- Is most likely to arise from accumulation of

lactic acid in the muscle from anaerobic ATP

production

Cramped

- A sustained, painful, involuntary muscle

contraction

- Decreased electrolyte concentration, occurring

in the extracellular fluid surrounding the muscle

Muscular System


fibers and their motor neurons trigger

uncontrolled stimulation of the muscle

MUSCULAR RESPONSES

Threshold Stimulus

- When an isolated muscle fiber is exposed to a

series of stimuli of increasing strength, the fiber

remains unresponsive until a certain strength of

stimulation called threshold stimulus is applied

- Once threshold is reached, an action potential is

generated, resulting in a muscle impulse that

spreads throughout the muscle fiber, releasing

enough calcium ions from the sarcoplasmic

reticulum to activate cross-bridges binding and

cause a contraction of that fiber

RECORDING OF A MUSCLE CONTRACTION

Twitch

- A contractile response of a single muscle fiber

to a muscle impulse

- Consists of a period of contraction, during

which the fiber pulls at its attachments,

followed by a period of relaxation, during which

the pulling force declines.

- These events can be recorded in a pattern

called a myogram

Latent Period

- A brief delay between the time of stimulation

and the beginning of contraction

- In human muscle may be less than 2

milliseconds

Summation

- The force of individual twitches combines by

the process of summation

Tenatic Contraction

- When the resulting forceful, sustained

contraction lacks even partial relaxation

Multiple Motor Unit Summation or Recruitment

- An increase in the number of activated motor

units

Sustained Contractions

- During sustained contractions, smaller motor

units which have smaller diameter axons are

recruited earlier. The larger motor units, which

include larger diameter axons, respond later

and more forcefully. The result is a sustained

contraction of increasing strength

Muscle tone (tonus)

- Even when a muscle appears to be at rest, a

certain degree of sustained contraction occurs

in its fiber. This is called muscle tone.

TYPES OF CONTRACTIONS

Isotonic – (equal force – change in length)

Concentric – shortening occurs

Eccentric Contraction

- Lengthening

- Occurs when the force a muscle generates is

less than that requires to move or lift an object.

- Even if such a contraction, cross-bridges are

working but not generating enough force to

shorten the muscle

Isometric – (equal length-change in force)

Fast and Slow-Twitch Muscle Fibers

Slow-twitch fibers (type I)

- Always oxidative and are therefore resistant to

fatigue

Muscular System


- Often called red fiber because they contain the

red, oxygen-storing pigment myoglobin

Fast-twitch fibers (type II)

- May be primarily glycolytic (fatigable) or

primarily oxidative (fatigue resistant)

Fast-twitch glycolytic fibers (type IIa)

- Also called white fibers because they have less

myoglobin and have a poorer blood supply then

red fibers

Fast-twitch fatigue-resistant fibers (type IIb)

- Also called intermediate fibers

- These fibers have the fast-twitch speed

associated with white fibers combined with a

substantial oxidative capacity more

characteristic of red fibers

SMOOTH MUSCLES

- Smooth muscle contraction resembles skeletal

muscle contraction in a number of ways. Both

mechanisms reflect reactions of actin and

myosin; both are triggered by membrane

impulses and release of calcium ion; and both

use energy from ATP molecules

Calmodulin

- Binds to calcium ions released when its fiber are

stimulated, activating actin-myosin contraction

CARDIAC MUSCLE

- Appears only in the heart. It is composed of

striated cells joined end to end, forming fibers

that are interconnected in branching, three-

dimensional networks.

- The opposing ends of cardiac muscle cells are

connected by cross-bands called intercalated

disc. These bands are complex membrane

junctions. Not only do they help join cells and

transmit the force of contraction from cell to

cell, but the intercellular junctions of the fused

membranes of intercalated disc allow ions to

diffuse between the cells. This allow muscle

impulses to travel rapidly from cell to cell

SKELETAL MUSCLE ACTIONS

- Skeletal muscle generates a great variety of

body movements. The action of each muscle

mostly depends upon the kind of joint it is

associated with and the way the muscle is

attached on either side of that joint

Origin and Insertion

Origin – immovable end

Insertion – movable end

Interaction of Skeletal Muscles

Prime mover or Agonist

- Is the muscle primarily responsible for

producing an action

Synergists

- Muscles that contract and assist a prime mover

Antagonists

- These muscles can resist a prime mover’s action

and cause movement in the opposite direction

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MAJOR SKELETAL MUSCLES

MUSCLES OF FACIAL EXPRESSION

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MUSCLES MOVING THE HEAD

MUSCLES OF MASTICATION

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HYOID MUSCLE

TONGUE MUSCLE

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MUSCLES OF SWALLOWING AND THE LARYNX

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MUSCLES MOVING THE EYES

MUSCLES ACTING ON THE VERTEBRAL COLUMN

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MUSCLES ACTING ON THE VERTEBRAL COLUMN

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MUSCLES OF THORAX

MUSCLES OF ABDOMINAL WALL

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MUSCLES OF THE PELVIC FLOOR AND PERINEUM

MUSCLES ACTING ON THE SCAPULA

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MUSCLES ACTING ON THE ARM

SUMMARY OF MUSCLE ACTIONS ON THE SHOULDER AND ARM

MUSCLES ACTING ON THE FOREARM

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MUSCLES ACTING ON THE FOREARM

MUSCLES OF THE FOREARM ACTING ON WRIST, HAND AND FINGERS

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MUSCLES OF THE FOREARM ACTING ON WRIST, HAND AND FINGERS

INSTRINSIC HAND MUSCLE

Muscular System


INSTRINSIC HAND MUSCLE

MUSCLES ACTING ON THE THIGH

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SUMMARY OF MUSCLE ACTION ON THE HIP AND THIGH

MUSCLES OF THE THIGH

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MUSCLES OF THE LEG ACTING ON THE LEG, ANKLE AND FOOT

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INSTRINSIC MUSCLE OF THE FOOT

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DISEASES

Moebius Syndrome

- absence of the 6th and 7th cranial nerves which carry impulses from the brain to the muscles of the face, leads to an odd collection of symptoms

- 1st signs: difficulty sucking, excessive drooling and sometimes crossed eyes TENDINITIS and TENOSYNOVITIS

- A tendon or the connective tissue sheath of a tendon (tenosynovium) may become painfully inflamed and swollen following an injury or the repeated stress of athletic activity

- The tendons most commonly affected are those associated with the joint capsules of the shoulder, elbow, hip and knee and those involved with moving the wrist, hand, thigh and foot

COMPARTMENT SYNDROME

- A condition wherein an injury causes fluid, such as blood from an internal hemorrhage, to accumulate within a compartment, the pressure inside will rise. The increase pressure, in turn, may interfere with blood flow into the region, reducing the supply of oxygen and nutrients to the affected tissues

- Treatment may require immediate intervention by a surgical incision through the fascia (fasciotomy) to relieve the pressure and restore circulation

MUSCLE STRAIN

- A type of injury that is common to athletes, muscle fibers and connective tissues, can be tear if overstretched - Mild strain – only a few muscle fibers are injured, the fascia remains intact and little function id lost - Severe Strain – many muscle fibers as well as fascia tear, and muscle function may be lost completely

MYASTHENIA GRAVIS

- An autoimmune disorder, the immune system attacks part of the body, that part is the muscular system, particularly receptors for acetylcholine on muscle cells at neuromuscular junctions.

TERMINOLOGIES COMPARTMENT

- The space that contains a particular group of muscles, blood vessels, and nerves, all tightly enclosed by fascia. DYSTROPHIN

- Rod-shaped muscle proteins that are vital to muscle function - It accounts for only 0.002% of total muscle protein in skeletal muscle, but its absence causes the devastating

inherited disorder RIGOR MORTIS

- A condition wherein a few hours after death, the skeletal muscles partially contracts, fixing the joints - May continue for seventy-two hours or more - It results from an increase in membrane permeability to calcium ions which promotes cross-bridge attachment

and a decrease in availability of ATP in the muscle fibers

muscular system - human anatomy and physiology · muscular system bmls ii-e (2012) human anatomy...

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