108458727 muscular system

P h y s i o l o g y a n d A n a t o m y – L e c t u r e | 1

By: JMJS This review outline is based on Principles of Anatomy and Physiology, 8

th Edition (White Book), Gerard Tortora and Bryan Derrickson

MMUUSSCCUULLAARR SSYYSSTTEEMM

OOVVEERRVVIIEEWW OOFF MMUUSSCCUULLAARR TTIISSSSUUEE

II.. TTYYPPEESS OOFF MMUUSSCCUULLAARR TTIISSSSUUEE

A. Skeletal Muscle Tissue attached to bones; move parts of the

skeleton striated voluntary has limited capacity for regeneration multinucleated, at the periphery

B. Cardiac Muscle Tissue

forms the bulk of the heart wall striated voluntary can regenerate under certain conditions fibers are branched single, centrally located nucleus

C. Smooth Muscle Tissue

located in the walls of hollow internal structures

participates in internal processes nonstriated involuntary oval, centrally located nucleus

IIII.. FFUUNNCCTTIIOONNSS OOFF MMUUSSCCUULLAARR TTIISSSSUUEE A. Producing body movements B. Stabilizing body positions C. Storing and moving substances within the

body D. Producing heat

SSKKEELLEETTAALL MMUUSSCCLLEE TTIISSSSUUEE

II.. CCOONNNNEECCTTIIVVEE TTIISSSSUUEE CCOOMMPPOONNEENNTTSS Connective tissue surrounds and protects muscle fibers.

A. Subcutaneous layer/Hypodermis composed of areolar connective tissue

and adipose tissue provides pathway for nerves, blood

vessels, and lymphatic vessels to enter and exit the muscles

adipose tissue serves as an insulator, protects muscle from physical trauma

B. Fascia

dense sheet or broad band of dense irregular connective tissue

lines the body wall and limbs supports and surrounds muscles and

other organs of the body allows free movements carries nerves, blood vessels and

lymphatic vessels supports and surrounds muscles and

other organs of the body fills empty spaces three layers:

1. epimysium wraps the entire muscle

2. perimysium surrounds bundles of muscle

fibers called fascicles 3. endomysium

wraps individual muscle fibers

These three extend beyond the muscle as a tendon which is a cord of dense regular connective tissue composed of parallel bundles of collagen and functions as an attachment between muscles and bones

IIII.. NNEERRVVEE AANNDD BBLLOOOODD SSUUPPPPLLYY Contraction

chief characteristic of muscles requires ATP an artery and one or two veins

accompany each nerve that penetrates skeletal muscle




IIIIII.. HHIISSTTOOLLOOGGYY A. Muscle Fibers

elongated, cylindrical cells arranged parallel to one another

components 1. sarcolemma

plasma membrane 2. transverse tubules

tunnel in from the surface toward the center of each muscle fiber

3. sarcoplasm cytoplasm contains several mitochondria

4. sarcoplasmic reticulum network of fluid filled membrane-

enclosed tubules which store Ca2+ ions

5. myoglobin reddish pigment stores oxygen

B. Myofibrils cylindrical structures extending along the

entire length of muscle fiber components:

1. sarcomeres compartments formed by

overlapping of thin and thick filaments

basic functional units of striated muscle fibers

2. Z discs zigzagging zones of dense protein

material which separate sarcomeres from one another

3. A band

darker area within a sarcomere extends through the entire length

of thick filaments at both ends, both thick and thin

filaments overlap

4. H zone center of each A band contains only thick filaments

5. I band

lighter area at either side of A band contains the rest of thin filaments extends into two sarcomeres

divided by a Z disc C. Myosin (thick filaments)

shaped like two golf clubs twisted together

have tails and heads D. Actin (thin filaments)

anchored to Z discs contain two other proteins:

1. tropomyosin cover myosin-binding sites on

actin 2. troponin

holds tropomyosin in place lets go of tropomyosin as it

changes shape when it binds to calcium ions

Actin filaments join together to form actin molecules which contain myosin-binding sites where myosin heads attach

CCOONNTTRRAACCTTIIOONN AANNDD RREELLAAXXAATTIIOONN OOFF SSKKEELLEETTAALL MMUUSSCCLLEE

II.. NNEEUURROOMMUUSSCCUULLAARR JJUUNNCCTTIIOONN A. Muscle Action Potential

electrical signal that stimulates skeletal muscle contraction

B. Motor Neuron

delivers muscle action potential




C. Motor Unit combination of a single motor neuron and

all the muscle fibers it stimulates D. Motor End Plate

region of the sarcolemma near the axon terminal

E. Synaptic Cleft

space between the axon terminal and sarcolemma

F. Neuromuscular Junction

synapse formed between the axon terminals of a motor neuron and motor end plate of a muscle fiber

In the neuromuscular junction, motor neuron excites a muscle fiber in the following way… 1. Release of acetylcholine (ACh)

triggered by nerve impulse at synaptic end bulbs

diffuses across synaptic cleft between motor neuron and motor end plate

2. Activation of ACh receptors - opens ion channels

3. Generation of muscle action potential generated by inflow of sodium ions travels along sarcolemma and through T

tubules

4. Breakdown of Ach acetylcholinesterase breaks down

neurotransmitters in the synaptic cleft II. SLIDING-FILAMENT MECHANISM

occurs when level of calcium ions is high enough and ATP is available

IIIIII.. PPHHYYSSIIOOLLOOGGYY OOFF CCOONNTTRRAACCTTIIOONN

calcium ions and ATP are needed in muscle contraction

there is low level of calcium ions in the sarcoplasm when the muscle is relaxed

axon

branches into…

axon terminals

synaptic end bulbs

synaptic vesicles

neurotransmitters

whose ends enlarge into

swellings called…

which contain

filled with

myosin heads of the thick

filament pull on thin filaments

thin filaments slide toward the

center of sarcomere

I bands and H zones become

narrower, eventually

disappear




* Part of the contraction cycle

during a maximal contraction, the sarcomere can shorten by as much as half its resting length.

IIVV.. RREELLAAXXAATTIIOONN

two changes/conditions that permit relaxation:

1. ACh is rapidly broken down by AChE

Generation of muscle action potential stops and calcium ion channels close

2. Calcium ions are rapidly transported

from sarcoplasm into the sarcoplasmic reticulum

Low level of calcium in the sarcoplasm makes tropomyosin cover the myosin- binding sites on actin, then thin filaments slide back to their relaxed position. IV. Muscle Tone

few motor units are involuntary activated to produce a sustained contraction even when a muscle is not contracting.

when motor neurons are damaged or cut, muscles become flaccid (limpness and loss of tone)

MMEETTAABBOOLLIISSMM OOFF SSKKEELLEETTAALL MMUUSSCCLLEE TTIISSSSUUEE

II.. EENNEERRGGYY FFOORR CCOONNTTRRAACCTTIIOONN A. Creatinine Phosphate

made from excess ATP one P group of ATP is transferred to

creatinine result: ADP and creatinine phosphate sustains contraction for 15 seconds

creatinine

small, amino-acid like molecule synthesized in the liver, kidneys

Ca2+ binds to troponin

Troponin changes shape

Tropomyosin moves away; myosin-

binding site exposed

*ATP splits. Myosin head has ATPase

which breaks down ATP into ADP and P.

Splitting reaction transfers energy to

myosin heads while ADP and P (phosphate)

remain attached.

*Crossbridges form. Energized

myosin heads attach to myosin-

binding sites (once attached, myosin

heads are called crossbridges) and

release P.

*Power stroke. Crossbridges

rotate/swivel and releases ADP.

Force created by swiveling/rotating

slides the thin filament past thick

filament toward the center of the

sarcomere

*Binding ATP and detaching.

Another ATP binds the myosin heads

detach from the actin

When action potentials travel through sarcolemma, Ca2+ release channels open




and pancreas; derived from certain foods

B. Anaerobic Cellular Respiration conversion of pyruvic acid to lactic acid

when oxygen level is low where does pyruvic acid come from? glycolysis

- series of cytosolic reactions that produce 2 ATPs by breaking down a glucose to pyruvic acid

sustains 30-40 seconds of muscle contraction

C. Aerobic Cellular Respiration

series of oxygen-requiring reactions that produce ATP in the mitochondria

two sources of oxygen: 1. blood 2. myoglobin

yields 36 molecules of ATP sustains 10 minute-activities

II. MUSCLE FATIGUE

inability of a muscle to contract after prolonged activity

possible causes 1. lowered release of Ca2+ 2. depletion in creatinine phosphate 3. insufficient oxygen 4. depletion of glycogen 5. buildup of lactic acid and ADP 6. failure of nerve impulses in motor

neurons to release enough Ach III. OXYGEN CONSUMPTION AFTER EXERCISE A. Oxygen Debt

added oxygen, over and above oxygen consumed at rest, that is taken into the body after exercise

used to “pay back” or restore metabolic conditions to the resting levels by/through: 1. converting lactic acid back to glycogen 2. resynthesizing creatinine phosphate

and ATP

3. replacing oxygen removed from myoglobin

B. Recovery Oxygen Uptake

better term than oxygen debt for the elevated use of oxygen after exercise

CCOONNTTRROOLL OOFF MMUUSSCCLLEE TTEENNSSIIOONN

single muscle fiber frequency of stimulation

whole muscle number of muscles contracting in unison

I. TWITCH CONTRACTION

brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron

myogram

recording of a muscle contraction

latent period period between the application of

stimulus and start of contraction

contraction period occurrence of repetitive power

strokes generation of force or tension of

reaction

relaxation period power stroke ceases because calcium

level in the sarcoplasm decreases II. FREQUENCY OF STIMULATION If a second stimulus arrives before a muscle fiber has completely relaxed, the second contraction will be stronger than the first because the second contraction begins when the fiber is at a higher level of tension.




Wave Summation

a phenomenon wherein stimuli arrive after one another before a muscle fiber could completely relax

Unfused Tetanus

stimulation is 20-30 times per second muscle could only relax a little between

stimulation results in sustained by wavering

contraction Fused Tetanus

stimulation is 80-100 times per second muscle could not relax between

stimulation results in sustained contraction in which

individual twitches cannot be detected III. MOTOR UNIT RECRUITMENT

It is the process in which the number of contracting motor units is increased

A factor producing smooth movements rather than a series of jerky movements

IV. TYPES OF SKELETAL MUSCLE FIBERS A. Slow Oxidative (SO) Fibers

red fibers small in diameter appear dark red because of myoglobin contain many large mitochondria generate ATP by means of aerobic cellular

respiration resistant to fatigue and are capable of

prolonged, sustained contractions B. Fast Oxidative-Glycolytic (FOG) Fibers

intermediate in diameter among the three also appears dark red because of

myoglobin generate ATP by means of both aerobic

cellular respiration and anaerobic

glycolysis (because of their high glycogen content)

C. Fast Glycolytic (FG) Fibers white fibers largest in diameter contain the most myofibrils low myoglobin content and few

mitochondria contain large amounts of glycogen and

generate ATP by anaerobic glycolysis used for intense movements but fatigue

quickly Even though most skeletal muscles are a mixture of all three types of skeletal muscle fibers, the skeletal muscle fibers of any given motor unit are all of the same type.

EEXXEERRCCIISSEE AANNDD SSKKEELLEETTAALL MMUUSSCCLLEE TTIISSSSUUEE

Those with a lot of FG fibers…

excel in activities that require periods of intense activity e.g. weightlifting and sprinting

Those with a lot of SO fibers…

excel in activities that require endurance e.g. long-distance running

Endurance type of exercises cause some FG fibers to transform into FOG fibers

CCAARRDDIIAACC MMUUSSCCLLEE TTIISSSSUUEE Cardiac Muscles

interconnected with each other by irregular transverse thickenings of the sarcolemma called intercalated discs

has endomysium, perimysium but lacks epimyseum

require constant supply of oxygen and nutrients




larger and more mitochondria employs aerobic cellular respiration

Intercalated Discs

hold fibers together and contain gap junctions which allow action potentials to spread faster

Autorhythmicity built-in/intrinsic rhythm of the heart

contractions

SSMMOOOOTTHH MMUUSSCCLLEE TTIISSSSUUEE

contain intermediate filaments aside from thin and thick filaments

contraction starts more slowly and lasts longer

most contract in response to nerve impulses from autonomic nervous system

Dense Bodies

structures to which thin filaments attach Two kinds of Smooth Muscle Tissue 1. Visceral

single unit found in sheets that wrap around to form

part of the walls of small arteries, veins and hollow visceral organs

fibers are tightly bound together in a continuous network

2. Multiunit

consists of individual fibers, each with its own motor nerve endings

found in the walls of large arteries, large airways, arrector pili muscles and internal eye muscles

Smooth Muscle Tone

created by the prolonged presence of calcium ions in the cytosol

AAGGIINNGG AANNDD MMUUSSCCUULLAARR TTIISSSSUUEE

Relative number of SO fibers increase Selective loss of some fibers occur

HHOOWW SSKKEELLEETTAALL MMUUSSCCLLEE FFIIBBEERRSS PPRROODDUUCCEE MMOOVVEEMMEENNTT

Skeletal Muscle

organ composed of several types of tissues

ATTACHMENTS 1. Origin

attachment of a muscle to a stationary bone

2. Insertion

attachment to movable bone GROUP ACTIONS 1. Prime Mover

muscle that causes a desired action 2. Antagonist

relaxes while prime mover contracts 3. Synergists

help prime mover to function more efficiently by reducing unnecessary movement

4. Fixators

stabilizes the origin of the prime mover

108458727 muscular system

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