muscular system
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Muscular System. essential function of muscle is contraction or shortening muscles are responsible for essentially all body movement "machines" of the body. 3 types (skeletal, cardiac, smooth) differ in cell structure, body location, & how they are stimulated to contract - PowerPoint PPT PresentationTRANSCRIPT
Muscular System
essential function of muscle is contraction or shortening
muscles are responsible for essentially all body movement
"machines" of the body
3 types (skeletal, cardiac, smooth) differ in cell structure, body location, & how they are stimulated to contract
all muscle cells are elongated and called muscle fibers
the ability of muscle to shorten or contract depends on two types of myofilaments ◦ (the muscle cell equivalents of the microfilaments
of the cytoskeleton)terminology is different
◦ (“myo” and “mys” mean muscle / “sarco” means flesh)
Skeletal Muscle organs that attach to the body's skeleton help form the smoother contours of the body fibers are cigar-shaped, multinucleate cells, and the
largest of the muscle fiber types known as striated muscle because its fibers appear
to be striped called voluntary muscle because it is the only
muscle type subject to conscious control often activated by reflexes contract rapidly and with
great force tires easily and must rest after short periods of
activity soft and surprisingly fragile can exert tremendous power
thousands of their fibers are bundled together by connective tissue◦ (provides strength and support to the muscle as a whole)
each muscle fiber is enclosed in a delicate connective tissue sheath called an endomysium
several sheathed muscle fibers are then wrapped by a coarser fibrous membrane called a perimysium◦ (forms a bundle of fibers called a fascicle)
many fascicles are bound together by an even tougher layer of connective tissue called an epimysium◦ (covers the entire muscle)
epimysia blend into the strong, cordlike tendons◦ (tendons anchor muscles, provide durability, and conserve
space around rough bony projections)
Smooth Muscleno striations, involuntary (not under conscious
control), slow and sustained contractionsare spindle-shaped with a single nucleus
arranged in sheets or layers◦ (most often there are two Iayers, one running
circularly and the other longitudinally)found in the walls of hollow visceral organs
such as the stomach, urinary bladder, respiratory passages
propels substances along a definite tract (pathway) within the body
Cardiac Musclestriated but involuntary heart musclecardiac fibers are cushioned by small amounts
of soft connective tissuearranged in spiral or figure 8-shaped bundleswhen the heart contracts, internal chambers
become smaller, forcing blood into large arteries leaving the heart
cardiac muscle fibers are branching cells joined by special junctions called intercalated disks
structure of muscle fibers allow heart activity to be closely coordinated.
Muscle Functionfour important roles in the body
(produces movement, maintains posture, stabilizes joints, generates heat)
Muscle FunctionsProducing Movement
◦skeletal muscles are responsible for all locomotion and manipulation
◦respond quickly to changes in the external environment
◦express our emotionsMaintaining Posture
◦skeletal muscles that maintain body posture
◦makes one tiny adjustment after another almost continuously
Producing Muscle FunctionsStabilizing Joints
◦muscle tendons are extremely important in reinforcing and stabilizing joints
Generating Heat◦by-product of muscle activity◦nearly ¾ of energy used to power
muscle contraction escapes as heat◦lost energy is important in
maintaining normal body temperature
Show Nerve Stimulation Video:http://highered.mcgraw-hill.com/s
ites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html
The Nerve Stimulus and the Action Potential Part 1skeletal muscle cells must be stimulated by
nerve impulses to contractone motor neuron (nerve cell) may stimulate
hundreds of muscle cells◦ (depending on the particular muscle and the work
it does)one neuron and all the skeletal muscle cells it
stimulates are a motor unitnerve fiber (axon) forms neuromuscular
junctions with the sarcolemma of a different muscle cell ◦ they never touch and the synaptic cleft is filled with
tissue (interstitial) fluid
Part 2when nerve impulse reaches the axonal
terminals a neurotransmitter is released (acetylcholine - ACh)◦ACh diffuses across the synaptic cleft and
attaches to receptors in the sarcolemma◦ if enough acetylcholine is released the
sarcolemma becomes temporarily permeable to sodium ions (Na+)
◦Na+ rushes into the muscle cell◦cell interior has an excess of positive ions
which changes the electrical conditions of the sarcolemma
Part 3◦this generates an electrical current called an
action potential (unstoppable once it begins)
◦action potential travels over the entire surface of the sarcolemma
◦an electrical impulse is conducted from one end of the cell to the other
◦result is contraction of the muscle cell◦the cell returns to its resting state by
(1) diffusion of potassium ions (K+) out of the cell (2) activation of the sodium-potassium pump
(moves Na+ and K+ back to their initial positions)
Contraction of a Skeletal Muscle as a Whole
skeletal muscles are organs with thousands of muscle cells
muscles react to stimuli with graded responses (different degrees of shortening)
graded muscle contractions can be produced two ways◦(1) changing the speed of muscle
stimulation◦(2) by changing the number of muscle
cells being stimulated
muscle twitches single, brief, jerky contractions sometimes occur as a result of certain nervous system
problems nerve impulses are delivered to muscle at a very rapid
rate cells do not relax completely between stimuli contractions are "summed" and get stronger and
smoother when muscle is stimulated rapidly with no evidence of
relaxation, contractions are smooth/sustained, the muscle is said to be in tetanus
primary role of tetanus is to produce smooth and prolonged muscle contractions
depends mostly on how many muscle cells are stimulated
Providing Energy for Muscle Contraction
as a muscle contracts, ATP bonds are hydrolyzed to release energy
muscles only store 4 to 6 seconds' worth ATP
contracting muscles different pathways for ATP regeneration:
aerobic (cellular) respiration in the mitochondriaanaerobic glycolysis and lactic acid formation
◦ during intense muscle activity oxygen/glucose delivery is temporarily inadequate
◦ pyruvic acid generated during glycolysis is converted to lactic acid
◦ produces about 5% as much ATP as aerobic respiration
◦ works 2 ½ times faster and provides enough ATP for 30-40 seconds of activity
◦ uses huge amounts of glucose for a small ATP harvest◦ accumulated lactic acid promotes muscle fatigue and
muscle soreness
Muscle Fatigue and Oxygen Debta muscle is fatigued when it is unable to contract,
even if it is still being stimulatedwhen muscle begins to tire, it contracts more
weakly until it stops reacting /contractingbelieved to result from oxygen debt/lactic acid
accumulation occurring during prolonged muscle activity
muscle's ATP supply starts to run low increasing acidity / decreasing ATP cause muscle
to contract less effectively and finally stop individual breathes rapidly/deeply and muscles
receive sufficient oxygen◦ lactic acid broken down and ATP/creatine phosphate
made
Types of Muscle Contractions
Isotonic ◦ tension develops as actin/myosin
myofilaments attempt to slide past each other in muscle fibers
◦contractions occur when myofilaments slide, the muscle shortens, and movement occurs
Isometric ◦contractions in which the muscles do not
shorten because they are working against an immovable object
◦ tension in the muscle keeps increasing without movement
Muscle Toneeven a voluntarily relaxed muscle
has some contracting fibers contraction is not visible but
keeps muscle firm, healthy, ready
Effect of Exercise on Muscles
inactivity (loss of nerve supply, immobilization) leads to muscle weakness and wasting
regular exercise increases muscle size, strength, endurance
aerobic/endurance exercise (jogging, biking, or aerobics class)◦ stronger, more flexible muscles with greater
resistance to fatigue◦ cells form more mitochondria and store more
oxygen◦ overall body metabolism more efficient◦ improves digestion/elimination◦ enhances neuromuscular coordination◦ makes the skeleton stronger◦ heart enlarges (hypertrophies)
more blood is pumped with each beat, fat deposits are cleared, gas exchanges more efficient
resistances or isometric exercise ◦bulging muscles result mainly from
muscles being worked against some immovable object
◦require very little time and little or no special equipment
5 Golden Rules of Skeletal Muscle Activityall muscles cross at least one
jointbulk of the muscle lies proximal
to the joint crossedall muscles have at least two
attachments: the origin and the insertion
muscles puII not pushduring contraction the muscle
insertion moves toward the origin
Naming Skeletal Musclesmuscles come in many shapes/sizes
and named with several criteria◦direction of the muscle fibers - rectus
(straight), oblique (slanted)◦relative size of the muscle - maximus
(largest), minimus (smallest), longus (long)◦location of the muscle - named for the
bone with which they are associated◦number of origins - biceps, triceps, or
quadriceps have two, three, or four origins
◦location of the muscle's origin and insertion - named for their attachment sites sternocleidomastoid muscle – origin on
the sternum (sterno)/clavicle (cleido) and inserts on the mastoid process
◦shape of the muscle - distinctive shape that helps to identify them (deltoid means "triangular")
◦action of the muscle - flexor, extensor, abductor appear in names