muscle study notes

8/6/2019 Muscle Study Notes

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Muscle study notes

Muscles - Responsible for all types of body movement machines

- Dominant tissue in the heart and in the walls of other hollow organs of thebody.

- Half bodys mass

- Essential function of muscle is contraction.

Three basic types of muscles: Skeletal, cardiac and smooth.- Muscle cell = Muscle fiber- Contraction of muscles is due to microfilament

- Myo and mys refer to muscle

- Sarco refers to flesh

Skeletal: - Elongated

- Attached to the bodys skeleton

- Fibers huge

- Multi nucleate cell- Largest of muscle fiber types (30 cm)

- Striated, Voluntary- Can contract rapidly and with great force, but it tires easily

- Soft, Fragile

- Connective tissue involved: Epimysium, perimysium, and endomysium.

Connective tissue:

- Cells are surrounded and bundled by connective

tissue which provides strength and support.- Endomysium: Encloses a single muscle fiber

- Perimysium: Wraps around a fascicle (bundle)of muscle fibers.- Epimysium: Covers entire skeletal muscle

Aponeuroses

: Attach muscles indirectly to bones, cartilage or

connective tissue, Provides durability and conserve

space.

Smooth muscles:

- Involuntary

- No striation

- Found mainly in the walls of hollow organs.- Single nucleus, spindle shaped

- Two-layers- Alternately contract and relax,

they change the size and shape of organ.


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Cardiac muscles:

- Found only in heart

- Forms heart wall- Striated, involuntary

- Cushioned by small amounts of connective

tissue.- Branching cells joined by special junctions

called intercalated discs.

- Contracts at a fairly steady rate due to thepacemaker.

- One nucleus

Skeletal muscle functions:

Produce movement: all movement from the human body results from muscle

contraction.

Maintain posture: function almost continuously making one tiny adjustment after theother.

Stabilize joints: muscle tendons are extremely important in reinforcing and stabilizing

joints that have poorly fitting articulating surfaces.

Generating heat: As ATP is used to power muscle contraction nearly three quarters of

its energy escapes as heat. Skeletal muscles accounts for at least 40 percent of body mass.Muscle type most responsible for heat generation.

Microscopic anatomy of Skeletal muscles

Sacrolemma: Plasma Membrane.

Myofibrils: Long organelles inside musclefibers.

- Alternating light (I) and Dark(A) bands along the length of the perfectly aligned myofibrils

Light (I) Band- contains only thin filaments= Actin filaments- Midline interruption, dark area called the Z disc.(anchored)

Dark (A) Band- contains the entire length of the thick filament = myosin filament

- lighter centered called the H Zone- Composed of protein myosin (heads)

- The M line in the center of the H zone contains tiny protein rods that hold

adjacent thick filaments together.


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- Has ATPase enzymes which split ATP to generate the power for muscle

contraction

- Myosin and actin overlap

Sacromere: contractile unit of a muscle fiber.

At rest there is a base zonethat locks actin filamentscalled H zone.

Contraction occurs and theactin containing filaments

slide towards each other intothe center of the sacromere.

These light zones disappearbecause myosin and actinfilaments overlap.

Sacroplasmic Reticulum (SR)

- Stores and releases calcium- Surrounds the myofibril

Stimulation and Contraction of Single Skeletal Muscle Cells:

Excitability: (also called responsiveness or irritability)ability to receive andrespond to a stimulus

Contractilityability to shorten when an adequate stimulus is received

Extensibilityability of muscle cells to be stretched

Elasticityability to recoil and resume resting length after stretching

The Nerve Stimulus and Action Potential:

Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract


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Motor unit

one motorneuron and all

the skeletal

muscle cells

stimulated bythat neuron

Neuromuscular junction- Association site of axon terminal of the motor neuron and

muscle

Synaptic cleft

Gap between nerve and

muscle

Nerve and muscle do notmake contact

Area between nerve and

muscle is filled with

interstitial fluid

Neurotransmitter impulse -Chemical released by nerve upon arrival of nerve

- The neurotransmitter for skeletal muscle is acetylcholine

Acetylcholine attaches to receptors on the sarcolemma


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Sarcolemma becomes permeable to sodium (Na+)

More Na+ enters then K+ leaves. This gives the cell

interior and excess of positive ions, which reverses theelectrical conditions of the sacrolemma and opens more

channels that allow Na+ entry only.

Action Potential: is unstoppable, it travels over the

entire surface of the sacrolemma, conducting the

electrical impulse from one end of the cell to the other.The result is contraction of the muscle cell.

- While the action potential is occurring,

acetylcholine, which begins the process,

is broken down to acetic acid and cholineby enzymes.

- The muscle cell relaxes until stimulated

by the next round of acetylcholine

release.

The Sliding Filament Theory of Muscle Contraction:

Each cross bridges attaches and detaches several times during a contraction, generating

tension that helps to pull the thin filaments toward the center of the sacromere. The cell

shortens.


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Contraction of Skeletal Muscle

Within a skeletal muscle, not all fibers may be stimulated during the same interval

Different combinations of muscle fiber contractions may give differing responses

Graded responsesdifferent degrees of skeletal muscle shorteningcan beproduced by changing

The frequency of muscle stimulation

The numberof muscle cells being stimulated at one time

Types of Graded Responses

Twitch

Single, brief contraction

Not a normal muscle function


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Tetanus (summing of contractions)

One contraction is immediately followed by another

The muscle does not completely

return to a resting state

The effects are added

Unfused (incomplete) tetanus

Some relaxation occurs between contractions

The results are summed

Fused (complete) tetanus

No evidence of relaxation before the following contractions

The result is a sustained muscle contraction

Muscle Response to Strong Stimuli

Muscle force depends upon the number of fibers stimulated

More fibers contracting results in greater muscle tension

Muscles can continue to contract unless they run out of energy

Primary role is to produce smooth and prolonged muscle contraction.

Energy for Muscle Contraction

Initially, muscles use stored ATP for energy

ATP bonds are broken to release energy

Only 46 seconds worth of ATP is stored bymuscles

After this initial time, other pathways must be utilized to

produce ATP

1. Direct phosphorylation of ADP by creatine phosphate

(CP)

Muscle cells store CP

CP is a high-energy molecule

After ATP is depleted, ADP is left

CP transfers energy to ADP, to regenerate ATP

CP supplies are exhausted in less than 15 seconds


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2. Aerobic respiration

Glucose is broken down to carbondioxide and water, releasing

energy (ATP)

This is a slower reaction thatrequires continuous oxygen

A series of metabolic pathways

occur in the mitochondria

95 percent of the ATP used for

muscle activity comes from

aerobic respiration

3. Anaerobic glycolysis and lactic acid

formation Reaction that breaks down glucose

without oxygen

Glucose is broken down to pyruvic acid

to produce some ATP

Pyruvic acid is converted to lactic acid

This reaction is not as efficient, but is fast

Huge amounts of glucose are

needed

Lactic acid produces muscle

fatigue

Muscle Fatigue and Oxygen Deficit

When a muscle is fatigued, it is unable to contract even with a stimulus

Common cause for muscle fatigue is oxygen debt

Oxygen must be repaid to tissue to remove oxygen deficit

Oxygen is required to get rid of accumulated lactic acid

Increasing acidity (from lactic acid) and lack of ATP causes the muscle to

contract less

Types of muscle contraction

Isotonic contractions

Myofilaments are able to slide past each other during contractions

The muscle shortens and movement occurs

Isometric contractions

Tension in the muscles increases

The muscle is unable to shorten or produce movement


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They are trying to slide but the muscle pitted against some more or less

immovable object.

Muscle Tone

Some fibers are contracted even in a relaxed muscle

Different fibers contract at different times to provide muscle tone The process of stimulating various fibers is under involuntary control

Effect of Exercise on Muscles

Exercise increases muscle size, strength, and endurance

Aerobic (endurance) exercise (biking, jogging) results in stronger, moreflexible muscles with greater resistance to fatigue

Makes body metabolism more efficient

Improves digestion, coordination

Resistance (isometric) exercise (weight lifting) increases muscle size and

strength

Five Golden Rules of Skeletal Muscle

Activity

Muscles and Body Movements

Movement is attained due to a muscle moving an

attached bone

Muscles are attached to at least two points

Origin: Attachment to a moveable bone Insertion:

Attachment to an immovable bone

Types of Ordinary Body Movements

Flexion

Decreases the angle of the joint

Brings two bones closer together


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Typical of hinge joints like knee and elbow

Extension

Opposite of flexion

Increases angle between two bones

Rotation

Movement of a bone around its longitudinal axis Common in ball-and-socket joints

Example is when you move atlas around the dens of axis (shake your

head no)

Abduction

Movement of a limb away from the midline

Adduction

Opposite of abduction

Movement of a limb toward the midline

Circumduction

Combination of flexion, extension, abduction, and adduction

Common in ball-and-socket joints

Dorsiflexion

Lifting the foot so that the superior

surface approaches the shin

Plantar flexion

Depressing the foot (pointing the toes)

Inversion

Turn sole of foot medially

Eversion

Turn sole of foot laterally

Supination

Forearm rotates laterally so palm faces anteriorly

Pronation

Forearm rotates medially so palm faces posteriorly

Opposition

Move thumb to touch the tips of other fingers on the same hand

Types of Muscles

Prime movermuscle with the major responsibility for a certain movement

Antagonistmuscle that opposes or reverses a prime mover Synergistmuscle that aids a prime mover in a movement and helps prevent

rotation

Fixatorstabilizes the origin of a prime mover

Naming Skeletal Muscles

By direction of muscle fibers

Example: Rectus (straight)

By relative size of the muscle

Example: Maximus (largest


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By location of the muscle

Example: Temporalis (temporal bone)

By number of origins

Example: Triceps (three heads)

By location of the muscles origin and insertion

Example: Sterno (on the sternum) By shape of the muscle

Example: Deltoid(triangular)

By action of the muscle

Example: Flexorand extensor(flexes or extends a bone)

Convergent: Fasicles converge

toward a single insertion tendon.

Fusiform: results in a spindleshaped muscle with an expanded

belly.Parallel: the length of the fasicles

runs parallel to the long axis of themuscle.

Circular: typically surrounding

external body openings which theyclose by contracting.

Pennate: pattern, short fasicles

attach obliquely to a central tendon.

Unipennate: the fasicle only

inserts into only one side of the

tendon

Bipennate/Multipennate: ifthe fasicles insert into opposite

sides of the tendon or from several

different sides.

Head and Neck Muscles

Facial muscles

Frontalisraises eyebrows,

covers frontal bone

Orbicularis oculihas fibers

that run in circles around the eyes.

Closes eyes, squints, blinks,winks

Orbicularis orisCircular

muscles or the lip. Closes mouth

and protrudes the lips


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Buccinatorflattens the cheek, chews

Zygomaticusraises corners of the mouth smiling

Chewing muscles

Massetercloses the jaw and elevates mandible

Temporalissynergist of the masseter, closes jaw

Neck muscles

Platysmapulls the corners of the mouthinferiorly

Sternocleidomastoidflexes the neck,

rotates the head

Anterior muscles

Pectoralis majoradducts and flexes the

humerus

Intercostal muscles

External intercostalsraise rib cageduring inhalation

Internal intercostalsdepress therib cage to move air out of the lungs

when you exhale forcibly

Muscles of Trunk, Shoulder, Arm

Muscles of the abdominal girdle

Rectus abdominisflexes vertebralcolumn and compresses abdominal

contents (defecation, childbirth, forced

breathing) External and internal obliquesflex

vertebral column; rotate trunk and bend it

laterally

Transversus abdominiscompressesabdominal contents, deepest muscle of

the abdominal wall.

Posterior muscles

Trapeziuselevates, depresses, adducts,

and stabilizes the scapula

Latissimus dorsiextends and adductsthe humerus

Erector spinaeback extension

Quadratus lumborumflexes the spinelaterally

Deltoidarm abduction(injections ofless than 5 ml)


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Biceps brachiisupinates forearm, flexes elbow

Brachialiselbow flexion

Brachioradialisweak muscle Triceps brachiielbow extension (antagonist to

biceps brachii)

Muscles of the Lower Limb

Gluteus maximuship

extension

Gluteus mediuship abduction, steadies pelvis when

walking

Iliopsoaship flexion, keeps the upper body from fallingbackward when standing erect

Adductor musclesadduct the thighs

Muscles causing movement at the knee joint

Hamstring groupthigh extension and knee flexion

Biceps femoris

Semimembranosus

Semitendinosus

Muscles causing movement at the knee

joint

Sartoriusflexes the thigh Quadriceps groupextends the

knee

Rectus femoris

Vastus muscles (three)


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Muscles causing movement at ankle and foot

Tibialis anteriordorsiflexion and foot inversion

Extensor digitorum longustoe extension and dorsiflexion of the foot

Fibularis musclesplantar flexion, everts the foot

Soleusplantar flexion


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