MUSCLE PHYSIOLOGY

CHAPTER 11

I. MUSCLES

• 600+

• 40-50% of body weight

A. 3 Types of muscle

• 1. Skeletal

• 2. Cardiac

• 3. Smooth

• **majority of chapter will be focused on skeletal muscle

II. Functions of Skeletal Muscle

1. Movement

2. Posture

3. Support

4. Guard entrances/exits

5. Body Temperatures

III. Anatomy of Skeletal Muscle

a. Skeletal muscle contains bundles of skeletal muscle fibers.

• The cells actually called fibers

b. Components of skeletal muscle

i. Connective tissue

ii. Blood vessels

iii. nerves

c. Connective Tissue

A. Fascia - connective tissue found underskin and surrounding deeper organs

B. Epimysium - covers entire muscle• Surounded by fascia

C. Perimysium - covers fasicles or groups of skeletal muscle fibers

• Within epimysium• Tough connective tissue

D. Endomysium - covers skeletal muscle fiberDelicate connective tissue within perimysium

MUSCLE

IV. TENDON

• Epimysium, perimysium, and endomysium continue beyond the muscle to form the tendon of a muscle

• Connect muscle to bone

• Tough connective tissue

• Aponeuroses - merging of tendons to create a flat strong connective tissue

TENDON

d. Blood vessels

• Innovate muscles to provide nourishment muscle needs to function and rid of wastes.

e. Nerves

• Innovate muscles to control movements

IV. Overview of Skeletal Muscle/fiber

• Composed of bundles of skeletal muscle fibers that run entire length

• Have same structural parts as cells just different names

a. Structures found in skeletal muscle

i. Multinucleated

ii. Sacrolemma

iii. Sarcoplasm

iv. Sarcoplasmic reticulum

v. Mitochondria

vi. Myofibrils

vii. Sarcomere

Skeletal Muscle Cell

i. multinucleated

• Muscle have many nuclei

• Allows to make ribosomes which important for protein synthesis

ii. Sarcolemma

• Plasma membrane of muscle fiber

iii. sarcoplasm

• Cytoplasm of muscle cell

iv. Sarcoplasmic reticulum

• Network of tubules and sacs

• Equates to ER

• Contains Calcium ions

• Plays a role in muscle contraction

v. mitochondria

• Many mitochondria

• To produce ATP

vi. myofibrils

• Bundles of very fine fibers

• Extend lengthwise along skeletal fibers

• Made of thick and thin myofilaments

vii. sarcomere

• Basic unit of the muscle

• Like an osteon is to bone

V. Structure of Sarcomere

Structure cont….

• A band– Entire length of THICK filaments– Within A band is

• M line - line down the middle of thick filament• H zone - middle region of THICK filaments

ONLY Zone of overlap - where thick and thin fibers

overlap

Structure cont….

b. I banda. Segment that includes the Z line and

ends of THIN filaments.

b. THIN filaments ONLY

c. Z lines

• Signif a sarcomere

• Z line to Z line = 1 sarcomere

• Many sarcomeres make up a myofibril

d. Transverse Tubules

• T-tubules• Run transversely across sarcoplasm

and rt. angles to long axis of the cell• Formed by inward extensions of

sarcolemma• Function - allows electrical impulses

traveling along sarcolemma to move deeper into the cell

e. Triad

• T-tubules sandwiched between 2 sarcolemma reticulum

• Important because impulse travels through t-tubules and stimulates release of Ca+ needed for contraction

Sarcomere

Sarcomere

Triad

f. Myofibrils

• Each muscle fiber contains thousands of subunits called myofibrils

• Within myofibril are thick and thin myofilaments

i. Thin myofilament

• Made from 3 proteins1. Actin

2. Tropomyosin

3. troponin

1. Actin

• Globular

• Bead like strand of protein

• Twists around each other to form bulk of thin filament

• Chemically attracted to myosin

2. Tropomyosin

• Strand of protein that twists around actin

3. Troponin

• Spaced at intervals

• Blocks active sites (on actin) needed for muscle contraction

Actin, troponin, tropomyosinThin filament

ii. Thick Filament

1. Myosin– Shaped like golf clubs

2. Long flat shafts bundled together to form their crossbridges (heads) – Heads stick out and are chemically

attracted to actin active site of thin filament

Myosin

VI. Muscle PhysiologyA. Sliding filament theoryi. As a result of contraction

H zone gets smallerI band smallerZone overlap largerZ lines closer togetherA band - same

Fibers shorten by 30%When I band completely gone, contraction ends.

Thin filaments sliding toward center of sarcomere along side of the thick filaments

b. Nervous Stimulation of contraction

i. Motor neuron - nerve that sends signalii. Action potential - the actual signaliii. Motor end plate-where motor neuron

meets sarcolemma(forms neuromuscular junction)

iv. Neuromuscular junction- contact point between nerve and muscle

CONTRACTION

• Muscle contraction has 3 phases– Latent– Contraction– relaxation

i. Latent stage of contraction

a. Action potential (nerve impulse) of motor neuron reachs motor end plate, neurotransmitters (acetylcholine) released into synaptic cleft -goes across sarcolemma to excite cell

b. The Ach diffuses across synaptic cleft and binds to receptors which changes the sacrolemma

i. Latent Stage cont….

c. Impulse travels over sarcolemma inward along T-Tubules which release Ca+ from Sarcoplasmic Reticulum (adjacent to T-tubules)

ii. Contraction

• The Ca+ combine with troponin molecules of the thin filaments which causes tropomyosin to shift and expose active sites of actin

b. Once active sites exposed, the myosin heads (containing lots of ATP) of thick filament bind to actin and bend. This pulls thin filaments past thick filaments

ii. Contraction cont…

c. Each head then releases itself and binds to the next active site and pulls again (until ATP ends or I band disappears).

d. Thin filaments slide toward center of sarcomere to shorten each myofibril which shortens the muscle

iii. Relaxation

a. Sarcoplasmic reticulum pumps Ca+ back into sacs (within millisec. Most Ca+ are recovered).

b. Ca+ ions stripped off troponin which hides active site and myosin can’t attach, so filaments not being pulled and the relax.

videos• http://video.google.com/videosearch?gbv=2&

hl=en&q=%20latent%20phase%20of%20contraction&ie=UTF-8&sa=N&tab=iv#q=sarcomere+contraction&hl=en&emb=0

• http://video.google.com/videosearch?gbv=2&hl=en&q=%20latent%20phase%20of%20contraction&ie=UTF-8&sa=N&tab=iv#q=sarcomere+contraction&hl=en&emb=0

• http://www.youtube.com/watch?v=EdHzKYDxrKc&NR=1

d. Energy source

• ATP– Provides nrg to pull thin myofilaments

during contraction– Muscles must continually make ATP

because can only store small amounts of it.– When run out of ATP contraction stops and

relaxation begins

e. Length-tension relationship

• Amount of tension is proportional to number of cross bridges interacting with the thin filament

• The number of cross bridges interacting is determined by degree of overlap between thick and thin filaments

• When muscle fiber stimulated to contract, only myosin heads with in zone of overlap can bind to active sites to produce tension.

f. Rigor Mortis

• When die, circulation stops and skeletal muscles deprived of nutrients and oxygen.

• Within few minutes skeletal fibers run out of ATP and SR can’t pump Ca+ back into SR so cross bridges stay attached and stay contracted or stiff

Motor UnitMotor unit - nerve and muscle cell

a single motor neuron divides into branches

1 neuron can control a few muscle fibers

1 neuron can control hundreds of muscle fibers

**The fewer the # of fibers controlled by neuron, the more precise the movement

VII. Muscle Tone

• Tone of muscle due to continual, partial contraction • Small # of fibers contracted causing a taut (tight)

muscle• This is tonic contraction

– Important for posture– Ex. Loss of consciousness - unable to maintain posture

• Muscle with more than normal tone - spastic• Muscles with less tone = flaccid

• Muscle tone maintained by negative feedback– Sensors - stretch sensors in muscle/tendon– Integrator - spinal cord/brain– Effectors - somatic motor neurons

– Ex. Stretching - if stretch beyond limits, sensors in muscle tendon detect this and send signal to spinal cord/brain and tell somatic neuron to pull back

– This is called a spinal reflex

VIII. Classification of Muscle Contraction

• Skeletal muscles contract with varying degrees of strength

• 5 factors contribute to this principle:– 1. Amt ATP in muscle fiber– 2. # fibers contracting simultaneously (more

fibers-stronger contraction– 3. Intensity and freq. of motor neuron stimul.

• More motor units recruited, stronger contraction

• 4. Length-tension relshp – Muscle can’t contract strongly if initial length is

shortened (can’t slide much more)– Muscles can’t contract strongly when

overstretched b/c myosin heads can’t interact with actin

– Best contraction occurs when muscle is optimal length

– Ex. Biceps, slightly bent is greatest contraction

• 5. Amount of load imposed on muscle– Heavier load, harder contraction

– Ex. Hold a book on hand, then hold a pencil on hand. --- body uses negative feedback to control this.

Types of contractions

1. Isotonic - “same tension”

2. Isometric - “same length”

3. Tetnus

4. Treppe

Isotonic• Tension of muscle remains the same as

length of muscle changes• 2 types of isotonic contraction

– 1. Concentric - shortening of muscle– Ex. Pick up a book - same tension throughout the

movement, but muscle shortens

- 2. Eccentric - lengthening of muscle- Ex. When lower a book, same muscles but you are actually

lengthening them.

Ex. Walking - Flex knee then extend it, flex hip then extend it

Isometric• Muscle length remains same while muscle

tension increases.

• Ex. Push against a wall - not moving object b/c load is too heavy, tighten muscles but not lengthening or shortening

Tetnus• Smooth sustained contraction• Series stimuli come so fast that muscle

never has time to completely relax• This caused by coordinated contractions by

different motor units within the muscle• Contraction in muscle fibers overlap causing

a sustained contraction

• Ex. Posture, movement of most muscles• Our nervous system “smooths” out these

movements so we don’t hurt ourselves

Treppe• “staircase phenomenon”

• Gradual increase in strength of contraction

• This accounts for the fact a muscle contracts more forcefully after it contracts a few times (after it is warmed up)

• This is why warm up is important

IX. Types of Skeletal Muscle Fibers

• 3 types of muscle fibers

• 1. Fast - “white”

• 2. Slow - “red”

• 3. Intermediate -

Fast

• Not a lot of myoglobin (white)

• Fire faster b/c have faster type of myosin

And more efficient SR and t-tubules

• Deplete ATP faster

• Less mitochondria

• Can’t contract long prds.

• Generates tremendous force when contract

Slow• Contain high amts myoglobin (red)

• Myosin heads react slower

• Can keep up with ATP demand so don’t fatigue as easily

• Large amts mitochondria and oxygen

• Can sustain contractions longer

• Ex. Posture muscles

Intermediate

• Combo slow and fast

• More fatigue resistant then fast, less then slow

• Ex. Calf muscles, quads,

X. Exercise and muscle

• Improves muscle tone, strength and posture

• More efficient heart and lungs - – Decreases resting heart rate, less fatigue

• Less fatigue – More endurance– Do things more efficiently

• Hypertrophy – Increase in muscle size– Increase in # myofilaments in each fiber

NRG use and level of muscle activity

A. Muscle fatigue depend on – Glucose, oxygen supplied– Muscles store glucose in form called glycogen– Myoglobin attracts oxygen– More of each, less fatigue

B. Lactic Acid removal– Anaerobic resp. results in formation of lactic acid– Lactic acid accumulates in muscle causing burning

sensation– Some lactic acid goes to liver- converted back to glucose

d. Muscle atrophy– When don’t use muscles they get smaller

e. Physical conditioning

aerobic - endurance training

doesn’t create hypertrophy

anaerobic -

heavy weight training

produces hypertrophy

XII. Cardiac Muscle

• Aka striated involuntary muscle

• Found only in heart

• Made of cardiocytes

Function:

Pumps blood rhythmically and continuously

Structure:

•Cardiocytes

•Striated

•Intercalated discs- allows cells to “pump” as one unit

•Self excited cells – Contractions are longer b/c calcium remains in

SR longer

•Diads– T-tubules are larger and forms a diad with SR

•Pacemaker cells – stimulate electrical impulses

Smooth Muscle

• Small tapered cells with single nuclei

• Does not have t-tubules

• Lack striations

• Filaments arranged differently– Thin criss-crossed fibers– When myosin pulls the thin filaments, the muscle

“balls up”.

• Most flexible of all types of muscle

2 types of smooth muscle1. Visceral

– Single unit – Units join together to form continuous large

sheet of muscle

Ex. Digestive, urinary, reproductive– Self excited that spreads across entire tissue,

like a wave of contraction (peristalsis)

Peristalsis- moves food along digestive tract, urine to bladder and birth contractions

2. Multi unit– Not act as a single unit– Each individual unit – fiber does not generate its

own impulse– Responds to nerve input

ex. Walls of blood vessels, arector pili

Aging and Muscular System• Loss of muscle mass

(by age of 80 loss of 50%)

• Most muscle fibers develop into intermediate fibers (muscles slower)

• Muscle fibers contain less ATP, glycogen, and myoglobin

• Skeletal muscles become less flexible

• Tolerance of exercise less

• Ability to recover from musclular injuries decreases

Muscle Disorders1. Myopathies – muscle disorders

2. Strain – overexertion or trauma to muscle, overstretch or tear muscle fibers

3. Myositis – muscle inflammation

4. Fibromyositis- tendon inflames along with muscle inflammation.

ex. Charlie horse

5. Cramps – muscle spasms

can result from myositis or fibromyositis

also caused by irritation

ion and water imbalance

6. Contusion – muscle bruise, internal bleeding and inflammation

7. Muscle Infections –

virus, bacteria, parasites

causing myositis

trichinosis (parasite)

ex. muscle pain when get pain

8. Muscular Dystrophy –

• atrophy of skeletal muscle

• muscle replaced by fat and fibrous tissue

• begins with leg weakness and spreads

• lack of DNA code for protein dystrophin which forms strands in skeletal muscle fiber and helps hold cytoskeleton to sarcolemma. Helps keep muscle fiber from breaking during a contraction.

• 9. Myasthenia Gravis– Muscle weakness especially in face and throat– Autoimmune disorder where body attacks muscle

cell at neuromuscular junction.

10.Hernia – – Weakness in abdominal muscles– Abdominal organ protrudes through muscles

(usually small intestines or fat)