Ch 9 - 11: Anatomy and Physiology

skeletal muscle tissues are composed of..

• Skeletal muscle tissue

• Nervous tissue

• Blood

• Connective tissues

connective tissue of skeletal muscle

• Fascia: Thin covering of connective tissue around a muscle

• Tendon: Cord-like mass of connective tissue that connects muscle to a bone

• Aponeurosis: Sheet-like mass of connective tissue that connects a muscle to bone, skin, or another muscle

compartment syndrome

• Fluid accumulation within a compartment

• Results in increase in pressure in compartment

• Leads to deficiency of oxygen and nutrients

• Causes severe pain

thick vs thin filaments

a) Composed of myosin protein, heads form cross-bridges with thin filaments (creates chain of binding that allows ATPase enzyme in heads myosin to convert to energy for muscle contraction)

b) Composed of actin protein, associated with troponin and tropomyosin, which prevent cross-bridge formation when muscle is not contracting

neuromuscular junction

synapse where axon of motor neuron and skeletal muscle fiber interact to contract skeletal muscle fibers

parts:

• Motor neuron: Neuron that controls skeletal muscle fiber

• Motor end plate: Specialized folded portion of skeletal muscle fiber sarcolemma

• Synaptic cleft: Space between neuron and muscle fiber, across which neurotransmitter travels

• Synaptic vesicles: Membrane-bound sacs containing neurotransmitters

• Neurotransmitters: Chemicals released by motor neuron to deliver message to muscle fiber

Acetylcholine

neurotransmitter that provides stimulus for muscle contraction

• Nerve impulse causes release of ACh from synaptic vesicles

• ACh binds to ACh receptors on motor end plate

• ACh causes changes in membrane permeability to sodium and potassium ions, which generates a muscle impulse (action potential)

• Impulse causes release of calcium ions from SR, which leads to muscle contraction

excitation-contraction coupling

• muscle relaxation - Ca+2 ions are stored in SR, Troponin-tropomyosin complexes cover binding sites on actin filaments

• muscle stimulation - Muscle impulses cause SR to release +2 Ca ions into cytosol, ion binds to troponin to change its shape, tropomyosin is held in place by a troponin molecule; change in shape of troponin alters the position of tropomyosin → binding sites on actin are now exposed

• Myosin heads bind to actin, forming cross-bridges

sliding filament model of muscle contraction

1. When sarcomeres shorten, thick and thin filaments slide past each other

2. H zones and I bands narrow, Z lines move closer together, Thin and thick filaments do not change length

3. Overlap between filaments increases

cross bridge cycling

1. Myosin head attaches to actin binding site, forming crossbridge

2. Myosin cross-bridge pulls thin filament toward center of sarcomere

3. ADP and phosphate are released from myosin

4. New ATP binds to myosin

5. Linkage between actin and myosin cross-bridge break and ATP splits

6. Myosin cross-bridge goes back to original position, ready to bind to another binding site on actin

muscle relaxation

1. Acetylcholinesterase (enzyme) rapidly decomposes ACh remaining in the synapse (Muscle impulse stops when ACh is decomposed)

2. Stimulus to sarcolemma and muscle fiber membrane ceases.

3. Calcium pump moves +2 Ca back into sarcoplasmic reticulum (SR).

4. Troponin-tropomyosin complex again covers binding sites on actin.

5. Myosin and actin binding are now prevented (Muscle fiber relaxes)

energy sources for muscle contraction

`1. ATP reserves - first source of energy for muscle contraction

2. Creatine phosphate - Initial source of energy to regenerate ATP from ADP and P, Stores energy in phosphate bond, like ATP

3. cellular respiration - Must be used to fuel longer periods of muscle contraction, breaks down glucose to produce ATP, glucose stored as glycogen in muscle cells

myoglobin

stores extra oxygen in muscles carried from lungs by hemoglobin, increases the amount of oxygen available to support aerobic respiration

anaerobic (lactic acid) threshold

shift in metabolism from aerobic to anaerobic during strenuous muscle activity when the above systems cannot supply the necessary O2 → produces lactic acid

oxygen debt

• At end of strenuous exercise, muscles may be left with oxygen debt

• amount of oxygen needed by liver cells to convert the lactic acid to glucose, and to restore muscle ATP and creatine phosphate concentrations (stabilize metabolic activity)

muscle fatigue

inability to contract muscle

caused by: decreased blood flow, ion imbalances across sarcolema, loss of desire to continue the exercise, accumulation of lactic acid

muscle cramp

• Sustained, involuntary muscle contraction

• May be caused by changes in electrolyte concentration in extracellular fluids in the area

threshold stimulus

Minimum strength of stimulation of a muscle fiber required to cause contraction

• action potential is generated when strength of stimulus reaches threshold

post threshold reached:

• impulse spreads through muscle fiber, releasing +2Ca from SR and activating cross-bridge formation

• One action potential from a motor neuron releases enough ACh to produce threshold stimulus in muscle fiber, causing a muscle impulse

twitch

Contractile response of a single muscle fiber to a single impulse

Periods of time associated with a twitch:

• Latent period: Delay between stimulation and start of contraction

• Period of contraction: Fiber pulls at attachments

• Period of relaxation: Pulling force decreases

length - tension relationship

length of muscle fiber before stimulation determines amount of force it can develop

• depends of number of cross bridges able to be formed which depends on optimal overlap

• Optimum starting length is resting length of the muscle fiber; this allows the greatest force to develop

• Stretched muscle fibers develop less force, since some myosin heads cannot reach binding sites on actin (too little overlap)

• Shortened muscle fibers also develop less force, since compressed sarcomeres cannot shorten further (too much overlap)

summation

Process by which the force of individual muscle fiber twitches combine, when frequency of stimulation increases

• Produces sustained contractions (partial tetany of tetany)

tetanus (partial vs complete)

• partial - Occurs at higher frequencies of stimulation, time spent in relaxation between twitches becomes very brief

• complete tetany - Occurs at very high frequencies of stimulation, only in laboratory, forceful sustained contraction has no relaxation between twitches

motor unit

motor neuron plus all the muscle fibers it controls

• whole muscle has many motor units

• coarse movements - produced with large number of fibers in a unit

• precise movements - produced with fewer muscle fibers in a motor unit

recruitment

increase in the number of motor units activated to produce more force

• smaller diameter axons recruited first and larger diameter axons when intensity of the stimulus increases bc they can produce sustained contractions of increasing strength

• recruitment continues as intensity increases until all units activated

______ and ______ can produce sustained interactions of increasing strength

summation and recruitment

_____ muscle contractions are smooth movements

whole

muscle tone

continuous state of partial contraction in resting muscles; normal tension/firmness

• maintains body posture

• increases metabolic energy used

isotonic contraction

Muscle contracts and changes length

Concentric: when muscle tension is greater than load, muscle shortens

Eccentric: when muscle tension is less than load, muscle lengthens

isometric contraction

muscle contracts but does not change length, and tension develops but parts attached to muscle do not move

slow twitch fibers (type I)

• Always oxidative

• Resistant to fatigue

• Red fibers (Abundant myoglobin)

• Good blood supply

• Many mitochondria

• Slow ATPase activity; slow to contract

fast twitch fatigue resistant fibers (type IIa)

• Intermediate twitch fibers

• Intermediate oxidative capacity

• Intermediate amount of myoglobin

• White fibers

• Resistant to fatigue

• Rapid ATPase activity

fast twitch glycolytic fibers (type IIb)

• Anaerobic respiration (glycolysis)

• White fibers (less myoglobin)

• Poorer blood supply than slow-twitch fibers

• Fewer mitochondria than slow-twitch

• More SR than slow-twitch

• Susceptible to fatigue

• Fast ATPase activity; contract rapidly

smooth muscle fibers

• Shorter

• Single, centrally located nucleus

• Elongated with tapering ends

• Myofilaments randomly organized

• Lack striations

• Lack transverse tubules

• Sarcoplasmic reticulum (SR) not well developed

multi unit smooth muscle vs visceral smooth muscle

A) Cells are less organized, Function as separate units, Fibers function independently, Iris of eye, walls of blood vessels, Stimulated by neurons/hormones

B) Single-unit smooth muscle; cells respond as a unit, Sheets of spindle-shaped muscle fibers, Fibers held together by gap junctions, Exhibit rhythmicity, Conduct peristalsis, Walls of most hollow organs, More common type of smooth muscle

smooth muscle characteristics

location: blood vessels, reproductive system, glandular system, digestive, urinary and intergumentary system

Description: non-striated, no sliding filaments, single central nucleus, loose arrangement of filaments,

Filaments structure: myosin fibers have more heads per filament, thin filaments attached to dense bodies

cellular characteristics: free calcium ions in cytoplasm triggers contraction

How does ATP function in skeletal muscles?

muscles store enough ATP to start the contraction and manufacture more as needed

• ATP - active energy

• creatine phosphate - NRG storage in resting muscle

• creatine phosphokinase - enzyme that regens ADP to ATP

Layers of connective tissue of skeletal muscle

Epimysium

• D: collagen later connected to the deep fascia

• F: separates the muscles from surrounding tissue

Perimyseum

• D: surrounds muscle fiber bundles (fascicles)

• F: contains blood vessels and nerve supply to vessicles

Endomysium

• D: surrounds muscle fiber cells (fibers)

• F: contains capillaries and nerve fivers contacting muscle fibers and myosattelite cells (stem cells) that repair damage

What cells do skeletal muscles develop from?

Mesodermal cells (myoblasts)

function of sarcomeres

transmission of action potential for muscle contraction

actin vs myosin

a) twisted strands of globular molecules with myosin binding site

b) has head and tail; tail- binds to other myosin molecules and head -2 globular protein that reaches the nearest thin filament (form cross bridge with actin by a pivoting motion

tropomyosin and troponin

a) double strands that cover 7 active sites on actin, binds to troponin

b) protein w 3 binding subunits (subunit binding to tropomyosin, subunit binding to actin to hold complex in place, subunit with receptor that binds to Ca2+ ions)

Excitation contraction coupling

1. action potential arrives at neuromuscular junction

2. neurotransmitter acetocholine released at terminal and binds to receptors on sarcolemma

3. acetocholine at receptor causes change in membrane permeability allowing sodium to enter from outside the cell

4. action potential created in the sarcolemma due to depolarization as positively charged sodium ions make membrane less negatively charged

5. depolarization causes waves through tubule that lead to the release of calcium ions from the sarcoplasmic reticulum

6. action potential traveling through T tubule causes release of calcium from the sarcoplasmic reticulum

7. calcium ions bind to receptors on troponin which react by changing shape and moving away from tropmyosin (complex broken)

8. Actin can now bind to myosin initiating sliding filaments

9. relaxation - signal from nervous system makes acetylcholine disappear and remaining are reabsorbed by neuron or broken down by enzymes

10. repolarization - causes calcium to come off troponin receptors and be reabsorbed

11. troponin goes back to OG shape covering binding sites

frequency of stimulation

how many successive twitches reach a muscle fiber

treppe

stair step increase in twitch tension that is caused by repeated stimulations immediately after relaxation phase

wave summation

increasing tension of summation twitches (tension builds more rapidly and relaxation phase overlaps with twitch cycle)

maximum tension

all motor units reach tetanus, only can be sustained for a very short time

sustained tension

less than maximum tension allows for rest periods and facilitates smoother movement

aerobic metabolism

prinmary NRG source of resting molecules (breaks down fatty acids to produce 34 ATP per glucose)

anaerobic glycolysis

primary NRG source for peak muscular activity, produces 2 moles ATP per one mole glucose (stored as glycogen in the skeletal muscles)

• lactic acid is byproduct of this

• lack oxygen to support mitochondria

recovery period

time taken for muscles to return back to normal

• oxygen becomes more available

• mitochondrial acitvity resumes

cori cycle

removal and recycling of lactic acid in the liver to produce pyruvic acid which becomes energy

muscle metabolism

• muscles at rest - metabolise fatty acids and store glycogen

• light activity - generate ATP through the breakdown of carbs lipids and amino acids

• peak activity - NRG provided by anaerobic reactions

• horomones influence

power vs endurance

a) max tension that muscle can produce

b) max time an activity can be sustained

both depend on types of fibers and conditioning

types of muscle fibers

1. fast fibers - contract quickly, large glycogen reserves, few mitochondria (for coarse mvmnt)

2. slow fibers - slow to contract and fatigue, sm diameter, more mitochondria, contain myoglobin (pigment that binds oxygen)

3. intermediate fibers - mid sized, low myoglobin, more capillaries, slow to fatigue

muscle hypertrophy vs muscle atrophy

a) muscle growth from heavy training increases diameter of fibers, mitochondrial acitvation, glycogen reserves

b) lack of activity reduces tone/size/power, and prolonged inactivity may result in muscle being replaced with fibrous muscle

cardiocytes

small, 1 nucleus, striated, short wide tubules, aerobic, intercalated discs for communication

intercalated discs

specialized intercellular junctions that join cell membranes of adjacent cardiocytes via gap junction or desmosome

functions: maintain structure, enhance molecular/electrical connections, conduct action potentials

characteristics of cardiac tissue

1. automaticity - contraction w/o stimulation (controlled by pacemaker cells)

2. variable contraction tension - influenced by nervous system

3. extended contraction time

4. prevention of wave summation and tetanic contractions by cell membranes

types of smooth muscle

1. multi unit smooth muscle - D: Cells are less organized, Function as separate units stimulated by neurons and horomones, fibers function independently L: Iris of eye, walls of blood vessels

2. visceral smooth muscle - D: Single-unit smooth muscle; cells respond as a unit, Sheets of spindle-shaped muscle fibers, Fibers held together by gap junctions, Exhibit rhythmicity • Conduct peristalsis L: Walls of most hollow organ, More common type of smooth muscle

smooth muscle contraction

• calmodium instead of troponin •

• Two neurotransmitters affect smooth muscle: Acetylcholine (Ach) and norepinephrine (NE)

• Hormones can stimulate or inhibit smooth muscle

• Stretching can trigger smooth muscle contraction

• slower to contract and relax

• more resistant to fatigue

• can change length without changing tautness

agonist

muscle that causes an action

• includes prime movers - Agonist primarily responsible for movement

• e.g. bicep is agonist (flexion) and antagonist is triceps (extension)

synergist

Muscles that assist agonist/prime mover

antagonist

Muscles whose contraction causes movement in the opposite direction of the prime mover

parallel muscles

fibers parallel to the long axis of the muscle

Ex. biceps brachii - fibers run paralell in vessicle arrangement

convergent muscles

a broad area converges on an attachment site that pull in different directions that include tendons, apneurosis, or raphe (groove of connective tissue)

e.g. pectoralis muscle

Pennate muscles

form an angle with the tendon

• do not have as large range of motion as parallel muscles

• contain more myofibrils than parallel muscles

• develop more tension

types

• unipennate - fibers on one side of the tendon (e.g. extensor digitorum)

• bipennate - fibers on both sides of the tendon (e.g. rectus femorus)

• multipennate - tendon branches within the muscle, more complex (e.g. deltoid muscle)

circular (sphincters)

open and close to guard the entrances to the body

• e.g. orbicularis oris and muscles around eyes

Lever

bones are rigid moving structure with a fulcrum (fixed point aka joint)

first class lever

seesaw like structure with central fulcrim applied between force and load

e.g. sternocleidomastoids - weight that must be overcome is weight of head and fulcrum is C1 and joint

second class levers

wheelbarrow; center load between applied force and fulcrum

• small force moves large weight

• e.g. gastricnemeus and soleus muscles raising the leg

third class levers

most common in the body, center applied forced between load and fulcrum and greater force moves smaller load

• greater force maximizes speed and distance traveled

• e.g. biceps brachii and shoulder joint

origin and insertion

origin: fixed point

insertion: moving point

• most muscles originate or insert on the skeleton

• origin is usually proximal to insertion

axial muscles vs appendicular muscles

a) position head and spinal collumn, move rib cage (60% skeletal muscles)

b) support pectoral and pelvic girdles, limbs (40%)

orbicularis oris

constricts the mouth opening

buccinator

muscle responsible for moving food around the cheeks

masseter

strongest jaw muscle

rotator cuff muscles

SITS - frequently injured

• supraspinatous

• infraspinatous

• teres minor

• subscapularis

and tendons

muscles that move the forearm and the hand

• originate on humerus and insert on forearm

• extensors - mainly on posterior and lateral surfaces of the arm

• flexors - mainly on the anterior and medial surfaces

fixator

a muscle that acts to stabilize the origin and other parts of the body effective for movement

sternocleidomastoid

rotates the head

membrane voltage is generated by..

first by the movement of sodium ions (Na⁺) into the cell, and later the movement of potassium ions (K⁺) out of the cell through specified protein channels in the plasma membrane (referred to in muscle cells as the sarcolemma)

power stroke

movement of myosin when binding to actin

summation

excitatory postsynaptic potentials and inhibitory possynaptic potentials are added together at trigger zone → combined voltage determines yes or no action potential

vessicle trafficking

membrane recycling'; synaptic vessicle becomes part of cell membrane as it releases neurotransmitter → endocytosis returns membrane tp cytoplasm and forms new vessicles

neuropeptides

act as neurotransmitters or neuromodulators (substances which alter a neurons response to a neurotransmitter or block relase)

e.g. ekephalins - relieve pain sensations

neuronal pools

groups of interneurons taht connect with each other and are located in CNS (cell bodies may be located in different parts) → work together to perform a common function

• each recieves input and generates output to/from other neurons

• may affecr other pools/peripheral effectors

faciliatation

repeated impulses on an excitatory presynaptic neuron may cuase that neuron to release more neurotransmitters in response to a single impulse → increases likelihood of postsynaptic cell reaching threshold

convergence vs divergence

1 neuron recieves input from several neurons → allows for collecting, processing, responding, to info from diff types sensory receptors

1 neuron sends impulses to several neurons via branching of its axon → may activate several motor units in a skeletal muscle

multipolar neurons

99% of neurons with processes extending from cell body

bipolar neurons

1 dendrite to 1 axon; located in the eyes, ears, and nose sensory receptors

unipolar neurons

1 process from cell body and 2 branches that function as an axon

L: mainly in ganglia of PNS

sensory/afferent neurons

unipolar or bipolar

interneurons

link neurons in CNS to relay info from 1 pt CNS to another

motor neurons

multipolar neurons; in somatic control skeletal and in autonomic control smooth and cardiac glands

astrocyte

type neuroglia that connects neurons to blood vessels exchanaging nutrients and growth factors (neurons that stimulate cell division)

• form scar tissue

• aid metabolism in some substance

• regulate ion concentration

• part of makeup blood brain barrier

oligodendrocytes

type of neuroglia that myelinate CNS axons and provide structural support

ependymal cells

line central spinal cord and ventricles of brain, cover choroid plexuses (CSF secreting), help regulate composition CSF

• ciliated cuboidal or columnar cells

microglia

phagocytes that provide structural support

neuroglia of the PNS

• Shwann cells

• sattelite cells - support ganglia by nourishing and balancing ionic concentrations

neurom regeneration of PNS

1. axon separated from body and myelin sheath degenerates

2. shwann cells and neurilemma (surrounds myelin sheath) remain

3. remaining shwann cells provide guiding sheath for growing axon

neuron regeneration of the CNS

regeneration unlikely because no neurilemme to act as guiding sheath and oligodendrocytes dont proliferate post injury