physio exam pt. 4 (8)

What are three types of muscle tissue?

Skeletal, smooth, and cardiac muscle tissue

What is skeletal muscle tissue structure and function? Are they voluntary or involuntary?

Part of skeletal muscles, long and striated, contract rapidly, tire easily; Functions: voluntary, maintenance of posture, & stabilization of joints

What is smooth muscle tissue structure and function? Are they voluntary or involuntary?

Found in walls of hollow internal organs, long and non-striated, & involuntary; Function: Move fluids and other substances through internal body channels & dilation and constriction of eye pupils

What is cardiac muscle tissue structure and function? Are they voluntary or involuntary?

Found in the heart, make up the heart walls, striated, involuntary; Function: Heartbeat

What are the four characteristics of muscle tissue?

Excitability, contractility, extensibility, and elasticity

What does the excitability of muscle tissue?

The ability to receive and respond to stimulus by changing its membrane potential and contracting

What does the contractility of muscle tissue?

The ability to shorten when adequately stimulated

What does the extensibility of muscle tissue?

The ability to extend or stretch

What does the elasticity of muscle tissue?

The ability to recoil and resume its resting length

What is the structure of skeletal muscles? What is each muscle covered by? What makes up a muscle?

Each muscle is an organ; Covered by epimysium; Bundles of fascicles

What make up a muscle?

Epimysium

What are fascicles covered by?

Perimysium

What makes up fascicles?

Group of muscle fibers

What is muscle fiber covered by?

Endomysium

What is an epimysium?

Connective tissues that surrounds the whole muscle

What are the functional units of muscle cells (fibers)?

Sarcomere

What does the muscle fiber consist of?

Bundles of the organelle myofibril

What is a myofibril?

Composed of bundles of myofilaments

What is the organizational level of a skeletal muscle?

Myofibril, muscle fiber, fascicle, epimysium, muscle

What are the components of a muscle fiber?

Cell membrane (sarcolemma), nuclei, mitochondrion, cytoplasm (sarcoplasm), glycosomes, myoglobin, sarcoplasmic reticulum, T tubules, & myofibril

What do myofibrils consist of?

Chains of sarcomeres

What do sarcomeres contain?

Myofilaments (rodlike structures)

What constitutes one sarcomere?

Region of myofibril between two successive Z discs

What are the two types of myofilaments?

Thick and thin filaments

What is the thick filaments position in sarcomeres?

Extend entire length of A band

What is the thin filaments position in sarcomeres?

Extend across the I band and partway into A band & anchored to Z discs

What is the thick filaments’ structure and components?

Made up of \~300 myosin molecules; Myosin molecule; 2 actin-binding sites; 1 ATP-binding site

What is the thin filaments’ structure and components?

Globular actin; Has myosin-binding sites; Polymerize to form long actin filaments; 2 actin filaments twisted; Contain actin, tropomyosin, troponin

What two forms does the myosin head have? How does it convert between the two forms?

Low and high energy form; ATP is broken down

What is the purpose of tropomyosin?

Polypeptide; Stabilize actin core & during relaxation, block myosin from binding

What is the purpose of troponin?

Polypeptide (3 subunits); One subunit binds to actin; One subunit binds to tropomyosin and helps position it on actin; One subunit binds calcium ions

What does troponin and tropomyosin do when calcium binds?

Shift exposing myosin-binding sites

I band

Appears light on microscope & contains only thin filaments

A band

Appears dark on microscope & runs the entire length of thick filaments

Z disc

Dark area in the middle of I band & made of proteins that anchor thin filaments

H zone

Light area in middle of A band & contains thick filaments that do not overlap with thin filaments (heavy only)

M line

Dark line in the middle of A band, within the H zone, & contains proteins that anchor thick filaments

What is the purpose of the sarcoplasmic reticulum?

Smooth endoplasmic reticulum & regulates intracellular levels of ionic calcium

Where is the sarcoplasmic reticulum located?

Surround each myofibril

What is the purpose of transverse tubules?

Sarcolemma protrude into cell; Lumen is continuous with extracellular space; Encircle each myofibril, penetrate deep into cell, & allow action potential to conduct to each sarcomere

Where are transverse (T) tubules located

At A and I band junction

What happens when a muscle fiber contracts?

Myosin heads on thick filament latch onto myosin-binding sites on actin in the thin filaments (cross bridge), sliding begins, the cross-bridge attachments form and break several times, propel the thin filaments towards the center of the sarcomere, the muscle shortens

What happens to the H zone while the muscle fiber contracts?

Disappears

What is the neuromuscular junction

Also called motor end plate, region where motor neurons \n contacts the skeletal muscles, one per muscle fiber, & consists of multiple axon terminals

What are the steps of skeletal muscle contraction?

1. Events at the neuromuscular junction
2. Muscle fiber excitation
3. Excitation-contraction coupling
4. Cross-bridge cycling

What are the events that occur at the neuromuscular junction?

1) Motor neuron fires an action potential, it arrives at the axon terminal; 2) The axon terminal releases ACh; 3) ACh binds receptors on the junctional folds of the sarcolemma; 4) ACh binding causes local __depolarization__ called end plate potential (EPP); 5) Acetylcholinesterase breaks down ACh and stops its actions

Why does ACh binding cause a local depolarization called an end plate potential in the neuromuscular junction?

Due to Na + entry and K + exit

What is the mechanism of action for sarin?

Chemical weapon & inhibitor of acetylcholinesterase; Nerve impulses continually transmitted causes muscle contraction

How does sarin lead to death?

Death occurs due to asphyxia and losing the ability to control of muscles involved with breathing

What does the action potential of a muscle cell look like?How does it differ from a neuronal action potential?

What are the steps of muscle fiber excitation?

1) The EPP triggers __depolarization__, if it reaches threshold... 2) Voltage-gated Na+ channels open → __AP__; 3) AP spreads across sarcolemma from one voltage-gated Na+ channel to the next 4) Na+ voltage-gated channels close and voltage-gated K+ channels open → __repolarization__

What are the steps of excitation-contraction coupling?

1. AP propagates along sarcolemma and down T tubules; 2) Voltage sensitive tubule proteins change shape; 3) Ca++ channels in terminal cistern of SR open; 4) Ca++ flows into the cytosol; 5) Calcium binds troponin and removes blocking actions of tropomyosin; 6) Myosin head (high energy form) from thick filament binds to actin of thin filament → cross bridge is formed

How does calcium binding allow the myosin head to bind to actin?

Calcium binds troponin and removes blocking actions of tropomyosin; Myosin head from thick filament binds to actin of thin filament → cross bridge is formed

What energy form of the myosin head bind to the thin filaments?

High energy form

Does acetylcholine binding cause depolarization or hyperpolarization?

Depolarization

How are the actions of acetylcholine terminated?

Acetylcholinesterase breaks down ACh and stops its actions

What are the steps of cross bridge cycling?

1) Cross bridge formation: High energy myosin head attaches to actin myofilament forming cross bridge; 2) Pi is released, the connection between the myosin head and actin strengthens; 3) ADP is released myosin head bends to low energy state. Doing so it pulls the actin filament towards the M line; 4) ATP attaches to myosin head, the link between the myosin and actin weakens. The myosin \n head detaches. Cross bridge breaks; 5) Myosin hydrolyzes ATP to ADP. Myosin returns to high energy state; 6) Cross bridge cycling continues until Ca++ levels drop and there is no ATP

What causes the myosin head to pull the thin filament towards the M line in cross bridge cycling?

Pi is released, the connection between the myosin head and actin strengthens & ADP is released, myosin head bends to low energy state pulling towards the M line

The binding of which molecule causes the cross bridge to \n break in cross bridge cycling?

ATP attaches to myosin head, the link between the myosin and actin weakens. The myosin head detaches. Cross bridge breaks

How does the myosin return to the high energy state in cross bridge cycling?

Myosin hydrolyzes ATP to ADP

What is rigor mortis?

Stiffness/rigidity of muscles postmortem (after death

What causes rigor mortis?

Cells die, membranes lose integrity, Ca++ leaks in, causing crossbridge formation; Actin and myosin cannot detach from one another b/c __no ATP__

What is muscle tension?

The force exerted by a contracting muscle on an object

What is load?

The opposing force exerted on the muscle by the weight of the object to be moved

What is motor unit?

One motor neuron and all the muscle fibers it innervates

What motor units are muscles controlling fine, precise movements controlled by?

Small motor units (10-20 fibers/units)

What motor units are muscles controlling large, powerful movements controlled by?

Large motor units (2000 fibers/unit)

What is a muscle twitch?

Response of a muscle to a singlestimulation

Muscle contracts ____ than it relaxes.

Faster

What is the latent period of a muscle twitch?

The few milliseconds following stimulation; When excitation contraction coupling is occurring; Cross bridges begin to cycle; Muscle tension not measurable

What is the period of contraction of muscle twitch?

Cross bridges are active & from onset to peak of contraction

What is the period of relaxation of muscle twitch?

Due to pumping of Ca++ back into the SR; Number of active cross bridges declining; Muscle tension decreases to zero

What is a temporal summation?

An increase in the frequency of stimulation

What causes temporal summation?

If 2 nerve impulses are delivered to a muscle in rapid succession, the 2nd twitch will be __stronger__ than the 1st; The 2nd twitch is greater b/c the muscle is already partially contracted; Produces __smooth, continuous muscle contraction__

What is recruitment for muscle contraction?

\n Also called multiple motor unit summation & an increase in the strength of stimulation

How does unfused/incomplete tetanus occur

If a muscle is stimulated an increasingly faster rate: The relaxation time between twitches becomes __shorter and shorter__; The concentration of Ca++ in the cytosol rises higher and higher; The degree of temporal summation becomes greater and greater; Becomes a sustained by __quivering contraction__

How does fused/complete tetanus occur

If a muscle is stimulated an increasingly faster \n rate: If stimulation frequency continues to increase, muscle tension __increases__ until it reaches __maximal tension__; There is no muscle relaxation; __Smooth, sustained__ contract

For recruitment, what happens as the load increases?

The number of motor neurons firing increases

What increases in recruitment?

Number of motor units activated, number of muscle fibers participating in contraction, & tension generated increases

What is the function of recruitment?

Controls the force of the contraction more precisely

What is subthreshold stimuli?

Produce no observable contractions

What is threshold stimulus?

The stimulus at which the the first observable contraction occurs

What is maximal stimulus?

The strongest stimulus that increases contractile force & all the muscle’s motor units are recruited

What is asynchronous recruitment?

All motor units of a muscle may be recruited, but at a given instant __some are contracting while others are resting__

Why is asynchronous recruitment important?

Prevents or delays fatigue & gives rise to muscle tone which helps stabilize joints and maintain posture

What are the two main categories of contraction

Isotonic and isometric contractions

What is isotonic contractions?

Muscles change length & muscle tension increases but does not exceed load

What is isometric contractions?

Muscles do not change length because muscle tension exceeds load

What are the types of isotonic contraction?

Concentric and eccentric

What happens in concentric in isotonic contraction? EX?

Muscle shortens and picking up a book

What happens in eccentric in isotonic contraction? EX?

Muscle lengthens and walking up a hill

What is an example in both concentric and eccentric in isotonic contraction?

Curling your bicep

What is an example of an isometric contraction?

Trying to lift something heavy and not lifting it & maintaining upright posture

In isotonic contractions, what are the results of the electrochemical and mechanical events?

Actin filaments shorten and cause movement

In isometric contractions, what are the results of the electrochemical and mechanical events?

Cross bridges generate force, but actin filaments __do__ \n __not__ shorten & myosin heads “spin their wheels” on same actin-binding site

What are the three ways ATP levels are maintained?

Direct phosphorylation, anaerobic pathway, & aerobic pathway

Why is ATP needed for muscle contraction?

Detach cross bridges, operate the calcium pump in the SR, & operate the sodium potassium pump in the plasma membrane

What is direct phosphorylation? Oxygen use? How much ATP is made in each pathway? Duration of energy provided?

Creatine phosphate (CP) stored in muscles; Oxygen use: none; Products: 1 ATP per CP; Duration: 15 seconds

What is anaerobic pathway? Oxygen use? How much ATP is made in each pathway? Duration of energy provided?

Glucose break down → 2 ATPs (glycolysis); Oxygen use: none; Products: 2 ATP per glucose, lactic acid; Duration of energy provided: 30-40 seconds