Physiology exam 3

Function of the muscular system

Movement

Muscles are classified into 3 groups based on

Characteristics and function

Smooth, cardiac, skeletal

Term for a single cell

Muscle fiber

Skeletal muscle

Moving muscle

Smooth muscle

Moving components, usually within a tube

Controlled by brain

Cardiac muscle

Pumping blood

Thick filaments are made up of

Myosin

Polypeptide chains form

Two globular heads and a tail

Crossbridge

Area that exerts force on the thin filament

Heads contain

ATP binding sites and actin binding sites

Thin filaments are made up of

Actin and troponin and tropomyosin

Thin filaments have an important role in

Regulating contractions

Tropomyosin

Overlaps binding sites blocking cross bridges

Troponin

Ca2+ binding to troponin regulates skeletal muscle contraction

Moves tropomyosin away and allows myosin to interact with the actin

Excitation-contraction coupling occurs

At axon terminal of neuron

Motor end plate is

ESPS on muscle fiber

Ca2+ enables…

ACh to be released across the space between axon terminal and motor end plate

ACh binds to

Nicotininc ACh (muscle fibers) receptors

Nervous system stimulates

Muscle fibers

Action potential in muscle fibers

Contract

Action potential starts in

Muscle cell

T-tubule voltage gated calcium channel

Open when membrane is depolarized

Relaxation occurs as

Ca2+ is pumped into Sarcoplasmic reticulum when an action potential stops

Cross bridge cycle is initiated when

Excitation contraction coupling increases Ca2+ and binding sites on actin are exposed

Each cross bridge goes through its cycle ____ of other cycles

Independently

Step 1 in cross bridge cycle

The active site on actin is exposed as Ca2+ binds to troponin

Step 2 in cross bridge cycle

Myosin head forms a cross bridge with actin

Step 3 in cross bridge cycle

During the power stroke, myosin head bends and adp and phosphate is released

Step 4 in cross bridge cycle

A new molecule of atp attaches to the myosin head causing the cross bridge to detach

Step 5 in cross bridge cycle

ATP hydrolyzes to adp and phosphate, which returns the myosin to the cocked position

The myosin head serves as a….

Myosin ATPase enzyme

What is happening in step one and two of the cross bridge cycle

Energy present excitement, ca2+ concentration needs to increase and bind troponin and tropomyosin to move to bind myosin and actin

Release of phosphate upon binding creases a change on myosin head to produce a

Power stroke

What is happening in step three and four of cross bridge cycle

Binding actin and myosin creates a release of phosphate

After the power stroke….

Adp is released and a new atp binds, to make myosin release actin

What is happening in step five and six of cross bridge cycle

“Resetting”

Filaments do not change length but they….

Slide

Smooth muscle

Undergo changes in volume with accompanying changes in lengths of the smooth muscle fibers

Examples of smooth muscle

Stomach, intestine, blood vessels

Smooth muscle cells have a ___ nucleus

Single

Nerves are part of the ____ division instead of somatic

Autonomic

In smooth muscle….

Thick and thin filaments are not organized into myofibrils

In smooth muscles, calcium binds to….

Calmodulin

Pacemaker cells

Action potential spontaneously in absence of neuronal or hormonal input

Depolarization opens

Voltage gated ca2+ channels

Prolonged stimulation holding ca2+ concentrations is called

Latch state

Latch state

Muscles hold tension for long periods

Ex. Sphincter muscles of GI tract

Two sources of Ca2+ that contribute to the rise of cytosol in ca2+ in smooth muscle

1. Sarcoplasmic reticulum
2. Extracellular ca2+ enters the cell through plasma membrane

To relax….

Ca2+ has to be removed using Ca-ATPase pump

Cellular structure of cardiac muscle

Striated using sliding filament mechanism

Arranged like smooth muscle

Myocardium

Contracts fully every time its stimulated

Cells are linked by

Gap junctions

Gap junctions

Spread currents quickly

Autonomic nervous system hormones and neurotransmitters modulate

Amount of ca2+ released

Heart cannot exhibit

Summation and tetanus due to refractory period and fulling heart

Three main functions of the cardiovascular system

Transportation, circulation, protection

Transportation

O2 and co2, products of digestion, waste

Regulation

Hormones, temperature (cycling blood through deep to surface vessels)

Protection

Clotting and immune system

Cells of cardio

Myocardial cells, node (pacemaker) cells, erythrocytes, endothelial cells

Circulatory system is impacted by which systems

Endocrine, nervous, respiratory, Kidneys

Arteries

Away

Veins

In

Systemic

Arteries carry oxygenated blood and veins carry deoxygenated blood

Pulmonary

Carry deoxygenated blood to the lungs and the pulmonary veins vary oxygenated blood to the heart

Atari empty into _____

Ventricles

Atrioventricular valve (AV)

Permits blood flow from atrium to ventricles but not backwards

Left AV/mitral

Bicuspid

Right AV

Tricuspid

Pulmonary valve

Right ventricle to pulmonary trunk

Aortic valve

Left ventricle to aorta

Conducting system

Special cells in electrical contact with cardiac muscle cells via gap junction

Conducting system functions

Initiated heartbeat and spreads action potential

Signal starts in the

SA node

SA node is located in

Right atrium

Discharge rate of the SA node determines

Heart rate

Action potential jumps from cell to cell via

Gap junctions

Action potential passage through AV node is

Slow

After AV node is excited…

Action potential moves down the septum to the bundle of His

AV node and bundle of his

Separates atrial and ventricular contraction

Purkinji fibers

Spread the potential quickly throughout the ventricles causing them to depolarize together

Slow predictable depolarization is called

Pacemaker potential

K+ channels

Gradually closing from previous action potential

HCN channels

Open in response to hyperpolarization and Na+ enters causing spontaneous depolarization

HCN channels also called

Funny channels

T (transient) type CA2+

Provide final depolarizing boost

Ca2+ influx through

L (long lasting) type voltage gated channel

Long action potential

L type gated channels located in

Sarcoplasmic reticulum

K+ opens =

Repolarization

Opens because of change in voltage

Change in heart rate can be because of

Change in concentration, change at receptor (beta blockers)

Voltage gated Na+ open

Depolarization

Transient K+ channels and L type Ca2+ channels…

Open slow and balance

A long refractory period….

Prevents summation and tetanus

A long refractory period is almost as long as…

Contraction itself

Prevents re-excitation during contraction

P wave

Atrial depolarization

Qrs complex

Ventricular depolarization

Path of depolarization differs and currents in the fluid change direction accordingly

T wave

Ventricular repolarization

Atrial repolarization typically….

Does not register

Happens at same time as QRS complex

Bradycardia

Cardiac rate slower than 60 beats per minute

Tachycardia

Cardiac rate faster than 100 beats per minute