Fundamentals of Human Physiology Exam 3 UIOWA

skeletal muscle

A muscle that is attached to the bones of the skeleton and provides the force that moves the bones

- Striated

- Voluntary

cardiac muscle

Muscle of the heart

- Striated

- Involuntary

smooth muscle

involuntary muscle found in internal organs

- Unstriated

- Involuntary

Sarcomere

contractile unit of a muscle fiber

Myosin

thick filament

Actin

thin filament

motor neurons

neurons that carry outgoing information from the brain and spinal cord to the muscles and glands

Motor unit

A motor neuron and all of the muscle fibers it innervates

neuromuscular junction

point of contact between a motor neuron and a skeletal muscle cell

in-series sarcomeres

sarcomeres that run on top of each other (longer fiber)

in-parallel sarcomeres

sarcomeres that run parallel to one another (thicker fiber)

- greater maximum contraction

Cross-bridge cycle

repeated sequential interactions between myosin and actin filaments at cross-bridges that cause a muscle fiber to contract

Ca+

What molecule controls the cross bridge cycle?

T-tubules (transverse tubules)

Action potential travels down ________________________

sarcoplasmic reticulum

Organelle of the muscle fiber that stores calcium

- Releases and removes Ca+ from the sarcomere

- Stimulated by action potential from T-tubule

Troponin, tropomyosin

Ca binds to ________________, which changes shape and prevents ________________________ from blocking binding sites on Actin

Contraction

turning on the cross-bridge cycle so that a muscle attempts to shorten

Tension

internal force generated within a contracting muscle

Load

external force against which the muscle acts

Isotonic contraction

constant load, but muscle changing lengths

- Concentric and eccentric

concentric contraction

muscle shortens against the load (tension > load)

Eccentric contraction

muscle attempts to shorten, but is forced to lengthen by the load (load > tension)

- muscle is generating tension while lengthening

isometric contraction

Muscle contracts but there is no movement, muscle stays the same length

- Tension = load

- Immoveable load

twitch contraction

the brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron

mechanical factors affecting muscle force

length, velocity, cross-sectional area

Muscle Length-Tension Relationship

maximal ability of a muscle to develop tension and exert force varies depending upon the length of the muscle during contraction

force-velocity relationship

force decreases as velocity increases

Type I fibers

Low force

Low velocity

Slow myosin ATP activity

High mitochondrial density

Type IIA Fibers (Fast Oxidative Fibers)

- Faster myosin ATPase activity

- Higher force production

- Higher velocity

- Less fatigue resistant than type I

- Intermediate mitochondrial density, myoglobin, capillary density

Type IIX fibers (fast-glycolytic)

- Fastest myosin ATPase

- Highest force production

- Fastest velocity

- Highest lactate production

- Low mitochondrial density, myoglobin, capillary density

- Highest glycogen storage

creatine phosphate system

The energy pathway that consists of adenosine triphosphate (ATP) and phosphocreatine (PC)

- provides immediate energy (between 10 and 15 seconds) through the breakdown of these stored high-energy phosphates

- All muscle fibers use

ATP

Maximum shortening velocity is determined by how fast a fiber can hydrolyze ______ to release myosin heads (myosin ATPase)

Motor unit

All muscle fibers in a single ____________ ________ are the same type

Slower

A muscle twitch is much _________________ than an action potential

Calcium

If another action potential arrives before complete relaxation, _________________ concentration increases

- Muscle continues to contraction

size principle of recruitment

motor units fire in order from small to large

principle of orderly recruitment

motor units are generally activated on the basis of a fixed order of fiber recruitment (slow twitch --> fast twitch)

Spinal cord

Motor neurons originate in the ______________ __________

Motor neuron pool

all the motor neurons that innervate a single muscle

Abundancy of neurotransmitters released to the motor neuron pool

- Faster (hence more) fibers recruited if excitatory signal increases

How does the nervous system decide if it should modify force via frequency or via # of motor units?

Cardiac differences similarities to skeletal muscle

- Smaller

- Un-nucleated

- Branched

Cardiac muscle fibers

Connected end-to-end via intercalated discs which contain gap junctions

- Gap junctions allow resistance free transfer of electrical current

- Optimize pumping

Myocardium

muscular, middle layer of the heart

- Atrial and ventricular are separate

Atrial

Excitation is initiated by pacemaker cells in the atrium, which excites the ______________ myocardium

ventricular

Excitation spreads from the atrial myocardium to the _________________ myocardium through conducting cells

Smooth muscle

- Found in walls of hollow organs and tubes

- Spindle-shaped cells with single nucleus

- Arranged in sheets

- Excitation-contraction coupling mechanism

myofilament arrangement of smooth muscle

No striations

- Filaments not arranged in sarcomeres or myofibrils

- Much longer thin filaments

- Dense bodies instead of z discs

excitation inputs of smooth muscle

- ANS (SNS/PNS)

- Hormones

- Local chemical factors

- Stretch

- Pacemaker potentials

Voltage-gated channels OR Sarcoplasmic reticulum

Where does Ca+ come from in smooth muscle contraction?

excitation-contraction coupling (smooth muscle contraction)

1. Ca+ binds to calmodulin

2. Activates myosin light chain kinase

3. MLCK phosphorylates myosin heads and allows them to form cross bridges and muscle contracts

4. Myosin light chain phosphate dephosphorylates myosin heads and inactivates the cross bridges and muscle relaxes

1 gallon/5L on average

Average blood volume?

55, 45

Blood is composed of ____% plasma, ____% hematocrit (everything else)

Erythrocytes

red blood cells

- carry oxygen

Leukocytes

white blood cells

- immune system

Platelets

protein cell fragments

- participate in blood clotting

Plasma

90% water

- Stuff dissolved in water: electrolytes, nutrients, gasses, plasma proteins

RBC structure

- No nucleus/organelles

- Structure: biconcave discs, flexible membrane

Helps blood flow, maximizes surface area

Why do red blood cells biconcaved?

fit through capillaries

Why do RBC's have flexible membranes?

Hemoglobin

Oxygen carrying pigment in red blood cells

- also binds CO2 and H+

Erythropoesis

production of red blood cells

Bone marrow

Where are red blood cells produced?

hematopoietic stem cells

form blood cells

Erythropoetin

Hormone produced by kidneys which stimulates red bone marrow to increase production of red blood cells

Spleen

______________ removes most of old erythrocytes

Anemia

Below normal number of hemoglobin

- Diagnosed by blood tests

Causes:

- Nutrient deficiencies (Iron, folate, B12)

- Blood loss

- Bone marrow failure

- Hemolytic anemia

Megakarocyte

Platelets come from _________________________ cells

Hemostasis

stoppage of bleeding from a broken blood vessel

3 processes:

1. Vascular spasm

2. Formation of a platelet plug

3. Blood coagulation (clotting)

Vascular spasm

constriction of blood vessels to reduce blood flow through a damaged vessel

formation of platelet plug

- platelets aggregate on contact with exposed collagen in damaged wall of the vessel

- platelets release substances (ADP) which causes surface of nearby circulating platelets to become sticky

An undamaged endothelium constantly releases factors that prevent it

Why don't platelets aggregate on a normal endothelium?

blood coagulation (clotting)

transformation of blood from liquid into a solid gel (coagulation proteins)

- reinforces the platelet plug

Leukocytes function

- Defends against invading pathogens

- Identifies and destroys cancer cells

- Removes worn-out cells and debris

Pulmonary circuit

carries blood to the lungs for gas exchange and returns it to the heart

- Oxygenates blood

systemic circuit

transports blood between heart and rest of body

Atria

two upper chambers of the heart

Ventricles

the two lower chambers of the heart

atrioventricular valves

between atria and ventricles

- controls blood entering the heart

semilunar valves

controls blood flow out of the heart

- pulmonary and aortic

prevents blood from flowing in the wrong direction

- only open one way

Purpose of valves in the heart?

Systole

Contraction of the heart

- ejection of blood

Events:

1. Isovolumetric contraction

2. Ejection

Diastole

Relaxation of the heart

- filling of blood

Events:

1. Isovolumetric relaxation

2. Rapid filling

3. Atrial contraction

isovolumetric contraction (systole)

- start of systole

- Ventricular pressure rises above atrial pressure resulting in closing of AV valves

- ventricles contract but no blood ejected

- both valves closed

Ejection (systole)

ventricular pressure exceeds arterial pressure resulting in semilunar valves to open

isovolumetric relaxation (diastole)

pressure in ventricles drops below arterial pressure resulting in closing of semilunar valves

- atria begin to fill

Rapid filling (diastole)

pressure in ventricles falls below atrial pressure opening the AV valves

- Begins filling of the ventricles

autorhythmicity

heart's ability to control its own contractions

autorhythmic cells

initiate action potentials and spread impulse throughout heart

- do not contract

contractile cells

produce contractions that propel blood

- 99% of myocardial cells

SA node

pacemaker of the heart

AV node

relays electrical impulses from atria into ventricles

- conduction delay because don't want atrium and ventricle to contract at same time

Bundle of His

transmits the cardiac impulse from the AV node to the ventricles causing them to contract

Purkinje fibers

fibers in the ventricles that transmit impulses to the right and left ventricles, causing them to contract

ECG

potential difference at the body surface due to electrical activity of heart

Mechanism of Autorhymicity

potential changes due to changes in permeability to various ions (K+, Na+, Ca)

- unique voltage gated channel (F type) causes pacemaker potential

- Once threshold is reached, AP due to Ca+

Hemodynamics

the science of the blood flow through the vasculature

Viscosity

A liquid's resistance to flowing

Arteries

carry blood away from the heart

Arterioles

small vessels that receive blood from the arteries

Capillaries

Microscopic vessel through which exchanges take place between the blood and cells of the body