BIOL2040 EXAM 2

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neuromuscular junction steps

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neuromuscular junction steps

  1. Ap spreads across the synaptic knob

  2. AP triggers opening of voltage gated Ca2+ channels

  3. Ca2+ floods into synaptic knob

  4. Ca2+ binds proteins on Ach vesicles

  5. Ach vesicles merge with plasma membrane and Ach is expelled via exocytosis into synaptic cleft

  6. Ach diffuses across the synaptic cleft

  7. Ach Binds receptors on motor end plate (sarcolemma)

  8. Ach receptors are chemically gated, so Ach binding opens the channels

  9. Na+ diffuses into motor end plate and K+ diffuses out (more Na+ diffuses in that K+ moves out)

  10. The flow of ions quickly slows due to resistance, but sufficient to change the RMP from -90mV to -65mV (an end plate potential)

  11. This is enough to trigger opening of voltage gated channels in the sarcolemma to initiate an action potential across the muscle

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three types of muscle tissue

skeletal, cardiac, smooth

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cardiac muscle

Cardiac, striated, involuntary (not conscious)

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smooth muscle

found in walls of hollow visceral organs (stomach, urinary bladder, airways) -visceral, no striated and involuntary

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skeletal muscle

Organs attached to bones and skin

  • Elongated cells called muscle fibers

  • Striated (striped)

  • Voluntary (i.e., conscious control)

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2 types of protein found in skeletal contraction

actin and myosin

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actin

thin filament

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myosin

thick filament

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muscle functions

  • Movement of bones or fluids (e.g., blood)

  • Maintaining posture and body position

  • Stabilizing joints

  • Regulating - circular muscle bands called sphincters contract and relax to regulate passage of material - -Generation heat (especially skeletal muscle)

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Special Characteristics of Muscle Tissue

  • Excitability (responsiveness Nervous control): ability to receive and respond to stimuli

  • Conductivity: can transmit/propagate electrical signals along membranes (action potentials)

  • Contractility: ability to shorten forcibly when stimulated, unique to muscle cells

  • Extensibility: ability to be stretched/lengthen

  • Elasticity: ability to recoil to resting length after stretching

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Layers of skeletal muscle

epimysium, perimysium, endomysium

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epimysium

dense irregular connective tissue surrounding entire muscle

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Perimysium

dense irregular connective tissue surrounding fascicles (groups of muscle fibers)

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endomysium

fine areolar connective tissue surrounding each muscle fiber.

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Aponeurosis

Broad, sheet-like tendon that fuses muscle to bone, abdominal muscles

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flexors

if the center of the connected bones are brought closer together when the muscle contracts (biceps)

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extensor

if the bones move away from each other when the muscle contracts Flexor-extensor pairs are called antagonistic muscle groups (triceps)

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generate an action potential

  1. Resting state, no ions move through voltage-gated channels

  2. Depolarization caused by massive inflow of Na+

  3. Repolarization is caused by K+ flowing out of the cell

  4. Hyperpolarization caused by continued K+ outflow -hyperpolarization more negative

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satellite cells

Cells that do not fuse and remain as single cells in adults (adult stem cells)

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myoblasts

stem cells that fuse to form each muscle fiber

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Sarcolemma (plasma membrane)

invaginates to form T-tubules extending into sarcoplasmic reticulum

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T tubules

tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side

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sarcoplasm (cytoplasm)

Has typical organelles plus contractile proteins and other specializations

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sarcoplasmic reticulum

Surrounds myofibrils like a net sheet

  • stores calcium •Has pumps that import Ca2+ into sarcoplasmic reticulum where it binds to calmodulin and calsequestrin

•Has channels that allow Ca2+ to be released into surrounding sarcoplasm to trigger contraction

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what structures are associated with energy production

-mitochondria -myoglobin -glycogen -creatine phosphate

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terminal cisternae

  • large regions of sarcoplasmic reticulum adjacent to T-tubules and serve as reservoirs for calcium ions and have calcium release channels and calcium pumps (discussed later)

  • Two cisternae and T-tubule is called a triad -T-tubules contain voltage gated calcium channels

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Myoglobin

within cells allows storage of oxygen used for aerobic ATP production

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Glycogen

stored for when fuel is needed quickly

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creatine phosphate

can quickly give up its phosphate group to help replenish ATP supply

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myofibrils

(hundreds to thousands per cell)

  • Bundles of myofilaments (contractile proteins) enclosed in sarcoplasmic reticulum

  • Make up most of the cell's volume

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myofilaments

contractile proteins bundled in myofibrils

  • These filaments do not extend the length of the muscle but are found in units - contain thick and thin filaments

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I band of sarcomere

regions occupied only by thin filaments

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A bands of sarcomere

central region of the sarcomere (thick filament region)

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H zone of sarcomere

central region with no thin filament overlap, just thick filaments

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M line of sarcomere

thin transverse protein mesh work in center of H zone, an attachment site for thick filaments

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sliding filament theory

theory that actin filaments slide toward each other during muscle contraction, while the myosin filaments are still

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crossbridge cycling

  1. Crossbridge formation

  2. Power stroke

  3. Release of myosin head

  4. Reset myosin head

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rigor mortis

stiffness of the body that sets in several hours after death

  • no more ATP

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Myokinase

transfers Pi from one ADP to another

  • 5 to 6 seconds of max exertion

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creatine kinase

transfers Pi from creatine phosphate to ADP

  • Can 10-15 seconds of energy during max exertion

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describe two mechanisms for phosphate transfer

myokinase and creatine kinase

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glycolysis

the breakdown of glucose by enzymes, releasing energy and pyruvic acid.

  • occurs in cytosol

  • short term supply of ATP

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aerobic cellular respiration

the process by which cells use oxygen to obtain usable energy from an energy source

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lactic acid

byproduct of anaerobic respiration

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oxygen debt

the amount of oxygen required after physical exercise to convert accumulated lactic acid to glucose

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what activated action potential in smooth muscle?

  • stretch

  • hormones -temperature

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glycolitic fibers

use anaerobic cellular respiration

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Oxidative fibers (fatigue-resistant)

use aerobic cellular respiration Extensive capillaries Many mitochondria Large supply of myoglobin (red fibers)

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Periods of Muscle Contraction

latent period, contraction period, relaxation period

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latent period of muscle twitch

Time after stimulus but before contraction begins No change in tension

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contraction period of muscle twitch

Time when tension is increasing, if tension becomes great enough to overcome the load, the muscle will shorten

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relaxation period of muscle twitch

  • Time when tension is decreasing to baseline

  • Begins with release of cross bridges

  • Ca2+ reentry into SR -Generally, lasts a little longer than contraction period

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isometric contraction

no shortening; muscle tension increases but does not exceed load

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isotonic contraction

muscle shortens because muscle tension exceeds load

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lever

a rigid structure that pivots around a fixed point known as a fulcrum

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smooth muscle cells

single, fusiform, uninucleate; no striations

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smooth muscle contraction steps

  1. stimulus leads to opening of voltage gated Ca 2+channels

  2. Ca2+ enters sarcoplasm and binds to calmodulin

  3. Calcium-calmodulin complex binds to myosin light-chain kinase (MLCK)

  4. MLCK phosphorylates myosinhead

  5. cross bridges form, pull on actin, similar to skeletal muscle but more slowly

  • as thin filament slides, it pulls on dense bodies -dense bodies attached to intermediate filaments, which are attached to dense plaques in sarcolemma

  • these filaments move inward, entire cell shortens

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relaxation of smooth muscle contraction

  1. cessation of stimulation

  2. removal of Ca2+ from sarcoplasm

  3. dephosphorylation of myosin by myosin light-chain phosphatase

  4. can be slow to relax due to latch bridge mechanism

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fatigue resistant

  • Energy requirements low compared to skeletal muscle

  • Can maintain contraction without additional ATP through latch-bridge mechanism

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myogenic response

contraction in reaction to stretch, stretch of muscle opens Ca2+ channels

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Arteries

carry blood away from the heart

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Veins

carry blood to the heart

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cardiovascular system

composed of the both heart (pump), blood vessels (tubes) and blood (fluid) To remain healthy, our bodies cells require: • Continuous supply of oxygen and nutrients • Removal of carbon dioxide and wastes

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pulmonary circulation

flow of blood from the heart to the lungs and back to the heart

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systemic circulation

Transports blood from the left side of the heart to the systemic cells of the body for nutrient and gas exchange - blood brought back to the right side of the heart

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Pericardium

Membrane surrounding the heart

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fibrous pericardium

dense fibrous irregular connective tissue

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parietal pericardium

covers the wall of the pericardial cavity, simple squamous epithelium

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visceral pericardium

simple squamous and delicate areolar connective tissue, adheres directly to the heart

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epicardium

outermost layer, composed of simple squamous epithelial tissue and an underlining areolar connective tissue

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myocardium

composed of a thick layer of cardiac muscle, generates force for contraction

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endocardium

internal surface of the heart, simple squamous epithelial tissue and underlying areolar connective tissue

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right atrium

three veins drain blood into this chamber, superior and inferior vena cava and the coronary sinus (blood draining from the myocardium) • Separating the right atrium from the right ventricle is the tricuspid valve

  • deoxygenated blood

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right ventricle

deoxygenated blood enters the right ventricle from the atrium and is pumped through the pulmonary semilunar valve into the pulmonary artery - blood is delivered to left and right lungs

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left atrium

oxygenated blood moves from the lungs into the left atrium via left and right pulmonary veins • Separating the left atrium from the left ventricle is the bicuspid/mitral valve

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left ventricle

blood moves from the left ventricle through the aortic semilunar valve into the aorta and delivers oxygenated blood to the body

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divisions of the aorta

-brachiocephalic artery -left common carotid artery

  • left subclavian artery

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brachiocephalic artery

splits into the right subclavian artery and right common carotid artery - supplies right arm, head and neck

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left common carotid artery

supplies neck and face

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left subclavian artery

supplies left arm, head and thorax

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intercalated disks

Cardiac muscle cells are branched and join with their neighbors via junctions

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desmosomes

Anchoring junctions that prevent cells from being pulled apart

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coronary arteries

run across the surface of the heart and branch extensively

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heart conduction system

SA node, AV node, bundle of His, bundle branches, and Purkinje fibers

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sinoatrial node

located on the posterior wall of the right atrium, adjacent to the entrance of the superior vena cava. SA node is the pacemaker of the heart

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atrioventricular (AV) node

located on the floor of the right atrium

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atrioventricular bundle

extends from the AV node into and through the interventricular septum - divides in two

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purkinje fibers

extend left and right and continue through the walls of the ventricles

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reaching threshold (SA node)

slow leak Na+ channels cause potential to rise, low voltage gated Ca+ channels open, Ca+ flows into nodal cells, RMP -60mV to -40mV

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depolarization (SA node)

reaching threshold, causes opening of fast Ca2+ voltage gated channels, Ca2+ enters nodal cell, membrane charge -40mV to just above 0mV

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repolarization (SA node)

Ca2+ channels close and voltage gated K+ channels open, K+ flows out of cell, membrane potential returns to -60mV -Process begins again, each process takes about 0.8 sec, results in about 75 beats/min

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cardiac conduction system

a system of specialized muscle tissues that conducts electrical impulses that stimulate the heart to beat

  • found in hearts walls

  • SA node, AV node, Bundle of HIS, Bundle Branches, perkinje fibers

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cardiac muscle cell RMP

-90 mV

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SA node RMP

-60 mV

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depolarization in cardiac muscle cell

An AP transmitted through the conduction system triggers the opening of fast voltage gated Na+ channels in the sarcolemma, Na+ enters the cell, membrane potential -90mV to +30mV, then voltage gated Na+ channels enter an inactivated state

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initial repolarization in cardiac muscle cell

Na+ channels inactivate and K+ leaves through open K+ channels

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plateau in cardiac muscle cell

due a decrease in K+ permeability and an increase in Ca2+ permeability. Slow Ca2+ voltage gated channels open, Ca2+ enters the cell, Ca2+ entry causes sarcoplasmic reticulum to release stores of Ca2+ - overall no real change in electrical charge (plateau phase), fast K+ channels close

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mechanical events in crossbridge cycling

  1. crossbridge formation

  2. power stroke

  3. release of myosin head

  4. reset of myosin head

  • muscle relaxation in initiated by closing of voltage gated Ca2+ channels and pumping Ca2+ back into SR or interstitial fluid

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crossbridge formation

myosin heads attach to actin

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power stroke

myosin head pivots and pulls the thin filament, decreasing sarcomere length

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