apk2105c uf exam3

Skeletal Muscle Tissue

smallest to largest: myofilaments (actin and myosin) bundled to make myofibrils -\> bundles of myofibrils wrapped in sarcolemma and wrapped in endomysium make up muscle fibers -\> bundles of muscle fibers wrapped in perimysium make up fascicles -\> bundles of fascicles wrapped in epimysium make up skeletal muscles (organs).

Myofibril

contractile organelle that runs the length of the myocyte

Thick filament

Myosin

Thin filament

Actin

T tubule

Runs around and in between myofibrils
Invagination of the sarcolemma as it is diving down into the cell's interior

Sarcoplasmic Reticulum

Network, membrane bound organelle that surrounds the myofibrils
Function: stores calcium
Terminal cisternae: enlarged regions of the SR that make contact with the T-tubules

Triad

T tubule, and lateral sacs
2 terminal cisternae and an individual T-tubule cutting between \= triad
2 triads for every sarcomere

Sarcomere

The functional unit of organization of the myofibril and its overlapping arrangement of actin and myosin given the striated appearance
Goes from one Z disc to other Z disc

How many actin encircle each myosin thick filament?

6

M line (midline)

Chunk of proteins running straight down the middle of sarcomere
Ends of myosin thick filaments are holding on to each other (end to end)

A band

length of myosin
no change in contraction

I band

only have actin myofilaments
on either side of Z line

H zone

represented by length of myosin
in the middle of A band, immediately surrounding M line

Z disc

Actin extending from one sarcomere to the next
Zippered seam between adjacent sarcomeres

Contractile Proteins

Actin and myosin

Regulatory proteins

Tropomyosin and troponin

Contractile proteins: the thin myofilament (actin)

Double helix structure, each strand made up of individual globular-looking protein structures called G actins
Each G actin has a specific myosin-binding site

Strand of G actin

F actin

Two strands of F actin with a double helix

actin thin myofilament

Tropomyosin

Long strand that lays on top of myosin binding site

Tropomyosin v Troponin

Tropomyosin: long, fibrous type of protein
Troponin: a complex of several smaller globular proteins
Function: keep myosin binding sites covered or exposed

What uncovers tropomyosin?

Calcium
When it is released from the sarcoplasmic reticulum, It will bind to one of the proteins in the troponin complex.
When calcium binds you get conformational change in that troponin.

When myosin sites are exposed

Myosin and actin can come together and you get contraction every time

Contractile Protein: the Thick Myofilament (myosin)

Fibrous double helix tail that terminates as double headed globular structure
Final structure: 300 double helixed strands

Bare zone of myosin

Tails of strands

Titin

At end of myosin, attaches myosin to Z disc
Large, highly elastic protein
Allows recoil

Head of myosin

Actin binding site
ATPase site- hydrolyze ATP, dephosphorylate them

Sarcomere is

smallest functional unit of skeletal muscle contraction

The Sliding-Filament Mechanism of Contraction

actin filament and myosin filament overlap during contraction

How do we initiate muscle contraction?

-Somatic motor neurons release ACh onto the sarcolemma
-Somatic motor neurons always activate muscle cells to contract
-Muscle cells are electrically excitable, so they can also generate action potentials...called end plate potentials

Excitation-contraction coupling

series of events that link the end-plate potential to muscle contraction

The motor unit

One somatic motor neuron and all the muscle fibers it innervates

Large motor unit

dependent on how many muscle fibers the neuron innervates

The muscle twitch

the mechanical response of a muscle cell, or a motor unit, or a whole muscle to a single end-plate potential

Latent period of muscle twitch

millisecond time delay between the action potential and initiation of contraction (time for ECC)

Contraction phase of muscle twitch

crossbridge cycling is occurring and cytosolic Calcium levels are rising

Relaxation phase

cytosolic Calcium is returned to the SR and the number of crossbridges decline

Not all twitches are equal

Variability in speed of contraction and amount of force generated
Depends on diameter of the muscle cell
Depends on type of myosin ATPase

Isotonic twitch/ contraction

muscle generates a force that just exceeds the load resulting in muscle length change
-concentric
-eccentric

Isometric twitch/ contraction

muscle generates a force that does not exceed the load and results in no change in muscle length

limited muscle to decrease in length causing a maximal contraction

Isometric contraction

Muscle contracts but does not shorten because contractile element decreased in length but elastic element increased in length (accommodated change)

Concentric contraction

Both contractile and elastic element shorten, shortening entire length of muscle

Treppe

Warming up phase for the myocyte

smaller motor units

activate smaller fibers

when ATP utilization increases

ATP decreases
ADP increases

The creatine-phosphate system

CP+ADP yields ATP + Creatine

slow oxidative fibers

red

fast oxidative-glycolytic

pink

fast glycolytic

white

Endurance exercise enhances the oxidative capacity

fast glycolytic transitions to fast oxidative glycolytic
more mitochondria, bigger mitochondria
increased capillary density
fiber diameter decreases

High intensity exercise enhances glycolytic capacity

fast oxidative-glycolytic transitions into fast glycolytic
less mitochondria, smaller mitochondria
decreased capillary density
increased concentration of glycolytic enzymes
fiber diameter increases

myosatellite cells

cells that hang out along the periphery of the cell that fuse themselves into the skeletal muscle, adding their nuclei and organelles to the structure

biceps brachii

elbow flexion
attaches in front of elbow
agonist

triceps brachii

attaches behind elbow
elbow extension
antagonist

muscle spindles

detect length
combo of intrafusal fibers with their sensory axons
type 1 and type 2 afferent

golgi tendon organs

detect tension

alpha motor neurons

type of axons innervating skeletal muscle cells (somatic)

gamma motor neuron

synapse on intrafusal fibers

muscle spindle stretch

stretched: lots of action potential
relaxed: still some action potential
contracted: very few

atria

receive blood

ventricles

pump blood out

wall of left ventricle

very thick because blood is going to entire rest of body

wall of right ventricle

not as thick as left ventricle
because blood is going to lungs that are close

arteries

carry blood away from heart

endothelium

simple squamous epithelial

arterie structure

endothelium-smooth muscle-connective tissue

arteriole

lots of smooth muscle tissue

capillary

endothelium-basement membrane (thin CT)

venule

small vein

vein vs artery

artery-more smooth muscle
vein-larger lumen

venous valves

like semilunar valves

blood anatomy

plasma- 55% of blood volume
Buffy coat (leukocytes and platelets)- less than 1%
Erythrocytes- 45% HCT

Erythrocytes (RBCs)

red because of hemoglobin
biconcave disc imparts flexibility and increased surface area
slightly larger diameter than capillaries- go through one by one single file

pulmonary circuit

associated with lungs
arteries bring deox blood
veins bring ox blood

veins

bring blood back to heart

in series blood flow

pulmonary- systemic

right heart

pulmonary

left heart

systemic (rest of body)

why is parallel blood flow necessary

same blood delivered to all organs
-same nutrients/oxygen
-same capacity to remove wastes
regional control of blood distribution
-decrease blood to one organ
-increase blood to another organ

GI tract and liver
Kidneys

have parallel and series blood flow

heart has myogenic contractile activity

skeletal muscle has neurogenic contractile activity

autorhythmic cells

specialized cardiac myocytes
-pacemaker cells:
-conduction fibers

pacemaker cells

spontaneously generate action potentials and establish heart rhythm
-located in high concentration at SA node and AV node

Conduction fibers

transmit action potentials
larger diameter cardiac myocytes

SA node

high posterior wall of right atrium where the superior vena cava opens

AV node

interatrial septum, floor of right atrium

ECG

non invasive technique for recording ELECTRIC activity in the heart

reflects patterns of action potential firing in the entire population of cells that make up the myocardium

P-wave

Atrial depolarization

QRS complex

ventricular depolarization

T wave

ventricular repolarization

Lead 2

LL-RA
down and towards left
atria to ventricle

systole

ventricular contraction

diastole

ventricular relaxation

systolic blood pressure

maximal aortic pressure occurs during systole
blood entering the aorta from the left ventricle

diastolic blood pressure

minimum aortic pressure occurs during diastole
spend more time in DP
blood leaving aorta as it moves downstream

mean arterial pressure

average aortic pressure during a cardiac cycle
overall driving force for blood to reach organs

end diastolic volume

volume when blood is about to be pushed out of ventricles
avg- 130ml

end systolic volume

volume when all blood has been pushed out of ventricles
avg- 60ml