Exam 3 - Muscles

what type of muscle is this?

skeletal muscle

Characteristics of skeletal muscle/where it is found

has striations and is very structured

• voluntary

• found in tendons to attach bones

What type of muscle is this?

smooth muscle

Characteristics of smooth muscle/where it is found

involuntary muscle that lacks striations

-cells are a fusiform shape

found in walls of hollow organs

• bladder, stomach, intestine, blood vessels, ariways

arranged in stacking sheets that are arranged in 90 degree angle from each other to encourage contraction

What type of muscle is this?

cardiac muscle

Characteristics of cardiac muscle/where it is found

striated with intercalated disc (where two cells come together from end to end)

• located in the heart

• has ion channels to spread charge

Functions of muscle tissue

movement

stabilization of body position

storage and movement of substances

heat generation

Properties of muscle tissue

electrical excitability

• response to stimuli to produce contraction

contractility

• muscles shorten forcibly when stimulated

extensibility

• able to stretch between contractions

elasticity

• able to return to resting length

what muscle feature is this?!

tendon

what muscle feature is this?!

fascicle

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epimysium

what muscle feature is this?!

muscle fiber/cell

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endomysium

what muscle feature is this?!

myofibril

what muscle feature is this?! (covering)

perimysium

Epimysium

fibrous connective tissue covering the entire muscle unit

• continuous with tendon

Perimysium

fibrous connective tissue covering the fascicle

Endomysium

fibrous connective tissue covering the muscle fiber (each cell)

Tendon

fibrous connective tissue that attaches muscle to bone

• continuous with periosteum to convey force of contraction to bone

Aponeurosis

thin sheet of connective tissue connecting muscles to bone

-similar to tendons

Fascicle

bundle of fibers surrounded by perimysium

Myofibrils

the contractile elements separated into sarcomeres

• bundles of protein within a cell

what muscle feature is this?!

sarcolemma

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sarcoplasma

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transverse tubule

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terminal cisternae

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Sarcoplasmic reticulum

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myofilaments

what muscle feature is this?!

myofibril

Sarcolemma

plasma membrane deep to the endomysium, covering entire muscle cell

Sarcoplasm

cytoplasm of muscle fiber

• not a lot of it, encases myofibrils

• contains glycogen and myoglobin

T-tubules

infolding of sarcolemma penetrating through the cell

• associate with 2 terminal cisternae of SR to form a triad

• convey electrical signals deep into muscle cell

Myofibrils

long protein cords that contract- composed of myofilaments

• thick, thin, and elastic

Sarcoplasmic reticulum

smooth ER surrounding myofibril

• stores calcium and end in terminal cisternae

Sarcomere

1 unit of myofibril from one Z-disc to the next

• contractile unit

what muscle feature is this?!

M-line

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Z-disc

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H-zone

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A-band

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I-band

A Band

composed of overlapping thin and thick filaments except in the H zone (just thick)

-bisected by M-line

I band

composed of thin filaments

• bisected by Z-line

What are thick filaments made of? describe the orientation

made of myosin

• myosin dimerizes and each has a globular head and long fibrous tail

• the myosin head stick out of the filament everywhere except the H-zone, ready to bind to actin

What are thin filaments made of? describe the orientation

made of actin, troponin, and tropomyosin

• actin is the main globular protein that looks like a pearl necklace

  • has an active site for myosin

• troponin has a binding site for calcium

  • when attached, rolls tropomyosin off of actin active side to initiate contraction

• tropomyosin blocks the actin active site

what is this?

troponin of thin filament

what is this?

tropomyosin of thin filament

what is this?

actin of thin filament

What part of sarcomere moves during contraction?

thin filaments

pulls Z-disc toward midline to shorten sarcomere

What is the first step of sliding filament theory?

Myosin heads hydrolyze ATP into ADP and P

• heads pivot to enter high energy state

What is the second step of sliding filament theory?

after hydrolyzing ATP, myosin binds to actin to form crossbridges

What is the third step of sliding filament theory?

myosin cross-bridges rotate toward the center of the sarcomere - called the power stroke

• ADP and P are released

• myosin rotates and pulls actin with it

What is the fourth (final) step of sliding filament theory?

Myosin head binds to ATP and the cross-bridges detach from actin

Resting Membrane Potential

maintained by the sodium-potassium pump, it is the transmembrane potential when the cell is at rest

• separation of charges where inside of the cell is more negative

What tells myofibril to shorten?

electrical impulse in neuron → chemical signal at neuromuscular junction → electrical impulse travelling along sarcolemma

Action potential

all-or-nothing electrical signal produced by ion movements across the membrane of excitable tissues

• causes excitation of muscle cell

Neuromuscular Junction

way of communicating between the nervous system and muscular system along the synaptic cleft

• Acetylcholine (neurotransmitter) is released from neurons and exits in vesicles via exocytosis

• binds to receptors on muscle cell → generating electrical signal that tells muscle to contract

Acetylcholinesterase

an enzyme that breaks down the neurotransmitter ACh to terminate the signal that causes muscles to contract

Steps of Action Potential

1. start at resting potential

   1. Na+ and K+ channels closed

2. Depolarization

   1. Na+ channels open, Na+ enters the cell, K+ channels beginning to open

3. Depolarization ends, repolarization begins

   1. Na+ channels closed, K+ channels fully open, K+ leaves the cell

   Repolarization/ hyperpolarization

   1. Na+channels closed, K+ channels closing

Threshold

voltage that must be reached to enact all or nothing action potential

Depolarization

membrane potential becomes very positive

• opening of Na+ voltage-gated channel → Na+ rushes into the cell

Repolarization

membrane potential quickly decreases

• K+ exits the cell when opening voltage-gated K+ channel

• cell becomes more negative again

Hyperpolarization

voltage goes below resting membrane potential because potassium channels are slower to respond

• eventually evens out to resting membrane potential

Absolute refractory period

can’t respond to any stimulus because channels are already open and responding to a different stimulus

• during depolarization and repolariztion

Relative refractory period

could respond to a stimulus, but it has to be larger

• during the hyperpolarization phase when voltage is more negative, it takes more to reach the threshold

Excitation-contraction coupling

sequence of events by which an electrical signal leads to sliding of microfilaments

How is AcH released during excitation?

exocytosis

What kind of receptor is acetylcholine receptors?

ligand-gated ion channels

-then, na+ flows in and K+ flows out at the same time to produce a local potential

How does the charge from an action potential get down into the cell?

t-tubules , Ca2+ then stored in SR→ diffused into cytoplasm

What is happening during relaxation of a muscle?

troponin holds tropomyosin in position to block myosin binding site on actin

Calcium channels are closed

What is happening during contraction of a muscle?

Ca2+ binds to troponin which changes shape of the troponin-tropomyosin complex and uncovers myosin binding sites on actin

Ca2+ channels open

Length-tension relationship

length of the sarcomere at rest affects the amount of force generated by a muscle contraction

• optimal length of 80-120 results in the highest tension

  • gives best overlap between thin filament and place where myosin heads are exposed

Creatine phosphate pathway

stores ATP as ADP and adds a phosphate (From creatine phosphate or ADP) back to ATP when energy is needed

• quickest pathway, but very limited and short bursts

anaerobic respiration

generates ATP from a pathway that uses glucose for glycolysis, forming 2 ATP, lactic acid, and pyruvic acid

• a lot of steps, very little product

• used in the short-term

aerobic respiration

generates 34-36 ATP, along with heat, CO2,H20

• can be other things rather that glucose going into pathway

• requires oxygen to carry out cellular respiration in the mitochondria

motor unit

a motor neuron plus all muscle fibers innervated by it

twitch contraction

when all of motor unit contracts in response to single action in a neuron

Contraction period

Ca2+ binds to troponin

active sites exposed on actin

cross-bridges form

filaments slide toward the m-line

**The actual shortening of the muscle cell-

Relaxation period

decreased tension after contraction

• Ca2+ removed from sarcpllasm and stored in the SR

• troponin changes conformation

• tropomyosin occludes active sites

• cross bridges dissociate

• filaments slide away from midline

Latent period

when the action potential depolarizes sarcolemma

tension formed

Ca2+ released from SR, and increases in sarcoplasm

wave summation

stimulation delivered to a muscle fiber before it is completely able to relax

• no latent period because Ca+ is already i sarcoplasm and shortened elastic elements

results in more forceful contraction

Fused tetanus

during wave summation, if stimuli are frequent enough -results in a stable contraction force

• unfused is the in between

Isotonic contractions

muscle retains the same amount of tension, but changes in length to maintain a load

• aids in movement

two types are eccentric and concentric

Concentric contraction

type of isotonic

• muscle shortens to lift load

  • ex. flexing bicep

Eccentric contraction

type of isotonic

• muscle lengthens to lift load

  • ex. extending arm to put groceries on the counter

Isometric contraction

“same measure” - muscle stays the same length while developing tension

• doesn’t actually move a load, but has stabilizing effect

• ex. holding a yoga pose

Slow oxidative fibers

red fibers, slow fibers, slow-twitch fibers

• contract/hydrolyze ATP more slowly through aerobic respiration

• has blood vessels that contribute to red color

very fatigue resistant- prominent in marathon runner

Fast Glycolytic Fibers

white fibers. fast-twitch fibers

• uses glycolysis to quickly generate ATP

• no blood vessels to deliver oxygen → white

very fast contraction but not fatigue resistant - prominent in sprinters

Fast oxidative-glycolytic fibers

an intermediate

• uses both glycolytic and oxidative pathways to generate ATP

• pinkish color

• fast AND fatigue resistant

Factors that affect tension

• length of sarcomere befor contraction

• frequency of stimulation

• hydration status

• temperature

• fatigue

Compare the diameter of each fiber type

SO: smallest

FO: intermediate

FG: largest

Compare the fatigue resistance of each fiber type

SO: high

FO: intermediate

FG:low

compare the myoglobin content of each fiber type

SO: large amount

FO: large amount

FG: small amount

Compare the capillary supply of each fiber type

SO: many

FO: many

FG: few

• same trend with mitochondria

name the structure of smooth muscle cell

intermediate filament

name the structure of smooth muscle cell

dense body

name the structure of smooth muscle cell

thin filament

name the structure of smooth muscle cell

thick filament

Features of a smooth muscle cell

• single nucleus

• - tapered fusiform shape

• intermediate filaments connected by dense bodies

• no striations

Role of dense bodies

connect thin filaments to intermediate filaments like a fishnet

• similar to the Z-disc

Calmodulin

analogous to troponin in skeletal muscle

• binds to Ca2+ to become activated

• then activates myosin light chain kinase enzymes