Physiology Muscles, CV system, Blood vessels

General overview of ch 12,13, 14 to help remember definitions and equations to deepen other study methods

myofibril

contractile organ that runs the length of the myocyte

t/f: myofibrils are not the only organelles in a muscle fiber

true

sarcoplasmic reticulum (SR) definition

membranous organelle that surrounds the myofibrils; thought of as a specialized version of the smooth ER

what is a feature of the SR

terminal cisternae

terminal cisternae

enlarged region of the SR that makes contact with the t-tubules

what does the terminal cisternae store

Ca++ (calcium ions)

Transverse tubules (t-tubules)

invaginations of the sarcolemma into the cell’s interior

t/f the T tubules are continuous with the sarcolemma

true

How many triads for every sarcomere?

2

what are the components of a triad

1. terminal cisternae

2. t tubule

3. terminal cisternae

sarcomere

functional unit of the organization of the myofibril and it’s overlapping arrangement of actin and myosin give the striated appearance

cross action of the a band shows

where thick and thin filaments overlap

why is the great amount of overlap of thick and thin filaments important?

for generating force

how many actin encircle each myosin thick filament

6

I band

only contains actin that is not interacting with myosin

A band

actin and myosin are overlapping

Z line

anchor points for actin on either side of the sarcomere

M line

middle of sarcomere, anchors myosin

thin contractile myofilament

actin

building of actin molecules

progression: g actin; f actin (fiber); double-helical actin strands

regulatory protiens

troponin and tropomyosin

relaxed state of muscles

myosin binding sites are covered

contracting state of muscles

calcium is present and bound to troponin, causing the myosin binding site to be exposed for the binding of the myosin head

what happens to titin when the sarcomere lengthens

the stretching force causes titin to elongate

what are features of myosin’s globular head

actin binding site and ATPase site

what happens at the ATPase site of the myosin globular head

ATP is dephosphorylated

what happens to the distance between the z lines when the sliding filament mechanism is employed and the sarcomere goes from a relaxed state to a contracted state

it shortens

what happens to the I bands when the sliding filament mechanism is employed and the sarcomere goes from a relaxed state to a contracted state

it shortens

what happens to the H zone when the sliding filament mechanism is employed and the sarcomere goes from a relaxed state to a contracted state

it shortens

what happens to the A band when the sliding filament mechanism is employed and the sarcomere goes from a relaxed state to a contracted state

it remains the same

t/f: the crossbridge cycle occurs simultaneously for all crossbridge

false

overview of the steps of the crossbridge cycle

1. the binding of myosin to actin

   1. inorganic phosphate is released

2. power stroke

   1. actin gets pulled toward the middle of the sarcomere

3. Rigor

   1. myosin is in a low energy form

   2. low affinity for actin

4. ADP is released

5. New ATP binds to myosin head

6. Unbinding of myosin and actin

7. ATP is hydrolyzed

8. cocking of the myosin head

   1. myosin is in high energy form

   2. high affinity for actin

how do we initiate muscle contraction? somatic motor neurons release ________ onto the sarcolemma

Acetylcholine (ACh)

how do we initiate muscle contraction? somatic motor neurons _____ active muscle cells to ______

always, contract

how do we initiate muscle contraction? muscle cells are electrically excitable, so they can generate action potentials called _____

end plate potentials (EPPs)

what kind of receptors are found at the neuromuscular junction?

Nicotinic cholinergic receptors

what is a feature of the motor end plate

junctional folds

excitation-contraction coupling (ECC)

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

you cant have coupling without _______, and you cant have excitation without ________

excitation, coupling

overview of the steps of excitation-contraction coupling

1. ACh is released from the axon terminal of a motor neuron and binds to receptors in the motor end plate. This binding elicits an end-plate potential, which triggers an action potential in the muscle cell

2. action potential propagates along the sarcolemma and down t tubules

3. the action potential triggers Ca2+ release from SR

4. Ca2+ binds to troponin, exposing myosin-binding sites

5. crossbridge cycle beings; muscle fiber contracts

6. Ca2+ is actively transported back into lumen of SR following the action potential

gating of the SR Ca2+ channels, how to get Ca2+ from SR to cytosol (brief overview)

1. DHP receptor undergoes a conformational change

2. Ryanodine receptor open channel

t/f: despite the huge variability in force and duration of whole muscle contractions, all muscle cells respond the exact same way to an action potential

true

a motor unit

one somatic motor neuron (alpha) and all the muscle fibers it innervates

the size of the motor neuron depends on

the number of fibers innervated

the larger motor neuron will have a _____ force production capacity

stronger

all ________ will contract if the neuron fires

myocytes

muscle twitch

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

characteristics of a muscle twitch

• reproducible

• all or non event

• one end plate potential always leads to the same amount of Ca2+ release

The contraction phase of a muscle twitch is characterized by

Ca2+ release

the latent period of a muscle twitch (graph)

the amount of time for excitation cycle to start

the peak of the muscle twitch (graph) is based on

Ca2+ availability

Phases of the muscle twitch

1. Latent period to contraction

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

2. contraction phase

   1. cross bridge cycling is occurring and cytosolic Ca2+ levels are rising

3. relaxation phase

   1. Cytosolic Ca2+ is returned to the SR and the number of crossbridge decline

not all twitches are equal: variability in ______

speed of contraction and amount of force generated

factors that affect the variability of twitches

• depends on the diameter of the muscle cell

• depends on the type of myosin ATPase (fast vs slow twitch)

note for the Y axis of the muscle twitch graph

tension is expressed as a percentage of max. All muscle twitches in the figure are generating 100% max force. the absolute force produced by each muscle will be very different

examples of variability in muscle twitches (graphical example)

• narrow curve

  • fast

  • extraocular muscle - eyes moving quickly

• less narrow curve (in the middle of narrow and wide)

  • more force is generated, more force over time

  • gastrocnemius (calf muscle) - sprint up on toes, run, jump

• very wide curve

  • larger absolute force

  • soleus (deep calf muscle) - standing, stabilizing, moving

types of twitches and contractions

isometric and isotonic

isometric twitch/contraction

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

ex: holding something out

isotonic contraction/twitch

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

ex: bicep curl

types of isotonic contractions

concentric and eccentric

isometric contraction

muscle contracts but does not shorten

concentric contraction

shortening

eccentric contraction

lengthening