kin 131 module 3

muscle tissue is excitable. what does that mean?

muscle responds to nervous stimultation

how do the elastic properties of muscle contribute to force generation?

why are muscle fibres multinucleated

highly metabolic therefore they need lots of gene transcription

what myofilaments are found in the A band of the sarcomere?

thin and thick filaments

position of myosin when muscle is at rest

not interacting with actin

position of tropomyosin when muscle is at rest

covering the myosin binding site on actin

position of Ca 2+ when muscle is at rest

absent

what happens to length of sarcomere when muscle is fully contracted

shortens

what happens to length of myofilaments when muscle is fully contracted

do not change

What are the functions of costameres in skeletal muscle?

lateral transmission of force, and initiates intracellular signaling that links contractile activity with the regulation of muscle cell remodeling

Where are costameres found?

linking z-disks of outermost myofibrils to sarcolemma and ecm

Is it true that a muscle fibre can be simultaneously innervated by an a1 and a2 motor neuron?

no

Is it true that when a motor unit is stimulated, only half of the myofibres in that MU will contract unless another action potential arrives?

false

What is the junction called where the motor neuron meets the myofibre?

neuromuscular junction

Explain the role of Ca2+, Ach, AChE and Na+ in the propagation of an action potential from the motor neuron to the myofibre.

• An action potential is propagated from a motor neuron to a myofibre through the action of calcium, ACh, AChE, and sodium ions

• An action potential arriving at the motor neuron terminal causes calcium gates to open

• Channels open trigger ACh into synaptic cleft

• ACh binds to myofibre receptors

• Sodium gates open

Explain Botox’s mechanism of action.

blocks release of ACh, therefore muscles don’t receive signal to contract and relaxes muscles 

The up phase of a bicep curl is a(n) __________________ contraction for

your biceps brachii. The down phase of a bicep curl is a(n)

_______________________ contraction for your biceps brachii.

concentric, eccentric

What will happen to the length of the muscle fibre when muscle tension = the load applied to it?

muscle length will say the same (constant length) because sarcomeres cannot shorten while contracting

How does the load-velocity relationship differ between concentric and eccentric contractions?

• concentric contractions show an inverse relationship between force and velocity (force decreases = velocity increases)

• eccentric contractions - force stays constant/ increases a little = velocity increases

Describe the difference between a twitch, unfused tetanus and fused

tetanus. Which can generate the most force? What must take place in

order for a fused tetanus to occur?

• Twitch: mechanical response of a single muscle fibre to an action potential

• Unfused tetanus: muscle fibre has time to partially relax between contractions/ stimuli

• Fused tetanus: muscle fibre does not have time to relax between contractions/ stimuli which results in maintained muscle tension

• Fused tetanus produced the most force

• In order for fused tetanus to occur, muscle must be stimulated at a frequency high enough to prevent any relaxation between twitches

What are the neural influences on force generation?

function of muscle tissue

specialized to produce force for movement by contracting

properties of muscle tissue

• excitable

• contractile

• extensible

• elastic

what does contractile mean

muscles contract to create movement

what does extensible mean

muscle can be stretched

what does elastic mean

muscle recoils to its original size and position after being stretched

where is muscle tissue found in human body

everywhere

functions of skeletal muscle

• to move

• venous return of blood to heart

• breathing

• communication 

• thermogenesis

• metabolic homeostasis

what is a muscle cell

myofibre

when does differentation of myofibres stop?

around time of birth

can you make more muscle cells?

no

what is the growth of muscle in adulthood

hypertrophy of muscle cells

what is sarcolemma

lipid bilayer membrane of myofibres

what is sarcoplasm

cytoplasm of myofibres

what are myofibrils

• rod-like Contractile organelles that fill the myofibre

•  Composed of myofilaments

what are striations

result of arrangments of proteins making myofibrils

what is a fascicle

groupings of myofibrils, bundled together to form muscle

what is a tendon

connects muscle to bone

what is aponeurosis

flat extension of connective tissues at ends of tendons

what is fascia

• band of fibrous connective tissue

• lies deep to skin, surronds muscle groups

what are the two layers of fascia

superficial fascia and deep fascia

superficial fascia function

• separates skin from muscle

• insulates 

• provides protections

superficial fascia contains…

adipose tissue, blood vessels, and lymph vessels

deep fascia function

separates groupings of muscle

deep fascia contains…

nerves and blood vessels

what are the extensions of the deep facia

epimysium, perimysium, endomysium

epimysium function

surrounds entire muscle

perimysium function

wraps muscle fascicles

endomysium

wraps each individual myofibre

list extensions of deep fascia from deepest to most superficial

1. endomysium

2. perimysium

3. epimysium

where are nuclei located in myofibres

periphery/surface

what are satelite cells

muscle stem cells

satellite cells function

important for muscle adaption and regeneration 

where are satellite cells located

in satellite cell niche, right outside of sarcolemma encased in basal lamina 

what is basal lamina

layer of connective tissue below endomysium and above sarcolemma

3 fates of satellite cells after activation

1. replace damaged muscle fibre

2. fuse to damaged region and donate nucleus

3. return back to dormant state

sarcoplasmic reticulum function

Stores, releases and reuptakes Ca2+ during muscle contraction and relaxation

t-tubular network

Carries the electrical signal from the sarcolemma into the sarcoplasmic reticulum during muscle contraction

mitochondria

energy supply

myofilaments

Contractile proteins that make up myofibrils

what is thin myofilament

actin

what is thick myofilament

myosin

functional unit of skeletal muscle

sarcomeres

where are sarcomeres

in myofibrils

why do myofibres differ in size

contain different amount of myofibrils

A band

length of thick filaments

I band

zone of only actin

H zone

area of only myosin

M line

middle of sarcomere

Z disk

middle of I band, where proteins connect thin filaments of adjacent sarcomeres together

as sarcomere contracts what does A band do

stay the same

as sarcomere contracts what does I band do

shortens

as sarcomere contracts what does H zone do

shortens as actin overlaps more

as sarcomere contracts what does M line do

nothing

as sarcomere contracts what happens to zone of overlap

increases

what gives striated appearances

sarcomeres

what is the darker stripe of a striation

A band, myosin and actin

what is the white stripe of a striation

only actin

hierarchy of skeletal muscle

actin and myosin → sarcomere → myofibrils → myofibres → fascicles → skeletal muscle

what is a motor neuron

neuron that innervates myofibres

how many muscle neurons can a cell be controlled by

1

how many muscle cells can a motor neuron control

many

what is a motor unit

motor neuron + all myofibres it innervates

what happens when a motor neuron firess

all myofibres in that motor unit contract to full extent

what is a neuromuscular junction

where axon terminal meets with motor end plate

how is tension formed in a muscle

interaction of thin and thick filaments within sarcomere

how is force created in a sarcomere

sliding of thin and thick filaments over one another

where does myosin tail point towards

m-line

where is myosin head pointing to

z-disk

what is actin binding site

site of attachment of thick filament to thin filament

what is ATP binding site

binds and breaks down ATP to use it 

what do light chains do

helpm regulate angle of myosin head to make it interact with thin filament

what is actin

spherical proteins joined together in helical shape with bonding site for myosin

tropomyosin

Filament protein found on actin

what does tropomyosin do

blocks actin’s active binding sites when muscle at rest

what do tropomyosin and troponin do together

regulate accessibility of actin and myosin binding 

troponin

anchors tropomyosin to actin when at rest

3 binding sites of troponin

actin, tropomyosin, calcium 

actin - binding site function

inhibits binding sites along myosin

tropomyosin - binding site function

anchors tropomyosin to actin filament