Class 10

how many muscles are there

~ 1 billion

how many heart muscles are there

1

muscle consists of

muscle fibers lying parallel to one another and held by connective tissue

a single skeletal muscle cell is known as a 

muscle fiber

properties of muscle fibers

• multinucleated

• elongated and cylindrical

• extend entire length of muscle

the contractile elements of a muscle fiber

myofibrils

myofibrils are within

muscle fibre

myofibrils are the regular arrangement of

thick and thin filaments 

thick filaments made of

myosin

thin filaments made of

actin

what gives the striated appearance on myofibrils

alternating light and dark bands 

which is the light band and which is the dark

(A) is dark, (I) is light

each parallel muscle fibre that makes up muscle is equal to

a single skeletal muscle

each muscle is covered by

dense connective tissue

each skeletal muscle has:

• multiple nuclei

• SR + terminal cisternae that contain Ca2+

• myofibrils

the contractible element of muscle fibre

myofibril

alternating A and I bands

myofibrils

what causes muscles to change in length

the dark and light bands overlap, slide against each other, and change length

the functional unit of striated muscle

sarcomere

where is the sarcomere located

between two Z lines

these connect thin filaments of two adjoining sarcomeres

Z lines

made of thick filaments along with portions of thin filaments that overlap on both ends of thick filaments

A band

lighter area within middle of A band where thin filaments do not reach

H zone

extends vertically down middle of A band within center of H zone

M line

consists of remaining portion of thin filaments that do not project into A band

I band

main component of thick filament

myosin

protein made of 2 identical subunits similar to golf clubs

myosin

the heads from myosin form cross-bridges between thick and thin filaments that is critical for

contraction

A cross bridge has 2 important sites for contraction

1. actin-binding site

2. myosin ATPase site

primary structural component of tin filaments 

actin

each molecule of actin has special binding sites for

attachment with myosin cross bridge

what shape is actin

spherical

actin binding with myosin cross bridge causes

contraction of muscle fibre

what are the proteins that belong to thin filaments

actin, tropomyosin, troponin

thread-like molecules that lie end-to-end alongside the groove of actin spiral

tropomyosin

when tropomyosin lies end-to-end alongside the groove, they cover ________ blocking the interaction that leads to ______________

actin sites, muscle contraction

made of 3 polypeptide units

troponin

what do the 3 polypeptide units of troponin bind to

1. binds to tropomyosin

2. binds to actin

3. binds with Ca2+

what is the key molecule to initiate contraction

Ca2+

what is troponin doing when not bound to Ca2+

stabilizes tropomyosin in blocking the position over actin’s cross-bridging sites

what happens when Ca2+ binds to troponin

tropomyosin moves away from blocking position

what happens when tropomyosin moves away from the blocking position

actin and myosin bind and interact at cross bridges and muscle contraction results

what does the increase of Ca2+ do for filament sliding

starts it

what does decreasing Ca2+ do for filament sliding

turns it off

during contraction, ____________ on each side of sarcomere slide inward over stationary ___________ towards center of A band

thin filaments, thick filaments

what happens when thin filaments slide inwards

they pull Z lines closer and the sarcomere shortens

when Ca2+ binds, ___________ moves out of the way. ____ and ____ shortens, ______ stays the same

tropomyosin, H zone, I band, A band

how do muscles create force

power stroke

how is a power stroke formed

• activated cross bridge bends towards middle of thick filament

• it pulls the thin filament along in a rowing motion

• SR releases Ca2+

• myosin heads bind to actin 

• heads swivel toward center of sarcomere

• ATP binds to myosin head

• This detaches it from actin

power stroke happens when

heads swivel t

cross bridge bends, pulling in thin myofilaments

powerstroke

once we’re active, how do we relax

• depends on reuptake of Ca2+ into SR

• Acetylcholinesterase breaks down ACh at neuromuscular junction

• Muscle fibre action potential stops

• when the local AP is no longer present, Ca2+ moves back to SR

what are the 2 primary factors that can be adjusted to accomplish gradation of whole muscle tension

1. number of muscle fibers contracting within a muscle (motor unit recruitments)

2. tension developed by each contracting fibre (frequency of stimulation)

motor neuron and the muscle fibres it innervates

motor unit

muscles that produce precise, delicate movements contain ______ fibres per motor unit

fewer

muscles performing powerful, coarsely controlled movement have a _______ number of fibers per motor unit

larger

what are the 4 factors influencing extent to which tension can be developed

1. frequency of stimulation

2. length of fiber at onset of contraction

3. extent of fatigue

4. thickness of fiber

results from sustained elevation of cytosolic calcium

twitch summation

occurs if the muscle fibre is stimulated so rapidly that it does not have the chance to relax between stimuli

tetanus

contraction of ______ is usually 3-4x stronger than a single twitch

tetanus

produced internally within sarcomeres but must be transmitted to a bone by connective tissue and tendons before the bone can be moved

tension

how is a muscle typically attached to a skeleton

to at least 2 different bones across a joint

what is the origin of a muscle

The end of the muscle attached to the more stationary part of the skeleton.

what is the insertion of a muscle

The end of the muscle attached to the skeletal part that moves.

there are 2 types of __________ contraction and 1 type of _________ contraction

dynamic, static

what are the types of dynamic contraction

1. concentric contractions

2. eccentric contractions

what is the type of static contraction

isometric contraction

the type of contraction where muscle shortens

concentric

the type of contraction where muscle lengthens

eccentric

the type of contraction where tension develops without change in joint angle

isometric

within each muscle there is a great diversity of size and properties of motor units

Henneman’s size principle

muscle fibre types within a single motor unit are classified based on

differences in ATP hydrolysis and synthesis

what are the 3 major types of muscle fibre types in a single motor unit

1. slow-oxidative 

2. fast-oxidative

3. fast-glycolytic

What determines the percentage of muscle fiber types in a muscle?

Largely genetic endowment + type of activity the muscle is specialized for.

Which fiber type would an athlete with a higher percentage of fast-glycolytic fibers excel in?

Short-duration, high-intensity exercise (e.g., sprinting, weightlifting).

Why are fast-glycolytic fibers suited for explosive activity?

They contract quickly, generate high force, and rely on anaerobic metabolism.

an increase in mass/girth of a muscle and can be induced by a number of stimuli

hypertrophy

what can induce muscle hypertrophy

resistance training

What structural change occurs in muscle during hypertrophy?

increases myofibrils

What cellular process is hypertrophy based on?

the injury-regeneration- cycle

loss of muscle mass

atrophy

when skeletal muscles are not physically stressed regularly

disuse atrophy

when supply to a muscle is lost

denervation atrophy

the two fast-twitch muscle fibre types are _____________ but slow and fast are _____________

interconvertible, not interconvertible