muscular system lecture

The muscular system is comprised solely of

skeletal muscle

what is skeletal muscle?

muscle directly attached to the skeletal system

skeletal muscle functions

Provides skeletal movement, maintains posture, support soft tissue, guards entrances and exits, maintains body temperature, stores nutrient reserves.

what are the muscles of mastication

masseter muscles

temporalis muscles

medial pterygoid muscles

lateral pterygoid muscles

epimysium

how muscle where it goes, dense layer of collagen fibers that surrounds the entire muscle, responsible for separating the muscle from organs and tissues

perimysium

surrounds muscle fasciles, number of muscle fibers differ

fascile

bundle of muscle fibers, surrounded by perimsium

endomysium

connective tissue that rounds individual muscle fibers (smallest)

myosatellite cells

stem cells that repair muscular tissue within the endomysium

tendon forms a

band

aponeurosis forms a

sheet

epimysium, perimysium, endomysium come together to form

tendons or aponeurosis

tendons and aponeurosis connect

muscle body to bone

sarcolemma

the cell membrane of the muscle fibers, propagates the action potential

sarcoplasm

the cytoplasm of a muscle fiber

at rest the sacroplasm has

little calcium

sacroplasmic reticulum

responsible for storing large amounts of calcium

triad

consits of one T-tubercle and two cisternae

cisternae

concentrate Ca2+ via ion pumps

T- tubules (transverse tubules)

help bring action potentials into cell interior

T- tubules (transverse tubules)

help bring action potentials into cell interior

thin filaments are composed primarily of

actin

thick filaments are composed primarily of

myosin

why does the mitochondria surround myofibrils

to provide energy to muscles required for muscular contraction

thin and thick filaments are arranged into functional units called

sacromeres

each myofibril contains

10,000 individual sacromeres end to end

A bands

center of each sacromere, contain 3 subdivisions (zone of overlap, h band, m line)

M line

anchors proteins of thick filaments

in A bands we find

thick filaments (both)

in H bands we find

only thick filaments

in the zone of overlap we find

both thin and thick

in the I bands we find

thin filaments

z line marks

the boundary of one sacromere from another and consists of actinins

titin

a protein that extends from z line, keeps thin and thick filaments in proper configuration

what do thin filaments consist of

actin (filamentous)

nebulin

tropomysium

troponin

what do thick filaments consist of

300 twisted myosin subunits

what can the globular head of a thick filaments consist do

interact with thin filament

what does the tail of thick filament do

binds to other myosin molecules

cross bridge

when the myosin head interacts with a thin filament during a contraction

sliding filament theory

how muscles contract, thin and thick filaments slide past each other (myosin and actin)

neuromuscular junction

allows muscle contraction to happen by sending controls from the brain and spinal cord via neurons

how do contractions work

calcium is released from cisternae of the sacroplasmic reticulum

calcium ions trigger interactions beteen thin/thick filaments

this causes muscle contractions & consumption of ATP

filaments produce active tension

the duration of a contraction depends on

1. the period of stimulation at the neuromuscular junction

2. the presence of free Ca2+ ion in the sacroplasm

3. the availability of ATP

the amount of tension produced by a contracted muscle fiber depends on three factors

1. the number of pivoting cross bridges

2. the fibers resting length at stimulation

3. the frequency of stimulation

what does the number of cross bridges that are available depend on

interactions/overlap between thick and thin filaments

(optimum, overlap producers, greatest amount of tension)

resting sacromere length should be between

75%- 130%

twitch

A single neuron stimulation to a muscle fiber

how long does a single twitch typically last?

7-100 msec

what are the three stages involving twitch in order to produce tension?

1. latent period

2. contraction phase

3. relaxation phase

what happens during the latent period

• the action potential moves throughout the sacrolemma

• ca2+ is released

what happens during the contraction phase

• ca2+ ions bind to sacromeres

• tension builds to a peak

what happens during the relaxation phase

• ca2+ levels fall in the sacrolemma

• active sites are covered and tension falls to a resting level

treppe

an increase in peak tension with each successive stimulus delivered shortly after the completion of the relaxation phase

wave summation

occurs when successive stimuli arrive before the relaxation phase has been completed

incomplete tetanus

occurs if the stimulus frequently increases further

complete tetanus

the stimulus frequency is so high that the relaxation phase is eliminated, tension plateaus at maximal levels

tension production depends on

• internal tension provided by the muscle fibers

• external tension exerted by muscle fibers on elastic extracellular fibers

• total number of muscle fibers stmulated

motor units

all muscle fibers controlled by one particular motor neuron

recruitment

the smooth and steady increase of muscular tension by increasing the number of active motor neurons

muscle tone

the resting tension in skeletal muscle

what is resting muscle tone responsible for

Stabilizing the position of bones and joints, it also prevents bones and joins from suddenly performing, jerking or uncontrolled movements

how are contractions classified?

Classified based on patterns of tension production

isotonic contraction

When a skeletal muscle changes length

concentric contraction

The muscle tension exceeds the load, and the muscle shorten as a result

eccentric contraction

The peak tension developed is less than the load and the muscle elongates

isometric contraction

The muscle as a hole does not change the length, and the tension produce never exceeds the load

elastic forces

Elasticity gradually helps return muscle fibers to their original resting length

opposing muscle contractions

Agonist/antagonist mechanisms help return muscles back to their original conformations quicker than elastic forces

gravity

while gravity can help in stretching muscles, the rate of movement may need to be controlled in order to prevent damage to the joint

at rest skeletal muscle produces

More energy than it needs

The additional energy is transferred to creatine phosphate

how can ATP be made?

Via aerobic respiration and anaerobic respiration

aerobic respiration

Yield about 34 atp, uses fatty acids as an energy source

anaerobic respiration

yields only to ATP, produces the waste product lactic acid

oxygen debt

Explains how muscles borrow energy when oxygen demand is elevated above resting levels

heat production

up to 70% of the energy harnessed by an active muscles able to produce heat

hormone influences in metabolism

Growth hormone-able able to stimulate muscle growth and promote muscle enlargement

Testosterone-able to stimulate growth and promote muscle enlargement

Thyroid hormone-elevates the rate of energy consumption on resting skeletal muscle

epinephrine- able to stimulate muscle metabolism and increase the force of contraction

Force

The overall or maximum amount of tension produced by a particular muscle or muscle group

endurance

The amount of time in which an individual can perform a particular activity

what are the three muscle fiber types?

1. Fast fibers

2. Slow fibers

3. Intermediate fibers

fast fibers

Large in diameter, reach peak tension, quickly, found in majority of skeletal muscle fibers and fatigue quickly due to the fact, they contain a few mitochondria

slow fibers

Only half the diameter of fast fibers and take nearly 3 times as long to reach peak tension, they have numerous mitochondria which are able to sustain aerobic metabolism, extensive capillary networks around slow fibers, contain the oxygen, loving protein myoglobin

intermediate fibers

have properties between fast fibers and slow fibers, more closely resemble fast fibers, they contain little myoglobin, have a moderate mitochondria supply

White muscle

Muscle dominated by fast fibers, only used for brief powerful movements and action actions

red muscles

Characterized by slow fibers and the associated extensive blood supply and high myoglobin content.

most muscles appear to be pink because

human muscles typically contain a combination of fast fibers and slow fibers

muscle hypertrophy

enlargement of stimulated muscle

• Increases diameter of muscle, fiber, number of microfibrils, mitochondria, glycogen reserves

muscle atrophy

Reduction in muscle size, tone, power (can be prevented or reduced by electrical stimulation)

fascicle arrangement

Parallel muscles

Convergent muscles

Pennate muscles

Circular muscle muscles

Origin

Fixed point of attachment of a muscle

insertion

One moving point of attachment

where do most origins and insertions attach to?

The skeleton

Origins are proximal to

Insertion

action

movement produced by muscle contraction

what do smaller muscles reach first?

they meet tension

agonist

known as the prime mover, produces a particular movement

antagonist

Opposes movement of a particular agonist

Synergist

smaller muscle that assists a large agonist, may act as a fixator by stabilizing The Agonist muscle, may act as an initiator by starting a movement

extrinsic eye muscles

1. Inferior rectus

2. Lateral rectus

3. Superior rectus

4. Medial rectus

5. Superior oblique

6. Inferior oblique

7. trochlea

mastication

Processed by which found is ground and crushed up by teeth/chewing

pharyngeal constrictor muscles

move food into the esophagus

(superior, middle, inferior)