anatomy and physiology - muscular system

what is the main function of the muscular system?

movement

how do muscles produce movement?

muscles contract

they __ but never __

pull, push

insertion

where the muscle is attached to a movable bone

origin

where the muscle is attached to an immovable bone

what are the other functions of the muscular system?

maintain posture, stabilize joints, and generate heat

prime movers (agonists)

muscles most responsible for producing a certain movement

antagonists

muscles that oppose or do the reverse of a certain movement

Usually stretched or relaxed when a prime mover is active

Can regulate prime movers by adding resistance

Located on the opposite side of a joint from the prime mover

synergists

muscles that help the prime mover, such as stabilizing across a joint or adding some “oomph”

fixators

synergist muscles that specifically immobilize the muscle’s origin bone to increase the prime mover’s effectiveness.

Fixators also help maintain an upright posture

cardiac muscle tissue

striated muscles of the heart that contract involuntarily to pump blood throughout the body

smooth muscle

nonstriated muscles in the walls of visceral organs that contract involuntarily to propel objects/substances down internal passageways

skeletal muscle

striated muscles generally attached to bones that contract voluntarily to produce movement

what is every muscle made of?

muscles are their own organ, mainly made of skeletal muscle, but also has blood vessels, nerves, and connective tissue.

what are the layers of muscles?

muscle, fascicle, muscle fiber, myofibril, and myofilaments.

muscle

Skeletal muscle is attached to bone by tendons. Made of many bundles of fibers

fascicle

Bundles within muscles

muscle fiber

Long, thin muscle cells. Each is covered by sarcoplasmic reticulum, which transmit an impulse to the muscle fiber

myofibril

Thread-like organelles of the muscle fibers. Structured in long, striated units called sarcomeres

myofilaments

2 types of filaments: actin (thin) & myosin (thick) make up the sliding filament model of the muscle. Responsible for contracting activity of muscle fibers

myofilbrils

organelle that makes up most of muscle cells. Thin filaments called myofilaments (actin and myosin) run the length of each myofibril. Are subdivided lengthwise into sarcomeres = the contractile unit of the muscle.

muscle fibers

Groups of myofibrils bunched together = muscle cells. They are specialized to contract so they contain multiple mitochondria, nuclei, a specialized ER (sarcoplasmic reticulum), cytoplasm (sarcoplasm) and a cell membrane (sarcolemma), in addition to the myofibrils

membranes

allow the muscle fibers to SLIDE and keeps them contained to prevent bursting during contractions.

what are the three types of connective tissue?

epimysium, perimysium, and endomysium. They wrap around different parts of the muscle to support it.

epimysum

covers the whole muscle, wraps around the entire outside of the muscle

perimysium

covers / surrounds each fascicle

endomysium

covers / surrounds each muscle fiber

sacromeres

contractile unit of the muscle

z disc (z line)

this separates the sacromere and borders each end

what do thick filaments contain?

myosin

what do thin filaments contain?

actin

why do muscles contract?

sarcomeres contract when the myofilaments slide past each other. The heads of the thick myosin filament heads grab on to the thin actin filaments. Pulls the thin ones to slide past the thick ones

what do myosin need to touch actin?

they need energy from ATP and access

how do they gain access?

Neuron signals an action potential in a muscle cell that triggers Ca+2 channels in the sarcoplasmic reticulum to open and release stored Ca+2. Ca+2 grabs troponin (another regulatory protein) which grabs tropomyosin and pulls it out of the way = access granted

how do they get energy from ATP?

Myosin grabs an ATP and rips a phosphate off, releases the energy it needs to bind to the actin (power stroke) = muscle contraction

how do they relax?

ADP (and the free P) unbind to the myosin, allowing fresh ATP to bind. Causes myosin to release from the actin until the new ATP is broken down to release energy needed to grab actin again. When Ca+2 unbinds from troponin the actin gets blocked again by tropomyosin, and it all has to be repeated

somatic motor neurons

the nervous system uses these to connect to the skeletal muscles and tells them to contract

excitable cells

This means they respond to external stimuli by changing their resting membrane potential → a signal. Neurons and muscle cells are these.

resting membrane potential

the voltage across the cell membrane (usually between -50 to -90 mV)

action potential (AP)

a large change in membrane potential that spreads rapidly over long distances within the cell. the movement of ions through ion channels can create this large change

neuromuscular junction (motor end plate)

where the axon terminals of the motor neuron meets the muscle fiber, including the space between them (the synaptic cleft)

acetylcholine (ACh)

is the neurotransmitter motor neurons use in muscle contraction

what is used to name muscles?

its location, shape, size, direction of muscle fiber, number of origins, location of attachment, and type of motion

motor unit

a neuron and the muscle fibers it innervates

twitch

The rapid, brief contraction of a muscle fiber following a single stimulus

graded muscle contraction

summation

occurrence of additional twitch contractions before the previous twitch has completely relaxed. Summation can be achieved by increasing the frequency of stimulation, or by recruiting additional muscle fibers within a muscle.

tetanus

When the frequency of muscle contraction is such that the maximal force is tension is generated without any relaxation of the muscle.