PSIO 201 - Unit III

what do all 3 muscle tissues have in common?

they all exhibit a quality called excitability as their plasma membranes can change their electrical states (from polarized to depolarized) and send an electrical wave called an action potential along the entire length of the membrane

skeletal muscle completely depends on what?

signaling from the nervous system to work properly

contractility

allows muscle tissue to pull on its attachment points and shorten with force.

actin

a protein pulled by myosin (contracting)

what is the basic function of all three types of muscle tissue?

generate tension

skeletal muscle functions include what?

locomotion (movement), facial expressions (chewing and showing emotion), posture and body position (balance and stabilization), body temp regulation (for homeostasis)

when we say skeletal muscle is voluntary what do we mean by that?

requires nervous system input, but we can “override” it. (e.g. blinking)

muscle contraction

protein filaments interact which shortens the length of the muscle (overlap of fibrils changes)

muscle action

skeletal systems transform muscle contraction into movement, how the skeleton moves as the muscles do.

where do muscles pull?

on bone

origin

where muscle “starts” on a bone (stationary)

insertion

where muscle “ends” on a bone (moves toward origin)

muscle action is based on the movement of what?

the movement of insertion towards origin

correctly naming an action or movement requires what two pieces of information?

the action + the name of the region that moves

movement to reduce the angle of the joint

flexion

movement to increase the angle of the joint

extension

movement away from the midline

abduction

movement toward the midline

adduction

medial rotation

rotation of limb toward the midline (inwards)

lateral rotation

rotation of limb away from midline (outwards)

to move palm up

supination (spine of hand on the bottom)

to move palm down

pronation (p, palm down)

reverse muscle action

when the origin moves towards the insertion

muscle primarily responsible for a movement “prime mover”

agonist

muscle which opposes the action of the agonist

antagonist

assists agonist; makes action more efficient or powerful

synergist

special synergists which help prevent movement at muscle origin

fixator

how do you determine the prime mover?

by identifying the muscle that produces the most dominant force during a specific joint action or movement

how do lever systems work?

muscles act to facilitate movement at a fulcrum by exerting force on a lever.

lever

rigid bar e.g. bone

fulcrum

fixed point around which the rigid bar (bone) moves (joint)

first class levers

effort, fulcrum, load - not very common in the human body

second class levers

force, lever, effort - not many examples, sacrifices speed and range of motion for force

third class levers

force, effort, load - most common, favors speed and range of motion over force

deep fascia

covers groups of muscles

what covers/ surrounds each muscle?

epimysium

what surrounds fascicles? (label 2)

perimysium

what surrounds individual muscle fibers (cells)? (label 6)

endomysium

what holds muscle fibers and is surrounded by endomysium? (label 5)

fascicles

what is label 4?

muscle fibers or the cells!

structural organization of skeletal muscle

organ: muscle

tissue: fascicles

cell: muscle fibers

sub cellular: myofibrils

what does it mean when we say that muscle fibers multinucleate?

arises from fusion of myoblasts

muscle fibers cannot undergo what after birth?

mitosis

myoblasts turn into what after birth?

become myocytes (mature muscle cells!)

hyperplasia

increased number of cells

hypertrophy

increase cell size (big boi)

after birth, growth of muscle fibers happens by hyper_____ rather than hyper____.

happens by hypertrophy rather than hyperplasia.

satellite cells DO undergo mitosis after birth and aid in what?

muscle regeneration

functional organization of skeletal muscle

1. conduction of electrical signals

2. control of muscle contraction

3. contraction

conduction

how information travels via electrical signals

sarcolemma (plasma membrane) surrounds sarcoplasm (cytoplasm)

transverse tubules (t-tubules) arise from sarcolemma

control

regulation of activities of the SR

sarcoplasmic reticulum (SR) surrounds myofibrils

stores Calcium which helps generate muscle contractions

contraction

shortening of myofibrils inside the cytoplasm of skeletal muscle fibers

longitudinal bundles of protein filaments inside muscle fiber (actin and myosin)

highly organized into repeating units (sarcomeres)

sarcomeres

repeating units that are highly organized. the sarcomeres are what make the striations visible when looking under a microscope.

I band

thin only (actin)

A band

thick/overlap or not

h zone

thick only (myosin)

m line

middle line

z disc

edges of sarcomeres with thin filaments

what happens to the sarcomere during contraction?

A-band stays the same

i-band shortens

z lines come closer together

greater area of overlap

crossbridge

when myosin heads bind to actin

what causes thin filaments to slide along thick filaments?

a conformational change charged by ATP hydrolysis

name contractile proteins

actin and myosin

name regulatory proteins

troponin and tropomyosin

name structural proteins

titin, dystrophin, alpha-actinin, myomesin, nebulin

actin

thin filaments, has bonding site for myosin

myosin

motor protein in thick filaments, myosin head binds to actin forming cross bridge during contraction

tropomyosin

in thin filaments, covers myosin binding sites when muscle is relaxed.

troponin

in thin filaments, holds tropomyosin in place when muscles are relaxed.

during contraction, ca binds to troponin and causes a conformational change that shifts tropomyosin away from myosin binding sites on actin → exposing binding sites to allow for crossbridge formation.

titin

stabilizes position of thick filament, gives muscle elasticity and extensibility.

gives sarcomere bounce back needed once stretched out.

dystrophin

links thin filaments to sarcolemma, transmits tension from sarcomeres to tendons. aids in allowing for the movement of bone alongside muscle.

nebulin

anchors thin filaments to z disc

alpha-actinin

found in z disc, binds to actin to titin

myomesin

found in m line, binds to titin and thick filaments that connect them at the M line.

where does crossbridge cycling occur?

only in the area of overlap! where actin and myosin are binded!

how does the contraction cycle begin?

when calcium is released from the sarcoplasma reticulum - which causes the tropomyosin to move leaving myosin binding sites on actin to be exposed

before binding to actin, what happens with myosin head?

atp binds to the head, causes a conformational change “cocking” the myosin head, the atp is now into ADP-Pi, making it ready to bind.

what is the power stroke?

when the myosin heads pivot toward the center of the sarcomere. “pulling action”

how does the myosin head detach from the actin?

atp binds to the head which causes the crossbridge to break

how does the cycle continue?

myosin heads hydrolyze ATP used to break the crossbridge, and this energy is used to become reoriented, recocked, and then a new crossbridge begins.

rigor complex

attached head group after the power stroke

rigor mortis

rigor of death because of the lack of ATP (energy) to help detach the crossbridge.

what is needed for the binding of actin and myosin TO BEGIN?

calcium attachment to the troponin

what is needed for the ACTUAL binding of actin and myosin?

ATP on the myosin head that is hydrolyzed into ADP-Pi.