muscle anatomy quiz

muscles are responsible for

body movement

what structures create the contractions exhibited by muscles?

myofilaments: contractile proteins

cardiac muscle control

involuntary

smooth muscle control

involuntary

skeletal muscle control

voluntary

number of nuclei in cardiac muscle

uninucleate

number of nuclei in skeletal muscle

multinucleate

number of nuclei in smooth muscle

uninucleate

cardiac muscle cell shape

branching cell

skeletal muscle cell shape

large, cigar-shaped

smooth muscle cell shape

spindle-shaped

cardiac muscle striations

striated

skeletal muscle striations

striated

smooth muscle striations

nonstriated

cardiac muscle location

heart walls

skeletal muscle location

attached to bones via tendons

smooth muscle location

hollow tubes

4 major functions of skeletal muscles

1. produce movement

2. maintain posture and body position

3. stabilize joints

4. generate heat

4 types of connective tissues found in skeletal muscles

1. endomysium: encloses a single muscle fiber

2. perimysium: wraps around a fascicle (bundle) of muscle fibers

3. epimysium: covers entire skeletal muscle

4. fascia: on the outside of epimysium for large areas of body

endomysium

inner-most layer of connective tissue found in skeletal muscle

• encloses a single muscle fiber

perimysium

connective tissue found in skeletal muscle

• wraps around a fascicle (bundle) of muscle fibers

epimysium

outer layer of connective tissue found in skeletal muscle

• covers entire skeletal muscle

fascia

outer-most layer of connective tissue found in skeletal muscles

• wraps epimysium for extra support to large areas

2 structures that can form from the epimysium

1. tendons: stiff cord-like structures composed of collagen fibers

2. aponeuroses: sheet-like structures that attach muscles indirectly to bones, cartilages, and connective tissue coverings

tendons

attach skeletal muscles to bones and form from the epimysium

• cord-like structures that are very stiff

• composed of collagen fibers

• located on a joint because of their toughness and small size

aponeuroses

attach muscles indirectly to bones, cartilages, and connective tissue coverings

• sheet-like structures that form from the epimysium

origin

a muscle’s starting point

insertion

a muscle’s ending point → part doing the movement

how does a muscle move?

moves the insertion (end) towards the origin (beginning)

shape of a muscle fiber

long, cylindrical, and has multiple nuclei

sarcolemma

muscle fiber plasma membrane

sarcoplasm

muscle fiber cytoplasm

glycosome

glycogen (glucose) storage

myoglobin

for oxygen storage and transport

sarcoplasmic reticulum

specialized smooth endoplasmic reticulum

• surrounds myofibril

• stores and releases calcium ions

t tubules

extension of sarcolemma

• allows for faster nerve impulse transmission deeper into the muscle fiber

• stimulates sarcoplasmic reticulum to release calcium ions

myofibrils

densely packed, rodlike elements that are striated

• a single muscle fiber contains thousands

• account for around 80% of cell volume

• sarcomeres are packed into myofibrils

i band

in myofibril → light band

• contains only thin filaments called actin (acthin)

• z disc interrupts this band midway

a band

in myofibril → dark band

• contains only thick filaments called myosin

• h zone is the lighter central region within the a band

• m line is the center of the h zone

  • anchor point for myosin

sarcomere

contractile unit of a muscle fiber → all contractions result from the shortening of sarcomeres

• sarcomere shortened when z discs are pulled to m line

• consists of myosin and actin

myofilaments

type of contractile protein found in sarcomeres

• thick filaments = myosin

• thin filaments = actin

thick filaments

• composed of myosin

• contain proteins called ATPase: enzyme that breaks down ATP to release energy for contractions

• contain myosin heads that allow myosin to bind to actin filaments

  • allows for formation of cross bridges

ATPase

found in thick filaments → enzyme that breaks down ATP to release energy for contractions

myosin heads

found in thick filaments → allow myosin to bind to actin filaments

cross bridges

links that form when myosin heads attach to actin filaments

thin filaments

• composed of actin → anchored at z disc

  • at rest, h zone within a band lacks actin

  • during contraction, h zone disappears as actin and myosin filaments overlap

• tropomyosin and troponin: regulatory proteins bound to actin

tropomyosin and troponin

regulatory proteins bound to actin

satellite cells

type of stem cell found in muscle fibers or outside sarcolemma

• aid muscle repair and growth via protein synthesis and nucleus donation

• repair capacity is limited

3 reasons why connective tissue wrappings of skeletal muscle are important

1. provide extra support

2. durability and protection

3. keep blood vessels in place

characteristics of skeletal muscle

1. irritability: ability to receive and respond to a stimulus

2. contractibility: ability to forcibly shorten when adequate stimulus is received

3. extensibility: can be stretched

4. elasticity: can recoil to original or resting length after stretching

irritability

ability to receive and respond to a stimulus

contractibility

ability to forcibly shorten when adequate stimulus is received

extensibility

can be stretched

elasticity

can recoil to original or resting length after stretching

cell that stimulates a muscle to contract

motor neurons activate muscle fiber

action potentials

electrical signal at the membrane

• excitable cells (neurons and muscle cells) can change the resting membrane potential voltages

neurotransmitter that stimulates muscle fibers

acetylcholine → transmits signal from neuron to muscle cell

role of ion channels

changing membrane potentials → required for muscle contractions to occur

chemically-gated ion channels

opened by neurotransmitters

ex. acetylcholine receptors on muscle cells

voltage-gated ion channels

open or close in response to voltage changes in membrane potential

axon of motor neurons

long, threadlike extension of motor neurons that carry signals from the cell body to the axon terminal

• central nervous system to skeletal muscle

• axon divides into many branches as it enters the muscle

axon terminal

end of axon

• contains synaptic vesicles that contain acetylcholine

synaptic vesicles

intracellular containers located in the axon terminal that contain acetylcholine

• moves transmitters around the cell

synaptic cleft

gel-filled gap between the neuron and the next cell

junctional folds

infolding of sarcolemma

• increase surface area of sarcolemma

• contain millions of acetylcholine receptors

3 components of neuromuscular junction

1. axon terminal

2. synaptic cleft

3. junctional folds

neuromuscular junction

where axon terminal meets sarcolemma

motor unit

one motor neuron and all the skeletal muscle cells stimulated by that neuron

• more units are used each time for bigger things

• each cell talks to one neuron but one neuron can talk to a group of cells