Chapter 10 Part 1 Flashcards
Describe Skeletal muscle cell
very long & thin; often called muscle fibers
Describe 2 traits of skeletal muscle fibers
Multinucleate-each skeletal muscle cell contains several hundred nuclei
Amniotic- don’t divide; don’t grow back
Define myoblasts
stem cells that produce muscle fibers; fuse together during development in the womb
What are myosatellite cells?
myoblasts that hang around and transform
What is the function of myosatellite cells?
involved in repair of damaged muscle fibers and growth that occurs to physical conditioning
-merge w/ myoblasts to create more nuclei
what are striations
the stripes- due to the arrangement of the actin and myosin protein filaments
define voluntary muscles
skeletal muscles won’t control until signalled by nerve fibers
why are skeletal muscles so vascular?
to supply large amounts of O2 and nutrients –> needs to make ATP in order to function
6 Functions of skeletal muscle
- produce skeletal movement
-facial expressions - Maintain body position
- support soft tissue-
- guard body openings
- maintain body temperature
- store nutrient reserves
how does skeletal muscle maintain body position?
posture, holding head up, shoulder positioning, et.c
stops movement as well
how does skeletal muscle support soft tissue?
muscles= important part of walls of abdominal and pelvic cavities
how does skeletal muscle guard body openings?
e.g. functions like urination, defecation, swallowing –> under voluntary control
how does skeletal muscle maintain body temperature?
muscles produce heat when they contract –> sweating
how do skeletal muscle store nutrient reserves?
e.g. glycogen (stored form of glucose)
can be broken to get glucose
can break down proteins in skeletal muscles to get amino acids- not healthiest way to operate
Level of organization for skeletal muscles
- Skeletal muscle
- muscle fasicle
- muscle fiber
- myofibrils
Level of organization for CTs (superior to inferior)
- epimysium
- perimysium
- endomysium
Define epimysium
exterior collagen layer; separates muscle from surrounding tissues connected to deep fascia
Define perimysium
collagen layer that surrounds bundles of muscle cells–> fasicles
- contains the blood vessels & nerves supply for the fasicle
Define endomysium
collagen layer that surrounds individual muscle cells
contains capillaries & nerve endings that contact individual muscle cells
contains myosatellite cells
Aponeurosis
a place where the epimysium, perimysium and endomysium come together at the ends of the muscle aside from the tendon
Describe aponeurosis
a broad sheet made out of regular CT
Define the sarcolemma
cell membrane of muscle fiber; an excitebale membrane that surrounds the sarcoplasma- the cytoplasm of the muscle cell
what is the 1st step that leads to a contraction?
a sudden change in transmembrane potential
define a transmembrane potential
electrical difference b/w inside of outside of cell
measured in millivolis
Why are cells normally slightly negative of the inside?
the NaK pumps 3 Na+ out of the cell for every 2K+ into the cell; large negatively charged proteins are inside cells
why do Na+ ions flow into the cell
chemical diffusion and electrically attracted
How is an action potential triggered?
when sodium enters the cell and it causes a change in the transmembrane potential
define an action potential potential
a signal that ends up travelling throughout the interior of the cell; message–> time to contract
What are t-tubules
exciteable membranes; transmits action potentials through out the inside of the cell;
what are t-tubules wrapped around
myofibrils
what are myofibrils
lengthwise subdivisions within a muscle fiber
What are myofibrils made up of?
bundles of protein filaments called myofilaments which are responsible for muscle contractions
define protein filaments
made of many protein molecules bound together in a long strand
Define Sarcoplasmic reticulum
a membranous structure that surrounds each myofibrils
define the Terminal Cisternae
chambers formed by SR which are attached to the t-tubules
define a triad
formed by 1 t-tubule plus 2 terminal cisternae
Function of terminal cisternae and & SR in general
is to collect & store calcium ions by using ion pumps and they release Ca+ into the sarcoplasm at the proper moment
What are sarcomere
contractile unit of skeletal muscle- contain myofilaments– they make up myofibrils
What creates patterns of striations?
arrangement of protein filaments in sarcomeres; alternating a and I bands
what are a-bands?
has darker, thick filaments, and zone of overlap which as thin filaments
what is an i-band?
has the lighter, thin filaments
M lines and Z lines
structural proteins that stabilize and hold the sarcomere together
Define M line
at the middle of the sarcomere
Define Z- lines
Z ends of a sarcomere when the sarcomere contracts, the Z lines get pulled together
Define Zones of overlap
where thick and thin filaments overlap
- must interact for contraction
Define H-band
area around the M line- has thick but no thin filaments
thin filaments get pulled into H band during contraction
What do the thin filaments do?
strands of protein that stabilize thick filaments
where do t-tubules encircle sarcomere?
near the Zones of overlap
Where does the action potential travelling on a t-tubule arrive?
On a triad–> terminal cisternae of the SR release Ca2+= allow thick and thin filaments to interact with each other
What does thick filament consist of?
myosin filament
What are the parts of the thick filament?
tail, head and hinge
define the tail part of the thick filament
binds to other myosin molecule to form the filament
Define the head part of the thick filament
binds to active sites on actin molecules
Define the hinge portion of the thick filament
allows to head to pivot
pivoting drives muscle contraction
Define the cross-bridge
name for a myosin head while it’s attached for actin
What do thin filaments consist of?
actin filaments
What are the active sites of the actin filament?
the part of an actin molecules that myosin can attach to
What is tropomyosin
a protein that covers active sites when a muscle is at rest
What is troponin?
a protein that holds tropomyosin in place
How does the tropomysoin and troponin complex moves?
Ca2+ binds to troponin resulting the complex moving and the active site is uncovered
Cycle of contraction
- active sites are exposed –> myosin head binds to the thin filament
- Then, the myosin head pivots – which uses ATP energy to pull thin filaments towards the center of the sarcomere
- Once the pivot is done, the cross bridges dettach from the thin filament, then reload with ATP energy, then reattach and pivot again
What is the sliding filament model?
thin filaments in a sarcomere slide between the thick filaments towards the M line
-width of the A band stays the same (ie. the thick filaments don’t slide anywhere)
what is the excitation-contraction coupling
excitation- action potential
contraction- sliding filaments
where is the exact location of the coupling
triads
what is the neuromuscular junction?
where a nerve signals a muscle; where a neuron communicated with the cell
what is the motor end plate?
part of the sarcolemma that is involved in the NMJ- has receptors for neurotransmitters; folds for increased SA
Describe the steps of skeletal muscle innveration(excitation)
- vesicles full of neurotransmitter chemicals are seen in the synaptic terminal = Acetylcholine- only neurotrasmitters the body uses to signal skeletal muscle fibers
- action potential reaches synaptic terminal
- Neuron responds by sending thousands of Ach molecules into synaptic cleft (small space b/w neuron and muscle cell)
- The ACh diffuses across the synaptic cleft & binds to receptors on the motor end plate
- Na+ channels opens= flows into muscle cell= generate on action potential - Action potential generate on the sarcolemma travels down the t-tubules into the interior of the muscle fiber
what is acetylcholinesterase
AChE- an enzyme that removes the ACh molecules from their receptors
What are the contraction cycle
- Ca+ released into sarcoplasm (near Zones of overlap)
- Exposure of active sites - Ca2+ binds to troponin which changes shape which causes tropomyosin to move off the active sites
- Formation off cross-bridges (myosin- actin complex)
–> happens as soon as active sites are uncovered - Pivoting of cross-bridges- uses ATP energy
- Cross bridge detachment- when new ATP molecules attaches to the head
- Reactivation of myosin- the ATP splits into ADP & P which releases energy to charge myosin–> ready for the next round of cycle
what is rigor mortis?
stiffness after death bc of fixed muscle contraction
Why is the body in fixed muscle contraction during rigor mortis?
ATP runs out (can’t pump or store Ca2+) diffusion takes over–> Ca2+ leaks out- causes uncovering do active sites so myosin heads are loaded with energy and can’t deattach bc of no more ATP
describe the steps of muscle relaxation
- nerve signals stop
- Ca2+ concentrations fall in sarcoplasm–> Ca2+ get pumped back into SR
- Ca2+ detaches from thin filaments (troponin of thin filament )
- Active sites are no longer exposed- when Ca2+ detaches from troponin- it changes shape; troponin moves and covers the active sites
list the 3 mechanisms for returning to resting length
elastic forces, opposing muscle contractions and gravity
How do elastic forces help return muscles to returning length?
during contraction, elastic elements e.g. tendons, ligaments and other CTs get pulled and stretch a bit, so when they bounce back to resting lengths, it helps muscle cells go back to their resting lengths
How do opposing muscle contractions help muscles return to resting lengths?
skeltal muscles tend to be arranged in opposing pairs e.g. biceps & triceps to move the forearm
- direction of the original motion is reversed by the other member of the pair
How does gravity help muscles return to resting lengths?
can help a contracting muscle return to its resting position
