muscles test part 1

muscle tissue

one of four primary tissue types

3 types of muscle tissue

- skeletal
- cardiac
- smooth

skeletal muscle tissue

- voluntary muscles
-mostly attached to bones

cardiac muscle tissue is in

only in the heart

smooth muscle is in

generally in walls of hollow organs

smooth muscle changes diameters of tubes in

- circulatory system
- respiratory system
- digestive system

how long can skeletal muscle cells be

less than or equal 30 cm or a foot

skeletal muscle cells aka

skeletal muscle fibers

characteristics of muscle cells

- multinucleate
- amitotic (dont divide)

muscle fiber formation

myoblasts fuse together in the womb

muscle fiber growth due to

physical conditioning

myosatellite cells

myoblasts involved in repairing muscle fibers when damaged

muscle fiber appearance

- striped/striated
- banded (alternating dark and light bands)

muscle fiber appearance due to

arrangement of actin and myosin protein filaments that are arranged like graph paper

actin and myosin

two key proteins responsible for muscle contractions

why are muscle fibers voluntary tissue?

don't contract unless stimulated by nerve cells

muscle

an organ with all 4 tissue types

cardiac muscle cells aka

cardiocytes

characteristics of cardiocytes

- smaller than muscle fibers
- usually have one nucleus
- branched shape
- connected to each other in branching network
- striated appearance
- involuntary (contractions coordinated by pacemaker cells)

intercalated discs

structure where the branches of cardiac cells connect

intercalated discs contain

gap junctions and desmosomes (for very strong connections)

reason cardiac cells have striated appearance

because they have the same arrangement of actin and myosin as skeletal muscle cells

smooth muscle cells characteristics

- very thin and tapered with pointy ends
- described as spindle-shaped
- single nucleus
- can divide and regenerate (unlike skeletal/cardiac)
- different arrangement of actin and myosin where they're scattered around

neural stimulation of skeletal muscle cells

1. electrical signal travels down axon of neuron
2. chemical signal travels between neuron and muscle fibers
3. electrical signal in muscle fiber now (triggers contraction)

why do skeletal muscles have extensive vascular systems?

- to supply large amounts of oxygen and nutrients
- to make ATP and energy in cells

functions of skeletal muscles

1. produce skeletal movement
2. maintain body position
3. supports soft tissues
4. maintain body temp
5. guard body openings
6. store nutrient reserves

examples of maintaining body position

- posture
- shoulder position
- holding up head

how do skeletal muscle fibers support soft tissues

are part of cavities walls (abdominal and pelvic cavities)

how do skeletal muscle maintain body temp

muscle contraction produces heat (ex: shivering)

how to skeletal muscles guard body openings?

voluntary control of swallowing, urinating, and defacation

what nutrients do skeletal muscles reserve?

glycogen and proteins

glycogen

large storage molecule of glucose

glycogen found in

liver and muscle fibers

glycogen aka

animal starch

how/why do skeletal muscle fibers store proteins?

- can be broken down to get amino acids
- muscle can be broken down to increase protein and energy
- proteins are not just stored

organization of skeletal muscles

- epimysium
- perimysium
- endomysium

epimysium characteristics

- exterior collagen layer
- separates skeletal muscle from surrounding tissues
- connects to deep fascia

perimysium

collagen layer that surrounds bundles of muscle cells

perimysium contains

- fascicles (bundles of muscle fibers)
- blood vessels and nerve supply for fascicles

endomysium

collagen layer that surrounds individual muscle cells

endomysium contains

- capillaries and nerve endings that contact individual muscle fibers
- myosatellite cells

skeletal muscles are attached to

tendons/aponeurosis

difference between tendons and aponeurosis

tendon \= cord/rope-like
aponeurosis \= sheet-like

parts of skeletal muscle fibers

- sarcolemma
- T-tubules
- myofibrils
- sarcoplasmic reticulum (SR)

sarcolemma

cell membrane of skeletal muscle cell

sarcolemma characteristics

- surrounds sarcoplasm
- example of excitable membrane

sarco-

from "sarkos" meaning flesh (aka muscle/meat)

-lemma

comes from "husk" meaning outside covering of something

excitable membrane can carry

electrical impulses

first step that leads to contraction

a sudden change in transmembrane potential

transmembrane potential

- a form of potential energy
- electrical difference between inside and outside of cell
- measure in millivolts (mV)

voltmeter

- gives a number that compares inside and outside of cell
- number always in point of view of inside of the cell
- normally slightly negative

sudden change in transmembrane potential happens when

sarcolemma opens Na+ (sodium) channel and sodium ions flow in

how does a sudden change in transmembrane potential lead to contraction

voltage change triggers an electrical impulse that travels all throughout the cell that signals it's time to contract

T-tubules

yellowish looking tubes that carry electrical signals from sarcolemma throughout inside of muscle cell

T-tubules aka

transverse tubules

characteristics of T-tubules

- walls are another example of excitable membrane
- has action potentials
- connect to and continuous with sarcolemma
- wrapped around myofibrils

myofibrils

length-wise subdivisions within a muscle fiber

characteristics of myofibrils

- each fiber has anywhere from hundreds of myofibrils
- made of myofilaments

myofilaments

binds of protein filaments/fibers that carry out contraction

difference between protein and protein filaments

protein: single molecule
protein filament: many individual protein molecules joined together in a long strand

characteristics of sarcoplasmic reticulum (SR)

- wraps around myofibrils
- membranous structure
- similar structure to smooth ER
- contains terminal cisternae

terminal cisternae

chambers formed by SR that are attached to t-tubules

triad

- formed by 2 terminal cisternae and one t-tubule
- spot where excitation-contraction coupling occurs (aka where electrical signal is received)
- includes structures that release calcium ions

general function of terminal cisternae and SR is to

collect and store calcium ions

more specific functions of terminal cisternae

- use ion pumps to concentrate and store calcium ions (used ATP and active transport)
- release calcium ions into sarcoplasm at proper moment to directly initiate contraction

sarcomeres are known as

"contractile units" of skeletal muscle

characteristics of sarcomeres

- make up myofibrils
- thick and thin filaments arranged in grid-like patterns
- alternative A and I bands cause striated appearance

how many sarcomeres make up a muscle fiber?

100,000

bands in sarcomeres

A band and I band

A band

darker, thick filaments and zone of overlap (dArk)

zone of overlap

where thick and thin filaments overlap, which is important because they have to interact to cause contraction

I band

lighter, thin filaments (l I ght)

characteristics of M and Z lines

- protein structures
- stabilize and hold sarcomeres together

location of M line

at the midline

Z lines

- are at the ends
- when sarcomeres contract, 2 z lines get pulled closer together

H band

area around M line

H band is important because

when sarcomere contracts, thin filaments get pulled into H band

titin

- strands of protein that stabilize thick filaments
- connect thick filaments to Z lines

sarcomere function

1. t-tubules encircle sarcomere near zones of overlap
2. when an action potential is traveling out t-tubule and arrives at the triade (terminal cisternae of SR)
3. when they get the signal, release calcium ions
4. calcium causes thick and thin filaments to interact with each other
5. once they interact, they cause a contraction (thick filaments attach to thin filaments and pull it in - H band will fully disappear with I band becoming narrow)

thin filaments contain

actin

thick filaments contain

myosin

thin filaments characteristics

- each actin molecule contains an active site
- also contains tropomyosin and troponin

active site

part of actin molecule that myosin can bind to when make contact with thick molecule

when do active sites get uncovered?

when calcium ions bind to troponin which causes it to change shape so old troponin-tropomyosin complex moves out of way

tropomyosin

covers active site when muscle is at rest ("green vines")

troponin

holds the tropomyosin in place

troponin-tropomyosin complex

formed when the 2 respective proteins move together

parts of myosin molecule

- tail
- hinge
- head

tail of myosin molecule

binds to other myosin molecules, which is how to form a filament

hinge of myosin molecule

allows head to pivot

head of myosin molecule

its pivot is what drives action of muscle contraction (uses ATP which burns calories)

cross-bridge

name for a myosin head while its attached to actin

muscle contraction (sliding filament model) steps

1. calcium ion binds to troponin on thin filaments to expose active sites
2. myosin heads binds to thin filament and pivot
3. action is repeated over and over until thin filament is pulled fully in and contraction occurs

how long does a contraction occur

as long as muscle fiber is being signaled by neuron and as long as ATP is available to fuel pivoting cross-bridges

what occurs during muscle contraction?

- muscle gets pulled back by gravity or other muscles
- width of A band stays the same (aka thick filaments aren't going anywhere)
- Z lines move closer together (akak I band gets shorter)

process of contraction

1. neural stimulation of sarcolemma causes excitation-contraction coupling
2. cisternae of SR release Ca2+ which triggers interaction of thick and thin filaments consuming ATP and producing tension

interactions of thick and thin filaments include

- sliding
- pivoting cross-bridges

innervation

to supply nerves to

neuromuscular junction

location of neural stimulation of a muscle fiber; type of synapse