muscle tissue Flashcards
what are the functions of muscle tissue
- produce movements of skeleton
- maintain posture and body position
- stabilize joints
- generate heat
- store and move things through body
- serve as nutrient reserve
what are the characteristics and properties of muscular tissue
- excitable
- contractible
- extensibility
- elasticity
what does excitable mean
has the ability to respond to a stimuli by producing action potentials
what is contractility
ability to contract when stimulated by an action potential
what is extensibility
ability to stretch without being damaged
what is elasticity
ability to return to its original shape
what are the characteristics of muscle
- organs made up of muscles, connective tissues and nerve tissue
- all have one artery and veins
- has a nerve ending
- they span a joint and attach to 2 bones
what is the basis of the organization of a muscle
- each skeletal muscle is a separate organ composed of 100s of muscle fibers –> cells
- a skeletal muscle contains CT wrapped around muscle fibers, blood vessels and nerves
what are the 3 layers of connective tissue involved in the organization of a muscle
epimysium
perimysium
endomysium
what is epimysium (also known as a fascia)
- the outer layer of CT
- the membrane that surrounds the whole muscle + acts as a covering
what is perimysium
- the membrane that surrounds and wraps around 100s of muscle fibers into bundles (fascicles)
what is a fascicle
- bundle of muscle fibers
- a muscle is define as a group of fascicles working together
what is endomysium
- is inside each fascicle
- wraps around each individual muscle fiber
what is the basis of the organization of a muscle fiber
each muscles fiber is made from the fusion of 100s of myoblasts
what are the parts included in the organization of the muscle fiber
myofibrils
myofilaments
t tubues
sarcoplasmic reticulum
cisternae
sarcolemma
sarcoplasm
sarcomere
what is the sarcolemma
the cell membrane of muscle fibers
what are transverse tubules
- enfolding’s in the sarcolemma that encircle the muscle fibers
- ensures the act pot excites all parts of the muscle fiber
what is the sarcoplasm
- cytoplasms of the muscle cell
- contains glycogen and myoglobin
what is the role of glycogen
synthesizes atp
what role of myoglobin
release oxygen when needed by the mitochondria
what is the role of the mitochondria
site of oxidative respiration
what is sarcoplasmic reticulum
membrane system that wraps around myofibrils
- net pattern
what are myofibrils
- bundles of myofilaments wrapped in sarcoplasmic reticulum
what are terminal cisternae
- sac-like area of the sarcoplasmic reticulum
- stores calcium
what are triads
- junction site between T tubules and 2 cisternae
- it’s the site where electrical impulses can enter inside a muscle cell
what is a sarcomere
- the contractile unit of a muscle fiber
- contains myofilaments
what are myofilaments
- the contractile elements
what are the 2 kinds of myofilament
- actin
- myosin
what’s actin
- the thin filaments
- light bands
what is myosin
- the thick filaments
- dark bands
in the overlap region of the actin and myosin, what is the ratio
1 myosin for every 2 actin
what are the components that are found/make up the sarcomere
myosin
actin
z line
A bands
I bands
H zone
M line
what is the A band
- dark band
- the entire length of dark band/thick filament
- contains myosin with overlapping actin
what is the I band
- the light band
- contains only thin filaments and no thick filaments
what is the Z line
- found in the middle of the I band
- holds actin in place
what is the H zone
- area in the center of each A band
- thick but no thin (no overlap)
what is the m line
- in the middle of the A band
- holds myosin in place
what are the 3 types of muscle proteins
contractile
regulatory
structural
what is the role of the contractile proteins
generates force during the muscle contraction
what is the role of regulatory proteins
help switch the contraction process off and on
what is the role of structural proteins
- keeps thick and thin filaments in their proper alignment
- give elasticity to myofibril
- link myofibrils and sarcolemmas
describe the molecular structure of myosin (thick)
- 1 myosin is shaped like 2 golf clubs twisted together
- rod like tails with globular heads
what is the importance of the myosin heads
- each head contains 2 binding sites: actin binding and atp binding
- act as the cross bridges
describe the molecular structure of actin
form a helix shape
what important elements does actin contain
- myosin binding sites for myosin heads
- regulatory proteins
what are the 2 regulatory proteins that actin contains
tropomyosin
troponin
what is the role of tropomyosin
- covers the actin binding sites when at rest
what is the role of troponin
- binds calcium and changes shape
- attached to tropomyosin
what is the role of atp during contraction
activates myosin
detached flexed myosin head from actin
what is the role of calcium in contraction
- trigger for muscle contraction
- binds to troponin that pulls on tropomyosin, which exposes the active sites of actin
where is calcium stored
in terminal cisternae
what are the changes in the sarcomere when contraction occurs
- sarcomeres shorten
- z lines move closer together
- A bands move closer together but stay the same width
- I bands get smaller
- H zone gets smaller
what is the sliding filament mechanism
- thin filaments are pulled towards each other, sliding over thick filaments
- this increases overlap of actin and myosin
- occurs in all sarcomeres at the same time
why does the sliding occur in the sliding filament mechanism
- cross bridges attach and detach
- myosin heads attach and walk along thin filaments at both ends of the sarcomere
what are the steps of a contraction
step 0: muscle at rest
step 1: trigger and atp hydrolysis
step 2: attachment of myosin to actin
step 3: power stroke
step 4: cross bridge detachment
what is the step 0 of the contraction
muscle is at rest
1. myosin heads are activated
2. atp is hydrolyzed to to adp + P and is attached to the myosin head
3. actin sites are covered by troponin
4. actin and myosin overlap slightly
5. calcium is in cisternae
what is the step 1 of contraction
- electrical signal travel along the sarcolemma and down the t tubules
- when the signal reaches the cisternae, it causes the release of calcium into the sarcoplasm
- the calcium binds to troponin, which pulls at the tropomyosin to expose the actin binding sites
what is step 2 of contraction
- the myosin heads are energized (when atp initially binded to the atp binding site of the myosin head, it works as an enzyme to break down the atp and store the energy from the hydrolysis) and is standing at high alert
- the heads bind to the myosin binding site and released the bound phosphate group that it was holding onto
- binding forms a cross bridge
what is step 3 of contraction
- myosin head flexes and goes from 90 deg to 45 deg
- the change in angle pulls the thin actin towards the center of the sarcomere
- this causes tension
- the energy for the power stroke comes from the stored energy from the hydrolyzed atp
- adp + p falls off the head
what is the step 4 of contraction
- myosin head only detaches when another atp binds to it
- atp reactivates the head and it returns to upright position (90 deg)
- cycle repeats as long as atp and calcium are present
what is rigor mortis
whe the cross bridges dont disconnect due to lack of atp
what is a neuromuscular junction
when the electrical signal travels down the axon of a neuron to the axon terminal, where the axon terminal forms a junction with the muscle
how is an electrical signal transferred from neuron to muscle
by the release of a NT
what is a motor end plate
specialized area of the muscle that binds NT
what is a motor neuron
neuron that connects to a muscle rather than another neuron
describe the steps that trigger the release of calcium from the neuron to the muscle
- motor neuron sends the electrical signal to the muscle, where it travels down the axon of the motor neuron and arrives at the axon terminal
- calcium gates open due to the arrival of the act pot and calcium moves into the synapse.
- the presence of calcium triggers the vesicles containing ACH
- ACH is released into the synaptic cleft and diffuses across the cleft
- ACH binds to receptors on the motor end plate
- the binding opens channels which causes ions to move in or out. when Na moves in, it triggers an electrical impulse that travels along the sarcolemma
- ach esterase in synaptic cleft removes NT
what’s an isotonic contraction
muscle contraction results in change of muscle length
whats an isometric contraction
tension forms but no change in length
- cross bridge forms but no sliding happens
what is muscle tone
partial contraction of muscle
how is tension/forced produced by a muscle
- it pulls on the tendon that overcomes a resistance
what causes the force produced by a muscle to vary
- degree of overlap of filaments (30% change in sarcomere = optimal tensions)
- frequency of stimulation (inc internal cytoplasmic calcium)
- recruitment
what is recruitment
increase in muscle tension is due to inc in number of stimulated motor units
what is a muscle twitch
single stimulus contraction relaxation cucle in a muscle fiber
how long does a muscle twitch last
7-100 msec
what are the periods in a muscle twitch
- latent period
- contraction phase
- relaxation phase
what is the latent period
time for molecular events that release calcium
what is the contraction phase
increased tension due to cross bridge formation
what is the relaxation phase
- calcium levels are falling
- tension returns to resting state
what is a wave summation
when many successive stimuli arrive before relaxation phase can go to completion
why are the following contractions after the initial contraction in a wave summation have a high contraction
- due to higher amounts of calcium in sarcoplasm
- pumps has too little time to restore sarcoplasm conditions
what is a treppe
- when a second stimulus occurs after rexation
- causes step wise increase in muscle response
does a treppe or wave summation have more muscle tension
wave summation
what is complete tetanus
- sustained maximum smooth contraction
- result of rapid delivery of stimuli overtime with no relaxation
what is incomplete tetany
quivery contraction
