Muscles 1 Flashcards
Muscles
Are tissues that transform chemical energy(ATP) into mechanical energy that produces force
Functions
- produce movement
- maintains posture and body position
- stabilizes joints
- generates heat as they contract
The 3 types of muscle tissues
Skeletal, cardiac and smooth muscle
- all differ in location, structure, function and type of control
Skeletal Muscle
- attached. To bones and the skin
- they are voluntary: controlled consciously and we are aware of these moving
- the skeletal muscle cells are multinucleate and has a striated patterm
Cardiac Muscle
- only in the heart
- they are involuntary, we don’t control them
- the cardiac muscle cells are branched and stratified with 1 centrally located nucleus
- neighbouring cells are connected by gap junctions called intercalated discs
Smooth Muscle
Forms the walls of hollow organs like the stomach, urinary bladder and airways
- they are involuntary
- the smooth muscle cells are non striated and have only 1 centrally located nucleus to conform to a spindle cell shape
All muscles tissues share 4 main characteristics
- Excitability: ability to receive and respond to stimuli
- Contractility: ability to shorten forcibly when stimulated
- Extensibility: being able to get stretched
- Elasticity: being able to get recoiled to its resting length
Muscles are both
An organ and a tissue type
The skeletal muscle is organized by connective tissue
Epimysium: covers the outer skeletal muscle
Perimysium: surround a bundle of muscle fibres called a fascicle
Endomysium: surround a single muscles fibre( the cells of muscles)
- look at diagrams
Muscle fibres contain
Sarcolemma: muscle fibre plasma membrane
Sarcoplasm: muscle fibre cytoplasm
Sacroplasmic reticulum(SR)
- a specialized smooth ER
-surrounds contractile organelles called myofibrils - stores and releases calcium ions
- termiap cisternae are attached to T tubules
Transverse(T) tubules
Invitations of the sacrilege rich in ion channels that runs transversely through a muscle fibre
A Triad
Is the terminal cisternae of neighbouring SR and 1 T tubule
Myofibrils
- specialized organelles that account for around 80% of muscle fibre volume
- consists of contractile units called sarcomeres that are aligned end to end
Sacromere
- has bundles of thick and thin filaments
- the different regions form dark and light bands called striations
What does each region contain?
I band: thin filament only(light region)
A band: overlapping thick and thin filaments(Dark region)
H zone: thick filaments only
During contraction , what occurs to each region?
I band: shortens
A band: doesn’t change in length
H zone: shortens and can disappear
Myofilaments
Consists of both thick and thin filamebts
Thin filaments
- are made up of actin
- each actin has a myosin binding site
Topomysin and troponin are regulatory protein complexes bound to this - troponin binds calcium
Thick filaments
are made of bundles of myosin.
Each myosin has a head and a tail region
• heads are staggered and have actin-binding sites and ATP-binding site
Neuromuscular Juction(NMJ)
- also known as the motor end plate or motor synase
- where signals from the nervous system reach the skeletal muscle fibres
The order of which happens at the NMJ
- An electrical impulse called action potential arrive at the axon terminal of the NMJ
- Calcium enters the neuron’s terminal.
- Neurotransmitter called acetylcholine (ACh) stored in vesicles are released into the synaptic cleft.
- (ACh) binds receptors on the muscle fibre membrane
- Ligand-gated sodium channels lead to depolarization known as end-plate potential.
Excitation-Contraction(E-C) Coupling
A co fraction is the result of the excitation of skeletal muscle cells by the nervous system
- it’s in the form of action potential that travels down the sarcolemma to the triad
- the T tubules trigger Ca from the SR
What role does calcium pay in the sarcomere to initiate contraction?
• Ca+ binds to troponin, which moves tropomyosin away and exposes myosin-binding sites on actin
• Enables binding between thin and thick filaments to form a structure called a cross bridge
- required for it to take place
The cross bridge cycle
- also know as the sliding filament model
- is the molecular mechanism of muscle contraction:
- thin filaments constantly slide over thick filaments and generate muscle tension
Has 4 steps
- Reactivation if myosin head
- Cross-bridge formation
- Power-stroke
- Cross-bridge detachment
Look at diagram
What role does ATP play in the cycle
ATP binding is needed to break the cross-bridge (detachment stage)
• ATP hydrolysis is needed to “cock” the myosin head into place (reactivation stage)
Rigor mortis is a post-mortem process where chemical changes in the myofibrils lead to stiffening of body muscles. What is the cause of this?
A) the cells are dead
B) sodium ions leak into the muscle causing continued contractions
C) no ATP is available to release attached actin and myosin molecules
D) proteins are beginning to break down, thus preventing a flow of calcium ions
C
