Chapter 12 Flashcards
What are the three muscle types?
Skeletal muscle , cardiac muscle, smooth muscle
Where is cardiac muscle found
It is only found in the heart
What are most skeletal muscles attached to?
The bones of the skeleton by tendons made of collagen.
Where is smooth muscle located
The primary muscle of the stomach, urinary bladder, and blood vessels
What are skeletal muscles used for?
To move the skeleton
What is smooth muscle used for?
To influence the movement of material into, out of, and within the body.
What does cardiac muscle do?
Moves blood through the circulatory system.
What is skeletal muscle made out of?
Muscle cells that are called Muscle fibers. (Largest cells in body)
Each muscle fiber is a long cylindrical cell with up to several hundred nuclei near the surface of the fiber.
Muscle fiber
A collection of muscle cells
Satellite cells
Committed stem cells that lie just outside the muscle fiber membrane. They become active and differentiate into muscle when needed for muscle growth and repair.
Fascicles
Each muscle fiber is sheathed in connective tissue, with groups of adjacent muscle fibers bundled together into these units called fascicles
Sheath
A structure of living tissue which closely envelops another
Tendon
Made of collagen, attach bones to muscle
Sarcolemma structure and uses
The cell membrane of a muscle fiber, it acts as a barrier between the extra cellular and intracellular compartments, it defines each muscle fiber from its surroundings
Sarcoplasmic reticulum (SR) structure and uses
A form of modified endoplasmic reticulum that wraps around each myofibril like a piece of lace. It consists of longitudinal tubules with enlarged end regions.
The main function is to store calcium ions
Terminal cisternae uses and structure
The enlarged end regions of the longitudinal tubules of the sarcoplasmic reticulum.
Ensures rapid calcium delivery
Myofibril
The main intracellular structures in striated muscles
They are highly organized bundles of contractile and elastic proteins that carry out work of contraction
Sarcomere uses and structure
A structural unit of a myofibril in striated muscle, consisting of a dark band and a light band
Each sarcomere is composed of two main protein structures call actin and myosin which are the active structures responsible for muscular contraction.
Transverse tubule (t-tubule) structure and uses
Extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscles
Allow close interaction between the sarcoplasmic reticulum and sarcolemma
Components of a sarcomere
- Z disks
- I bands
- A band
- H zone
- M line
What does the Z disks do
One sarcomere has 2 Z disks. Zigzag protein structures that serve as the attachment site for thin filaments.
What do I bands do
These are the light color bands of the sarcomere , they represent a region occupied only by thin filaments. A Z disks run through the middle of every I band (each I band belongs to a different sarcomere)
What does the A band do
Dark colored sarcomere band, encompasses the entire length of a thick filament. The center of the A band is occupied by thick filaments only.
What does the H zone do
Central region of the A band, lighter than the outer edges of the A band because the H zone is occupied by thick filaments only.
What does the M line do
This band represents proteins that form the attachment site for thick filaments. Each M line divides an A band in half.
What are thick filaments
About 250 myosin molecules join to create a thick filament. Each thick filament is arranged so that the myosin heads are clustered at each end of the filament of myosin tails
Myosin
A motor protein with the ability to create movement
Thin filament / actin
Actin is a protein that makes up the thin filaments of the muscle fiber. One actin molecule is a globular protein
What is troponin
Allows calcium signal to turn muscle contraction on and off.
Calcium binding complex of three proteins
Tropomysin
Protein polymer that wraps around actin filaments and partially covers actins myosin- binding sites
What is nebulin
Inelastic giant protein that lies alongside thin filaments and attaches to the Z disk. Nebulin helps align the actin filaments of the sarcomere
What is Titin
Huge elastic molecule and the largest known protein, composed of more than 25,000 amino acids. A single titin molecule stretches from one Z disk to the neighboring M line
Two functions of titin
1) stabilizes the position of the contractile filaments
2) its elasticity returns stretched muscles to to their resting length.
why are myosin and actin interactions important for contractions ?
They generate their movements relative to one another they slide / bind past eachother in muscle contraction
How do ATP and calcium influence the interaction between myosin and actin
The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin. ATP then binds to myosin moving the myosin to its high energy state.
What is rigor state
Tight binding between actin and myosin in the absence of ATP.
What is the power stroke
The movement of the myosin head that is the basis for muscle contraction.
The events that lead up to muscle relaxation
Calcium must be removed from the cytosol. The sarcoplasmic reticulum pumps calcium back into its lumen using Ca2+ - ATPase
As the free cystolic calcium concentration decreases, the equilibrium between bound and unbound calcium is disturbed and calcium releases from troponin . This allows tropomyosin to slide back and block actins myosin binding site.
Define twitch
A single contraction-relaxation cycle in a skeletal muscle fiber
Events in excitation-contraction coupling and relaxation
1) somatic motor neuron releases ACh at neuromuscular junction
2) net entry of Na+ through ACh receptor- channel initiates a muscle action potential
3) action potential in t-tubule alters conformation of DHP receptor.
4) DHP receptor opens RyR Ca2+ release channels in sarcoplasmic reticulum, and Ca2+ enters cytoplasm
5) Ca2+ binds to troponin, allowing actin-myosin binding
6) myosin heads execute the power stroke
7) actin filament slides toward center of sarcomere
8) sarcoplasmic Ca2+ -ATPase pups Ca2+ back into SR
9) decrease in free cytosolic calcium cause Ca2+ to unbind from troponin
10) tropomyosin re-covers binding site. When myosin heads release, elastic elements pull filaments back to their relaxed position
Latent period
Delay between the muscle action potential and beginning of muscle tension that represents the time required for
Ca2+ release and binding troponin.
Why is phosphocreatine useful to skeletal muscle?
It is a backup source of energy for muscles. it is a molecule whose high-energy phosphate bonds are created from creatine and ATP when muscles are at rest. It is quickly turned into ADP creating more ATP to power the muscles
What is central muscle fatigue
Arise in the central nervous system, central fatigue includes subjective feelings of tiredness and a desire to cease activity. It may be a protective mechanism.
What is peripheral muscle fatigue ?
Arise anywhere between the neuromuscular junction and the contractile elements of the muscle .
Structural and functional difference between slow twitch and fast twitch muscle fibers
Fast twitch muscle fibers develop tension two to three times faster than low twitch fibers.
Fast twitch fibers split ATP more rapidly and can therefore, complete multiple contractile cycles more rapidly than slow twitch fibers
Why is myoglobin useful to muscle fibers
It functions as an oxygen storage unit. Providing oxygen to working muscles
Define summation
If the interval of time between muscle action potential is shortened, the muscle fiber does not have time to relax completely between two stimuli, resulting in a more forceful contraction
Define the two types of tetanus
Incomplete tetanus: the stimulation rate of the muscle fiber is not at a maximum value, and the fiber relaxes slightly between stimuli.
Complete tetanus: the stimulation rate is fast enough that the muscle fiber does not have time to relax , instead it reaches a maximum tension and remains there
Describe a motor unit
The basic unit of contraction in an intact skeletal muscle
What is the benefit of asynchronous recruitment
Prevents fatigue only in submaximal contractions.
How is isotonic and isometric muscle use different
Isotonic contraction is a contraction that creates force and moves a load (taking dumbells and lifting them to touch your shoulder )
Isometric contraction is a contraction that creates force without moving a load (holding the weights out in front of you )
Phasic smooth muscle contraction
Muscles that undergo periodic contraction and relaxation cycles . ( wall of the lower esophagus that contracts only when food passes through it
Tonic smooth muscle contraction
Muscles that are continuously contracted . (The esophageal and urinary bladders)
Single unit smooth muscle
Connected in gap junctions and they contract in a coordinated unit
Multi-unit smooth muscle
The cells are not linked electrically and each muscle cell functions independently
Difference between smooth and skeletal muscle features
1) smooth muscle must operate over a range of lengths.
2) within an organ, the layers of smooth muscle run in several different directions
3) smooth muscles contract and relax much more slowly
4) smooth muscle uses less energy to generate and maintain a given amount of force
5) smooth muscle can sustain contractions for for extended periods without fatiguing
6) smooth muscles have, small, spindle-shaped cells with a single nucleus
7) the contractile fibers are not arranged in sarcomeres
