Ch. 10 - Muscle Test 4

Phosphorylation of ATP

Converting ATP to ADP and Pi

Cardiac Muscle Tissue

-striated and organized into sarcomeres -shorter than skeletal muscle and usually only contain one nucleus located in the center of the cell -possess many mitochondria and myoglobin -branched and have intercalated discs

Smooth Muscle Contraction

- Cytosolic Ca++ increases - Binds to calmodulin - Calmodulin activates myosin light chain kinase - Myosin is phosphorylated - Myosin binds to actin - Cross bridges form; muscle shortens; tensions develops

Aerobic Respiration

-Breakdown of glucose or other nutrients in the presence of oxygen to produce carbon dioxide, water, and ATP. -95% of the ATP required for resting or moderately active muscles is provided by aerobic respiration -Takes place in mitochondria -Inputs = glucose, pyruvic acid, fatty acids -Very efficient, 36 ATP for one glucose -Needs steady supply of oxygen and is slow

Anaerobic Glycolysis

-Breaks down glucose to produce ATP -Slower rate of ATP availability to muscle than creatine phosphate -Sugar used is either from blood glucose or by metabolizing glycogen that is stored in the muscle -1 glucose molecule produces 2 ATP and 2 molecules of pyruvic acid -It cannot be sustained for a very long time (1 min) but it can be useful in facilitating short bursts of high intensity output

What happens when muscle fibers are stimulated frequently?

-Contraction response changes -Ca++ in sarcoplasm -Shortened elastic elements (tendons and connective tissues)

What happens to the features of the sarcomere when the skeletal muscles contract?

-Decrease size of H zone and I bands. -Z discs come closer to the M line. -A band is anchored in the middle of the sarcomere so it does not slide.

What prevents the filaments from sliding back to their original position each time a myosin head releases?

-Each myosin head does not pull at the same time, if one lets go, there is always another one that is pulling. The contraction in the net result. -Multiple myosin heads, and they alternate when they pull.

What tells the myofibril to shorten?

-Electrical impulse from a neuron (a nerve cell in the central nervous system) -The neuron communicates with the muscle fiber chemically, and the chemical signal is converted into an electrical signal. -The signal in the muscle fiber causes Ca++ release from the sarcoplasmic reticulum.

Action Potential

-Electrical signal produced by ion movements across the plasma membrane of excitable tissues. -Nervous tissue and muscular tissue. OpenStax section 12.4 p. 525

Creatine Phosphate

-In a resting muscle, ATP transfers its energy to creatine, producing ADP and creatine phosphate. -When the muscle starts to contract and needs energy, creatine phosphate transfers its phosphate back to ADP to form ATP and creatine. -Catalyzed by the enzyme creatine kinase -Powers the first few seconds of muscle contraction -Can only provide 15 sec worth of energy

Concentric contraction

-Isotonic: muscle shortening to move a load (lift a weight)

Eccentric contraction

-Isotonic: muscle tension diminishes and muscle lengthens (lowering a weight)

Intercalated discs

-Located at the end of cardiac muscle cells and connect them to one another. -They allow the cells to contract in a wave-like pattern so that the heart can work as a pump.

Muscle Tone

-Low levels of muscle contraction that occur when a muscle is not producing movement. -Allows muscles to continually stabilize joints and maintain posture. -Hypotonia= no muscle tone -Hypertonia= excessive muscle tone

Repolarization phase (in relation to action potential)

-Na channel inactivation gates close and K channels open. -Outflow of K causes depolarization and restores the resting potential membrane. -Electrical potential that is positive causes Na channels to close at +30mV. -Repolarization continues: potassium outflow restores resting membrane potential. Na+ channel inactivation gates open. Return to resting state when K+ gates close.

Graded Muscle Response

-Normal muscle contraction is more sustained and it can be modified by input from the nervous system to produce varying amounts of force. -Frequency of action potentials from a motor neuron and the number of motor neurons transmitting action potentials both affect the tension produced in skeletal muscle.

Depolarizing phase (in relation to action potential)

-Opening of the Na channels and sodium goes INTO THE CELL (because it goes down the electrochemical gradient). -This further depolarizes the membrane, opening more Na+ channel activation gates. -Charge inside of the cell begins to increase and become more (+) than outside of the cell.

Pyruvic acid

-Produced by anaerobic glycolysis -If oxygen is available it is used in aerobic respiration -If oxygen is not available, it is converted to lactic acid, which can contribute to muscle fatigue. This conversion allows the recycling of the enzyme NAD+ from NADH, which is needed for glycolysis to continue.

Multi-unit smooth muscle cells

-Rarely possess gap junctions and thus are not electrically coupled -Contraction is confined to the cell that was originally stimulated -Stimuli come from ANS or hormones, not from stretching -found around large blood vessels, in respiratory airways, and in the eyes

Neuromuscular Junction (NMJ)

-The point of communication between the central nervous system and the muscular system -Electrical signal to chemical signal to electrical signal

Starting with a resting cell: the resting membrane potential

-The transmembrane potential of a cell at rest -The separation of charges across a membrane in an excitable cell at rest

Pacemaker cells

-control contractions of the heart -respond to signals from the ANS to speed up or slow down -respond to various hormones that modulate heart rate to control blood pressure -begins the wave of contraction that allows the heart to work as a unit -are self-excitable and able to depolarize to threshold and fire action potentials on their own

Gap Junction

-forms channels between adjacent cardiac muscle fibers that allow the depolarizing current produced by cations to flow from one cardiac muscle to the next

Pacesetter Cell

-in visceral muscle in the walls of hollow organs -spontaneously trigger action potentials and contractions in the muscle

Single-unit smooth muscle

-muscle fibers joined by gap junctions so that the muscle contracts as a single unit -found in the walls of all visceral organs -called visceral muscle -it has a stress-relaxation response

Smooth Muscle

-no striations or sarcomeres -spindle-shaped and have a single nucleus -have actin and myosin and thick and thin filaments -do not have troponin

Sliding Filament Model of Contraction 2

1. Calcium ions are released from the sarcoplasmic reticulum into the sarcoplasm, where they bind to troponin. 2. Tropomyosin changes shape, revealing the myosin-binding sites on the actin which allows cross-bridge formation. 3. The myosin heads bind to the myosin-binding sites on the actin and they pull the thin filaments past the thick filaments towards the center of the sarcomere.

Cross-Bridge Cycle

1. Cross bridge formation occurs when the myosin head attaches to the actin while ADP and Pi are still bound to the myosin. 2. Pi is then released, causing myosin to form a stronger attachment to actin, after which the myosin head is moved towards the M-line (power stroke). 3. Myosin head has binding site for actin and ATP. ATP binding causes the myosin head to detach from the actin. 4. The myosin head hydrolyzes the ATP into ADP and Pi, creating energy which changes the angle of the myosin head into a cocked position. 5. The cocked position is a high energy configuration. The energy is expended as the myosin head moves through the power stroke into a low energy position. 6. After the power stroke, ADP is released, however the cross-bridge is still in place and actin and myosin are bound together. 7. If ATP is still available, it readily attaches to myosin and the cycle recurs and muscle contraction continues.

Smooth Muscle Contraction 2

1. External Ca++ ions pass through opened calcium channels in the sarcolemma and they attach to calmodulin. 2. The Ca++-calmodulin complex then activates an enzyme called myosin light chain kinase, which activates the myosin heads by phosphorylating them. 3. The heads then attach to actin-binding sites and pull on the thin filaments. 4. When the thin filaments slide past the thick filaments, they pull on the dense bodies which pull on the intermediate filaments networks throughout the sarcoplasm. 5. The entire muscle fiber contracts in a manner whereby the ends are pulled toward the center, causing the midsection to bulge in corkscrew motion.

Two Criteria to Consider When Classifying Types of Muscles

1. How fast some fibers contract relative to others. 2. How fibers produce ATP

Phases of a Twitch

1. Latent Period 2. Contraction Phase 3. Relaxation Phase

Action potential to Muscle Contraction steps

1. Motor neuron depolarizes 2. ACh is released 3. Motor neuron repolarizes 4. Ligand gated Na+ channels are activated at the motor end plate 5. Muscle fiber is depolarized 6. Action potential is propagated across the membrane of the muscle fiber 7. Voltage gated Ca++ channels in the SR open 8. Ca++ flood into the sarcoplasm, binds to troponin 9. Tropomyosin changes shape; crossbridges are formed 10. ... and filaments side

Excitation-Contraction Coupling

1. Muscle contraction is stimulated by a signal from a nerve cell. 2. An electrical signal, called an action potential, is generated within the muscle cell. 3. Action potential produces a change in the calcium concentration in the cytosol. 4. Excitation-contraction coupling is thus the sequence of events by which an electrical signal leads to the sliding of the microfilaments.

Contraction Cycle of Muscle

1. Myosin heads hydrolyze ATP and become reoriented and energized. 2. Myosin heads bind to actin, forming cross-bridges. 3. Myosin cross-bridges rotate toward center of sarcomere (power stroke) 4. As myosin head bind ATP, the cross-bridges detach from actin -Contraction cycle continues if ATP is available and Ca++ level in sarcoplasm is high.

Excitation-Contraction Coupling 2

1. Neuronal action potential travels down neuron to NMJ. 2. At the NMJ, the axon terminal releases acetylcholine, which then cross the synaptic cleft. 3. Acetylcholine binds to its receptors located within the motor end plate of the sarcolemma. 4. Once ACh binds, a channel in the ACh receptor opens and positively charged ions can pass through into the muscle fiber, causing it to depolarize. 5. As the membrane depolarizes, another set of ion channels called voltage-gated sodium channels are triggered open. 6. Sodium ions enter the muscle fiber and an action potential rapidly spreads along the membrane. 7. The membrane repolarizes. 8. Calcium ions are released from the sarcoplasmic reticulum into the sarcoplasm, initiating muscle contraction.

Steps for Action Potential Propagation

1. Voltage gated Na+ channels open 2. Na+ enters motor neurons 3. Motor neuron depolarizes; membrane potential ~ +30mv 4. ACh is released 5. Voltage gated K+ channels open; Na+ channels close 6. K+ leaves motor neuron 7. Voltage gated K+ channels close 8. Motor neuron repolarizes membrane potential ~ -75 mV 9. ACh diffuses across synaptic cleft 10. Action potential is propagated in the muscle fiber

Sliding Filament Theory Steps

1. myosin forms cross bridges with thin filaments (actin) 2. thick filaments propel the thin filaments towards the M line 3. thin filaments slide past the thick filaments, therefore shortening the sarcomere

Varicosity

A neurotransmitter-filled bulge that releases neurotransmitters into the synaptic cleft of smooth muscle.

What happens to end muscle contraction?

ACh - ACh is broken down by acetylcholinesterase in the synaptic cleft Ca++ - Ca++ is sequestered in the sarcoplasmic reticulum Actin and myosin - active sites occluded; cross bridge formation inhibited; filaments do not slide

Why are the A bands the darkest region of the sarcomere when viewed under a microscope?

Actin and myosin OVERLAP with each other in the A band, therefore making it darker due to more fibers being there

How do we start a muscle contraction?

Action potential - from nervous system that tells skeletal muscle to move

Latent Period

Action potential is being propagate along a sarcolemma and Ca++ ions are released from the SR. Phase where excitation and contraction are being coupled but contraction has yet to occur.

Large Motor Unit

An arrangement where a single motor neuron supplies a large number of muscle fibers in a muscle, concerned with simple or "gross" movements

Small Motor Unit

An arrangement where a single motor neuron supplies a small number of muscle fibers in a muscle cell, permit very fine motor control of the muscle

Dense Body

Anchor the thin filaments of smooth muscle. Analogous to the Z-discs of skeletal and cardiac muscle fibers and is fastened to the sarcolemma.

Myosin molecules have binding sites for what molecules?

Binds to ATP and actin

Contraction Phase

Ca++ ions in the sarcoplasm have bound to troponin, tropomyosin has shifted away from actin-binding sites, cross-bridges formed, and sarcomeres are actively shortening to the point of peak tension.

What causes contraction?

Calcium is released, movement of the actin and myosin due to cross bridges.

Desmosomes

Cell structures that anchor the ends of cardiac muscle fibers together so the cells do not pull apart during the stress of individual fibers contracting

Where are there only THIN filaments?

I band

Slow Oxidative Skeletal Muscle

Fibers contract relatively slow and use aerobic respiration to produce ATP

Fast Oxidative Skeletal Muscle

Fibers have fast contractions and primarily use aerobic respiration, but because they may switch to anaerobic glycolysis, can fatigue more quickly than SO fibers.

Fast Glycolytic Skeletal Muscle

Fibers have fast contractions and primarily use anaerobic glycolysis, fatigue more quickly than the others.

What two structures make up intercalated discs?

Gap Junctions and Desmosomes

Where are there only THICK filaments?

H zone (right in the center)

Twitch

Isolated contraction produced by a single action potential

Calveoli

Membrane indentions in smooth muscle fiber that allows for the sequestration of calcium ions from the extracellular fluid

Motor unit

Motor neuron PLUS all the muscle fibers innervated by that neuron

If ATP is depleted in the muscle fiber, what would happen?

No muscle contraction

Tetanus

No relaxation phase between contractions, contractions are continuous. Ca++ ions in the sarcoplasm allows all of the sarcomeres to form cross-bridges and shorten.

Isometric contraction

Occurs as the muscle produces tension without changing the angle of a skeletal joint. -Does not move a load -Maintain posture and bone/joint stability

Calmodulin

Regulates cross bridge formation in smooth muscle cells

Cell at rest (in relation to action potential)

Separation of charges across the cell membrane. Inside is negative and outside is positive. Inside the cell is -70mV at rest

Hyperplasia

Smooth muscle can divide to produce more cells

Twitch Contraction

The contraction that results when all the fibers in a motor unit contract in response to a single action potential in a motor neuron

Motor Unit

The group of muscle fibers in a muscle innervated by a single motor neuron

Stress-Relaxation Response

The muscle of a hollow organ is stretched when it fills, the mechanical stress of the stretching will trigger contraction, but this is immediately followed by relaxation so that the organ does not empty its contents prematurely.

Wave summation

The rate at which motor neurons fire action potentials affects the tension produced in the skeletal muscle, if the fibers are stimulated while a previous twitch is still occurring, the second twitch will be stronger.

Isotonic contraction

The tension of the muscle stays constant, a load is moved as the length of the muscle changes

Treppe

When muscle tension increases in a graded manner that looks like a set of stairs. The contractions become more efficient.

Relaxation Phase

When tension decreases as contraction stops. Ca++ ions are pumped out of the sarcoplasm into the SR, and cross-bridge cycling stops, returning the muscle fibers to their resting state.

Troponin is on the

actin

Calcium is released into the cytoplasm from the sarcoplasmic reticulum, it is regulated by

calcitonin and parathyroid hormone

Sarcoplasm

cytoplasm of muscle fibers

Calcium leaves the sarcoplasmic reticulum through

facilitated diffusion through an ion channel (because Ca++ is charged and an ion)

Sarcomere

longitudinally, repeating functional unit of skeletal muscle, with all of the contractile and associated proteins involved in contraction

Tropomyosin is on the

myosin

Sarcolemma

plasma membrane of muscle fibers

Calcium is put BACK into the sarcoplasmic reticulum through

primary active transport (active transport pump)

Sarcoplasmic Reticulum

the specialized smooth endoplasmic reticulum, which stores, releases, and retrieves calcium ions (Ca++)