A&P 1 test 3 (muscles)

Differentiate the three types of muscle tissue (histologically, functionally) (cardiac)

histologically: striated, branched, one nucleus. Functionally: involuntary, generates the rhythmic pumping action of the heart.

Differentiate the three types of muscle tissue (histologically, functionally) (skeletal)

Histologically: striated, long, cylindrical, unbranched fibers, multinucleated. Functionally: voluntary via the somatic nervous system, produces body movement

Differentiate the three types of muscle tissue (histologically, functionally) (smooth)

histologically: non-striated, spindle-shaped cells, single nucleus. Functionally: involuntary, found in walls of hallow organs, produces slow, wave-like contractions.

What unique characteristics do muscle tissues have?

Excitability, contractibility, extensibility/elasticity

excitability

the ability to respond to stimuli

contractibility

to shorten and produce force

extensibility/elasticity

ability to stretch and return to original length

What are three functions of muscle tissue?

movement of the body and internal materials, maintenance of posture and stability, and heat production

Is an entire muscle an organ, tissue, or system? Why?

An organ, because it is made of multiple tissue types working together for a common function.

What is the difference between superficial and deep fascia? Where are they found? (Superficial fascia function)

Provides insulation, padding, and a pathway for vessels and nerves traveling to the skin. Allows the skin to move freely.

What is the difference between superficial and deep fascia? Where are they found? (Superficial fascia location)

The subcutaneous layer, just beneath the skin, is made of loose connective tissue.

What is the difference between superficial and deep fascia? Where are they found? (Deep fascia location)

beneath the superficial fascia.

What is the difference between superficial and deep fascia? (superficial fascia) function

Provides insulation, padding, and a pathway for vessels and nerves traveling to the skin.

What is the difference between superficial and deep fascia? (deep fascia function)

Helps transmit muscular force, reduces friction between muscles, and creates functional compartments in regions like the limbs and neck.

What is the difference between a muscle fascicle, muscle fiber, myofibril, and myofilament? (muscle fascicle)

a bundle of muscle fibers wrapped in perimysium, organizes fibers so they can contract as a group.

What is the difference between a muscle fascicle, muscle fiber, myofibril, and myofilament? (muscle fiber)

A single skeletal muscle cell (long, cylindrical, multinucleated), wrapped in endomysium and surrounded by the sarcolemma. The basic contractile cell of skeletal muscle.

What is the difference between a muscle fascicle, muscle fiber, myofibril, and myofilament? (Myofibril)

A long, threadlike contractile rod inside each muscle fiber. Actually, shortens during contraction.

Myofilament

The protein filaments inside each sarcomere (actin, myosin). Perform the sliding filament mechanism that generates force.

Sarcolemma

The cell membrane of a skeletal muscle fiber or a cardiomyocyte helps anchor the muscle cell to surrounding tissues.

transverse tubules:

Invaginations of the sarcolemma that penetrate deep into the muscle fiber. They wrap around myofibrils and serve as pathways for rapid electrical excitation. They ensure that each action potential reaches the cell at the same time.

Sarcoplasm

The cytoplasm of the muscle cell, it is enclosed by the sarcolemma and supports the metabolic processes needed for muscle activity.

sarcoplasmic reticulum

The smooth ER in muscle fibers. It forms a network of membranous tubules that store and release calcium ions, which are essential for triggering muscle contraction.

What type of organic compound is actin?

A globular multifunctional protein

What type of organic compound is myosin?

A motor protein

What is the myosin head?

The active ATP-powered part of the myosin molecule that attaches to actin and generates force during muscle contraction

What are three functions of the myosin head?

Binds to actin to form cross-bridges, Hydrolyzes ATP (acts as an ATPase) to provide energy, and performs the power stroke by pivoting and pulling the filament.

Name two proteins that are bound to actin:

Tropomyosin, Troponin

What is the function of the troponin-tropomyosin complex?

It prevents myosin from binding to actin at rest and allows binding when calcium is present

To what mineral does troponin bind?

Calcium

What triggers the release of calcium from the sarcoplasmic reticulum?

An action potential reaches the T-tubules and triggers the SR to release calcium.

Is ATP required for calcium release from the sarcoplasmic reticulum?

No

Is ATP required to pump calcium back into the sarcoplasmic reticulum? Why?

Yes, uphill process powered by the SERCA ATPase

What is meant by a voltage-sensitive calcium channel?

A membrane protein that opens in response to a change in electrical charge across the membrane

What is meant by a voltage-sensitive calcium channel? Explain

When action potential changes the electrical charge across the membrane, the voltage-sensing domains causes the channel to change shape and open its pores, allowing for calcium to flow in or out.

What is the power stroke?

The force-producing pivot of the myosin head that pulls actin toward the M-line during muscle contraction.

Which steps in muscle contraction requires ATP?

Detachment of the myosin head from actin, Reactivation of the myosin head, pumping Calcium back into the sarcoplasmic reticulum

What happens to each of these parts of the sarcomere when the sarcomere contracts? (A- band)

Stays the same length

What happens to each of these parts of the sarcomere when the sarcomere contracts? (I- band)

Gets shorter

What happens to each of these parts of the sarcomere when the sarcomere contracts? (H-zone)

Gets smaller or disappears

What happens to each of these parts of the sarcomere when the sarcomere contracts? (Z-line)

Moves closer together.

When does muscle contraction stop?

When calcium is removed from the cytosol.

What actually stops contraction?

When Ca^2+ is pumped back into the sarcoplasmic reticulum

Can skeletal muscle contract without intracellular calcium? Why or why not?

No, calcium is the essential trigger that allows myosin to bind to actin.

How is a low concentration of calcium maintained in the sarcoplasm?

Maintained by actively pumping calcium back into storage inside the sarcoplasmic reticulum

neuromuscular junction

The synapse between a motor neuron and a skeletal muscle fiber. Function: The site where motor neuron communicates with the muscle

motor end plate

The specialized region of the muscle fiber’s sarcolemma directly beneath the nerve terminal. Contains ACh receptors

synaptic cleft

The tiny space between the motor neuron terminal and the motor end plate. Allows diffusion of acetylcholine from the neuron to the muscle

Neurotransmitter

A chemical messenger released by neurons to communicate with other cells. In skeletal muscle, the neurotransmitter is Ach (acetylcholine

action potential

A nerve action potential arrives at the axon terminal of the motor neuron, the electrical signal is the trigger that starts neurotransmitter release.

synaptic end bulb

The swollen end of the motor neuron

What is in a synaptic end bulb?

Synaptic vesicles filled with ACh, voltage-gated calcium channels, and mitochondria.

Calcium

When the action potential reaches the terminal, voltage-gated Ca^2+ channels open, calcium rushes into the neuron. Calcium is the signal that triggers vesicle fusion and neurotransmitter release.

exocytosis

The process by which vesicles fuse with the membrane and release their contents

What is released from the axon terminal?

ACh is released into the synaptic cleft

What is the neurotransmitter at the neuromuscular junction?

Acetylcholine

How does the neurotransmitter move across the synaptic cleft?

ACh moves by simple diffusion across the synaptic cleft no ATP required.

What does the neurotransmitter do once it reaches the motor end plate?

ACh binds to nicotinic ACh receptors on the motor end plate.

What happens when acetylcholine binds to its receptor on the motor end plate?

The receptor opens, and sodium rushes into the muscle fiber, creating a local depolarization. If the EPP is strong enough, it triggers a muscle action potential.

What is a chemically-gated channel?

A protein on the cell membrane that opens when a chemical binds to it.

What does the chemically-gated channel on the motor end plate do?

The channel opens and allows sodium to enter the cell, depolarizing the muscle membrane and starts the excitation process.

What initiates the action potential in a muscle cell?

The end-plate potential reaches threshold, which opens the voltage-gated sodium channels in the sarcolemma, beginning muscle action potential.

Once the action potential begins on the motor end plate, how is it transmitted across the muscle cell?

Spreads along the sarcolemma, then dives into the T-tubules, this carries the electrical signal deep into the muscle fiber, triggering calcium release from the SR

What is a motor unit?

One motor neuron and all the skeletal fibers it innervates.

Which muscles would have small motor units? Why?

Laryngeal muscles, extraocular muscles. They have small motor units for precise, fine-controlled movements.

Which have large motor units?

Quads, calves, gluteus maximus.

What is meant by the all-or-none principle in muscle contraction?

A single muscle fiber contracts fully or not at all when it reaches threshold.

What is muscle tone?

The baseline, partial contraction of skeletal muscles at rest.

(Muscle tone) Hypotonic

abnormally low muscle tone.

muscle tone (hypertonic)

Abnormally high muscle tone.

What is recruitment?

The process of activating more motor units to increase the strength of a muscle contraction

What is atrophy?

The decrease in the size of a muscle due to a reduction in the size of its individual muscle fibers.

Name two mechanisms that can lead to atrophy

Disuse atrophy, caused by lack of muscle use, Denervation atrophy, caused by loss of nerve supply to the muscle

What leads to muscle hypertrophy?

Happens when muscle fibers experience increased workload or stress, leading to a larger, stronger muscles

What is the role of phosphocreatine?

To donate a phosphate group to ADP to quickly regenerate ATP

How long can phosphocreatine stores supply ATP during vigorous exercise?

around 10-15 seconds

How is glycogen present in muscle cells?What is its purpose?

Stored in muscle fibers as granules in the sarcoplasm. Provides a rapid, readily available source of glucose for ATP production.

Muscle cells can “store” oxygen by binding O₂ to the protein,            . Why do muscle cells need oxygen? 1.       Oxygen is required for aerobic cellular respiration

If oxygen is available, how do muscle cells produce ATP?

Glycolysis, Krebs cycle, the electron transport chain + oxidative phosphorylation

Where in the muscle cell does cellular respiration occur?

muscle cell does cellular respiration occur? Glycolysis (cytosol), Krebs cycle (mitochondrial matrix), Electron transport chain (inner mitochondrial membrane)

Does cellular respiration require oxygen?

Yes

What happens when no oxygen is present and the cell needs ATP?

Muscle cells switch to anaerobic glycolysis

What is oxygen debt?

The extra oxygen the body needs after exercise to restore the muscle to its resting state.

What energy sources / compounds are replaced in the cell after strenuous exercise?

ATP stores, Phosphocreatine stores, Glycogen stores.

What happens if muscle cannot generate all of the ATP it needs?

Cross-bridge cycling fails, calcium cannot be pumped back into the SR, and the muscle becomes fatigued and unable to contract.

What is a twitch?

a quick, involuntary contraction and relaxation of a muscle fiber after a single electrical stimulus.

Do all muscle fibers predominantly use cellular respiration for ATP production?

No, muscle fibers differ in how they make ATP, and only some rely mainly on aerobic cellular respiration

How does a glycolytic muscle fiber differ from an oxidative muscle fiber? (glycolytic)

relies primarily on anaerobic glycolysis for ATP. contains few mitochondria

How does a glycolytic muscle fiber differ from an oxidative muscle fiber? (oxidative)

Relies primarily on aerobic cellular respiration. contains many mitochondria

What is tetanus?

A sustained muscle contraction that occurs when a muscle is stimulated by rapid, repeated action potentials with no time to relax between them fully.

What is treppe?

The phenomenon where a muscle produces increasingly stronger contractions when it is stimulated repeatedly, with complete relaxation between each stimulus.

What is an isotonic contraction? Give examples

A type of muscle contraction in which the muscle changes length while tension remains relatively constant. Concentric contraction (muscle shortens while producing force

List some differences between cardiac muscle and skeletal muscle cells: Nuclei

Cardiac has 1, skeletal has many

List some differences between cardiac muscle and skeletal muscle cells: Cell shape

Cardiac is branched skeletal is long, cylindrical

List some differences between cardiac muscle and skeletal muscle cells: intercalated disc

cardiac they are present and in skeletal they are absent

List some differences between cardiac muscle and skeletal muscle cells: control

cardiac is involuntary, and skeletal are voluntary

How is cardiac muscle contraction similar to skeletal muscle contraction?

They both rely on sarcomere, actin-myosin cross-bridges, and calcium-triggered contraction, both use calcium troponin regulation.

How is smooth muscle similar to cardiac muscle?

Both are involuntary, autonomically regulated, capable of spontaneous activity, use calcium-dependent contraction, and often contract as coordinated units through gap junctions