PHYSIO EXAM 2

What are the different ways in which muscle cells can be excited?

• Chemically

• Electrically

• Mechanically

The cytoplasm of muscle cells

Sarcoplasm

The smooth ER is the

Sarcoplasmic reticulum

The muscle cell membrane

Sarcolemma

What is the oxygen-binding protein?

Myoglobin

Contraction of what muscle is quick, forceful, and usually under voluntary control?

Skeletal

Contraction of what muscle is involuntary, vigorous, and rhythmic?

Cardiac muscle

Contraction of what muscle has slow, involuntary contractions?

Smooth muscle

Myoblasts align and fuse together to make longer, multinucleated tubes called?

Myotubes

Myoblasts synthesize the protein to make up what structures?

Myofilaments

What do myoblasts become when they don’t differentiate what cells do they become that can proliferate and produce new muscle fibers after injury?

Satellite cells

Smallest components of muscle that contain the proteins actin and myosin?

Myofilament

What does a bundle of myofilaments form?

Myofibril

Many of what makes up a muscle fiber?

Myofibrils

What structure surrounds an individual muscle fiber?

Endomysium

Muscle fibers group together to form a fascicle which is surrounded by what?

Perimysium

Multiple fascicles bundle together to form a whole muscle which is wrapped in?

Epimysium

Which surrounding layer of muscle is continuous with the tendon?

Epimysium

What is the synapse between a skeletal muscle cell and motor neuron?

Neuromuscular junction

How many neuromuscular junctions does each skeletal muscle cell have around the midpoint of the cell?

1

What is released from synaptic vesicles on the motor neuron?

Acetylcholine

Where does acetylcholine bind to and activate receptors?

Motor end plate

What enzyme breaks down ACh left in the synaptic cleft to “turn off” the signal?

Acetylcholinesterase

What toxin prevents the vesicles of acetylcholine from fusing to the membrane which decreases amount of acetylcholine released in the synapse?

Clostridium botulinum

How many nerve endings is each muscle fiber innervated by located in the middle of the fiber?

1

What is a group of muscle fibers working together controlled by?

A single motor neuron

What motor units?:

• Only a few muscle fibers per neuron

• Allows for fine muscle control

• Ex: eye muscles

Small motor units

What motor unit?:

• Up to several hundred muscle fibers innervated by a single neuron

• Ex: large postural muscles

Large motor units

What muscle fibers are adapted for slow contractions over long periods without fatigue, having many mitochondria, many surrounding capillaries, and much myoglobin?

Slow oxidative

What type of muscle fibers would you find in a marathon runner?

Slow oxidative

What muscle fibers are specialized for rapid, short-term contraction, having few mitochondria and depend largely on anaerobic metabolism of glucose derived from stored glycogen?

Fast glycolytic

What muscle fibers appears dark or red in color?

Slow oxidative

What muscle fibers appear white?

Fast glycolytic

What muscle fibers?:

• Many mitochondria

• Many capillaries

• Small fiber diameter

• Small size of motor unit

• High myoglobin (red fibers)

• Low glycogen

• Oxidative phosphorylation

• Slow rate of fatigue

• Slow speed of contraction

Slow oxidative

What muscle fibers?:

• Sparse mitochondria

• Sparse capillaries

• Large fiber diameter

• Large size of motor unit

• Low myoglobin content (white fibers)

• High glycogen content

• Anaerobic glycolysis

• Fast rate of fatigue

• Fast speed of contraction

Fast glycolytic

Which NTM is responsible for the initiation of skeletal muscle contraction?

Acetylcholine

Which type of skeletal muscle fiber would likely be highest in an athlete that excels at both endurance training and strength training?

Fast oxidative glycolytic

A long, golf club-shaped polypeptide

Myosin

What is a thick filament?

A bundle of myosin molecules whose shafts point toward and overlap in the bundle’s middle and whose heads project from the bundle’s ends

What do the myosin heads interact with in muscle contraction?

Actin

What does a thin filament contain?

Two F-actin strands wound in a double helix

What is a long, thin, polypeptide that wraps around the actin double helix and lies in the grooves, covering the myosin binding sites at rest?

Tropomyosin

What is a complex of three globular proteins (I,T,C)?

Troponin

What subunit of troponin attaches to actin and blocks myosin binding sites?

Troponin I

What subunit of troponin attaches to tropomyosin and anchors the complex to the filament?

Troponin T

What subunit of troponin will bind to calcium?

Troponin C

What is the midpoint of actin filaments?

Z line

What is the region between two z lines?

Sarcomere

What is formed by entire length of thick myosin ligament (dark)?

Anisotropic bands

What is the area of the actin filament that is not bound to myosin?

Isotropic bands

What is the best description of a sarcomere?

The distance between two Z lines

What is step 1 of muscle contraction?

ACh triggers an action potential in the muscle fiber

What is step 2 of muscle contraction?

Calcium is released from the sarcoplasmic reticulum

What is step 3 of muscle contraction?

Crossbridges form

What is step 4 of muscle contraction?

Power stroke

What is step 5 of muscle contraction?

SERCA pumps calcium into SR

What triggers the released of ACh from the synaptic knob into the synaptic cleft?

Nerve impulse

Where does ACh bind to the ACh receptors when initiating a muscle impulse in the sarcolemma of the muscle fiber?

Motor end plate

As the muscle impulse spreads quickly from the sarcolemma along T tubules, where are calcium ions released from to end up in the sarcoplasm?

Terminal cisternae

What do calcium ions bind to?

Troponin

What protein changes shape, moving tropomyosin on the actin to expose active sites on actin molecules of thin filaments?

Troponin

What component of the thick filaments attach to exposed active sites to form crossbridges?

Myosin heads

As myosin head pivot during the power stroke, how does it move thin filaments?

Toward sarcomere center

What determines the length of the repeating cycle of attach-pivot-detach-return?

Calcium ions remaining bound to troponin which keep active sites exposed

How are calcium ions transported into the sarcoplasmic reticulum when the nerve impulse stops?

Actively

What molecules are released during the power stroke as the myosin head bends?

ADP and P

What molecule attaches the the myosin head causing the crossbridge to detach?

ATP

What molecule returns the myosin to the “cocked position” after the crossbridge detaches?

ADP

Mechanism of rigor mortis

• As ATP is depleted, there is no energy to pump calcium back to sarcoplasmic reticulum

• Buildup of calcium triggers normal muscle contraction

• Without ATP, myosin heads cannot release, and muscle remains in contracted state

• Muscles remain in rigor until the proteins deteriorate (15-25 hours)

What band in the sarcomere gets narrower during muscle contraction?

I band

What is the adding of individual twitch contractions to increase the intensity of the overall muscle contraction?

Summation

What summation occurs by increasing the number of motor units contracting simultaneously?

Multiple fiber summation

What summation occurs by increasing the frequency of contraction?

Frequency summation

When the central nervous system sends a weak signal to contract a muscle, what units may be stimulated?

Smaller motor units

What occurs when enough calcium ions are maintained in the muscle sarcoplasm between action potentials that a full contractile state is sustained without allowing relaxation between action potentials?

Tetany

As the frequency of stimulation increases, there comes a point when each new contraction occurs before the preceding one is over. What is the result of this?

The second contraction is partially added to the first, and thus the total strength of contraction rises with inc. frequency

What muscle tissue contains calmodulin and myosin light-chain kinase (MLCK)?

Smooth muscle

Where is smooth muscle located?

• Blood vessels

• Airways

• Urinary system

• Male and female reproductive tract

• Eye

• Kidney

• Skin

What smooth muscles are normally contracted and relax only briefly to allow passage?

Sphincters

What smooth muscles maintain a partial, constant contraction (tone) to regulate diameter and flow?

Blood vessels and airways

What smooth muscles show phasic activity, contracting and relaxing in cycles to facilitate mixing and propulsion?

Stomach and intestines

What smooth muscles are normally relaxed but undergo rapid, strong contractions when activated?

Esophagus and urinary bladder

Type of smooth muscle where there is a nerve for each cell, allowing for fine, graded control

Multiunit

Type of smooth muscle where there are 1 or 2 nerves for multiple cells joined by gap junctions

Unitary

What muscle tissue consists of discrete, independent muscle fibers, each function separate from its neighbors?

Multi-unit smooth muscle

Examples of multi-unit smooth muscle

• Ciliary muscle of the eye

• Iris muscle of the eye

• Piloerector muscles

What kind of smooth muscles involves large groups of muscle fibers that contract together as a coordinated unit?

Unitary

How are the cells in unitary smooth muscle often arranged?

In sheets or bundles with adherent membranes that transmit force from one cell to the next

What do the gap junctions that connect the unitary smooth muscle cells do?

Allow ionic currents and action potentials to spread efficiently across the tissue

Examples of unitary smooth muscle

• GI tract

• Bile ducts

• Ureters

• Many blood vessels

What proteins does smooth muscle use instead of troponin?

Calmodulin and myosin light-chain kinase (MLCK)

In smooth muscle, what are actin filament anchored to?

Dense bodies

In smooth muscle, dense bodies from adjacent cells are connected by protein bridges which allow what?

The force of contraction to transmit from one cell to another

In smooth muscle, how are contractile filaments oriented to allow a twisting motion during contraction?

Oblique angles

What are the multiple “swellings” distributed along the axon’s length?

Varicosities

What do the axon varicosities contain?

Synaptic vesicles with either acetylcholine or norepinephrine

What do sympathetic neurons typically release?

Norepinephrine

What do parasympathetic neurons typically release?

Acetylcholine

What can trigger smooth muscle contraction?

• Spontaneous electrical activity in plasma membrane

• NTM

• Hormones

• Local changes in chem concentration of the tissue

• Stretch

Process of smooth muscle contraction

1. Influx of calcium from extracellular fluid or release from sarcoplasmic reticulum

2. Calcium ions bind to calmodulin

3. Calcium-calmodulin complex joins with and activates myosin light chain kinase (MLCK)

4. Myosin head becomes phosphorylated in response to myosin kinase