Anatomy- Chapter 9 Homework

The maintenance of a resting membrane potential is due to three factors:

(1) The concentration of K+ INSIDE the membrane is HIGHER than that OUTSIDE the membrane (2) The concentration of Na+ OUTSIDE the membrane is HIGHER than that INSIDE the membrane. (3) The membrane is MORE permeable to K+ than Na+.

T/F: In a contracting muscle, the A bands narrow as the length of each thick filament shortens.

False

T/F: Myofibrils are composed of protein filaments called actin and myosin.

True (?)

The function of the approximately 200 G actin monomers that make up the F actin strands is to

bind to myosin during muscle contraction

The electrical properties of cells are the result of

ion concentration differences across the plasma membrane. Correct

Which of the following statements regarding the sliding filament model is false? (33)

?

Check all that apply as it pertains to functions of the muscular system.

- body movements such as running, chewing, using hands - necessary movements for respiration - speaking, writing, typing, smiling - body heat production - beating of the heart - maintenance of posture - propulsion of food through the digestive system

Match the muscle fiber type with its characteristics.

1. Respond rapidly to nervous system stimulation: Fast-twitch 2. Fatigue quickly: Fast-twitch 3. Contain large amounts of myoglobin: Slow-twitch 4. Break down ATP relatively slowly: Slow-twitch 5. High glycogen concentration: Fast-twitch 6. High aerobic capacity: Slow-twitch

Which region of the sarcomere does not change length between muscle relaxation and muscle contraction?

A Band

Match what happens during maximum muscle contraction to the following areas of a sarcomere.

A Band- Width remains constant I Band- narrows H Zone- disappears

Complete each sentence with the correct word from the list. (30)

A sarcomere consists of actin and myosin MYOFILAMENTS Actin myofilaments are attached at either end to a ?? G actin molecules make up ACTIN myofilaments The ends of myosine molecules contain four small LIGHT MYOSIN moleculeS The rod portion of the myosine molecules is made of two HEAVY MYOSIN molecules tightly wound together. Each myosin myofilament contains MULTIPLE myosin molecules

The actin-myosin bond is broken by the binding of __________ to the myosin head.

ATP

Complete each sentence with the correct word from the list.

An action potential arriving at the presynaptic terminal causes Ca²⁺ channels to open in the PRESYNAPTIC MEMBRANE. Synaptic vesicicles in the presynaptic terminal release ACETYLCHOLINE. ACh is released into the SYNAPTIC CLEFT via exocytosis. ACh binds to Na⁺ channels in the MOTOR END-PLATE. When Na+ channels open in the membrane, Na+ enters the MUSCLE CELL. (?) If depolarization in the muscle cell passes threshold, a(n) ACTION POTENTIAL is generated.

Match the functional property of muscle tissue with its description.

Contractility- A muscle shortens forcefully. Excitability- A muscle responds to a stimulus. Extensibility- A muscle can stretch beyond its normal resting length and still contract Elasticity- A muscle recoils to its original resting length after having been stretched

Which of the following is not an age-related change in skeletal muscle?

Decreased recovery time

Which connective tissue wrapping separates individual muscle fibers?

Endomysium

Match the connective tissue with the skeletal muscle component that it surrounds.

Endomysium- Muscle fibers Perimysium- Fascicles Epimysium- Muscles

Complete each sentence about the functions of muscle.

Examples of how muscles are used in COMMUNICATION include speaking, gesturing, and facial expression. Examples of how muscles are used to MAINTAIN TONE (OR POSTURE) include sitting or standing erect. Propelling and mixing food and propelling blood are examples of functions of the SMOOTH muscles in digestive tract and CARDIAC muscles of the heart, respectively.

T/F: The I-band of a sarcomere is widest when a muscle is relaxed.

False (?)

When cross-bridges cycle and a muscle shortens, the relative positions of the thick and thin filaments change. Classify the following as becoming greater, less, or staying the same. (36)

GREATER - amount of overlap between thick and thin filaments SAME - width of the A-Band - width of the M-Line (?) LESS - distance between the z-lines - width of the H-zone - width of the I-bands

The area between two Z discs is termed a/an

H Zone (?)

Which of the following is not a function of the muscular system?

Immune system support

Use the following terms to correctly complete the sentences regarding the origin and growth of muscle cells.

Muscle fibers originate from immature, cells known as MYOBLASTS when ? proteins form in the cell cytoplasm. These cells contain MANY NUCLEI caused by the fusion of precursor cells Following that, INNERVATION occurs as nerves grow into the area of developing muscle fibers. Physical exercise results in the growth of muscles, or HYPERtrophy, and occurs due to an increase in the SIZE of muscle fibers.

Which of the following structures contains the other four items listed?

Neuromuscular junction

Match the component of a neuromuscular junction with its location.

Postsynaptic membrane- Muscle plasma membrane Presynaptic terminal- Axon Synaptic cleft- Between the presynaptic terminal and the muscle fiber

Which of the following is not a function of the myosin heads?

Produce tropomyosin to facilitate binding to actin molecules

Match the muscle fiber component with its description.

Sarcolemma- Plasma membrane Endomysium- Connective tissue Sarcoplasm- Cytoplasm of a muscle cell Myofibril- Bundle of protein filaments

Which of the following lists the structures in the order they participate in excitation-contraction coupling?

Sarcolemma; T tubules; sarcoplasmic reticulum; calcium ions

Match the characteristic of each muscle type with its function.

Skeletal Muscle- Constitutes 40% of the body's weight; voluntarily controlled Smooth Muscle- The most widely distributed muscle type; involuntarily controlled Cardiac Muscle- Found only in the heart; involuntarily controlled

An action potential enters a muscle cell at the ____________.

T Tubule

Complete each sentence about the major functional properties of muscles.

The capacity of the muscle to be stretched beyond its normal resting length is called EXTENSIBILITY, while the ability of muscle to recoil to its original resting length is called ELASTICITY. The capacity of muscle to respond to a stimulus is EXCITABILITY, and the ability of muscle to shorten forcefully is CONTRACTILITY.

T/F: According to the all-or-none principle, all action potentials are identical.

True

The neurotransmitter at the neuromuscular junction is _____________.

acetylcholine

The myofilaments that contain two strands of F actin coiled together to form a double helix are ________ myofilaments, and the myofilaments that are composed of molecules that are shaped like golf clubs are _________ myofilaments.

actin; myosin

Thin myofilaments are _______ myofilaments, and thick myofilaments are _________ myofilaments.

actin; myosin

Increased calcium ion permeability of the presynaptic terminal cell membrane is caused by an ______________.

action potential (?)

Smooth muscle and cardiac muscle are similar in that they both

are under involuntary control

Uncovering binding sites for myosin on actin myofilaments involves troponin binding to ____________.

calcium ions

Muscle myofibrils

contain myosin and actin myofilaments

The capacity of a muscle cell to shorten forcefully is known as

contractility

The cycle of a mysosin molecule forming cross-bridges, moving, then releasing and returning to its original position is called _____________.

cross-bridge movement

Movement of sodium ions into the muscle cell at the neuromuscular junction causes _____________.

depolarization of the muscle cell membrane

During the ___________ phase, the inside of the cell becomes positively charged, and during the _________ phase, the membrane potential returns to its resting value.

depolarization; repolarization

In a fully contracted sarcomere, the H zone _____________

disappears

What is a bundle of muscle fibers called?

fascicle

During ___________, muscle fibers partially relax between contractions, whereas during ___________, no relaxation occurs between contractions.

incomplete tetanus; complete tetanus

Hypertrophy means that there is a/an ______________ in the size of the muscle fibers, and there is usually _________ muscle fibers.

increase; no change in the number of

Physiological contracture

is a condition in which cross-bridges cannot release.

A fascicle

is surrounded by perimysium

The length of the resting sarcomere is

longer than the length of a contracted sarcomere.

A single motor neuron and the muscle fibers that it innervates is called a/an ___________.

motor unit

Which of the following actions is caused by contraction of skeletal muscle?

moving your feet in walking

Muscle cells originate from __________.

myoblasts

Cross-bridges form between binding sites on actin myofilaments and __________.

myosin heads

Energy produced when ATP is converted to ADP and phosphate is stored in ___________.

myosin heads

The point where the axon terminal synapses with the muscle fiber sarcolemma is called the _____________.

neuromuscular junction

Acetylcholine causes an end-plate potential by triggering the ______________________.

opening of sodium channels

In a fully contracted sarcomere, the actin myofilaments ____________.

overlap

When myosin heads attach to actin filaments, ___________ is released.

phosphate

The time between application of the stimulus to a motor neuron and the beginning of contraction is called the __________ phase.

relaxation (?)

The charge difference across the plasma membrane of an unstimulated cell is called the __________.

resting membrane potential

What is a muscle cell membrane called?

sarcolemma

Calcium ions released from the sarcoplasmic reticulum enter the ______________.

sarcoplasm

An action potential for a muscle cell is propagated along the __________.

sarolemma

Depolarization of the cell membrane occurs when there is a rapid influx (inflow) of

sodium ions

The neurotransmitter at the neuromuscular junction increases permeability of the muscle cell membrane to ____________.

sodium ions (?)

Acetylcholine (ACh) is released from motor neurons and enters the __________________.

synaptic cleft

Each presynaptic terminal contains ___________, which contain the neurotransmitter __________ that, when released, cause ligand-gated Na+ channels to open in the motor end-plate. This causes __________ in the muscle cell.

synaptic vesicles; acetylcholine; depolarization

The plasma membrane of an excitable cell is more permeable to potassium ions because

there are more leak channels for K+ than Na+ (?)

Myosin is also known as the

thick myofilament

A muscle fiber will respond to a stimulus when that stimulus reaches the __________ level.

threshold

During muscle contraction, binding sites for myosin are uncovered by the movement of ___________.

tropomyosin

During muscle contraction, calcium ions bind to ___________.

troponin