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
