A&P Chapter 9 "Muscles & Muscle Tissue"
Skeletal muscles are stimulated to contract when _________.
ACh binds to receptors on the sarcolemma, causing an electrical disturbance
Step 1 Excitation-Contraction Coupling Process
AP (action potential) - arrives at neuromuscular junction on sarcolemma
Step 2 Excitation-Contraction Coupling Process
AP triggers the release of calcium at the junction terminal, diffusing into the axon
What does Synaptic vesicles of axon terminal contain?
Acetylcholine (ACh)
Step 4 Excitation-Contraction Coupling Process
Acetylcholine activates sarcolemma once it reaches the desired threshold
What is the primary method for terminating the acetylcholine signal at the neuromuscular junction?
Acetylcholine is degraded by the enzyme acetylcholinesterase. The rapid breakdown of acetylcholine by the enzyme acetylcholinesterase quickly terminates the signal.
What chemical compound is necessary for contraction?
Ca2+ (calcium)
relaxation phase of muscle twitch
Ca2+ reentry into the SR; tension declines to zero.
Which ion links excitation to contraction in a skeletal muscle fiber?
Calcium
Step 7 Excitation-Contraction Coupling Process
Calcium binds to Troponin which causes Tropomyosin to move put of the way, leaving myosin active site available
The first thing that occurs when the axon terminal releases ACh is _________.
Diffusion across the synaptic cleft
Which of the following statements is FALSE? During contraction, thin filaments slide past thick filaments so that actin and myosin filaments do not overlap. During contraction, actin-myosin cross bridges form. During contraction, thin filaments slide past thick filaments so that actin and myosin filaments overlap. During contraction, the distance between Z discs of a sarcomere decreases.
During contraction, thin filaments slide past thick filaments so that actin and myosin filaments do not overlap.
Anatomy of Skeletal Muscle
Epimysium Perimysium Endomysium
Characteristics of a muscle fiber
Many nuclei (fibers) Many mitochondria Glycosomes for glycogen storage (sugar) Myoglobin for O2 storage in muscles
Match the muscle fiber to the appropriate characteristic. Fast Oxidative Muscle Fiber
Moderately Fatigue Resistant
What are the muscle's functions?
Movement of bones or fluids (blood lymph) (smooth & cardiac) Maintaining posture & body position (skeletal) Stabilizing joints (tendons & ligaments) Heat generation (homeostatic imbalance helped by skeletal muscle)
At the neuromuscular junction, calcium ions act to _________.
Release synaptic vesicles from the axon terminal
The functional unit of a skeletal muscle fiber is the ________.
Sarcomere
What happens to the sarcomeres, muscle cells and muscle during contraction?
Sarcomeres shorten, muscle cell shorten and the whole muscle shortens.
The elaborate network of membranes in skeletal muscle cells that functions in calcium storage is the _________.
Sarcoplasmic reticulum
Which event allows the formation of cross bridges by myosin?
Shifting tropomyosin away from binding sites on actin
What would occur if a contracting muscle became totally depleted of ATP?
The muscle would remain in a contracted state because of an inability to break actin-myosin cross bridges.
Epimysium
a sheath of dense irregular connective tissue surrounding a muscle.
The thin myofilaments of skeletal muscle are composed chiefly of __________.
actin
The most efficient means of producing ATP for muscle contraction is __________.
aerobic respiration
The final "go" signal for skeletal muscle contraction is __________.
an increase in intracellular calcium ion levels
Where in the neuromuscular junction Click to read the definition do you find voltage-gated calcium ion channels?
axon terminal
Acetylcholinesterase __________.
breaks down acetylcholine
Which ion diffuses out of the terminal cisterns for excitation-contraction to occur?
calcium
indirect muscle attachment
connective tissue wrappings extend beyond the muscle as a rope-like tendon or sheetlike aponeurosis (flat)
Myofibrils
contractile elements; chains of sarcomeres
Calcium ion who is responsible for ______________________.
coupling the shift from an action potential signal to contraction of a muscle fiber when I bind to the regulatory protein.
contraction phase of muscle twitch
cross bridge formation; tension increases.
Sarcoplasma
cytoplasm of a muscle fiber
What causes the indicated sodium channels along the sarcolemma to open?
depolarization reaches their threshold value
Which one of the following components stimulates contraction of a skeletal muscle?
motor neuron
The synapse between a motor neuron and muscle fiber is called the _______________________________________.
neuromuscular junction
Sodium Channel who is responsible for conduction of an action potential by ____________________________.
opening and allowing Na+sodium to diffuse into the muscle fiber
Sarcolemma
plasma membrane of a muscle fiber
2 muscle states
relaxed & contracted
What is a muscle twitch?
response of a muscle to a singe, brief threshold stimulus.
somatic motor neurons
responsible for stimulating reflexes and voluntary control of skeletal muscles
Myofibrils are composed of repeating contractile elements called __________.
sarcomeres
Which of the following muscle types is/are both voluntary and striated? cardiac muscle only skeletal muscle only smooth muscle only cardiac muscle and skeletal muscle
skeletal muscle only
Sarcomere
smallest contractile unit (functional unit) of a muscle fiber Composed of thick (Myosin) and thin (Actin) myofilaments made of contractile proteins
Terminal Cisterns
stores and releases calcium ions. Calcium ions, once released, can bind to the regulatory protein.
direct muscle attachment
the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage
If a muscle is applied to a load that exceeds the muscle's maximum tension, __________.
the muscle length will not change during contraction
Troponin
the regulatory protein that calcium ions bind to. When calcium ions bind to me, it can change shape, causing tropomyosin to shift, and exposing the myosin binding sites on actin.
When an action potential arrives at the neuromuscular junction, the most immediate result is __________.
the release of acetylcholine from the motor neuron
consequences of high Ca2+ concentrations in contraction
- Ca2+ binds to troponin - Troponin changes shape and moves tropomyosin away from active sites - Events of the cross bridge cycle occur - When nervous stimulation ceases, Ca2+ is pumped (energy required) back into the Sarcoplasmic Reticulum and contraction ends.
Thin Filaments (ACTIN)
- Composed of proteins Actin, Tropomyosin and Troponin - Actin has Myosin binding sites
Thick Filaments (MYOSIN)
- Composed of the protein myosin - Myosin heads form cross bridges with Actin of thin filaments and binding sites for ATP
consequences of low Ca2+ concentrations in contraction
- Tropomyosin blocks the active sites on actin - Myosin heads cannot attach to actin - Muscle fiber relaxes
latent period of muscle contraction
-Time when Excitation-Contraction coupling events occur -Time when Action Potential and the begining of contraction
3 phases of twitch contraction
1. latent period 2. contraction phase 3. relaxation phase
What is the name of the enzyme that degrades ACh?
Acetylcholinesterase
Step 5 Excitation-Contraction Coupling Process
Activation moves along the sarcolemma and enters T-tubules
Characteristics of Skeletal Muscle
Attached to bones and skin = somatic Striated Voluntary Powerful Some controlled by somatic nerves
Fascicles
Bundles of muscle fibers wrapped in perimysium
Which of the following statements is(are) TRUE about the excitation-contraction coupling mechanism in skeletal muscle?
Calcium binds to troponin causing a shift in tropomyosin exposing the binding sites on actin for myosin. An action potential in a T tubule opens calcium channels in the membrane of the sarcoplasmic reticulum.
During muscle contraction, all of the following occur EXCEPT ________. Myosin heads bind to actin Calcium concentration in the sarcoplasm increase ATP is hydrolyzed Calcium binds to troponin Calcium concentrations in the sarcoplasm decrease
Calcium concentrations in the sarcoplasm decrease
What is the role of calcium ions in the contraction of skeletal muscle?
Calcium ions bind to the troponin-tropomyosin complex and remove their inhibitory action on actin/myosin interaction.
Step 3 Excitation-Contraction Coupling Process
Calcium triggers release of acetylcholine (Ach Chemical neurotransmitter)
Identify the transport process by which ACh is released into the synaptic cleft.
Exocytosis
T/F Muscle cells initiate nerve impulses.
FALSE
T/F Duchenne muscular dystrophy is more common in females than in males.
False
Match the muscle fiber to the appropriate characteristic. Slow Oxidative Muscle Fiber
Fatigue Resistant
Match the muscle fiber to the appropriate characteristic. Fast Glycolytic Muscle Fiber
Fatigues Quickly
The cross bridge cycle ends when the calcium ________.
Is actively transported back into the sarcoplasmic reticulum
What is excitation-contraction coupling?
It is an electrical stimulus (action potential) combined with a mechanical response (muscle cell contraction)
How does neurotransmitter to read the definition binding to it's receptor activate a muscle fiber?
It opens chemically-gated ion channels that allow sodium ions to diffuse into the junctional folds.
Which of the following is present in muscle cells but absent in most other cell types? Muscle cells have mitochondria; most other cells do not. Muscle cells use ATP to do work; most other cells do not. Muscle cells have myoglobin; most other cells do not. Muscle cells have a nucleus; most other cells do not.
Muscle cells have myoglobin; most other cells do not.
Interactions between thin and thick myofilaments of the sarcomere are responsible for ________.
Muscle contraction
Which protein forms the thick filaments in a sarcomere?
Myosin
Step 8 Excitation-Contraction Coupling Process
Myosin bind to Actin in a sliding filament model creating a contraction motion
What happens during contraction of a muscle?
Myosin heads bind to Actin, detach, and bind again, to propel the think filaments toward each other.
An individual has just ingested a chemical that binds irreversibly to the ACh receptors on the motor end plate of the sarcolemma. This prevents normal ACh binding. The consequence to skeletal muscle would be __________.
No contraction at all by nervous stimulation
Which of the following is FALSE regarding smooth muscle? Contraction of smooth muscle is regulated by the autonomic nervous system. Smooth muscle is not striated. Once damaged, smooth muscle is unable to regenerate. Smooth muscle tends to be organized in sheets.
Once damaged, smooth muscle is unable to regenerate.
Does the depolarization of the junctional folds cause the voltage-gated sodium channels to open or close?
Open
Choose the true statement. Unlike skeletal muscle, smooth muscle does not depend on ATP to fuel contractions. Unlike skeletal muscle, contraction in smooth muscle does not involve a sliding filament mechanism. Smooth muscle depends on the calcium-calmodulin system to regulate contraction, while skeletal muscle relies on the calcium-troponin system to regulate contraction. The final signal for contraction in smooth muscle is a rise in extracellular calcium, while the final signal for contraction in skeletal muscle is a rise in intracellular calcium.
Smooth muscle depends on the calcium-calmodulin system to regulate contraction, while skeletal muscle relies on the calcium-troponin system to regulate contraction.
Which one of the following components conducts an action potential throughout the interior of the muscle fiber?
T-tubule
The __________ are inward invaginations of the sarcolemma that run deep into the cell and ensure that every myofibril in the muscle fiber contracts at virtually the same time.
T-tubules
Step 6 Excitation-Contraction Coupling Process
T-tubules direct SR (sarcoplasmic reticulum) to release calcium
What effect does the diffusion of sodium ions through the chemically-gated ion channels have on the membrane potential across the junctional folds?
The voltage becomes smaller (less negative on the inner surface).
What is the function of T tubules?
They conduct action potentials from the sarcolemma to the interior of the muscle cell.
During a muscle contraction, muscle fibers shorten when ________.
Thin myofilaments are pulled toward the center of the sarcomere by the pivoting of the myosin heads
Calcium ions bind to which regulatory protein during excitation-contraction coupling?
Troponin
T/F In the relaxed state, thin and thick filaments overlap only slightly
True
T/F The reentry of Ca2+ into the SR required active transport and use of ATP.
True
What type of ion channel opens in response to an action potential arriving at the axon terminal?
Voltage-gated calcium
Conduction of an action potential along the sarcolemma requires the opening of what type of ion channels?
Voltage-gated sodium channels
Motor unit
a motor neuron and all (4 to several hundred) muscle fibers it supplies.
Muscle fibers are stimulated to contract by _________________.
a motor neuron.
latent period of muscle twitch
events of excitation-contraction coupling; no muscle tension
Perimysium
fibrous connective tissue that surrounds groups of muscle fibers called fascicles (groups of muscle fibers)
Endomysium
fine areolar connective tissue surrounding each muscle fiber
synaptic cleft
gel-filled space that separates axon terminals and muscle fibers.
Properly controlled skeletal muscle contractions produced by changing the frequency of stimulation and the strength of stimulation are referred to as __________.
graded muscle responses
As an axon enters a muscle, it branches into a number of axon terminals, each of which makes contact with a single muscle fiber. The portion of the sarcolemma in contact with the axon terminals is called the ________.
motor end plate
