Physiology Chapter 12 Part A

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Questions and Answers

What type of muscle is primarily affected by the somatic motor pathway?

Skeletal muscle (correct)

Smooth muscle

Adipose tissue

Cardiac muscle

What is the primary neurotransmitter used in the somatic motor pathway?

Acetylcholine (correct)

Serotonin

Dopamine

Norepinephrine

How does the somatic motor system primarily cause muscle contraction?

Inhibiting the muscle fibers

Using multiple neurons in sequence

By increasing blood flow to the muscles

Activating nicotinic ACh receptors (correct)

What distinguishes the somatic motor pathways from the autonomic pathways?

Somatic pathways are always excitatory. (C) Signup and view all the answers

Where is the cell body of a somatic motor neuron primarily located?

In the ventral horn of the spinal cord (D) Signup and view all the answers

What characterizes the neuromuscular junction?

The motor end plate is part of the skeletal muscle fiber. (A) Signup and view all the answers

What occurs when somatic motor neurons are inhibited?

Skeletal muscles relax. (C) Signup and view all the answers

Which receptor is involved at the neuromuscular junction for somatic motor control?

Nicotinic ACh receptor (A) Signup and view all the answers

What occurs during a muscle twitch?

A single contraction-relaxation cycle takes place. (D) Signup and view all the answers

Which metabolic pathway produces lactate and does not require oxygen?

Anaerobic glycolysis (B) Signup and view all the answers

What distinguishes cardiac muscle fibers from skeletal muscle fibers?

Cardiac muscle fibers have intercalated disks. (A) Signup and view all the answers

Which of the following statements about smooth muscle fibers is true?

Smooth muscle fibers are small and lack striations. (A) Signup and view all the answers

What is the primary function of the elastic elements in muscle contraction?

To return filaments to their relaxed position after contraction. (D) Signup and view all the answers

What triggers the opening of voltage-gated Ca2+ channels at the axon terminal?

Arrival of an action potential (B) Signup and view all the answers

What effect does ACh have when it binds to the nicotinic cholinergic receptor?

It opens a nonspecific monovalent cation channel (B) Signup and view all the answers

What causes the fusion of synaptic vesicles with the presynaptic membrane?

Entry of Ca2+ into the axon terminal (A) Signup and view all the answers

What happens to acetylcholine (ACh) after it is released into the synaptic cleft?

It is broken down by acetylcholinesterase (AChE) (D) Signup and view all the answers

What is the primary ionic movement when the nicotinic receptor is activated?

Net Na+ influx causing depolarization (B) Signup and view all the answers

Which component of the synaptic junction helps degrade ACh to terminate its action?

Acetylcholinesterase (AChE) (A) Signup and view all the answers

The process by which the motor end plate is modified occurs as a result of which event?

Binding of ACh to its receptor (B) Signup and view all the answers

What role does the Sarcoplasmic Ca2+-ATPase play during the relaxation phase?

It pumps Ca2+ back into the sarcoplasmic reticulum. (D) Signup and view all the answers

Which of the following is NOT involved in the excitation-contraction coupling process?

Rough Endoplasmic Reticulum (A) Signup and view all the answers

What is the role of the synaptic cleft in the neuromuscular junction?

It is a site for neurotransmitter diffusion between neurons and muscle fibers (D) Signup and view all the answers

What triggers the opening of the Ryanodine receptor-channel?

Voltage change from DHP channels (B) Signup and view all the answers

Which ion primarily contributes to the depolarization of the muscle fiber when ACh binds to its receptors?

Na+ (A) Signup and view all the answers

What is the primary function of the dihydropyridine (DHP) calcium channel during muscle contraction?

To facilitate calcium influx from the extracellular space. (C) Signup and view all the answers

Why is the influx of sodium ions (Na+) significant in muscle fiber activity?

It generates an action potential in the muscle fiber (D) Signup and view all the answers

During relaxation, which structure is primarily responsible for the removal of calcium ions?

Sarcoplasmic reticulum (A) Signup and view all the answers

Which of the following best describes the relaxation phase of muscle contraction?

Involves decreased intracellular calcium concentration. (B) Signup and view all the answers

What happens to calcium ions during the relaxation phase?

They are sequestered in the sarcoplasmic reticulum. (B) Signup and view all the answers

Which of the following is correct about the ryanodine receptor-channel in the context of muscle relaxation?

It plays a critical role in the release of calcium from the sarcoplasmic reticulum. (B) Signup and view all the answers

What is the relationship between ATP and calcium ions in the relaxation phase?

ATP is necessary for the reuptake of calcium into the sarcoplasmic reticulum. (B) Signup and view all the answers

What role does the DHP receptor play in excitation-contraction coupling?

It opens RyR Ca2+ release channels. (A) Signup and view all the answers

What triggers the release of Ca2+ from the sarcoplasmic reticulum?

Alteration of DHP receptor conformation. (B) Signup and view all the answers

In the process of excitation-contraction coupling, what happens to the actin filament?

It slides toward the center of the sarcomere. (D) Signup and view all the answers

Which structures are involved in the release of calcium ions during muscle contraction?

DHP receptors and RyR channels. (B) Signup and view all the answers

What is the function of troponin in muscle contraction?

It binds calcium and allows actin-myosin interaction. (D) Signup and view all the answers

What ultimately allows myosin heads to execute the power stroke?

Calcium binding to troponin. (D) Signup and view all the answers

During excitation-contraction coupling, where does Ca2+ move after being released?

Into the cytoplasm. (A) Signup and view all the answers

What is the consequence of calcium binding to troponin on the myofilaments?

Actin's binding sites become exposed. (C) Signup and view all the answers

Which of the following accurately describes the first step in excitation-contraction coupling?

An action potential travels along the t-tubule. (A) Signup and view all the answers

What is the end result of excitation-contraction coupling?

Muscle fibers contract. (C) Signup and view all the answers

Study Notes

Autonomic & Somatic Motor Control

The somatic motor division primarily operates under voluntary control.
Somatic pathways are exclusively excitatory; autonomic pathways can be excitatory or inhibitory.
Somatic motor neurons originate from the ventral horn of the spinal cord or the brain, with their axons myelinated.
Neuromuscular junction is the synapse between somatic motor neurons and skeletal muscle fibers, utilizing acetylcholine (ACh).

Neuromuscular Junction

ACh is released into the synaptic cleft from presynaptic vesicles upon action potential arrival, facilitated by voltage-gated calcium (Ca2+) channels.
ACh binds to nicotinic receptors on the postsynaptic membrane, causing depolarization of the muscle fiber through Na+ influx.
Acetylcholinesterase (AChE) metabolizes ACh in the synaptic cleft, terminating the signal.

Excitation-Contraction Coupling

Action potentials in T-tubules trigger conformational changes in dihydropyridine (DHP) receptors, which open ryanodine receptors (RyR) in the sarcoplasmic reticulum.
Calcium is released into the cytoplasm, enabling binding of calcium to troponin, allowing interaction between actin and myosin for muscle contraction.
Myosin heads execute a power stroke, pulling actin filaments toward the center of the sarcomere.

Relaxation Phase

Sarcoplasmic Ca2+-ATPase pumps Ca2+ back into the sarcoplasmic reticulum to facilitate muscle relaxation.
Calcium detaches from troponin, and tropomyosin re-covers the binding sites on actin.
Elastic elements in the muscle return the fibers to their relaxed position after myosin heads release.

Muscle Contraction Dynamics

A muscle twitch is defined as a singular contraction-relaxation cycle of muscle fibers.

Energy Metabolism in Muscles

Three primary metabolic pathways for energy:
- Phosphocreatine breakdown: Provides a quick burst of energy with no oxygen requirement.
- Anaerobic glycolysis: Produces lactate and acid rapidly but releases limited energy.
- Aerobic respiration: Involves the citric acid cycle and electron transport chain, requiring oxygen and yielding significant energy.

Types of Muscle Tissue

Skeletal Muscle: Large, multinucleated and striated; primary muscle responsible for voluntary movement.
Cardiac Muscle: Smaller, branched, and striated with intercalated disks enabling coordinated contraction.
Smooth Muscle: Small, non-striated, and involuntary; found in walls of hollow organs.

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Description

Dive into the complexities of autonomic and somatic motor control with this quiz based on Chapter 12, Part A of physiology. Explore the distinctions between voluntary and involuntary muscle movements, and understand the role of each system in motor control. Perfect for students looking to reinforce their understanding of these fundamental concepts.