Muscle Physiology Part 2: EMG and Smooth Muscle

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Questions and Answers

What happens to myosin ATPase activity when myosin phosphatase removes phosphate from myosin?

It becomes inactive

It remains the same

It increases

It decreases (correct)

What role do varicosities play in smooth muscle innervation?

They anchor the muscle to the bone

They connect muscle cells via gap junctions

They store and release neurotransmitters (correct)

They facilitate muscle fiber contraction

Which type of smooth muscle contracts as a unit due to gaps junctions between fibers?

Multi-unit smooth muscle

Cardiac muscle

Single-unit (visceral) smooth muscle (correct)

Skeletal muscle

What is the effect of decreased myosin ATPase on muscle tension?

It decreases muscle tension Signup and view all the answers

What determines the target cell response in smooth muscle innervation?

The receptor type on the target cell Signup and view all the answers

What is a gap junction in the context of smooth muscle cells?

An intercellular connection allowing ion flow Signup and view all the answers

Which nervous system component can have both excitatory and inhibitory effects on smooth muscle?

Autonomic nervous system Signup and view all the answers

What is a primary characteristic of multi-unit smooth muscle?

Requires nerve stimulation for contraction Signup and view all the answers

What is the primary mechanism by which free Ca2+ concentration in the cytosol decreases during smooth muscle relaxation?

Ca2+ is pumped out of the cell or into the sarcoplasmic reticulum. Signup and view all the answers

What occurs after Ca2+ unbinds from calmodulin (CaM) during smooth muscle relaxation?

Myosin phosphatase removes phosphate from myosin. Signup and view all the answers

What is the impact of myosin phosphatase activity during the relaxation of smooth muscle?

It removes phosphate from myosin, thereby decreasing ATPase activity. Signup and view all the answers

Which of the following processes contributes to smooth muscle relaxation?

Pumping of Ca2+ into the sarcoplasmic reticulum. Signup and view all the answers

What role does ATP play in the process of smooth muscle relaxation?

It facilitates the pumping of Ca2+ out of the cytosol. Signup and view all the answers

What happens to the myosin ATPase activity during smooth muscle relaxation?

It decreases as the phosphate is removed from myosin. Signup and view all the answers

How does the binding of Ca2+ to calmodulin affect smooth muscle contraction?

It activates myosin light chain kinase, promoting contraction. Signup and view all the answers

Which ion plays a crucial role in the cytosolic process of smooth muscle relaxation?

Ca2+ Signup and view all the answers

What is the primary function of electromyography (EMG)?

To evaluate and record the electrical activity produced by skeletal muscles Signup and view all the answers

Which type of electrode is primarily used in intramuscular EMG?

Needle electrode or fine-wire electrode Signup and view all the answers

What distinguishes bipolar recording from unipolar recording in surface EMG?

Both electrodes are active in bipolar recording Signup and view all the answers

What type of information can surface EMG provide?

A general picture of muscle activation Signup and view all the answers

In which scenario would intramuscular EMG be particularly useful?

To diagnose neuromuscular diseases Signup and view all the answers

Which characteristic is NOT associated with smooth muscle contraction?

Higher energy consumption for a given force Signup and view all the answers

What does the electromyogram (EMG) record?

The electrical activity of muscle cells during stimulation Signup and view all the answers

What feature distinguishes smooth muscle fibers from skeletal muscle fibers?

Lack of striations due to no sarcomeres Signup and view all the answers

Which statement about surface electrodes in EMG is true?

They can monitor biochemical activities of skeletal muscle Signup and view all the answers

How does the actin to myosin ratio in smooth muscle compare to that in skeletal muscle?

It is higher than in skeletal muscle Signup and view all the answers

How is the electric field formed around a muscle cell during stimulation?

By the potential differences that arise between the muscle cell and its environment Signup and view all the answers

What is a key structural feature of smooth muscle myosin?

Has hinged heads distributed along its length Signup and view all the answers

Which of the following best describes the role of dense bodies in smooth muscle?

Transmitting contractions from cell to cell Signup and view all the answers

Which component is absent in smooth muscle that is found in skeletal muscle?

Myofibrils Signup and view all the answers

What initiates spontaneous stimulation in smooth muscle?

Self-excitatory cells Signup and view all the answers

What structural feature helps smooth muscle to sequester Ca2+?

Pouchlike infoldings known as caveolae Signup and view all the answers

What is the primary difference between unipolar and bipolar recording in electromyography?

Unipolar records potential differences between a ground and an active electrode. Signup and view all the answers

During contraction, what is the effect of the longitudinal layer of smooth muscle on an organ?

It leads to dilation and shortening of the organ. Signup and view all the answers

What are the parameters derived from the EMG signal?

Amplitude, frequency, and temporal changes of the signal. Signup and view all the answers

Which statement accurately describes the circular layer of smooth muscle during contraction?

Fibers encircle the organ, constricting the lumen and elongating it. Signup and view all the answers

In the context of surface electromyography, what role do surface electrodes play?

They capture muscle impulses for analysis of contraction characteristics. Signup and view all the answers

What anatomical feature distinguishes smooth muscle from other types of muscle?

It is located in hollow organs and tubes, typically in two layers. Signup and view all the answers

What does EMG stand for and what does it primarily measure?

Electromyography; electrical activity of muscles. Signup and view all the answers

What occurs to the potential difference in a bipolar recording?

It captures differences between two points of muscle contact. Signup and view all the answers

What initiates the contraction of smooth muscle cells in the sliding filament mechanism?

Activation of calmodulin by calcium ions Signup and view all the answers

Which statement best describes the role of calcium ions during the contraction process of smooth muscle?

Calcium ions facilitate the transfer of phosphate to myosin. Signup and view all the answers

What is essential for the relaxation of smooth muscle following contraction?

Active transport of calcium ions back to the SR and ECF Signup and view all the answers

Which mechanism allows calcium ions to enter the cytosol during smooth muscle contraction?

Voltage-dependent or independent calcium channels Signup and view all the answers

During the contraction process, what directly activates myosin light chain kinase?

Calmodulin bound to calcium ions Signup and view all the answers

What is the result of phosphorylating the myosin molecule in smooth muscle contraction?

Phosphorylation activates myosin for cross-bridge formation with actin. Signup and view all the answers

What is the primary source of calcium ions for smooth muscle contraction?

Both sarcoplasmic reticulum and extracellular space Signup and view all the answers

What is the consequence of calcium detachment from calmodulin during smooth muscle relaxation?

Reduction of myosin ATPase activity Signup and view all the answers

Which statement accurately describes the role of myosin phosphatase in smooth muscle relaxation?

It removes phosphate groups from myosin, decreasing ATPase activity. Signup and view all the answers

What initiates the decrease in free Ca2+ concentration in the cytosol during smooth muscle relaxation?

The active transport of Ca2+ out of the cell or into the sarcoplasmic reticulum. Signup and view all the answers

What happens to the calmodulin (CaM) when Ca2+ concentration in the cytosol decreases?

Ca2+ unbinds from CaM, leading to relaxation. Signup and view all the answers

Which of the following is NOT a consequence of decreased Ca2+ binding to calmodulin (CaM)?

Smooth muscle fibers initiate contraction. Signup and view all the answers

During which step of smooth muscle relaxation does myosin phosphatase directly engage?

When free Ca2+ unbinds from calmodulin. Signup and view all the answers

What is the relationship between myosin ATPase activity and smooth muscle relaxation?

Decreased ATPase activity contributes to muscle relaxation. Signup and view all the answers

What ion is crucial in modulating the activity of calmodulin and myosin during smooth muscle relaxation?

Ca2+ Signup and view all the answers

During smooth muscle relaxation, what primarily leads to the inactivation of myosin?

The removal of phosphate from myosin by myosin phosphatase. Signup and view all the answers

What characterizes the signaling mechanism of single-unit (visceral) smooth muscle compared to multi-unit smooth muscle?

Single-unit smooth muscle fibers are connected by gap junctions, allowing synchronous contraction. Signup and view all the answers

How does the activation of myosin light chain kinase influence smooth muscle contraction?

It phosphorylates the myosin molecule, enhancing its ATPase activity. Signup and view all the answers

Which aspect of smooth muscle innervation allows for varied responses depending on receptor type?

The distinct neurotransmitters released at diffuse junctions. Signup and view all the answers

What primarily leads to the decrease of muscle tension in smooth muscle relaxation?

The unbinding of calcium from calmodulin leads to decreased ATPase activity. Signup and view all the answers

What role do varicosities play in the innervation of smooth muscle?

They store and release neurotransmitters at diffuse junctions. Signup and view all the answers

Which statement about the gap junctions in single-unit smooth muscle is accurate?

They facilitate intercellular communication and synchronized contraction. Signup and view all the answers

What is the significance of autonomy in smooth muscle contraction?

It allows for spontaneous contractions without neuronal input. Signup and view all the answers

In the context of smooth muscle, how does reduced myosin ATPase activity affect muscle functioning?

It decreases the overall contractility and force production. Signup and view all the answers

What is the primary structural difference between the longitudinal and circular layers of smooth muscle?

The fibers of the longitudinal layer run parallel to the long axis of the organ, while the circular layer runs around the circumference. Signup and view all the answers

Which of the following aspects of muscle activity can be determined from an electromyography (EMG) signal?

The time course of muscle contraction, contraction force, and coordination of muscles. Signup and view all the answers

What type of electrodes are used for bipolar recording in electromyography?

Two active electrodes measuring potential differences between muscle points. Signup and view all the answers

During contraction of the circular layer of smooth muscle, which of the following describes the resultant effect on the organ?

The organ shortens and its lumen constricts. Signup and view all the answers

In what way do surface electrodes in surface electromyography provide useful data?

By registering the potential differences between an active electrode and a ground electrode. Signup and view all the answers

What occurs during the contraction of smooth muscle when the longitudinal layer is activated?

The organ dilates and shortens. Signup and view all the answers

Which of the following factors is NOT derived from the analysis of an EMG signal?

Duration of muscle fatigue. Signup and view all the answers

When comparing unipolar recording to bipolar recording in electromyography, which statement is accurate?

In unipolar recording, only the potential difference to a ground electrode is measured. Signup and view all the answers

What is the main consequence of calcium ions entering the cytosol during smooth muscle contraction?

Activation of calmodulin Signup and view all the answers

Which of the following steps directly follows the activation of calmodulin in smooth muscle contraction?

Activated calmodulin activates myosin light chain kinase Signup and view all the answers

What role does myosin light chain kinase (MLCK) play in smooth muscle contraction?

Transfers phosphate to myosin Signup and view all the answers

What is required for the relaxation of smooth muscle after contraction?

Dephosphorylation of myosin Signup and view all the answers

In which way is calcium obtained during smooth muscle contraction?

From both extracellular fluid and sarcoplasmic reticulum Signup and view all the answers

What is the primary driving factor for the slow, synchronized contractions of smooth muscle?

Low energy consumption due to slow ATPase activity Signup and view all the answers

What occurs after myosin is phosphorylated in the contraction process of smooth muscle?

Myosin forms cross-bridges with actin Signup and view all the answers

What mechanism is involved when calcium ions are transported back into the sarcoplasmic reticulum during smooth muscle relaxation?

Active transport using ATP Signup and view all the answers

What characterizes single-unit (visceral) smooth muscle compared to multi-unit smooth muscle?

Single-unit smooth muscle has numerous gap junctions allowing coordinated contraction. Signup and view all the answers

Which of the following locations is typical for multi-unit smooth muscle?

Ciliary muscle of the eye Signup and view all the answers

What is the main neurotransmitter associated with the sympathetic innervation of smooth muscle?

Noradrenaline Signup and view all the answers

In multi-unit smooth muscle, how does contraction occur?

As a result of individual fiber innervation with neural stimulation. Signup and view all the answers

Which type of receptor is predominantly involved in parasympathetic control of gastric muscle?

Muscarinic receptors Signup and view all the answers

What primarily differentiates the contraction duration between single-unit and multi-unit smooth muscle?

Single-unit muscle contractions are prolonged and take time to fade. Signup and view all the answers

What effect do alpha-1 adrenergic receptors have on vascular smooth muscle?

Contraction, leading to vasoconstriction Signup and view all the answers

Which option correctly describes the autonomic innervation characteristics of multi-unit smooth muscle?

Each muscle fiber requires its own nerve supply and has minimal gap junctions. Signup and view all the answers

What distinguishes intramuscular EMG from surface EMG in terms of recording technique?

Intramuscular EMG requires needle electrodes inserted into muscle tissue. Signup and view all the answers

Which statement about the recording process of electromyography is incorrect?

Electrodes need to be placed in the intracellular environment for accurate readings. Signup and view all the answers

In which scenario is the use of surface EMG indicated over intramuscular EMG?

For a general picture of muscle activation in a larger area. Signup and view all the answers

What is a primary advantage of using needle electrodes for intramuscular EMG?

They allow for the measurement of action potentials from individual muscle fibers. Signup and view all the answers

Which of the following electrodes configuration is utilized in unipolar recording?

One electrode is placed on the muscle with another far away as a ground. Signup and view all the answers

What is the primary difference between bipolar and unipolar surface EMG configurations?

Bipolar configuration measures the difference in potential between two electrodes on the skin. Signup and view all the answers

What can be determined from the electromyogram (EMG)?

The overall muscle activation trends during specific tasks. Signup and view all the answers

During an examination, what is the main limitation of employing surface EMG without intramuscular EMG?

Surface EMG cannot record signals from deep muscle structures. Signup and view all the answers

Study Notes

Muscle Physiology Part 2: Electromyography (EMG) and Smooth Muscle

Electromyography (EMG): A technique for evaluating and recording the electrical activity of skeletal muscles.
EMG measures potential differences between the interior of a muscle cell and the extracellular environment, which create an electrical field around the muscle cell.
Special electrodes positioned within or on the surface of the muscle are used to record these potential differences.
EMG is performed using an electromyograph to produce an electromyogram (a record of the electrical activity).
Intramuscular EMG: A needle electrode or needle containing fine-wire electrodes is inserted into the muscle tissue.
This type of EMG records the action potentials of individual muscle fibers, a part, or the entire motor unit.
Intramuscular EMG is primarily used to diagnose neuromuscular disease and motor control disorders.
Surface EMG: Recording electrodes are placed on the skin surface above the muscle to pick up the electrical activity.
Surface EMG can show the overall muscle activation (global electromyogram) or be used for biochemical studies of skeletal muscle.
Unipolar Recording: The active recording electrode is placed above the tested muscle, and a separate, reference zero electrode is placed some distance away. This records potential difference between the zero and active electrode.
Bipolar Recording: Two active electrodes are placed on the muscle, and the potential difference between the two points is recorded.
What can be learned from an EMG? EMG analysis reveals the time course of muscle contractions, contraction force, and coordination of several muscles in a movement sequence.
EMG Parameters: These parameters are derived from the signal's amplitude, frequency, and changes over time.

Smooth Muscle

Location: Walls of most hollow organs and tubes (excluding heart). Usually in two layers (longitudinal and circular).
Structure: Small, slender, and spindle-shaped fibers. Single, centrally-located nucleus. No T-tubules, myofibrils, or sarcomeres (no striations). No tendons.
Function: Longitudinal layer → organ dilates and shortens. Circular layer → constricts the lumen and elongates the organ.
Characteristics: Slower contraction and relaxation, uses less energy to generate force. Maintains force for long periods with low oxygen consumption rates.
Smooth Muscle Contraction:
- Sliding filament mechanism: Actin and myosin filaments slide past each other.
- Ca²⁺: Obtained from the sarcoplasmic reticulum and extracellular space, triggers contraction by binding to calmodulin.
- Calmodulin: The activated calmodulin activates the myosin light chain kinase (MLCK) enzyme.
- MLCK: MLCK catalyzes transfer of phosphate to myosin, activating the myosin ATPases.
- Cross-bridge formation: Activated myosin forms cross-bridges with actin, and filament shortening begins.
Smooth Muscle Relaxation:
- Active transport of Ca²⁺ back into the sarcoplasmic reticulum and extracellular space.
- Ca²⁺ detaches from calmodulin.
- Dephosphorylation of myosin reduces myosin ATPase activity.
- Myosin phosphatase removes phosphate from myosin.
- Reduced muscle tension.

Neural Regulation of Smooth Muscle

Innervation: Innervated by the autonomic nervous system (sympathetic and parasympathetic).
Varicosities: Bulbous swellings of nerve fibers store and release neurotransmitters.
Diffuse junctions: Autonomic nerve fibers innervate smooth muscle at diffuse junctions.
Target cell response: The smooth muscle response depends on the receptor type.

Types of Smooth Muscle

Single-unit (visceral) smooth muscle:
- Most common type.
- Muscle fibers contract synchronously as a unit (connected by gap junctions).
- Often exhibit spontaneous action potentials (pacemaker cells).
- Innervation to few cells
- Stimulation and contraction last long period and slowly disappear.
- Location: intestinal tract, respiratory, reproductive system, etc.
Multi-unit smooth muscle:
- Few, if any, gap junctions (each fiber acts individually).
- Doesn't have automaticity (pacemaker cells).
- Graded contractions only occur in response to neural stimuli.
- Arranged in motor units (each muscle fiber receives its own innervation).
- Very dense innervation.
- Location: large airways and arteries, eye (ciliary muscle and iris).
- Stimulation of muscle contraction is short and soon disappear.

Innervation

Sympathetic (Norepinephrine): Effects depend on receptor type.
Parasympathetic (Acetylcholine): Effects depend on receptor type.
Gastric Muscle: Types of receptors and action.
Aortic Muscle: Types of receptors and action.

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Description

This quiz explores the fundamentals of electromyography (EMG) and its applications in muscle physiology. It covers techniques for assessing electrical activity in both skeletal and smooth muscles, including intramuscular and surface EMG. Test your knowledge on how these methods are used to diagnose neuromuscular diseases and motor control disorders.