Physiology of Smooth Muscle Contraction

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is responsible for the inward current that brings about depolarization in smooth muscle?

Chloride ions

Sodium ions

Calcium ions (correct)

Potassium ions

What is the function of calmodulin in smooth muscle contraction?

To combine with calcium ions and activate myosin kinase (correct)

To phosphorylate myosin

To cleave ATP

To bind with ATP

What is the result of myosin kinase phosphorylating myosin in smooth muscle?

Depolarization of the muscle

Activation of myosin ATPase (correct)

Inhibition of calcium ions

Relaxation of the muscle

What is necessary for the relaxation of smooth muscle?

Calcium ions dissociating from calmodulin Signup and view all the answers

What is similar between contraction in smooth muscle and skeletal muscle?

The mechanism of myosin ATPase Signup and view all the answers

What is the function of myosin ATPase in smooth muscle contraction?

To cleave ATP Signup and view all the answers

What is the direction of neuromuscular transmission?

From nerve to muscle Signup and view all the answers

What is the reason for the delay of about 0.5ms in neuromuscular transmission?

Time needed for release of ACH and change in permeability of muscle fiber Signup and view all the answers

What causes fatigue in neuromuscular transmission?

Depletion of ACH and ATP Signup and view all the answers

What is the effect of magnesium ions on neuromuscular transmission?

Decreases the release of ACH Signup and view all the answers

What type of synapse is divided into two main categories?

Chemical synapse Signup and view all the answers

What is the type of synapse between an axon and a dendrite?

Axodendritic synapse Signup and view all the answers

What is the primary function of neurotransmitters in a chemical synapse?

All of the above Signup and view all the answers

What is a characteristic of electrical synapses?

They allow conduction in both directions Signup and view all the answers

What type of molecules can pass through gap junctions in electrical synapses?

Water-soluble molecules up to a certain molecular weight Signup and view all the answers

What is the result of the autoimmune response in Myasthenia Gravis?

The formation of antibodies against acetylcholine receptors Signup and view all the answers

What is the primary difference between Myasthenia Gravis and Lambert-Eaton Syndrome?

The type of antibodies formed Signup and view all the answers

What is the approximate molecular weight of molecules that can pass through gap junctions?

1200-1500 Signup and view all the answers

What is the direction of transmission in a chemical synapse?

Unidirectional Signup and view all the answers

How many different chemical transmitters have been discovered so far?

Over 40 Signup and view all the answers

What is the ability of the heart to work independently of any extrinsic stimuli?

Autorythmicity Signup and view all the answers

Which property of cardiac muscle allows impulses to spread easily between cardiac muscle fibers?

Conductivity Signup and view all the answers

What is the duration of contraction in the heart?

300ms Signup and view all the answers

What is the term for the contraction of a cardiac chamber?

Systole Signup and view all the answers

What leads to the release of calcium ions into the muscle's sarcoplasm from the SR?

Depolarization of sarcolemma by sodium influx Signup and view all the answers

What is the type of calcium ions released from the SR during muscle contraction?

Activator calcium ions Signup and view all the answers

What is the term for the ability of the heart to contract in response to intrinsic stimuli?

Contractility Signup and view all the answers

What is the pathway of the conducting system in the heart?

Sinoatrial node to atrioventricular node to bundle of His Signup and view all the answers

What is the significance of the absolute refractory period in cardiac muscle?

It lasts for the whole period of systole and early part of diastole Signup and view all the answers

What type of contraction occurs in cardiac muscle when it contracts and shortens under a constant load?

Isotonic contraction Signup and view all the answers

What is the space between the plasma membrane of the axon ending and the muscle fiber sarcolemma called?

Synaptic cleft Signup and view all the answers

What is the neurotransmitter released by the motor neuron that binds to receptors on the muscle fiber sarcolemma?

Acetylcholine Signup and view all the answers

What is the process by which the release of acetylcholine from the axon ending is stimulated?

The arrival of the action potential at the axon ending Signup and view all the answers

What happens to the acetylcholine released by the neuron after it binds to its receptors on the muscle fiber sarcolemma?

It is rapidly hydrolyzed by choline esterase to inactive acetic acid and choline Signup and view all the answers

What is the term for the period during which the muscle length is constant as the myocardium contracts?

Isometric contraction Signup and view all the answers

What is the main function of the acetylcholine released by the neuron onto the muscle fiber?

To increase the permeability of the muscle fiber membrane to sodium ions Signup and view all the answers

What is the term for the point at which the axon ending of a motor neuron meets a muscle cell?

Neuromuscular junction Signup and view all the answers

What happens to the action potential once it is produced in the muscle fiber?

It spreads on both sides of the endplate Signup and view all the answers

Study Notes

Smooth Muscle Contraction

Unlike action potentials in nerves and muscle, in smooth muscle, calcium ions are responsible for the inward current that brings about depolarization.
Contraction in smooth muscle contains actin that slides over myosin during contraction, but slower than skeletal muscle.
Also contains tropomyosin and calmodulin (but no troponin).
Contraction is activated by calcium ions, which combine to calmodulin.
Calmodulin-calcium combination joins and activates myosin kinase (MK).
MK phosphorylates myosin, leading to activation of myosin ATPase.
Myosin binds with actin, producing contraction.

Cardiac Muscle

Autorythmicity

The heart has the ability to work independently of any extrinsic stimuli.
It beats regularly independent of any extrinsic stimuli.
It has automatic action potential generation capability.
Spontaneous rhythmic electrical impulses are generated by the conducting system, especially the pacemaker.

Properties of Cardiac Muscle

Conductivity (Dromotropic Action)
- Impulses can spread easily between cardiac muscle fibres.
- Conduction in the heart is normally carried out by the specialized conducting system.
- Conducting system starts with the pacemaker at the sinoatrial node in the right atrium to the atrioventricular nodes, then to the bundle of His and then purkinje fibres.
Contractility (Inotropic Action)
- The heart has the ability to contract in response to intrinsic stimuli in a rhythmic way.
- Contraction of a cardiac chamber is called systole, and relaxation is called diastole.
- Like skeletal muscle, action potential gets to the cardiac membrane, excitation-contraction coupling starts with the depolarization of sarcolemma by sodium influx.

Neuromuscular Junction (Myoneural Junction)

The point at which the axon ending of a motor neuron meets a muscle cell.
The plasma membrane of the axon ending remains separated from the muscle fibre sarcolemma by a small space (20-30nm) called the synaptic cleft.

Neurotransmission

For skeletal muscle to contract, the motor nerve controlling it must signal it to do so.
The signals sent to muscle fibres by motor nerves are through chemical messengers called neurotransmitters.
Neurotransmitters released onto the skeletal muscle fibre at the NMJ is acetylcholine.
Acetylcholine is released by the process of exocytosis.

Properties of Neuromuscular Transmission

Unidirectional - it occurs in one direction only, from nerve to muscle.
Delay of about 0.5ms, which represents the time needed for release of ACh, change in permeability of muscle fibre, influx of sodium ions and building of depolarization to firing level.
Easily fatigued due to repeated stimulation, caused by depletion of Ach and ATP needed for synthesis of Ach.
Can be blocked by drugs, such as curare, a toxic drug that competes with ACh for binding site.

Synaptic Transmission

Synapses are junctions where the axons or some other part of one nerve cell (presynaptic cell) terminates on the soma, dendrites or some other part of another neuron (the post-synaptic cell).
Types of synapses: axodendritic, axosomatic, axoaxonic, dendrodenritic, somatosomatic, dendroaxonic.

Clinical Conditions Associated with the Neuromuscular Junction

Myasthenia Gravis: an autoimmune disease in which antibodies are formed against the acetylcholine receptors, resulting in muscle weakness.
Lambert-Eaton Syndrome: an autoimmune disease of the neuromuscular junction, affecting the presynaptic neurons.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about the contraction mechanism in smooth muscle, including the role of calcium ions, calmodulin and tropomyosin. Compare and contrast with skeletal muscle contraction.