Name: how muscles receive signals to contract
Uploaded: 2023-04-30T10:12:01.000Z
Duration: 1 min 10 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.14

SC.912.L.14.17

Muscle Contraction

A voluntary skeletal muscle contraction begins in the brain as a conscious effort from the frontal lobe to the primary motor cortex before activating an alpha motor neuron located in the anterior horn of the spinal cord.
The signal continues down a nerve to the specific muscle fiber such as those found in the biceps, where the action potentials terminate at the motor endplate. There, the motor neuron establishes synaptic contact with the muscle fiber and triggers the release of the neurotransmitter acetylcholine, which diffuses across the synaptic cleft and binds to receptors.
As a result, the sarcolemma becomes more permeable to sodium ions, resulting in more action potentials that spread along its external surface and into the interior of the muscle fiber through transverse or T-tubules. This triggers the release of calcium ions from the sarcoplasmic reticulum into the myofibrils.
This release of calcium initiates actin-myosin cross-bridge activity and the observation of the muscle shortening and contracting.

muscle contraction

In skeletal muscles, acetylcholine is released by nerve terminals at the motor endplate&#8212;the point of synaptic communication between motor neurons and muscle fibers. The binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle stimulation.
Individuals with the disorder myasthenia gravis develop antibodies against the acetylcholine receptor. This prevents the transmission of electrical signals between the motor neuron and muscle fiber and impairs skeletal muscle contraction. Myasthenia gravis is treated using drugs that inhibit acetylcholinesterase (allowing more opportunities for the neurotransmitter to stimulate the remaining receptors) or suppress the immune system (preventing the formation of antibodies).
Smooth Muscle Contraction
Unlike skeletal muscles, smooth muscles present in the walls of internal organs are innervated by the autonomic nervous system and undergo involuntary contractions. Contraction is mediated by the interaction between two filament proteins&#8212;actin and myosin. The interaction of actin and myosin is closely linked to intracellular calcium concentration. In response to neurotransmitter or hormone signals or stretching of the muscle, extracellular calcium enters the cell through calcium channels on the sarcolemma or is released intracellularly from the sarcoplasmic reticulum. Inside the cell, calcium binds to the regulatory protein calmodulin. The calcium-calmodulin complex then activates the enzyme myosin light chain kinase, which phosphorylates myosin and allows it to interact with actin, causing the muscle to contract.

In skeletal muscles, acetylcholine is released by nerve terminals at the motor endplate&#8212;the point of synaptic communication between motor neurons ...

Education

JoVE Core

Cell Biology

Unit 1

Channels and the Electrical Properties of Membranes

channels-and-the-electrical-properties-of-membranes

KEY TERMS AND CONCEPTS

how muscles receive signals to contract

Muscle contraction begins when a nerve signal reaches a skeletal muscle fiber. At the motor endplate, a motor neuron releases acetylcholine, a neurotransmitter that carries the signal to the muscle cell. Acetylcholine binds to receptors on the sarcolemma, the muscle cell membrane, and lets sodium ions enter the cell. This starts an action potential in the muscle fiber and helps pass electrical signals from the brain to the muscle.

The signal must also be controlled so the muscle does not stay overstimulated. An enzyme called acetylcholinesterase breaks down acetylcholine after it has done its job. In myasthenia gravis, the immune system makes antibodies against the acetylcholine receptor. This blocks communication between the motor neuron and muscle fiber and weakens skeletal muscle contraction. Treatment may use drugs that inhibit acetylcholinesterase or medicines that suppress the immune system.

Smooth muscle contraction works differently from skeletal muscle contraction. Smooth muscle is found in the walls of internal organs and is controlled by the autonomic nervous system, so its contractions are involuntary. Its contraction depends on the interaction of actin and myosin, two filament proteins. That interaction is closely tied to the amount of calcium inside the cell.

When smooth muscle receives neurotransmitter or hormone signals, or when it is stretched, calcium enters through channels in the sarcolemma or is released from the sarcoplasmic reticulum. Inside the cell, calcium binds to calmodulin, a regulatory protein. The calcium-calmodulin complex activates myosin light chain kinase, which phosphorylates myosin. This change lets myosin interact with actin and causes the muscle to contract.

How Muscles Receive Signals to Contract

aquaporins

Aquaporins and Membrane Transport

Aquaporins are membrane proteins that move water across cell membranes. Some aquaporins, called aquaglyceroporins, also transport glycerol. A few aquaporins may also help move volatile substances such as carbon dioxide and ammonia. These channels are found in many different tissues. Water-selective aquaporins are important in the kidneys, exocrine glands, and central nervous system. Aquaporins that may act as gas channels are often highly expressed in red blood cells, epithelial cells, and...

non-gated ion channels

Leak Channels in Resting Membranes

Leak channels are ion channels that let charged ions move across the plasma membrane without a gate. These proteins help maintain membrane potential, which is essential for cell survival. They can move more than a thousand ions in milliseconds during a cellular event. Unlike gated ion channels, non-gated channels have no opening trigger. They are also called leakage or passive channels. Instead, they switch between open and closed states at an intrinsic rate, so ions keep “leaking” through...

ligand-gated ion channels

How Ligand-Gated Ion Channels Work

Ligand-gated ion channels are membrane proteins that open when a chemical signal binds to them. They have a channel for ions to pass through and a ligand-binding site. When the ligand attaches, the channel opens and ions can move across the cell membrane. These channels are grouped into three subfamilies. The Cys-loop group includes nicotinic acetylcholine receptors, gamma-aminobutyric acid (GABA) receptors, glycine receptors, and 5-hydroxytryptamine receptors. The pore-loop group includes...

voltage-gated ion channels

How Voltage Gated Channels Control Signals

Voltage-gated ion channels control electrical signals in neurons, heart cells, and muscle cells. These transmembrane proteins open and close when the membrane potential changes. They sit in the cell membrane of electrically excitable cells and help ions move across it. Each channel includes a voltage-sensing domain that spans the lipid bilayer. Charged residues in this sensor shift when the membrane potential changes. That movement opens the channel and allows ions to pass through. Different...

mechanically-gated ion channels

Touch and Heat Sensors in Cell Membranes

Mechanically-gated ion channels are membrane proteins that open when cells experience physical stress. Tension, compression, swelling, and shear stress can change the shape of the protein. That change opens a transmembrane pore and lets ions pass to help transmit signals. In eukaryotes, these channels are found in several body regions, including neurons, lungs, skin, bladder, and heart. They support many normal physiological processes. They are also involved in disease when their function...

neuron structure

Neuron Signaling and Synapses

Neurons are the main cells of the nervous system that generate and pass along electrochemical signals. They communicate with one another mainly through neurotransmitters at special connections called synapses. Neurons can have different shapes, and those shapes often match their function. Most, however, share three main parts: a cell body, dendrites, and an axon. The cell body, or soma, contains the nucleus and the organelles needed for cell activity. Dendrites extend from the soma and usually...

resting membrane potential

How Neurons Keep a Negative Voltage

Neurons keep a negative voltage across their membrane when they are at rest. This membrane potential is the voltage difference between the inside and outside of a cell. In a resting neuron, it is usually around -70 millivolts, which means the inside is more negative than the outside and the cell is polarized. This negative charge depends on two main factors. The membrane is selectively permeable, so most ions and molecules cannot cross the lipid bilayer without help from ion channel proteins.

resting potential decay

Resting Membrane Potential Maintenance

The resting membrane potential stays near -70 mV in a neuron because the membrane allows ions to move in a selective way. At rest, the membrane is slightly permeable to sodium ions (Na+) and chloride ions (Cl-) and highly permeable to potassium ions (K+). Ion channels and pumps keep the concentration differences between the inside and outside of the cell in place. Potassium leak channels let K+ move out of the cell at rest. This outward movement makes the inside of the cell more negative. A...

action potential

How Nerve Signals Travel Down Axons

Nerve signals travel down axons as action potentials, which are electrochemical pulses that let neurons communicate. This signal moves to the axon terminals and triggers neurotransmitter release, passing information through the nervous system. An action potential is an all-or-none change in membrane potential that produces a fast spike in voltage. Neurons usually rest at about -70 millivolts. When they receive input from neurotransmitters or sensory stimuli, the membrane potential can become...

channel rhodopsins

Light-Gated Ion Flow in Channel Rhodopsins

Channel rhodopsins are light-sensitive ion channels found in some organisms. They belong to the rhodopsin family, which also includes photoreceptors in bacteria, plants, and the vertebrate retina. These proteins use bound chromophores, such as retinal in rhodopsins and bilin in phytochromes, to respond to light. Rhodopsins are a group of cell surface proteins called G-protein coupled receptors. These proteins help move signals across biological membranes. Over evolution, the rhodopsin family...

patch clamp

Recording Ion Channel Currents with Patch Clamp

Patch clamp is a lab method used to record electrical currents across a cell membrane. It helps scientists study how ions move through channels in the membrane. These electrical signals are important for functions such as muscle contraction and nerve transmission. The method uses a glass micropipette filled with electrolyte solution. The pipette is sealed tightly to a small part of the cell membrane. This creates an electrically isolated patch, so ions moving through the channels flow into the...

electrical synapses

Gap Junctions in Electrical Signaling

Electrical synapses use gap junctions to pass signals directly between neurons and other cells. The presynaptic and postsynaptic membranes sit very close together, about 3.5 nm apart. Channel proteins connect the two cells and create a direct path for current. Unlike a chemical synapse, an electrical synapse does not rely on neurotransmitters crossing a synaptic cleft. The gap junction is built from two hexameric connexin hemichannels, also called connexons. Each adjacent cell contributes one...

chemical synapses

How Neurons Signal at Synapses

Chemical synapses let neurons pass signals to another neuron, a muscle cell, a gland cell, or a sensory cell. They use neurotransmitter molecules released from synaptic vesicles to carry the message. Because of that process, there is a short delay of about one millisecond between the arrival of the action potential and the opening of ion channels on the postsynaptic cell. Chemical synapses also send information in one direction only. A synaptic cleft separates the presynaptic and postsynaptic...

excitatory and inhibitory effects of neurotransmitters

excitatory-and-inhibitory-effects-of-neurotransmitters

How Neurotransmitters Trigger or Block Signals

Neurotransmitters can either trigger or block signals at a chemical synapse. When an action potential reaches the presynaptic axon terminal, it causes the neuron to release neurotransmitters into the synaptic cleft. The released molecule then binds to specific receptors on the postsynaptic cell membrane. A molecule is usually identified as a neurotransmitter when it is present in the presynaptic neuron, released in response to strong presynaptic depolarization, and matched with receptors on...

Muscle contraction begins when a nerve signal reaches a skeletal muscle fiber. At the motor endplate, a motor neuron releases acetylcholine, a neurotransmitter that carries the signal to the muscle cell. Acetylcholine binds to receptors on the sarcolemma, the muscle cell membrane, and lets sodium ions enter the cell. This starts an action potential in the muscle fiber and helps pass electrical signals from the brain to the muscle. The signal must also be controlled so the muscle does not stay...

the role of ion channels in neuronal computation

the-role-of-ion-channels-in-neuronal-computation

How Ion Channels Shape Neuron Firing

Ion channels help neurons decide when to fire an action potential. A postsynaptic neuron often receives signals from many presynaptic neurons, and the axon hillock adds those inputs together to judge whether firing is likely. In some cases, one strong EPSP, or excitatory postsynaptic potential, is enough to trigger a spike. In many cases, several EPSPs must arrive close together for the cell to reach threshold. This signal adding process is called summation. It can be temporal when one...

long-term potentiation

How Synapses Strengthen During Learning

Long-term potentiation, or LTP, is a way the brain strengthens synapses over time. A synapse is the chemical connection between neurons. LTP is one form of synaptic plasticity, which means changes in synapse strength. It works opposite to long-term depression, or LTD, which weakens synapses. Together, LTP and LTD are major mechanisms behind learning and memory. LTP can happen when a presynaptic neuron repeatedly fires and stimulates a postsynaptic neuron. This is called Hebbian LTP. It follows...

long-term depression

Synaptic Weakening in Memory Circuits

Long-term depression, or LTD, is a form of synaptic weakening in the brain. It is one way synaptic plasticity, or changes in the strength of chemical synapses, can occur over time between presynaptic and postsynaptic neurons. LTD works opposite long-term potentiation, or LTP, which strengthens synapses. Together, LTD and LTP help support learning and memory. LTD also helps keep the brain flexible. If synapses stayed maximally strengthened for too long, the brain would become less efficient and...

key terms and concepts

Explore how nerve signals trigger skeletal muscle contraction, how acetylcholinesterase controls the response, and how calcium drives smooth muscle contraction.

How Muscles Receive Signals to Contract | JoVE K12

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How Muscles Receive Signals to Contract

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