Synapses

Summary

This video explains how neurons transmit nerve impulses and communicate with other cells through synapses. It outlines the types of cells neurons connect with, including sensory receptors, interneurons, and effector cells. The process of synaptic transmission is detailed, covering neurotransmitter release, receptor binding, and the 'all or nothing' response. The video also highlights acetylcholine's role and its breakdown, as well as the harmful effects of neonicotinoid insecticides on insects like honeybees, which block acetylcholine receptors, leading to paralysis and death.

Takeaways

• 🧠 Neurons transmit nerve impulses and communicate with other cells by sending chemicals across synapses.
• 🔗 Synapses are junctions between neurons and other cells, including sensory receptors, other neurons, and effector cells.
• 👂 Sensory receptor cells are involved in sensing stimuli from places like the eyes, ears, nose, and skin.
• 🌀 Interneurons act as intermediaries between sensory neurons and effector cells, transmitting signals to the central nervous system.
• 💪 Effector cells, such as muscle cells, receive signals to initiate a response, like moving away from pain.
• ⚡ Synaptic transmission involves the release of neurotransmitters into the synaptic cleft, which then bind to receptors on the post-synaptic membrane.
• 🔋 Neurotransmitters, like acetylcholine, are broken down and recycled after triggering an action potential.
• 🌐 The 'all or nothing' response ensures that an action potential only occurs if enough neurotransmitters bind to receptors.
• 🧪 Acetylcholine is broken down by acetylcholinesterase, an enzyme present in the synaptic cleft, allowing reuse of its components.
• 🐝 Neonicotinoid insecticides can paralyze insects by permanently binding to acetylcholine receptors, affecting non-target species like honeybees.

Q & A

What is the function of synapses in the nervous system?

Synapses are junctions between neurons and the next cell, allowing for the transmission of nerve impulses from one cell to another across a small gap.

What are the three major types of cells that neurons form synapses with?

The three major types of cells are sensory receptor cells, other neurons (interneurons), and effector cells.

How does a sensory cell involved in pain sensation transmit its message?

A sensory cell picks up pain sensations and sends the message to another neuron, potentially in the spinal cord or brain, which then processes the information.

What is the role of effector cells in a reflex arc?

Effector cells are responsible for the action part of a reflex arc, such as signaling a muscle cell to move the skin away from a source of pain.

What are neurotransmitters and how are they released?

Neurotransmitters are chemicals released into the synapse that facilitate communication between neurons. They are released by exocytosis from vesicles in the pre-synaptic neuron into the synaptic cleft.

What is the synaptic cleft and how wide is it?

The synaptic cleft is the small fluid-filled gap between the pre-synaptic and post-synaptic cells, which is approximately 20 nm wide.

What happens during synaptic transmission when a nerve impulse reaches the end of the pre-synaptic neuron?

Calcium ions enter the cell, causing vesicles with neurotransmitters to fuse with the membrane and release their contents into the synaptic cleft.

How do neurotransmitters affect the post-synaptic neuron?

Neurotransmitters bind to receptors on the post-synaptic membrane, triggering the opening of sodium ion channels and potentially generating an action potential.

What is the 'all or nothing' response in synaptic transmission?

The 'all or nothing' response refers to the fact that if there isn't enough neurotransmitter to bind to receptors and reach the threshold potential, no action potential is generated.

What is Acetylcholine and how does it function in the nervous system?

Acetylcholine is a neurotransmitter composed of an acetyl group and choline. It is released into the synaptic cleft, binds to receptors, and is then broken down by acetylcholinesterase for reuse.

How do neonicotinoids affect insect nervous systems and why are they harmful to beneficial insects?

Neonicotinoids are synthetic compounds that bind permanently to acetylcholine receptors, preventing the action of acetylcholinesterase and leading to paralysis and death in insects. This indiscriminate effect also harms beneficial insects like honeybees.

Outlines

00:00

🧠 Neuron Communication and Synaptic Transmission

Neurons transmit messages through nerve impulses, utilizing synapses to communicate with other cells. Synapses are junctions with three major cell types: sensory receptors, interneurons, and effector cells. Sensory receptors detect stimuli like pain, interneurons relay this information within the nervous system, and effector cells initiate responses such as muscle movement. Neurotransmitters are chemicals that facilitate this communication across a synaptic cleft, which is a tiny gap about 20 nm wide. The process of synaptic transmission involves the release of neurotransmitters into the cleft, their binding to receptors on the post-synaptic membrane, and the subsequent generation of an action potential if enough neurotransmitters bind. This process is all-or-nothing, requiring a threshold level of neurotransmitter binding to initiate a response. After transmission, neurotransmitters are broken down and removed or reused.

Keywords

💡Neuron

A neuron is a specialized cell that transmits nerve impulses and is the fundamental unit of the nervous system. In the video, neurons are described as transmitting messages through electrical impulses and chemical signals, particularly across synapses. The neuron's role is central to the video's theme of communication between cells in the nervous system.

💡Synapse

A synapse is a junction between two neurons where a signal is transmitted from one neuron to another. The video explains that most neurons send chemicals across the synapse to communicate with the next neuron, which is crucial for the functioning of the nervous system. The synapse is a key concept in understanding how neurons interact and transmit information.

💡Sensory receptor cells

Sensory receptor cells are specialized cells that respond to stimuli such as light, sound, or touch. In the context of the video, these cells are connected to the skin and can pick up pain sensations, which they then transmit to other neurons. The concept of sensory receptor cells is essential for understanding how the nervous system receives and processes information from the external environment.

💡Interneurons

Interneurons are neurons that are part of the central nervous system and act as intermediaries between sensory and motor neurons. The video mentions that these neurons can be part of the spinal cord or brain and play a role in processing and relaying sensory information. Interneurons are integral to the reflex arc, which is a simple neural pathway described in the video.

💡Effector cells

Effector cells are cells that respond to neural signals and produce a specific effect, such as muscle contraction or gland secretion. The video gives an example of an effector cell signaling a muscle cell to move the skin away from a painful stimulus. Effector cells are a critical component of the reflex arc, demonstrating the action phase of the neural response.

💡Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. The video describes how neurotransmitters are released into the synaptic cleft and bind to receptors on the post-synaptic neuron, triggering further neural activity. Neurotransmitters are central to the video's discussion of synaptic transmission and the 'all or nothing' response of neurons.

💡Synaptic cleft

The synaptic cleft is the small gap between the pre-synaptic and post-synaptic neurons where neurotransmitters are released. The video emphasizes its tiny size, approximately 20 nm wide, which is critical for the precise transmission of signals between neurons. Understanding the synaptic cleft is essential for grasping the mechanics of neural communication.

💡Action potential

An action potential is an electrical signal that travels along a neuron's membrane, initiating the process of transmitting a nerve impulse. The video explains that the binding of neurotransmitters to receptors can trigger the opening of sodium ion channels, leading to an action potential. This concept is fundamental to the video's explanation of how neurons communicate and propagate signals.

💡Acetylcholine

Acetylcholine is a neurotransmitter that plays a crucial role in muscle activation and is the focus of a detailed example in the video. It is synthesized in the pre-synaptic neuron, released into the synaptic cleft, and then broken down by the enzyme acetylcholinesterase. The video also discusses how certain insecticides, like neonicotinoids, interfere with acetylcholine receptors, which is relevant to the broader implications of neurochemistry.

💡Neonicotinoids

Neonicotinoids are synthetic compounds similar to nicotine that bind to acetylcholine receptors, as mentioned in the video. Unlike natural neurotransmitters, neonicotinoids cannot be broken down by acetylcholinesterase, leading to paralysis and death in insects. The video uses neonicotinoids to illustrate the unintended consequences of chemical interference with neurotransmitter systems, highlighting the importance of understanding neurochemical processes.

Highlights

Neurons transmit nerve impulses through themselves but rely on chemicals to send messages to other cells across synapses.

There are three major types of cells that neurons form synapses with: sensory receptor cells, other neurons, and effector cells.

Sensory cells, such as those in the eye, ear, or skin, detect stimuli and send pain messages to neurons in the spinal cord or brain.

Intermediate neurons, also known as interneurons, help transmit signals between sensory cells and effector cells.

Effector cells respond to stimuli, such as muscle cells that contract to move away from a pain source.

Neurons, sensory receptors, and effector cells form a simple reflex arc from sensation to action.

Neurotransmitters are the chemicals released into the synapse to transmit messages between neurons.

The synaptic cleft, the gap between neurons, is only about 20 nanometers wide.

Calcium ions diffuse into the presynaptic cell, triggering neurotransmitter release through exocytosis.

Neurotransmitters bind to receptors on the postsynaptic membrane, causing sodium ion channels to open and propagate an action potential.

The process follows an 'all or nothing' response—either enough neurotransmitter triggers an impulse, or no impulse is sent.

Acetylcholine, a neurotransmitter, is broken down by acetylcholinesterase after binding, allowing reuse of its components.

Neonicotinoid insecticides bind to acetylcholine receptors in insects, leading to paralysis and death by preventing signal transmission.

Neonicotinoids are harmful to beneficial insects like honeybees, as they indiscriminately affect all types of insects.

The process of neurotransmitter release and signal propagation is critical to understanding how neurons communicate in the nervous system.

Transcripts

A neuron transmits nerve impulses through itself but when its time to send a message

to another cell, most neurons will send chemicals to the next neuron across a very small gap

between them.

The junctions between neurons and the next cell are called synapses.

There are three major types of cells that neurons will form synapses with:sensory receptor

cells, other neurons, and effector cells.

A sensory cell could be part of the eye, ear, nose, skin or any other place where senses

are used.

This sensory cell is connected to the skin and will pick up pain sensations.

The pain message may be sent to another neuron that could be part of the spinal cord or brain.

These intermediate neurons are also called interneurons.

The message can then be sent to a cell that will have an effect on another cell so they

are called effector cells.

In this example the effector cell is going to signal a muscle cell which would move this

area of the skin away from the source of pain.

These three cell types together make a simple reflex arc, going from sensation, to the central

nervous system to an action.

The chemicals released into the synapse are called neurotransmitters.

Many neurons have a very small fluid filled gap between the pre-synaptic cell and the

post-synaptic cell.

This gap is called the synaptic cleft and it’s only about 20 nm wide.

It’s a really, really tiny gap.

Now that we know some of the basics, we can look at the steps of synaptic transmission

in more detail.

First, a nerve impulse in the pre-synaptic neuron reaches the end of the membrane.

This causes calcium ions to diffuse into the cell through channels in the membrane.

the influx of calcium causes vesicles with neurotransmitters in them to move and fuse

to the membrane.

The neurotransmitters are released into the synaptic cleft by exocytosis.

They diffuse across the synaptic cleft and bind to receptors on the post-synaptic membrane.

The binding of neurotransmitters trigger sodium ion channels to open and pass the threshold

potential.

The action potential is propagated along the post-synaptic neuron.

Then the neurotransmitters are broken down and removed from the synaptic cleft.

If there isn’t enough neurotransmitter binding to receptors, then there won’t be enough

sodium flowing into the cell to reach the threshold potential.

This means that there is an “all or nothing” response.

Either there is enough neurotransmitter to start the action potential and the impulse

is sent, or there is no impulse.

In this case, there was not enough neurotransmitter released to trigger an action potential, so

the neurotransmitters will be broken down and the sodium potassium pumps will restore

resting potential in the post-synaptic cell.

There are many different types of neurotransmitter, but we’ll look at one in more detail right

now: Acetylcholine.

This neurotransmitter is made of an acetyl group and choline which must be combined together

in the pre-synaptic cell before it’s packaged into a vesicle.

Then it can be released into the synaptic cleft.

After acetylcholine binds with a receptor it is rapidly broken down by acetylcholinesterase,

an enzyme that is present in the synaptic cleft.

The acetyl group and choline can then be reabsorbed by the pre-synaptic neuron and combined again

into acetylcholine for reuse.

One type of insecticide takes advantage of the acetylcholine receptors to paralyze and

kill insects.

Neonicotinoids are synthetic compounds that are similar to nicotine but bind permanently

to the acetylcholine receptors.

the acetylcholinesterase cannot break the neonicotinoids down and the neurons can no

longer receive messages or send action potentials.

This is what leads to paralysis and death in the insects.

The effects are very small in humans and mammals, but the neonicotinoids don’t discriminate

between types of insects.

Honeybees and other beneficial insects are inadvertently killed by neonicotinoids too.