- How do neurons communicate?
- How does a signal travel from one neuron to the next?
- The role of the axon in signal propagation
- Myelin sheaths and signal conduction
- Saltatory conduction
- The synaptic cleft and neurotransmission
- Excitatory and inhibitory neurotransmitters
- The role of the dendrites in signal reception
- Spatial summation
- Temporal summation
The nervous system is an amazing feat of engineering. It is made up of billions of cells called neurons, which use electrical signals to communicate with each other. But how does a signal travel from one neuron to the next?
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How do neurons communicate?
Neurons are the cells in the nervous system that transmit information. They communicate with each other via electrical and chemical signals.
The electrical signal is generated by the movement of ions across the cell membrane. This creates a voltage difference between the inside and outside of the cell, which is called an action potential. The action potential travels along the axon of the neuron to the synapse, where it triggers the release of chemicals called neurotransmitters.
The neurotransmitters bind to receptors on the next neuron, which causes changes in the electrical properties of that cell. This can either excite or inhibit the neuron, depending on the type of neurotransmitter and receptor involved.
How does a signal travel from one neuron to the next?
In order for a signal to travel from one neuron to the next, it must first be received by the dendrites of the receiving neuron. The dendrites are like tree branches, and they are covered in tiny receptor sites. When the neurotransmitters released by the sending neuron bind to these receptor sites, they cause an electrical charge to build up. This electrical charge then travels down the axon of the receiving neuron to the synapse.
At the synapse, the electrical charge causes neurotransmitters to be released from the axon of the receiving neuron. These neurotransmitters then bind to receptor sites on the dendrites of the next neuron in line, and the process repeats itself.
The role of the axon in signal propagation
The axon is a long, thin extension of a neuron that carries electrical impulses away from the cell body. When an electrical impulse (action potential) reaches the end of an axon, it triggers the release of chemical messenger molecules (neurotransmitters) from the axon terminal. These neurotransmitters cross the synapse and bind to receptor proteins on the post-synaptic cell, which can be another neuron, muscle cell, or gland cell. This binding process alters the membrane potential of the post-synaptic cell, either excitatory (depolarizing) or inhibitory (hyperpolarizing), and thus influences whether or not that cell will generate an action potential.
Myelin sheaths and signal conduction
The myelin sheath is an insulating covering that surrounds the axons of some neurons. The myelin sheath is composed of lipid (fatty) cells that wrap around the axon in a spiral fashion. The myelin sheath acts to increase the speed of signal conduction by providing a supporting structure for the axon and by reducing electrical resistance.
Myelin-forming cells are called oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. The myelin sheath is composed of lipid (fatty) cells that wrap around the axon in a spiral fashion.
When an action potential reaches the end of an unmyelinated axon, it triggers the release of neurotransmitters from small sacs called vesicles. The neurotransmitters travel across the synapse (the gap between neurons) and bind to receptors on the postsynaptic neuron, causing an electrical change in that cell. This change can either increase or decrease the likelihood that an action potential will be generated in that cell.
Saltatory conduction is the name given to the way in which electrical signals travel along nerve cells. The vast majority of neurons in the human body are myelinated, which means they are surrounded by a lipid (fatty) layer. This layer is known as the myelin sheath, and it acts as an insulator for the electrical signal.
Myelinated neurons have gaps in their myelin sheath, known as nodes of Ranvier. The signal does not flow continuously along the length of the neuron, but instead ‘jumps’ from one node to the next, a process known as saltatory conduction. This causes the signal to travel much more rapidly than it would if it were travelling along an unmyelinated neuron.
The synaptic cleft and neurotransmission
Neurons are specialized cells that transmit signals throughout the nervous system. Signals are passed from one neuron to the next via the synaptic cleft, a small gap between the two cells. In order for a signal to be passed across the synaptic cleft, a neurotransmitter must be released from the presynaptic neuron (the neuron sending the signal). The neurotransmitter then binds to receptors on the postsynaptic neuron (the neuron receiving the signal), and this binding triggers a change in the postsynaptic cell that allows the signal to be passed on.
Excitatory and inhibitory neurotransmitters
In order for a signal to travel from one neuron to the next, it must first be passed through the synapse. The synapse is a small space between the axon of one neuron and the dendrite of another. In order for the signal to be passed, an electrical charge must first build up at the end of the axon. Once this charge reaches a certain level, it will cause the release of neurotransmitters into the synapse.
There are two main types of neurotransmitters: excitatory and inhibitory. Excitatory neurotransmitters will cause the next neuron in line to fire an action potential, while inhibitory neurotransmitters will prevent this from happening. In most cases, there is a mix of both types of neurotransmitters being released, which will either amplify or dampen the signal depending on their individual effects.
The role of the dendrites in signal reception
Dendrites are the branching structures that extend from the cell body of a neuron. They are covered with small protrusions called dendritic spines, which increase the surface area for signal reception.
When an action potential (a brief surge of electrical activity) reaches the dendrites of a neuron, it causes a change in the membrane potential. This change in membrane potential is called depolarization. Depolarization occurs when there is an influx of positively charged ions into the cell.
If the depolarization is strong enough, it will trigger an action potential in the neuron. The action potential will travel along the axon to the next neuron, where it will cause depolarization and potentially trigger another action potential.
When a neuron receives input from other neurons, it will sum that input to determine whether or not to fire an action potential. This process is known as spatial summation. If the input is strong enough, the neuron will fire an action potential. If the input is not strong enough, the neuron will not fire.
When an action potential (nerve impulse) arrives at the axon terminal of a neuron, it causes the release of chemicals called neurotransmitters. These neurotransmitters cross the synapse and bind to specific receptors on the dendrites or cell body of the post-synaptic neuron. This binding triggers a change in the electrical properties of the post-synaptic cell membrane, which sets off a new action potential.