An unexpected error occurred. Previous Video They come in a variety of shapes and sizes but generally have some common features. All neurons have a cell body, also called the soma, that contains the nucleus. Most neurons also have dendrites and an axon that extends from the cell body. Dendrites are often highly branching and they receive signals from other neurons at junctions called synapses. The axon, on the other hand, transmits signals to neurons and other cells.
The axon hillock, where the cell body meets the axon, generates the action potential, the primary form of electrical signaling in the nervous system. Axons are often wrapped in a fatty myelin sheath, made by support cells called glia, which insulates them, helping to maintain the electrical signal as it is transmitted along. The nodes of ranvier, gaps in the myelin sheath, are regions where the action potential is repeatedly regenerated down the axon.
At the end of the axon is the terminal, containing synaptic vesicles filled with neurotransmitter molecules. When an action potential reaches the terminal, neurotransmitter is released into the synaptic cleft, a region of space between cells at a synapse.
Depending on the type of channel, the neurotransmitter can help transmit the signal to the next cell. Neurons are the main type of cell in the nervous system that generate and transmit electrochemical signals. They primarily communicate with each other using neurotransmitters at specific junctions called synapses. Neurons come in many shapes that often relate to their function, but most share three main structures: an axon and dendrites that extend out from a cell body. The neuronal cell body—the soma— houses the nucleus and organelles vital to cellular function.
Extending from the cell body are thin structures that are specialized for receiving and sending signals. Dendrites typically receive signals while the axon passes on the signals to other cells, such as other neurons or muscle cells.
The point at which a neuron makes a connection to another cell is called a synapse. Neurons receive inputs primarily at postsynaptic terminals, which are frequently located on spines—small bumps protruding from the dendrites. These specialized structures contain receptors for neurotransmitters and other chemical signals. Dendrites are often highly branched, allowing some neurons to receive tens of thousands of inputs.
Neurons most commonly receive signals at their dendrites, but they can also have synapses in other areas, such as the cell body. The signal received at the synapses travels down the dendrite to the soma, where the cell can process it and determine whether it should send the message forward or not. The action potential is the main electrical signal generated by neurons.
It carries the information forward onto the next cell. It is first generated at the axon hillock—the junction between the soma and the axon. Axons vary in length but can be quite long. For example, some extend from the spinal cord all the way to the foot.
Longer axons are usually wrapped in a fatty myelin sheath that insulates the axon, helping to maintain the electrical signal.
The myelin sheath is created by glia—another type of cell in the nervous system. In myelinated axons, the action potential is regenerated at each node of Ranvier—repeated gaps in the myelin—until it reaches the terminal at the end of the axon, or presynaptic terminal. The presynaptic terminal has vesicles that contain pools of neurotransmitters.
Action potentials trigger the vesicles to undergo exocytosis by fusing to the cell membrane and releasing neurotransmitter into the synaptic cleft—the gap between cells at a synapse. Different neurotransmitters can have varying effects on the postsynaptic cell. An excitatory synapse increases the chances of initiating an action potential on the postsynaptic cell, while an inhibitory synapse decreases the chances of an action potential. The overall shape of neurons—their morphology—can vary dramatically and often relates to their function.
Some neurons have few dendritic processes and a single axon, others have very convoluted dendritic arbors, while others have axons that can span the length of the organism. The diverse morphologies are often used to define the type of neuron.
Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. Neurons are the basic building blocks of the nervous system. These specialized cells are the information-processing units of the brain responsible for receiving and transmitting information.
Each part of the neuron plays a role in communicating information throughout the body. Neurons carry messages throughout the body, including sensory information from external stimuli and signals from the brain to different muscle groups in the body. In order to understand exactly how a neuron works, it is important to look at each individual part of the neuron. The unique structures of the neuron allow it to receive and transmit signals to other neurons as well as other types of cells.
Dendrites are tree-like extensions at the beginning of a neuron that help increase the surface area of the cell body. These tiny protrusions receive information from other neurons and transmit electrical stimulation to the soma. Dendrites are also covered with synapses. Most neurons possess these branch-like extensions that extend outward away from the cell body. These dendrites then receive chemical signals from other neurons, which are then converted into electrical impulses that are transmitted toward the cell body.
Some neurons have very small, short dendrites, while other cells possess very long ones. The neurons of the central nervous systems have very long and complex dendrites that then receive signals from as many as a thousand other neurons.
If the electrical impulses transmitted inward toward the cell body are large enough, they will generate an action potential. This results in the signal being transmitted down the axon. The soma, or cell body, is where the signals from the dendrites are joined and passed on. The soma and the nucleus do not play an active role in the transmission of the neural signal. Instead, these two structures serve to maintain the cell and keep the neuron functional.
Think of the cell body as a small factory that fuels the neuron. The soma produces the proteins that the other parts of the neuron, including the dendrites, axons, and synapses, need to function properly. The support structures of the cell include mitochondria, which provide energy for the cell, and the Golgi apparatus, which packages products created by the cell and dispatches them to various locations inside and outside the cell.
The axon hillock is located at the end of the soma and controls the firing of the neuron. If the total strength of the signal exceeds the threshold limit of the axon hillock, the structure will fire a signal known as an action potential down the axon.
The axon hillock acts as something of a manager, summing the total inhibitory and excitatory signals. Like other cells, each neuron has a cell body or soma that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components.
The cell body contains a specialized structure, the axon hillock, which serves as a junction between the cell body and the axon. The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next. It is a gap where specialized chemical interactions can occur, rather than an actual structure.
The specialized structure and organization of neurons allows them to transmit signals in the form of electric impulses from the brain to the body and back. Individually, neurons can pass a signal all the way from their own dendrites to their own axon terminals; but at a higher level neurons are organized in long chains, allowing them to pass signals very quickly from one to the other.
This is the basic chain of neural signal transmission, which is how the brain sends signals to the muscles to make them move, and how sensory organs send signals to the brain.
It is important that these signals can happen quickly, and they do. Think of how fast you drop a hot potato—before you even realize it is hot. Dendrites, cell bodies, axons, and synapses are the basic parts of a neuron, but other important structures and materials surround neurons to make them more efficient. Some axons are covered with myelin, a fatty material that wraps around the axon to form the myelin sheath.
This external coating functions as insulation to minimize dissipation of the electrical signal as it travels down the axon. This insulation is important, as the axon from a human motor neuron can be as long as a meter—from the base of the spine to the toes.
Periodic gaps in the myelin sheath are called nodes of Ranvier. The myelin sheath is not actually part of the neuron. Glia function to hold neurons in place hence their Greek name , supply them with nutrients, provide insulation, and remove pathogens and dead neurons. In the central nervous system, the glial cells that form the myelin sheath are called oligodendrocytes; in the peripheral nervous system, they are called Schwann cells. Neuron in the central nervous system : This neuron diagram also shows the oligodendrocyte, myelin sheath, and nodes of Ranvier.
There are three major types of neurons: sensory neurons, motor neurons, and interneurons. All three have different functions, but the brain needs all of them to communicate effectively with the rest of the body and vice versa. Sensory neurons are neurons responsible for converting external stimuli from the environment into corresponding internal stimuli. They are activated by sensory input, and send projections to other elements of the nervous system, ultimately conveying sensory information to the brain or spinal cord.
Unlike the motor neurons of the central nervous system CNS , whose inputs come from other neurons, sensory neurons are activated by physical modalities such as visible light, sound, heat, physical contact, etc. Most sensory neurons are pseudounipolar , meaning they have an axon that branches into two extensions—one connected to dendrites that receive sensory information and another that transmits this information to the spinal cord.
Multipolar and pseudounipolar neurons : This diagram shows the difference between: 1 a unipolar neuron; 2 a bipolar neuron; 3 a multipolar neuron; 4 a pseudounipolar neuron. Motor neurons are neurons located in the central nervous system, and they project their axons outside of the CNS to directly or indirectly control muscles. The interface between a motor neuron and muscle fiber is a specialized synapse called the neuromuscular junction. The structure of motor neurons is multipolar , meaning each cell contains a single axon and multiple dendrites.
This is the most common type of neuron. Located in the CNS, they operate locally, meaning their axons connect only with nearby sensory or motor neurons. Interneurons can save time and therefore prevent injury by sending messages to the spinal cord and back instead of all the way to the brain. Like motor neurons, they are multipolar in structure. The central nervous system CNS goes through a three-step process when it functions: sensory input, neural processing, and motor output.
The sensory input stage is when the neurons or excitable nerve cells of the sensory organs are excited electrically. Neural impulses from sensory receptors are sent to the brain and spinal cord for processing. After the brain has processed the information, neural impulses are then conducted from the brain and spinal cord to muscles and glands, which is the resulting motor output.
A neuron affects other neurons by releasing a neurotransmitter that binds to chemical receptors. The effect upon the postsynaptic receiving neuron is determined not by the presynaptic sending neuron or by the neurotransmitter itself, but by the type of receptor that is activated. A neurotransmitter can be thought of as a key, and a receptor as a lock: the key unlocks a certain response in the postsynaptic neuron, communicating a particular signal.
However, in order for a presynaptic neuron to release a neurotransmitter to the next neuron in the chain, it must go through a series of changes in electric potential. The action potential is a rapid change in polarity that moves along the nerve fiber from neuron to neuron.
In order for a neuron to move from resting potential to action potential—a short-term electrical change that allows an electrical signal to be passed from one neuron to another—the neuron must be stimulated by pressure, electricity, chemicals, or another form of stimuli. The level of stimulation that a neuron must receive to reach action potential is known as the threshold of excitation, and until it reaches that threshold, nothing will happen.
Different neurons are sensitive to different stimuli, although most can register pain. Action potentials : A neuron must reach a certain threshold in order to begin the depolarization step of reaching the action potential. This process of depolarization, repolarization, and recovery moves along a nerve fiber from neuron to neuron like a very fast wave. While an action potential is in progress, another cannot be generated under the same conditions.
In unmyelinated axons axons that are not covered by a myelin sheath , this happens in a continuous fashion because there are voltage-gated channels throughout the membrane. Saltatory conduction is faster than continuous conduction. The diameter of the axon also makes a difference, as ions diffusing within the cell have less resistance in a wider space. Damage to the myelin sheath from disease can cause severe impairment of nerve-cell function. In addition, some poisons and drugs interfere with nerve impulses by blocking sodium channels in nerves.
The amplitude of an action potential is independent of the amount of current that produced it. In other words, larger currents do not create larger action potentials. Therefore, action potentials are said to be all-or-none signals, since either they occur fully or they do not occur at all.
The frequency of action potentials is correlated with the intensity of a stimulus. This is in contrast to receptor potentials, whose amplitudes are dependent on the intensity of a stimulus. Reuptake refers to the reabsorption of a neurotransmitter by a presynaptic sending neuron after it has performed its function of transmitting a neural impulse.
Reuptake is necessary for normal synaptic physiology because it allows for the recycling of neurotransmitters and regulates the neurotransmitter level in the synapse, thereby controlling how long a signal resulting from neurotransmitter release lasts. The synapse is the site at which a chemical or electrical exchange occurs between the presynaptic and postsynaptic cells. The synapse is the junction where neurons trade information. It is not a physical component of a cell but rather a name for the gap between two cells: the presynaptic cell giving the signal and the postsynaptic cell receiving the signal.
There are two types of possible reactions at the synapse—chemical or electrical.
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