Overview of Neuron Structure and Function - Molecular Cell Biology - NCBI Bookshelf
tional wisdom about the relationships between neuronal structure and function. In addition, recent advances in single cell staining techniques now allow. In this video lesson, you'll learn about neurons, which are specialized cells in the nervous system. Check out how far neurons can send signals. These unique functions have forced the neuron to adopt a cell structure unlike Neurons comprise a cell body (or soma), dendrites, and an axon that ends at a.
These include nerve cells or neurons and glial cells or glia. Neurons are the basic functional units of the nervous system, and they generate electrical signals called action potentials, which allow them to quickly transmit information over long distances.
Relationships between neuronal structure and function.
Glia are also essential to nervous system function, but they work mostly by supporting the neurons. In this article, we'll take a closer look at neurons, glia, and nervous systems. We'll see how the structure of neurons supports their function, and how they can be organized into circuits that process information and generate a response. The human nervous system In humans and other vertebrates, the nervous system can be broadly divided into two sections: The central nervous system CNS consists of the brain and the spinal cord.
It is in the CNS that all of the analysis of information takes place. The peripheral nervous system PNSwhich consists of the neurons and parts of neurons found outside of the CNS, includes sensory neurons and motor neurons. Diagram of the human nervous system. Also marked on the diagram are ganglia, clusters of cell bodies bodies in the PNS, and nerves, bundles of axons that travel along the same route.
The marked ganglia are located near, but not in, the spinal cord. The marked nerves are spinal nerves. These motor neurons have long extensions axons that run from the CNS all the way to the muscles they connect with innervate.
The cell bodies of other PNS neurons, such as the sensory neurons that provide information about touch, position, pain, and temperature, are located outside of the CNS, where they are found in clusters known as ganglia. The axons of peripheral neurons that travel a common route are bundled together to form nerves.
Classes of neurons Based on their roles, the neurons found in the human nervous system can be divided into three classes: Sensory neurons Sensory neurons get information about what's going on inside and outside of the body and bring that information into the CNS so it can be processed.
For instance, if you picked up a hot coal, sensory neurons with endings in your fingertips would convey the information to your CNS that it was really hot. Motor neurons Motor neurons get information from other neurons and convey commands to your muscles, organs and glands.
For instance, if you picked up a hot coal, it motor neurons innervating the muscles in your fingers would cause your hand to let go. Interneurons Interneurons, which are found only in the CNS, connect one neuron to another. They receive information from other neurons either sensory neurons or interneurons and transmit information to other neurons either motor neurons or interneurons.
Relationships between neuronal structure and function.
For instance, if you picked up a hot coal, the signal from the sensory neurons in your fingertips would travel to interneurons in your spinal cord. Some of these interneurons would signal to the motor neurons controlling your finger muscles causing you to let gowhile others would transmit the signal up the spinal cord to neurons in the brain, where it would be perceived as pain. Interneurons are the most numerous class of neurons and are involved in processing information, both in simple reflex circuits like those triggered by hot objects and in more complex circuits in the brain.
It would be combinations of interneurons in your brain that would allow you to draw the conclusion that things that looked like hot coals weren't good to pick up, and, hopefully, retain that information for future reference. The basic functions of a neuron If you think about the roles of the three classes of neurons, you can make the generalization that all neurons have three basic functions. Receive signals or information.
Integrate incoming signals to determine whether or not the information should be passed along.
Communicate signals to target cells other neurons or muscles or glands. These neuronal functions are reflected in the anatomy of the neuron. Anatomy of a neuron Neurons, like other cells, have a cell body called the soma. The nucleus of the neuron is found in the soma.
Neurons need to produce a lot of proteins, and most neuronal proteins are synthesized in the soma as well. Various processes appendages or protrusions extend from the cell body. These include many short, branching processes, known as dendrites, and a separate process that is typically longer than the dendrites, known as the axon. Dendrites The first two neuronal functions, receiving and processing incoming information, generally take place in the dendrites and cell body.
Incoming signals can be either excitatory — which means they tend to make the neuron fire generate an electrical impulse — or inhibitory — which means that they tend to keep the neuron from firing. Most neurons receive many input signals throughout their dendritic trees.
A single neuron may have more than one set of dendrites, and may receive many thousands of input signals. Whether or not a neuron is excited into firing an impulse depends on the sum of all of the excitatory and inhibitory signals it receives.
If the neuron does end up firing, the nerve impulse, or action potential, is conducted down the axon.
Structure of a neuron. At one end of the cell body and indeed, around most of its periphery are many small, branching protrusions called dendrites. Extending from the other end of the cell body at a location called the axon hillock is the axon, a long, thin, tube-like protrusion. The axon is wrapped in myelin, which ensheathes some sections but leaves sections of the axon bare between the sheathed portions. At its far end, the axon splits up into many axon terminal.
Each forms a synapse with a dendrite or cell body of another neuron. The cell to which the axon terminal belongs sending cell is called the presynaptic cell, while the cell to which the dendrite or cell body belongs receiving cell is called the postsynaptic cell.
There is a space between the two cells, across which they communicate. The neuron is the integral element of our five senses and of countless other physical, regulatory, and mental faculties, including memory and consciousness.
A neuron consists of a nerve cell body or somaan elongated projection axonand short branching fibers called dendrites. Neurons receive nerve signals action potentialsintegrate action potentials, and transmit these signals to other neurons or effector organs, such as muscles and glands. The structure and function of neurons is essentially the same in all animals, although the human nervous system is much more specialized and complicated than that of lower animals.
Humans are born with a large, but finite, supply of neurons and those cells that are lost through aging, injury, or disease cannot be replaced. The unique morphological and intercellular structure of the neuron is dedicated to the efficient and rapid transmission of neural signals.
Within the neuron, the neural signal travels electrically. At the synapsethe gap between neurons, neural signals are conveyed chemically by a limited number of chemicals termed neurotransmitters. Such circuits allow an organism to respond to a sensory input by the coordinated action of sets of muscles that together achieve a single purpose. However, such simple nerve systems do not directly explain higher-order brain functions such as reasoning and computation.
Figure The knee-jerk reflex arc in the human. Positioning and movement of the knee joint are accomplished by two muscles that have opposite actions: Contraction of the quadriceps muscle straightens the leg, whereas contraction of the biceps muscle bends the more The sensory and motor neurons of circuits such as the knee-jerk reflex are contained within the peripheral nervous system Figure These circuits send information to and receive information from the central nervous system CNSwhich comprises the brain and spinal cord and is composed mainly of interneurons.
Highly specialized sensory receptor cells, which respond to specific environmental stimuli, send their outputs either directly to the brain e. The peripheral nervous system contains two broad classes of motor neurons. The somatic motor neurons stimulate voluntary muscles, such as those in the arms, legs, and neck; the cell bodies of these neurons are located inside the central nervous systemin either the brain or the spinal cord.
The autonomic motor neurons innervate glands, heart muscle, and smooth muscles not under conscious control, such as the muscles that surround the intestine and other organs of the gastrointestinal tract. The two classes of autonomic motor neurons, sympathetic and parasympathetic, generally have opposite effects: Somatic sensory neurons, which convey information to the central nervous system, have their cell bodies clustered in gangliamasses of nerve tissue that lie just outside the spinal cord.
The cell bodies of the motor neurons of the autonomic nervous system also lie in ganglia. Each peripheral nerve is actually a bundle of axons; some are parts of motor neurons; others are parts of sensory neurons. Figure A highly schematic diagram of the vertebrate nervous system.
Neuron - Structure And Function, Structural Classification, Glial Cells, Functional Classification
The central nervous system CNS comprises the brain and spinal cord. It receives direct sensory input from the eyes, nose, tongue, and ears. The peripheral nervous system PNS comprises three more Having surveyed the general features of neuron structure, interactions, and simple circuits, let us turn to the mechanism by which a neuron generates and conducts electric impulses. SUMMARY The cell body of a neuron contains the nucleus and lysosomes and is the site of synthesis and degradation of virtually all neuronal proteins and membranes.
Axons are long processes specialized for the conduction of action potentials away from the neuronal cell body.
- Overview of neuron structure and function
Action potentials are sudden membrane depolarizations followed by a rapid repolarization. They originate at the axon hillock and move toward axon terminals, where the electric impulse is transmitted to other cells via an electric or chemical synapse see Figure Most neurons have multiple dendrites, which receive chemical signals from the axon termini of other neurons.
When an action potential reaches a chemical synapsea neurotransmitter is released into the synaptic cleft.