Introduction
The nervous system functions are conducted by two types of neuron cells: the nerve cells (or neurons), which relay electrical or chemical information-carrying impulses between them or from one part of the body to another, and the glial cells.
The neurons are the primary type of cells of the central nervous system which support all of its functions and processes. On the other hand, the glial cells regulate homeostasis, in that way providing support and protection to the function of the neurons.
Based on the number of processes that branch out from the neuron cell body, neurons are classified as unipolar, bipolar, multipolar, and pseudopolar nerve cells. The multipolar nerve cells or neurons are the most common type of neurons located in the central nervous system, i.e. the brain and the spinal cord.
What Is the Difference Among the Multipolar, Unipolar, Bipolar, and Pseudopolar Nerve Cells?
Multipolar neurons have only one axon but several dendrites and dendritic branches. This neuronal structure provides the integration of abundant information received from the other synapsing neurons in the brain.
While unipolar nerve cells have only one structure that branches out from the soma, the bipolar nerve cells have a single axon and dendrite that protrudes from the soma.
As for the pseudopolar nerve cell, it has one cell element that stems from the soma and continues to branch into two separate cellular structures.
Which Types of Cells Are Included in the Multipolar Nerve Cell Class?
The multipolar class of nerve cells includes the following types:
- Motor neurons
- Interneurons
- Dogiel cells
- Ganglion cells
- Purkinje cells
- Pyramidal cells
Motor Neurons
The motor neurons are part of the peripheral nervous system of the brain. They carry impulses from the brain and spinal cord to skeletal muscles or glands, controlling and regulating the movements of both the arms and legs. This type of multipolar nerve cell has long axons that stem from the central nervous system and branch up to the muscles they innervate.
The motor nerve cells receive the sensory stimuli information from the neighboring neurons and relay it as a command to the muscles, organs, and glands. For instance, if we touch something hot, the motor neurons that synapse with the muscles in our fingers would inform the brain and command our fingers to release the grip on the hot item, preventing the fingers from being burned.
Interneurons
The interneurons can be located only in the central nervous system, i.e. the brain and spinal cord. Being the main processing cells in the brain, they receive the sensory information from either sensory nerve cells or interneurons, and relay the interpretation to the motor nerve cells or interneurons in order to trigger an action or reaction.
Upon touching something hot, some of these neurons would signal the motor neurons to command the finger muscles to release the hot item or inform the spinal cord of the perceived pain via the neurons in the brain.
Dogiel Cells
The dogiel cells are a type of multipolar neuronal cells located within the prevertebral sympathetic ganglia. These cells have a significant role in the enteric nervous system, which participates in the functions of the gastrointestinal system.
These types of multipolar nerve cells communicate through many neurotransmitters, such as acetylcholine, dopamine, and serotonin.
Ganglion Cells
The ganglion cells are the projection neurons of the vertebrate retina. As light rays enter the eyes, these cells provide us with vision, i.e. allow us to see the world that surrounds us by sending the visual information received from other retinal nerve cells to the dedicated processing center of the brain via their axons.
Purkinje Cells
These neurons are located in the cerebellar cortex of the brain, with massive outward-directed dendrites. They participate in the cognitive processes of the brain, as well as the motor control of the body.
Even though they receive sensory signals form hundreds of thousands of neuron cells, the Purkinje cells are the sole type of multipolar neuron cells that relay the electric signals from the cerebral cortex.
Pyramidal Cells
The pyramidal nerve cells are a type of multipolar neurons characteristic of the gray matter of the cerebral cortex. They receive both excitatory (glutamatergic) and inhibitory (GABAergic) inputs from the other neurons in the brain.
What Is the Structure and Function of the Multipolar Nerve Cell?
The multipolar nerve cells are composed of three or more fibers that are attached to the neuron cell bodies. One of the neuron fibers functions as the axon, transmitting the electrochemical impulses (action potentials) between the neuron cells. The fibers that remain are referred to as dendrites.
Together, the nerve cell body (or the perikaryon) and the dendrites comprise the receiving area of the multipolar neurons. The body of the multipolar nerve cells contains a nucleus made up of Nissl bodies.
The Perikaryon of the Multipolar Nerve Cells
This perikaryon refers to the cell body of the neuron that contains its nucleus. The nucleus of the multipolar nerve cell that is located in the center of the perikaryon has specific characteristics that are typical for any nuclei of a very active nerve cell.
Namely, it’s large, spherical in shape, and contains a little bit of condensed chromatin spreading along the sheath of the nucleus. The microtubules, actin filaments, and neurofilaments can also be found in the perikaryon.
The perikaryon also has special connection spots to the targeted multipolar neurons and glial cells.
The Nissl Bodies of the Multipolar Nerve Cells
This large, granular structure, found in the neurons, and produces and releases both proteins and amino acids, thus functioning as the basic protein-synthetic machinery of the cell. The ribosomes are the key constituents found in the Nissl bodies of the multipolar nerve cell.
Axons of the Nerve Cells
The axons of the multipolar nerve cells have an extensive length and are able to relay the action potential of neuron cells to the cortical structures. The axons are lined up with a multitude of Schwann cells. The neural impulses occur exclusively at the gaps located between the Schwann cells. This speeds up the relay of the electrical and chemical impulses that carry the sensory information.
The nerve cell axons differ from the dendrites in several ways:
- Unlike the dendrites that are often covered with spines, the axons tend to maintain the same diameter for most of their length and don’t have spines.
- The nerve cell axons stem from the cell body at a specialized area that’s labeled as the axon hillock.
- The nerve cell axons are covered with myelin that helps them convey the nerve impulse in a swift manner. On the other hand, myelin is never found on dendrites.
Finally, the endings of nerve cell axons branch profusely into many branches referred to as telodendria. These axon terminals create the synapses with the targeted neuron cells.
Synapses of the Nerve Cells
Brain synapses are functional connections between the neurons present in the central nervous system and peripheral nerves. A brain synapse is formed by membranes of a presynaptic neuron and a postsynaptic neuron, which may or may not be separated by a synaptic cleft.
Namely, the molecules of the neurotransmitter pass through the synapse and stimulate the receiving neuron to fire an impulse of its own (i.e. to pass the sensory information between two neurons via the axons). When the neurotransmitters diffuse across the synaptic cleft, they bind to the neuroreceptors in the postsynaptic membrane.
Synapses of the multipolar nerve cells provide synaptic connections between the neuron cell bodies that support the cognitive processes of learning and memory.
Dendrites of the Nerve Cells
The dendrites stem out from the multipolar nerve cell’s body. They can branch into additional first, second, and third-grade branches. Also, there are a number of protrusions that are labeled as dendritic thorns.
Both the receiving and processing of information gained from the sensory stimuli takes place in the dendrites and the multipolar nerve cell body. Those received signals can be either excitatory (they trigger the neuron to fire, i.e. to generate an electrical impulse), or inhibitory (they tend to prevent the neuron from firing an electrical impulse).
What Is the Main Function of the Multipolar Nerve Cell?
By consolidating the data from numerous neurons, the multipolar nerve cells allow for the integration of a significant amount of information gained from other neurons.
Namely, the multipolar nerve cells relay the chemical or electrical signals through the cell body via specialized structures such as dendrites, axons, and synapses. Since they are characterized by numerous dendrites and a single axon, the large number of dendrites and dendritic branches have a very active role in processing a large quantity of information received from the sensory stimuli.
Fun Facts
Did you know?
- Without a constant stimulation of the targeted neuron cell, the synapse cannot be supplied with sufficient neurotransmitting molecules in order to transmit the information-carrying impulse across the synaptic cleft.
- The neuron cells have their small ‘antennas’ labeled as filopodia that support cell migration and speed up the wound healing processes.
- When an axon connects with the dendrites of the same neuron cell, it’s referred to as an auto synapse.
- The human brain consists of more than 100 billion neurons, while it weighs only 1.4 kilograms approximately.
- The term telodendria originates from the Greek language, meaning “end of a tree”.
- The Nissl substance (or Nissl bodies) are named after the Heidelberg neurologist Franz Nissl.
- The Russian anatomist and physiologist Alexandre Dogiel (1852–1922) discovered the dogiel nerve cells.
- The human retina consists of over a million ganglion cells.
- The pyramidal cells are connected to each other via recurrent glutamatergic synapses.
- Santiago Ramón y Cajal is the first neuroscientist who discovered and studied the pyramidal neurons.