Neurons

(noun)

Electrically excitable cells that are the structural unit of the nervous system.

Related Terms

Examples of Neurons in the following topics:

  • Classification of Neurons

    • Afferent neurons convey information from tissues and organs into the central nervous system (e.g. sensory neurons).
    • Efferent neurons transmit signals from the central nervous system to the effector cells (e.g. motor neurons).
    • Another way in which neurons are classified is by their effect on target neurons.
    • A neuron releases a neurotransmitter that binds to chemical receptors on the target neuron .
    • Other types of neurons include excitatory motor neurons in the spinal cord that release acetylcholine, and inhibitory spinal neurons that release glycine.

  • Structural Diversity of Neurons

    • A typical neuron consists of a cell body and neuronal processes such as dendrites and axon.
    • These extensions are the conducting region of the neuron.
    • The cell body is the major biosynthetic center of the neuron.
    • Interneurons act as relays between neurons in close proximity to one another.
    • 1: Unipolar neuron, 2: Bipolar neuron, 3: Multipolar neuron, 4: Pseudounipolar neuron

  • Organization of the Nervous System

    • The nervous system is a network of cells called neurons that coordinate actions and transmit signals between different parts of the body.
    • Central to the functioning of the nervous system is an extensive network of specialized cells called neurons.
    • The peripheral nervous system (PNS) consists of sensory neurons, motor neurons, and neurons that communicate either between subdivisions of the PNS or connect the PNS to the CNS .
    • Central neurons, which in humans greatly outnumber the sensory and motor neurons, make all of their input and output connections with other neurons.
    • Electrical impulses travel along the axon of a neuron.

  • Clusters of Neuronal Cell Bodies

    • A nucleus can either by a relatively compact collection of neurons or a distinctly identifiable group of neurons spread over a large area.
    • In the peripheral nervous system, a cluster of neurons is called a ganglion.
    • Ganglia are composed mainly of neuron cell bodies (somata) and dendritic structures.
    • Satellite glial cells (SGCs) also surround neuron cell bodies within ganglia.
    • They supply nutrients to the surrounding neurons and also have some structural function.

  • Preganglionic Neurons

    • The ANS is unique in that it requires a sequential two-neuron efferent pathway; the preganglionic neuron must first synapse onto a postganglionic neuron before innervating the target organ.
    • The preganglionic, or first neuron will begin at the "outflow" and will synapse at the postganglionic, or second neuron's cell body.
    • These cell bodies are GVE (general visceral efferent) neurons and are the preganglionic neurons.
    • There are several locations upon which preganglionic neurons can synapse with their postganglionic neurons:
    • These are the preganglionic neurons, which synapse with postganglionic neurons in these locations :

  • The Synapse

    • A synapse is a structural junction that mediates information transfer from one neuron to the next or from one neuron to an effector cell as in muscle or gland.
    • The neuron conducting impulses towards the synapse is called presynaptic neuron.
    • The neuron transmitting the electrical impulse away from the synapse is called postsynaptic neuron.
    • At a synapse , the presynaptic neuron sends information and postsynaptic neuron receives the information.
    • Most neurons, function as both as presynaptic and postsynaptic neurons.

  • Types of Nervous Tissue

    • They also help in the guiding the migration of young neurons.
    • Astrocytes control the chemical environment around the neurons.
    • Neurons consist of cell body and one or more slender processes.
    • Arm like processes extend from the cell body to all neurons.
    • Dendrites are motor neurons that are short and have a large surface area for receiving signals from other neurons.

  • Organization of Motor Neuron Pathways

    • There are upper and lower motor neurons in the corticospinal tract.
    • These are the upper motor neurons of the corticospinal tract.
    • These axons also synapse with lower motor neurons in the ventral horns.
    • The midbrain nuclei include four motor tracts that send upper motor neuronal axons down the spinal cord to lower motor neurons.
    • The lateral tract contains upper motor neuronal axons that synapse on dorsal lateral lower motor neurons, which are involved in distal limb control.

  • Components of a Reflex Arc

    • A reflex arc defines the pathway by which a reflex travels, from the stimulus to sensory neuron to motor neuron to reflex muscle movement.
    • Most reflex arcs involve only three neurons.
    • This travels to the spinal cord where it passes, by means of a synapse, to a connecting neuron called the relay neuron situated in the spinal cord.
    • When a reflex arc consists of only two neurons, one sensory neuron, and one motor neuron, it is defined as monosynaptic.
    • It causes stimulation of sensory, association, and motor neurons.

  • Neuroglia of the Central Nervous System

    • Their numerous radiating processes cling to neurons and their synaptic endings.
    • They support and brace the neurons and anchor them to their nutrient supply lines.
    • They also play an important role in making exchanges between capillaries and neurons.
    • Microglial cells are small and have thorny processes that can touch the neighboring neurons.
    • They are also able to monitor the health of neurons by detecting injuries to the neuron.