neuron

Examples of neuron 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

• Introducing the Neuron

  • The brain is made up entirely of neurons and glial cells, which are non-neuronal cells that provide structure and support for the neurons.
  • There are three primary types of neuron: sensory neurons, motor neurons, and interneurons.
  • Although some neurons do not have any dendrites, other types of neurons have multiple dendrites.
  • There are three major types of neurons: sensory neurons, motor neurons, and interneurons.
  • This diagram shows the difference between: 1) a unipolar neuron; 2) a bipolar neuron; 3) a multipolar neuron; 4) a pseudounipolar neuron.

• Neurons

  • A human brain contains around 86 billion neurons.
  • While some neurons have no dendrites, other types of neurons have multiple dendrites.
  • Neurons usually have one or two axons, but some neurons, like amacrine cells in the retina, do not contain any axons.
  • Dendrites from a single neuron may receive synaptic contact from many other neurons.
  • Multipolar neurons are the most common type of 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.

• Signal Summation

  • Signal summation occurs when impulses add together to reach the threshold of excitation to fire a neuron.
  • Each neuron connects with numerous other neurons, often receiving multiple impulses from them.
  • One neuron often has input from many presynaptic neurons, whether excitatory or inhibitory; therefore, inhibitory postsynaptic potentials (IPSPs) can cancel out EPSPs and vice versa.
  • If the neuron only receives excitatory impulses, it will also generate an action potential.
  • A single neuron can receive both excitatory and inhibitory inputs from multiple neurons.

• 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.

• Preganglionic Neurons

  • The ANS is unique in that it requires a sequential two-neuron efferent pathway; the preganglionic neuron must first cross a synapse onto a postganglionic neuron before innervating the target organ.
  • The preganglionic, or first neuron will begin at the outflow and will cross a 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 where preganglionic neurons create synapses with their postganglionic neurons:
  • These are the preganglionic neurons that synapse with the postganglionic neurons in these locations :

• 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.