THE NEURON
things? , what is its function?
what is neuron? the neuron is the fundamental cellular unit of our nervous system, it has the function of RECEIVE , INTEGRATE and TRANSMIT nerve impulses. In neurons THERE IS NO MITOSIS or cell division (reproductive phase of the cell cycle), but they can assume different sizes and have various types like other cells.
Structure:
Cell body
Dendrites
Axon or Neuritis
Types of Neurons
A. Sensitives ( afferent fibers) participate in the acquisition of stimuli, transporting information from the sensory organs to the central nervous system -> external signal transduction (mechanical, thermal, electromagnetic, chemical, nociceptive stimuli)
B. Motors (efferent fibers) emit motor-type impulses to the organs of the body periphery • Somatomotors (innervate smooth striated muscles) + Visceroeffectors
C. . Interneurons within the central system, integrate data provided by sensory neurons and transmit them to motor neurons
SIGNAL TRANSMISSION
Neurons are excitable cells specialized in receiving stimuli and conducting electrical impulses from nerves and are used to transmit information to other parts of the body.
From the dendrites , electrical impulses integrate at the axonal cone . If they exceed a threshold level, an action potential (electrical impulse) is triggered which travels along the axons and releases neurotransmitters which activate adjacent neurons (chemical synapses).
CHEMICAL SYNAPSE
In chemical synapses, the action potential of the presynaptic cell determines the release of neurotransmitter molecules that bind to specific receptors located in the postsynaptic cell. The interaction between neurotransmitter and receptor determines a variation of potential inside the cell (depolarization or hyperpolarization) which allows a passage of the message or nerve impulse from one neuron to another.
A neurotransmitter is a chemical mediator that allows nerve impulses to pass from one cell to another. Most neurons release more than one neurotransmitter
CHEMICAL SYNAPSE: the transmission
Type of Neurons and Transmission Speed
There are two types of neurons: myelinated and unmyelinated. Myelin is a protective sheath of insulating material that surrounds some axons.
It envelops the neuron fiber and, thanks to its high lipid content, acts as an electrical insulator, avoiding the dispersion of charges during the PA transmission process. This allows the nerve impulse to travel more rapidly along the axonal fiber.
On the basis of the presence or absence of myelin sheath, nerve fibers without myelin sheath can therefore be distinguished, which are generally of small diameter with low speed conduction of the nerve stimulus and nerve fibers with myelin sheath, usually of large diameter , with high speed of conduction of the stimulus. Axon fibers insulated by myelin can transmit electrical messages at a rate of 90 meters per second, while fibers without myelin can send messages at a rate of only one or two meters per second.
Conduction of the stimulus in a myelin fiber is called saltatory type since the impulse travels/JUMPS between the myelin-coated tracts separated by axonal portions devoid of myelin and rich in voltage-dependent sodium and potassium channels (nodes of Ranvier) in which pulse regeneration takes place.