Signals related to sensation, muscle control, and cognition move through neurons, which are are excitable cells found in the central nervous system, the peripheral nervous system, and the enteric nervous system. Excitable cells are cells which can be stimulated to create a small electric current. A neuron is generally comprised of a cell body (Soma), and projecting input structures (dendrites) and an output structure (axon). Neurons connect to other neurons at synapses, as well as to muscle cells and glands, and some neurons receive inputs from sensory receptors. There may also be dendritic spines on dendrites for receiving signals from synapses. Output signals start at the beginning of an axon, the axon hillock, as an action potential (a momentary change or spike in the electrical potential at a point on the cell membrane of the neuron), which is then propagated along the axon to an end structure, an endfoot or bouton..

The movement of a signal through a neuron involves being received, processed with regard to other signals, and output to other neurons at synapses, or to muscles or glands. Signals move through different parts of a neuron in different ways.

Neurons

Characteristics

Neurons are excitable cells
Neurons connect with other neurons
Neurons remember

Structure

Neurons have a main cell body called a Soma, with input projections called Dendrites, and an output projection called an Axon. The dendrites have smaller projections studding them called dendritic spines. The axon projects from a swelling on the soma called the axon hillock, has a length which may split into collaterals, and ends in an end foot (bouton, or end terminal).

Types

Unipolar
bipolar
psuedo-unipolar
multi-polar

Reception of a Signal

at a Synapse

A synapse is a multi-part structure comprised of the end of one neuron (the axon terminal), the beginning of another (usually a dendrite, though there are axosomatic and axoaxonic synapses also), and the space in between the two (synaptic cleft). This gap is about 20-30 nanometers wide & filled with fluid. http://www.albany.edu/faculty/cafrye/apsy601/Ch.04feb10,psychopharmacology.html Signals are sent from an axon terminal into the synaptic cleft on the receipt of a signal reaching the terminal, which opens calcium pores in the terminal which cause small packets of neurotransmitters called vesicles to fuse to the end of the terminal's membrane and release quantities of neurotransmitters into that cleft. As those neurotransmitters diffuse across that cleft, they reach and then bind to sites on receptors embedded in the membrane of another neuron. (note: diffusion time, and synaptic adhesion molecules, and CITATIONS!) http://www.ncbi.nlm.nih.gov/books/NBK21521/

The receptors are protein molecules whose structures span the neuron membrane, from the outside of the cell through the membrane to the inside of the neuron, and are like a tunnel and a cave, where the cave is the receptor site on the outside of the neuron, and the tunnel is the pore starting on the outside, going through the membrane, and exiting in the inside. (The cave and the tunnel are all one molecular structure.)

The relation of a neurotransmitter and its receptor site is like that of a key and a lock, in that the shape of the inside surface of the receptor site is the opposite of some part of the neurotransmitter, such that part of the neurotransmitter fits into the receptor site like a key into a lock, or a hand into a glove. When a neurotransmitter fits into a receptor site, the molecules of the part of the neurotransmitter in the receptor site are in such close proximity to parts of the receptor site that intermolecular forces act on the receptor site and its connected pore, causing the pore to be twisted into an alternative stable shape in which the pore is opened to the passage of ions through it.

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at a Sensory Receptor

Passage to & through Soma to Axon Hillock

to test for the table of contents

electrotonic conduction

just a test to see if watchlist shows changes in bold

info about refractory period : http://www.physiologyweb.com/lecture_notes/neuronal_action_potential/neuronal_action_potential_refractory_periods.html