The Biological Bases of Behavior: The Neuron What is the nervous system?

Nervous system Is a complex communication network in which signals are constantly being transmitted, received and integrated. It handles information to and from the different parts of your body.

Nervous Tissue The nervous system is composed of two cells; glia and neurons. Glia cells are the glue that provide structural support, nourishment and insulation for neurons. Neurons are individual cells in the nervous system that receive, integrate and transmit information.

Structure of the Neuron The cell body or soma is the part that contains the cell nucleus and much of the chemical machinery common to most cells. Dendrites are the parts of a neuron that look like trees and are specialized to receive information. Most receive information from MANY cells, sometimes thousands so they have extensive dentritic systems.

The structure: continued The axon is a long thin fiber that transmits signals away from the soma to other neurons or to muscles or glands. They can be several feet long and can branch off to communicate with a number of other cells. They are wrapped in a myelin sheath, or a fatty white substance called myelin. It is an insulating material, derived from glia cells that encases the axons. It speeds up the transmission of signals that move along the axon. Without the sheath, signals are not sent effectively and there is a loss of muscle control (Multiple Sclerosis).

And more still…. The terminal buttons are small knobs located at the end of the neuron and are responsible for sending the signal on to other neurons through the secretion of chemicals called neurotransmitters. At the end of the terminal button is a gap known as a synapse. This is a junction where information is transferred from one cell to another. Neurotransmitters are used to carry the signal across the synapse to other neurons.

Absolute Refractory Period The absolute refractory period is the minimum length of time after an action potential during which another action potential cannot begin.

All-or-None Law Even though action potential are an all or nothing event, neurons can convey information about the strength of a stimulus. They do so by varying the rate at which they fire action potentials.

Sending Signals Two neurons do not actually touch. They are separated by the synaptic cleft, a microscopic gap between the terminal button of one neuron and the cell membrane of another neuron. The arrival of an action potential at an axon’s terminal buttons triggers the release of neurotransmitters- chemicals that transmit information from one neuron to another. The chemicals are stored in small sacs called synaptic vesicles. Once released, the neurotransmitters diffuse across the synaptic cleft to the membrane of the receiving cell.

Spindle Neurons New neurons of interest that are thought to be a part of the “old brain” and responsible for aspects of human responses such as sex, hunger, addictions and emotions. Far fewer than other types of neurons. Found using new technology.

Receiving Signals

Neurotransmitters Acetylcholine: (Ach) Acetylcholine is particularly important in the stimulation of muscle tissue. Contributes the regulation of attention, arousal and memory. The poison curare blocks transmission of acetylcholine. Some nerve gases inhibit the breakdown of acetylcholine, producing a continuous stimulation of the receptor cells, and spasms of muscles such as the heart. Norepinephrine: (NE) This compound is secreted principally from the adrenal gland. Contributes to the modulation of mood and arousal. Cocaine and amphetamines elevate activity at the NE synapses. Dopamine: (DA) Dopamine facilitates critical brain functions and voluntary movement, pleasurable emotions and, when unusual quantities are present, abnormal dopamine neurotransmission may play a role in Parkinson's disease (decreased levels), certain addictions, and schizophrenia (over activity). Cocaine and amphetamines elevate activity at the DA synapses.Parkinson's disease Serotonin: Involved in regulation of sleep and wakefulness, eating aggression. Serotonin is assumed to play a biochemical role in mood and mood disorders, including anxiety, depression, and bipolar disorder. Prozac and similar antidepressant drugs affect serotonin circuits.depression GABA: Serves as widely distributed inhibitory transmitter. Valium and similar anti-anxiety drugs work at GABA sites. Endorphins: Resemble opiate drugs in structure and effects. Contribute tot pain relief and perhaps to some pleasurable emotions.

Agonists and Antagonists An agonist is a chemical that mimics the action of a neurotransmitter i,.e.: Nicotine is an agonist for Ach and binds to the receptor site, fooling the body that Ach has been secreted and bound. An antagonist is a chemical that opposes the action a a neurotransmitter. For example: The drug curare is an antagonist for Ach and binds to the receptor site, blocking the action so the person cannot move.