Download The Biological Bases of Behavior: The Neuron

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.
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.
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.