The cells in the nervous system
fall into two major categories:
Glia and Neurons
Neurons are individual cells in the
nervous system that receive,
integrate, and transmit information
Glia's are cells found throughout the
nervous system that provide various
types of support for neutrons
Soma: (Greek for body) contains the
cell nucleus and much of the chemical
machinery common to most cells
Dendrites: (Greek for tree) are the parts of the
neurone that are specialized to receive information
Axon: (Greek for axle) is a long, thin fibre that transmits signals
away from the soma to other neurons or to muscles or glands
Myelin sheath is insulting material,
derived from glial cells, that encases
some axons
The axon ends in a cluster of terminal buttons,
which are small knobs that secrete chemicals
called neurotransmitters
Synapse: (Greek word for junction) is where
information is transmitted from one neurone to
another
THE
NEURAL
IMPULSE
The resting
potential of a
neurone is its
stable, negative
charge when the
cell is inactive
When the neurone is stimulated, for an
instant its charge is less negative, or even
positive creating an action potential
Action Potential: very brief shift in the neurones
electrical charge that travels along a axon
The absolute refectory
period is the minimum
length of time after an
action potential during
which another action
potential cannot begin
Various neurones transmit neural
impulses at different speeds.
EXAMPLE: thicker axons transmit
neural impulses more rapidly
than thinner ones do
THE SYNPSE: WHERE
NEURONES MEET
Transmissions take place at special junctions, which
depend on chemical messengers
Sending signals: chemicals as couriers
Synaptic cleft, a gap between the terminal button of one
neurone and the cell membrane of another neurone
Signals have to cross the gap to permit neurones to
communicate. The neurone that sends a signal across
the gap is called the presynaptic neurone
The arrival of an action potential at an axons terminal buttons triggers the release of
neurotransmitters (chemicals that transmit information from one neurone to another)
Receiving signals:
Postsynaptic potentials
They vary in size and they
increase or decrease the
probability of a neural
impulse in the receiving cell
in proportion to the amount
of change in voltage
When a neurotransmitter and a
receptor molecule combine,
reactions in the cell membrane cause
a postsynaptic potential (PSP)
PSP: a voltage change at a
receptor site on a
postsynaptic cell membrane
Two types of messages that
can be sent from cell to cell:
Excitatory and Inhibitory
Excitatory psp: a
positive voltage
shift that
increases the
likelihood that
the postsynaptic
neurone will fire
action potentials
Inhibitory psp: a negative voltage shift
that decreases the likelihood that the
postsynaptic neurone will fire action
potentials
NEUROTRANSMITTERS
Acetylcholine: activates motor
neurones controlling skeletal
muscles
Contributes to the regulation of
attention, arousal, and memory
Some ACh receptors
stimulated by nicotine
Dopamine: contributes to
control of voluntary movement,
pleasurable emoticons
Decreased levels
associated with
Parkinson's
disease
Overactivity at DA
synapses
associated with
schizophrenia
Cocaine and
amphetamines
elevate activity at
DA synapses
Norepinephrine:
Contributes to
modulation of mood
and arousal
Cocaine and
amphetamines
elevate activity at
NA synapses
Serotonin: involved in
regulation of sleep and
wakefulness, eating,
aggression
Abnormal levels may
contribute to depression and
obsessive compulsive
disorder
Prozac and similar depressant drugs affect serotonin circuits
GABA: serves as widely
distributed inhibitory
transmitter
Valium and similar
anti anxiety drugs
work at GABA
synapses
Endorphines: resemble opiate
drugs on structure and effects
Contribute to pain relief
and perhaps to some
pleasurable emotions
Glutamate: an amino
acid that has both
excitatory and inhibitory
effects. It has been
implicated in learning
and memory
THE NERVOUS SYSTEMS
The peripheral nervous
system: its made up of all
those nerves that lie outside
the brain and spinal cord. (It
can be divided into the
somatic nervous system and
the autonomic nervous
system)
The somatic nervous system: its made up of
nerves that connect to voluntary skeletel
muscles and to sensory receptors
The autonomic nervous
systems: Its made up of
nerves that connect to
the heart, blood vessels,
smooth muscles and
glands (It can be
subdivided into two
branches)
The sympathetic branch mobilizes bodes recourses for emergencies
The parasympathetic branch generally conserves bodily recources
The central nervous system:
consists of the brain and
spinal cord
(its bathed in its own special nutritive
soup called "the cerebrospinal fluid")
THE BRAIN
The hindbrain: it includes the cerebellum and two structures found in
the lower part of the brain stem: the medulla and the pons
The medulla which attaches to the spinal cord,
is in charge of largely unconscious but vital
functions
The pons includes a
bridge of fibres that
connects the brainstem with the
cerebellum
The cerebellum is a large and
deeply folded structure
located adjacent to the back
surface of the brainstem (its
critical to the coordination of
movement and to the sense
of equilibrium, or physical
balance)
The midbrain: segment of the brainstem
that lies between the hindbrain and the
forebrain. It contains an area that is
concerned with integrating sensory
processes
The forebrain: largest and most complex region of the
brain, encompassing a variety of structures, including
the thalamus, hypothalamus,limbic system, and
cerebrum
The thalamus: a
structure through
which all sensory
information (except
smell) must pass to
get to the cerebral
cortex
The
hypothalamus:
a structure that
is involved in
the regulation
of basic
biological drives
related to
survival
The limbic system:
involved in the
regulation of emotion,
memory, and
motivation, and
recently it has been
linked to the tendency
of some people to be
optimistic in their
approach to life
The cerebrum:
the brain areas
that are
responsible for
the most
complex mental
activities,
including
learning,
remembering,
thinking, and
consciousness
itself
BASIC
PRINCIPLES
OF
GENETICS
Chromosomes
are strands of
DNA molecules
that carry
genetic
information
Every cell in
humans (except
sex cells)
contain 46
chromosomes.
They operate in
23 pairs, with
one
chromosome of
each pair being
contributed by
each parent
Fertilization create a zygote: a
single cell formed by the union of
a sperm cell and an egg
Genes are DNA segments that serve as they
key functional units in heredity transmission
A dominant gene one
that is expressed
when paired genes are
different.
A recessive gene is one
that is masked when
paired genes are different
Genotype refers to a persons genetic makeup
Phenotype refers to the ways in which a
persons genotype is manifested in observable
characteristics
Polygenic traits, or characteristics are
influenced by more than one pair of
genes
INVESTIGATING
HEREDITARY
INFLUENCE:
RESEARCH
METHODS
Family studies:
researchers assess
hereditary influence
by examining blood
relatives to see how
much they resemble
one another on a
specific trait
Family studies can indicate whether a
trait runs in families
Can also offer useful insights
about the possible impact of
heredity
Twin studies: researchers
assess hereditary influence
by comparing the
resemblance of identical
twins and fraternal twins
with respect to a trait
Identical twins emerge
from on zygote that splits
for unknown reasons
Fraternal twins result when two eggs
are fertilized simultaneously by
different sperm cells, forming two
separate zygotes
Adoption studies: researchers assess
hereditary influence by examining the
resemblance between adopted
children and both their biological and
their adoptive parents
If adopted children
reusable their biological
parents in a trait, even
though they were not
raised by them, genetic
factors probably influence
that trait
If adopted children
resemble their
adoptive parents,
even though they
inherited no genes
from them,
environmental
factors probably
influence the trait