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CELLS OF THE NERVOUS
SYSTEM - - -
Nervous System

Composed of two basic cell types:
Glial Cells: provide scaffolding on which the
nervous system is built, help neurons line up
closely with each other to allow neuronal
communication, provide insulation to neurons,
transport nutrients and waste products, and mediate
immune responses.
1:1 ratio of glia cells to neurons.
Neurons: interconnected information processors
that are essential for all of the tasks of the nervous
system. This
NEURON STRUCTURE
Neurons: Central building blocks; 100 b strong at birth
PARTS
Semipermeable Membrane: neuron’s outer surface; allows
smaller molecules and without electrical charge to pass
through it
Soma: cell body, contains the
nucleus of the neurons
Dendrites: branching extensions of
soma; serve as input sites where
signals are received from other
neurons
Neuron: small info. Processor
Axon: major extension of soma;
ends at multiple terminals
Synaptic vesicles: contained by
terminals that house
neurotransmitters
Neurotransmitters: chemical
messengers of the nervous system
Myelin Sheath: fatty substance w/c
coats the axon and acts as an insulator, increasing the speed at
w/c the signal travels; crucial for normal operation of the
neurons
Nodes of Ranvier: gaps in the myelin sheath
Synaptic Cleft: small space bn 2 neurons and imp. Site where
communication bn neurons occurs
Receptors: proteins on the cell surface where neurotransmitters
attach
How does a neurotransmitter “know” which receptor
to bind to? The neurotransmitter and the receptor
have what is referred to as a lock-and-key
relationship—specific neurotransmitters fit specific
receptors similar to how a key fits a lock. The
neurotransmitter binds to any receptor that it fits.
signal that passes through the neuron depends on the intra- and
extracellular fluids being electrically different.
- Membrane potential: diff in charge across the membrane
provides energy for the signal
- Electrical charge: caused by charged molecules (ions)
dissolved in the fluid
- Semipermeable nature of the neuronal membrane somewhat
restricts the movement of these charged molecules
- Resting potential: state of readiness of the neuron
- In the resting state, sodium (Na+) is at higher
concentrations outside the cell - move into the cell.
- Potassium (K+): more concentrated inside the cell
- move out of the cell
- Neuron state changes abruptly after receiving signal
- Neuron receives signals at the dendrites → small pores open
on the neuronal membrane → Na+ ions, propelled by charge
and concentration differences move into the cell → influx of
positive ions → internal charge of the cell becomes more
positive → charge reaches a certain level ( threshold of
excitation ) → the neuron becomes active → action potential
begins.
- Additional pores open → massive influx of Na+ ions →
positive spike in the membrane potential, the peak action
potential → peak of the spike → the sodium gates close →
potassium gates open. Positively charged potassium ions leave
→ the cell quickly begins repolarization.
- At first, it hyperpolarizes → become slightly more negative
than the resting potential → levels off → return to resting
potential.
Action Potential
- constituted by the positive spike
- the electrical signal that typically moves from the cell body
down the axon to the axon terminals.
Electrical signal moves down the axon with the impulses jumping between the
Nodes of Ranvier
↓
At each point, some of the sodium ions that enter the cell diffuse to the next
section of the axon
↓
Charge raises past the threshold of excitation and triggering a new influx of
sodium ions
↓
The action potential moves all the way down the axon in this fashion until
reaching the terminal buttons.
NEURONAL COMMUNICATION
- Neuron exists in a fluid environment- surrounded by
extracellular fluid and contains intracellular fluid. The
neuronal membrane separates the 2 fluids- electrical
- all or none phenomenon
-this means that an incoming signal from another neuron is
either sufficient or insufficient to reach the threshold of
excitation. There is no in-between, and there is no turning off
an action potential once it starts.
- the action potential is recreated, or propagated, at its full
strength at every point along the axon.
- Explains the fact that your brain perceives an injury to a
distant body part like your toe as equally painful as one to your
nose
- Action potential arrives at terminal→ synaptic vesicles
release neurotransmitters → neurotrans travels across synapse
→ binds to receptors on
dendrites → process
repeats in the neuron →
signal delivered →
excess neurotrans in
synaptic cleft drift away
→ broken into inactive
fragments → or reabsorbed in reuptake process
- Reuptake: neurotransmitter being pumped back into the
neuron that released it to clear the synapse
-Clearing the synapse serves both to provide a clear “on” and
“off” state between signals and to regulate the production of
neurotransmitter
Neuronal communication is often referred to as an electrochemical
event. The movement of the action potential down the length of the
axon is an electrical event, and movement of the neurotransmitter across
the synaptic space represents the chemical portion of the process.
NEUROTRANSMITTERS AND DRUGS
- diff. types of neurotransmitters are released by diff. Neurons
- biological perspective: focus on physiological causes of
behavior
- Psychotropic medications: drugs that treat psychiatric
symptoms by restoring neurotransmitter balance
Major Neurtransmitters And How they Affect Behavior
Neurotransmitter
Involved in
Potential Effect on
Behavior
Acetylcholine
Muscle action,
Increased arousal,
memory
enhanced cognition
Beta-endorphine
Pain, pleasure
Decreased anxiety
and tension
Dopamine
Mood, sleep,
Increased pleasure,
learning
suppressed appetite
Gamma-aminobutyric Brain function, sleep Decreased anxiety
acid (GABA)
and tension
Glutamate
Memory, learning
Increased learning,
enhanced memory
Norepinephrine
Heart, intestines,
Increased arousal,
alertness
suppressed appetite
Serotonin
Mood, sleep
Modulated mood,
suppressed appetite
Psychoactive drugs: acts as antagonists or agonists for a given
neurotransmitter
: represent drugs that are prescribed to correct imbalance

Agonists - chemical that mimic a neurotransmitter at the
recepor site

Antagonists - blocks or impedes the normal activity of a
neurotransmitter at the receptor
Example:
PARKINSON’S DISEASE
- progressive nervous system disorder
- low levels of dopamine
- common treatment strategy: increase dopamine agonists
SCHIZOPHRENIA
- overactive dopamine
- antagonists for dopamine
Reuptake Inhibitors: prevent unused neurotransmitters from
being transported back to the neuron; allows neurotransmitters
to remain active in the synaptic cleft for longer durations =
increased effectiveness
Example:
DEPRESSION
- reduced serotonin levels
- commonly treated w/ selective serotonin reuptake
inhibitors (SSRIs).