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Behavioural Neuroscience
4/19/2012 5:30:00 PM
Structure and Function of Cells in the Nervous System
Major Divisions of the Nervous System (l):
 Central Nervous System (CNS) comprises the brain and the spinal
cord
 Peripheral Nervous System (PNS) consists of everything outside
the skull and spinal column
Major Divisions of the Nervous System (II):
 Afferent: Going towards (approach, advance)
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Efferent: Going away (exit, escape)
Somatic
Interacts with external environment
o Afferent nerves
Carry sensory signals from eyes, ears, skin,
etc TO CNS
o Efferent nerves
Carry motor signals FROM CNS to skeletal
muscles
Autonomic
Regulates body’s internal environment
o Afferent nerves
Carry sensory signals from internal organs
TO CNS
o Efferent nerves
Carry motor signals FROM CNS to internal
organs
Santiago Ramón y Cajal (1852 - 1934, a pioneer of neuroscience):
 Hippocampus
 Retina
 Pyramidal cell
Basic structure of the cell:
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Dendrites: treelike extensions of the soma
o They receive information from other cells and carry it to the
soma.
Soma (cell body): the Metabolic centre of the neuron.
Axon: projects from the soma
o It carries information from the soma to the terminal buttons
o It carries the action potentia

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Myelin Sheath: insulates the axon and prevents messages
spreading between adjacent axons
Terminal buttons: button-like endings of the axon branch
o They release neurotransmitters after receiving an action
potential.
o They connect with another neuron via a synapse.
Classes of Neurons:
 Multipolar neurons: have one axon and many dendrites
attached
to its soma
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o Several dendrites allow for integration of a great deal of
information
Bipolar neurons: two processes leaving the soma
o At one end, there is a single dendritic tree
o They transmit sensory information (e.g. vision, audition).
Unipolar neurons: one process extending from the soma
o the axon then divides into two branches
o They detect touch, temperature changes, pain and other
sensory events that affect the skin
Interneurons link sensory and motor neurons.
The Synapse:
 A synapse is a junction between the terminal button of the sending
neuron and a portion of the dendritic membrane of the receiving
neuron.
 Communication proceeds in one direction only: FROM the terminal
button To the membrane of the other cell.
Inside the Soma (cell body):
 The nucleus houses the nucleolus and the chromosomes.
 Cytoplasm: a gelatinous, semi- transparent fluid in which organelles
are suspended.
 Mitochondria are the site of energy production.
 Microtubules allow for rapid transport of material throughout the
neuron.

Membrane defines the outer boundary of the cell. It is embedded
with protein molecules that have special functions.
Protein Synthesis:
 The chromosomes consist of deoxyribonucleic acid (DNA).
 The gene is a DNA unit that occupies a certain location on a
chromosome.
 When the gene is active, it makes a copy of the information
(transcription).
 The copy is received by the messenger ribonucleic acid (mRNA).


The mRNA leaves the nucleus and attaches itself to a ribosome
where the protein is produced.
The genome is a sequence of proteins located on the chromosome.
This genome provides the information necessary to synthesize all
the proteins for a particular organism.
Supporting cells:
 Neuroglia (or Glial cells)
Glia surround the neuron and support
the nervous system


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1. Astrocyte is a glial cell that provides physical support and cleans
up debris in the brain. They control chemical composition and
nourish the neuron.
2. Oligodendrocytes provide support to the axon of the cell and
produce the myelin sheath which forms a tube around the axon for
insulation. The sheath is not continuous; it is a series of segments.
The exposed axon is called the node of Ranvier.
3. Microglia are the smallest of the glial cells. They provide an
immune system for the brain and protect the brain from invading
microorganisms.
The Blood-Brain Barrier:
 Blood-brain barrier:
o A semipermeable barrier between the blood and the fluid that
surrounds the cells of the brain
 Functions of the blood-brain barrier:
o 1. To provide a balance between substances within neurons
and in the extracellular fluid. An imbalance can disrupt the
transmission of messages thus affecting brain function.
o 2. Impedes the passage of toxic substances.
Measuring Electrical Potentials of Axons:
 An action potential is sent from the soma down the axon to the
terminal button
 Recording from an axon:
o 1. A wire electrode is placed in the extracellular fluid; it is an
electrical conductor that provides a path for the electricity to
enter or leave the medium.
o 2. A fine glass microelectrode is inserted into the axon. This
records activity of the neuron.
o 3. The oscilloscope, a sensitive voltmeter, turns electrical
fluctuations into visible signals
Membrane Potentials:
 The difference in the charge between the inside of the axon and the
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extracellular fluid is the membrane potential.
The neurons resting potential is when the steady membrane
potential is -70mV. The inside of the axon is negative.
In its resting state, the neuron is polarized.
We can stimulate the neuron by passing a positive charge through
another microelectrode. This changes the value of the membrane
potential (towards zero). The neuron is now depolarized.
The Action Potential:
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The action potential is a rapid reversal of the membrane potential
(i.e. the inside of the membrane becomes positive). It’s peak is +30
mV.
The membrane quickly restores to normal (within 2 msec), but first
the potential overshoots the resting potential and becomes
hyperpolarized (more negative).
The value of the membrane potential that must be reached to
produce an action potential is called the threshold of excitation.
How the movement of ions creates electrical charges:
 A ion is a charged molecule. Cations are positive, and anions are
negative.
(e.g. NaCl = Na+ cation; Cl! anion).
 Forces of diffusion move ions from high concentration to low
concentrations
 Electrostatic pressure refers to the attractive or repulsive forces
between the charged ions.
 The membrane potential is maintained by the balance of diffusion
and electrostatic forces. These forces are influenced by the
concentration of the fluids inside the cell (intracellular) and outside
of the cell (extracellular).
The Resting Potential:
 Four important ions produce the resting potential:
o an organic Anion (A!); Sodium (Na+); potassium (K+);
Chloride (Cl!).
 The cell membrane is semipermeable: it allows certain molecules to
pass but not all of them
The Sodium-Potassium Transporter:
 The sodium-potassium pump continuously pushes Na+ ions out of
the cell.
 The membrane is not very permeable to Na+ .
 Sodium-potassium transporters, energised by adenosine
triphosphate (ATP) molecules produced by the mitochondria,
exchange 3 Na+ ions for 2 K+
What causes the Action Potential?:
 The action potential occurs when there is a sudden influx of positive
Na+ ions into the cell.
 This influx is caused by a transient increase in the permeability of
the membrane to NA+ which is then followed by a transient
permeability to K +.
 This permeability is provided by ion channels that act as pores
which open or close.
Conduction of the Action Potential:
 1. The movement of the information along the axon is referred to
as conduction of the action potential.
 2. Conduction occurs in a unidirectional manner.
 3. The size of the action potential remains constant.
 4. All-or-none law states that the action potential occurs or does
not occur, and once triggered, will propagate down the axon
without growing or diminishing in size, to the end of the axon.
 5. The rate law states that the strength of the stimulus is
represented by the rate of the firing axon.
4/19/2012 5:30:00 PM
4/19/2012 5:30:00 PM