Chapter 3: Neuroscience (09/20/2013)
How Do Scientists Study the Nervous System?
-Examining autopsy tissue, testing the behaviour of patients with brain damage, use
electroencephalograms (EEG)—records brain activity from the surface of the scalp, animal
studies & neuroimaging techniques that show visual images in awake humans.
-Brain imaging: watching the brain in action:
-Structural imaging techniques use advanced technology to create images of the living,
healthy brain. Eg. CAT or CT scan (computerized axial tomography) and MRI (magnetic
resonance imaging)—more expensive but higher resolution.
-Functional brain imaging techniques allow us to watch the brain in action. Eg. PET scan
(positron emission tomography)—warmer colours that indicate high activity in the brain
but the down side is it involves injecting a harmless radioactive isotope into the patient as
well as the resolution is not as good; an advantage is that it is more readily available b/c
it’s an old technology and cheaper when 1 bought. And fMRI (functional magnetic
resonance imaging)—shows where the activity in the brain is concentrated; the red areas
indicate heavy activity; quicker to capture changes in brain activity than PET; shows 2
phases, gesture preparation and gesture production.
How Does the Nervous System Work?
-Neurons are cells in the nervous system that communicate w/ one another to perform info-
processing tasks; there are 100 billion neurons in the brain.
-Glia are cells that help support neurons; they outnumber neurons 10:1; there are diff types:
-astrocyte/astroglia=creates the blood-brain barrier (there are also tightly packed blood
vessels that surround the brain to avoid things from easily getting into the brain),
influences the communication between neurons and helps heal brain damage. One type
of astrocyte are stem cells which creates new neurons and may help cure degenerative
-oligodendroglia=provides myelin (fatty insulation) to speed up transmission of neurons;
enables transmission of electrical signal along an axon to be faster, more efficient and
-ependymal cells=creates & secrete cerebrospinal fluid (CSF)
-microglia=thought of as miniature vacuum cleaners; cleans up dead cells & prevents
infection to the brain.
-There are different kinds of neurons, they vary in size and shape depending on their location and
function: motor neurons (moving muscles), sensory neurons (taking info from the
environment/senses) and interneurons (connecting neurons that help span physical distance, eg.
-Structure of neurons: (refer to figure)
C. Cell body=has the nucleus w/ chromosomes (contain DNA, proteins, ie genetic
material) and organelles (produce energy)
B. Dendrites=from the greek work of “tree”; are specialized extensions that revieves
messages from other neurons; numerous and similar to tree branches
D. axon=only 1 per neuron; sends/carries info away from the cell body and into axon
terminals to other parts of the body.
E. axon terminals=where axon ends; enables axons to connect to other neurons; transmit
signals to dendrites
F. myelin sheath=layers of myelin; comprise of oligodendroglia; a substance that speeds
up the firing of a neuron. *In multiple sclerosis, body attacks own myelin, myelin sheath
deteriorates thus neural transmission breaks down
A. Nodes of Ranvier=the small gaps on the neuron that have no myelin covering; only on
myelinated axons. Signals are able to jump from nodenode allowing for quick
transmission of info. In those w/ degenerative diseases, info can’t travel as fast b/c of lack
How Do Neurons Communicate?
-Neurons are not in direct contact w/ one another. There are synapses which are regions of
neural transmission b/w axon of a neuron & dendrites or cell body of another cell. The presynaptic neuron is the neuron before the synapse (gives the info) and the postsynaptic neuron
is the neuron after the synapse (receives the info)
-Synaptic Transmission b/w neurons: An action potential reaches end of axon & at a certain
threshold, activates the release of neurotransmitters into the synapse which are then collected at
the receptors of the receiving neurons. Treshold is at ~ -40mVelectrical charge increase to
+50mv (height of an action potential). Neurotransmitters are chemicals that transmit info across
synapse to receiving dendrites. Receptors are parts of cell membrane that receive
neurotransmitters & start new electric signal.
-There are ions that move around, in & out of the axon and this allows the spread of the
action potential. The Na/K pump as well as Na & K channels influence the spread of an action
potential. Sections of the axon experiencing the action potential have Na channels open & K
channel close; sections of the axon w/ diminishing action potential have Na channels close and K
channels open to get back to resting potential.
-How do Neurons Work? The resting potential is when the neuron is at rest; it is negatively
charged inside & positively charged outside and the resting charge is maintained through the
actions of Na/K pumps (~ -70mv). The action potential is when a neuron fires; there are pores in
the neuron/ion channels that open to let the positive charge come in (Na+) and negative charge
go out, this shift in electrical charge triggers the axon terminals to release neurotransmitters.
-Communication between neurons: an action potential triggers the release of neurotransmitters.
Neurotransmitters are chemicals that help neighbouring neurons talk to each other; they float
from the synaptic vessel of one neuron & are taken up by neurotransmitter receptors in the
neighbouring neurons. The synapse is the small space b/w neurons.
-Plasticity—the repeated release of neurotransmitters can cause permanent change to
neurons. How your brain looks like now is not gonna be the same as how it will look like a few
years later when you’ve learned more stuff. Your brain changes based on experiences. To
remember/learn something new, there has to be a new complexity tangibly built into your brain.
-All-or-none principle: either a neuron is sufficiently stimulated to start an action potential (all) or it
isn’t (nothing), ie. Action potential have no different degress, no in-between just the 2 opposite
-Refractory period=after firing, a neuron can’t fire again for 1000 of a second.
-Absolute refractory period=a short time after an action potential, during which a
neuron is COMPLETELY unable to fire again, no matter what.
-Relative refractory period=just after the absolute refractory period, during which
a neuron can only fire if it receives a stimulus stronger/more intense than its usual
-Neurotransmitter receptors: Postsynaptic potentials are electrical events in postsynaptic neurons
occurring when a neurotransmitter binds to a receptor; the electrical response of the postsynaptic
cell is determined by the receptor. It can either cause depolarization—regions of postsynaptic
membranes have become less negative making it more likely that the neuron will initate an action
potential b/c the value is closer to the threshold +50mv OR hyperpolarization—opposing influence
in which areas of the cell have become more negative making it less likely the cell will generate
an action potential b/c the value is farther from the threshold and exceeds resting potential (-80,
-90, -100 mv). Some areas are depolarized and some are hyperpolarized, the sum of these
charges add up to the threshold level of action potential generation.
-Types of Neurotransmitters:
-dopamine (DA)=involved in normal mov