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Lecture 8

Psychology 1000 Lecture Notes - Lecture 8: Sympathetic Nervous System, Prenatal Development, Antidepressant

Course Code
PSYCH 1000
Derek Quinlan

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Chapter 3 Psych 1000 Week 2
= Basic building blocks of NS (nervous system)
Linked together like circuits
Birth: 100 B in brain
3 main parts:
1. Cell body
o Contents needed to keep neuron alive
o Nucleus contains genetic info; determines develops and function
o Combines and processes the info
o Has receptor areas; can be directly stimulated from other neurons
2. Dendrites
o “Receiving units”
o Collect messages from other neurons and sends them to the soma
o Can receive info from >1,000 neighboring neurons
3. Axon
o Conducts electrical signal away from cell body
o Branches out to form multiple axon
o Can connect with many dendritic branches of other neurons
Neurons can vary greatly in size and shape
1 cell body can extend its axon ~1 m, e.g., from spinal cord to fingertips
In brain, neuron can be <1 mm long
Main functions of neurons: receiving, processing, and sending messages
Supported by glial cells, functions:
Surround neurons and hold them in place
Manufacture essential nutrient chemicals for neurons
Form myelin sheath
Absorb toxins/waste materials that may damage neurons
Modulate communication among neurons
Prenatal development: guide new neurons to place in the brain
Outnumber neurons 10:1
Blood-brain barrier: prevents many substances from entering the brain
BV’s in brain have smaller gaps than elsewhere in the body
These BV’s are also covered by a specialized type of glial cell
Electrical Activity of Neurons
Generate electricity that creates nerve impulses
Release chemicals that allow them to communicate with other neurons,
muscles, and glands
Nerve activation steps:
1. At rest, neuron has resting potential due to the distribution of positively
and negatively charged chemicals (ions) inside and outside the neuron
2. When stimulated, a flow of ions in and out through the CM reverses the
electrical charge of the resting potential, producing and AP
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Chapter 3 Psych 1000 Week 2
3. The original distribution of ions is resorted, and the neuron is again at rest
CM is semi-permeable; allows only select substances to pass though ion channels
Chemical environment differs from internal and external environment of a neuron
Nerve impulse is created by exchanging electrically called atoms (i.e., ions)
Outside: Na+ and Cl-
Inside: K+ and A-
High concentration of Na+ outside, together with the A- inside, results in an
uneven distribution of (+) and (-) ions that makes the interior of the cell (-)
compared to the outside
This internal difference = ~70 mV, i.e., resting potential
At rest, the neuron is in a state of polarization
The Action Potential
Hodgkin & Huxley:
If mildly stimulated axon, internal voltage changed from -70 to +40 mV
Action potential: sudden reversal of neuron’s membrane voltage
Shift from (-) to (+) = depolarization
Action of Na+ and K+ ion channels = key mechanism for generating AP
Resting state: both channels are closed and Na+ concentration 10x higher outside
Na+ channels open; attracted by (-) interior, they flood in the cell
State of depolarization is created
Interior is now (+), i.e., +40 mV
To restore resting potential:
Na+ channels close
K+ then flows out to restore (-) resting potential
Eventually, Na+ and K+ recover to original location
Right after impulse passes the axon, there is a recovery pd.:
When K+ is flowing out from the interior
Absolute refractory pd.: CM not excitable; cannot generate another AP
Relative refractor pd.: CM excitable, but needs very strong stimulus
All-Or-None Law
= AP’s occur at a uniform and max intensity, or they do not occur at all
(-) Potential inside cell needs to be changed from -70 to -50 mV (i.e., threshold)
Graded potentials: changes in (-) potential that do not reach -50mV
For proper neuron functioning, Na+ and K+ must leave cell at just the right rate
Certain drugs can alter this rate, such as local anesthetics (e.g., Novocain)
o Attach to Na+ channels in neurons; stops pain impulses
Myelin Sheath
= Fatty, whitish insulation layer derived from glial cells during development
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Chapter 3 Psych 1000 Week 2
Interrupted at regular intervals by nodes of Ranvier; myelin either thin or absent
Unmyelinated: AP travels like burning fuse
Myelinated: AP travels like “great leaps”, >300 km/h
Myelin sheath found in NS of higher animals
Not completely formed until after birth (for most nerve fibers)
MS: progressive disease; persons own immune system attacks myelin sheath
Disrupts timing of nerve impulses
Jerky, uncoordinated movements
Final stages = paralysis
How Neurons Communicate: Synaptic Transmission
Santiago Ramón y Cajal & Charles Sherrington:
Argued that neurons were individual cells that did not make actual
physical contact with each other, but communicate at a synapse
Synapse: functional connection between a neuron and its target
Otto Loewi:
Found that neurons release chemicals
These chemicals are what carried the message from one neuron to other
Therefore, Loewi discovered chemical neurotransmitters
Electron microscope invention:
Allowed researchers to see a tiny gap between communicating neurons
Synaptic cleft: between axon terminal and dendrites of the next neuron
= Carry message across synapse to either excite or inhibit other neurons firing
Five steps of chemical communication:
1. Synthesis
o Chemical molecules formed inside the neuron
2. Storage
o Molecules stores in synaptic vesicles within the axon terminals
3. Release
o AP arrives
o Vesicles release molecules from pre- to post-synaptic neuron
4. Binding
o Molecules cross synaptic space and bind to post-synaptic neuron
o Receptor sites: big proteins embedded in post-synaptic neuron CM
o These sites fit a specific transmitter molecule, like a lock and key
5. Deactivation
Excitation, Inhibition, & Deactivation
Binding of NT to the post-synaptic neuron can have 1 of 2 effects:
1. Depolarize neuron via excitatory NTs
o Na+ flows in
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