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Lecture 8

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


Department
Psychology
Course Code
PSYCH 1000
Professor
Derek Quinlan
Lecture
8

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Chapter 3 Psych 1000 Week 2
Neurons
= 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
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
Stimulated:
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
Neurotransmitters
= 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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