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Chapter 2

PSYB65H3 Chapter Notes - Chapter 2: Autonomic Nervous System, Active Transport, Microglia


Department
Psychology
Course Code
PSYB65H3
Professor
Ted Petit
Chapter
2

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Chapter 2 Neuroanatomy
MODULE: Cells of the Nervous System
- humans > specialized cells that perform specialized functions
- neurons [communicators] and glia [support] cells are specialized cells of
the nervous system [structure and function]
- neurons > react to stimuli and are the basis of beh
Neurons and Glia: Structure and Function
Gross anatomy of the neuron
- shape of neuron > related to its function [receive, conduct, transmit signals]
- 3 main compents:
o dendrites > receives info from other neurons
increases surface area available for the reception of signals
form axons of other neurons
info sent to the rest of the neuron as a electrical charge
extent of branching indicates of num of connections
o soma [cell body] > contains genetic machinery and most f the
metabolic machinery needed for celluar functions
o axon > sends neural info to other neurons
info sender [only one per neuron]
can divide to increase num of synapses
long thin fiber > can send info to many cells simulataneously
covered with insulation, myelin
speeds rate of info transfer/ensures msg get to end
end of a axon, terminal button
o info sent from button across synapse to dendrite
info sent across the axon to is in the form of neurotransmitter
[can b transformed into electrical message within the dendrite]
o synapse > gap that axons pass info to dendrites across
- presynaptic > events that occur in the axon
- postsynaptic > events that occur in the dendrite
Internal Anatomy of the Neuron
- neuron is covered w/ a membrane
- plasma membrane: consists of bilayer of continuous sheets of phospholipids
that separate the cytoplasm and the fluid enviro outside the cell
- proteins/channels that allow the passage of materials in and out of the cell
- organelles > nucleus [genetic], ribosome/endoplasmic reticulum [synthesis],
mitochondria [metabolic]
- nucleus > processes genetic info and contains all the genetic info needed to
code proteins
Structure and function of neurons
- structurally named neurons > uniplor, bipolar, multipolar [most common]
o uniploar > have only one process emanating from the cell body
- neurons w/ no/short axons > inter-neurons > integrate info w/i structure
- functionally can be classified by the types of signals they send

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- the type of info that is represented by neural sctivity related to the function of
the neuron
- afferent > bringing info to the CNS
- efferent > sending info from the brain/away from a structure
- neurons can change as a result of experience
Glia
- support functions, there are diff types of glia
- satellite cells> support cells outside the brain/spinal cord
- 3 types
o astrocytes > largest glia, star shaped
fill the space btwn neurons > growth of neurons?
involved in brain-blood barrier
nutritive/metabolic functions for neurons
regulate how far neurotransmitters can spread
storage of neurotransmitters
o oligodendrocytes > make myelin
wrap their processes around most axons in the brain/spinal
can provide many segments to many axons [schawann only 1]
o microglia > smallest, are phagocytes that remove debris from the NS
are made outside the brain and spinal by microphages
excessive may = Alzheimer’s/MS
Communication within the Neuron: The Action Potential
- commun within neurons is largely electrical and rely of AP to transmit info
- resting potential > initial state, electrical charge > -70millivolts
o depends of the concentrations of ions across the neuron membrane
- sodium ions [Na+] and potassium ions [K+]
- at rest High > K inside cells, H Na outside
- brain > heterogeneous concentration of ions inside and outside cell > why?
o 1 - permeability > some are allowed thru ion channels
at rest > K passes through while Na cannot easily
o 2 neuron active transport of ions [some K leaks out as Na goes in]
- sodium-potassium pump >actively import K and export Na [3 Na for 2 K]
- when a neurotransmitter diffuses > opens sodium ion channels
o Na goes in > -70mv to +50mv, depolarization > action potential occur
- action potential occur w/I one neuron they release NT > commun btwn neurons
- then hyperpolarization > K channels open > result in charge beyond -70
- features of action potential >
o absolute refactory period >period after a AP where no additional
action potential can be produced [closing of sodium channels]
o all of none > all are of the same size
o nodes of Ranvier > gaps in the myelin [ion channels only occur here]
in myelinated axons ions can cross the membrane only here
o salutatory conduction > jumping of AP from one node to another
o since AP is actively propagated > neural transmission in myelineted
neurons is faster that in neurons w/o myelinaton
Communication between Neurons: The Synapse
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- communication between neurons is largely chemical
- axosomatic synapses > made of axons forming synapses with the soma of the
neurons [very common]
- axoaxonix synapses > axons forming synapses w/ other axons
- dendritic synapse > dendrites forming synapses w/ other dendrites
- axodendritic > synapses that consist of axons that form synapses w/
dendritic spines [most common]
o terminal buttons have small packages [vesicles] that contain NT
- NT release:
o NT release triggered by AP at TB
o causes calcium [Ca2] channels to open > incre in Ca2
o causes NT released into the synapse by exocytosis [membrane of
vesicle fuses w/ axonal membrane > opens vesicle allowing NT flw]
o NT diffuses across synapse >
producing postsynaptic effects [when NT binds to a protein
embedded in the postsynaptic membrane aka receptor]
- specificity of receptors > key analogy
- 2 types of receptors on postsynaptic membrane >
o transmitter-gated ion channels > aka ionotropic receptors are
proteins that control an ion channel > when NT binds = quick change
in ion concentration
o function > depends on the ion channel controlled [ie. Na > AP]
excitatory post-synaptic potential, EPSP > dendrite depolarized
> toward AP > by release of NT from presynaptic
inhibitory post-synaptic potential, IPSP > dendrite
hyperpolarized > away from AP > by release of NT from
presynaptic
o G-protein-coupled receptors aka metabotropic
slower, more diverse, sustained responses than above
more freq in NS
steps:
NT binding w/ receptor
subunit of g-protein break away
o move and bind to ion channel OR trigger
synthesis of other chemicals
can result in IPSP or EPSP or change in gene expression
therefore more diverse effects
o both types of receptors bind diff NT
- receptors of the presynaptic membrane > autoreceptors > metabotropic
receptors that are located on presynaptic > bind the NT release by the presyn
o thought to regulate the amount of NT in the synapse
- mechanisms responsible for terminating activity of [removing] NT:
o reuptake > more common, presyn neuron reabsorbing the NT from
synapse and repacking in the vesicles to be used again
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