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UCONN - PNB 2264 - PNB 2264 - week 5 notes - Class Notes

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UCONN - PNB 2264 - PNB 2264 - week 5 notes - Class Notes

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background image Week 5  Membrane Potential in Neurons Neurons  -use changes in membrane potential to send messages throughout the entire body  Characteristics of Neurons: -high metabolic rate -extreme longevity -non-mitotic  Neuronal Structures: -dendrites (branched processes protruding from the cell body, receive signals 
using receptors, variation in number) 
-cell body (also known as soma, contains organelles (e.g. nucleus, Golgi), and has 
specializations: many mitochondria and ribosomes) 
-axon (action potentials are sent through axon, neurons have either one axon or no 
axon at all, region where axon connects to the cell body is the axon hillock)
-axon terminal (distal part of the axon, forms synapse(connection) with another 
Electrical Signals Within Neurons  Passive Electrical Signals:  A transient change in membrane potential that dissipates as it propagates in space 
and time (e.g. a graded/synaptic potential)
Active Electrical Signals: A change in membrane potential that is maintained over a long distance (e.g. an 
action potential)
Changes in Membrane Potential Depolarization: more positive then resting Repolarization: more negative to return to resting
background image Hyperpolarization: more negative then resting  Model Neuron structure: Dendrites- input Soma- integration (net change summation), receives many ESPSs and IPSPs at 
Axon Hillock- action potential generated (highest density of Nav channels) Axon- Action potential propagates Synapse- signal output (chemical) Synaptic Potentials: -are passive and primarily by ligand gated ion channels -binding of neurotransmitter causes receptors to open which increases the 
permeability to ions through that ion channel  
Goldman-Hodgkin-Katz In Action -At rest, Vm is near Ek, because cell mostly permeable to K+  -If a neurotransmitter receptor opens and increases permeability to an Ion+ , Vm 
will increase towards E(ion).
Synaptic Potential Terminology  Excitatory (EPSP)- are graded potentials that can initiate an AP in the axon Inhibitory (IPSP)- produce a graded potential that lessens the chance of an AP in 
an axon
- EPSP - small depolarization is created; IPSP - small hyperpolarization is created. Synaptic Potentials Are Graded -Graded potentials are changes in membrane potential that vary in size, as opposed
to being all-or-none. 
-They arise from the summation of the individual actions of ligand-gated ion channel
proteins, and decrease over time and space. 
- If the neuron is able to produce enough depolarization (through summation of 
EPSPs), then an action potential can be produced.
background image Summation -a neuron may receive postsynaptic potentials from thousands of other neurons. -Whether threshold is reached, and an action potential generated, depends upon 
the spatial (i.e. from multiple neurons) and temporal (from a single neuron) 
summation of all inputs at that moment
Action Potential “Firing” - A burst of electrical activity that rapidly propagates through the cell - Active electrical currents - Are cyclical Phases of Action Potentials  1. Resting membrane potential
2. Depolarizing stimulus
3. Membrane depolarizes to threshold. Voltage-gated Na+ channels activate 
and Na+ enters cell. Voltage-gated K+ channels begin to open slowly. 4. Rapid Na+ entry depolarizes cell. 
5. Na+ channels inactivate and slower K+ channels open. 
6. K+ moves from cell to extracellular fluid.
7. K+ channels remain open and additional K+ leaves cell, hyperpolarizing it.
8. Voltage-gated K+ channels close, less K+ leaks out of the cell. 
9. Cell returns to resting ion permeability and resting membrane potential.
Ligand Channels VS Voltage Gated ion channel Voltage gated ion channels open in response to voltage (i.e. when the cell gets 
depolarized) where as ligand gated channels open in response to a ligand (some 
chemical signal) binding to them.
Both types of channels are critical for proper activation of the post synaptic neuron. 
The pre synaptic neuron releases neurotransmitters into the synaptic cleft, these 
neurotransmitters then bind to the ligand gated channels, thus activating them. The
ligand gated channels open up and allow the influx of sodium, which depolarizes the
cell. This depolarization activates nearby voltage gated ion channels, which open up
and let in even more sodium. Voltage gated sodium channels open up one region at 
a time, the previous region providing enough depolarization to activate the next 
regions voltage gated channels. This effectively allows the action potential to 
propagate through the cell.
Voltage-Dependent Membrane Permeability

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School: University of Connecticut
Department: Physiology
Course: Human Physiology and Anatomy
Professor: Kristen Kimball
Term: Fall 2018
Name: PNB 2264 - week 5 notes
Description: These notes extensively cover all information on the power-points as well as in-class examples.
Uploaded: 09/30/2018
11 Pages 95 Views 76 Unlocks
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