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Physiology: Neurons

Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The InternetProvided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke

Eric Friberg

on 23 April 2015

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Transcript of Physiology: Neurons

Weak point of nervous system
any substance that affects neurotransmitters or mimics them affects nerve function
: nitrous oxide, carbon monoxide
mood altering drugs
amphetamines, caffeine, nicotine
quaaludes, barbiturates
hallucinogenic drugs: LSD, peyote
SSRIs: Prozac, Zoloft, Paxil
How is a neuron's structure related to its function?

Why are neurons an “animals only” phenomenon?
Big Questions
Characteristics of a nervous system

reset quickly
Structure fits function
many entry points for signal
one path out
transmits signal
Most specialized cell in animals
Longest cell
blue whale neuron: 10-30 meters
giraffe neuron: 5 meters
human neuron: 1-2 meters
Fun facts about neurons
Think dominoes!
the signal-
knock down line of dominoes by tipping 1st one
the signal-
do dominoes move down the line? no, just a wave through them!
the system-
before you can do it again, have to set up dominoes again

The Neuron has a similar system
protein channels are set up
1. once the first one is opened, the rest open in succession
2. a “wave” action travels along neuron
3. have to re-set channels so neuron can react again
Cells live in a sea of charged ions

more concentrated within the cell
charged amino acids (

more concentrated in the extracellular fluid
Opposite charges on opposite sides of cell membrane

membrane is
membrane potential
negative inside; positive outside
charge gradient
stored energy (like a battery)
1. Wave: nerve impulse travels down neuron

Change in charge opens next Na+ gates down the line
“voltage-gated” channels
Na+ ions continue to diffuse into cell
“wave” moves down neuron = action potential
3. Re-set: 2nd wave travels down neuron

K+ channels open more slowly than Na+ channels
K+ ions diffuse out of cell
charges reverse back at that point
negative inside; positive outside
Combined waves travel down neuron
wave of opening ion channels moves down neuron
signal moves in one direction     
flow of K+ out of cell stops activation of Na+ channels in wrong direction
Action potential generation:
wave = nerve impulse
brain to fingertips in milliseconds!
2. After firing a neuron has to re-set itself

Na+ needs to move back out
K+ needs to move back in
both are moving against concentration gradients
need a pump!! We have one!
1. Resting potential

2. Stimulus reaches threshold potential

3. Rising (Depolarization):
Na+ channels open; K+ channels closed

4. Falling:
Na+ channels close;
K+ channels open

5. Undershoot:

K+ channels close slowly, reset charge gradient
Axon coated with Schwann cells insulates axon, speeds signal

Signal hops from node to node

Saltatory conduction:
Myelinated vs. Unmyelinated
150 m/sec vs. 5 m/sec (330 mph vs. 11 mph)
Impulse has to jump the
junction between neurons
has to move quickly from one cell to next
Events at synapse
action potential depolarizes membrane
opens Ca++ channels
vesicles fuse with membrane
release neurotransmitter to synapse (diffusion)
neurotransmitter binds with protein receptor
ion-gated channels open
neurotransmitter degraded or reabsorbed
Post-synaptic neuron
triggers nerve impulse in next nerve cell
chemical signal opens ion-gated channels
Na+ diffuses into cell
K+ diffuses out of cell
switch back to voltage-gated channel
transmit signals to skeletal muscle
Epinephrine (adrenaline) & norepinephrine stimulate release
fight-or-flight response

widespread in brain
affects sleep, mood, attention & learning
lack of dopamine in brain associated with Parkinson’s disease
excessive dopamine linked to schizophrenia

widespread in brain
affects sleep, mood, attention & learning
Compare the regulatory structures and functions of the nervous and endocrine systems

Diagram the processes by which nervous signals are transmitted by and between neurons.

Label all parts of a neuron

Explain the causes and effects of major disruptions to neuron function
Make Sure You Can
The need for fast,
long-distance messages
Neurons Do These Things!
sensory neuron Interneuron Motor Neuron
Signal moves from
Glial cells help neurons
neurons stained with "Brainbow" flourescence
Incoming signals enter here.
Each dendrite is connected to another neuron at a
Cell Body
Axon Hillock
Myelin Sheath
Schwann Cell
Node of Ranvier
Nerve Terminals
How membrane potential is measured
Lots of pump proteins and ion channels
Maintain concentrations of ions

Reset concentrations following nerve signal

Different kinds of "
" control the openings to the channels:
mechanical gates
: Opened by force
voltage gates
: Opened by voltage
ligand gates
: Opened by ligand binding
Action Potential
A nerve signal
(ion exchange)
(all or nothing)
Action Potential Propagation
Incoming Impulses Come in 2 Flavors

An "All or None" Signal
Neural membrane polarity is constantly fluctuating around the
resting potential.

For an action potential to be generated, the membrane must be
to a "
threshold potential
Action Potential Generation
1. Neuron is at rest:
All gated channels are closed

2. Neuron Depolarizes:
Na+ gated channels begin to open.

3. Rising Phase of AP:
Na+ gated channels all open.

4. Falling Phase of AP:
Na+ gates shut. K+ gates open

5. Undershoot:
K+ gates begin to close. Na/K
pump restores resting potential
"Na+ in, K+ out"
Action potential travel by jumping ("
") between
Schwann cells
Multiple Sclerosis:
Results from De-mylenation of motor neurons
Layers of
insulate neurons.
Speeds Transmission of AP's
Saltatory Conduction
Major Neurotransmitters
Snake venom (
) blocking the active site of
Cone Snail Venom Blocks Na+ channels on post synaptic neurons
Why are axons so long?
Why have synapses at all?
How do “mind altering drugs” work?caffeine, alcohol, nicotine, marijuana…
Do plants have a nervous system?
Do they need one?
Any Questions?
Complexity Emerges!
So Cool!
Contains all organelles for the neuron. Signals move from Dendrites to cell body to axon to nerve terminals

Where an
Action Potential
begins (if it's going to).
The Action Potential moves through the Nodes of Ranvier by
saltatory conduction
The start of the axon.
Modes of action of some of the major venoms
Full transcript