Download CHAPTER 4 How do neurons transmit information?

Inside a neuron…
Fig. 3-14, p.91
CHAPTER 4
How do neurons transmit
information?
Fig. 4-4 Pg.116
Fig. 3-5 Pg.79
Information flow
in a neuron
How do neurons convey information?
A wave induced by stimulation of a
neuron travels from the source on the
cell body along the axon to its terminal.
Afferent Info.
Integration
Efferent Info.
Synaptic
transmission to a
neighbouring
neuron
1
How can we measure the “wave”?
- As a change in electrical current:
Negative pole: more electrons
Positive pole: fewer electrons
Current: Flow of electrons from an area of
higher charge (more electrons = negative
pole) to an area of lower charge (fewer
electrons = positive pole)
Electrical potential: difference in electrical
charge between negative and positive poles
(measured in Volts)
Fig. 4-2 Pg.114
How was the discovery of the neuron’s
electrical activity made?
Pg.117
Some useful terms
Fig.4-5 Pg.117
Won the Nobel Prize in 1963 for
their work on ionic nerve
conduction.
2
Fig. 4-6 Pg.119
An Oscilloscope
• Electrical recording
• Electrical stimulation
- what is it all good for? Can be used as a very
sensitive voltmeter to
measure small (mV) rapid
(ms) changes in electrical
current.
Pg. 115
… one example: neurosurgery
Hot News from Research
- The Adult Brain is Plastic!
How can one recognize parts of the brain?
- functionally (stimulation)
- anatomically (location)
3
Hot News from Research
- The Adult Brain is Plastic!
Physical Exercise Changes the Brain!
Cortical Map Derived from Stimulation
Single-cell recordings of a head direction cell
Head direction cell preferentially fires when
head is pointed in a particular direction.
Fig. 4-24 Pg.139
4
Place cell
Place field
How is the neuronal activity produced?…
5
Fig. 4-8 Pg.119
The Principle of Diffusion
(gradual dispersion of molecules/ions)
Fig. 4-8 Pg.119
The Principle of Diffusion
(gradual dispersion of molecules/ions)
Concentration Gradient
Voltage (Electrostatic) Gradient
Concentration Gradient
Voltage (Electrostatic) Gradient
(relative difference in concentration
between two locations)
(difference in distribution of positively
and negatively charged ions)
(relative difference in concentration
between two locations)
(difference in distribution of positively
and negatively charged ions)
Problem: How does the diffusion through
a cell membrane work?
Fig. 3-15 Pg. 92
6
Mechanisms of Ion Transport Through Cell Membrane
Fig. 3-23 Pg. 97
Fig. 4-9 Pg.120
Presence of a semi-permeable membrane allows a
sustained voltage gradient to establish. Charge is highest a
the surface of the membrane.
Fig 4-10 Pg.121
7
Tactile Stimulation
Massage - Our rat version…
- Reduces stress/stress hormone levels
- Improves immune system functions
- Promotes recovery from brain damage in newborns and adults:
-> larger brains
-> enhanced cognitive and motor performance,
-> enhanced expression of neurotrophic factors and their
receptors
Postnatal Infant
A. Postnatal Adult
B. Prenatal
Fig 4-10 Pg.121
Tactile Stimulation
How does it work? One possible explanation…
- production of epidermal growth factor in the skin
-> reaches the brain -> promotes neuronal survival and
tissue repair
8
Fig.4-11 Pg.124
Resting Potential:
Voltage across the cell membrane produced by a
greater negative charge on the intracellular side in
the absence of stimulation (-70 mV).
• Concentration gradient
• Voltage gradient
• Permeability of membrane
Fig. 4-12 Pg.125
Action potential: large, brief, reversing change
in the voltage of a neuron
Pg. 125
Potassium channel
 Hyperpolarization
 Depolarization
 Threshold potential (-50 mV)
9
Fig. 4-14 Pg. 128
Potassium channel - a complex protein
Ionic events during an Action Potential
Absolutely refractory: impossible to fire another action potential.
Relatively refractory: can fire again but threshold potential is higher
Fig.4-21 Pg.134
The Action Potential
• Happens over about 1 ms
• Traveling wave
• Summation = graded membrane potentials
At axon hillock cell
makes the decision
of whether or not to
fire
• Spatial
• Temporal
– All-or-none Law: Once threshold is reached an action potential is generated.
– No degradation in the size of the AP as it
travels down the axon.
http://faculty.washington.edu/chudler/son.html
10
Fig. 4-15 Pg.129
• Refractory: AP is unidirectional
• Electrical energy associated
with AP opens neighboring
voltage-gated channels
• Signal is transmitted without
degradation down the length of
the axon
Focus on Disorders: Epilepsy
• Caused by abnormal brain activity: neurons
begin to fire synchronously
• Activity often spreads to adjacent areas
• Abnormal brain activity often accompanied by
abnormal movements, loss of consciousness
• 1 in 20 will experience an epileptic seizure
• 1 in 200 will experience multiple seizures (->
epilepsy)
• Seizures often linked to cause, e.g. tumor,
stroke, trauma, infection or other brain damage
11
Focus on Disorders: Epilepsy
Three symptoms:
1) Aura
2) Loss of consciousness, amnesia
3) Abnormal movements
Pg. 144
Normal seizure
clonic
coma
Epileptiform activity recorded
on EEG.
• Categories:
• Petit mal
• Grand mal
• Diagnosis: EEG recordings, brain scan
• Treatment: antiepileptic drug treatment, surgery
Pg. 143
First recorded electrical
activity at the surface of the
skull
EEG: measure of summed graded potentials
from thousands of neurons
12
Beta rhythm - 15-30 Hz
Alpha rhythm - 7-11 Hz
Delta rhythm - 1-3 Hz
The world’s first EEG (electroencephalogram)
Fig. 4-25 Pg.143
Pg. 142
Recording EEG from a relaxed subject
Saltatory Conduction and
Myelin Sheaths
13
Fig. 4-16 Pg.129
CNS
Fig. 4-17 Pg.130
PNS
• Nodes of Ranvier = no
myelin, rich in voltage gated
channels
• Saltatory conduction =
skipping of action potential
between nodes
• Unmyelinated axons: conduction is 30m/sec.
• Myelinated axons: conduction is 120 m/sec.
Focus on Disorders: Lou Gehrig’s Disease
= Amyotrophic Lateral Sclerosis (“muscle weakness
& hardening of lateral spinal cord”)
• Death of motor neurons
• Age at onset usually 50-75
• 10% have family history
• Nodes are close enough that
AP at in one node will open
the voltage gated channels at
the next
Focus on Disorders: Lou Gehrig’s Disease
• Progressive course
• Symptoms include general weakness, walking
becomes difficult, no use of hands and legs possible,
• Death occurs often within 5 years after diagnosis
• Causes: unknown (genetic, autoimmune, toxic,
leading to mitochondrial dysfunction?)
• …no cure
About 2,000 Canadians currently live with ALS
14