Neurophysiology
– Afferent impulses
– Efferent impulses
and
are the
result of electrical changes in neurons (ion
movement)
Membrane Potential
How is the Resting Membrane Potential
Changed?
Changes in Membrane Potential
• From -70 mV
to +30 mV
Channels and Changes in the
Membrane Potential
Chemically Gated Channels
Voltage-Gated Channels
When these gates are opened, ions move down their
electrochemical gradient!
How are Graded Potentials Different
from Action Potentials?
 Only occur in ‘excitable membranes’
 Muscle cells
 Neurons
 Axon Hillock
 Graded potentials may turn into action
 Summation
○ Temporal and Synaptic
 Comments
 Strength does not decrease
 Self propagating
potentials
Propagation
(fig. 11.13)
Thresholds
Do all depolarization events cause an AP?
 Must reach threshold (-50 mV) or 15-20 mV from
resting potential
 More Na+ channels open and increased
depolarization occurs
All or Nothing
Ion channels - open
 Neuron cannot respond to another stimulus
 Na+ channels must close first!
○ Resets normal polarized state
Types
 Absolute
 Relative
Pre-Synaptic and Post-Synaptic Activity
• Depolarization waves
– Moves towards the synapse
• Conduction speed depends on
– Diameter of axon
– Myelination
• Nerve Fiber Types
– Group A, B, C
Saltatory Conduction
 Autoimmune Disease
 Demyelination of the myelin sheath
 Scleroses
 Lesions are formed
 Disturbance of nerve transmissions
 Axon not damaged
 Consequences
 Relapse and remission
 Speech, incontinence, blindness, muscular weakness
When the Nerve Transmission Reaches
the Synapse
Electrical Synapse – less
common; coordinate neuron
activity between neurons;
ions move through gap
junctions; most abundant in
embryonic tissue; brain find
stereotyped movements
(hippocamus); glial cells of
CNS
Chemical Synapses – ions flow
between channels;
Neurotransmitters are
released
Chemical Synapse
At the Synapse
 Synaptic Delay
 Signal Variation
 EPSP
○ NT binding ------------- depolarization (post-synaptic membrane)
○ AP usually not occur at the membrane
○ Only contain chemically gated channels (axons can – have voltage
gated channels
○ EPSPs are created --- trigger AP at the axon hillock
○ Only lasts milliseconds ---- returns to polarized state
 IPSP
○ Reduces post-synaptic membrane’s ability to produce AP
 Summation – EPSPs
Summation
• Neurons of CNS – neuronal pools
– Integrate incoming information
1. Discharge zone
2. Facilitated zone
• 1. Diverging
– Common in sensory and motor systems
• 2. Converging
– Sensory and motor systems
• 3. Oscillating
– Rhythmic activities
• Sleep-wake; breathing, etc.
• 4. Parallel after – discharge
– only involved in complex, mental processing
• Serial and Parallel Processing
Neural Circuits
Developmental Aspects
• Surface Ectoderm
– Dorsal neural tube and neural crest (12.1)
• Neural tube – forms CNS
• Origin of the neurons
– Neuroepithelial cells – second month
• differentiate and proliferate
• Become neuroblasts