1. Chapter 11-Part II Biology 2121
Neurophysiology

2. Neurophysiology Nerve impulses
Afferent impulses
Efferent impulses
Nerve impulses and action potentials are the result of electrical changes in neurons (ion movement)

3. Membrane Potential Leaky channels
Potential difference (–70 mV) across the membrane of a resting neuron
Ionic (charge) differences are the consequence of:
Na+ and K+ permeability difference across the membrane
sodium-potassium pump
Restoration
Na leaks into, and K leaks out of the membrane
Leaky channels

4. How is the Resting Membrane Potential Changed?
Membrane charges - reversed
Graded potential
Action potential
Events
Polarized  depolarization
Hyperpolarization
Repolarization

5. Changes in Membrane Potential
From -70 mV to +30 mV

6. Channels and Changes in the Membrane Potential
Chemically Gated Channels
Voltage-Gated Channels
When these gates are opened, ions move down their electrochemical gradient!

7. What are Graded Potentials?
Short-lived
Decrease in intensity with distance
Their magnitude varies directly with the strength of the stimulus
Sufficiently strong graded potentials can initiate action potentials
Any membrane can become ‘depolarized’
But it cannot form an action potential

8. How are Graded Potentials Different from Action Potentials?

9. Action Potentials Only occur in ‘excitable membranes’
Muscle cells
Neurons
Axon Hillock
Graded potentials may turn into action potentials
Summation
Temporal and Synaptic
Comments
Strength does not decrease
Self propagating

10. Generation of an Action Potential

11. Propagation (fig )

12. Thresholds Do all depolarization events cause an AP? All or Nothing
Must reach threshold (-50 mV) or mV from resting potential
More Na+ channels open and increased depolarization occurs
All or Nothing

13. Refractory Periods Ion channels - open Types
Neuron cannot respond to another stimulus
Na+ channels must close first!
Resets normal polarized state
Types
Absolute
Relative
Absolute: Time from the opening of the Na+ activation gates until the closing of inactivation gates
The absolute refractory period:
Prevents the neuron from generating an action potential
Ensures that each action potential is separate
Enforces one-way transmission of nerve impulses
Relative refractory period: The interval following the absolute refractory period

15. 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

16. Saltatory Conduction

17. Multiple Sclerosis Autoimmune Disease Scleroses Consequences
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

18. When the Nerve Transmission Reaches the Synapse

19. Synapses
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

20. Chemical Synapse

21. At the Synapse Synaptic Delay Signal Variation Summation – EPSPs 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

22. Summation

23. Neural Integration Neurons of CNS – neuronal pools
Integrate incoming information
Discharge zone
Facilitated zone

24. Types of Circuits 1. Diverging 2. Converging 3. Oscillating
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

25. Neural Circuits

26. 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