1. Western Gateway Building, UCC
PL3020 Neurophysiology
Gordon Reid
Dept of Physiology
Western Gateway Building, UCC

2. Textbooks Purves, Augustine et al “Neuroscience” 5th edition
Sinauer 2011

3. Textbooks Nicholls et al “From Neuron to Brain” 4th edition
Sinauer 2001

4. “Principles of Neural Science”
Textbooks
Kandel et al
“Principles of Neural Science”
4th edition
McGraw-Hill 2000

5. Online resources Teaching website: http://epu.ucc.ie/greid/PL3020/
Bookmark this link – everything will be available there on one page 5

6. The diversity of neuroscience
Levels of organisation:
Molecular neuroscience
Cellular neurophysiology
Developmental neuroscience, plasticity and repair
Systems,behavioural and cognitive neuroscience
Neurobiology of disease
…or looked at in terms of questions:
What are the signals?
What are the connections?
How do the signals relate to behaviour/perception?
How are signals and connections modified by experience? 6

7. This course Levels of organisation: Molecular neuroscience
Cellular neurophysiology
Developmental neuroscience, plasticity and repair
Systems,behavioural and cognitive neuroscience
Neurobiology of disease
…or looked at in terms of questions:
What are the signals?
What are the connections?
How do the signals relate to behaviour/perception?
How are signals and connections modified by experience? 7

8. The neuron(e): development of our understanding
Schleiden, Schwann: Cells as the fundamental unit of life (1830s)
Easy to see in some tissues
But not initially accepted for the nervous system:
cells couldn’t be seen microscopically 8

9. The neurone: development of our understanding
Example: a section of liver tissue
Cells are obvious 9

10. The neurone: development of our understanding
Contrast with a section of spinal cord
Appears as a continuous mesh; no obvious discrete cells 10

11. The neurone: development of our understanding
Golgi staining method (Camillo Golgi):
- ~1% of neurones stained
- stains them completely
Used by Santiago Ramon y Cajal (early 1900s) to explore the nervous system
Made clear the existence of neurones
Cajal and Golgi shared the 1906 Nobel Prize for this work 11

12. The neurone: Golgi stained sections
Hippocampal pyramidal neurones 12

13. The neurone: Golgi stained sections
Hippocampal pyramidal neurones 13

14. Many neuronal morphologies
Golgi stain revealed all sorts of shapes of neurone…do they have anything in common? 14

15. Some guiding (simplifying) principles
Information flows only one way: neurones have input and output zones
Rapid neuronal signalling is electrical
Electrical signals are the same in all neurones regardless of function
A neurone’s function is defined by its connections
(except for sensory receptors) 15

16. Unity within diversity: 4 zones16

17. Input zone In most cases, the sum of all synaptic inputs
Exception: sensory neurones, where the input zone transduces the stimulus into an electrical signal 17

18. The sum of all synaptic inputs… what it really looks like
Each neurone can have from 10, ,000 synaptic inputs
In some regions, essentially the whole neurone surface is covered 18

19. Integrative (“trigger”) zone
This is the point where the neurone “decides” whether to fire an action potential in response to its input(s)
In many neurones this zone is the “axon hillock”; in sensory neurones the first node of Ranvier
They have this in common: a high density of Na+ channels - necessary for action potentials to be initiated 19

20. Conductile zone The axon of the neurone
Function: conduction of an action potential unaltered from integrative zone to output zone
May be very short - almost nonexistent 20

21. Why use action potentials?
Without action potentials, voltage falls off quickly with distance
This is OK in a short interneurone
Over longer distances we need a digital code 21

22. Action potentials as a digital code
The signal is the same, regardless of what it signifies
“All or nothing”: if threshold is exceeded, AP is initiated
Squid axon: the first recorded action potential (1939)
Turtle retinal ganglion cell 22

23. Action potentials as a digital code
How do you signal intensity with an all-or-nothing signal?
The key is to code frequency 23

24. The axon doesn’t think...
The axon delivers the sum of the neurone’s inputs to the output zone, as a frequency-coded message
George Bishop, axonologist:
“The axon doesn’t think, it only ax”
- its job is just to faithfully transmit what is given to it
The axon was the first part of the neurone to begin to be understood: the first part we will look at too 24

25. Output zone Output always involves secretion of neurotransmitter
Usually at a synapse onto neurone or muscle cell
May secrete direct into circulation 25

26. Bringing it all together26

27. A simple neural circuit27

28. What the connections really look like
Simple textbook diagram
Reality:
Thousands of connections
Divergence and convergence 28

29. Divergence and convergence29

30. Monosynaptic stretch reflex30

31. Reading for today’s lecture:
Purves et al chapter 1
Nicholls et al chapter 1
Kandel et al chapter 2
Next lecture: How the resting potential is generated
Reading for next lecture:
Purves et al chapter 2
Nicholls et al chapter 5
Kandel et al chapter 7