Western Gateway Building, UCC PL3020 Neurophysiology Gordon Reid Dept of Physiology Western Gateway Building, UCC E-mail g.reid@ucc.ie

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

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

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

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

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

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

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

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

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

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

The neurone: Golgi stained sections Hippocampal pyramidal neurones 12

The neurone: Golgi stained sections Hippocampal pyramidal neurones 13

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

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

Unity within diversity: 4 zones 16

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

The sum of all synaptic inputs… what it really looks like Each neurone can have from 10,000 - 100,000 synaptic inputs In some regions, essentially the whole neurone surface is covered 18

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

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

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

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

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

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

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

Bringing it all together 26

A simple neural circuit 27

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

Divergence and convergence 29

Monosynaptic stretch reflex 30

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