Welcome to 632Nerve Muscle and Movement

Chris Elliott - cje2@york.ac.ukSean Sweeney sts1@york.ac.ukJohn Sparrow - jcs1@york.ac.uk

Web page: http://biolpc22.york.ac.uk/632/

Course Overview Lectures

Chris 2 : Nerve and Synapse Sean 2: Synapse development Chris 2: Channels John 4: Muscle Chris 4: Movement

Nerve & brain lectures In B006 Nerve

1 Ionic basis of Resting and Action potentials

2 Mechanism of synaptic actions and neuromodulation

3 The Patch clamp approach to Neurobiology

4 Effect of Insecticides on Neural function

Movement lectures

Neural Control of singing and hearing in insects

Locomotion Types & Principles of locomotion Walking running & jumping

Swimming floating

Flying – birds, bats & insects

Not only lectures…

Practicals - No Group Case Study 30% Exam

70% paragraph answers; paper criticism

Case Study

group of 4 - 7 work on problem together submit single report choice of 4 Studies

Group list: Wednesday 3 May 1115 e-mail appointment; or come Wed 31

May deadline : Friday 2 June

Books, etc

Purves, D (et al) (2001) Neuroscience Sinauer

Simmons PJ and Young D (1999) Nerve Cells and Animal Behaviour CUP

McNeill - Alexander R. How Animals Move [CD Rom borrow in teaching]

Other books on nerve Shepherd, G. M. (1994) Neurobiology.

OUP An excellent text Nicholls, J et al (2002) From Neuron to

Brain (4th ed) Robinson, D. Neurobiology (ISBN 3-540-

63778-8): (1998)

What needs explaining? what are nerve cells like? what happens at rest ?

Resting potentials dynamic equilibrium

what happens when activated? Action potentials All-or-none speed comparative differences

Mammalian cells

Brain has neurons 109

glia 3 • 109

blood vessels

Parts of a neuron dendrite soma axon

Identifying cells

silver staining fluorescent dyes antisera

Invertebrate cells

Ganglion 400 to 106 cells

nerve or neuron?

Summary so Far

Brains made of neurons and glia

Squid neurobiology

Contract mantle as fast as possible

Big axon (250µM) insert electrodes replace contents

Resting potential

Cells are all negative

contain K+

outside Na+

anions e.g. Cl-

have semi-permeable membranes

Squid giant axon

Animations of resting potential Bezanilla

http://pb010.anes.ucla.edu/

Resting potential

Balance between diffusion and electrical force?

Use Nernst Equation to test this out

out

indiff K

K

zF

RTE ln

mVEdiff 20

440log56

mVEdiff 75

Conclusion: passive balance is OK for squids

Summary so Far

Brains made of neurons and glia All cells have resting potentials Normally maintained passively by

balance of diffusion and electrical forces

Action potential

membrane becomes permeable to Na+

Na+ floods in diffusion electrical

K+ still goes out

Squid giant axon

Action potential

Two crucial properties of the Na+ current starts at a voltage

threshold stops itself

Arise from Na+ channel channel is voltage

sensitive and opens closes with a second

mechanism

closed

open

inactivated

-30mV

-70mV

1ms

How do we know ? (i)

Hodgkin & Katz replaced Na+ in the seawater

How do we know ? (ii) Hodgkin & Huxley

devised the voltage clamp experiment

separates the ionic and capacitative currents

use replace ions to determine role of each

Interlude What are current and voltage?

Write it down now

Use V for voltage use I for current

What is resistance ? Write it down now

Rule (Ohm’s law)

V = IR

V

I

R

Interlude What is capacitance? Write it down now

Rule

Q=CV dQ/dt = CdV/dt I = dQ/dt = CdV/dt

C

+-

Resistance Rule (Ohm’s law)

V = IR

V

I

R

H&H Experiment

Voltage

Current

Step the clamp from -70mV to different voltages

H &H (ii) Add

tetrodotoxin and block Na+ current

tetra-ethyl-ammonium and block K+ current

H&H reconstruction

H&H measured the kinetics of the currents used this to postulated the kinetics of

channels used this to build a mathematical model

Animations of H&H model Bezanilla see http://biolpc22.york.ac.uk/632

Summary so Far

Brains made of neurons and glia All cells have resting potentials Normally maintained passively by

balance of diffusion and electrical forces Properties of Na and K channels

determine action potential

How does it spread?

electrostatically

How fast is the action potential? Up to 100m/s major component of latency to respond

for 2m high human, 2/100*1000 = 20ms for a 40m dinosaur...

slowed by capacitance

How do we know? Myelinated

axons run faster, capacitance is

reduced channels only at

Nodes of Ranvier

Myelination

Schwann cell (blue) grows round axon (orange)

In Multiple sclerosis (MS) myelin sheath is disrupted

Comparative neurobiology Action potentials are not all the

same in vertebrates K+ current is very

small in molluscs, Ca++ current

supplements the Na+

only vertebrates have myelination, but all animals have glia

protozoa have action potentials too

A word of caution

students often write conductance when they mean conduction

conductance is a measure of permeability how easy it is for ions to cross

the membrane conduction is the process of

movement along the axon e.g. conduction velocity

Final Summary

Brains made of neurons and glia All cells have resting potentials Normally maintained passively by balance

of diffusion and electrical forces Properties of Na and K channels determine

action potential Capacitance (myelination) determines

speed Web page: http://biolpc22.york.ac.uk/632/