- system that generates behavior of the body modulated by sensory input.

= receives input from sensory system.

- behavior expressed through effector organs: muscles and glands

- cells of nervous system that generate and transmit nerve signals (action potentials)

- modulated by glial cells

wave-like voltage change the travels along the plasma membrane of a neuron.

- fundamental to function of neuron

- generated/travel along plasma membrane of axons, sometimes in pm of soma and dendrite.

- up to 1m in humans

- first observed in axon of squid

- two thin metal wire/glass tube electrodes: one outside pm of neuron, one inside

- voltages are detected/displayed by oscilloscope (classically) or computer (today)

voltage of inactive axon-- -60 mV

- 1mV = .001 volts; 60 mV = 0.060 volts

- inside of membrane is negative, outside is 0.

1. Mechanical stimulation (pinching)

2. Chemical stimulus

3. Electrical stimulus (externally generated voltage)

- most common way to stimulate axon.

- allows precise control of magnitude (V) and duration of stimulus.

- stimulating voltage is applied through a second set of electrodes (stimulating electrodes)

A BREIF positive swing that occurs with any stimulus.

- voltage goes to about +40mV, then decreases to just below resting potential, and finally recovers to resting potential. (1-2 ms)

- travels along plasma membrane

- in an axon: travels from point of origination (near soma) to tips of axon branches.

- record at two positions of axon.

- measure the distance between two points and the difference in arrival times: V = D/t

varies depending on neuron, from 1-100 meters/second

- electric current in a wire travels at the speed of light (300million meters/second), so action potential is NOT an electrical current.

K+ and Na+

- produce excess of K+ inside cell, and excess of Na+ outside of cell.

- membrane of axon contains gated sodium and potassium ion channels, both of which are normally closed.

more K+ inside, more Na+ outside

- occasionally, potassium ion channels leak K+ ions to outside, leaving inside very negative

- source of negative resting potential

sufficient stimulation of axon opens sodium-potassium channels, and Na+ to enter the axon.

- this leads to a positive inside axon (rise in action potential)

Opens and changes shape of Na+ channels.

- voltage more positive than threshold voltage opens Na+ channels

(changing the +/- of vicinity of protein changes the forces and shape of the protein)

1. Na+ channels open for brief time, then snap shut.

2. K+ channels open at voltage near the peak of the action potential, and K+ ions rush out (hi to lo concentration!)

loss of + charges make inside negative-->action potential drops (falling phase)

- during falling phase, voltage drops slightly below resting potential.

- K+ channels close, resting potential is restored

- few moments of latency before new action potential start

1. Negative/Resting Potential: Leaky K+channels of axon make K+ escape to outside, and inside of axon is mostly negative

2. Stimulation/rising phase: Na+ channels open, and Na+ rushes into axon, making it positive

3. Falling phase: Na+ channels shut, K+ channels open. K+ leaves axon, removing +positive charges.

weak + stimulus doesn't result in action potential.

- stimulus above certain threshold results in ap

- there is no intermediate.

schwann cells, oligodendrocytes

- increase speed of action potential

- 2 types of glial cell are wrapped around axon. wrapping contains insulating lipid called myelin.

- regions of bare axon between schwann cells: nodes of ranvier

in CNS, gray matter=non-myelinated areas

white matter=myelinated areas

non-myelinated areas of CNS

- mainly dendrites, cell bodies and synapses.

- Carry out information processing, often called associative areas

myelinated areas of CNS

- called tracts

- carry nerve signals from one associative end to another

weakness, poor coordination, impaired vision/speech.

- caused by loss of myelin from white areas of CNS.

- may be autoimmune disease (immune system attacks myelin-producing cells)

local anaesthetics (lidocaine, novocaine)

- block action potentials by blocking voltage-gated Na+ channels

junction between two neurons. site of inter-neuron communication

- formed by axons in close proximity to dendrites, soma and other axons.

- tips of axons are called boutons.

- boutons leave a space between next neuron = synaptic cleft

swelled tips of axon branches

- membrane called presynaptic membrane

- receiving neuron called post-synaptic membrane

- contain packets of NTs, called synaptic vesicles

ap at bouton triggers release of NT through exocytosis of synaptic vesicle (Ach).

- ach molecules diffuse across synaptic cleft, bind to receptor proteins on postsynaptic membrane

- open Na+ channels, enterNa+

excitatory post-synaptic potential

- entry of Na+ in postsynaptic membrane causes more +

- if epsp is large enough to reach threshold, leads to action potential in postsynaptic neuron

epsp

- voltage shift to more +

several aps arrive closely together, and cause enough NT to be released, leading to postsynaptic potential to cross threshold--resulting in an action potential.

(one action potential arriving at bouton isn't always enough to make postsynaptic membrane reach threshold)