Using your textbook, (page 418-420) find and define the following terms:

•Action potential

•Polarized membrane

•Depolarization, repolarization

•Sodium-potassium pump

•Refractory period

Explain the contributions of the following researchers:

•Galvani, Einthoven, Dubois-Raymond, Berger, Bernstein, and Cole and Curtis

Propagating an Action Potential: Method and Speed

An action potential propagates along an axon by a process in which, once triggered, the influx of positive ions causes the adjacent Na+ gate to open and, in turn, this causes the next Na+ gate to open, and so on. Hence, an action potential is actually self-propagating.

Myelin sheaths permit speeds up to 100 m/s.

How?

Saltatory conduction

Saltus is Latin for jump

•When the Na+ ions enter the inside of the axon, they quickly spread.

•The insultation of the myelin allows the ions to move quickly to the next Na+ gate at a node of Ranvier.

•The movement of ions from one node to the next is known as local current flow.

•The action potential jumps from one node to the next.

How fast does an action potential move along an axon?

The thinnest axons propagate an action potential at less than 1 meter per second (1 m/s).   

Thick axons propagate action potentials at about 10 m/s.  

WHAT YOU SHOULD KNOW

•identify the three major components of an neuron and their function

•identify the benefits of myelination to a neuron

•distinguish between the basic types of neurons

•explain the role of sodium and potassium in an action potential

•explain the components of an action potential

•explain the concept of threshold

•explain how salutatory conduction enhances neuron activity

Neuron to Neuron Communication

Two types of communication occur

1. Electrical synapses

2. Chemical synapses

Electrical Synapsesdistinct minority

found in all mammalian nervous systems, including the human brain.

two communicating neurons extremely close at the synapse are linked by an intercellular specialization called a gap junction

Gap Junction

How gap junctions work:

•They are communication portholes

•Portholes are formed by proteins that span two cells

•They form a pipe between the cells

•Pore of a gap junction channel is much larger than the pores of the voltage-gated ion channels that create action potentials.

•As a result, a variety of substances can diffuse between the cytoplasm of the pre- and postsynaptic neurons.

•Current (ions) can pass both directions

Chemical Synapses

Transmission Across a Synapse

The minute space between the axon bulb and the cell body of the next neuron is the synaptic cleft.

NEUROTRANSMITTER1. The release of a

neurotransmitter is triggered by the arrival of an action potential

2. AP causes occurs cellular secretion, also known as exocytosis:.

Neurotransmitter ReleaseA. Synaptic vesicles store

neurotransmitters that move across the synapse.

B. When action potential arrives at presynaptic axon bulb, synaptic vesicles merge with presynaptic membrane.

C. Release chemicals into cleft

D. Neurotransmitter molecules diffuse across synaptic cleft to postsynaptic membrane where they bind with specific receptors.

E. The type of neurotransmitter and/or receptor determines if the response is excitation or inhibition.

• The action that follows activation of a receptor site may be either depolarization (an excitatory postsynaptic potential) or hyperpolarization (an inhibitory postsynaptic potential).