Neuronal structure and communication

Class 3

NEURON STRUCTURE & FUNCTION

The Neuron’s Structure

The Cell Membrane: Barrier and Gatekeeper

• Concentration of dissolved substances in the extracellular and intracellular fluid is different

What do Membrane Proteins Do?

How the Movement of Ions Creates Electrical Charges

– Cations - Positively charged ions; Na+, K+– Anions - Negatively charged ions; Cl-, protein anions

(A-)– Ions move from areas of high charge to areas of low

charge and substances move from areas of high concentration to low concentration.

– Cell-Membrane Structure is impermeable to salty solutions

– Protein molecules in the membrane allow certain ions to pass

Resting Potential

• Neurons at rest– Unequal distribution of ions – Intracellular fluid has a negative charge

relative to the extracellular fluid– Difference in charge is about -70mV (Resting

Potential)

Resting Potential

The Action Potential

• Action Potential– Brief but extremely large flip in the polarity of

an axon’s membrane– Voltage across the membrane reverses

• The inside becomes positive relative to the outside

– Occurs when depolarization of the membrane occurs

– Membrane must reach Threshold Potential at about -50mV

Triggering an Action Potential

Sending a Message Along an Axon

NEURONAL COMMUNICATION: NEUROTRANSMISSION

The Structure of Synapses

Steps in Neurotransmission

Classifying Neurotransmitters

• Three classes of neurotransmitters– Small-Molecule Transmitters– Peptide Transmitters– Transmitter Gases

Small-Molecule Transmitters

• Small organic molecules

• Synthesized and packaged in axon terminals

• Derived from the food we eat

• Act quickly

Peptide Transmitters

• Neuropeptides

– Multifunctional chains of amino acids made by the cell’s DNA

– Process is longer to make and transport than small molecules

• Peptide transmitters:

– Serve as hormones

– Active in response to stress

– Encourage mother-child bonding

– Facilitate learning

– Regulate eating and drinking

– Respond to pleasure and pain

Transmitter Gases

• Synthesized as needed by the cell• Can be produced in many regions of the cell• After production diffuse away from the cell right

through the cell membrane (don’t need channels)– Nitric Oxide (NO) – Carbon Monoxide (CO)

Receptors for Direct and Indirect Effects

• Ionotropic– Direct effects– Allow the movement of

ions across the membrane

– Rapid– Do not last long

• Metabotropic– Indirect effects– Slower– Last longer– G-Protein

• Three subunits

– Second messenger• Carries the message to

other structures in the cell

Activating Systems

• Activating Systems– Cell bodies located in the brainstem, axons

distributed throughout the brain– Neurotransmitter pathways. The NTs are

manufactured in the cell bodies and released throughout the system.

Activating Systems: Noradrenergic Pathway

Activating Systems: Serotonergic Pathway

Activating Systems: Dopaminergic Pathway

Activating Systems: Cholinergic Pathway

CLINICAL VIGNETTES