Biological Psychology-Lecture Slides 04-Psychology-Andrew Weeks, Slides of Biological Psychology

Download Biological Psychology-Lecture Slides 04-Psychology-Andrew Weeks and more Slides Biological Psychology in PDF only on Docsity!

Topics

4.1 Resting Membrane Potential 4.2 Generation and Conduction of Postsynaptic Potentials 4.3 Integration of Postsynaptic Potentials 4.4 Conduction of Action Potentials 4.5 Synaptic Transmission: Chemical Transmission of Signals among Neurons 4.6 Neurotransmitters 4.7 Pharmacology of Synaptic Transmission

• Recording the membrane potential: difference in electrical charge between inside and outside of cell
• Inside of the neuron is negative with respect to the outside
• Resting membrane potential is about – 70mV
• Membrane is polarized (carries a charge)

Resting Membrane Potential

Even Distribution Uneven Distribution

Factors contributing to even distribution of ions (charged particles)

• Random motion – particles tend to move down their concentration gradient
• Electrostatic pressure – like repels like, opposites attract

Factors contributing to uneven distribution of ions

• Selective permeability to certain ions
• Sodium-potassium pumps

Ionic Basis of the Resting Potential

The Neuron at Rest

Neuron at Rest

Ions move in and out through ion-specific channels

K+ and Cl- pass readily

Equilibrium Potential (Hodgkin-Huxley model)

Little movement of Na+

A- don’t move at all, trapped Na+ is driven in by^ inside both electrostatic forces and its concentration gradient

Cl- is at equilibrium

K+ is driven in by electrostatic forces and out by its concentration gradient

Sodium-potassium pump – active (uses ATP) force that exchanges 3 Na+ inside for 2 K+ outside

The Neural Membrane

The passive and active factors that influence the distribution of Na+, K+, and Cl- ions across the neural membrane

An EPSP, and IPSP, and an EPSP followed by a typical AP

EPSPs and IPSPs

• Travel passively from their site of origination
• Decremental (graded) – they get smaller as they travel

Integration of Postsynaptic Potentials and Generation of Action Potentials

Integration of PSPs and Generation of Action Potentials

• One EPSP typically will not suffice to cause a neuron to “fire” and release neurotransmitter – summation is needed
• In order to generate an AP (or “fire”), the threshold of activation must be reached near the axon hillock
• Integration of IPSPs and EPSPs must result in a potential of about -65mV in order to generate an AP

The three possible combinations of spatial summation

The two possible combinations of temporal summation.

Integration

• All-or-none – when threshold is reached the neuron “fires” and the action potential either occurs or it does not
• When threshold is reached, voltage- activated ion channels are opened

Conduction of Action Potentials

Refractory Periods

Absolute – impossible to initiate another action potential

Relative – harder to initiate another action potential

Prevent the backwards movement of APs and limit the rate of firing

PSPs POTENTIALS (APs)

EPSPs/IPSPs

• Decremental
• Fast
• Passive (energy is not used)

Action Potentials

• Nondecremental
• Conducted more slowly than PSPs
• Passive and active (use ATP)

PSPs vs. Action Potentials (APs)

Velocity and Conduction

Velocity of Axonal Conduction

Conduction in interneurons is typically passive and decremental

Maximum velocity of conduction in human motor neurons is about 60 meters per second

Conduction in Neurons without Axons

The Hodgkin-Huxley Model in Perspective

The Hodgkin-Huxley Model in Perspective

• This model was based on squid motor neurons
• Cerebral neurons behave in ways that are not always predicted by the model