Chapter 3:Biological Psychology

• Neurons (structure)

• Action Potentials (process)

• ***1. Distinguish the parts of a neuron and what they do• ***2.  Describe electrical responses of neurons and what makes

them possible.• ***3.  Explain how neurons use neurotransmitters to

communicate with eachother• **4.  Describe how the brain changes as a result of

development, learning and injury.• ***5.  Identify what roles different parts of the central nervous

system play in behavior.• **6.  Clarify how the somatic and autonomic nervous systems

work in emergency and everyday situations.• **7.  Describe what hormones are and how they affect behavior.• **8.  Identify the different brain-stimulating, -recording and -

imaging techiques.• **9.  Evaluate results demonstrating the brain's localizaiton of

function• **10.  Describe genes and how they influence psychological

traits.• **11.  Explain the concept of heritability and the misconceptions

surrounding it.

Neurons and how they work

• http://www.youtube.com/watch?v=FR4S1BqdFG4&feature=related

Structure

Neurons

• The basic units of the nervous system• Nerve cells that specialize in communication• Neurons receive info from neighboring neurons

and pass those signals to other neurons• There are about 100 billion neurons in the brain

Parts of the Neuron

• Dendrites– Branchlike extension that detect signals from

other neurons

Dendrites

Parts of the Neuron

• Dendrites– Branchlike extension that detect signals from other

neurons

• Cell body (soma)– Center of neuron; contains the nucleus; builds new

cell components – where signals from other neurons are collected,

integrated and then sent to the axon

Cell Body

Nucleus

Dendrites

Neurons and their dendrites (shown stained pink) with their nuclei (shown stained purple)

Parts of the Neuron• Dendrites

– Branchlike extension that detect signals from other neurons

• Cell body (soma)– Center of neuron; contains the nucleus; builds new

cell components – where signals from other neurons are collected,

integrated and then sent to the axon

• Axons– Carries signals away from cell body and transmit

information

Cell Body

Nucleus

Axon

Dendrites

Neurons

• Myelin: a fatty substance that wraps around axons and speeds up the transmission of info from the cell body to the terminal buttons

Outer Membrane

Cell Body

Nucleus

Axon

Myelin

Dendrites Terminal Buttons

Parts of the Neuron• Dendrites

– Branchlike extension that detect signals from other neurons

• Cell body (soma)– Center of neuron; contains the nucleus; builds new cell

components; Where signals from other neurons are collected, integrated and then sent to the axon

• Axons– Carries signals away from cell body and transmit

information

• Axon Terminal:

– Small knobs on the end of axons that release the signals into the synapse

Outer Membrane

Cell Body

Nucleus

Axon

Dendrites Axon Terminals

Neuronal Components• Neurotransmitters (NTs)

– Chemical messengers that allow neuron to neuron communication

– Stored in the axon terminals, in synaptic vesicles

– Glutamate, GABA, Acetylcholine

• Synapse– Space between neurons through which NTS

travel– Signals leave one neuron’s terminal buttons,

cross the synapse and then are picked up by the dendrites of other neurons

Neuron 1

Neuron 2

SynapseSynapse

*The small space between Neuron 1’s axon terminals & the dendrites of Neuron 2 is the synapse -- messages are sent across this from one neuron to the other

Process

Action Potentials

• Normally, neurons are at what we call the resting potential

• But, when a neuron’s dendrites pick up neurotransmitters, the neuron will generate electrical activity

• The electrical activity creates a charge inside the neuron

• When there is enough of a charge inside the neuron, an action potential will occur

Action Potentials

• The electrical signal that passes along the axon to the axon terminals– When an action potential shoots down the

axon, the neuron is said to have fired

• To understand action potentials, you need to learn a bit more about neurons…

Neurons & Charges

• Usually, the electrical charge inside the neuron is negative– At it’s resting potential (-60 millivolts)

• Outside the neuron there is intercellular fluid– Usually, this fluid has a positive electrical

charge

Resting Potential

_ ____

__

_

_ _

__

_

_

___ _

+ ++

++ +

+ +

+

+ +++

+

++

Intercellular Fluid

* Resting Potential: negative charge inside the neuron & positive charge outside

++

+

_

_

• Neurons are surrounded by a cell membrane

• The cell membrane has “gates” along it that can be open or closed - normally they are closed

• The neurotransmitters will begin the action potential by opening the gates

• When the gate open, positive particles in the cellular fluid rush in to the neuron

• The neuron’s charge starts to change from negative to positive

• The neuron’s charge will reach its threshold (-55 mV)

• When the threshold is reached, the neuron fires an action potential

Voltage Across the Membrane

Source: Adapted from Sternberg, 2004a

Voltage Across the Membrane

Source: Adapted from Sternberg, 2004a

Refractory Period

• Between action potentials there is a brief rest called the absolute refractory period

– The neuron cannot fire during this period

– Once the cell returns to its resting potential, it can fire again

• Neurons can fire over and over again

• Eventually, the action potential reaches the synaptic vesicles at the end of the axon (inside the axon terminals)

• The vesicles are filled with neurotransmitters

• The action potential causes vesicles to burst

• Release NTs into the synapse• NTs bind with receptor sites on neighboring neurons’ dendrites• Process starts over with another neuron

• During the action potential, positively charged particles fire rapidly down the axon

Direction of action potential

Action Potentials

During an action potential, positive ions first flow into the axon. There is little or no net

change in the distribution of negative ions.

When the inside of the axon accumulates maximal levels of positive charge, an

action potential fires

Direction of action potential When the action

potential reaches the axon terminal, it triggers the release of neurotransmitters.

Neurotransmitter release

Source: Adapted from Sternberg, 2004a

At rest.

Action Potentials• Neurons have an “all or none” law - either they fire an action potential completely, or they do not fire one at all

-Don’t have weaker/stronger action potentials

Outer Membrane

Cell Body

Nucleus

Axon

Myelin

Dendrites Terminal Buttons

http://science.education.nih.gov/supplements/nih2/addiction/activities/lesson2_neurotransmission.htm