Biological Psychology

Key Point for this Unit: Everything psychological is simultaneously biological!!

Dendrites – receive messages from other cells and conduct impulses toward the cell body

DendritesNEURON

Cell Body – the cell’s life-support center

Dendrites

Cell Body

NEURON

Axon – the extension of a neuron through which messages are sent to other neurons or to muscles or glands

Dendrites

Cell BodyAxon

NEURON

Myelin Sheath – a layer of fatty cells covering the axon, helps speed neural impulses

Dendrites

Cell BodyAxon

Myelin Sheath

NEURON

Terminal branches of axon – form junctions with other cells

Dendrites

Cell BodyAxon

Myelin Sheath

Terminal branches of axonNEURON

Biological Psychology

It is all about the body!!!!Concerned with the links between biology

and behavior (also called Neuroscience)

The Nervous System

It starts with a NEURON: an individual nerve cell; the basic building block of the nervous system

How does a Neuron fire?• Resting Potential: slightly

negative charge.• Reach the threshold when

enough neurotransmitters reach dendrites.

• Threshold: level of stimulation required to trigger a neural impulse; excitatory signals minus inhibitory signals must equal a minimum intensity

• Go into Action Potential; a neural impulse (brief electrical charge) that travels down an axon.

• All-or-none response.

Neurons – How do they work?

• Neurons send messages to other neurons – this is what keeps every part of our body in communication with every other part.

• Neurons “fire” – send an impulse (message) down their length – or they don’t “fire”

Action Potentials

• This “firing” of impulse messages is called the action potential.

• An action potential is a brief electrical charge that travels down the axon of the neuron.

Play Animation

Watch “The Action Potential” movie at home:

http://brainu.org/files/movies/

action_potential_cartoon.swf

What causes an impulse to fire or not fire?

• When a neuron is at rest and capable of generating an action potential, it is called the resting potential

• There are fluids inside and outside of the neuron, filled with electrically charged particles (ions)

• When the neuron is at rest, there is a negative charge on the inside of the neuron compared to the outside.

• At rest, the inside of the cell is at -70 millivolts

Neuron CommunicationResting Potential

Action Potentials, cont.

• Stimulation from inputs to dendrites causes the cell membrane to open briefly

• Positively charged sodium ions flow in through the cell membrane

• If resting potential rises above threshold, an action potential starts to travel from the cell body down the axon– Threshold - Each neuron receives excitatory and

inhibitory signals from many neurons. When the excitatory signals minus the inhibitory signals exceed a minimum intensity (threshold) the neuron fires an action potential.

Figure 2.3 Action potentialMyers: Psychology, Ninth EditionCopyright © 2010 by Worth Publishers

Action Potential, cont.

• The shift in electrical charge travels along the neuron

• The intensity of an action potential remains the same throughout the length of the axon

• Refractory period - The “recharging phase” when a neuron, after firing, cannot generate another action potential

For more information on action potentials, see http://faculty.washington.edu/chudler/ap.html

For an interactive game/demo to help you learn about action potentials, see http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf

To help a mad scientist make a “mad, mad, mad neuron” in a cartoon game, see http://learn.genetics.utah.edu/content/addiction/reward/madneuron.html

Neuron CommunicationAll-or-None Principle

• The principle that if a neuron fires it will always fire at the same intensity

• A strong stimulus can trigger more neurons to fire, and to fire more often, but all action potentials are of the same strength and speed.

• A neuron does NOT fire at 30%, 45% or 90% but at 100% each time it fires.

Just like a gun, there is no

“part-way” firing

• Consider the following concepts:– Depolarization– All-or-none principle– Direction of impulse– Refractory period– Threshold– Resting potential– Action potential

How is a neuron firing similar to a toilet flushing?

How about a school bus? See “The School Bus Story” ppt. here: http://ap-psychology-1st.grandblanc.high.schoolfusion.us/modules/locker/files/group_files.phtml?gid=1316804&parent=4425886&sessionid=8b85e917de8943dc49c835c286f82aff

The School Bus Story

A tale of ionic influence on action potentials

Setting the stage

• Imagine a school bus, filled with unhappy kids on their way to school…

Meanwhile…

• Outiside, it’s a BEAUTIFUL day!– Sun is shining– Birds are chirping– Everything is happy

The point is…• The unhappy (negative) kids, sealed

inside their impermeable school bus, cannot get to the happiness (positivity) outside!

All of a sudden…

• The bus driver opens the door! Yay! The bus is now permeable… but only in a selected place.

Area of selective permeability

And then?

• Sunlight, happiness, butterflies, and positivity fill the negative kids on the bus with deep inner joy.

Yay, happy kids!

• If enough kids go from sad to happy when the beautiful air whooshes in, they have reached the “threshold.” If/when this threshold is reached, they start getting rambunctious ("action potential"). 

• After having wasted their energy being rambunctious, there's a short time ("refractory period") before they can start it up again.

How does this relate?

• The kids = negative ions.• The bus = an axon.• The sunlight = positive sodium ions.• The bus pre-open door = a polarized neuron in

its resting potential.• The driver = cell nucleus.• The opened door = selectively permeable gates.• The happy kids = an action potential… but only if

enough of them become happy!

What happens when an action potential reaches the end of the

axon and enters the terminal buttons?

TYPES OF NEUROTRANSMITTERS

Chemical messengers that that traverse the synaptic gap between neurons

REVIEW… remember agonists and antagonists???

Agonist – mimic neurotransmitters**Example: Morphine mimics endorphins

Antagonist – block neurotransmitters**Example: Poison blocks muscle movement

Did you know? Botox is an antagonist that paralyzes facial muscles!

Acetylcholine (ACH)

• Involved with voluntary muscle movement, learning and memory

• Lack of ACH has been linked to Alzheimer’s disease.

Dopamine

• Deals with motor movement and alertness.

• Lack of dopamine has been linked to Parkinson’s disease.

• Too much has been linked to schizophrenia.

Serotonin

• Involved in mood control.

• Lack of serotonin has been linked to clinical depression.

Endorphins

• Involved in pain control.

• Many of our most addictive drugs deal with endorphins.

“Runner’s High” occurs when your brain signals the release of endorphins to reduce pain!

Did you know? The word “endorphin” literally means “morphine within”!

The Nervous System

The Nervous System - body’s speedy, electrochemical communication network consisting of nerve cells

Central Nervous System (CNS)

•The Brain and spinal cord

• Neural networks – interconnected neural cells; more connections made as experience gained

Peripheral Nervous System (PNS)

• All nerves that are not encased in bone.

• Sensory and motor neurons that connect the CNS to the rest of the body

• Is divided into two categories….somatic and autonomic.

Somatic Nervous System

• Controls voluntary muscle movement.

• Uses motor neurons.

Autonomic Nervous System• Controls the

automatic functions of the body.

• Divided into two categories…the sympathetic and the parasympathetic

Sympathetic Nervous System

• Arouses the body• Fight or Flight

Response.• Automatically

accelerates heart rate and breathing, dilates pupils

Parasympathetic Nervous System

• Calms the body• Automatically

slows the body down after a stressful event.

• Heart rate and breathing slow down, pupils constrict

Sympathetic and Parasympathetic

Types of Neurons

• Sensory Neurons – sends receptors to CNS

• Interneurons – internal communication neurons

• Motor Neurons – CNS to muscle and glands

Reflexes• Normally, sensory

neurons take info up through spine to the brain.

• With reflexes though, some reactions occur when sensory neurons reach just the spinal cord.

• Automatic response to sensory stimulus; interneurons react to sensory neurons w/o going to brain