The Neuron: Part I
Biological Psychology
Biopsychology/Psychobiology
 Branch of psychology that is concerned with the links
between biology and behavior
 Behavior Genetics
 Evolutionary Psychology
 Neuroscience: specifically focuses on the study of
the brain and nervous system
 Behavioral Neuroscientists
 Neuropsychologists
Nervous System
 Electrochemical communication system of the body
 Neuron: basic building block (cell) of the nervous system
 Nerve: bundles of neurons
 Brain contains 100 billion neurons
 If each neuron was a second, it would take over 3,170 years
to count all of your neurons
Types of Neurons
 Involved in all neural communication:
 Sensory Neurons (afferent): carry messages from the
tissues/sense organs inward to the brain and spinal cord
 Interneurons (association neurons): carry messages from
neuron to neuron within the brain and spinal cord
 Motor Neurons (efferent): carry messages from the spinal
cord/brain to the muscles/glands
 Mirror neurons: involved in mimicking the behavior of
others; Allows us to identify and empathize with others
Neural Communication
 A two step process
 1. Takes place within a single neuron and involves the
generation of an electrical signal (today)
 2. Takes place between two neurons and involves
the release of a chemical messenger (tomorrow)
Parts of the Neuron
Parts of the Neuron - Dendrites
Other cells do not have dendrites;
unique to the neuron
Parts of the Neuron - Soma
Nucleus: Contains
chromosomes
Parts of the Neuron - Axon
Can vary in length (fractions of a
millimeter to three feet)
Stub your toe: Cell body in lower
back, axon down to toe!
Parts of the Neuron – Myelin Sheath
Degeneration of myelin =
multiple sclerosis
Parts of the Neuron - Terminals
Terminal Buttons
Glial Cells (or glia; glue in Latin)
 Hold neurons in place
 Provide nourishment
 Remove waste products
 Prevent harmful substances from passing from the bloodstream
to the brain (blood-brain barrier)
 When damaged some glia form scar tissue, inhibiting repair(in
brain and spinal cord); Glia in the other parts of the nervous
system do not form scar tissue and help damaged axons regrow
 Form the myelin sheath
 Myelinated tissue = white matter
 Unmyelinated tissue = gray matter
 Not done growing until early adulthood (by 25)
Neural Communication
 Neurons speak in a “yes” or “no” language –
electrochemical impulses
Three Phases of Neural Activity
 Resting Potential
 Action Potential
 Refractory Period
Resting Potential
 Neuron is not processing information
 Neuron is polarized
 More negative ions (charged particles) inside the
neuron than outside
 Like a spring that has been compressed by not released
+
Na+
-
K+
-
-
Na+
Na+
Na+
Na+
K+
K+
-
K+
K+
-
-
Action Potential
 When an incoming impulse exceeds the threshold of excitation,
the membrane will open allowing an inflow of sodium ions
 Trigger of a gun
 Happens in steps down the axon of the neuron (channels
open in a chain reaction; row of dominoes)
 Neuron is now depolarized (inside is positively charged
compared to outside)
 This is an action potential (or neural impulse) – ELECTRIC
Na+
K+ Na+
K+ Na+ K+ Na+
Action Potential Cont.
 As a result of the depolarization, the potassium ions
will flow out of the neuron (“wants” to repolarize)
 Neuron is now the opposite of how it needs to be to
fire
 Can travel from 2 mph to 200 mph (3 million times
slower than electricity)
K+
K+
K+
Na+
K+ Na+
K+
Na+
Na+
Refractory Period
 Period where the neuron cannot create another
action potential
 It is recharging
 A sodium-potassium pump replaces the ions to their
correct place (sodium outside, potassium inside)
 (1/1000 second)
Unmyelinated v. Myelinated Neurons
 Action potentials do not affect the entire axon at once
 Takes place in small segments of the axon  electrical charge is
duplicated along the length of the axon
 Unmyelinated Axon: action potentials happen in a step-by-step process
 Myelinated Axon: action potentials are formed only at the sections of
the axon between the myelinated “sausages” (called nodes of Ranvier)
 Can skip the sections that are myelinated (20 x faster)
Neural Signals
 Neurons communicate an excitatory effect, telling other
neurons to fire OR
 An inhibitory effect, telling other neurons to rest
 A single neuron may have hundreds of dendrites and its axon
may branch out to touch hundreds or thousands of other cells
All-Or-None Principle
 Neurons either fire or they don’t
 Cannot fire at 50%, 75%, 2%
 Strong signals CAN make a neuron more likely to
fire
The Neuron Part II
Communication Between Neurons
Neurons Do Not Touch
 Neurons do not touch each other
 Synaptic Gap (cleft): fluid filled gap in between a
sending and receiving neuron
 Need something to cross the gap….
 Neurotransmitters: chemical messengers that
cross the gap and latch onto receptor sites on the
dendrites of a receiving neuron
 Key and lock fit
When They are Done…
 Neurotransmitters do not stay on receptor
sites forever
 They are either:
 Reabsorbed by the sending neuron
 Broken down and recycled by the body
 Reuptake: Process where unused/finished
neurotransmitters are reabsorbed by the sending
neuron
Neurotransmitters: Psychologists have
discovered at least 50 kinds
Perfect Fit Neurotransmitters
ACh - Acetylcholine
 The messenger at every junction between a motor
neuron and a skeletal muscle – important in
movement (ACh released, muscles moves)
 Also found in brain circuits related to learning and
memory
 These circuits are the first to deteriorate in
Alzheimer’s patients
Dopamine
 Associated with systems that govern movement,
planning, reward
 Parkinson’s Disease results when dopamine-releasing
neurons in the brain’s movement circuits die
 Involved in reward centers that are active when we do
things that promote survival – sex, eating
 Addictive drugs (cocaine, methamphetamines)
increase dopamine production
 Implicated in schizophrenia and ADHD
Serotonin
 Involved with systems regarding sleep, appetite, and
mood (all closely related)
 Low levels are associated with depression
Norepinephrine
 Arousal, vigilance
 Also released by the autonomic nervous system
(fight or flight system)
 Implicated in disturbances of arousal and vigilance
like bipolar disorder and posttraumatic stress
disorder
Endorphins
 Endogenous Morphine
 Modify our natural response to pain
 “Runners high” (sense of well being and reduced
pain, due to release of endorphins)
GABA (Gamma-Amionbutyric Acid)
 Inhibitory neurotransmitter
 Too much: sleep and eating disorders
 Too little: anxiety
 Anxiety Meds (Xanax, Valium) increase the
supply of GABA to decrease brain activity
Glutamate
 Excitatory neurotransmitter
 Oversupply can overstimulate brain, producing
migraines or seizures
 Contained in MSG (monosodium glutamate)
Neurotransmitters and Medicines
 Many antidepressant medicines (Prozac) are SSRIs
 Selective Serotonin Reuptake Inhibitors
 Stops Serotonin from being “sucked back up” into sending
neuron
 More serotonin available in synapse for binding on receptor sites
 ADHD (There are several types)
 Associated with: GABA, dopamine, norepinephrine, and
serotonin
 Drugs to treat ADHD either redistribute existing
neurotransmitters, imitate certain neurotransmitters, or
cause the production of neurotransmitters
 Adderall, Ritalin
Neurotransmitters and Medicine cont.
 Antipsychotic medication (chlorpromazine –
Thorazine) prevents dopamine from binding to
receptor sites, which reduces hallucinations in
schizophrenic patients
Imposters! Agonists
 Agonist: compound that mimics neurotransmitters
 Sort of fits in the lock
 Black Widow Venom
 Chemical structure is similar to ACh
 Latches on to ACh receptor sites and mimics effect (movement)
 Venom +ACh = excessive, uncontrollable movements aka
convulsions
Agonists (cont)
 Morphine, Oxycotinin, Heroin : Fake endorphins
 Body stops making own endorphins
 Everything hurts when taken off quickly!
Antagonists
 Block the receptor sites so that neurotransmitters
cannot latch on
 Curare: Poison used by native tribes
 Blocks ACh sites  paralysis!
 Botulin: Found in botox
 Paralyzes muscles by blocking ACh receptor sites
Caffeine
 Blocks the action of adenosine
 Adenosine inhibits the release of neurotransmitters
related to arousal
 Forced wakefullness!