PSYC 4035 - Drugs and Behavior Exam 3 Study Guide

The neuron - Nerve cell

Neurons are highly organized cells that are specialized to communicate information.

Estimate: 100-1000 billion neurons in human nervous system.

Each part of the neuron plays a specific role in this communication.

Cell Body

Variable shape and size Contains nucleus. Functions: metabolic machinery of cell (i.e., Protein Synthesis, Metabolism,Energy Production, etc.)

Axon Hillock 

site where the axon exits the soma. Functions: establishing the action potential

Axon 

Function: electrochemical transmission - sometimes covered with myelin.

Axon Terminals 

swelling at end tip of axonal branch. Functions: release of neurotransmitters into synapse

Dendrites

thin branching fibers, spiny or aspiny, decreasing diameter. Functions: inputs- reception of transmissions from adjacent neurons.

How Neurons Work

• Electrochemical process

Propagation of impulse within neuron (electrical).

Transmission of impulse between neurons (chemical).

• Resting Potential

Neuron at rest.

Not firing.

Stable, negative charge inside neuron relative to outside (- 70 mV)

Where does the resting potential come from? 

1. Elemental ions: 

K+ (potasium) 

Na+ (sodium) 

CA++ (calcium)

Cl-  (chloride)

2. Elemental forces:

diffusion / concentration gradient

electrical potential (voltage) / electrostatic gradient

cell membrane at rest is largely impermeable to Na+ ions 

although ion channels or ionophores allow some ions through
Na/K ion pump – moves 3 Na+ outside moves 2 K+ inside 

results in: more (+) ions outside than inside.

the membrane permeability determines resting potential through 2 types of ion channels:

1. gated – let certain ions through under certain circumstances. 

2. Non gated – always lets certain ions through, but not fast enough to neutralize the ion pumps. 

• Action Potential

Neuron receives sufficient stimulation from receptor, other neurons, etc.

Na+ ions rush in.

Interior of axon becomes positive relative to the outside (+ 40 mV)

This release of energy passes down the axon and is the firing of the neuron.

Once neuron fires, resting potential returns.

• All or None Law

Once neuron fires, the impulse moves down the axon at the same intensity.

No stopping it.

• Impulse frequency

While there are differences in speed of transmission between neurons, increase in neuron stimulation doesn’t cause stronger impulse. Speed and electrical change remains the same regardless of intensity.

Stronger stimulation leads to more frequent firing of the neuron or more neurons activated.

• Absolute Refractory Period

Brief period of time after firing when neuron won’t fire no matter how much stimulation given.

As brief as 1/1000 of a second. HOWEVER, means a limit as to how many times neuron can fire per

second (the maximum is 500-600 times/second).

• Think of neuron like a toilet that works well

Information flows in 1 direction (out to the sewage!)

It is all or none - the toilet doesn't have "half flush" days

There is a period of time that, no matter how much you jiggle the handle, no flushing will occur

Depolarization – resting potential decreases (towards zero and positive numbers) hyperpolarization - resting potential increases (larger negative numbers) 

When depolarized past the threshold, the resting potential breaks down. 

Voltage-gated Na+ ion channels open and ions flow in along diffusion and electrostatic gradients. 

K+ channels then open allowing K ions to flow out. 

Gates close and ion pumps restore normal resting potential. 

All-or-None Law: 

All action potentials are the same. You either have one or you don’t.

Post synaptic potentials are generated on dendrites ans cell bodies 

Action potentials move along the membranes of a neuron. They are initiated at the axon hillock and travel along axons away from the cell body. 

Where do action potentials come from naturally? 

Sensory neurons 

They are generated in cell bodies which depolarize in response to specific stimulation. Called Post Synaptic Potentials (PSP). 

The more depolarization, the faster action potentials are generated at the axon hillock. 

Neurons do not touch each other 

How does activity in one neuron influence activity in another? 

Synapses 

Presynaptic neuron: 

• terminal bouton at the end of axons

• synaptic cleft

Post synaptic neuron 

-receptor sites 

Activity at synapses 

The arrival of an action potential at terminal causes C++ ion channels to open. This causes the release of a neurotransmitter from synaptic vesicles into the synaptic cleft. 

The neurotransmitter interacts with receptor sites located on the surface of large protein molecules. This causes a change in the resting potential of the membrane of the cell body of the post synaptic cell by opening ion channels . 

May directly (gated ion channel) or indirectly (second messenger) open ion channels. 

Depolarization causes excitation (opens Na+ channels) and increases firing rate. (Excitatory post synaptic potential, EPSP) 

Hyperpolarization causes inhibition (opens Cl- channels) and decreases firing rate. (Inhibitory post synaptic potential, IPSP) 

Summation of excitation and inhibition 

• spatial

• temporal

Slow, long acting changes 

Second messengers 

• may open ion channels

• may alter other aspects of cell functioning

Long term changes 

Kinases – Longer acting than second messengers 

Permanent changes 

Transcription factors – alter the expression of DNA and can change the production of ion pumps, ion channels and even synapses. 

Transmitter action terminated by reuptake or enzymes. 

Neuromodulator: cause changes in reactivity of postsynaptic membrane to other neurotransmitters. 

May act internally, or externally 

Neurotransmitters 

Acetylcholine 

Monoamines (biogenic amines) 

--catecholamines 

--Norepinephrine (NE) 

--Dopamine (DA) 

--Epinephrine (E) 

--Indoleamine 

--Serotonin (5-HT) 

Amino acids: 

GABA 

Glycine 

Glutamate 

Peptides: 

--Substance P 

--endogenous opiates (mrphinelike substances) 

--enkephalins 

--endorphins 

various hormones 

• somatostatin

• vasopressin

Dale’s Law: neurons always produce the same neurotransmitter (s) at all synapses. 

Cholinergic, dopaminergic, serotonergic, etc 

The effect of a transmitter depends on the nature of the receptor. Each transmitter may have many types of receptor. 

Level of neurotransmitter release can be governed by autoreceptors on the presynaptic membrane 

Drugs interfere with neurotransmission by interfering with what happens at synapses can block or facilitate.

Acetylcholine (Ach): 

deactivated by acetylcholinesterase (AchE) 

Acetylcholinesterase inhibitors: 

• organic phosphates – insecticides like Maticil

• nerve gasses like sarin

two types of Ach receptor sites: 

stimulated blocked 

muscarinic muscarine atropine 

nicotinic nicotine curare 

Monoamines: 

• Norepinephrine

• Epinephrine

• Dopamine

• Serotonin

Destroyed by two enzymes: 

Monoamine Oxidase (MAO) 

COMT 

Reuptake – blocked by cocaine – SSRIs 

Receptor subtypes: 

E and NE: 

alpha-1 alpha-2 beta-1 beta-2 

Dopamine: 

D1........D6 

Serotonin: 

5-HT1 (4 subtypes).....5-HT4 

Gamma-aminobutyric Acid (GABA) 

universally inhibitory – linked to a Cl- ion channel. 

Glutamate: 

excitatory transmitter 

NMDA receptor 

non NMDA receptor 

Peptides: 

endorphins – 16-30 amino acids 

enkephalins – 5 amino acids 

receptor types: 

mu, kappa and delta receptors 

blocked by nalorphine 

The nervous system 

CNS – brain and spinal cord 

PNS – everything else 

bundles of axons – white matter nerves (PNS) or tracts (CNS) clusters of cell bodies - grey matter 

ganglia (PNS) or centres (nuclei) (PNS) Peripheral Nervous system (PNS) somatic: 

-----conscious senses 

-----voluntary motor 

autonomic: 

-----sympathetic NS – fight-or-flight – epinephrine 

-----parasympathetic NS – vegetative functions - ACh Central Nervous system (CNS) spinal cord 

relay center 

reflexes 

ventral – motor output 

dorsal – sensory input 

Brain 

100,000,000,000 neurons each with synapses on 1000 other neurons and 10,000 synapses from other neurons 

medulla – autonomic control 

• breathing

• vomiting

RAS and Raphé System 

RAS – arousal 

Raphé System 

• sleep

• mood

Locus Coeruleus 

mood: fear, panic, anger 

primarily NE, 

stimulated by monoamines 

inhibited by GABA 

Cerebellum: 

coordination of motor control 

Basal Ganglia: 

striatum – input from thalamus and cortex 

globus palladus – output side with feedback to thalamus 

coordination of motor control 

• - -extrapyramidal motor system

• - -DA receptors

• - -DA deficiency – Parkinsons Disease

Periaquiductal gray: 

pain control – mu receptors and morphinelike transmitters punishment system 

Limbic system: 

hypothalamus – eating and drinking control 

medial forebrain bundle 

--- reinforcement centres 

---mesolimbic system (DA) 

------ ventral tegmental area 

------nucleus accumbens

hippocampus – leraning and memory 

amygdala and septum – serotonergic input from the Raphé system Aggression and emotion 

Cortex 

sensory input areas 

motor control output areas 

language 

memory and thinking 

glutamate – excitatory transmitter 

GABA – inhibitory transmitter 

Development of the Nervous system 

cells formed during first 12 weeks 

migrate to appropriate location 

send out axons to correct target 

form synapses 

controlled by chemical signals 

psychoactive drugs can disrupt the process because: 

1. get into the brain 

2. confuse or block chemical signals 

Teratology – brain malformation, eg, 

Fetal Alcohol Syndrome 

Functional or behavioral teratology: there may be no anatomical malformations, but functioning of the brain may be disturbed. There may be behavioral changes.