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Summary PSYCH1000 Chapter 3 textbook & lecture notes
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PSYCH1000: CHAPTER 3: BIOLOGICAL FOUNDATIONSOF BEHAVIOUR
Parts of the Neuron
• Neurons
• Dendrites: receive nerve impulses from other neurons
• Cell body (soma): controls vital cell processes
• Axon: transmits nerve impulses to adjacent neurons/glands/muscles
• Axon terminals & synaptic knobs: communicate between neurons
• Myelin Sheath: fatty insulating layer around some axons, speeds up reaction time
• Broken up by nodes of ranvier (axon open to external fluid at these gaps)
Types of Neurons
Sensory neurons bring info in —> afferent fibres
Motor neurons go to effectors (muscles) —> efferent fibres
Interneurons relay between neurons
Nervous impulses not instantaneous
Can be bipolar, unipolar, multipolar
How Neurons Work: Neural Transmission
• Nerve impulse (action potential): quick reversal of charge (potential) inside/outside cell
membrane as sodium ions flow in channels from outside fluid (depolarization)
• Graded potentials = levels of stimulation, Action potentials = all-or-nothing (must reach
threshold or doesn’t happen at all)
• Cell membrane = semipermeable
• Extracellular fluid is more positively charged, inside more negative (at resting potential -70mV)
• The action potential
• Stimulation
• Membrane becomes more permeable (+ sodium floods in)
• Depolarization: inside becomes more positive
• Threshold: potential reaches -55mV
• Gates open and more sodium rushes in (potential reaches +40mV)
• Repolarization: potassium gets pumped out (inside becomes more negative)
• Absolute refractory period —> from peak positive charge to lowest negative charge (neuron
cannot be stimulated during this period)
• Hyperpolarization: potential dips below resting potential
• Relative refractory period: returns to resting potential (can be stimulated during this period
but more stimulation is required)
• Action potential gets sent down the axon (chain reaction)
• Graded potential (stimulation that doesn’t go past the dendrites/axon helix)
How Neurons Work: Synaptic Transmission/Neural Communication
• Axons and dendrites don’t physically touch —> communicate via chemicals over gap
(synaptic cleft)
• Synaptic transmission
• Electrical activity from AP in presynaptic neuron makes vesicles move to gap, open +
diffuse chemicals into synapse
• Vesicles in axon contain neurotransmitters (chemical messengers)
• Neurotransmitters bind to / stimulate postsynaptic neurons that have the matching shape
receptor sites
, • Chemicals make postsynaptic sodium channels open (depolarization) = EPSP (excitatory)
• Chemicals make postsynaptic K channels open (hyperpolerization) = IPSP (inhibitory)
• Many graded potential IPSP / EPSPs at once (add together/cancel each other out)
• if the added stimulation is enough, AP occurs
• Re-uptake: presynaptic neuron vacuums the chemicals back out of the gap (need to keep
gap clean)
• leftovers get broken down by MAO
How Neurons Code for Intensity
• Height of peak (+40) always the same no matter intensity of stimulus
• Rate of firing (there is a max firing rate —> can’t fire during absolute refractory period)
• # neurons activated
Dis-inhibition: (inhibiting the inhibitor neuron)
Notable Neurotransmitters
Norepinephrine (NE)
inhibitory & excitatory
related to arousal, eating
Acetycholine (ACh)
excitatory & inhibitory
memory, motor, behaviour inhibition
Dopamine (DA)
inhibitory & excitatory
voluntary movement, arousal, pleasure
Serotonin (5-HT)
inhibitory & excitatory
sleep, thermoregulation
GABA
inhibitory ONLY
motor behaviour
How Drugs Work
• increase or decrease amount of neurotransmitter
• terminate transmitter action
• stimulate (agonist) / block (antagonist) receptor sites
• mimics / blocks effects of neurotransmitter
• prevent reuptake of neurotransmitter
Central Nervous System
• Spinal cord
• Interneurons inside SC connect sensory & motor neurons
• Simple stimulus/response connections —> spinal reflexes (don’t go to brain)
• Brain
• Hindbrain
• Medulla (vital bodily functions)
• Pons (sensory + motor neurons, timing schedules?)
• Cerebellum (fine-tuned motor coordination)
• Basal ganglia (
• Midbrain
• Reticular formation (consciousness, attention, sleep)
• Ascending: prepares higher areas of brain to respond to stimulation
• Descending: “gate”, decides which stimuli enter to consciousness
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