Nervous System Function
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Neurons
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Base unit that has very simple function – “decide” whether to
transmit signal or not
Organization
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Billions of Neurons (estimates of 100 billion)
Very complex interconnections
Create systems/circuits that can function independently (parallel
processing)
“Simple decisions” passed to “higher” levels for that add
additional information to create generate more complex
decisions (hierarchical processing)
Very expensive - less than 2% of weight but uses 20% of
energy
Neuron Structure
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Cell Body
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Dendrites
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Receive information
Axon
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Nucleus – genetic information
Carry information “long” distances
Myelin (Multiple Sclerosis)
Axon Terminals
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Transmit information
Neuron - Structure
Neuron Function
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Electrical Activity
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Used to transmit signal within neuron
Chemical Activity
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Used to transmit signal between neurons
Synapse – small gap that physically separates
neurons
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Neurotransmitters – special “chemicals” that
neurons use to transmit message across the
synapse
Neuron Function
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Electrical Activity
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Resting Potential
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Inside negative (-70 mV) compared to outside
Inside has high K+ (negativity comes from proteins
& other negative ions)
Outside has high Na+
Forces at work
 Electrical
 Diffusion
Neuron Function
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Electrical Activity
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Graded Potential
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Depolarization – Inside less negative (e.g., Na+ enters)
Hyperpolarization – Inside more negative (e.g., Cl- enters)
Action Potential
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When graded reaches approximately -55mV
Electrical impulse that travels down cell – axon to axon
terminals
Axon terminals release neurotransmitter
Neuron Function
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Electrical Activity
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Restoring Resting Potential
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Sodium-Potassium Pump – moves Na+ out of cell
and K+ into cell
This requires cell to use energy
Neuron Function
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Chemical (Neurotransmitter) Activity
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Leads to graded potentials in neuron
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Excitatory NTs – causes depolarization in neuron
Initiatory NTs – causes hyperpolarization in
neuron
Neuron – Excitation & Inhibition
Neuron - Synapse
Synapse Types
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Multiple ways of connecting
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Examples
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Axon to Dendrite – excite or inhibit neuron
Axon to Axon Terminal – moderate NT release
Axon to Extracellular Space or blood – potential
for diffuse effects
Synapse Types
Synapse Function
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Neurotransmitter cycle in Axon Terminals
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Synthesis
Storage
Release
Inactivation
Reuptake
Degradation
Neural transmission problems if cycle disrupted
(e.g., drugs) at any step
Synapse Function
Synapse Function
Neurotransmitter Types
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Small Molecules
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Nine – Acetylcholine (ACh), dopamine (DA),
norepinephrine (NE), epinephrine (adrenaline), serotonin
(5-HT), histamine, GABA, glycine, glutamate
Simple (or no) alterations to basic food components
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Glutamate & glycine are amino acids
DA and NE from tyrosine & 5-HT made from tryptophan
Manufactured in axon terminals
Large quantity and have short duration
Neurotransmitter Types
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Peptides
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50+ and grouped into families depending on function
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2 or more amino acids and made in cell body (ribosomes)
from DNA instruction
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Opoids (enkephalins, dynorphin) – pain
Gastrins (gastrin, cholocystokinin) – food digestion
Slower to manufacture & transport
Small concentrations and longer durations
Gases
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At least 2 – nitric oxide (NO) & carbon monoxide (CO)
Can work on releasing cell
Neurotransmitter Function
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No one to one relation between type and
function
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Same NT can be used in different places with
very different effects
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Acetylcholine – contracts muscles, used in
autonomic nervous system, and brain
Neurotransmitter Receptor Proteins
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Channel Proteins
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NT binding site and channel trough membrane
NT opens a channel to allow chemical flow (Na+) across
membrane
Second Messengers
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NT binding site – NT activates a “second messenger” (1st
is the NT) inside the cell
Change function of cell (e.g., change protein production to
permanently alter cell function for learning)
Neurotransmitter Receptor Proteins
Neurotransmitter Receptor Proteins
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Usually multiple receptors for a given NT
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Acetylcholine
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Nicotinic receptor – found a junction between
neuron and muscle
Muscarinic receptor – more prevalent in brain
Acetylcholine affects both
Drugs can have more specific effects (or not
depending on the drug)
 Nicotine & curare –affect nicotinic but not muscarinic
Neurotransmitter Receptor Proteins
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Usually multiple receptors for a given NT
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Serotonin (5-HT)
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13 known receptors grouped into 6 families
People with schizophrenia have an excess of one
type
 Demonstrates how genetic differences can influence
motivational temperaments
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Dopamine
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5 known receptors grouped into 2 families
Psychoactive Drug Overview
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Two Broad effects on NT function
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Facilitate or increase function of a specific NT
Inhibit or Decrease function of a specific NT
2 Broad effects accomplished by altering
any of the 7 synapse functions (previous
slide)
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Acetylcholine
Psychoactive Drug Overview
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Acetylcohine Example
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Axon Release
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Synapse Stimulation
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Black widow spider venom – released from axon terminals
Botulinum toxin (Botox) – blocks release from axon
terminals
Nicotine – mimics ACh
Curare – blocks ACh from getting to terminals
Inactivation
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Physostigmine – blocks effect of enzyme that destroys ACh
Psychoactive Drug Overview
Psychoactive Drug Overview
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Nervous System adapts drug presence
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Inhibitory drug – may create more protein
receptors to detect smaller amounts of NTs that
are getting to postsynaptic cell
Excitatory drug – may remove protein receptors
NS now requires drug for functioning
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Inhibitory drug – “normal” signals are too strong
Excitatory drug – “normal” signals not strong
enough
Nervous System Organization
Nervous System Organization
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Central Nervous System (CNS)
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Spinal Cord – simple decisions & information transmission
Brain – “complex” decisions
Peripheral Nervous System (PNS)
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Somatic – sensory information & voluntary movement
Autonomic
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Sympathetic – increases support increased physical activity
Parasympathetic – increases support decreased physical
activity
Enteric – gastrointestinal system
Autonomic Nervous System
Nervous System Organization
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Neuron Groups
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Peripheral NS
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Central NS
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Nerve – collection of axons in PNS
Ganglia – collection of cell bodies & dendrites
Tract – collection of axons in CNS (White Matter)
Nuclei – collection of cell bodies (Grey Matter)
Glial Cells
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Support and assist neurons (many types)
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Produce myelin, nourishment, repair, waist disposal, etc.
Spinal Cord
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31 segments with pairs (left & right) nerves
carrying sensory and efferent information
Functions
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Ascending and descending neural tracts
Interneurons responsible for spinal reflexes
(relatively simple decisions)
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Link sensory information (e.g., pain) with motor
response (e.g., muscle contraction)
Brain
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Structure
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Very Complex
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Many different ways of describing brain
structures (location, function, etc.)
General Principles
Layered
 Lateralized
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Brain
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Neural Systems
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Brain circuits responsible for brain function
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E.g., - vision, hearing, movement, reward
System could be
 Localized (vision) or diffuse (arousal)
 General (vision) or specific (color vision)
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Broad Divisions
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Sensory
Motor
Association
Brain
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Complex behaviors (fear/defensive learning)
depend on many systems
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Sensory
Learning
Memory
Output
Differences in a function (e.g., motivation) might
be due to different reasons (e.g., sensory,
learning, etc.)
Studying Brain Function
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Gross lesions
Structural assessments
Selective lesions
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Local functioning
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specific neurotoxins
transient lesions
Single-cell recording
Neurotransmitter measurement & manipulation
Gene expressions
Non-invasive measures
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Functional MRI
EEG & ERP