WEEK 1:
NEUROPHYSIOLOGY
REVIEW
• CNS vs. PNS
• Nerves: 12 cranial + 31 spinal
Major components of neuron:
1.
Dendrites
2.
Body (soma)
3.
Axon (nerve fiber)
NERVE IMPULSES
Neurons are excitable
• Respond to stimuli by producing electrical signals
• Conduct electrical signal to neurons, muscles, or
glands
Resting membrane potential – difference in electrical
charge across a resting neuron
• Interior of neuron more negative than outside (-70 mV)
• [K+] higher inside & [Na+] higher outside
• Maintained by Na+/K+ pump & ion channels
RESTING POTENTIAL
HYPER/DEPOLARIZATIONS
Stimulus causes opening
of voltage-gated ion
channels for Na+ & K+
(effects vary)
HYPERPOLARIZATION
Hyperpolarization – opening
of K+ channels
• K+ moves out of neuron
• Increases negativity of
neuron
DEPOLARIZATION
Depolarization – opening of
Na+ channels
• Na+ moves into neuron
• Decreases the negativity of
the neuron
ACTION POTENTIAL
Action potential – reversal of the
resting potential that results in
transmission of an electrical
signal within a neuron
• Occurs in axon hillock
• Must reach threshold (-55 mV)
• All or none event!
• Last < 2 msec
ACTION POTENTIAL
Know this figure!
ACTION POTENTIAL
ACTION POTENTIAL
SYNAPTIC TRANSMISSION
The action potential sends the electrical signal to the end of
the neuron (synaptic end bulb) where another electrical
signal OR a chemical signal can be released
• Presynaptic neuron
• Postsynaptic neuron
• Chemical released –
neurotransmitter
POSTSYNAPTIC POTENTIALS
Neurotransmitter binds to ligand-gated ion channels
• Selectively permeable to either Na+ or K+, or both
• Excitatory postsynaptic potential (EPSP) –
depolarization towards threshold
• Inhibitory postsynaptic potential (IPSP) –
hyperpolarization away from threshold
• Summation – combine multiple postsynaptic potentials
• typically require more than one EPSP/IPSP to generate
action potential
SUMMATION
TERMINATION
Two mechanisms:
1.
Enzymatic breakdown
in cleft
2.
Reuptake
NEUROTRANSMITTERS
Acetylcholine – vital for NS functions including muscle
stimulation, memory formation & learning
Two classes of receptors:
1. Ligand-gated ion channel – produces EPSPs in
skeletal muscle cells
• Broken down in cleft by acetylcholinesterase
• Botox blocks synaptic transmission in facial muscles
2. G protein-coupled – produces IPSPs in the heart &
CNS
NEUROTRANSMITTERS
• GABA – Valium reduces
anxiety by binding to GABA
receptors & increasing
response to GABA (IPSPs)
• Dopamine – Parkinson’s
disease assoc. with
decreased dopamine in
brain
• Serotonin – Prozac works by
inhibiting the reuptake of
serotonin