The Brain

What is a neuron?
The Neuron
A neuron is a nerve cell
•like any other cell in the body
Neurons are similar to other cells in the
body in some ways
However, neurons differ from other cells in
the body in some ways
3 major classes of neurons
Sensory (afferent)
Motor (Efferent)
Glia cells
Simple Reflex Pathway
The process of neural
Within cells - action potential
Between cells - synaptic transmission
Components: dendrites, soma (cell body),
axon, and terminal buttons of axon
The Neuron at Rest
Resting potential - Cell is Polarized
neuron membrane separates charged
ions, producing a voltage potential
sodium (NA+), potassium (K+), chloride
(Cl-), and protein molecules (A-)
selectively permeable (semi-permeable)
sodium-potassium pump maintains ionic
inside of neuron is negative relative to
outside (about -70mV)
Reception of Input
Graded potentials:
•Excitatory potentials -depolarizing current
•Inhibitory potentials - hyperpolarizing current
determines which ion channels open
•Excitatory input causes the ion channels to
allow sodium ions into neuron
–allows neuron to fire
•Inhibitory input causes ion channels to keep
neuron negatively charged
–prevents neuron from firing
Synaptic Transmission
Presynaptic and postsynaptic neurons
Transmission involves movement of
neurotransmitters across synaptic cleft
•about 200 angstroms (one ten-millionth of a
millimeter) in width b/t neurons
Once AP reaches terminal button, vesicles
spill contents into gap
Traverse cleft, attach to receptor
Either increase (E) or decrease (I) neural
Acetylcholine, ACH
•learning and memory
•motor neurons and muscles
•major excitatory neurotransmitter
Gamma-Amino Butyric Acid (GABA)
•major inhibitory neurotransmitter
–undersupply - depression
–oversupply - schizophrenia
–undersupply - Parkinson’s
•mood, sleep, and eating
•natural pain killers