25 September 2012
A single cell that is responsible for much of what happens in our brain (thoughts, feelings, and actions).
1) Soma – The nucleus of the cell body.
2) Dendrites – Branch-like fibres that come out of the cell body and between neurons.
3) Axon – Elongated part that comes out of cell body; varies in size. Ends of them have terminal endings.
Information comes into the neuron from the dendrites (this process is called afferent).
Information leaves the neuron through the axon (this process is called efferent).
1) Sensory neurons – Carry messages from tissues/sensory organs inwards to brain and spinal cord.
Sensation process (taking the environment in) is an afferent process
Its dendrites are outside the central nervous system while axons are inside it
2-3 million sensory neurons
2) Motor neurons – Efferent process – information leaves the neuron through the axon
Allows us to perform actions by sending message to muscles
Dendrites are in the central nervous system while axons are in the muscles and glands
3) Interneurons – Between sensory input and motor output, information is processed in brain's internal
communication system via interneurons
Exist entirely the central nervous system
Have no connections to sensory processes or muscles; only have contact with other neurons
THE E LECTRICAL COMPONENT
Electrical charge travels down neuron's axon to transmit messages (called action potential).
Opposition said that a slight electrical charge would activate all the neurons instead of sending a
message to one specific neuron.
THE C HEMICAL C OMPONENT
The way neurons communicate is solely chemical.
Galvani: Italian physicist believed in electrical theory
o Experimented using a dead frog, attached a wire to its legs and passed direct current through
frog's legs and saw that it would jump.
Loewi: tried to do an experiment to prove it was only chemical.
o Filled a beaker with distilled water, took a freshly removed heart from a frog and put it in the
water, attached electrode to heart and passed electrical stimulus through it, and the heart
o In a second beaker, he had a second heart without water or electricity; he poured the water
from the first beaker into the second one and that one began beating (chemicals in distilled
- 1950s: British neurologists theorized neuron communication is both electrical and chemical.
The meeting point between neurons is called a synapse; dendrites and axons don't quite touch, but are
separated by synapses.
When action potential reaches the terminals at the end of an axon, chemical messengers are released
o These messengers close the gap for a split second, and then the sending neuron reabsorbs the
excess neurotransmitters (this process is called reuptake).
Excitatory signals must overtake inhibitory signals to trigger an action potential. 25 September 2012
Neurotransmitters can control depression, euphoria, hunger, addiction, etc.
Our brain naturally produces opiates in response to pain and vigorous exercise – these are called