All receptor cells are transducers,
in which one form of energy, the
stimulus energy, is converted into
another form, electrical energy.
Receptors in mammals are
adapted to respond to
different aspects of the
environment such as: • light
intensity and wavelength •
sound • touch and pressure •
temperature • chemicals
sensory neurons transmit
nerve impulses from a
receptor to the central
nervous system (brain or
spinal cord)
Structure of a motor neuron
Large nucleus, large
quantities of rough er and golgi
bodies, short dentrites that
carry nerve impulses towards
the cell body
Structure of a sensory neuron
Long dendrite, short axon,
transmit impulses from a
receptor to the CNS
When not conducting a nerve impulse, there is a p.d
across the plasma membrane, such that the inside has a
-70mV charge compared with the outside
Na+-K+ pumps in the plasma membrane actively transport
K+ ions into the cell and Na+ ions out
3 Na+ ions actively transported out for every 2 K+ ions
actively transported in. The axon contains organic anions
tro which the membrane is impermeable
This and a slight loss of K+ ions through the permeable
membane, accounts for the resting potential
The membrane is effectively impermeable to Na+ ions
Resting potential
Action potential
generated by a stimulus that excites
the neurone causing sodium ion
channels to open allowing Na+ to
diffuse in making the inside less
negative