RECEPTORS & EFFECTORS
RECEPTORS
 Receptors are groups of specialized cells. They can
detect changes in the environment, which are
called stimuli, and turn them into electrical impulses.
 Receptors are often located in the sense organs, such
as the ear, eye and skin. Each organ has receptors
sensitive to particular kinds of stimulus.
SENSE ORGAN
SKIN
TONGUE
NOSE
EYES
EARS
RECEPTORS SENSITIVE TO
Receptors
SENSE ORGAN
RECEPTORS SENSITIVE TO
SKIN
Touch, pressure, pain & temperature
TONGUE
Chemicals in food
NOSE
Chemicals in the air
EYES
Light
EARS
Sound and head position
Effectors
 An effector is any part of the body that produces the
response. Here are some examples of effectors:
 a muscle contracting to move the arm
 a muscle squeezing saliva from the salivary gland
 a gland releasing a hormone into the blood
The nervous system is divided into:
 Central nervous system:
this includes the BRAIN
and the SPINAL CORD.
 Peripheral nervous
system: this includes the
nerves that connect the
spinal cord to the body.
The brain, the spinal cord
and the nerves are made of
nerve cells or NEURONS.
NEURONES
 Neurons are nerve cells. They carry information as tiny
electrical signals.
The diagram in the next slide shows a typical neuron in this case, a motor neuron. It has tiny branches at
each end and a long fiber carries the signals.
Label the Neurons
 DENDRITE  Fine hair-like extensions on the end of a neuron.
 Function: receive incoming stimuli.
 CELL BODY OR SOMA  The control center of the neuron.
 Function: Directs impulses from the dendrites to the axon.
 NUCLEUS  Control center of the Soma.
 Function: Tells the soma what to do.
 AXON Pathway for the nerve impulse (electrical message) from the
soma to the opposite end of the neuron.
 MYELIN SHEATH  An insulating layer around an axon. Made up of
Schwann cells.
 NODES OF RANVIER  Gaps between schwann cells.
 Function: Saltatory Conduction (Situation where speed of an
impulse is greatly increased by the message ‘jumping’ the gaps in an
axon).
There are three different types of neurons, each with
a slightly different function.
 Sensory neurons carry signals from receptors to the
spinal cord and brain.
 Relay neurons carry messages from one part of
the CNS to another.
 Motor neurons carry signals from the CNS to
effectors.
Types of neurons
TYPES OF NEURONS
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
Nerve fibers, Nerves and Tracts
 A nerve is a bundle of nerve fibers, located outside the
brain and spinal cord, that connect various parts of the
body.
 Sensory nerves carry messages to the CNS (brain) and
the motor nerves carry messages away from the CNS.
 Groups of nerve fibers within the CNS are known as
tracts.
Telling the difference
 How can your brain tell the difference between a
strong chocolate smell and a faint chocolate smell?
 If a stimulus is strong, then a greater number of
impulses will be sent out. This is because more nerve
cells will be stimulated and transmit their messages to
your brain. If the smell was faint, then fewer impulses
would be sent out and fewer nerve cells would be
stimulated. In this way the brain is able to detect
differences.
What if a stimulus is applied for a
long time?
If you ate chocolate all day long, for example, the sensory
receptors would stop reacting to it and eventually you
would not taste it anymore. We say the sensory
receptors have adapted. Similarly, when you put jeans
on fi rst thing in the morning, you feel the material
against your skin. But soon you don’t notice the
material is there because your skin receptors have
adapted to its presence.
SYNAPSES
 Where two neurons meet, there is a tiny gap called a
synapse. Signals cross this gap using chemicals. One
neuron releases the chemical into the gap. The
chemical diffuses across the gap and makes the next
neuron transmit an electrical signal.
Synapses
Based on Harvard Medical School
Family Health Guide
Neurotransmitter being released
into synapse and attaching to
receptors on dendrite
50 Known Neurotransmitters
 Examples include:
 Acetylcholine
 Dopamine
 Serotonin
Why do we need a
neurotransmitter like
dopamine?
Importance of Dopamine
Human behavior is controlled by natural chemical
reward systems in the body
For example, we like to eat fatty foods because it
make us feel good
It is the release of dopamine that is the chemical
reward system responsible for the good feeling
Dopamine “reinforces behaviors essential to our
survival.”
 Dopamine is released by cells of the nervous system during
pleasurable activities such as eating or having sex.
 Once released, dopamine travels across a gap between nerve
cells, called a synapse, and binds to a receptor on a
neighboring nerve cell (also called a neuron). This sends a
signal to that nerve cell, which produces a good feeling.
 Under normal conditions, once the dopamine sends that
signal it is reabsorbed by the neuron that released it. This
reabsorption happens with the help of a protein called
the dopamine transporter.
 Cocain interrupts this cycle. It attaches to the dopamine
transporter, preventing the normal reabsorption process. As
dopamine builds up in the synapse, it continues to stimulate
the receptor, creating a lingering feeling of exhilaration or
euphoria in the user.
 http://health.howstuffworks.com/wellness/drugs-
alcohol/crack.htm/printable
(Somatic) REFLEX ACTIONS
 When a receptor is stimulated, it sends a signal to
the central nervous system, where the brain coordinates the response. But sometimes a very quick
response is needed, one that does not need the
involvement of the brain. This is a reflex action.
 Reflex actions are rapid and happen without us
thinking. For example, you would pull your hand away
from a hot flame without thinking about it. The
animation below allows you to step through each stage
of the reflex arc.