Unit 4 Human beings
The interaction function
We interact in three different stages:
a) Detecting stimuli: Stimuli is information generated inside or outside
our body, we detect the stimuli with our receptors (our sense
organs) that contain receptor cells that send signals to the nervous system.
b) Generating orders: Generated by our nervous system. The brain
interprets the signals, create a response and send the information to
the effectors.
c) Responding to the orders: Responses are executed by effectors
(the muscles and the skeleton).
Nerve impulses and neurons
The nervous system is made up of neurons
that transmit impulses. They are star-shaped cells formed by the neuron,
a projection called axon and shorter projections called dendrites
They connect each other to form nerves and then they
connect to the effectors.
The Senses
Sight
The eye is the organ of sight and detects light and
send the message to our brain.
It has an eyeball and other parts:
a) The eyeball is a sphere which contains:
-
Retina at the
back, made up of receptor cells.
-
Iris (coloured
area) and Pupil that opens and closes according to the light we receive.
-
Lens that focus
the images received onto the retina.
b) Auxiliary structures: Eyelids, eyebrows, eye
muscles and lacrimal glands.
Light enters the pupil through the lens to the retina. The receptor cells send the information
to the brain through the optic nerve that interprets the signals
and colours
Hearing
The ears are the organs of hearing and enable us to
detect sound vibrations that travel though the air and water and help us to
keep our balance.
It is divided into three parts:
-
Outer ear: Pinna and ear canal
-
Middle ear: Made up of the eardrum (tímpano), the
chain of ossicles (cadena de huesecillos) formed by malleus, incus and
stapes (martillo, yunque y estribo).
-
The inner ear: formed by the cochlea that contains
the receptor cells and three semicircular canals which contain receptor
cells sensitive to movements (our balance organ).
Smell
We have a part in our nasal passages called olfactory
bulb that detects substances in the air. It´s covered by receptor
cells that send information to the brain (that interprets the
information) through the olfactory nerve.
Taste
We have taste buds in our tongue that are receptor
cells. They send the information to our brain through the gustative
nerve. The brain generates the sensation of flavor.
Touch
The skin is the organ we use to identify touch,
pressure, pain, temperature... Under our skin there are receptor cells
that send the information to the spinal cord and the brain that produces a
touch sensation.
