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 balanceorgan).
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.
