Unit 4. Human beings

UNIT 4. HUMAN BEINGS 

The test will be next Wednesday 19th January

Humans complete the three vital functions of nutrition, reproduction and interaction.

 INTERACTION FUNCTION Humans interact with their environment in three different stages: 

• Detecting stimuli: Stimuli are the information generated outside or inside our body. Humans first detect the stimuli and then react to it.
• We detect the stimuli by the organs called receptors (sense organs). Receptors contain special cells called receptor cells. Receptor cells detect the stimuli and send signals to the nervous system.
• Our sense organs are: eyes, nose, ears, tongue and skin.
• Generating orders: after detecting the stimuli, response orders are generated by our body coordination systems (nervous system).  We interpret the signals and send the orders through the nerve impulses.
• Responding to orders: these orders are executed by organs called effectors(muscles and bones), which carry out an action.

 NERVOUS SYSTEM 

The nervous system is made up of star-shaped cells called neurons.

Neurons specialize in transmitting nerve impulses. They are connected to our receptor cells of the senses and to the effectors.

 NEURON PARTS 

• AXON: a long slender projection
• DENDRITES: various shorter projections

How nerve impulses are transmitted? The neuron receives the nerve impulse and travels along the neuron to the end of it. The neuron transmits the nerve impulse to the next.

    THE SENSES

SIGHT

The eyes are the organs of sight. Our eyes detect light around us and send messages to the brain that allow us to see.

PARTS 

• Eye ball: is a sphere that contains:
• A retina at the back with the receptor cells.
• Iris a colored area at the front with a hole in the middle called pupil. The pupil opens and closes depending on the amount of light.
• Lens are behind the iris and changes shape
• Auxiliary structures: protect the eyeball ad enable it to move. They include the eyebrows, eyelids, eye muscles and lacrimal glands.

How we see? Light enters the pupil through the lens to the retina. The receptor cells send signals through the optic nerve to the brain, which interprets the signals as colors, shapes and distances. 

HEARING 

The ears are organs of hearing. Hearing is the sense that enables us to detect sound vibrations.

 PARTS: 

• The outer ear: made up of:
  • Pinna: the visible part of the ear.
  • Ear canal
• The middle ear: made up of:
  • Eardrum: is a membrane
  • Chain of ossicles: which are 3 tiny bones: malleus, incus and stapes.
• The inner area made up of:
  • Cochlea: contains the receptor cells.
  • Three semicircular canals which contain the receptor cells sensitive to movement which help us to keep balance.

How we hear?

• Our ears detect sound vibrations, they enter the ear drum through the ear canal. The eardrum and the ossicles transmit the vibrations to the receptor cells in the cochlea.
• These cells send signals through the auditory nerve to the brain. The brain interprets the sounds that we hear.

SMELL

• The olfactory bulb in the nose is the responsible for our sense of smell.
• Smell is the sense that enables us to detect substances in the air.
• PARTS:
• Olfactory bulb which contains the receptor cells
• Nostrils the two holes in the nose.

SMELL

The olfactory bulb in the nose is the responsible for our sense of smell.

Smell is the sense that enables us to detect substances in the air.

PARTS:

• Olfactory bulb which contains the receptor cells
• Nostrils the two holes in the nose.

How do we smell? The receptors in the olfactory bulb detect substances in the air and send this information to the brain. The brain interprets the information.

 TASTE

The taste organ is made up of around 10.000 taste buds that are in the tongue.

How do we taste? 

The receptor cells in the taste buds detect substances that enter the mouth and send this information to the brain. The brain interprets the information generating the sensation of flavour.

We can detect 4 flavours: bitter, salty, sweet and sour

TOUCH

 The organ which identifies touch is the skin. Our sense of touch allows us to identify touch, light and hard pressure, pain and temperature. The touch receptors in the skin can be found all over our body. 

How do we touch? 

When the receptor cells in the skin detect a stimulis, they send this information though the nerves to the spinal cord and the brain.