Human body: 5 senses.
Sight
The eye helps you to see the visual world around you. It is a very important sense as it helps us to
where we are going and what we are doing. Here are the different parts of the eye and a brief
description of how we see.
Sclera
The sclera covers all the white part of the eye. It has four layers: The episclera which is the
upper-most layer and covers everything, the stroma which supports the organ, the lamina fusca
connective tissue (muscle-skin type oranganism) that connects to the choroid, and corneal
endothelium which connects the cornea and sclera.
Iris
The Iris is the coloured part of the eye. It is a thin circular structure that controls the size of the
pupil. The pupil is what lets in and controls light in your eye. The muscle in your iris controls the
pupil. The Iris is part of your eyes stroma. The two main parts of the Iris are the pupilliary zone
which covers the pupil and the cilliary zone which is the rest half seen part of the Iris.
Choroid
The Choroid is the connective tissue between the retina and sclera. The choroid gives the retina
oxygen through blood vessels. It is also split in four layers:
Hallers layer, innermost layer containing big vessels.
Sattlers layer, which consists of smaller vessels that take blood to the retina.
Chorocapillaris which is a layer of capillaries (microscopic vessels)
Bruchs membrane a transparent layer that leads light to a pigmented layer (coloured
layer)
Retina
Is a light sensitive part of the eye that signals the brain to interpret what you see. When light hits
the retina the retina sends an assortment of chemical and electrical signals to the brain via the
optic nerve. As the retina is part of the central nervous system (inside your brain) it is composed
mainly of neurons (brain cells that send messages) Light sensitive neurons called ‘photoreceptor
cells’ sense most light, and there are two types Rods and Cones.
Rods can focus black and white colours and are more sensitive than cone cells as they can see
shadows. They are more sensitive as cones because cones sense wave-lengths (travelling light)
and rods sense single photons (particles of light) Rods are positioned around the edges of the
retina. Rhodopsin, a protein (building block) in a rod cell, absorbs light and its shape is changed
giving off energy. This leads to an electrical signal.
Cones are less sensitive to single photons and more to wavelengths. Giving us perception of
colour. There are three types of cone cells Blue, Green and Red cone cells. They perceive different
wavelengths of light the same way cones detect photons: by using a protein.
Optic nerve
The optic nerve cable delivers messages of vision to the brain, the optic nerve is where there is a
blind spot.
Vitreous humours
The Vitreous humours is a gel that gives the eye a ball. It is between the lens and retina. It is
composed mainly of water and sugar and other stuff that makes it a gel.
Ciliary muscle
The ciliary muscle changes the shape of the lens to focus on distant or near objects. It is able to
make the lens bigger or flatter. When the ciliary muscle contracts it bulges, when it relaxes it
becomes flatter. The ciliary muscle also lets out aqueous humour which is constantly produced.
Lens
The lens is a see through disc that fine tunes our vision. The lens refracts (changes reflection) of
light to direct it to the retina. Light from a distant or near object can be focused by changed curve
of the lens.
Aqueous humour
The aqueous humour maintains a globe of the eye, provides nutrition to the lens and cornea. It is
made of amino acids which help every chemical reaction in your body. (trust me there are a lot)
Cornea is the front “outside” of the eye, it helps refract part of the light for the lens.
How you see
Light travels through the cornea, aqueous humour and lens, which refract the light to the retina.
Light is further refracted by the humours and the optic nerve carries the signal to the brain,
which interprets them into your perception.
Smell
Things you can smell are volatile, meaning it can evaporate easily, anything volatile can be smelt.
(called odours) How? Your smell is called olfaction so your nose sends signals to your brain’s
olfactory cortex. The nerve ends sense odours by their chemical signature. Olfactory receptors
are positioned at the back of the nose called the olfactory epithelium. Receptors are connected to
the epithelium, which is covered in cilia. Mucus traps the odorants. Olfactory receptors (OR) are
proteins. When they bind with the OR it sends a signal to a neuron which sends it through an
axon (joining neuron) to the brain. It knows it as an odour. Your brain stores this as a memory.
Touch
There are lots of nerve endings in your skin. These help you to touch. They can tell you if
something is hot or cold, painful or pressured. Most nerve endings are located in your dermis or
epidermis (skin). If the receptor is in some way stimulated it sends signals through the spinal
cord to the brain.
Taste
Taste buds are called chemo receptors. They translate chemical signals from food to the brain.
You taste five tastes on your taste buds - salty, sweet, bitter, sour and savoury. We find sweet,
salty and savoury foods good and sour and bitter bad. Taste buds are again receptors meaning
protein. Others are ion channels (ions are atoms with less electrons)
Hearing
Simply the air atoms travel through the outer ear canal, through the middle and hit our eardrum.
Our eardrum hits two bones called the hammer and the anvil which mimic the sound vibrations
through to the cochlea via the stirrup and oval window. The cochlea has a fluid in it which waves
around hairs which send signals through the nerves to your brain. Your hearing helps with your
balance. There are loops on the cochlea, called the posterior (diagonal) canal, superior (vertical)
canal and horizontal canal. Liquid in these canals detect movement of the head helping you to
keep your balance.
Bonus track
Hysterical Strength: no laughing matter
A quote from how stuff works.com states ‘in 2006, in Tuscon Tim Boyle watched as a Chevrolet
Camaro hit 18-year-old Kyle Holtrust. The car pinned Holtrust, still alive, underneath. Boyle ran to
the scene of the accident and lifted the Camaro off the teenager, while the driver of the car pulled
him to safety.’ The ‘scenes’ come without warning due to small scientific evidence. When
someone is electrocuted they can be thrown very far, because our muscles do so. We can’t
suddenly throw ourselves across the room nor can we suddenly lift a car. So what happens? Well,
we start to feel stressed, our muscles contract and we go nuts. We can’t just do this all the time
because it would kill us.