eye and senses

• sensory receptor- specialized nerve endings or sensory neurons which initiate nerve impulse
• sensation is felt when the nerve impulse arrives at the cerebral cortex
• perception- how the cerebral cortex interprets sensory information
• smell- olfactory cells in nasal cavity are stimulated by smells and create action potential
• photoreception- photoreceptors in the eye detect photons of light and convert the light energy into electrochemical energy (action potential to the brain)
• eye has 3 layers: sclera(outer layer), choroid layer(middle layer), retina(inner layer)
• sclera: the white outer layer of the eyeball. At the front of the eye it is continuous with the cornea. its protective and maintains eye shape

  
• cornea-window allowing light through and bending it towards the pupil

  
• pupil-black hole at centre of iris, allows light to enter the eye

  
• iris(colored part) controls the amount of light that enters the pupil

  
• lens- behind the iris, focuses images on the retina

  
• ciliary muscles- alter the shape of the lens to adjust to near and far objects

  
• vitreous humor- cloudy jelly material, helps maintain the shape of the eyeball

  
• retina- part of the eye containing photoreceptors and is made of 4 layers of cells: pigmented epithelium(prevent light from scattering), light sensitive cells(contain rods and cones), bipolar cells(relay messages to optic nerve, optic nerve cells(carries nerve impulse to occipital lobe)

  
• rods- responsible for seeing in dim light(intensity of light). cones- responsible for seeing color(red,blue,green)
• fovea centralis- the depression in the retina, most sensitive area of the eye, only contains cones

  
• blind spot- area where the optic nerve attaches to the retina, there are no rodes or cones
• color blindness occurs when one or more cones dont work
• focusing the image: light enters the eye and is bent towards the pupil by the cornea, and is then bent further by the lens to a focal point on the retina. an inverted image is projected on the retina and a nerve impulse is sent to the brain
• to see near objects: ciliary muscles contract and the lens becomes thicker. to see far objects: ciliary muscles relax and lens flattens
• the ear- converts sound waves to electrochemical energy(nerve impulse) and has the outer ear, middle ear and inner ear
• the pinna is the outer ear and is the part that funnels sound waves into the auditory canal(ear canal)

  
• auditory canal[ear canal]- carries sound to the eardrum, produces wax through sweat glands

  
• tympanic membrane[eardrum] - thin elastic tissue that receives sound waves from the auditory canal

  
• malleus [hammer], incus [anvil] and stapes [stirrup]: three bones that transmit vibrations from the tympanic membrane to the oval window
• eustachian tube- tube leading to the mouth and nose area. the tube permits equalization of air pressure between the middle ear and the environment

  
• cochlea-snail shell structure containing specialized hair cells that identify and respond to sound waves then send nerve impulses
• vestibule- contains utricle and saccule for head position
• semicircular canal- fluid filled canals placed at different angles that sense motion