ciliary muscle and zonules:
ciliary muscle is a ring-shaped muscle that contracts and relaxes to change the shape of the lens. 
zonules are tiny fibers that connect the lens to the ciliary body.

macula in vestibule with otoliths

       how you orient and balance

when the ciliary muscle contracts, it relaxes the tension on the zonules so the lens becomes more spherical for focusing on nearby objects. 


when the ciliary muscle relaxes, the zonules are pulled taut which flattens the lens so it can focus on distant objects.

     identify:
 lacrimal gland
 lacrimal sac
 palpebral
 sclera
 cornea
 choroid
 ciliary body
 pupil
 iris
 lens
 zonules
 ciliary muscle
 retina
 macula lutea
 fovea 
 optic disc
​optic nerve
​ vitreous body

      vision

  corrective vision

   the three semicircular canals are are positioned at right angles to each other which lets them them to detect rotational movements in all three planes of space. each canal is filled with a fluid. at the base of each canal is a swelling called an ampulla which contains a crista. the crista has hair cells embedded in a jello ish structure called the cupula. 

when the head rotates, the fluid in the canals swishes. the movement of fluid causes the cupula to bend, stimulating the hair cells. these hair cells convert this movement into nerve signals
sent to the brainstem and cerebellum via the vestibular nerve.

  the cochlea is the snail-shaped structure in the inner ear. it converts sound waves into electrical signals that the brain can interpret. Sound waves travel through the ear canal, causing the eardrum and middle ear bones to vibrate. These vibrations are transferred to the cochlea which is filled with fluid. Inside the cochlea, specialized cells called hair cells are stimulated by these vibrations, triggering nerve impulses which travel via the auditory nerve to the brain, where they are interpreted as sound. 

           sense organs

       how you hear

   hearing and balance

   there are also two otolith organs, the utricle and saccule
located in the vestibule.
otoliths (ear stones) are sensitive to gravity and linear acceleration.
when your head moves, the otoliths shift their position, pulling on tiny hair cells which stimulates nerve endings, sending a signal to your brain.

the retina

 identify:
 external ear:
 pinna
 external auditory canal (meatus)
 
​ middle ear:
   ossicles: malleus, incus, stapes
   eustachian tube (pharyngotympanic tube)
 inner ear:
   bony labyrinth
      w/ cochlea + vestibule + semicircular canals

   cochlea:
      oval window
      round window
  
   semicircular canals

    path of sound wave energy:
    External Auditory Canal🡪  Tympanic membrane 🡪 Malleus 🡪
    Incus 🡪 Stapes 🡪 Oval Window 🡪   Cochlea🡪 Round Window

    cochlear nerve
​    vestibular nerve

crista at base of
​semicircular canals  

focusing

 macula lutea:
small yellowy area in the center of the retina that's responsible for sharp vision with  details and colors.
It's yellow because of
 carotenoid pigments which help protect it from sun damage. 

the fovea is a small pit in the macula lutea that provides the sharpest vision.