Accommodation/Electrochemical Gradient

Accommodation Pupillary Reflex

or pupillary reflex

   - The process by which the pupils contract or dilate in response to the amount of light the eye is exposed to \

Low light

- reduced light stim sympathetic NS

- Dilator constricts = Dilation of pupil

Bright Light

- light  stim parasympathetic NS

- Sphincter constricts = Constriction of pupil

Convergence of the Eyeballs

- eyes converge medially to focus close-

     in, for distance focusing they are directed straight ahead

Dark Adaptation

- Rhodopsin produced (from?)

  - eyes more sensitive to light

  - enter darkness:>sensitivity by 10x in 1 min:  6000x in 20 min:        25,000x in 40 min

Light Adaptation

- Rhodopsin decomposes into?

  - this decomposition is known as Bleaching

  - eyes less sensitive to light (get used to it)

  - up to 25,000 x less sensitive

Accommodation of the Lens

- the process of changing the shape of the lens in order to focus the eyes

Lens

-biconvex -transparent protein fibers

     - changes shape in order to keep the focal point on the fovea

        centralis

Close-in Focusing

- ciliary muscles CONTRACT which causes the Ciliary Zonule to

       LOOSEN causing the lens to become rounder

    - caused by increasing Parasympathetic N.S.

Distant Focusing

- ciliary muscles RELAX which causes the Ciliary Zonule to TIGHTEN

     (sounds weird but its true) which causes the lens to flatten slightly

   - caused by increasing Sympathetic Nervous System, and decreasing

      Parasympathetic N.S. impulses

1.  Electrical Gradient

- A typical cell at rest is polarized i.e. “+”on the

      outside and “-” on the inside

2.  Chemical Gradient

– A typical cell at rest has more sodium on the

      outside and more potassium on the inside

In the Dark

1.cyclic Guanosine Monophosphate (cGMP)

 binds to Ligand Gated 

   Cation Channels and locks them OPEN

2. Sodium and Calcium

diffuses IN (influx)

3. depolarizes

the Rod's cell membrane & keeps Voltage-Gated Calcium

    channels open this Ca⁺⁺ causes the continuous release of the

    neurotransmitter Glutamate

4. Glutamate

causes an IPSP (Inhibitory Postsynaptic Potential) which

      INHIBITS the Bipolar Cells therefore, the Bipolar cells are unable to

      stimulate the Ganglion Cells making up the optic nerve

      in other words: the rods inhibit the bipolar cells so they cannot turn on the ganglion cells