BSN PHYSIOLOGY: SPECIAL SENSES PART 1

SPECIAL SENSES:

In this chapter,there are four major sections,e.g:sense of vision,sense of smell,sense of taste and    hearing.however,in this post we shall go through only two topics i.e sense of sight#EYE and sense of smell(olfaction).

After reading the section eye,you should be able to describe the following terms and questions:                                            

*State the functions of organs of eye?    Macula lutea                                              

*Optic disc or blind spot?                

*Physiology of sight?Visual acuity?          

*How size of the pupil changes with bright and dim light?                              

*Functions of the retina?               

*Functions of photo receptors( Rods&cones)?                                    

*Functions of extra-ocular muscles of the eye?                                                            

*Functions of the accessory organs of the eye(Eyebrows,eyelids,eyelashes,Lacrimal apparatus).  Pg#205                                                                  

* Retinal cells(Horizontal cells,Amacrine cells,Bipolar cells,Ganglion cells).              

*Light adaptation &dark adaptation?

*Eye movements and  their control? pg#666 (guyton ) pg #379 on mini guyton

*Myopia, Emmetropia, hyperopia. 

*Aqueous fluid &vitreous fluid?                

*Circulation of aqueous humor

    EXTENSIVE QUESTIONs:     

• Events of phototransduction        
• Explain how light is directed to the fovea centralis of the retina. 
• Describe the process by which images are focused on the retina Accommodation (near vision and distant vision) . 
• function of the retina’s layers of cells.
• Explain photo reception and how visual pigments are activated.                 
• Explain how the visual pathways.  distribute information to their destinations in the brain.     
• Visual cycle?     
  

  
                            

 IMPORTANT figures :

Fig#8.8,fig#8.9 Fig#8.10,Fig#8.11 Fig#8.12 Fig#8.13Fig# 8.14, Fig#8.18,Fig#8.19, Fig#8.20,Fig#8.21,Fig#8.22,Fig#8.23,Fig#8.24

Clinical Module: Describe various refraction problems associated with the cornea, lens, or shape of the eye.

.Inflammation of any of the smaller glands is called a sty.

.Inflammation of the conjunctiva, called conjunctivitis, results in reddened, irritated eyes.  

When movements of the external muscles of the two eyes are not perfectly coordinated, a person cannot properly focus the images of the same area of the visual field from each eye and so sees two images instead of one. This condition is called diplopia(dı˘-plope-ah), or double vision. It can result from paralysis or weakness of certain extrinsic muscles, or it may be a temporary consequence of acute alcohol intoxication.

Congenital weakness of the external eye muscles may cause strabismus (st rah-bizmus; “cross-eyed”), a condition in which the affected eye rotates medially or laterally. eye.Surgery is needed for unyielding conditions.

A cataract (“waterfall”) is a clouding of the lens that causes the world to appear distorted, as if seen through frosted glass If the drainage of aqueous humor is blocked, fluid backs up as in a clogged sink. Pressure within the eye may increase to dangerous levels and compress the retina and optic nerve—a condition called glaucoma (glaw-komah)

Color blindness is due to a congenital lack of one or more of the cone types. Inherited as an X-linked condition, it is far more common in males than in females. .

#Difference :AQUEOUS & VITREOUSFLUID:

• A. F It occurs in aqueous chamber
• V. F  It occurs in vitreous chamber
• A. F  It is a watery fluid
• V. F  It is a jelly like substance
• A. F  It is secreted by ciliary processes
• V. F  It is apparently  secreted by retina during development of eye.
• A. F  It is continuously absorbed into blood and replaced.
• V. F  It is absorbed or replaced.
• A. F  It contains most of the diffusible substances of the plasma
• V. F  It consists of water (90%), protein vitrein, hyaluronic acid and collagen fibres.
• A. F  Obstruction in its flow may damage retina by increasing intraocular pressure
• V. F  It does not flow.
• A. F  Maintains the shape of the cornea and supply nutrition to both lens and cornea.
• V. F  Maintains the shape of the eye ball and contribute to intraocular pressure and also to the focussing of light on the retina                                                
•  VISUAL CYCLE

The process of PHOTOTRANSDUCTION:

The process of photo transduction has not been mentioned in the book# Ross&Wilson properly so consult the guyton

 for this topic.A summary for the understanding purpose has  jotted here

Visual pathway:   pg#199         

An important short question that also not been mentioned in the book is  PUPILLARY LIGHT REFLEX:

light shone into the eye…..pupil constrict….help the eye adapt rapidly to changing light condition.

SUMMARY:light impinge on the retina,impulses pass from the optic nerve to the PRETECTAL NUCLEI…from here secondary impulses pass to the EDINGER WESTPHAL NUCLEUS….,and finally back throug….PARASYMPATHETIC NERVES to constrict the sphincter of iris.Conversely,in the darkness,the reflex becomes inhibited,which results in dilation of pupil.

Sense of smell:

Not a bumper section,only an important topic you should have to go through is stimulation of olfactory cells or summary of olfactory signal transduction

Process of olfaction:

Odorants bind to receptor protein activates adenylate cyclase(enzyme that convert ATP to cyclic AMP

Cyclic Amp open Na channels in the plasma membrane which begins to depolarize. By sufficient depolarization action potential triggered and information is relayed to CNS. 

This is all about these two topics, encompasses the content and all important topic. Hope it will be helpful for your preps. 

JAZAKALLAH!