Explain about the physiology of eyelid movements, Biology

Assignment Help:

Explain about the physiology of eyelid movements.

Physiology of Eyelid Movements:

It is quoted that the eyelids move more than any other part of the body. The major movement of the eyelids include opening and closing of the eye. Other movements that need to be understood are blinking, winking, peering and forceful closure. The opening movements of the upper and lower lids are determined by the contraction of yoke muscles known as the levator palpebrae superioris (LPS) (supplied by the 3rd nerve) and the smooth muscle fibres which arise from the under surface of the LPS (sympathetic nerve). Opening movements are bilaterally symmetrical in direction and amplitude. The upper eyelid can be raised by 15 mm by the LPS muscle arid an additional elevation of 3-5 mm by the frontalis muscle.

The closing action of the lids occurs through the movement of the orbicularis oculi muscle and is supplied by the 7th cranial nerve. The muscle contains pretarsal, preseptal and orbital fibres. The pretarsal fibres function in spontaneous blinking and tactile corneal reflex. The preseptal fibres are responsible for voluntary blinking and sustained activity. Lastly, the orbital fibres are used in forceful closure of the eyelids. The exposed zone between the upper and lower eyelids is known as the palpebral fissure. In adults, it is 27-30 mm long and 8-11 mm wide.

The upper lid moves vertically downwards while the lower lid moves medially. Their rate of movement is similar but the lower lid movement begins 10-20 milliseconds earlier than the upper lid. In this mechanism Shesington's law of reciprocal innervation is obeyed.


Related Discussions:- Explain about the physiology of eyelid movements

What is the vascular cambium, What is the vascular cambium? What is its fun...

What is the vascular cambium? What is its function? Vascular cambium is the secondary meristematic tissue that in roots and in the stem creates the vascular tissues (xylem and

Key skills for healthy coping, Key skills for healthy coping are: - Pr...

Key skills for healthy coping are: - Problem-solving and goal setting skills: Finding a problem and challenges, thinking of alternatives for dealing with them, testing those

Formation of aqueous humour, Formation of Aqueous  Humour It  is  unive...

Formation of Aqueous  Humour It  is  universally accepted that the aqueous  is  produced  by  the  ciliary processes. Although a great deal of  research has been done on the fo

Flower, flowers formation without any leaves?

flowers formation without any leaves?

Chromosomes/genes/heredidty, Plot the amount of DNA in the nucleus of a spe...

Plot the amount of DNA in the nucleus of a spermatogonia from the G1 stage prior to the first meiotic division through the completion of meiosis. Label each of the major stages of

What vector foce does particle b then exert on a, A charged particle A exer...

A charged particle A exerts a force of 2.39uN to the right on charged particle B when the particles are 12.3 mm apart. Particle B moves straight away from A to make the distance be

Why immune response involves the activities of proteins, The immune respons...

The immune response involves the activities of proteins, cells, and the lymphatic system.

Artificial insemination, ARTIFICIAL INSEMINATION - Artificial insemi...

ARTIFICIAL INSEMINATION - Artificial insemination is a technique to make a female pregnant by artificially introducing semen into the vagina. Artificial insemination has

Absorption of lipids, what are lipids? how ther absorption takes place in h...

what are lipids? how ther absorption takes place in human bodies?

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd