pupil

Examples of pupil in the following topics:

• Horner's Syndrome

  • Horner's syndrome presents with drooping eyelids and pupil constriction, and is indicative of a problem in the sympathetic nervous system.
  • Horner's syndrome, also known as oculosympathetic palsy, is a combination of drooping of the eyelid (ptosis) and constriction of the pupil (miosis) on one side of the face, accompanied by decreased sweating of the face on the same side .
  • Loss of ciliospinal reflex: dilation of the pupil in response to pain applied to the neck, face, and upper trunk
  • The pupil's light reflex is maintained as this is controlled via the parasympathetic nervous system.
  • Sympathetic and parasympathetic innervation of the pupil.

• Oculomotor (III) Nerve

  • The oculomoter nerve (cranial nerve III) controls eye movement, such as constriction of the pupil and open eyelids.
  • It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the levator palpebrae superiors muscle.
  • The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and controls the pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation).

• Autonomic Interactions

  • The SNS promotes a "fight or flight" response, corresponds with arousal and energy generation, and performs the following functions: inhibits digestion; diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction; blood flow to skeletal muscles and the lungs is enhanced (by as much as 1,200% in the case of skeletal muscles); dilates bronchioles of the lung, which allows for greater alveolar oxygen exchange; increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for the enhanced blood flow to skeletal muscles; dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye and far vision; provides vasodilation for the coronary vessels of the heart; constricts all the intestinal sphincters and the urinary sphincter; inhibits peristalsis; and stimulates orgasm.
  • Conversely, the PSNS promotes a "rest and digest" response, and promotes the following functions: dilates blood vessels leading to the GI tract, increasing blood flow; constrict the bronchiolar diameter when the need for oxygen has diminished; causes constriction of the pupil and contraction of the ciliary muscle to the lens, allowing for closer vision; stimulates salivary gland secretion, and accelerates peristalsis; and stimulates sexual arousal.

• Sympathetic Responses

  • Physiological changes induced by the sympathetic nervous system include accelerating the heart rate, widening bronchial passages, decreasing motility of the large intestine, dilating the pupils, and causing perspiration.
  • Fibers from the SNS innervate tissues in almost every organ system, providing physiological regulation over diverse body processes including pupil diameter, gut motility (movement), and urinary output.
  • These include the following: acceleration of heart and lung action; paling or flushing, or alternating between both; inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops; general effect on the sphincters of the body; constriction of blood vessels in many parts of the body; liberation of nutrients (particularly fat and glucose) for muscular action; dilation of blood vessels for muscles; inhibition of the lacrimal gland (responsible for tear production) and salivation; dilation of pupil (mydriasis); relaxation of bladder; inhibition of erection; auditory exclusion (loss of hearing); tunnel vision (loss of peripheral vision); disinhibition of spinal reflexes; and shaking.

• Divisions of the Autonomic Nervous System

  • The PSNS typically functions in contrast to the SNS by dilating blood vessels leading to the GI tract, causing constriction of the pupil and contraction of the ciliary muscle to the lens to enable closer vision, and stimulating salivary gland secretion, in keeping with the rest and digest functions.

• Control of Autonomic Nervous System Function

  • The ANS participates in the regulation of heart rate, digestion, respiratory rate, pupil dilation and sexual arousal among other bodily processes.

• Optic (II) Nerve

  • The light reflex refers to the constriction of both pupils that occurs when light is shone into either eye; the accommodation reflex refers to the swelling of the lens of the eye that occurs when one looks at a near object, as in reading.

• Brain Tumors

  • Consequences of intracranial hypertension: Large tumors or tumors with extensive perifocal swelling (edema) inevitably lead to elevated intracranial pressure (intracranial hypertension), which translates clinically into headaches, vomiting (sometimes without nausea), altered state of consciousness (somnolence, coma), dilation of the pupil on the side of the lesion (anisocoria), papilledema (prominent optic disc at the funduscopic eye examination).

• The Fight-or-Flight Response

• Brief Overview of Cranial Nerves

  • The oculomotor nerve (III): This controls most of the eye's movements, the constriction of the pupil, and maintains an open eyelid.