SENSORY SYSTEM Preeti Malik Structure and Function Sensory

SENSORY SYSTEM Preeti Malik

Structure and Function �Sensory system consists of receptors in specialized cells and organs that perceive changes in the internal and external environment �The stimuli cause nerve impulses that are sent to the brain for interpretation �Environmental stimuli are perceived with the senses of vision, hearing, touch, taste, position, and balance.

Eye �The most important sensory organ because 90% of the information about the environment reaches the brain from the eyes. �Movement of the eye is controlled by the extrinsic muscles. �Only one fifth of the eye is actually exposed to the environment.

Figure - 1 Structures of the Eye

Ear �Auditory or acoustic sense (hearing) is the primary function of the ear. �Helps maintain equilibrium. �Three parts of the ear v. External v. Middle v. Inner

Figure -2 Structures of the Ear

Tongue �Taste, or the gustatory sense, is perceived by specialized cells located in papillae on the tongue called taste buds. �Flavor is identified by smell as well as taste.

Nose �Olfactory sense originates in olfactory receptor cells in the nose that immediately transmit impulses to the brain through the olfactory cranial nerves. �Nasal cavity is divided into two sections by the septum. �Olfactory receptor neurons are stimulated by chemicals (gases) in the air. �Smells can reduce stress, affect blood pressure, recall memories, and aid in the sense of taste.

Figure -3 Nose and Surrounding Structures

Skin • Senses of the skin perceive touch, pressure, temperature, and pain through five specialized cells located in the skin ØMeissner's corpuscles ØPacinian corpuscles ØEnd-bulbs of Krause ØCorpuscles of Ruffini ØNociceptors

Assessment Techniques Ø Sight § Ophthalmoscope § Visual acuity § Tonometer § Color blindness chart Ø Hearing § Otoscope § Impedance testing § Rinne’s test § Weber's test

Disorders of the Sensory System �Achromatism ◦ Called color blindness, is a common inherited defect � Amblyopia ◦ Also called “lazy eye, ” is poor vision in one eye often resulting from better vision in the other eye during infancy or early childhood �Anacusis ◦ Hearing loss resulting from damage to neural tissues

(cont…) �Astigmatism ◦ A congenital defect causing imperfect curvature of the cornea resulting in blurred vision �Cataract ◦ Clouding of the lens that causes blurred or partial vision �Conjunctivitis ◦ Also called pink eye, is a bacterial or viral inflammation of the eyelid

(cont…) �Diabetic retinopathy ◦ Condition of damaged blood vessels in the retina caused by uncontrolled diabetes mellitus �Diplopia ◦ Or double vision, results from muscle imbalance or paralysis of an extraocular muscle �Epistaxis ◦ Nosebleed resulting from disease, trauma, or other conditions such as hypertension, leukemia, or rheumatic fever Copyright 2003 by Mosby, Inc. All rights reserved.

(cont…) �Glaucoma ◦ An increase in the pressure inside the eye, caused by trauma or hereditary factors �Hyperopia ◦ Farsightedness resulting from a congenital deformity in the eye �Macular degeneration ◦ A slow or sudden painless loss of central vision Copyright 2003 by Mosby, Inc. All rights reserved.

(cont…) �Meniere’s disease ◦ A collection of fluid in the labyrinth of the ear leading to dizziness, ringing in the ear or tinnitus, pressure, and eventual deafness �Myopia ◦ Nearsightedness resulting from a congenital deformity in the eye �Night blindness ◦ Poor vision in dim light that results from a deficiency in the rods of the retina Copyright 2003 by Mosby, Inc. All rights reserved.

(cont…) �Otitis media ◦ A middle ear bacterial or viral infection common in young children �Presbyopia ◦ A type of farsightedness related to aging �Retinal detachment ◦ Due to injury or uncontrolled diabetes mellitus Copyright 2003 by Mosby, Inc. All rights reserved.

(cont…) ü Rhinitis üInflammation of the lining of the nose caused by allergic reaction, viral infection, sinusitis, or chemical irritants ü Ruptured eardrum üResults from infection, an explosion, a blow to the head, or a sharp object inserted into the ear ü Sinusitis üA chronic or acute inflammation of the cranium Copyright 2003 by Mosby, Inc. All rights reserved.

(cont…) v. Strabismus ◦ A condition in which both eyes do not focus on the same point or direction v. Stye ◦ Bacterial infection of the sebaceous glands of the eyelid Copyright 2003 by Mosby, Inc. All rights reserved.

Issues and Innovations Ø Visual correction by surgery – Radial keratotomy – Epikeratophakia – Photorefractive keratectomy (laser surgery) Ø Noise pollution – Inner ear damage is permanent – Loud music and phones can cause hearing loss Copyright 2003 by Mosby, Inc. All rights reserved.