The special senses By-Jyoti joshi Nursing tutor. • The special senses are the senses that have specialized organs devoted to them: • vision (the eye) • and balance (the , which includes the and ) • smell (the nose) • taste (the tongue) • The special senses have specialized sensory receptors (nerve endings) outside the brain. • Functions of Special Senses

• The functions of the five special senses include: 1. Vision. Sight or vision is the capability of the eye(s) to focus and detect images of visible light on photoreceptors in the retina of each eye that generates electrical nerve impulses for varying colors, hues, and brightness. 2. Hearing. Hearing or audition is the sense of sound perception. 3. Taste. Taste refers to the capability to detect the taste of substances such as food, certain minerals, and poisons, etc.

4.Smell. Smell or olfaction is the other “chemical” sense; odor molecules possess a variety of features and, thus, excite specific receptors more or less strongly; this combination of excitatory signals from different receptors makes up what we perceive as the molecule’s smell. • Touch. Touch or somatosensory, also called tactition or mechanoreception, is a perception resulting from activation of neural receptors, generally in the skin including follicles, but also in the tongue, throat, and mucosa. Hearing and the ear

• The ear is the organ of hearing and is also involved in balance. • Blood and nerve supply: • 8th cranial nerve, i.e. the cochlear part of the • Except (pinna), the remaining part of ear encased within the temporal . STRUCTURE OF EAR • The ear is divided into three distinct parts. 1. 2. () 3. . 1.Outer ear: The outer ear collects the sound waves and transfer them to the inner ear via middle ear. • It consist of auricle (pinna) and the external acoustic meatus (auditory canal). • The auricle (pinna): The auricle is the visible part of the ear project from the side of the head, • Made-up of fibroelastic cartilage and covered with skin. • ceremonious gland

Conchae tympanum

Lobule

External acoustic meatus • Upper end called- Helix • Lower muscular end called lobule. • Grooves present in pinna - conchae • External acoustic meatus (auditory canal) • ‘S’-shaped tube about 2.5 cm long extending from the auricle to the tympanic membrane (). • Lined with modified () called which secretes cerumen (ear wax). • Cerumen filter the dust particle. • External acoustic meatus conducts sound waves from pinna to the tympanum. Middle Ear: Middle ear consist of tympanum, tympanic cavity, ear . 1.Tympanum: • Membranous structure present at the junction of auditory canal(EAM) and tympanic cavity • It amplifies the sound.

2. Tympanic cavity • Air filled cavity with the pharynx through to maintain the air pressure. 3. Ear ossicle or Auditory ossicle: • A chain of three includes- 1. Mallus ( hammer shaped) 2. (Avil Shaped) 3. (stirrup shaped) • Present in tympanic cavity • Extended from the tympanum to internal ear. • Ear ossicle enter through an oval opening called (fenestra ovalis) • Rounded opening present below oval window called (fenestra rotandus). Internal ear

• Inner (internal ear) or labyrinth (mean maze) • Contains the organ of hearing and balance. • Divided into two parts. 1. 2. .

Bony labyrinth:

• This is a cavity within the lined with periosteum. • It encloses the membranous labyrinth of the same shape that fits into it, like a tube within a tube. • It is larger than membranous labyrinth. • Watery fluid () is present between bony and membranous labyrinth. • within the membranous labyrinth there is a similarly watery fluid, . • The bony labyrinth consists of: • • the vestibule • • the • • three . 1. The vestibule The oval and round windows are located in its lateral wall. It contains two membranous sacs, the and the , which are important in balance. The cochlea • This resembles a snail’s shell. • spiral-shaped organ of hearing; transforms sound into signals that get sent to the brain The semicircular canals • Arrangement of three tubes and continous with vestibules. • filled with fluid • attached to cochlea and nerves • send information on balance and head position to the brain. Membranous labyrinth

This is a network of delicate tubes, filled with endolymph. It comprises: • the vestibule, which contains the utricle and saccule • the cochlea • three semicircular canals. The cochlea

• A cross-section of the cochlea contains three compartments: • • the scala vestibuli • • the scala media, or • • the scala tympani.