Auditory system

Anatomy and physiology Sense organ Ears are a pair of complex sensory organs located in the both sides of the head at approximately eye level Ears are housed in the temporal bones Each ear is divided into 3 parts – external ear, the middle ear and the inner ear

External ear The Pinna - cartilaginous, highly variable in appearance External Auditory Canal (or external auditory meatus) - 2.5 cm tube.

External ear It consist of the PINNA (auricle) and external auditory canal Pinna – composed of cartilage covered by skin The external auditory canal is irregular and constricts about midway and again near to the tympanic membrane The supporting wall of the first half of the external auditory canal is cartilaginous and second half is osseous

The skin lining this bone portion of the canal is thin and highly sensitive and contains fine hairs and sebaceous glands Ceruminous glands – modified sweat glands found in the external auditory canal, produce cerumen or ear wax – helps to cleanse the auditory canal of foreign matter

Tympanic membrane – thin and semitransparant, protects the middle ear and conducts sound vibrations from the external ear to the ossicles. 9 mm in diameter, nearly oval, It contains 3 layers – An outer layer continuous with the skin of the external auditory canal A fibrous middle layer Inner layer continuous with the lining of the middle ear

Middle ear Consists of air filled cavity and its content The Ossicles, the oval and round windows, and the opening of the Eustachian tube Ossicles – the malleus (hammer), the incus (anvil) and the stapes(stirrup) – smallest bones in the body Ossicles connects tympanic membrane to the labyrinth Function of ossicles is to transmit sound vibrations and also protect the inner ear from loud sounds

Oval window – covered by the footplate of the stapes is the opening into the inner ear were sound vibrations enter Round window – true window which provides an exit for sound vibrations from the inner ear Esutachian tube – 35 mm (1.5 inches) long that connects the middle ear with the naso pharynx. Tube composed of bone, cartilage and fibrous tissue lines with mucous membrane

It allows air to enter and leave the middle ear and is responsible for both ventilation and pressure regulation mastoid process (bony prominence over the mastoid bone)

INNER EAR Two Halves: Vestibule--transduces motion and pull of gravity Cochlea--transduces sound energy

Inner ear The inner ear contains the sensory organs for hearing and balance Two major structures – osseous labyrinth and the membranous labyrinth osseous labyrinth – covers the membranous labyrinth In between osseous labyrinth and membranous labyrinth there is a fluid called perilymph Membranous labyrinth contains a fluid called endolymph Consist of utricle, sacule and 3 semi circular ducts and canals, the cochlear and vestibular duct, and the organ of corti

Organ of corti – is the sensory receptor inside the cochlea which holds the hair cells, the nerve receptors for hearing.

Cochlea looks like a snail shell and has two compartments The upper compartment – scala vestibuli The lower compartment – scala tymapni The mastoid process is a conical prominence projecting from the undersurface of the mastoid portion of the temporal bone. It is located just behind the external acoustic meatus

Sound transmission Sound transmitted from external ear to the inner ear by two routes Air conduction and bone conduction

Air conduction Sound External auditory canal Tympanic membrane (TM) Ossicles vibrate Oval window

Round window Hair cells of organ of corti (energy converted to electrical energy) Cranial nerves VIII (VESTIBULOCOCHLEAR NERVE) Central nervous system interprets sound Auditory cortex – center of hearing in brain

Assessment of ear Health history General impression of the patients hearing ability by observing behavioral changes Ask for ear ache (otalgia), drainage (otorrhea), tinnitus, vertigo Environmental and work history Any history of tramua, foreign body

Use of ototoxic drugs Examples – gentamincin, vancomycin, loop diuriectis, aspirin, cisplatin etc These agents affect either eight cranial nerve or the organs of hearing and balance

Ask about the self care of ears History of ear infections and method of treatment Patients lifestyle and emotional response Ability to communicate Coping mechanisms

PHYSICAL EXAMINATION Inspects each ear for size, configuration . Color of the ear Check for any lumps or skin lesion Check all pierced ear holes for irritation or infection Inspect the external auditory canal – upward and backwards, use a pen torch to find out foreign objects, wax, redness, narrowing and swelling Palpate the pinna and the mastoid area for tenderness or nodules

Tympanic membrane Otoscope examination – Otoscope consist of a handle, a light source, a magnifying lens, and an attachment for visualizing the external auditory canal and tympanic membrane. Some ototscope have pneumatic device for injecting air in to the auditory canal to test the mobility and integrity of the tympanic membrane -A normal eardrum will flex inward and outward in response to the changes in pressure.

Diagnostic tests Assessment of balance Balance and equilibrium depend Vestibular (labyrinth of inner ear, the visual (eye), and the cerebellar system Any of the system impaired dizziness is most likely to occur

Balance is assessed by observation of gait, the gaze test for nystagmus, and romberg’s test Gait – ask the patient to walk away from the nurse and then turn and walk back. The nurse observe the posture, balance, swinging of the arms and movement of legs. To test nystagmus – asks the patient to follow the finger without moving the head.

Rombergs test – the patient stands with feet together and the arms at the sides, first with the eyes open and then with the eyes closed. A loss of balance when the eyes closed indicate an inner ear problem or cerebellar ataxia.

Laboratory tests Routine blood and urine test rarely provide significant information related to diseases of ear Elevated WBC – indicator of infection Culture of drainage – causative organism Rule out the drainage for CSF.

Radiologic tests CT SCAN MRI Arteriography and venography – contrast medium is injected into blood vessels. Especially useful for diagnosing vascular abnormalities in the temporal bone

Special tests Auditory acuity tests Whispered voice test – nurse softly whispers two syllable words towards one ear. The other ear supposed to be closed. The patient have to repeat the words The intensity of nurse voice should be – soft, medium, or loud whisper to soft, medium or loud voice. Test each ear separately.

Tuning fork tests Rinnes test – place the vibrating tuning fork against the patients mastoid process to assess the bone conduction until the vibrating sound is no longer heard The still vibrating fork is then placed 1 – 2 cm from the auditory canal to assess air conduction. The patient is asked to inform the nurse when the sound is no longer heard

Results – air conduction should be more than the bone conduction

Webers test The vibrating turning fork is placed on the patients head. Normally the sound should be heard equally in both ears.