Special Senses PDF

Special Senses Done by: Dr Khalatbary AR Professor of Anatomy, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran. [email protected]  Dr Khalatbary AR SPECIAL SENSES The special senses: » Vision » Hearing and balance » Taste » Smell T...

Special Senses Done by: Dr Khalatbary AR Professor of Anatomy, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran. [email protected]  Dr Khalatbary AR SPECIAL SENSES The special senses: » Vision » Hearing and balance » Taste » Smell The special senses have specialized sensory organs: » Eye for vision » Ear for hearing and balance » Tongue for taste » Nose for smell  Dr Khalatbary AR EYE SPECIAL SENSES Dr Khalatbary AR The eye consists of two parts: » Eyeball » Accessory organs: - Eyebrow - Eyelid - Extra-ocular muscles - Fascia - Conjunctiva - Lacrimal apparatus  Dr Khalatbary AR SPECIAL SENSES The eyeball consists of two parts: » Wall » Internal components The wall of the eyeball has three layers: » Outer fibrosis layer » Middle vascular layer » Inner retinal layer The outer fibrosis layer consists of two continuous parts: » Sclera is the opaque posterior five-sixths of the fibrosis layer which maintains the shape of the eyeball and is known as the white of the eye. » Cornea is the transparent anterior one-sixth of the fibrosis layer that refracts the light entering the eyes. Note: - At the corneoscleral junction, there is the scleral venous sinus (the canal of Schlemm). - Irregular curvature of the cornea leads to Astigmatism, which may cause symptoms such as blurred vision, double vision, or headache. - The cornea can be easily replaced by a cadaveric cornea because it lacks blood vessels.  Dr Khalatbary AR SPECIAL SENSES The Middle vascular layer consists of three continuous parts: » Choroid » Ciliary Body » Iris The choroid is the highly vascular-pigmented posterior two-thirds of the vascular layer. The ciliary body is a triangular-shaped structure, which has two features: » Ciliary muscle is composed of smooth muscle fibers oriented in three different directions (longitudinal, radial and circular) which is innervated by the parasympathetic nerve fibers of oculomotor nerve [III]. » Ciliary process Note: The zonular fibers (suspensory ligament of the lens) originate from the ciliary process and insert into the lens. The function of the ciliary body: » Suspension of the lens » Accommodation of the lens » Formation of the aqueous humor The iris is the colored part of the eye with a central opening called pupil. Iris has two groups of the smooth muscle fibers to control the size of the pupil: » Circular fibres (sphincter of the pupil), which is innervated by parasympathetic nerve fibers of oculomotor nerve [III]. Pupil » Radial fibres (dilator of the pupil), which is innervated by sympathetic nerve fibers of superior cervical sympathetic ganglion.  Dr Khalatbary AR SPECIAL SENSES The inner retinal layer consists of two continuous parts: » Visual part » Nonvisual part The visual (optic) part is sensitive to light, and has two features: » Optic disc (blind spot) is where the optic nerve leaves the retina. » Macula lutea has a higher visual sensitivity. The nonvisual (non-optic) part, which covers the internal surface of the ciliary body and the iris, is not sensitive to light. Note: The junction between the visual and nonvisual parts is called the ora serrata. Macula lutea  Dr Khalatbary AR SPECIAL SENSES Glaucoma The Internal components of the eyeball: » Aqueous humor » Lens Postremal chamber » Vitreous humor (body) Cataract There are three chambers in the eye: » Anterior chamber contains aqueous humor » Posterior chamber contains aqueous humor » Postremal (vitreous) chamber contains vitreous humor The aqueous humor is a transparent water-like fluid, which fills the anterior and posterior chambers. This fluid is secreted into the posterior chamber by the ciliary body, flows into the anterior chamber through the pupil and finally is absorbed into the scleral venous sinus. The function of the aqueous humor: » Nutrient supply to the avascular cornea and lens » Maintain the intra-ocular pressure Note: Increased intra-ocular pressure, as a result of the abnormal cycle of the aqueous humor, is called glaucoma, which can lead to a variety of visual problems and even blindness. The lens is a transparent biconvex elastic disc, which is attached to the ciliary process by zonular fibers. The main function of the lens is to transmit light and focus it on the retina. Note: The opacity of the lens is called cataract. The main symptom of the cataract is gradual, painless vision blurring. The vitreous humor is a transparent gelatinous substance, which fills postremal chamber and helps to maintain the round shape of the eye.  Dr Khalatbary AR SPECIAL SENSES The accessory organs The extra-ocular muscles: » Levator palpebrae superioris » Superior rectus » Inferior rectus » Medial rectus » Lateral rectus » Superior oblique » Inferior oblique Levator palpebrae superioris Innervation: Oculomotor nerve (III) Ptosis Function: Raising the upper eyelid Not: Paralysis of this muscle leads to drooping of the upper eyelid, which is called Blepharoptosis (Ptosis).  Dr Khalatbary AR SPECIAL SENSES Superior rectus Innervation: Oculomotor nerve (III) Function: Elevation, adduction, and internal rotation of the eyeball Inferior rectus Innervation: Oculomotor nerve (III) Function: Depression, adduction, and external rotation of the eyeball Medial rectus Innervation: Oculomotor nerve (III) Function: Adduction of the eyeball Lateral rectus Innervation: Abducent nerve (VI) Function: Abduction of the eyeball  Dr Khalatbary AR SPECIAL SENSES Superior oblique Innervation: Trochlear nerve (IV) Function: Directing the pupil downwards and outwards Inferior oblique Innervation: Oculomotor nerve Function: Directing the pupil upwards and outwards Note: Extra-ocular muscle weakness can leads to strabismus, a misalignmemt of the eyes. Strabismus  Dr Khalatbary AR SPECIAL SENSES The lacrimal apparatus: » Lacrimal gland and its ducts Lacrimal ducts » Lacrimal canaliculi » Lacrimal sac » Nasolacrimal duct The lacrimal gland is an exocrine gland located in the orbit above the eyeball and secretes lacrimal fluid through numerous lacrimal ducts onto the surface of the eyeball. This gland is divided into two connecting parts by the tendon of levator palpebrae superioris muscle: - Orbibal part - Palpebral part The lacrimal fluid is spread over the entire eye surface, with each blink, and subsequently transported into the lacrimal sac through the lacrimal canaliculi (two small channels within each eyelid); and finally, it is transported into the nasal cavity by the nasolacrimal duct.  Dr Khalatbary AR SPECIAL SENSES The arterial supply to the eye is provided by ophthalmic artery (a branch of the internal carotid artery), which has numerous branches such as central retinal artery. Note: The central retinal artery occlusion (CRAO) leads to blindness.  Dr Khalatbary AR SPECIAL SENSES The venous drainage of the eye is done by two veins: » Superior ophthalmic vein » Inferior ophthalmic vein Note: The superior and inferior ophthalmic veins communicate with the cavernous sinus (a venous sinus of the brain);so, the infections of the face (danger triangle of the face) can spread to the cranial cavity. Danger triangle of the face  Dr Khalatbary AR SPECIAL SENSES The eye is innervated by several nerves: » Optic nerve [II] for vision » Oculomotor nerve [III] for extra-ocular muscles » Trochlear nerve [IV] for extra-ocular muscles » Abducent nerve [VI] for extra-ocular muscles » Ophthalmic nerve [V] for general sensation of the eye » Autonomic nerves for smooth muscles and lacrimal gland Not:  Dr Khalatbary AR EAR SPECIAL SENSES The ear is the specialized sensory organ for hearing and balance. The ear is divided into three parts: » External ear » Middle ear » Internal ear  Dr Khalatbary AR SPECIAL SENSES The external ear consists of two parts: » Auricle (Pinna) » External acoustic meatus The auricle structurally consists of elastic cartilages, skeletal muscles, and ligaments coverd with skin. The auricle has two surfaces (external and internal). The external surface of the auricle has a number of elevations and depressions: » Helix » Antihelix » Tragus » Antitragus » Concha » Lobule Note: The auricular muscles change the shape of the auricle (intrinsic muscles) and also play a role in positioning of the auricle (extrinsic muscles), which innervated by the facial nerve [VII].  Dr Khalatbary AR SPECIAL SENSES The external acoustic meatus extends from the concha to the tympanic membrane with 2.5 cm in length, which is divided into two parts: » The cartilaginous part (lateral one-third part) » The bony part (medial two-thirds part in the tempral bone) Note: The external acoustic meatus is S-shaped (not straight).  Dr Khalatbary AR SPECIAL SENSES The tympanic membrane (eardrum) is a thin, semi-transparent, and oval- shaped membrane, approximately 1 cm in diameter, which separates the external acoustic meatus from the middle ear. It is placed obliquely at an angle of 55 degrees with the floor of the external acoustic meatus. The tympanic membrane consists of two parts: » Pars flaccida, the thin and slack part of the tympanic membrane » Pars tensa, the thick and taut part of the tympanic membrane The tympanic membrane has two surfaces: » The external (lateral) surface, which is concave. » The internal (medial) surface, which is convex and has two features: - Umbo, a convexity produced by the attachment of the malleus - Anterior and posterior malleolar folds Note: - The external acoustic meatus is S-shaped (not straight); so, the examination of the tympanic membrane with otoscope and drip medicine in the ear can be improved by pulling the auricle superiorly, posteriorly, and slightly laterally (to straighten the external acoustic meatus). - A bright reflection of light (cone of light) is visible in the lower anterior part of the tympanic membrane with an otoscope. Otoscope Pars tensa  Dr Khalatbary AR SPECIAL SENSES The Middle ear is located in the temporal bone and is divided into two parts: » Tympanic cavity, which is adjacent to the tympanic membrane. » Epitympanic recess, which is superior to the tympanic membrane. The middle ear has six walls: » Roof (tegmental wall) » Floor (jugular wall) » Posterior (mastoid) wall, which has three features: - Pyramidal eminence, which has an opening for the stapedius muscle. - Opening for the chorda tympanic nerve - Aditus to mastoid antrum » Anterior wall, which has two features: - Opening for the pharyngotympanic tube - Opening for the canal containing the tensor tympani muscle Roof » Lateral (membranous) wall » Medial (labyrinthine) wall, which has five features: Med. - Oval window, which is the point of attachment for the stapes. Post. Ant. - Round window, which is covered by the secondary tympanic membrane. - Promontary - Prominence of facial canal Floor - Prominence of lateral semicircular canal Note: The middle ear is connected to the pharynx through the pharyngotympanic tube.  Dr Khalatbary AR SPECIAL SENSES The pharyngotympanic (auditory, or eustachian) tube with 3.6 cm in length links the middle ear to the pharynx. The pharyngotympanic tube is devided into two parts: » The one-third bony part » The two-thirds cartilaginous part Note: The pharyngotympanic tube equalizes pressure on both sides of the tympanic membrane, and also drains the mucus from the middle ear to the pharynx.  Dr Khalatbary AR SPECIAL SENSES The Middle ear contains: » Auditory ossicles » Auditory muscles The auditory ossicles include: » Malleus » Incus » Stapes Note: There are two synovial joints between the ossicles. Ankylosis of these joints leads to hearing loss. The auditory muscles include: Tensor tympani Innervation: Mandibular nerve [V3] Function: Contraction of this muscle pulls the handle of the malleus medially and so tenses the tympanic membrane, reducing the force of vibration in response to loud noises. Stapedius Innervation: Facial nerve [VII] Function: Contraction of this muscle, usually is response to loud noises, pulls the stapes posteriorly and prevents excessive oscillation.  Dr Khalatbary AR SPECIAL SENSES The internal ear (labyrinth) is located in the temporal bone and consists of two parts: » Bony labyrinth » Membranous labyrinth The bony labyrinth, a bony mold containing the membranous labyrinth, consists of: » Three semicircular canals (anterior, posterior, and lateral semicircular canals) » Vestibule » Cochlea M odi ol us Each semicircular canal has a dilated end (ampulla) and a non-dilated end through which connected to the vestibule. The vestibule has two features: » Oval window, which is the point of attachment for the stapes » Vestibular aqueduct, which connects the vestibule to the cranial fossa The cochlea is a cone-shaped bony structure that wraps 2.5 times around a central bony column called modiolus. The cochlear canal is divided into two parts by the lamina of modiolus and the basilar membrane: » Scala vestibuli, which is continuous with the vestibule. » Scala tympani, which is separated from the middle ear by the secondary tympanic membrane covering the round window. Note: The bony labyrinth is filled with a clear fluid called the perilymph.  Dr Khalatbary AR SPECIAL SENSES The membranous labyrinth is located inside the bony labyrinth and consists of: » Three semicircular ducts (anterior, posterior, and lateral semicircular ducts) » Utricle » Saccule » Cochlear duct Each semicircular duct is located inside its semicircular canal and has a dilated end (ampulla) and a non-dilated end through which connected to the utricle. The utricle and scccule are located inside the vestibule and connected to each other by the utricosaccular duct. The continuation of the utricosaccular duct is called the endolymphatic duct, which is located inside the vestibular aqueduct and expands as the endolymphatic sac. The cochlear duct is located inside the cochlear canal (in scala vestibuli part) and has three walls: » Outer wall, which is made of the spiral ligament » Roof, which is made of the vestibular membrane » Floor, which is made of the basilar membrane Note: The membranous labyrinth is filled with a clear fluid called the endolymph.  Dr Khalatbary AR SPECIAL SENSES There are two sensory organs in the internal ear: » Organ of balance » Organ of hearing The organs of balance consist of: » The crista of the semicircular ducts (ampulla), which respond to movement in any direction. » The macula of the autricle and saccule, which respond to acceleration. Note: The inflammation of the organs of balance leads to vertigo. Vertigo Macula Crista  Dr Khalatbary AR SPECIAL SENSES The organ of hearing (or spiral organ) rests on the basilar membrane of the cochlear duct. Note: The inflammation of the organ of hearing leads to hearing loss or deafness.  Dr Khalatbary AR SPECIAL SENSES The arterial supply to the ear is provided by numerous arteries: » External carotid artery » Internal carotid artery » Superficial temporal artery » Maxillary artery » Basilar artery  Dr Khalatbary AR SPECIAL SENSES The venous drainage of the ear is done by several veins: » External jugular vein » Maxillary vein Pterygoid venous plexus » Pterygoid venous plexus » Superior petrosal sinus  Dr Khalatbary AR SPECIAL SENSES The ear is innervated by several nerves: » Facial nerve [VII] for skeletal muscle and general sensation » Mandibular nerve [V3] for skeletal muscle and general sensation » Vagus nerve [X] for general sensation » Cervical plexus for general sensation » Glossopharyngeal nerve [IX] for general sensation » Vestibulocochlear nerve [VIII], which has two branches: - Vestibular nerve for balance - Cochlear nerve for hearing