Human Anatomy Unit 4

NERVOUS SYSTEM: GENERAL AND SPECIAL SENSES In Anatomy Today Receptors

• Receptor sensitivity – Each receptor has a characteristic sensitivity • Pressure • Pain • Temperature • Chemical sensitivity • Receptive field Structural Classification

• Naked nerve endings • Encapsulated nerve endings • Neuroepithelium – epithelium modified for some neuron functions General Senses

• Nociceptors – involved in “pin prick” sensation, itching, tickling • Thermoreceptors – Respond to changes in temperature • Mechanoreceptors – Respond to physical distortion, contact, pressure on their plasmolemma • Chemoreceptors – Monitor chemical composition of body fluids – Respond to presence of specific chemicals Nociceptors

• Locations • Sensations – Numerous in superficial – Fast pain areas of skin • Prickling pain (cuts) – Joint capsules – Slow pain – Periostea of bone • Burning, aching – Walls of blood vessels – Referred pain – Few in deep tissue, organs • Respond to – Temperature – Mechanical damage – Dissolved chemicals Referred Pain

• Impulses from certain viscera mapped to other sites in dermatomes of skin • Mapped to ‘most likely source’ • Usually follows sympathetic nerve pathways (can also follow parasympathetic pathways) Thermoreceptors

• Locations – Dermis of skin – Skeletal muscles – Liver – Hypothalamus • Cold more numerous than hot • Free nerve endings Mechanoreceptors

• Respond to: – Stretch – Compressional force – Tensile force – Distortion • Types – Tactile receptors – Barroreceptors – Proprioceptors Chemoreceptors

• Detect small changes in the concentration of specific chemical or compounds • Dissolved in fluid (plasma) • Carotid/Aortic bodies Olfaction Gustation

• All taste qualities are • Chemoreceptors tasted everywhere on located in tongue tongue • Some areas are more • Five primary sensations sensitive to certain – Sweet, sour, salty, bitter, qualities and umami (savory) • Can change in an individual with time Gustation Equilibrium and Hearing

• External Ear • Inner Ear – Auricle/Pinna – Membranous labyrinth – External auditory meatus • Contains specialized cells that – Tympanic membrane detect sound and monitor – Ceruminous glands equilibrium • Middle Ear – Bony labyrinth • fluid filled cavity of the petrous – Tympanic cavity portion of the temporal bone – Eustacian tube – Cochlea – Auditory ossicles • Organ of Corti • Malleus – Vestibule • Incus • Semicircular canals • Stapes • Utricle – Muscles • Saccule • Tensor tympani – Hair cells • Stapedius muscle – Supporting cells Anatomy of the Ear The Middle Ear Vestibular Apparatus • Semicircular canals – 3 canals at right angles to each other (anterior, posterior, lateral) – each contains 2 ampullae with receptors – sense angular rotation • Utricle and Saccule – receptors for static equilibrium changes – Detect linear acceleration Semicircular Canals and Ducts Semicircular Canals and Ducts The Maculae of the Vestibule The Cochlea and Organ of Corti The Cochlea and Organ of Corti Vision Sectional Anatomy of the Eye Sectional Anatomy of the Eye Accessory Structures of the Eye Lacrimal Apparatus Extrinsic Eye Muscles Tunics of The Eye

• Fibrous Tunic – Fibrous outer tunic – composed of sclera proper and cornea • Vascular tunic – choroid • Neural tunic – Retina Fibrous Tunic

• Structures – Sclera – Cornea • Functions – Mechanical support – Physical protection – Attachment for extra-occular muscles – Assist in accomodation (focusing) Vascular Tunic

• Choroid • Functions – Posterior to lens – Route for blood vessels, – Network of capillaries lymphatics – Heavily pigmented with – Regulates the amount of light melanin that enters the eye • – Secreting and reabsorbing Ciliary body aqueous humor – heavily pigmented – Controlling the shape of the – has a muscle and processes lens (accomodation) • Iris – Pigmented muscle – 2 smooth muscle layers • Sphincter pupillae muscle • Dilator pupillae muscle – Pupil = hole in middle Vascular Tunic

• Choroid • Ciliary body – Posterior to lens – heavily pigmented – Network of capillaries – Ora serrata – Heavily pigmented with – Ciliary body melanin • Ciliary muscle • Iris • Ciliary processes – Pigmented muscle – Suspensory ligaments – 2 smooth muscle layers • Pupillary sphincter muscle • Pupillary dilator muscle – Pupil = hole in middle Vascular Tunic Neural Tunic

• Function of the retina = photoreception • Pigmented layer • Neural layer – retina – Photoreceptors • Rods, cones – Macula lutea – fovea centralis • in line with the visual axis • “focus point” – optic disc • blind spot • Exit site for blood vessels and optic nerve Retinal Organization Retinal Organization The Chambers of the Eye

• Anterior cavity – Anterior chamber – Posterior chamber – Aqueous humor – Canal of Schlemm – Lens • Posterior Cavity – Vitreous chamber The Lens

• Composed of alpha crystalline protein • Flexible • Bi-convex lens • Accommodates – focus at different distances