Sensory system Dr. Carmen E. Rexach Anatomy 35 Mt San Antonio College
Sensory receptors Detect stimuli Classified by structure Origin Distribution Modality
Structural Classification naked nerve endings Ex) nociceptors encapsulated nerve endings Ex) Meissner s corpuscles
Classification by stimulus origin Exteroceptors External environment Interoceptors Internal organs Proprioreceptors stretch receptors of muscles, tendons, & joints
Functional classification Photoreceptors Thermoreceptors 2 varieties 1) detects temperature increase 2) detects temperature decrease Nociceptors Mechanoreceptors Chemoreceptors Baroreceptors
Functional Classifications Photoreceptors sense changes in the intensity & wavelength (color) of light temperature receptors 2 varieties 1) detects temperature increase 2) detects temperature decrease nociceptors involved in pin prick sensation, itching, tickling
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)
Special Senses
The eye
Tunics of eye Sclera Fibrous outer tunic composed of sclera proper and cornea Vascular tunic Neural tunic (retina)
Vascular tunic Choroid Posterior Network of capillaries Heavily pigmented with melanin Ciliary body heavily pigmented has a muscle and processes Iris Pigmented muscle 2 smooth muscle layers Sphincter pupillae muscle Dilator pupillae muscle Pupil = hole in middle
the lens composed of alpha crystalline protein flexible, bi-convex lens instantly accommodates focus at different distances
retina inner (nervous) tunic Fxt of the retina = photoreception fovea centralis in line with the visual axis focus point optic disc blind spot Exit site for blood vessels and optic nerve
Optic fundus
The cavities of the eye Anterior filled with aqueous humor Two regions anterior chamber between the cornea and iris posterior chamber between the iris and lens posterior: filled with vitreous humor also called the vitreous chamber
Extrinsic Eye Muscles rectus Superior Inferior Medial lateral Obliques Superior Inferior
Cranial nerves supplying the eye
cranial nerves supplying the eye CN II Optic nerve fibers arise from the retina pass through the chiasma to the optic tracts CN III Oculomotor nerve Mixed nerve (motor and proprioception) Somatic fibers innervate extraocular muscles Parasympathetic fibers supply iris and ciliary muscle
Additional cranial nerves Trochlear nerve (CN IV) primarily motor supplies the superior oblique Abducens nerve (CN VI) supplies the lateral rectus muscle Trigeminal nerve (CN V) ophthalmic division conveys sensory impulses from the anterior scalp, upper eyelid, nose, nasal cavity, cornea and lacrimal gland)
Pathway of optic nerve Optic nerve to the optic chiasma 1/2 of the fibers cross to the opposite side fibers exit the chiasma as tracts To lateral geniculate nuclei of the thalamus to the superior colliculi (midbrain) to the visual cortex of occipital lobe
Conversion of image
The Ear Functions Detect sound Equilibrium and balance Regions Outer ear Middle ear Inner ear
Outer Ear pinna or auricle External funnel shaped structure composed of elastic cartilage and skin Function: to capture sound waves external auditory meatus Blind-ended canal leads into the temporal bone ends at the tympanic membrane
Middle ear air filled cavity lined with mucus membranes continuous with pharynx via eustachian tube Tympanic membrane a flexible, fibrous CT membrane that separates the outer and middle ear cavities Auditory ossicles malleus, incus, stapes
Auditory ossicles Smallest bones in body vibrate in response to sound waves attached to the tympanic membrane & oval window tensor tympani & stapedius (smallest) muscles
Inner Ear bony labyrinth fluid filled cavity of the petrous portion of the temporal bone membranous labyrinth Contains specialized cells that detect sound and monitor equilibrium
Cochlea Shaped like snail shell Contains Organ of Corti Hair cells = respond to sound waves Transmit signals to Vestibulocochlear nerve (CN VIII) Interpreted as sound by auditory cortex in temporal lobe of brain
The Cochlea
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
The Vestibular Apparatus
Ampula & cupula: At the base of each semicircular canal
Utricle and saccule
Vestibulocochlear Nerve CN VIII has a vestibular and cochlear branch
Taste Chemoreceptors located in tongue Five primary sensations Sweet, sour, salty, bitter, and umami
Taste maps All taste qualities are tasted everywhere on tongue Some areas are more sensitive to certain qualities Can change in an individual with time
Umami Common in Asian foods First associated with MSG Characteristic of fermented or aged products, such as soy sauce & cheese Taste produced by free glutamates binding to G-coupled receptors
Smell A special sense Olfactory receptors Receptor axons lead to olfactory lobe olfactory bulb receptor cell
Olfactory epithelium Thick, pseudostratified columnar epithelium with modified cilia that acts as olfactory receptors