Sensory systemSensory systemSensory system
Dr. Carmen E. RexachDr. Carmen E. RexachAnatomy 35Anatomy 35
Mt San Antonio CollegeMt 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 SensesSpecial SensesSpecial 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
• Chemoreceptorslocated 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
olfactorybulb
receptor cell
Olfactory epithelium
Thick, pseudostratified columnar epithelium with modified cilia that acts as olfactory receptors