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