Chapter 10

The Senses

The Senses

•General Senses/Receptors ●Special Senses

•Chemoreceptors ●Smell

•Pain receptors ●Taste

•Thermoreceptors ●Sight

•Mechanoreceptors ●Hearing

•Photoreceptors ●Equilibrium

Sensations

= feelings that occur when the brain interprets sensory impulses

***The brain uses projection to send the sensation back to its

point of origin so that a person can pinpoint the region of

stimulation.***

Sensory adaptation occurs when sensory impulses are sent at

decreasing rates until receptors fail to send impulses unless the

intensity and strength of the stimulus changes.

Somatic Senses

Touch and Pressure Senses

•Free nerve endings

•Meissner’s corpuscles

•Pacinian corpuscles

Temperature Senses

•Heat receptors

•Cold receptors

•Pain receptors

Sense of Pain***Consists of free nerve endings that are stimulated when

tissues are damaged***

Types of stimuli:

•Chemicals

•Oxygen deprivation

Visceral pain receptors detect sensations produced from the

viscera.

•Referred pain

Pain Nerve Fibers•Acute pain

•Chronic pain

Pain impulses are processed in the gray matter of the spinal cord

Regulation of Pain Impulses:

•Thalamus

•Cerebral cortex

•Hypothalamus

•Enkephalins

•Serotonin

•Endorphins

Sense of Smell•Olfactory organs

•Olfactory receptors

•Bipolar neurons with cilia

•Epithelial supporting cells (nasal cavity)

•Olfactory stimulation

•Olfactory nerve pathways

Sense of Taste•Taste organs: taste buds within the papillae of the tongue and

scattered throughout mouth and pharynx

Sense of taste: chemicals must be mixed with water (saliva)

Taste receptors:

•Taste cells

•Taste hairs

•Taste Nerve Pathways

Sense of Hearing1.External Ear 2.Middle Ear

*Auricle *Tympanic membrane

*External acoustic meatus * Tympanic cavity

*Malleus *Incus

* Stapes

3.Inner Ear

*Membranous labyrinth *Osseous labyrinth

*Perilymph *Endolymph *Cochlea

*Semicircular canals *Organ of Corti

Auditory Tube (Eustachian tube) --Equalize air pressure

Auditory Nerve Pathways

Sense of Equilibrium

•Static equilibrium

•Macula

•Otoliths

•Dynamic equilibrium

•3 semicircular canals

•Cristae ampullaris

•Cupula

Sense of Sight•Accessory structures

•Lacrimal apparatus

•Eyelids/Eyelashes

•Extrinsic muscles

Structure of the Eye

•Outer tunic(Fibrous) •Inner Tunic(Sensory)

•Cornea •Retina

•Sclera •Fovea centralis

•Optic nerve and blood vessels •Optic disk

•Middle tunic(Choroid) •Posterior cavity

•Choroid coat

•Ciliary body

•Iris

•Lens

•Anterior cavity

Light Refraction and Accommodation•Accommodation: The ability of the lens to adjust shape to facilitate

focusing

•Refraction: Bending of light waves in order to focus

•Visual Receptors

•Rods

•Cones

•Visual Pigments

•Rhodopsin

•Located in cones: 3 sets of cones –each with different visual

pigment

•Wavelength of light determines color perceived

•Visual Nerve Pathways