The General & Special Senses

Chapter 10

Introduction

• Senses – our perception of what is “out there”– General senses

• Includes senses that are not specific• Pass information through spinal nerves

– Special senses• Found within complex sense organs to cerebral

cortex• Pass information through cranial nerves to

cerebral cortex

General Senses

• Includes senses that are associated with skin– Temperature, pressure, touch, pain, vibration,

proprioception• Pass information along the spinal nerves

and pathways to specific areas of the cerebral cortex

Special Senses

• Olfaction, gustation, equilibrium, hearing, & vision

• Found within complex sense organs• Pass information along the cranial nerves to

specific areas of the cerebral cortex.

Receptors

• Sensory receptors are transducers – Change stimuli into electro-chemical impulses – Specific receptors can transduce only certain

types of stimuli

Interpretation of Sensory Information

• Occurs in cerebral cortex• Depends on the area of the cerebral cortex

that receives the information

Central Processing and Adaptation

• Sensory adaptation – the loss of sensitivity after continuous stimulation– Tonic receptors are always active– Phasic receptors only relay changes in the

conditions they are monitoring• Role – prevents brain from being

overloaded with unimportant information

Receptors of the General Senses

Nociceptors

• Detect pain– Referred pain– Phantom pain

Mechanoreceptors

• Respond to pressure & touch– Tactile receptors– Baroreceptors– Proprioreceptors– Thermoreceptors

Tactile Receptors• Found in the dermis

Baroreceptors• Monitor changes in pressure

Chemoreceptors• Detect chemicals in solution

– Blood composition

The Special Senses

Olfaction (the nose)• Olfactory receptors

– Can detect at least 50 different primary smells– Located in the epithelium of roof of nasal cavity

Olfactory Receptors• Molecules dissolve

in the mucus of the epithelium

• Olfactory neurons pass through the roof of the nasal cavity and synapse in the olfactory bulb

• Olfactory tracts go directly to the cerebral cortex

Gustation (the tongue)

• Taste receptors are in the taste buds

• 6 primary tastes– Sweet, sour,

salty, bitter, water, umami

Gustatory Receptors

• Located in papillae on the surface of the tongue

• Contain the gustatory receptors– Molecules dissolve

in saliva

Gustatory Receptors

Pathway of Gustatory Sense

• Cranial nerves relay sensory impulses to the cerebral cortex– All pass through the

medulla & thalamus

Equilibrium & Hearing (the ear)• External ear

– The auricle directs sound waves into the external auditory meatus to the tympanic membrane

The Middle Ear• Contains the auditory ossicles• Separated from the external ear by the tympanic

membrane– Malleus– Incus– Stapes

• Connected to the throat by the eustachian tube

The Inner Ear• Separated from the middle ear by the oval window

The Inner Ear

• Consists of a series of canals filled with fluid

The Inner Ear

• Consists of a series of canals filled with fluid– Vestibule– Semicircular

canals– Cochlea contains

• Organ of Corti

The Vestibule

• Detects static position

• Hair cells are embedded in a gelatinous material

Otoliths at Work• Otoliths are

balanced on top of gelatinous material– Slide when

head tips– Bend hairs– Generates

nerve impulse

The Semicircular Canals• Detect dynamic

balance• Arranged at right

angles to each other• Hair cells are

embedded in gelatinous material with fluid over it

• Movement of head– Bends the hairs – Creates nerve

impulses

Semicircular Canals at Work

The Cochlea

• Divided into 3 tunnels by membranes– Tunnels connect

with the oval window and round window

– Organ of Corti

Cochlear Chambers

The Organ of Corti• Consists of hair

cells on a basement membrane

• Tips of hairs touch the tectorial membrane

• Basement membrane vibrates– Sends a nerve

impulse– Hair cells bend

Pathway of Auditory Sense

Summary of Hearing• Sound waves enter the external auditory meatus• Tympanic membrane vibrates• Auditory ossicles vibrate• Oval window vibrates• Fluid in cochlea moves• Basement membrane moves• Hairs rub against the tectorial membrane• Nerve impulse is sent along the auditory nerve to

the brain

Vision (the eye) – Accessory Structures• Eyelids protect the eye

– Conjunctiva lines the eyelid

• Lacrimal apparatus– Lacrimal gland produces

tears– Lacrimal canals drain

tears into lacrimal sacs– Nasolacrimal duct drains

into the nasal cavity• Extrinsic muscles move the

eyeball

Structure of the Eye – 3 Tunics• Outer tunic

– Includes cornea & sclera

• Middle tunic

– Includes choroid coat, ciliary body, lens, iris & pupil

• Inner tunic (retina)– Contains

photoreceptors• Rods & cones

The Cavities of the Eye

• The lens separates the interior of the eye into 2 cavities– Anterior cavity

• Contains aqueous humor

• Glaucoma – Posterior cavity

• Contains vitreous humor

The Cavities of the Eye

The Vascular Tunic• Contains many blood

vessels & nerves• The iris controls the

size of the pupil• Suspensory

ligaments attach the lens to the ciliary body– Controls the shape

of the lens• Allows focusing on

near & distant objects• Cataract

The Retina• Cones allow for sharp

color vision in bright light– Contain pigments– Macula lutea – Fovea centralis

• Rods provide for vision in dim light– Contain the pigment

rhodopsin– Most dense at

periphery of retina

Photo of Posterior Eye

Human Anatomy, 3rd editionPrentice Hall, © 2001

Figure 18-22c

Pathway of Vision Sense

Summary of Vision

• Light rays enters through the pupil• Light rays cross in the lens• Retina receives reversed & upside down

image• Rods & cones are stimulated• Optic nerve carries impulse to the brain

Abnormal Vision

• Myopia• Hyperopia• Presbyopia• Astigmatism