Special Senses

Electrical Signal

Action Potential

Special senses

Lead to conscious (aware) sensation

Major special senses

Smell, tastes, vision, and hearing

General senses

Proprioception and visceral perception

Transduction

Converts a stimulus into an electric signal

Location of primary sensory cortical area for olfaction

Temporal Lobe

Location of primary sensory cortical area for vision

Occipital lobe

Location of primary sensory cortical area for hearing

Temporal lobe

Smell

Chemical sense

Function of smell

Detects molecules in air

Operants

Molecules that stimulate olfaction

Olfaction

Can detect a molecule at a concentration of 1 part per billion

Location of olfactory receptors

Olfactory epithelium

Location of olfactory epithelium

Roof of the oral cavity

Olfactory epithelium

Contains exocrine glands called olfactory glands

Role of secretion of olfactory glands

Dissolve odorants

Odorants

Bind to specific receptors at the membrane of olfactory sensory neurons

Olfactory sensory neurons

Bipolar neurons

Location of olfactory receptors

On the olfactory hairs of olfactory sensory neurons

Number of types of odorant receptors

Over 1,000 different types

Individual odors

Created by an odorant binding to several different types of specific odorant receptors

Binding of an odorant to a specific receptor of an olfactory sensory neuron

Generates an action potential along the axon of this neuron

Cribriform plate

Lets the axons of olfactory sensory neurons enter the brain

Axons of olfactory sensory neurons

Form synapses with axons in the olfactory bulb

Olfactroy nerve

Cranial nerve I

Role of olfactory nerve

Carries olfactory signals to various regions of the brain

Gustation

Chemical sense

Definition of gustation

The act or sensation of tasting

5 primary tastes

1. Sour

2. Sweet

3. Bitter

4. Salty

5. Umami

Complex flavors

Combinations of primary tastes

Taste buds

Clusters of gustatory receptors

Location of taste buds

On the tongue, soft palate, cheek, pharynx, and epiglottis

Near taste buds

Papillas

Papillas

ARE NOT directly involved with gustation

Three types of papilla associated with taste buds

1. Velvet

2. Fungiform

3. Foliate

Velate papilla

12 of them arranged in a V shape at the back of the tongue

Fungiform papilla

Mostly on tip and sides of tongue

Foliate papilla

Located in lateral trenches of tongue

Filliform papilla ARE NOT

Associated with taste buds and HAVE NO role in gustation

Filiform papilla

Most common type of papilla

Role of filiform papilla

Sense texture of food

CN VII, CN IX, CN X

Involved in gustation

Sound

Due to pressure waves

3 regions of ear

1. External ear

2. Middle ear

3. Internal ear

Components of external (outer) ear in order (exterior to interior)

1. Auricle/pinna

2. External auditory canal

3. Tympanic membrane (eardrum)

Auricle

Directs the pressure waves toward the auditory canal

External auditory canal

Directs pressure waves to the tympanic membrane

Pressure waves

Cause tympanic membrane to vibrate

Shape of tympanic membrane (eardrum)

Cone-shaped

Location of ceruminous glands

External auditory canal

Ceruminous glands

Produce cerumen

Cerumin

Cleans and waterproofs the external auditory canal

Three ossicles (bones) of the middle ear (eardrum to oval window)

1. Malleus

2. Incus

3. Stapes

Location of stapes

In contact with the oval window

Location of eustachian tube

Extends from the middle ear to the nasopharyngeal

Role of Eustachian tube

Relieve pressure in middle ear

Eustachian tube

Common source of ear infections

Components of inner ear

1. Cochlea

2. Vestibular apparatus

Role of cochlea

Hearing

Role of vestibular apparatus

Balance

Bony labyrinth

Bone carved to house the components of the inner ear

Role of bony labyrinth

Prevents the middle ear from moving

Hearing involves

Mechanotransduction

Only site of sound mechanotransduction

Cochlea

NO mechanotransduction

In external or middle ear

Hair cells

Perform the mechanotransduction of sound waves

Endolymph

Fluid in cochlear duct; rich in K+

Role of endolymph

Helps hair cells to generate electrical impulses

Perilymph

Fluid in bony labyrinth (vestibular canal and tympanic canal); rich in Na+ and Cl-

Role of perilymph

Transmits sound waves to the endolymph

3 sections of cochlea

1. Vestibular canal

2. Cochlear duct

3. Tympanic canal

Location of organ of corti

In cochlear duct

Hair cells

Part of the organ of Corti

Role of hair cells

1. Generating action potential in response to sound waves

2. Mechanotransduction of sound waves

Apical surface of hair cells

Has stereocilia

Waves in the endolymph

Make stereocilia bend

Bending of stereocilia

Generates action potential

Vestibular apparatus

Responsible for the maintenance of the body equilibrium (balance)

Components of vestibular apparatus

1. Semi-circular canals

2. Saccule and utricle

Part of the inner ear

Vestibular apparatus

Cochlea IS NOT

Part of the vestibular apparatus

Utricle

Responds to horizontal accelerations

Saccule

Responds to vertical accelerations (displacement)

Otoliths

Crystals of calcium carbonate in the vestibular apparatus

Has hair cells with stereocilia bending in response to changes in the position of otoliths

Vestibular apparatus

Cochlear nerve

Sends the brain information related to audition (hearing)

Vestibular nerve

Sends the brain information related to balance (equilibrium)

Cranial nerve VIII

Vestibulocochlear nerve

Vestibulocochlear nerve

Bundles the cochlear and vestibular nerves

Tinnitus

Ringing in the ears

Ménière’s disease

A balance disorder

Definition of light

electromagnetic radiation

Sound

Due to local pressure variations which need a medium such as air or water to propagate

Characterization of light

By its wavelength

Light

Tiny fraction of electromagnetic spectrum; only part of spectrum we can sense

Refraction

Bending of light as it goes through two different transparent mediums; creates images

Cornea and lens

Can form an image on the retina

Retina

Biological photo sensor

Electric signals for the retina

Reach the brain through the optic nerve

Optic nerve

Cranial nerve II