Transcript Special Senses

The Sensory System
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Introduction
A stimulated sensory receptor sends a signal
to the brain
 Signals are interpreted in the brain

Introduction

Five types of sensory receptors
 Mechanoreceptors – stimulated by changes in
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pressure or body movement
Thermoreceptors – stimulated by changes in the
external or internal temperature
Pain receptors – stimulated by damage or oxygen
deprivation to the tissues
Chemoreceptors – stimulated by changes in the
chemical concentrations of substances
Photoreceptors – stimulated by light energy
General Senses

Proprioceptors
 Mechanoreceptors involved in reflex actions
 Maintain equilibrium and posture
Fig 9.1
General Senses

Cutaneous Receptors
 Located in the deepest layer of the epidermis and the
entire dermis
 Make skin sensitive to touch, pressure, pain, and
temperature
General Senses

Pain Receptors (nociceptors)
 Somatic nociceptors
○ Skin and skeletal muscle
○ Respond to mechanical, thermal, electrical or
chemical damage
Senses of Taste and Smell
Chemical senses
 Sensitive to molecules in food and in the air
 Other chemoreceptors in the body

 Govern respiratory rate
 Sensitive to the hydrogen ion concentration of the
blood
Senses of Taste and Smell

Sense of Taste
 Sensory receptors located in the taste buds
○ Primarily on the tongue
○ Also present on the hard palate, the pharynx, and
the epiglottis
 Types of taste sensations
○ Sweet
○ Sour
○ Salty
○ Bitter
○ Umami – meat
Senses of Taste and Smell
 How the brain receives taste information
○ Molecules in food bind with receptor proteins on
microvilli on taste cells
○ Nerve impulses are generated and go to the brain
○ Sensory receiving and memory areas for taste are
located in the insula
Senses of Taste and Smell

Sense of Smell
 Dependent on olfactory cells
○ Located in olfactory epithelium in the roof of the
nasal cavity
○ Modified neurons
○ Olfactory cilia have receptor proteins for odor
molecules
 How the brain receives odor information
Senses of Taste and Smell
 How the brain receives odor information
○ Nerve fibers lead to the olfactory bulb
○ Combinations of activated receptor proteins account
for different odors
○ An odor’s signature is determined by which neurons
are stimulated in the olfactory bulb
○ Neurons send signals through the olfactory tract to
the olfactory areas of the cerebral cortex in the
temporal lobe
Senses of Taste and Smell
 Sense of taste and sense of smell
○ Both work together
○ Smell can enhance taste
○ Part of what is referred to as smell may actually be
taste
Sense of Vision

Accessory Organs of the Eye
 Eyebrows, eyelids, and eyelashes
○ Eyebrows shade the eyes from the sun and protect
eyes from perspiration or debris
○ Eyelids are continuations of the skin
○ Eyelashes can block debris from entering the eye
○ Secretions from sebaceous glands associated with
eyelashes lubricate the eye
○ Eyelids help keep the eye lubricated
Fig 9.5a
Sense of Vision
 Lacrimal apparatus
○ Lacrimal gland produces
tears
○ Tears collect in lacrimal
sac
○ Tears drain into the nose
by the nasolacrimal duct
Sense of Vision
 Extrinsic muscles
○ Contractions move the eyes
○ Superior rectus rolls eye upward
○ Inferior rectus rolls eye downward
○ Lateral rectus turns eye outward
○ Medial rectus turns eye inward
○ Superior oblique rotates eye counterclockwise
○ Inferior oblique rotates eye clockwise
○ Three cranial nerves control these muscles
Fig 9.6
Sense of Vision

Anatomy and Physiology of the Eye
 Three layers
○ Sclera
 White and fibrous
 Cornea is transparent
○ Choroid
 Middle, vascularized layer
 Becomes the iris towards the front
- Regulates the size of the pupil
- Colored portion of eye
 The ciliary body is behind the iris
- Contains the ciliary muscle
- Controls the shape of the lens
Sense of Vision
○ Lens – divides the eye into two compartments
 Anterior compartment contains aqueous humor
 Posterior compartment contains the retina and the vitreous
humor
○ Retina
 Contains photoreceptors
- Rod cells – night vision and peripheral vision
- Cone cells – distinguish colors
 Fovea centralis – area of retina where cone cells are
densely packed
 Optic nerve – formed from sensory fibers from the retina
Sense of Vision
 Function of the lens
○ Focuses images on the retina
○ Image produced is smaller than the object
○ Image on retina is inverted and reversed
○ Accommodation
 Maintaining focus on a distant and then near object
 Lens must change shape
- Controlled by the ciliary muscle
- Ciliary muscle is relaxed for a distant object
- Ciliary muscle contracts to view a near object
Sense of Vision
 Vision pathway
 Light is refracted by cornea, aqueous humor, lens, vitreous
humor
 Image is formed on the retina
 Nerve impulses travel to the visual area of the cerebral
cortex
○ Color vision
 Depends on three kinds of cones
 Color blindness is caused by the inherited absence of the
color pigments in the cones
Sense of Vision
○ Function of the retina
Rod cells and cone cells are located in the deepest layer
 Light must penetrate to the back of the retina
○ Blind spot
 No rods and cones where the optic nerve leaves the retina
 No vision is possible in this area
Sense of Vision
○ From the retina to the visual cortex
 The right and left visual cortex rebuilds and rights image
Sense of Hearing
Two sensory functions of the ear
 Sensory receptors located in the inner ear

 Consists of hair cells
 Sensitive to mechanical stimulation
(mechanoreceptors)
Anatomy of the Ear
 Sound Pathway
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Sense of Hearing
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Anatomy of the Ear
 Outer ear
○ Pinna
○ Auditory canal
 Lined with hair
 Modified sweat glands secret cerumen
 Middle ear
○ Begins at the tympanic membrane
○ Ends at bony wall with two small openings
 Oval window
 Round window
○ Three small bones (ossicles)
 Malleus
 Incus
 Stapes
○ Auditory tube (eustachian tube) extends from the middle ear to the
nasopharynx
 Inner ear
○ Filled with fluid
○ Three areas
 Semicircular canals
 Vestibule
 Cochlea
Sense of Hearing
 Sound pathway
○ Through the auditory canal and middle ear
 Sound travels by the vibrations of air molecules
 Sound waves strike the tympanic membrane causing it to
vibrate
 Pressure from the tympanic membrane causes the malleus,
the incus, and then the stapes, to vibrate
 The stapes strikes the oval window
 Vibrations from the oval window are passed to the fluid
within the cochlea of the inner ear
Sense of Hearing
○ Impulses travel From the cochlea to the auditory
cortex
 The spiral organ (organ of Corti) is the sense
organ for hearing
- Located in cochlear canal
 Pressure waves cause the hair cells to bend
 Nerve impulses begin in the cochlear nerve and
travel to the brain stem and then the auditory
cortex
Sense of Equilibrium
Mechanoreceptors in the semicircular canals
are responsible for rotational equilibrium
 Mechanoreceptors in the vestibule are
responsible for gravitational equilibrium

Sense of Equilibrium
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Rotational Equilibrium Pathway
 Involves the three semicircular canals
 Motion sickness
○ Continuous movement of fluid within the semicircular canals
○ Sensory input from the inner ear that is different from visual
sensations
 Vertigo is dizziness and a sensation of rotation
Effects of Aging
The lens of the eye does not accommodate as
well
 Three visual disorders seen frequently:
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 Cataracts- clouding of lens
 Age-related macular degeneration
 Glaucoma – build up of pressure in eye
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The need for a hearing aid increases with age
 Presbycusis (age-related hearing decline)
 Otosclerosis is the most frequent cause of conduction
deafness in adults
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Dizziness and the inability to maintain balance