Essentials of Human Anatomy & Physiology
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slides 8.1 – 8.19
Seventh Edition
Elaine N. Marieb
Chapter 8
Special Senses
Lecture Slides in PowerPoint by Jerry L. Cook
Special Senses
Title
• Somatosensation
Essential Question
• Describe the structures and functions of somatosensation.
Somatosensation Description
receives impulses from the body’s somatosensory receptors
Location in the Brain
Found in the postcentral gyrus of the parietal lobe
Posterior to the central sulcus, and anterior portion of the parietal lobe.
Body Regions with the Most
Sensory Receptors:
Lips and fingertips
Sensory and Motor Areas of the
Cerebral Cortex
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Figure 7.14
Sensory pathways are crossed pathways.
• The left side of the sensory cortex receives impulses from the right side of the body, and vice versa.
Right Hand
Pathways for Sensory System
• Pain
DRG (dorsal root ganglion) spinal cord thalamus SS cortex
DRG – Dorsal Root Ganglion
Pathways for Sensory System
• Touch/Temp
DRG spinal cord medulla thalamus SS cortex
What is a Penfield Homunculus?
• “little man” is a drawing that indicates the density of neurons in the somatosensory cortex
• The more dense the neurons are, the greater the volume that is taken up in the brain.
Special Senses
Title
• Vision
Essential Question
• Describe the structures and functions of vision.
Meibomian
Glands
Accessory Structures of the Eye
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Meibomian glands –modified sebaceous glands produce an oily secretion to lubricate the eye
Accessory Structures of the Eye
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Ciliary glands (no label) –modified sweat glands between the eyelashes
Figure 8.1b
Conjunctiva
Accessory Structures of the Eye
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Conjunctiva
Membrane that lines the eyelids
Connects to the surface of the eye
Secretes mucus to lubricate the eye
Lacrimal Apparatus
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Function
Protects, moistens, and lubricates the eye by producing lacrimal fluid (tears)
Lacrimal Apparatus
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StructuresLacrimal
Gland
Lacrimal
Canal
Lacrimal
Sac
Nasolacrimal Duct
Flow of Tears
Structure of the Eye
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The wall is composed of three tunics
Fibrous tunic –outside layer
Choroid –middle layer
Sensory tunic –inside layer
Figure 8.3a
Sclera
Cornea
The Fibrous Tunic
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Sclera
White connective tissue layer
The Fibrous Tunic
Cornea
Allows for light to pass through
Repairs itself easily
The only human tissue that can be transplanted without fear of rejection
YouTube - Cornea
Transplant
Structure of the Eye
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The wall is composed of three tunics
Fibrous tunic –outside layer
Choroid –middle layer
Sensory tunic –inside layer
Figure 8.3a
Lens
Ciliary
Body
Iris
Pupil
Choroid Layer
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Ciliary body
smooth muscle that attaches to and controls the lens
Choroid Layer
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Lens
Biconvex crystal-like structure
Can change shape to allow light to properly focus on the retina
Choroid Layer
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Iris
Pigmented layer that gives the eye color
Prevents light from scattering
Choroid Layer
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Pupil
Rounded opening of the iris that controls the amount of light to pass through
Structure of the Eye
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The wall is composed of three tunics
Fibrous tunic –outside layer
Choroid –middle layer
Sensory tunic –inside layer
Figure 8.3a
Fovea
Centralis
Retina
Optic
DiscOptic
Nerve
Sensory Tunic
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Retina
Contains millions of receptor cells, the rods and cones
Neurons of the Retina
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Figure 8.4
Sensory Tunic
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Optic Nerve
Receives information from the retina and sends it to the brain
Sensory Tunic
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Optic Disc
The site where the optic nerve leaves the eyeball
The “blind-spot”
Sensory Tunic
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Fovea Centralis
Portion of the retina that contains only cones
Area of greatest visual acuity (sharpest vision)
Structure of the Eye
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The wall is composed of three tunics
Fibrous tunic –outside layer
Choroid –middle layer
Sensory tunic –inside layer
Figure 8.3aVitreous
Humor
Canal of
Schlemm
Aqueous
Humor
Internal Eye Chamber Fluids
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Aqueous humor
Watery fluid found in chamber between the lens and cornea
Helps maintain intraocular pressure
Provides nutrients for the lens and cornea
Internal Eye Chamber Fluids
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Canal of Schlem
Located at the junction of the sclera and cornea
Reabsorbs aqueous humor into the venous blood
Aqueous humor
Internal Eye Chamber Fluids
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Vitreous humor
Gel-like substance behind the lens
Keeps the eye from collapsing
Lasts a lifetime and is not replaced
Aqueous & Vitreous humor
Neurons of the Retina and Vision
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Rods
Allow dim light vision and peripheral vision
Perception is all in gray tones
Neurons of the Retina and Vision
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Cones
Allow for detailed color vision
Function in bright light to help with discriminatory vision
Image formation on the Retina
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The image formed on the retina as a result of the light-bending activity of the lens is a real image – that is , it is reversed from left to right, upside down, and smaller than the object
Figure 8.9
Eye Reflexes
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Convergence Reflex
Moving both eyes to view close up objects
Controlled by extrinsic eye muscles
Eye Reflexes
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Pupillary Reflexes
Pupils constrict due to viewing close objects or exposure to bright light
Controlled by internal eye muscles and the autonomic nervous system
Prevents excessively bright light from damaging the photoreceptors
Visual Pathway to the optic cortex
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Photoreceptors of the retina
Optic nerve
Optic nerve crosses at the optic chiasma
Figure 8.11
Optic tracts
Thalamus (axons form optic radiation)
Visual cortex of the occipital lobe
Special Senses
Title
• Audition
Essential Question
• Describe the structures and functions of hearing.
Anatomy of the Ear
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The ear is divided into three areas
Outer (external) ear
Middle ear
Inner ear
Figure 8.12
The External Ear
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Pinna (auricle)
collects, funnels, and amplifies sound
Figure 8.12
The External Ear
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External auditory canal
Narrow chamber in the temporal bone
Has Ceruminous (wax) glands
The External Ear
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Tympanic Membrane
Separates the outer and middle ear
Vibrates when hit by sound waves
Tympanic Membrane
Bones of the Tympanic Cavity
Middle Ear
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Ossicles
Vibrations from eardrum move the malleus
These bones transfer sound to the inner ear
Figure 8.12
Middle Ear
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Oval Window
Opening at the head of the cochlea
Sound vibrations from the stapes is transmitted to inner ear
Figure 8.12
The Middle Ear or Tympanic Cavity
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Auditory Tube
connects the middle ear with the throat
Allows for equalizing pressure during yawning or swallowing
Auditory Tube
Inner Ear or Bony Labyrinth
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Cochlea
Contains the organ of Corti where the hearing receptors are found
Figure 8.12
Inner Ear or Bony Labyrinth
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Vestibule
Contains muculae which are involved in static equilibrium
Reports on the position of the head
Figure 8.12
Inner Ear or Bony Labyrinth
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Semicircular Canals
Involved in dynamic equilibrium
Responds to angular or rotary movements of the head
Figure 8.12
Pathways for Sensory System
• Audition
– Receptors: Mechanoreceptors
– Stimulus Energy: Sound
– Pathway
• Ear: hair cells Ear: vestibulochochlear nerve medulla midbrain thalamus auditory cortex (temporal lobe)
Organs of Hearing
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Organ of Corti
Contains the hearing receptors or the hair cells.
Organs of Hearing
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The receptors are positioned on the basilar membrane, and the hairs are embedded in the tectorial membrane
Organs of Hearing
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When the tectorial membrane is disturbed, this stimulates the hair cells which send information to the cochlear nerve.
Sensorineural Deafness
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Deafness that is caused by damage to neural structures (cochlear nerve or auditory cortex cells)
Can be caused by stroke or trauma
Conduction Deafness
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Deafness that is caused by any interference with the conduction of vibrations from the outer to the inner ear
Can be caused by wax accumulations, otitis media, fusion of the ossicles, or pressure imbalance between the middle and outer ear
Organs of Equilibrium
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Receptor cells are in two structures
Vestibule
Semicircular canals
Figure 8.16a, b
Static Equilibrium
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The vestibule helps us with static equilibrium or the position of the head with respect to the pull of gravity when the body is not moving.
Static Equilibrium
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Figure 8.15
Dynamic Equilibrium
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The semicircular canal helps with dynamic equilibrium, which responds to angular or rotary movements of the head, rather than straight-line movements.
Dynamic Equilibrium
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Figure 8.16c
OLFACTION
Olfactory Epithelium
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Figure 8.17
Olfaction – The Sense of Smell
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Olfactory Bulb
Contains the receptors for the sense of smell
Olfaction – The Sense of Smell
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Cribiform Plate
Portion of the ethmoid bone where the olfactory bulb sits
Olfaction – The Sense of Smell
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Olfactory Tract
The neural pathway from the olfactory bulb to the olfactory cortex in the brain
Olfaction – The Sense of Smell
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receptors are in the roof of the nasal cavity
Neurons with long cilia
Chemicals must be dissolved in mucus for detection
Pathways for Sensory System
• Olfaction– Receptors: Chemoreceptors
– Stimulus Energy: Chemical
– Pathway• Olfactory sensory neurons Olfactory bulb
neurons olfactory cortex (in temporal lobe)
Anatomy of the Tongue
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Figure 8.18
Taste Buds
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house the receptor organs
Location
Tongue
Soft palate
Cheeks
Figure 8.18a, b
Anatomy of the Tongue
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Figure 8.18
The Tongue and Taste
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Papillae
Small peglike projections that house the taste buds
Anatomy of the Tongue
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Figure 8.18
Structure of Taste Buds
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Gustatory cells
Specific epithelial cells that respond to chemicals dissolved in saliva
Anatomy of the Tongue
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Figure 8.18
Structure of Taste Buds
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Gustatory Hairs
Taste receptors that emerge from the taste pores
Gustation
Pathways for Sensory System• Gustation
– Receptors: Chemoreceptors
– Stimulus Energy: chemical (sweet, sour, bitter, salty)
– Pathway
• Taste bud Facial nerve (VII) or glossopharyngeal nerve (IX) or vagus nerve (X) medulla thalamus cortex (parietal lobe)
Taste Sensations
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Sweet receptors
Sugars
Saccharine
Some amino acids
Sour receptors
Acids
Taste Sensations
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Bitter receptors
Alkaloids
Salty receptors
Metal ions
Factors that affect Taste Sensations
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Stimulation of our olfactory aromas
Temperature and texture of food
Spicy foods can excite pain receptors in
our mouth
