The document provides an overview of the nervous system's general and special senses. It discusses the different types of receptors for senses like touch, temperature, and proprioception. It describes the pathways for senses like smell, taste, hearing and balance. Key details include the structures of the ear like the cochlea and semicircular canals that are important for hearing and balance. The document also outlines the pathways from sensory receptors to the central nervous system and discusses concepts such as receptive fields and sensory adaptation.

1. © 2012 Pearson Education, Inc.
18
The Nervous System:
General and Special
Senses
PowerPoint®
Lecture Presentations prepared by
Steven Bassett
Southeast Community College
Lincoln, Nebraska

2. © 2012 Pearson Education, Inc.
Introduction
• Stimulation of the receptor directly or indirectly
alters the production of action potentials in a
sensory neuron.
• The sensory information arriving at the CNS is
called a sensation.
• A perception is a conscious awareness of a
sensation.
• Sensory receptors are the interface between
the nervous system and the internal and
external environment

3. © 2012 Pearson Education, Inc.
Receptors
• General senses
• Refers to temperature, pain, touch, pressure, vibration,
and proprioception
• Receptors throughout the body
• These sensations arrive at the primary sensory cortex, or
somatosensory cortex
• Special senses
• Sensations of smell (olfaction), taste (gustation), balance
(equilibrium), hearing, and vision
• Specialized receptor cells that are structurally more
complex than those of the general senses

4. © 2012 Pearson Education, Inc.
Figure 18.1 Receptors and Receptive Fields
Receptive fields
Receptive
field 1
Receptive
field 2

5. © 2012 Pearson Education, Inc.
Receptors
• Receptor specificity — each receptor responds to
one type of stimulus
• Receptive field — the area that a receptor monitors
• Tonic receptors — always send signals,
thus information is based on the frequency of the
action potentials
• Phasic receptors — send action potentials only
if stimulated
• Peripheral adaptation — receptors may stop
sending AP even if the stimulus is still present
• Central adaptation — CNS ignoring a AP from
a receptor

6. © 2012 Pearson Education, Inc.
The General Senses
• Classification of the General Senses
• One classification scheme:
• Exteroceptors: provide information about the
external environment
• Proprioceptors: provide information about the
position of the body
• Interoceptors: provide information about the inside
of the body

7. © 2012 Pearson Education, Inc.
The General Senses
• Sensory Limitations
• Humans do not have receptors for every
possible stimulus.
• Our receptors have characteristic ranges of
sensitivity.
• A stimulus must be interpreted by the CNS.
Our perception of a particular stimulus is an
interpretation and not always a reality.

8. © 2012 Pearson Education, Inc.
The General Senses
• Receptors for general senses classified by location:
• Exteroceptors provide information about the external
environment.
• Proprioceptors monitor body position.
• Interoceptors monitor conditions inside the body.
• Receptors for general senses classified by type
of stimulus:
• Nociceptors = tissue damage
• Thermoreceptors = change in temperature
• Mechanoreceptors = physical distortion, contact, or
pressure
• Chemoreceptors = chemical composition of body fluids

9. © 2012 Pearson Education, Inc.
The General Senses
• Mechanoreceptors
• Encapsulated tactile receptors
• Tactile corpuscle: common on eyelids, lips,
fingertips, nipples, and genitalia
• Ruffini corpuscle: in the dermis, sensitive to
pressure and distortion
• Lamellated corpuscle: consists of concentric
cellular layers / sensitive to vibrations

10. © 2012 Pearson Education, Inc.
Figure 18.3e Tactile Receptors in the Skin
Capsule
Dendrites
Ruffini corpuscle
Sensory
nerve fiber
Collagen
fibers
Hair
Root hair plexus
Lamellated corpuscle
Ruffini corpuscle
Merkel cells and
tactile discs
Tactile
corpuscle
Free nerve
ending
Sensory
nerves

11. © 2012 Pearson Education, Inc.
Figure 18.3f Tactile Receptors in the Skin
Lamellated corpuscle
Dendritic
process
Concentric layers (lamellae)
of collagen fibers
separated by fluid
Concentric layers (lamellae)
of collagen fibers
separated by fluid
Accessory cells
(specialized fibrocytes)
Dendritic process
Dermis
LM × 125Lamellated corpuscle
Hair
Root hair plexus
Lamellated corpuscle
Ruffini corpuscle
Merkel cells and
tactile discs
Tactile
corpuscle
Free nerve
ending
Sensory
nerves

12. © 2012 Pearson Education, Inc.
Figure 18.4 Baroreceptors and the Regulation of Autonomic Functions
Provide information on volume of
tract segments, trigger reflex
movement of materials along tract
Provide information on volume of
urinary bladder, trigger urinary reflex
Baroreceptors of Bladder
Wall
Baroreceptors of Digestive
Tract
Baroreceptors of Carotid
Sinus and Aortic Sinus
Baroreceptors of Lung
Baroreceptors of Colon
Provide information on blood
pressure to cardiovascular and
respiratory control centers
Provide information on lung
stretching to respiratory
rhythmicity centers for
control of respiratory rate
Provide information on volume
of fecal material in colon,
trigger defecation reflex

13. © 2012 Pearson Education, Inc.
Figure 18.5 Chemoreceptors
Carotid body LM × 1500
Blood vessel
Chemoreceptive
neurons
Trigger reflexive
adjustments in
depth and rate of
respiration
Trigger reflexive
adjustments in
respiratory and
cardiovascular
activity
Via cranial
nerve IX
Via cranial
nerve X
Sensitive to changes in pH
and PCO2
in cerebrospinal
fluid
Sensitive to changes in pH,
PCO2
, and PO2
in blood
Sensitive to changes in
pH, PCO2
, and PO2
in blood
Chemoreceptors in and
near Respiratory Centers
of Medulla Oblongata
Chemoreceptors
of Carotid Bodies
Chemoreceptors
of Aortic Bodies

14. © 2012 Pearson Education, Inc.
The Special Senses
• The special senses include:
• Olfaction (smell)
• Gustation (taste)
• Equilibrium
• Hearing
• Vision

15. © 2012 Pearson Education, Inc.
Olfaction (Smell)
• Olfaction
• Olfactory organs
• Nasal cavity
• Olfactory epithelium
• Bipolar olfactory receptors (N I)
• Supporting cells
• Basal cells (stem cells)
• Lamina propria
• Olfactory glands (Bowman’s glands)
• Blood vessels
• Nerves (axons of N I)

16. © 2012 Pearson Education, Inc.
Figure 18.6a The Olfactory Organs
The distribution of the olfactory receptors
on the left side of the nasal septum is
shown by the shading.
Olfactory
bulb
Olfactory nerve
fibers (N I)
Olfactory
tract
Cribriform plate
of ethmoid
Olfactory
epithelium

17. © 2012 Pearson Education, Inc.
Figure 18.6b The Olfactory Organs
A detailed view of the olfactory epithelium
Substance being smelled
Olfactory
epithelium
Lamina
propria
Cribriform
plate
Knob
Olfactory cilia:
surfaces contain
receptor proteins
Mucous layer
Supporting cell
Olfactory
receptor cell
Developing olfactory
receptor cell
Olfactory
nerve fibers
To olfactory
bulb
Olfactory
(Bowman’s)
gland
Regenerative basal cell:
divides to replace worn-out
olfactory receptor cells

18. © 2012 Pearson Education, Inc.
Gustation (Taste)
• Gustation
• The tongue consists of papillae
• Papillae consist of taste buds
• Taste buds consist of gustatory cells
• Each gustatory cell has a slender microvilli
that extends through the taste pore into the
surrounding fluid

19. © 2012 Pearson Education, Inc.
Gustation (Taste)
• Gustation Pathways
• Dissolved chemicals contact the taste hairs
(microvilli)
• Impulses go from the gustatory cell through
CN VII, IX, and X
• The impulses eventually arrive at the cerebral
cortex

20. © 2012 Pearson Education, Inc.
Figure 18.8 Gustatory Pathways
Gustatory
cortex
Thalamic
nucleus
Medial
lemniscus
Nucleus
solitarius
Vagus nerve
(N X)
Facial nerve
(N VII)
Glossopharyngeal
nerve (N IX)

21. © 2012 Pearson Education, Inc.
Gustation (Taste)
Gustatory receptors are clustered in taste buds, which
contain gustatory cells that extend taste hairs through
a taste pore.
Three types of papillae (epithelial projections) on
human tongue:
 Filiform
 Fungiform
 Circumvallate
 Four primary tastes:
 Salty
 Bitter
 Sweet
 Sour
 Also water and umami (characteristic of broth)

22. © 2012 Pearson Education, Inc.

23. © 2012 Pearson Education, Inc.
Equilibrium and Hearing
The Ear
 External ear
 Middle ear
 Auditory ossicles
 Auditory tube
 Inner ear
 Vestible and semicircular canals
 Equilibrium
 Cochlea
 Hearing
ANIMATION The Ear: Ear Anatomy

24. © 2012 Pearson Education, Inc.
Figure 18.9 Anatomy of the Ear
EXTERNAL EAR MIDDLE EAR INNER EAR
Auricle
Auditory ossicles Semicircular
canals
Petrous part
of temporal
bone
Facial nerve
(N VII)
External
acoustic
meatus
Elastic
cartilage
Tympanic
membrane
Tympanic
cavity
Oval window
Round window
Vestibule
Auditory tube
Cochlea
To
nasopharynx
Bony labyrinth
of inner ear
Vestibulocochlear
nerve (N VIII)

25. © 2012 Pearson Education, Inc.
Figure 18.9 Anatomy of the Ear
EXTERNAL EAR MIDDLE EAR INNER EAR
Auricle
Auditory ossicles Semicircular
canals
Petrous part
of temporal
bone
Facial nerve
(N VII)
External
acoustic
meatus
Elastic
cartilage
Tympanic
membrane
Tympanic
cavity
Oval window
Round window
Vestibule
Auditory tube
Cochlea
To
nasopharynx
Bony labyrinth
of inner ear
Vestibulocochlear
nerve (N VIII)

26. © 2012 Pearson Education, Inc.
Figure 18.12a Semicircular Canals and Ducts
Anterior view of the bony
labyrinth cut away to show the
semicircular canals and the
enclosed semicircular ducts of
the membranous labyrinth
Cochlear duct
Vestibular duct
Saccule
Utricle
Tympanic
duct
Organ of
Corti
Cochlea
Endolymphatic sac
Maculae
Cristae within ampullae
Bony labyrinth
Membranous
labyrinth
KEY
Vestibule
Anterior
Lateral
Posterior
Semicircular
canal
Semicircular
ducts

27. © 2012 Pearson Education, Inc.
Figure 18.13 The Function of the Semicircular Ducts, Part I
Anterior view of
the maculae and
semicircular ducts
of the right side
A section through the ampulla of a
semicircular duct
Endolymph movement along the
length of the duct moves the cupula
and stimulates the hair cells.
Structure of a typical hair cell showing details
revealed by electron microscopy. Bending the
stereocilia toward the kinocilium depolarizes the cell
and stimulates the sensory neuron. Displacement in
the opposite direction inhibits the sensory neuron.
Supporting cell
Sensory nerve
ending
Hair cell
StereociliaKinocilium
Displacement in
this direction
inhibits hair cell
Displacement in
this direction
stimulates hair cell
At rest
Ampulla
Semicircular duct
Direction of
duct rotation
Direction of relative
endolymph movement
Direction of
duct rotation
Crista
Hair cells
Ampulla
filled with
endolymph
Cupula
Supporting cells
Sensory nerve
Saccule Maculae
Utricle
AmpullaAnterior
Posterior
Lateral
Semicircular
ducts
Vestibular branch (N VIII)
Cochlea
Endolymphatic sac
Endolymphatic duct

28. © 2012 Pearson Education, Inc.
Figure 18.15ab The Maculae of the Vestibule
A scanning electron micrograph
showing the crystalline structure of
otoliths
Detailed structure of a sensory macula
Otolith
Gelatinous
material
Statoconia
Hair cells
Nerve fibers
Statoconia
Otolith

29. © 2012 Pearson Education, Inc.
Figure 18.16 Neural Pathways for Equilibrium Sensations
Semicircular
canals
Vestibular
ganglion
Vestibular
branch
Vestibule
Cochlear
branch
Vestibulocochlear nerve
(N VIII)
Vestibulospinal
tracts
To
cerebellum
Vestibular nucleus
To superior colliculus and
relay to cerebral cortex
Red nucleus
N III
N IV
N VI
N XI

30. © 2012 Pearson Education, Inc.
Equilibrium and Hearing
• The Cochlea
• Consists of “snail-shaped” spirals
• Spirals coil around a central area called the
modiolus
• Within the modiolus are sensory neurons
• The sensory neurons are associated with CN
VIII
• Organ of Corti

31. © 2012 Pearson Education, Inc.

32. © 2012 Pearson Education, Inc.
Figure 18.17ab The Cochlea and Organ of Corti
Structure of the cochlea within the temporal
bone showing the turns of the vestibular duct,
cochlear duct, and tympanic duct
Structure of the cochlea in partial
section
KEY
From tip of spiral
to round window
From oval window
to tip of spiral
Round window
Stapes at
oval window
Semicircular
canals
Vestibulocochlear
nerve (VIII)
Cochlear
branch
Vestibular
branch
Tympanic duct
Vestibular duct
Cochlear duct
Apical turn
Spiral ganglion
Modiolus
Vestibular membrane
Tectorial membrane
Basilar membrane
Middle turn
Vestibular duct (scala
vestibuli—contains perilymph)
Organ of Corti
Cochlear duct (scala
media—contains endolymph)
Tympanic duct (scala
tympani—contains perilymph)
Basal turn
Temporal bone (petrous part)
Cochlear nerve
Vestibulocochlear nerve (VIII)
From oval
window
To round
window

33. © 2012 Pearson Education, Inc.
Figure 18.17d–f The Cochlea and Organ of Corti
A color-enhanced SEM
showing a portion of the
receptor surface of the
organ of Corti
Diagrammatic and histological sections through the
receptor hair cell complex of the organ of Corti
Three-dimensional section
showing the detail of the cochlear
chambers, tectorial membrane,
and organ of Corti
Bony cochlear wall
Vestibular duct
Vestibular membrane
Cochlear duct
Tectorial membrane
Basilar membrane
Tympanic duct
Organ of Corti
Spiral
ganglion
Cochlear branch
of N VIII
Cochlear duct (scala media)
Vestibular membrane
Tectorial membrane
Organ of Corti LM × 125
Tympanic duct
(scala tympani)
Basilar
membrane
Hair cells
of organ
of Corti
Spiral ganglion
cells of
cochlear nerve
Tectorial membrane
Outer
hair cell
Basilar membrane Inner hair cell Nerve fibers
Stereocilia of inner hair cells
Stereocilia of
outer hair cells
Surface of the organ of Corti SEM × 1320

34. © 2012 Pearson Education, Inc.
Figure 18.17de The Cochlea and Organ of Corti
Diagrammatic and histological sections through the
receptor hair cell complex of the organ of Corti
Three-dimensional section
showing the detail of the cochlear
chambers, tectorial membrane,
and organ of Corti
Bony cochlear wall
Vestibular duct
Vestibular membrane
Cochlear duct
Tectorial membrane
Basilar membrane
Tympanic duct
Organ of Corti
Spiral
ganglion
Cochlear branch
of N VIII
Cochlear duct (scala media)
Vestibular membrane
Tectorial membrane
Organ of Corti LM × 125
Tympanic duct
(scala tympani)
Basilar
membrane
Hair cells
of organ
of Corti
Spiral ganglion
cells of
cochlear nerve
Tectorial membrane
Outer
hair cell
Basilar membrane Inner hair cell Nerve fibers

35. © 2012 Pearson Education, Inc.
Figure 18.18 Pathways for Auditory Sensations
KEY
First-order neuron
Second-order neuron
Third-order neuron
Fourth-order neuron
High-frequency
sounds
Low-frequency
sounds
Cochlea
Cochlear branch
Vestibulocochlear
nerve (N VIII)
Cochlear nuclei
Vestibular
branch
To ipsilateral
auditory cortex
Superior olivary nucleus
Motor output to spinal
cord through the
tectospinal tracts
Motor output
to cranial
nerve nuclei
Inferior colliculus
(mesencephalon)
Medial geniculate
nucleus (thalamus)
Low-frequency
sounds
Auditory cortex
(temporal lobe) High-
frequency
sounds
Thalamus

36. © 2012 Pearson Education, Inc.
Vision
Accessory Structures
 Eyelids
 Lacrimal apparatus
 Eye
 Fibrous tunic
 Vascular tunic
 Neural tunic
 Chambers of the eye
 Visual pathways

37. © 2012 Pearson Education, Inc.
Figure 18.19a Accessory Structures of the Eye, Part I
Superficial anatomy of the right eye and its
accessory structures
Pupil
Corneal
limbus
Lateral
canthus
Sclera
Eyelashes
Palpebra
Palpebral
fissure
Medial
canthus
Lacrimal
caruncle

38. © 2012 Pearson Education, Inc.
Figure 18.19c Accessory Structures of the Eye, Part I
Diagrammatic representation of a deeper dissection
of the right eye showing its position within the orbit
and its relationship to accessory structures,
especially the lacrimal apparatus
Opening of
nasolacrimal duct
Inferior nasal
concha
Nasolacrimal duct
Lacrimal sac
Inferior lacrimal
canaliculus
Medial canthus
Superior lacrimal
canaliculus
Lacrimal punctum
Tendon of superior
oblique muscle
Inferior
oblique muscle
Inferior
rectus muscle
Superior
rectus muscle
Lacrimal
gland ducts
Lower eyelid
Lateral canthus
Lacrimal gland

39. © 2012 Pearson Education, Inc.
Figure 18.21ab Sectional Anatomy of the Eye
The three layers, or
tunics, of the eye
Fibrous
tunic
(sclera)
Vascular
tunic
(choroid)
Neural
tunic
(retina)
Major anatomical landmarks and features
in a diagrammatic view of the left eye
Central retinal
artery and vein
Optic nerve
Optic disc
Fovea
Retina
Choroid
Sclera
Posterior cavity
(Vitreous chamber filled
with the vitreous body)
Ora serrata Fornix
Palpebral conjunctiva
Ocular conjunctiva
Ciliary body
Anterior chamber
(filled with aqueous
humor)
Lens
Pupil
Cornea
Iris
Posterior chamber
(filled with aqueous
humor)
Corneal limbus
Suspensory
ligaments

40. © 2012 Pearson Education, Inc.
Figure 18.23a Retinal Organization
Histological organization of the retina. Note that the
photoreceptors are located closest to the choroid
rather than near the vitreous chamber.
LIGHT
Amacrine cell
Horizontal cell Cone Rod Choroid
Pigmented
part of retina
Rods and
cones
Bipolar cells
Ganglion cells
Nuclei of
ganglion cells
Nuclei of rods
and cones
Nuclei of
bipolar cells
The retina LM × 70

41. © 2012 Pearson Education, Inc.
Figure 18.24
Pigmented
epithelium
Suspensory
ligaments
Posterior
cavity
(vitreous
chamber)
Lens
Ciliary
process
Choroid
Retina
Sclera
Conjunctiva
Ciliary body
Body of iris
Canal of
Schlemm
Posterior
chamber
Anterior
chamber
Anterior
cavity
Cornea
Pupil

42. © 2012 Pearson Education, Inc.
Figure 18.21d Sectional Anatomy of the Eye
Sagittal section through the eye
Ora serrata
Conjunctiva
Cornea
Lens
Anterior chamber
Iris
Posterior chamber
Suspensory
ligaments
Ciliary body
Posterior
cavity
(vitreous
chamber)
Dura
mater Retina Choroid Sclera
Optic nerve
(N II)

43. © 2012 Pearson Education, Inc.
Figure 18.21e Sectional Anatomy of the Eye
Sagittal section through the eye
Orbital fat
Central artery
and vein
Medial rectus
muscle
Ethmoidal
labyrinth
Optic nerve
Optic disc
Fovea
Ora serrata
Ciliary body
LensCiliary
processes
Medial canthus
Lacrimal caruncle
Lacrimal punctum
Nose
Anterior cavity
Posterior
chamber
Anterior
chamber
Edge of
pupil
Visual
axis
Cornea
Iris
Suspensory ligament of lens
Corneal limbus
Conjunctiva
Lower eyelid
Lateral canthus
Sclera
Choroid
Retina
Posterior cavity
Lateral rectus muscle

44. © 2012 Pearson Education, Inc.
Figure 18.26 Anatomy of the Visual Pathways, Part II
LEFT SIDE RIGHT SIDE
Left eye
only
Right eye
only
Binocular vision
Optic nerve (N II)
Optic chiasm
Optic tract
Other hypothalamic
nuclei, pineal gland,
and reticular
formation
Suprachiasmatic
nucleus
Superior
colliculus
Lateral
geniculate
nucleus
Projection
fibers (optic
radiation)
Lateral
geniculate
nucleus
RIGHT CEREBRAL
HEMISPHERE
LEFT CEREBRAL
HEMISPHERE
Visual cortex of
cerebral hemispheres