Transcript Nervous System – PNS and Special Senses

The PNS and Special Senses
 Nerves and ganglia outside the
central nervous system
 Nerve = bundle of neuron fibers
 Neuron fibers are bundled by
connective tissue
 Endoneurium surrounds
each fiber
 Groups of fibers are bound
into fascicles by
perineurium
 Fascicles are bound
together by epineurium
 Mixed nerves
 Both sensory and motor fibers
 Sensory (afferent) nerves
 Carry impulses toward the CNS
 Motor (efferent) nerves
 Carry impulses away from the CNS
 12 pairs of nerves that mostly
serve the head and neck
 Only the pair of vagus nerves
extend to thoracic and abdominal
cavities
 Most are mixed nerves, but three
are sensory only
 I Olfactory nerve —
sensory for smell
 II Optic nerve — sensory
for vision
 III Oculomotor nerve —
motor fibers to eye muscles
 IV Trochlear — motor fiber
to eye muscles
 V Trigeminal nerve — sensory
for the face; motor fibers to
chewing muscles
 VI Abducens nerve — motor
fibers to eye muscles
 VII Facial nerve — sensory for
taste; motor fibers to the face
 VIII Vestibulocochlear nerve
— sensory for balance and
hearing
 IX Glossopharyngeal
nerve — sensory for taste;
motor fibers to the pharynx
 X Vagus nerves — sensory
and motor fibers for
pharynx, larynx, and viscera
 XI Accessory nerve —
motor fibers to neck and
upper back
 XII Hypoglossal nerve —
motor fibers to tongue
 There is a pair of spinal
nerves at the level of each
vertebrae for a total of 31
pairs
 Formed by the
combination of the ventral
and dorsal roots of the
spinal cord
 Named for the region from
which they arise
 Motor subdivision of the PNS
 Consists only of motor
nerves
 Also known as the
involuntary nervous system
 Regulates activities of
cardiac and smooth muscles
and glands
 Two subdivisions
 Sympathetic division
 Parasympathetic division
Figure 7.27
 Sympathetic—“fight or flight”
 Response to unusual stimulus
 Takes over to increase activities
 Remember as the “E” division
 Exercise, excitement, emergency,
and embarrassment
 Parasympathetic—
“housekeeping”
activities
 Conserves energy
 Maintains daily
necessary body
functions
 Remember as the “D”
division
 digestion, defecation,
and diuresis
 General senses of touch
 Temperature
 Pressure
 Pain
 Special senses
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Smell
Taste
Sight
Hearing
Equilibrium
RECEPTOR TYPE
STIMULATED BY
EXAMPLES
CHEMORECEPTORS
CHANGE IN
CHEMICAL
CONCENTRATION OF
A SUBSTANCE
TASTE
SMELL
PAIN RECEPTORS
TISSUE DAMAGE
FREE NERVE
ENDINGS IN SKIN
THERMORECEPTORS
CHANGE IN
TEMPERATURE
FREE NERVE
ENDINGS IN SKIN
MECHANORECEPTORS
CHANGE IN
PRESSURE OR
MOVEMENT
MEISSNER’S
CORPUSCLE
PACINIAN
CORPUSCLE
HEARING
EQUILIBRIUM
PHOTORECEPTORS
LIGHT ENERGY
SIGHT
 Touch and pressure
sensors
 Sensory nerve fibers
 Meissner’s corpuscles
 Pacinian corpuscles
 Temperature sensors
 Heat receptors –
2545*C
 Cold receptors –
1020*C
 Houses two senses
 Hearing
 Equilibrium (balance)
 Receptors are mechanoreceptors
 Different organs house receptors
for each sense
 The ear is divided into three areas
 External (outer) ear
 Middle ear (tympanic cavity)
 Inner ear (bony labyrinth)
 Involved in hearing only
 Structures of the external ear
 Auricle (pinna)
 External acoustic meatus (EAS)
(auditory canal)
 Narrow chamber in the temporal
bone
 Lined with skin and ceruminous
(wax) glands
 Ends at the tympanic membrane
 Air-filled cavity within the temporal
bone
 Only involved in the sense of hearing
 Two tubes are associated with the
inner ear
 The opening from the auditory canal
is covered by the tympanic
membrane
 The auditory tube connecting the
middle ear with the throat
 Allows for equalizing pressure during
yawning or swallowing
 This tube is otherwise collapsed
 Three bones (ossicles) span
the cavity
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrip)
 Function
 Vibrations from eardrum
move the malleus  anvil 
stirrup  inner ear
 Includes sense organs for hearing and balance
 Filled with perilymph
 A maze of bony chambers within the temporal bone
 Cochlea
 Vestibule
 Semicircular canals
 Static equilibrium
 Dynamic equilibrium
 Maintains stability and
 Detects motion and
posture when the head
and body are still
 Vestibule of semicircular
canals and cochlea
maintains balance
 Semicircular canals lie
in right angles to each
other
 Cerebellum interprets
impulses
 Maculae — receptors in
the vestibule
 Report on the position of
the head
 Send information via the
vestibular nerve
 Anatomy of the maculae
 Hair cells are embedded
in the otolithic
membrane
 Otoliths (tiny stones)
float in a gel around the
hair cells
 Movements cause otoliths
to bend the hair cells
 Organ of Corti
 Located within the cochlea
 Receptors = hair cells on the
basilar membrane
 Gel-like tectorial membrane
is capable of bending hair
cells
 Cochlear nerve attached to
hair cells transmits nerve
impulses to auditory cortex
on temporal lobe
 Auricle collects sound waves and directs them
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into external auditory meatus.
Sound waves change pressure on the eardrum,
causing vibrations.
Auditory Ossicles transmit vibrations to inner
ear.
Vibrations move fluid within inner ear and travel
through cochlea to the organ of Corti.
Hair of the organ of Corti vibrate against the
tectorial membrane and stimulate receptor cells.
Receptor cells release neurotransmitters that
stimulate sensory nerve fibers.
Impulses are transmitted to the auditory cortex.
 Orbital
 Eyelid – skin, muscle,
conjunctiva
 Lacrimal gland
 Extrinsic muscles
 Outer tunic
 Sclera
 white of the eye
 Cornea
 Transparent, central anterior
portion
 Middle tunic
 Lens
 Iris
 Pupil
 Aqueous humor
 Inner tunic (retina)
 Optic disk
 (blind spot) is where the
optic nerve leaves the
eyeball
 Vitreous humor
 Gel-like substance
posterior to the lens
 Prevents the eye from
collapsing
 Retina
 Contains pigments , rods,
and cones
 Fovea centralis only has
cones
Aqueous Humor located
between cornea and lens (Add
this to your notes)
 Rods
 Vision in dim light
 Colorless vision
 General outlines of objects
 Cones
 Sharp images
 Color vision – red, green,
blue
 Dense in fovea centralis
 Light must be focused to
a point on the retina for
optimal vision
 The eye is set for
distance vision
(over 20 feet away)
 Accommodation—the
lens must change shape
to focus on closer objects
(less than 20 feet away)
 Image formed on the retina is a real image
 Real images are
 Reversed from left to right
 Upside down
 Smaller than the object
 Optic chiasma
 Location where the
optic nerves cross
 Fibers from the medial
side of each eye cross
over to the opposite
side of the brain
 Optic tracts
 Contain fibers from
the lateral side of the
eye on the same side
and the medial side of
the opposite eye
nearsighted
farsighted
 Nasal cavity
 Olfactory receptors
 Olfactory organs
 Olfactory receptor cells
 Cilia
 Olfactory bulbs
 Chemicals enter nasal cavity as gases
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and dissolve in fluids that surround
cilia.
Receptors detect chemicals and send
impulses to olfactory bulbs.
Olfactory bulbs analyze impulses and
transmit info along olfactory tracts to
the limbic system.
Interpretation occurs within olfactory
cortexes.
Receptors adapt quickly.
 Taste buds
 Papillae
 Taste pore
 Taste cells
 Taste hairs
 Chemical stimulus dissolves in
saliva.
 Receptor cells are stimulated and
send impulses along facial,
glossopharyngeal, and vagus nerves
to the medulla oblongata.
 Impulses are sent to the thalamus
and then to the gustatory complex.
 Sweet receptors (sugars)
 Saccharine
 Some amino acids
 Sour receptors
 Acids
 Bitter receptors
 Alkaloids
 Salty receptors
 Metal ions
Draw this picture in your
notes. You need it for your lab.