Transcript Nervous System Pt. II

The Senses
Chapter 10
Senses
• General senses
– Receptors widely distributed throughout body
– Skin, various organs & joints
• Special senses
– Specialized receptors confined to structured in the
head
– Eyes, ears, nose, mouth
Sensation
• Sensory receptors
– Specialized structures that collect info from
environment
– Stimulate neurons to send impulses to brain
• Perception
– Person’s view of stimulus; interpretation
Different Types of Receptors
•
•
•
•
•
Chemoreceptors
Pain receptors
Thermoreceptors
Mechanoreceptors
Photoreceptors
Sensory Impulses
• Stimulation of receptor causes local change in
receptor potential
• Current is generated that reflects intensity of
stimulation
• Membrane potential may generate an action
potential
• Peripheral nerves transmit impulses to CNS
Perception
• Projection
– Process in which brain projects sensation back to
its apparent source
Sensory Adaptation
• Ability to ignore unimportant stimuli
• Decreased response to a stimulus from
receptor, or along the pathway leading to the
cerebral cortex
• Sensory impulses become less frequent and
may cease
• Stronger stimulus is required to trigger
impulse
General Senses
(of skin, muscles, joints, viscera)
• Exteroceptive senses
– Associated with body surface (touch, pressure,
temperature, pain)
• Viseroceptive senses
– Associated with changes in viscera
• Proprioceptive senses
– Associated with changes in muscles and tendons
Touch & Pressure
• Free nerve endings
– Epithelial tissue; simple; sense itching
• Tactile (Meissner’s corpuscles)
– Abundant in hairless areas (skin, lips)
– Detect fine touch (between two points on skin)
• Lamellated (Pacinian) corpuscles
– Common in deeper subcutaneous areas
– Heavy pressure, vibrations
Free nerve
endings
Section of
skin
Epithelial
cells
Epidermis
(a)
Sensory
nerve fiber
Epithelial
cells
Dermis
Tactile (Meissner’s)
corpuscle
(touch receptor)
(b)
Sensory nerve
fiber
Lamellated
(Pacinian) corpuscle
(pressure receptor)
Connective tissue
cells
Sensory nerve
fiber
(c)
Sense of Pain
• Where do we have them?
– Not in brain – lacks pain receptors
• Stimulated by tissue damage, chemical,
mechanical forces, or extremes in
temperature
• Adapt very little if at all
Pain
• Pain receptors respond differently to
stimulation, not well localized
• Referred pain – may feel as if coming from
other part of body
• Phantom limb pain
Liver and
gallbladder
Lung and diaphragm
Heart
Stomach
Pancreas
Small
intestine
Appendix
Ovary
(female)
Colon
Kidney
Ureter
Urinary bladder
Liver and
gallbladder
Regulation of Pain Impulses
• Thalamus – awareness of pain
• Cerebral cortex – judges intensity & location
of pain, and responds to pain
• Pain inhibitors:
– Enkephalins
– Serotonin
– Endorphins
Special Senses
•
•
•
•
Smell – olfactory organs
Taste – taste buds
Hearing & equilibrium – ears
Sight – eyes
Smell
• Chemoreceptors respond to chemicals dissolved in liquids
• Olfactory organs cover different parts of nose
Nerve fibers within
the olfactory bulb
OlfactoryOlfactory
tract
bulb
Cribriform
plate
Superior nasal
concha
Nasal cavity
Cilia Olfactory
Columnar
Cribriform
receptor cells epithelial cellsplate
(a)
(b)
Olfactory Stimulation
• Olfactory organs located high in nasal cavity
above the usual pathway of inhaled air
• Receptors undergo sensory adaptation quickly
• Sense of smell drops 50% within a second
after stimulation
Taste
• Taste buds located on
tongue papillae, roof of
mouth, linings of cheeks,
walls of pharynx
• Taste receptors are
chemoreceptors
– Taste cells, taste hairs
(microvilli)
Papillae
Taste buds
Epithelium
of tongue
(a)
Taste cell
Taste hair
Supporting
cell
Taste
pore
(b)
Connective
tissue
Sensory
nerve fibers
Taste Sensations
•
•
•
•
Sweet – stimulated by carbohydrates
Sour – stimulated by acids
Salty – stimulated by salts
Bitter – stimulated by many organic
compounds
• Spicy foods activate pain receptors
Hearing
• Three sections of ear – external, middle, inner
• Auricle
• Collects sounds waves
• External auditory meatus
• Lined with ceruminous glands
• Carries sound to tympanic membrane
• Terminates with tympanic membrane
• Tympanic membrane
• Vibrates in response to sound waves
Auricle
Semicircular
canals
Incus
Stapes
Malleus
Cochlea
Vestibulocochlear
nerve
Oval window (under stapes)
Round window
Tympanic cavity
Tympanic
membrane
External acoustic
meatus
Auditory tube
Pharynx
Auditory Tube
• Eustachian tube – connects middle ear to
throat
• Maintains equal pressure on both sides of
tympanic membrane
• Closed by valve-like flaps in throat
Inner Ear
• Made of complex system of labyrinths
• Within, are hair cells that move with different
frequencies of sound, and vibrate different
parts of the basilar membrane to generate a
nerve impulse
Equilibrium
• Static – senses position of head when body
not moving
• Dynamic – senses rotation and movement of
head and body
Eye
Eyelid – 4 layers:
• Skin
• Muscle – closes/opens eyelid
• CT
• Conjunctiva – mucous membrane
Lacrimal Apparatus
• Lacrimal gland – lateral
to eye/secretes tears
Lacrimal gland
Superior and
• Canaliculi – collects tears inferior canaliculi
• Lacrimal sacs – collects Lacrimal sac
from canaliculi
Nasolacrimal
duct
• Nasolacrimal duct –
collects from lacrimal
sac/empties tears into
nasal cavity
Eye Structure
• Hollow,
spherical, wall
with three
layers:
– Outer fibrous
tunic
– Middle
vascular tunic
– Inner nervous
tunic
Ciliary body
Suspensory
ligaments
Iris
Lens
Pupil
Lateral rectus
Retina
Choroid coat
Sclera
Vitreous humor
Fovea centralis
Cornea
Aqueous
humor
Anterior
Anterior chamber
Posterior
cavity
chamber
Optic nerve
Optic disc
Posterior cavity
Medial rectus
Outer Tunic
• Cornea
– Anterior; transparent
– Light transmission and refraction
• Sclera
– Posterior; opaque
– Protection
Middle Tunic
• Iris
– Anterior; pigmented
– Controls light intensity
• Ciliary body
– Anterior; pigmented
– Holds lens; moves lens for focusing
• Choroid coat
– Provides blood supply
– Pigments absorb extra light
Lateral rectus
Ciliary body
Suspensory
ligaments
Retina
Choroid coat
Sclera
Vitreous humor
Iris
Lens
Pupil
Fovea centralis
Cornea
Aqueous
humor
Anterior
Anterior chamber
Posterior
cavity
chamber
Optic nerve
Optic disc
Posterior cavity
Medial rectus
Anterior Eye
• Filled with aqueous humor
Cornea
Anterior chamber
Iris
Posterior
chamber
Ciliary process
Suspensory
ligaments
Ciliary
Ciliary muscles body
Conjunctiva
Vitreous
humor
Lens
Sclera
Anterior Eye
Lens
• Transparent, biconvex,
elastic
• Behind iris
• Composed of lens fibers
• Held in place by ligaments
of ciliary body
Ciliary Body
• Forms internal ring around
front of eye
• Has folds and muscles that
move the lens
Ciliary processes
of ciliary body
Suspensory
ligaments
Lens
Retina
Choroid coat
Sclera
Iris
• CT & smooth
muscle
• Pupil is hole
in iris
• Dim light
stimulates
muscles that
dilate pupil
• Bright light
stimulates
muscles that
constrict
pupil
Sympathetic
motor nerve
fiber
In dim light
Radially arranged
Smooth muscle fibers
of the iris
Circularly arranged
smooth muscle fibers
of the iris
Pupil
In normal light
Parasympathetic
ganglion
Parasympathetic
motor nerve fiber
In bright light
Aqueous Humor
• Fluid in anterior cavity of eye
• Provides nutrients and maintains shape
Cornea
Aqueous humor
Iris
Scleral venous sinus
(canal of Schlemm)
Sclera
Ciliary process
Ciliary
body Ciliary muscles
Vitreous humor
Posterior
chamber
Anterior
chamber
Lens
Inner Tunic
• Retina
– Contains visual receptors, continuous with optic
nerve
– Several layers
– Macula lutea – yellowish spot in retina
– Fovea centralis – center of above; produces
sharpest vision
– Optic disc – blindspot, no visual receptors
– Vitreous humor – thick gel; holds retina flat
against choroid coat
Retina Focusing
• As light enters eye, it is refracted by:
• Convex surface of cornea
• Convex surface of lens
• Image focused on retina is upside down and
reversed from left to right
Light waves
Image
Retina
Object
Cornea
Refraction Disorders
• Concave lens corrects
nearsightedness
• Convex lens corrects
farsightedness
Point
Lens of focus
Cornea
Light waves
Uncorrected
point of focus
Light waves
(a) Eye too long (myopia)
Point
of focus
Concave lens
(a)
Light waves
Retina
Corrected
point of focus
Uncorrected
point of focus
(b) Normal eye
Point
of focus
Light waves
Convex lens
(c) Eye too short (hyperopia)
(b)
Corrected
point of focus
Visual Receptors
Rods
• Long, thin
• Light sensitive pigment
rhodopsin
• 100x more sensitive to light
than cones
• Provide vision in dim light
• Produce colorless vision and
outlines of objects
Cones
• Short, blunt
• Light sensitive pigments—
erythrolabe, chlorolabe,
cyanolabe
• Vision in bright light
• Sharp images, color vision
Retinal pigment
epithelium
Cones
Rods
Single sensory
nerve fiber
(a)
Many sensory
nerve fibers
(b)
Rod
Cone
(c)
c: © Frank S. Werblin, PhD.
Visual Pigments
• Rhodopsin
• Pigments on cones
• Light-sensitive pigment in
• Each set contains different
rods
light-sensitive pigment
• Decomposes in presence of
• Each set is sensitive to
light
different wavelengths
• Triggers a complex series of
• Color perceived depends on
reactions that initiate nerve
which sets of cones are
impulses
stimulated
• Impulses travel along optic
• Erythrolabe – responds to
nerve
red
• Chlorolabe – responds to
green
• Cyanolabe – responds to
blue
Eye
Optic
nerve
Fibers from
nasal (medial) half
of each retina
crossing over
Optic
chiasma
Optic tract
Lateral
geniculate
body of
thalamus
Optic
radiations
Visual cortex of
occipital lobe
Aging and the Senses
• Age related hearing loss due to:
• Damage of hair cells in organ of Corti
• Degeneration of nerve pathways to the brain
• Tinnitus
• Age-related visual problems include:
• Dry eyes
• Floaters (crystals in vitreous humor)
• Loss of elasticity of lens
• Glaucoma
• Cataracts
• Macular degeneration
Helpful Videos on Senses
• https://www.youtube.com/watch?v=mFm3yA
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• https://www.youtube.com/watch?v=Ie2j7GpC
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