Transcript BIOL-2404-Mader8-chapt09_lecture

Chapter 09
Lecture Outline
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9.1 General Senses
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A. Introduction
1.
A stimulated sensory receptor sends a
signal to the brain
2. Signals are interpreted in the brain
3. Receptor Potentials
a. Begin with a stimulus
b. Can be weak or strong (not all-or-none)
c. Can add together
d. Do not generate action potentials, but
are part of neurons or synapse with
neurons that create action potentials
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4. Classification based on type of stimulus
a.
b.
c.
d.
e.
Mechanoreceptors – stimulated by
changes in 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
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5. Pathway to brain for general senses
a.
b.
c.
Receptor to spinal cord
Spinal cord tracts to the thalamus (all
senses except smell)
Thalamus to the somatosensory cortex in
the parietal lobe
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B. General Senses - Proprioceptors
1.
2.
3.
4.
Mechanoreceptors involved in reflex
actions to maintain muscle tone
Maintain equilibrium, posture, and
position of limbs
Muscle spindles – increase the degree of
muscle contraction
Golgi tendon organs – decrease the
degree of muscle contraction
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Muscle Spindle
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C. General Senses – Cutaneous Receptors
1.
Located in the deepest layer of the
epidermis and the entire dermis
2. Make skin sensitive to touch, pressure,
pain, and temperature
3. Three types sensitive to fine touch
a. Meissner corpuscles – in dermal
papillae of hairless skin
b. Merkel disks – deepest epidermis
c. Root hair plexus – around hair follicle
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Cutaneous Receptors, cont
4.
Three types sensitive to pressure
a. Pacinian corpuscles – deep in dermis
b. Ruffini endings – dermis and
hypodermis
c. Krause end bulbs – superficial dermis
5. Temperature receptors are free nerve
endings in epidermis and superficial
dermis
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Sensory Receptors in the Skin
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D. General Senses – Pain Receptors
1.
2.
Also called nociceptors
Somatic nociceptors
a. Skin and skeletal muscle
b. Respond to mechanical, thermal,
electrical or chemical damage
3. Visceral nociceptors – react to excessive
stretching, oxygen deprivation, or
chemicals released by damaged tissues
4. Referred pain – brain cannot distinguish
between somatic pain nociceptors and
internal visceral nociceptors because they
are in the same spinal cord tracts
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9.2 Senses of Taste and Smell
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A. Introduction
1.
2.
Chemical senses
Sensitive to molecules in food and in the
air
3. Other chemoreceptors in the body
a. Govern respiratory rate
b. Sensitive to the oxygen, carbon
dioxide, and hydrogen ion
concentration of the blood
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B. Sense of Taste (Gustation)
1.
Sensory receptors located in the taste
buds
a. Primarily on the tongue
b. Also present on the hard palate, the
pharynx, and the epiglottis
2. Types of taste sensations
a. Sweet
b. Sour
c. Salty
d. Bitter
e. Umami – meat
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Sense of Taste, cont
3.
How the brain receives taste information
a. Molecules in food bind with receptor
proteins on microvilli on taste cells
b. Nerve impulses are generated and go to
the brain
c. Sensory receiving and memory areas
for taste are located in the insula and
parietal lobes
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Taste Buds
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C. Sense of Smell (Olfaction)
1.
Dependent on olfactory cells
a. Located in olfactory epithelium in the
roof of the nasal cavity
b. Modified neurons
c. Olfactory cilia have receptor proteins for
odor molecules
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Sense of Smell, cont
2. How the brain receives odor information
a. Nerve fibers lead to the olfactory bulb
b. Combinations of activated receptor
proteins account for different odors
c. An odor’s signature is determined by
which neurons are stimulated in the
olfactory bulb
d. Neurons send signals through the
olfactory tract to the olfactory areas of
the cerebral cortex in the temporal lobe
e. Also has a direct connection to the
limbic system
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Olfactory cell location & anatomy
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D. Senses of Taste and Smell
1.
2.
3.
Both work together
Smell can enhance taste
Part of what is referred to as smell
may actually be taste
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9.3 Sense of Vision
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A. Accessory organs of the eye
1.
Eyebrows, eyelids, and eyelashes
a. Eyebrows shade the eyes from the sun
and protect eyes from perspiration or
debris
b. Eyelids are continuations of the skin
c. Eyelashes can block debris from
entering the eye
d. Secretions from sebaceous glands
associated with eyelashes lubricate the
eye
e. Eyelids help keep the eye lubricated
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Eyebrows, eyelids, and eyelashes, cont
f.
g.
h.
Muscle that closes the eyelid – orbicularis
oculi
Muscle that opens the eyelid – levator
palpebrae superioris
Inner surface of eyelid covered by the
conjunctiva; also covers the anterior
surface of the eye (except the cornea)
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Accessory structures of the orbit
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2. Lacrimal apparatus
1. Lacrimal gland
produces tears
2. Tears collect in
lacrimal sac
3. Tears drain into the
nose by the
nasolacrimal duct
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3. Extrinsic eye muscles
1. Contractions move the eyes; controlled by
three cranial nerves
2. Superior rectus rolls eye upward – CN III
3. Inferior rectus rolls eye downward – CN III
4. Lateral rectus turns eye outward – CN VI
5. Medial rectus turns eye inward – CN III
6. Superior oblique rotates eye counterclockwise
– CN IV
7. Inferior oblique rotates eye clockwise – CN III
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Extrinsic Eye Muscles
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B. Anatomy and physiology of the eye
1.
Three layers (coats)
a. Sclera – outer coat
1) White and fibrous
2) Cornea is transparent
b. Choroid - middle, vascularized layer
1) Becomes the iris towards the front
a) Regulates the size of the pupil
b) Colored portion of eye
2) The ciliary body is behind the iris
a) Contains the ciliary muscle
b) Controls the shape of the lens
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Three layers, cont
c. Retina – inner coat
1) Contains photoreceptors
a) Rod cells – night vision and peripheral
vision
b) Cone cells – distinguish colors
2) Fovea centralis – area of retina where
cone cells are densely packed
3) Optic nerve – formed from sensory fibers
from the retina
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2. Lens
a.
b.
Divides the eye into two compartments
Anterior compartment contains aqueous
humor
c. Posterior compartment contains the
retina and the vitreous humor
d. Function of the lens
1) Focuses images on the retina
(refraction)
2) Image produced is smaller than the
object; image is inverted and reversed
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Anatomy of the Eye
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Functions of Parts of the Eye
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3. Accommodation
a. Process of focusing objects on the retina
1) Lens must change shape
2) Controlled by the ciliary muscle
3) Ciliary muscle is relaxed for a distant
object; tightens the suspensory
ligament; lens flattens
4) Ciliary muscle contracts to view a near
object; loosens the suspensory ligament;
lens bulges
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Focusing
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b. Abnormalities of refraction
1)
Myopia – near-sightedness
a) Have an elongated eyeball
b) Light from far objects focus in front of the retina
c) Correction with concave lenses
2)
Hyperopia – far-sightedness
a) Have a short eyeball
b) Light from near objects focus behind the retina
c) Correction with convex lenses
3)
Astigmatism
a) Have an oval-shaped cornea or irregular lens
b) Correction with a lens ground to compensate
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Common abnormalities of the eye
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4. Vision pathway
a. Function of the photoreceptors
1) Begins when light is focused on the
photoreceptors
2) Rods and cones contain visual pigments called
rhodopsin
a) One type in rods
b) Three types in cones – red, blue, and green
1) Color blindness is caused by the inherited
absence of the color pigments in the cones
3) Rods and cones absorb light and rhodopsin
splits into opsin and retinal
4) The light stimulus stops the release of
neurotransmitter molecules from the synaptic
vesicles
5) Nerve impulses travel to the visual area of the
cerebral cortex
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Photoreceptors in the eye
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b. Function of the retina
1) Three layers of neurons
a) Rod cells and cone cells are located in the
deepest layer next to the choroid
b) Middle layer contains bipolar cells
c) Innermost layer contains ganglion cells whose
sensory fibers become the optic nerve
2) Light must penetrate to the back of the retina
3) Rod cells and cone cells synapse with the bipolar
cells
4) Bipolar cells synapse with the ganglion cells that
initiate nerve impulses
5) Considerable processing occurs in the retina
a) As many as 150 rods activate the same ganglion
cell
b) One cone activates one ganglion cell
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Function of the retina, cont
6)
Blind spot
a) No rods and cones where the optic nerve
leaves the retina
b) No vision is possible in this area
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Structure of the retina
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c. From the retina to the visual cortex
1) The optic nerves carry impulses to the
optic chiasma
a) Fibers from the right half of each retina
converge and continue through the
right optic tract
b) Fibers from the left half of each retina
converge and continue through the left
optic tract
2) Fibers from the optic tracts synapse with
neurons in the thalamus
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From the retina to the visual cortex, cont
3)
4)
Axons from the thalamus carry impulses to
the primary visual areas of the occipital
lobes by way of the optic radiations
The right and left visual cortex rebuilds and
rights the image
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Optic chiasma
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C. Eye diseases and disorders
1.
2.
3.
4.
5.
Cataract – clouded lens
Glaucoma – increased intraocular pressure
from the build-up of aqueous humor
Macular degeneration – damage to the
macula lutea in the fovea centralis leading
to blindness
Diabetic retinopathy – damage to retinal
blood vessels leading to blindness
Detached retina – sharp blow separates the
retina from the choroid
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Macular degeneration
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9.4 Sense of Hearing
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A. Introduction
1.
Two sensory functions of the ear –
hearing and equilibrium
2. Sensory receptors located in the inner
ear
a. Consists of hair cells with stereocilia
b. Sensitive to mechanical stimulation
(mechanoreceptors)
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B. Anatomy of the ear
1.
Outer ear
a. Pinna
b. Auditory canal
1) Lined with hair
2) Modified sweat glands secret
cerumen
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C. Middle ear
1) Begins at the tympanic membrane
2) Ends at bony wall with two small
openings
a) Oval window
b) Round window
3) Three small bones (ossicles)
a) Malleus
b) Incus
c) Stapes
4) Auditory tube (eustachian tube) extends
from the middle ear to the nasopharynx
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D. Inner ear
1) Lies in the bony labyrinth
2) Lined with membranous labyrinth
3) Filled with fluid
a) Perilymph – between the bony
labyrinth and the membranous labyrinth
b) Endolymph – within the membranous
labyrinth
4) Three areas
a) Semicircular canals - equilibrium
b) Vestibule - equilibrium
c) Cochlea - hearing
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Anatomy of the ear
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C. Sound pathway
1. Through the auditory canal and middle ear
a. Sound travels by the vibrations of air
molecules
b. Sound waves strike the tympanic
membrane causing it to vibrate
c. Pressure from the tympanic membrane
causes the malleus, the incus, and then
the stapes, to vibrate
d. The stapes strikes the oval window
e. Vibrations from the oval window are
passed to the perilymph within the
cochlea of the inner ear
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Sound pathway, cont
2. From the cochlea to the auditory cortex
a. Cochlea has three canals
1) Vestibular canal – with perilymph
2) Cochlear canal – with endolymph
3) Tympanic canal – with perilymph
b. The spiral organ (organ of Corti) is the sense
organ for hearing
1) Located in cochlear canal
2) Consists of hair cells and the tectorial
membrane
3) Hair cells sit on the basilar membrane and
their steriocilia are embedded in the
tectorial membrane
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Spiral organ, cont
4) Each part of the spiral organ is sensitive
to different wave frequencies or pitches
a) Tip – low pitches; base – high pitches
b) Pitch sensation depends of which
region of the basilar membrane
vibrates
5) Volume is the amplitude of the sound
wave; louder sound create more
pressure and then faster vibrations of the
basilar membrane
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Sound pathway, cont
c.
d.
e.
Pressure waves move across the basilar
membrane
The steriocilia bend
Nerve impulses begin in the cochlear
nerve and travel to the brain stem, the
thalamus, and then the auditory cortex in
the temporal lobe
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Mechanoreceptors for hearing
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D. Hearing damage and deafness
1.
2.
Conduction deafness – occurs from
mechanical blockage of the sound waves
Nerve deafness – disruption of the neural
pathway; most often because stereocilia
have been worn away
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9.5 Sense of Equilibrium
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A. Introduction
1.
Mechanoreceptors in the semicircular
canals are responsible for rotational
equilibrium
2. Mechanoreceptors in the vestibule are
responsible for gravitational equilibrium
3. Other structures in the body are
involved with equilibrium
a. Proprioceptors in muscles and joints
b. Photoreceptors in the eye
c. Cerebellum
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B. Rotational (dynamic) equilibrium
1.
2.
Involves the three semicircular canals
The ampulla is the enlarged base of the
three canals
a. Contains hair cells with steriocilia
embedded in the cupula
b. Each ampulla responds to head
rotation in a different plane of space
3. Displaced cupula causes the stereocilia
to bend
4. Creates changes in nerve impulses
traveling through the vestibular nerve
to the brain
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Rotational equilibrium, cont
5.
Motion sickness
a. Continuous movement of fluid within the
semicircular canals
b. Sensory input from the inner ear that is
different from visual sensations
6. Vertigo is dizziness and a sensation of
rotation
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Rotational Equilibrium
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C. Gravitational (static) equilibrium
1.
2.
3.
4.
5.
Depends on the utricle and saccule located in
the vestibule
a. Utricle is sensitive to horizontal movements
b. Saccule is sensitive to vertical movements
Contain hair cells with steriocilia embedded in
the otolithic membrane
Otoliths of calcium carbonate rest on the
membrane
When the head moves the otoliths are
displaced and the membrane is disturbed and
the steriocilia are bent toward or away from
the kinocilium
The cerebellum and other brain centers use
sensory input to maintain balance
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Gravitational equilibrium
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Functions of the parts of the ear
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9.6 Effects of Aging
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A. Vision
1.
The lens of the eye does not
accommodate as well – need for
corrective lenses and/or Lasix
2. Three visual disorders seen frequently:
a. Cataracts
b. Age-related macular degeneration
c. Glaucoma
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B. Hearing and equilibrium
1.
The need for a hearing aid increases with
age
a. Presbycusis (age-related hearing decline)
b. Otosclerosis is the most frequent cause
of conduction deafness in adults
2. Dizziness and the inability to maintain
balance
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