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7/29/2019 Sense Organs and Special Senses
http://slidepdf.com/reader/full/sense-organs-and-special-senses 1/39
Sense Organs and Special
Senses
Mid-Term
01/29/2013
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Overview
• Receptor
Classification
– Properties and types
• General senses• Chemical senses
• Hearing and
Equilibrium• Vision
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Properties of Receptors
• Sensory transduction
– convert stimulus energy into nerve energy
• Receptor potential – local electrical change in receptor cell
• Adaptation
– conscious sensation declines with continuedstimulation
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Receptors Transmit Information
• Modality - type of stimulus
• Location – each sensory receptor receives input from its receptive field
– sensory projection - brain identifies site of stimulation
• Intensity – frequency, number of fibers and which fibers
• Duration - change in firing frequency over time
– phasic receptor - burst of activity and quickly adapt (smell andhair receptors)
– tonic receptor - adapt slowly, generate impulses continually(proprioceptor)
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Receptive Fields
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Receptor Types
• By modality: – chemo-, thermo-, mechano-, photo- receptors and
nociceptors
• By origin of stimuli – interoceptors - detect internal stimuli
– proprioceptors - sense body position and movements
– exteroceptors - detect external stimuli
• By distribution – general senses - widely distributed
– special senses - limited to head
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Unencapsulated Nerve Endings
• Not wrapped in
connective tissue
• Types
– Free nerve endings• Warm
• Cold
• Nociceptors (pain)
– Tactile discs• Tonic for light touch
– Hair receptors
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Encapsulated Nerve Endings
• Wrapped in glial cells or connective tissue
• Types
– Meissner’s corpuscles
• Phasic for light touch,
sensitive to hairless areas likefingertips
– Krause end bulbs
• Phasic for light touch, mucousmembrane
– Pacinian corpuscles
• Phasic for deep pressure,stretch, tickle, vibration
– Ruffini endings
• Tonic for heavy touch,pressure and joint movement
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Pain
• Nociceptors – allow awareness of tissue injuries – found in all tissues except the brain
• Fast pain travels in myelinated fibers at 30 m/sec – sharp, localized, stabbing pain perceived with injury
• Slow pain travels unmyelinated fibers at 2 m/sec – longer-lasting, dull, diffuse feeling
• Somatic pain from skin, muscles and joints
• Visceral pain from stretch, chemical irritants or ischemia
of viscera (poorly localized)• Injured tissues release chemicals that stimulate pain
fibers (bradykinin, histamine, prostaglandin)
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Referred Pain
• Misinterpreted pain
– brain “assumes”
visceral pain is coming
from skin – heart pain felt in
shoulder or arm
because both send
pain input to spinal
cord segments T1 to
T5
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CNS Modulation of Pain
• Intensity of pain - affected by state of mind
• Endogenous opiods (enkephalins,
endorphins and dynorphins)
– produced by CNS and other organs under
stress
– in dorsal horn of spinal cord (spinal gating)
– act as neuromodulators block transmission of
pain
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Chemical Senses
• Smell
– Describe the olfactory receptors and the
neural pathways for olfaction
• Taste
– Describe the gustatory receptors and the
neural pathways for gustation
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Olfaction: Sense of Smell
• Nose has 10-100
million receptors for
olfaction
• Olfactory epithelium is5 cm2
• Sensitive up to
10,000 odors
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Olfactory Epithelial Cells
• Olfactory cells – olfactory hairs neurons with
20 cilia
• bind odor molecules inthin layer of mucus
– axons pass throughcribriform plate
– survive 60 days
• Supporting cells
• Basal cells – Divide
– Produce new receptors
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Anatomy and Physiology of Smell
• Olfactory Pathway
– Unmyelinated axons extendthrough the cribriform plate;forms olfactory (CNI) nerve
– CNI terminates in olfactory
bulbs – Olfactory tract project to the
lateral olfactory area of thetemporal lobe
– From lateral areas, pathwaysextend to frontal lobe.
• Molecules bind to receptor onolfactory hair
– hydrophilic - diffuse throughmucus
– hydrophobic - transport by
odorant-binding protein• Activate G protein and cAMP
system
• Opens ion channels for Na+ or Ca2+
– creates a receptor potential
• Action potential travels to brain
• Receptors adapt quickly
– due to synaptic inhibition inolfactory bulbs
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Gustation: Sense of Taste
• Five primary tastes can be distinguished
– Sour, sweet, bitter, salty and umani (meaty or savory)
• Odors from food can pass into nasal cavity
where they stimulate olfactory receptors.• Olfaction is more sensitive than taste, food may
stimulate olfaction over taste.
• People with colds may complain that they cannottaste their food. This is due to blocking olfaction,
not taste
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Anatomy of Gustatory Receptors
• Lingual papillae
– filiform (no taste buds)
• important for texture
– foliate (no taste buds) – fungiform
• at tips and sides of
tongue
– vallate (circumvallate)• at rear of tongue
• contains 1/2 of taste
buds
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Anatomy of the Taste Bud
• Gustatory hair
projects from receptor
through taste port.
• Receptor cells aresupported by basal
cells, which replace
receptor cells every
10 days.
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Physiology of Taste
• Three cranial nerves contain axons of 1st order gustatory neurons from taste buds. – Facial
– Glossopharyngeal
– Vagus
• Transfer signals to medulla oblongata
• Signal then goes to hypothalamus (salivation) or
thalamus.• Thalamus to parietal lobe of cerebrum
(conscious of the taste).
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Taste Aversion
• Strong link between taste and pleasant or unpleasant emotions
• Sweet tastes evoke pleasure, bitter
evokes disgust.• Taste aversion: avoiding foods if it upset
digestive system.
• Advantage: longer survival of species• Disadvantage: Radiation Rx cause taste
aversion in patients
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Vision
• Objectives:
– List and describe the accessory structures of
the eye and the structural components of the
eyeball
– Describe the neural pathway for vision
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Accessory Structures
• Eyelids
– Palbebral fissure
• Lateral commissure
• Medial commissure
– Conjunctiva• Mucous membrane,
vascular
• Bloodshot eyes
• Eyelashes/Eyebrows
– Protect from foreign
objects, perspiration and
the direct rays of the sun
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Accessory Structures
• Lacrimal Apparatus – Produces and drains tears.
– Lacrimal gland
• Fluid that contains abactericidal enzyme
– Moves medially to Lacrimalpunctum
– Drains into lacrimal sacand then into nasolacrimalduct
• Cry: Parasympatheticstimulation of lacrimalglands
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Accessory Stuctures
• Extrinsic Eye Muscles
– Superior rectus
– Inferior rectus
– Lateral rectus – Medial rectus
– Superior oblique
– Inferior oblique
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Anatomy of the Eyeball
• 2.5 cm in diameter
• Wall of the eyeball consists of:
– Fibrous tunic
– Vascular tunic
– Retina
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Fibrous tunic
• Cornea
– Allows light in
• Sclera
– Shape of eyeball – White of the eye
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Vascular tunic
• Choroid
• Ciliary body
• Iris
– Pupil
– Circular muscles
• Constriction
• Dilation
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Retina
• Posterior ¾ of inner eyeball• Optic part has two layers
– Pigmented layer • Absorbs scattered light in eyeball, keeps image sharp
– Neural layer • Multilayered outgrowth of brain, process visual image before sending
impulses to optic nerve
• Photoreceptors: Rod and cone cells – Rod: allow us to see in dim light, do not provide color, shades of gray
only
– Cone: Produce color vision
• Detached retina – Detached between two layers – Distorted vision and blindness in corresponding field of vision
– Re-attached through laser surgery
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Lens
• Posterior to pupil and
iris
• Focus images on the
retina to facilitateclear vision
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Interior of the eyeball
• Anterior cavity
– Anterior chamber
– Posterior chamber
– Aqueous humor • Vitreous chamber
– Vitreous body to keep
shape of eyeball and
keep retina attached tochoroid
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The visual pathway
• 1st order neurons: retina
• 2nd order neurons: optic nerve
– Advance toward optic chiasm, and split
• 3rd order neurons: thalamus to occipital
lobe
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Hearing and Equilibrium
• Describe the anatomy of the structures of
the three principle regions of the ear.
• List the principle events involved in
hearing.
• Identify the receptor organs for equilibrium
• Describe the auditory and equilibrium
pathway
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Anatomy of the Outer Ear
• Outer ear
– Auricle
• Helix and Lobule
– Auditory canal
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Anatomy of the Middle Ear
• Air-filled tympanic cavity
• Contains
– Tympanic membrane
– Ossicles
• Malleus
• Incus
• Stapes
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Anatomy of the Inner Ear
• Bony labyrinth
• Semicircular canals
– Right angles to each
other • Cochlea
– Transmission of sound
• Inner hair cells
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Stimulation of Cochlear Hair Cells
• Vibration of ossicles causes vibration of
basilar membrane under hair cells
– as often as 20,000 times/second