Sensory Systems
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Vision
Hearing
Taste
Smell
Equilibrium
Somatic Senses
Sensory Systems
• Somatic sensory
• General – transmit impulses from skin, skeletal
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muscles, and joints
Special senses - hearing, balance, vision
• Visceral sensory
• Transmit impulses from visceral organs
• Special senses - olfaction (smell), gustation (taste)
Properties of Sensory Systems
• Stimulus - energy source
– Internal
– External
• Receptors
– Sense organs - structures specialized to
respond to stimuli
– Transducers - stimulus energy converted into
action potentials
• Conduction
– Afferent pathway
– Nerve impulses to the CNS
• Translation
– CNS integration and information processing
– Sensation and perception – your reality
Sensory Pathways
• Stimulus as physical energy  sensory receptor acts
as a transducer
• Stimulus > threshold  action potential to CNS
• Integration in CNS  cerebral cortex or acted on
subconsciously
Classification by Function (Stimuli)
• Mechanoreceptors – respond to touch, pressure,
vibration, stretch, and itch
• Thermoreceptors – sensitive to changes in temperature
• Photoreceptors – respond to light energy (e.g., retina)
• Chemoreceptors – respond to chemicals (e.g., smell,
taste, changes in blood chemistry)
• Nociceptors – sensitive to pain-causing stimuli
• Osmoreceptors – detect changes in concentration of
solutes, osmotic activity
• Baroreceptors – detect changes in fluid pressure
Classification by Location
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Exteroceptors – sensitive to stimuli arising from outside the body
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Interoceptors – (visceroceptors) receive stimuli from internal viscera
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Located at or near body surfaces
Include receptors for touch, pressure, pain, and temperature
Monitor a variety of stimuli
Proprioceptors – monitor degree of stretch
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Located in musculoskeletal organs
Classification by Structure
Somatic Senses
• General somatic – include
touch, pain, vibration,
pressure, temperature
• Proprioceptive – detect
stretch in tendons and
muscle provide information
on body position, orientation
and movement of body in
space
Somatic Receptors
• Divided into two groups
– Free or Unencapsulated nerve endings
– Encapsulated nerve endings - consist of one or more
neural end fibers enclosed in connective tissue
Free Nerve Endings
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Abundant in epithelia and underlying connective tissue
Nociceptors - respond to pain
Thermoreceptors - respond to temperature
Two specialized types of free nerve endings
– Merkel discs – lie in the epidermis, slowly adapting receptors for light touch
– Hair follicle receptors – Rapidly adapting receptors that wrap around hair
follicles
Encapsulated Nerve Endings
– Meissner’s corpuscles
• Spiraling nerve ending surrounded by Schwann cells
• Occur in the dermal papillae of hairless areas of the skin
• Rapidly adapting receptors for discriminative touch
– Pacinian corpuscles
• Single nerve ending surrounded by layers of flattened Schwann cells
• Occur in the hypodermis
• Sensitive to deep pressure – rapidly adapting receptors
– Ruffini’s corpuscles
• Located in the dermis and respond to pressure
• Monitor continuous pressure on the skin – adapt slowly
Encapsulated Nerve Endings - Proprioceptors
• Monitor stretch in locomotory organs
• Three types of proprioceptors
– Muscle spindles – monitors the changing length of a muscle, imbedded
in the perimysium between muscle fascicles
– Golgi tendon organs – located near the muscle-tendon junction, monitor
tension within tendons
– Joint kinesthetic receptors - sensory nerve endings within the joint
capsules, sense pressure and position
Muscle Spindle & Golgi Tendon Organ
Special Senses
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Smell
Taste
Vision
Hearing
Equilibrium
Figure 10-4: Sensory pathways
Vision
External Structures of the Eye
Figure 17.3a, b
Internal Structures of the Eye
Eye anatomy
• Ciliary body and lens divide the
eye into posterior (vitreous)
cavity and anterior cavity
• Anterior cavity further divided
into anterior and posterior
chambers
• Aqueous humor circulates within
the eye
– diffuses through the walls of
anterior chamber
– re-enters circulation
• Vitreous humor fills the posterior
cavity.
– Not recycled – permanent fluid
The Pupillary Muscles
Figure 17.5
Sectional Anatomy of the Eye
• Outer fibrous tunic -sclera, cornea,
• Vascular tunic - iris, ciliary body, choroid
• Nervous tunic - retina
Figure 17.4a, b
Organization of the Retina
Figure 17.6b, c
Organization of the Retina
Figure 17.6a
Retina
Figure 10-38: Photoreceptors: rods and cones
Retina
• Rod cells
– Monochromatic
– Night vision
• Cone cells:
– Red, green, & blue
– Color & details
• Pigmented epithelium
– Melanin granules
– Prevents reflection
• Bipolar & ganglion cells converge, integrate
APs
Vision: Photoreceptors
• Reflected light translated into mental image
• Pupil limits light, lens focuses light
• Retinal rods and cones are photoreceptors
Figure 10-36: Photoreceptors in the fovea
Lens – Image Formation
• Lens helps focus
– Light is refracted as it passes through lens
– Accommodation is the process by which the
lens adjusts to focus images
– Normal visual acuity is 20/20
Accommodation
Figure 17.10
Visual Abnormalities
Figure 17.11
Photoreception and Local Integration
Figure 10-35: ANATOMY SUMMARY: The Retina
Visual physiology
Photoreception
Retinal Changes Shape
Retinal restored
Opsin inactivated
Figure 17.15
Convergence and Ganglion Cell Function
Figure 17.18
Visual Pathways
Figure 17.19
Equilibrium and Hearing
Both Equilibrium And Hearing Are Provided
By Receptors Of The Inner Ear
Anatomy of the ear
Middle Ear
Figure 17.21
Inner ear
• Membranous labyrinth contains endolymph
• Bony labyrinth surrounds and protects membranous labyrinth
– Vestibule
– Semicircular canals
– Cochlea
Cochlea
Figure 17.25a, b
Sound and Hearing
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Sound waves travel toward tympanic membrane, which vibrates
Auditory ossicles conduct the vibration into the inner ear
Movement at the oval window applies pressure to the perilymph of the
cochlear duct
Pressure waves distort basilar membrane
Hair cells of the Organ of Corti are pushed against the tectoral membrane
Figure 17.28a
The Organ Of Corti
Figure 17.26a, b
Equilibrium
Semicircular Canals
• Provide information about
rotational acceleration.
– Project in 3 different planes.
• Each canal contains a
semicircular duct.
• At the base is the crista
ampullaris, where sensory
hair cells are located.
– Hair cell processes are
embedded in the cupula.
• Endolymph provides inertia
so that the sensory
processes will bend in
direction opposite to the
angular acceleration.
Structure of the Macula
Utricle and Saccule
• Utricle:
– More sensitive to horizontal acceleration.
• During forward acceleration, otolithic membrane lags behind hair cells, so
hairs pushed backward.
• Saccule:
– More sensitive to vertical acceleration.
• Hairs pushed upward when person descends.
Smell (Olfacation) &
Taste (Gustation)
Olfactory organs
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Contain olfactory epithelium with olfactory receptors, supporting cells, basal
cells
Olfactory receptors are modified neurons
Surfaces are coated with secretions from olfactory glands
Olfactory reception involved detecting dissolved chemicals as they interact with
odorant binding proteins
Olfaction
• Olfactory pathways
– No synapse in the thalamus for arriving
information
• Olfactory discrimination
– Can distinguish thousands of chemical stimuli
• CNS interprets smells by pattern of receptor activity
– Olfactory receptor population shows
considerable turnover
– Number of receptors declines with age
Taste Receptors
• Clustered in taste buds
• Associated with lingual papillae
• Taste buds
– Contain basal cells which appear to be stem cells
– Gustatory cells extend taste hairs through a narrow taste pore
Gustatory pathways
• Taste buds are monitored by cranial nerves
– Synapse within the solitary nucleus of the medulla
oblongata
– Then on to the thalamus and the primary sensory
cortex
• Primary taste sensations
– Sweet, sour, salty, bitter
– Receptors also exist for umami and water
• Taste sensitivity shows significant individual
differences, some of which are inherited
• The number of taste buds declines with age