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Sensory Systems. Vision Hearing Taste Smell Equilibrium Somatic Senses. Sensory Systems. Somatic sensory General – transmit impulses from skin, skeletal muscles, and joints Special s enses - hearing, balance, vision Visceral sensory Transmit impulses from visceral organs

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Sensory Systems

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Sensory Systems

  • Vision

  • Hearing

  • Taste

  • Smell

  • Equilibrium

  • Somatic Senses


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Sensory Systems

  • Somatic sensory

    • General – transmit impulses from skin, skeletal muscles, and joints

    • Special senses - hearing, balance, vision

  • Visceral sensory

    • Transmit impulses from visceral organs

    • Special senses - olfaction (smell), gustation (taste)


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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


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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


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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


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Classification by Location

  • Exteroceptors – sensitive to stimuli arising from outside the body

    • Located at or near body surfaces

    • Include receptors for touch, pressure, pain, and temperature

  • Interoceptors – (visceroceptors) receive stimuli from internal viscera

    • Monitor a variety of stimuli

  • Proprioceptors – monitor degree of stretch

    • Located in musculoskeletal organs


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Classification by Structure


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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


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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


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Free Nerve Endings

  • 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


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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


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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


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Muscle Spindle & Golgi Tendon Organ


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Special Senses

  • Smell

  • Taste

  • Vision

  • Hearing

  • Equilibrium

Figure 10-4: Sensory pathways


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Vision


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External Structures of the Eye

Figure 17.3a, b


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Internal Structures of the Eye


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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


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The Pupillary Muscles

Figure 17.5


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Sectional Anatomy of the Eye

  • Outer fibrous tunic -sclera, cornea,

  • Vascular tunic - iris, ciliary body, choroid

  • Nervous tunic - retina

Figure 17.4a, b


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Organization of the Retina

Figure 17.6b, c


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Organization of the Retina

Figure 17.6a


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Retina

Figure 10-38: Photoreceptors: rods and cones


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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


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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


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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


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Accommodation

Figure 17.10


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Visual Abnormalities

Figure 17.11


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Photoreception and Local Integration

Figure 10-35: ANATOMY SUMMARY: The Retina


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Visual physiology


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Photoreception

Retinal Changes Shape

Retinal restored

Opsin inactivated

Figure 17.15


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Convergence and Ganglion Cell Function

Figure 17.18


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Visual Pathways

Figure 17.19


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Equilibrium and Hearing

Both Equilibrium And Hearing Are Provided By Receptors Of The Inner Ear


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Anatomy of the ear


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Middle Ear

Figure 17.21


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Inner ear

  • Membranous labyrinth contains endolymph

  • Bony labyrinth surrounds and protects membranous labyrinth

    • Vestibule

    • Semicircular canals

    • Cochlea


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Cochlea

Figure 17.25a, b


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Sound and Hearing

  • 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


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The Organ Of Corti

Figure 17.26a, b


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Equilibrium


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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.


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Structure of the Macula


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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.


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Smell (Olfacation) & Taste (Gustation)


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Olfactory organs

  • 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


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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


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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


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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


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