Sensory Systems Vision Hearing Taste Smell Equilibrium Somatic Senses.
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Transcript of Sensory Systems Vision Hearing Taste Smell Equilibrium Somatic Senses.
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)
• 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
Properties of Sensory Systems
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• 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
• 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 Senses
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• 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
• 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
Eye anatomy
Figure 17.4a, b
Sectional Anatomy of the Eye
• Outer fibrous tunic -sclera, cornea, • Vascular tunic - iris, ciliary body, choroid• Nervous tunic - 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
Retina
• Reflected light translated into mental image• Pupil limits light, lens focuses light• Retinal rods and cones are photoreceptors
Vision: Photoreceptors
Figure 10-36: Photoreceptors in the fovea
• 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
Lens – Image Formation
• Membranous labyrinth contains endolymph• Bony labyrinth surrounds and protects membranous labyrinth
– Vestibule
– Semicircular canals
– Cochlea
Inner ear
Figure 17.28a
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
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.
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.
• 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
Olfactory organs
• 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
Olfaction
• 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
Taste Receptors
• 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
Gustatory pathways