Somatic Senses Special 12 Senses Unit 1 Chapter

Somatic Senses & Special 12 Senses Unit 1 Chapter 12

special location • Smell (olfaction) • taste (gustation) • vision • balance • hearing 12 Unit 1 Special Senses

Somatic & Visceral • Temperature • Touch • Pressure • Vibration • Proprioception • Pain • Internal organ conditions 12 Unit 1 General Senses

Definition of Sensation • Conscious or subconscious awareness of change in external or internal environment Requires: 1. 2. 3. 4. Stimulus Sensory receptor Neural pathway Brain region for integration Unit 1 • 12

Characteristics 12 • Perception- conscious awareness • Adaptation- decreased receptor response with prolonged stimulation Þdecreased perception Adaptation speed varies with receptor Unit 1 Cerebral cortex function

Structural Types 12 • Free nerve endingspain, thermal, tickle, itch & some touch receptors Touch pressure & vibration • Specialized cells: e. g. hair cells in inner ear Unit 1 • Encapsulated nerve endings

Receptor Mechanisms 12 • Mechanoreceptors- • Thermoreceptors- temperature • Nociceptors – pain • Photoreceptors- light • Chemoreceptors- chemicals Taste, smell, body fluid content Unit 1 cell deformation, stretching or bending

• Receptors- distributed unevenly • In skin, mucous membranes, muscles, tendons, & joints • Dense receptors concentration in fingertips, lips & tip of tongue 12 Unit 1 Somatic Senses

• Touch, pressure, vibration, itch & tickle • Itch & tickle – free nerve endings • encapsulated mechanoreceptors 12 Unit 1 Tactile sensations

Touch 12 • Rapidly adapting receptors: Meisner corpuscles Hair root plexuses Type I mechanoreceptors= Merkel discssurface receptors- stratum basale Type II mechanoreceptors= Ruffini corpuscles- deep in dermis & tendons Unit 1 • Slowly adapting receptors:

Pressure & Vibration 12 • Sensation over large area • Vibration = rapidly repetitive stimuli Corpuscles of touch- low frequency Lamellated corpuscles- higher frequency Unit 1 Lamellated or Pacinian corpuscles Rapid adapting & widely distributed

Figure 12. 1

Itch & tickle 12 • Itch- chemical stimulation of free nerve endings • Tickle- from free nerve endings & lamellated corpuscles Requires someone else- blocked by signals from cerebellum Unit 1 Bradykinin from inflammation response

Thermal Sensations 12 • Two kinds of thermoreceptors • Between 10 o & 40 o C - cold Located in epidermis located in dermis • Outside these ranges – nociceptors • Both adapt rapidly but continue slow signals during prolonged stimulus Unit 1 • Between 32 o & 48 o C – warm

Pain Sensations Nociceptors- free nerve endings Found in every tissue but brain Very little adaptation Fast pain= acute, sharp pain (0. 1 sec) not felt in deep tissues and well localized • Slow pain- slow starting & increases Chronic, burning, aching or throbbing sensation • Visceral pain location displaced to surface = referred pain Unit 1 • • 12

Figure 12. 2

Proprioception 12 • Head and limb position & motion • Kinesthesia= perception of movements • Inner ear (hair ceils)- head position • Tracts to primary sensory area of cerebral cortex & cerebellum • Slow & slight adaptation Unit 1 Located in muscles (muscle spindles), tendons (tendon organs), in & around synovial joints (joint kinesthetic receptors)

Figure 10. 13

12 Smell- Olfaction • In upper surface of superior concha, below cribiform plate • Olfactory receptors- • Supporting cellsepithelial cells – support & electrical insulation • Basal cells- stem cells for receptors Unit 1 first order neurons of olfactory pathway Connect to olfactory bulb Have olfactory hairs containing chemoreceptors

Figure 12. 3 a

• Genetic evidence- 100’s of primary odors • Binding of chemical stimulates nerve • Recognition of 10, 000 odors from combination of primary receptor input • Rapid adaptation by ~50% in 1 sec. 12 Unit 1 Stimulation of Receptors

Olfactory Pathway 12 • Olfactory receptor’s axons = Olfactory nerves through cribiform plate olfactory bulbs To primary olfactory area of temporal lobe And limbic system - emotional response to smells, e. g. nausea or arousal Unit 1 • Olfactory tract

Figure 12. 3 b

• 5 primary tastes: salt, sweet, sour, bitter & umami • Perception of what we call taste includes olfactory input • Receptors in taste buds (~10, 000) • Located on tongue & pharynx & epiglottis • In structures called papillae Vallate (back), fungiform (all over) filiform- touch receptors only 12 Unit 1 Taste- Gustatory Sensation

Figure 12. 4 a

Figure 12. 4 b

Structure of Taste Bud 12 Gustatory hair projects from receptor through taste pore • Basal cells= stem cells Produce supporting cells that develop into receptor cells (10 day life span) Unit 1 • Epithelial cells: • Supporting cells surrounding • Gustatory receptor cells

Figure 12. 4 c

• Tastant- dissolved in saliva • Receptors respond to more than one tastant • Release neural transmitter to primary gustatory neuron • Tastes arise from mix of input form various areas 12 Unit 1 Stimulation

• Facial & glossopharyngeal-tongue • vagus- pharynx & epiglottis • to medulla oblongata • thalamus • primary gustatory areaconsciousness • Also medulla limbic system 12 Unit 1 Gustatory Pathway

Vision- Eyes 12 Superior Rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, inferior oblique • Lacrimal apparatus. Gland lacrimal duct surface of upper eyelid lacrimal canal & nasolacrimal duct nasal cavity Unit 1 • Accessory structures • eye brows, eyelashes- protection • eye lids- protection & lubrication (blinking) • extrinsic muscles- moving eyeball

Figure 12. 5

Layers of Eyeball • • 12 Fibrous tunic – Anterior clear cornea Sclera- white of eye Vascular tunic- contains: Choroid- Lines most of internal surface carries blood vessels • aqueous humor Iris- opens & closes pupilcontains pigment of eye color. • Pupil = hole for light passage Adjusted by iris to control amount of light through the lens Unit 1 • Ciliary body- focuses the lens and secretes

Figure 12. 6

Figure 12. 7

Layers of Eyeball (Cont. ) 12 • Retina- two layers • neural layer- outgrowth of brain • pigmented layer- helps absorb stray light between choroid & neural layer Unit 1 Photoreceptor layer Bipolar cell layer Ganglion cell layer

Photoreceptors 12 • Rods very sensitive, black & white • Cones- color sensitive, • 3 types-blue, green & red • Cones mostly in central fovea in center of macula lutea Area of highest visual resolution • Information bipolar layer ganglion cells axons = optic nerve Unit 1 Color vision results from combined input

Figure 12. 8

Interior of Eyeball 12 • Two cavities- Anterior cavity & Vitreous Chamber divided by lens • Anterior filled with aqueous humor • Vitreous chamber- filled with vitreous body Gel-like - holds retina against choroid Unit 1 Drains into canal of schlemm. - replaced ~90 min. Maintains eye shape & nourishes lens & cornea Responsible for intraocular pressure

Refraction of Light 12 • Lens- focuses light on the retina • Image is inverted but brain adjusts & interprets distance and size Unit 1 • Light rays bend on passing from medium of one density to another of different density = refraction • 75% occurs at cornea

Figure 12. 9 a

Figure 12. 9 b

Figure 12. 9 c

Accommodation 12 • Lens adjusts for distance to keep image focused on retina • Myopia= can’t accommodate distant objects- Eyeball is too long • Hyperopia = can’t accommodate far objects- Eyeball is too short • Astigmatism= irregular curvature of cornea or lens Unit 1 With distant objects ciliary muscle is relaxed Contracts as the object becomes closer

Figure 12. 10

Other visual controls 12 • Constriction of pupilautonomic reflex to center light on lens as object nears it is necessary to maintain focus on single object for binocular vision • Photoreceptors: light neural signal light is absorbed by a photopigment (rhodpsin) which splits into opsin & retinal Unit 1 • Convergence- eyes rotate toward midline

• Optic nerve through optic chiasm • About 1/2 cross over into optic tract • hypothalamus occipital lobes • Right brain sees left side of object • Left brain sees right side of object 12 Unit 1 Visual Pathway

Figure 12. 11

Structures 12 • Outer ear- Auricle, external auditory canal & tympanic membrane (ear drum) Canal contains hairs & ceruminous glands Ossicles = Malleus, incus, & stapes-attached to oval window • Inner ear- Bony labyrinth & membranous labyrinth filled with endolymph Cochlea- sense organ of hearing , vestibule & semicircular canals- organs of balance Unit 1 • Middle ear- auditory tube (eustachian tube) & ossicles

Figure 12. 12

Details of inner structure 12 • Vestibule includes Two sacs: utricle & saccule • Semicircular canals- orthogonal • Cochlea- 3 channels Cochlear duct- membranous & has endolymph Above: Scala vestibuli - ends at oval window Below: Scala tympani - ends at round window In cochlear duct- spiral organ = organ of Corti Unit 1 End in swelling called ampulla Semiscisular ducts connect to utricle

Spiral Organ 12 • Sits on basilar membrane • Contains supporting cells & hair cells • Hair cells =receptors for auditory sensations • Synapse with sensory & motor neurons in cochlear branch of vestibulocochlear nerve Unit 1 between scala tympani & cochlear duct

Figure 12. 13 a

Figure 12. 13 b

• • • Waves in air auditory canal tympanic membrane & ossicle movement pressure waves in perilymph scala vestibuli scala tympani pressure waves in endolymph basilar membrane bending hair cells neural transmitter to sensory neurons Pitch (wavelength) location in cochlea Volume (loudness) intensity of waves 12 Unit 1 Physiology of Hearing

Figure 12. 14

• Cochlear neurons end on same side in medulla • Through midbrain to thalamus • Auditory Cortex on Temporal lobe Receives input from both ears 12 Unit 1 Auditory Pathway

Physiology of Equilibrium 12 Unit 1 • Static equilibrium- position relative to gravity • Dynamic equilibrium- position in response to head movement

• Sensed in maculae of Utricle & Saccule • gravity pulls on otoliths in otolithic membrane • bends hair cells • Triggers nerve impulses in vestibular branch of vestibulochochlear nerve 12 Unit 1 Static equilibrium

Figure 12. 15 a

Figure 12. 15 b

• Semicircular canals- at right angles to each other • Cristae in each ampulla have hair cells and supporting cells • When head turns hair cells move • Endolymph lags and bends hair cells • Bend triggers nerve impulse in vestibular branch 12 Unit 1 Dynamic Equilibrium

Figure 12. 16 a

Figure 12. 16 b

• Axons from vestibular branch • medulla or cerebellum • Medulla motor for eye & head & neck • spinal cord tracts for adjusting muscle tone & postural muscles 12 Unit 1 Equilibrium Pathways