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Chapter 15. Senses. Hear no evil…… See no evil…. Smell no good…. Taste no good…. Intro. Millions of sensory neurons Two categories – general/special Most numerous – general General receptors sense touch, temp., pain, reflexes, homeostasis responses

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Chapter 15

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  • Millions of sensory neurons
  • Two categories – general/special
  • Most numerous – general
  • General receptors sense touch, temp., pain, reflexes, homeostasis responses
  • Special receptors sense vision, hearing, balance, taste, smell, reflexes
receptor response
Receptor response
  • Receptors respond to stimuli by converting them to nerve impulses
  • Receptors are the dendrite endings
  • Receptors vary according to their jobs – heat, pain, etc
  • Receptor potential determines the response required for the stimulus
  • These impulses travel to spinal cord to be determined as hot, cold, etc (sensation)
  • Adaptation allows for decrease of response when necessary
distribution of receptors
Distribution of receptors
  • Special sensory receptors – nose, tongue, eye, ear
  • General sensory receptors – skin, mucosa, connective tissue, muscle, tendons, joints, viscera (somatic senses)
  • Touch receptors very dense on hand and sparse on back
classification of receptors
Classification of receptors
  • Exteroceptors
  • Visceroceptors
  • Proprioceptors
  • On or near body surface – external stimuli
  • Cutaneous receptors
  • Pressure, touch, pain, temp.
  • Interoceptors
  • Internally – body organs – internal environment
  • Stimulated by pressure, stretching, chemical changes from blood vessels, organs, intestines
  • Hunger, thirst
  • Specialized visceroceptor
  • Less numerous and more specialized
  • Limited to skeletal muscle, joint capsules, and tendons
  • Info about body movement, orientation to space – don’t have to look to find hand
classification by stimulus detected
Classification by stimulus detected
  • Mechanoreceptors – activated by mechanical stimuli (pressure to skin)
  • Chemoreceptors – change in concentration of chemicals – blood glucose, oxygen, etc.
  • Thermoreceptors – temp. changes
  • Nociceptors – activated by intense stimuli of any type that results in tissue damage – welding light, battery acid, etc.
  • Photoreceptors – eye only – light receptors
classification by structure
Classification by structure
  • Free nerve endings
  • Encapsulated nerve endings
free birds
Free birds…..
  • Simplest, most common
  • Most widely distributed
  • Not in the brain
  • Primary receptor for pain
  • Responsible for itch, sting, tickling, touch, movement, heat, cold
  • Acute – sharp, intense, localized sensation
  • Chronic – persistent pain, dull, aching
caged birds
Caged birds……
  • Six types
  • Covering over dendrite end
  • Activated by mechanical response
  • Vary in size, shape, and distribution
  • Touch receptors – in none hair areas
  • Krause’s end bulbs- mucus membrane – low frequency vibration, cold receptor
  • Ruffini’s corpuscle – deep in dermis – persistent touch receptor (crude)- allows for grasp for long periods of time and still sense stimuli
caged birds cont
Caged birds cont…..
  • Stretch receptors – muscle/tendon – determines strength of contraction and duration – maintains posture
olfactory receptors
Olfactory receptors
  • Upper surface of nasal cavity
  • Chemoreceptors
  • Gas molecules/chemicals dissolve in mucus lining
  • Cilia help to mix the mucus as the solvent
  • Air flows around and down the airway – not to the top usually
  • That is why you sniff for better clarity
  • Filed in temporal lobe
  • Abnormalities sometimes impede normal processing
  • Papillae contain taste buds – each has 50-125 chemoreceptors
  • Determine texture, feel
  • Taste receptors are all over the tongue
  • Old maps are incorrect
  • Taste is stimulated by chemicals dissolved in saliva
  • Four flavors detected – fifth – metal?
taste to the brain
Taste to the brain..
  • Gustatory cells in taste buds begin assimilation of taste in seconds
  • Anterior two thirds of the tongue to facial nerve to glossopharyngeal nerve to the vagus nerve to medulla oblongata and the thalamus to the cerebral cortex in parietal lobe
what did you say
  • External ear – auditory meatus – 3 cm – in, forward, down
  • Modified sweat glands produce wax
  • Mechanoreceptors pick up vibrations in the cilia which are transmitted into the bony structures of the inner ear
  • External
  • Middle
  • Inner
external ear
External ear
  • Flap – modified trumpet (auricle/pinna)
  • Tube from the auricle – external auditory meatus (ear canal) 3cm – in, forward, down – meds. Pull up and back
  • Over-production of wax will cause pain/deafness
  • End of meatus is the tempanic membrane - eardrum
middle ear
Middle ear
  • Tempanic cavity
  • Three tiny ossicles (bones)
  • Malleus, incus, stapes
  • Hammer, anvil, stirrup
  • Tempanic membrane to malleus to the incus then to the stapes
  • Several openings – eustachian tube, oval window, round window, meatus
middle cont
Middle cont.
  • Air spaces at posterior surface by temporal bone
  • Great opportunity for infection!
  • Eustachian tube – bone, cartilage, fibrous tissue lined with mucus membrane
  • Goes down, forward, and in from the middle ear to nasopharynx
  • This tube allows for pressure equalization between inner ear and outer surface
inner ear
Inner ear
  • Labrynth – complicated shape
  • Two main parts – bony and membranous
  • Bony – three parts – vestibule (contains utricle and saccule), cochlea (means snail), semicircular canals
  • Membranous – utricle, saccule, cochlear duct, membranous semicircular canals
  • Vestibule and semicircular canals maintains balance
  • Cochlea – hearing
  • Cochlear nerve (8th) – extends from the base of the cochlear duct in the cochlea
  • Sound comes from vibrations from air, fluid, or solid material
  • How is sound created through your larynx?
  • Vibrating vocal cords create sound waves by producing vibrations in air passing over them
  • Volume – refers to amplitude (height of the wave)
  • Pitch – number of waves occuring during a specific time unit (frequency)
  • Ability to hear depends on volume, pitch, and healthy anatomy and cerebral cortex reception in the auditory area in the temporal lobe after going through relay stations in the thalamus, midbrain, medulla, and pons
causes of hearing loss
Causes of hearing loss:
  • 2 or 3 out of every 1000 babies are born deaf or with a major hearing deficit
  • Millions of individuals are choosing hearing loss due to sound pollution
  • Where do you go for pollution?
you tube videos

Cochlear implant

You tube videos:
  • Vestibule and semicircular canals
  • Static equalibrium – created in utricle and saccule – ability to sense position of the head relative to gravity – also acceleration/deceleration
  • Dynamic equilibrium – semicircular canals – helps to maintain balance when sudden movements occur – with spinning motion, semicircular canals move with the body but not at the same rate and the capula moves in an opposite direction until movement stops
hearing loss
Hearing loss
  • Conductive hearing loss – transmission
  • Middle ear infections
  • Glue ear – collection of fluid in middle
  • Wax accumulation
  • Otosclerosis
  • Ossicle damage – head trauma, inf.
  • Perforated tempanic membrane
loss cont
Loss cont.
  • Presbycusis – loss of hairy cells!
  • Acoustic trauma
  • Viral or bacterial inf
  • Meniere’s disease
  • Drugs
  • Acoustic neuroma – benign
  • MS, stroke, tumor
  • Pregnant woman with rubella
  • CMV in pregnancy
  • Whisper test
  • Tuning fork
  • Pure tone audiometry
  • Otoacoustic emissions – cochlea
  • Auditory brainstem response – cochlea and nerve impulse to the brain
  • MRI
  • Normal – 0-20 dB (range of frequencies)
  • Mild loss - 25-39 dB
  • Moderate loss – 40-69 dB
  • Severe loss – 70-94 dB
  • Profound – 95 dB or greater
  • Sign language
  • Hearing aids
  • Cochlear implant
  • Lip reading
  • Surgical excision of tumorous growth
  • Three layers: outside in – sclera, choroid, retina
  • Anterior portion – cornea (avascular)– covers iris – transparent, sclera is opaque
  • Middle – choroid – vascular – pigmented
  • Anterior choroid – three structures – ciliary body, suspensory ligament, iris
choroid structures
Choroid structures
  • Ciliary body – fits between the anterior retina and posterior iris
  • Iris – smooth muscle fibers – hole in middle – pupil
  • Retina – innermost coat of the eyeball (no anterior portion)
conduction of impulses
Conduction of impulses:
  • Photoreceptor neurons
  • Bipolar neurons
  • Ganglion neurons
blind spot
Blind spot
  • No rods and cones present
  • Optic disc (part of sclera) contains perforations through which fibers emerge from the eyeball creating the optic nerve
  • Pg 466
  • Anterior – two divisions – anterior/posterior chambers
  • Lies in front of the lens
  • Aqueous humor fills both chambers – clear, watery – formed from capillaries
  • Posterior – larger than anterior
  • Occupies all space posterior to the lens
  • Vitreous humor – semi solid jello
  • Maintains intraocular pressure to keep eye from collapsing – normal 20-25 mmHg
  • If over, glaucoma
accessory structures
Accessory structures
  • Eyebrow
  • Eyelashes
  • Eyelid – conjunctiva – blepharoplasty
  • Canthus – corner
  • Lacrimal gland/duct

Rods – photopigment – rhodopsin – light sensitivity

  • Grey tones
  • Cones – determines color perception
how do you see
How do you see?
  • Light enters the eye from the cornea