The Senses (Preception) - Biol, Anatomy & Physiology

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The Senses:
Perception

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• Senses allow perception of stimuli (internal/external)
• General senses: receptors found throughout the body
– Somatic: external
– Visceral: internal
• Special senses: receptors found in specific regions (‘the senses’)

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General senses

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receptors found throughout the body
– Somatic: external
– Visceral: internal

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Special senses

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receptors found in specific regions (‘the senses’)

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Overall Senses

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Anchor you in your environment through sensory receptors
– Mechanoreceptors: physical stimuli (stretching, proprioception)
– Chemoreceptors: chemical stimuli (taste, smell)
– Photoreceptors: light stimuli (sight)
– Thermoreceptors: temperature stimuli
– Nociceptors: painful stimuli

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Mechanoreceptors

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physical stimuli (stretching, proprioception)

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Chemoreceptors

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chemical stimuli (taste, smell)

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Photoreceptors

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light stimuli (sight)

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Thermoreceptors

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temperature stimuli

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Nociceptors

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painful stimuli

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How it works
• Stimuli to action potential

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– Sensory neurons can have free nerve endings (look like dendrites) or be more
complex (often found in a capsule)
– Nerve endings can be ‘triggered’ by certain stimuli to produce an action potential

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Special Senses

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• Smell (olfaction): occurs in nose
• Bipolar olfactory neurons in the olfactory epithelium of the superior (upper) nasal cavity
respond to odorants
– Olfactory receptors bind to multiple different odorants
– Transmit action potential to
olfactory bulb, then through
olfactory tracts to brain in
olfactory cortex

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Special Senses:
Smell (olfaction):

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occurs in nose

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Special Senses
• Taste

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occurs in the taste buds
– Found on papillae of the tongue and on palate, epiglottis
– Taste bud composed of epithelia over taste cells
• Taste hairs sit in taste pore exposed to mouth
– Brainstem --> thalamus --> cerebral cortex

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Path of Taste

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– Brainstem --> thalamus --> cerebral cortex

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Special Senses
• Sight

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occurs in the eyes
– Eye located in orbits, protected/supported by accessory structures
• Eyebrow (protect from sweat)
• Eyelid/lashes (protect from objects, lubricate)
• Conjunctiva (lubricate)
• Lacrimal apparatus (secrete tears, enzymes)
• Extrinsic eye muscles (move eyeball)

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Accessory Structures
Eyebrow

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Eyebrow (protect from sweat)

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Accessory Structures
Eyelid/lashes

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Eyelid/lashes (protect from objects, lubricate)

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Accessory Structures
Conjunctiva

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(lubricate)

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Accessory Structures
Lacrimal apparatus

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(secrete tears, enzymes)

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Accessory Structures
Extrinsic eye muscles

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(move eyeball)

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Eye anatomy: wall layers (‘tunics’)

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– Fibrous tunic: sclera (‘white’) + cornea
– Vascular tunic: choroid + ciliary body + iris
– Nervous tunic: retina

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Retina: Rods & Cones

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Photoreceptor cells (respond to light)
– Rods: good in low light; not much color discrimination
– Cones: require more light; good color discrimination
(blue, green, red)
• Based on wavelength of light

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Inner eye is fluid-filled chambers

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– Anterior + posterior (around iris) have aqueous humor (nutrient watery fluid;
maintains pressure)
– Vitreous (posterior to lens – essentially ‘eye’) has vitreous humor (thicker, clear substance; maintains shape & refracts light)
How it works:
– Light travels through iris, focused by cornea, lens, & humor onto nervous
tunic (retina) which starts action potentials, transferred to optic nerve

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Sight Con’t
• How it works

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– Light travels through iris, focused by cornea, lens, & humor onto nervous
tunic (retina) which starts action potentials, transferred to optic nerve

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Sight Pathway

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• Optic nerve --> optic chiasm (crossing) --> optic tract --> thalamus (then visual cortex) or superior colliculi

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Special Senses
• Hearing

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Hearing (+ balance): occurs in the ear
– External ear
– Middle ear
– Inner ear

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Hearing Con’t
• Translation from sound wave into action potential

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– Hit tympanic membrane, cause vibrations to auditory ossicles
– Transferred to oval window, though scalae to round window

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Hearing Pathway

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Cochlear nerves --> cochlear nucleus (in brainstem) --> brainstem or inferior colliculus (midbrain) --> thalamus --> auditory cortex

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Hearing "Balance"

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• Static equilibrium: orientation of stable head relative to gravity; vestibule key
• Dynamic equilibrium: understanding of head position during movement; semicircular canals key

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Vestibule

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• Contain maculae (epithelial tissue) with hair cells, surrounded by endolymph

– Hair cell microvilli embed in gel matrix(filled with otoliths to add mass); when
matrix moves, stimulates hair cells to create action potentials

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Semicircular Canals

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• Sit at different angles to give great diversity of signal
• At base of semicircular canals form ampulla filled with crista ampullaris, holding cupula: gel mass
– Similar to maculae, but without otoliths
– Movement of endolymph vs. movement of cupula --> formation
of action potential