general and special senses

Question 1

what are the two types of senses, and what do they include?

Answer 1

• general: receptors throughout the body, can be somatic or visceral. includes tactile, thermal, pain, and proprioception
• special: receptors are located in one specific place. includes gustatory, olfaction, vision, hearing, and equilibrium

Question 2

what are the olfactory or gustatory senses?

Answer 2

• olfaction/smell: travel through the cribiform plate to superior nasal cavity. transmitted by CN I
• gustation/taste: receptors locaed in papillae on tongue. transmitted by CN VII, IX

Question 3

what are the parts of the ear?

Answer 3

• external ear
• middle ear
• inner ear

Question 4

what is the external ear?

Answer 4

• auricle gathers sound waves and funnels into external auditory meatus. auricle is mostly elastic cartilage covered with skin
• external auditory meatus (EAM): short tube running from auricle to tympanic membrane (eardrum). EAM lined with hairs, sebaceous glands and ceruminous glands (produce earwax) to keep dust and insects out

Question 5

what is the tympanic membrane?

Answer 5

• aka the eardrum
• the boundary between external and middle ear
• sound waves entering external auditory meatus travel to tympanic membrane, cause it to vibrate

Question 6

what is the middle ear?

Answer 6

• air filled space medial to tympanic membrane
• located inside petrous portion of temporal bone
• holes in bony wall between middle ear and inner ear are the round window and oval window

Question 7

what are the auditory ossicles?

Answer 7

• 3 bones from lateral to medial: malleus, incus, stapes
• smallest bones in the body
• transmit vibrations from tympanic membrane across middle ear cavity to inner ear (eardrum vibrates against malleus; stapes vibrates against oval window)

Question 8

what are the muscles of the middle ear?

Answer 8

• two muscles help dampen loud sounds by reducing the movement of the ossicles
• this helps protect the inner ear during loud noises
• tensory tympani muscle (attached to malleus)
• stapedius muscle ( attached to stapes)

Question 9

what is the pharyngotympanic tube?

Answer 9

• aka the auditory or eustachian tube
• connects middle ear to nasopharynx
• allows equalization of pressure on both sides of tympanic membrane (reason ears pop on planes)

Question 10

what is otitis media?

Answer 10

• middle ear infection from nasopharynx (via pharyngotympanic tube)
• fluid builds up in middle ear, causes tympanic membrane to bulge
• common in babies and children, because pharyngotympanic tube is more horizontal

Question 11

what is the inner ear?

Answer 11

• aka labyrinth
• bony labyrinth is a cavity made of semicircular canals, vestibules, and cochlea
• membranous labyrinth is the walls and sacs inside the bony labyrinth

Question 12

what are the three parts of the inner ear?

Answer 12

• cochlea (hearing)
• vestibule (equilibrium/acceleration)
• semicircular canals (equilibrium/rotation)

Question 13

what is the cochlea?

Answer 13

• cochlea looks like a snail shell
• cochlear nerve (part of vestibulocochlear nerve/ CN VIII) runs through center of modiolus (axis of cochlea)
• the membranous portion is called the cochlear duct

Question 14

what is the spiral organ?

Answer 14

• receptor organ for hearing. it has stereocilia (hair cells). it is inside the cochlear duct
• supported by the basilar membrane
• pressure waves travel through cochlear, moving basilar membrane
• stereocilia bend and trigger nerve impulses

Question 15

describe the hearing pathway

Answer 15

• sound enters ear, make tympanic membrane vibrate
• ossicles move
• stapes makes pressure waves at oval window
• waves display basilar membrane, bending hair cells and sending nerve impulses via CN VIII
• remaining wave exits cochlea at round window

Question 16

what are the two types of hearing loss?

Answer 16

• conductive hearing loss: results from issues with external and middle ear. sounds like volume was turned upside down (earwax buildup, fluid in middle ear)
• sensorineural hearing loss: results from issues with inner ear, CN VIII and possibly brain. sounds like things aren’t tuned correctly (damage to hair cells in cochlea is usual cause)

Question 17

what is the vestibule?

Answer 17

• important for equilibrium or balance, specifically detecting linear acceleration, like starting and stopping
• has the utricle and saccule
• when you tilt your head, gelatinous otolithic membrane moves and bends the stereocilia of the macula

Question 18

what are the semicircular canals?

Answer 18

• detect rotation to help with equilibrium (balance)
• three semicircular canals are at right angles to each other
• expansion at end of each canal is the ampulla (receptor for movement)
• when head rotates, endolymph (fluid) in canals moves, cupula within ampulla bends, triggering stereocilia

Question 19

describe human vision

Answer 19

• dominant sense in humans; 70% of sensory receptors are in eyes, 40% of cerebral cortex devoted to processing visual information
• 5 cranial nerves are involved with the eye, lacrimal system and eye muscles
  + CN II (optic)
  + CN III (oculomotor)
  + CN IV (trochlear)
  + CN VI (abducens)
  + CN VII (facial)

Question 20

what are the external structures of the eyes?

Answer 20

• eyelids protect eyeball from excessive light and injury
• inside of eyelids is covered in conjunctiva
• conjunctiva keeps cornea moist by spreading lacrimal fluid (tears)

Question 21

what is the conjuctiva?

Answer 21

• a mucus membrane covering inner eyelids and sclera
• the ocular conjuctiva doesn’t cover the cornea, but still helps moisten the eyeball

Question 22

what is the lacrimal apparatus?

Answer 22

• lacrimal glands located in supero-lateral corner of orbit and supply eyes with lacrimal fluid (tears)
• lacrimal fluid has immune functions (mucus, antibodies, enzymes)
• frains into lacrimal sac and them nasolacrimal duct and nasal cavity = runny nose when you cry

Question 23

what are the extrinsic eye muscles?

Answer 23

• lateral rectus: abduct, VI
• medial rectus: adduct, III
• superior rectus: elevate, adduct, III
• inferior rectur: depress, adduct, III
• inferior oblique: elevate, abduct, III
• superior oblique: depress, abduct, IV

Question 24

what is the fibrous layer of the eye?

Answer 24

• most external layer, or tunic
• sclera: tough outer covering of the eye (white). protects eyeball
• cornea: continuation of sclera, transparent, allows light into eye, acts as fixed lens for focusing
• cornea is avascular (no blood vessels) but lots of nerve endings

Question 25

what is the vascular layer of the eye?

Answer 25

• middle layer or tunic of eyeball
• choroid: heavily pigmented vascular layer. melanin helps absorb light. posterior 2/3rds of eye
• cillary body/muscles surround the lens and control lens shape for precise focusing (adapting for near/far vision)
• iris: colored part of the eye, regulates light entering eye. controls pupil diameter. anterior portion of this layer
• the pupil is a space, not a structure. allows light to enter eye

Question 26

what controls pupil size?

Answer 26

• two sets of muscles control the size of the pupil
• in bright light, the sphincter pupillar contracts to make the pupil smaller (controlled by PNS)
• in low light light and high stress, the dilator pupillae contracts to make the pupil larger (sympathetic innervation)

Question 27

what is the retinal layer of the eye?

Answer 27

• deepest tunic or layer of the eyeball
• retina: converts light to nerve impulse
• optic nerve (CN II): transmits nerve impulses to brain

Question 28

what is the retina?

Answer 28

• innermost layer of eyeball, photosensitive
• two layers:
  + pigmented layer has melanocytes. absorbs light and keep it from scattering. pigmented layer is superficial to neural layer
  + neural layer is nervous tissue with photoreceptive cells (rods and cones)

Question 29

what are photoreceptor cells?

Answer 29

• two types of cells in the retina:
  + rods work best in dim light. rod-shaped. we have more rods than cones
  + cones used for bright light and color vision (perceive red, blue, green). cone-shaped

Question 30

what is the macula lutea, fovea, and optic disc?

Answer 30

three important areas in the back of the eye:
- macula lutea: area of concentrated cone cells at posterior pole
- fovea centralis: area of only cone cells in center of macula lutea. region with highest visual acuity
- optic disc: blind spot, location where optic nerve attaches. no photoreceptor cells

Question 31

what are the lens, anterior, and posterior chambers?

Answer 31

• lens: avascular, transpartent disc, its shape can be changed to adjust focus (deformable)
• lens divides eye into anterior cavity (anterior to lens. has aqueuous humor) and posterior cavity has vitreous humor (gelatinous). most volume of the eye

Question 32

what are focusing disorders?

Answer 32

• the lens is adjustable. the adjustment of the lens is called accomodation
• ciliary muscle contracts and allows lens to change shape. distance vision is out natural state
• as we age, lens becomes less flexible. called presbyopia and can be fixed by reading glasses

Question 33

what is binocular vision?

Answer 33

• humans have binocular vision (fields of vision from left and right eyes overlap). allows for good depth perception
• since lens of eye is convex, images are upside down and reversed
• visual cortex (occipital cortex) flips image back to “normal” so we see properly