W5b: the PNS- (senses) Flashcards
what is the function of the sensory cells
allow conversion of chemical, electromagnetic and mechanical stimuli into action potentials
how and what can we taste
can taste: sour, sweet, bitter, salty and umami
how: receptors are located in taste buds found on the tongue, pharynx, soft palate and epiglottis
have around 10000 buds but in declines with age (has a lifespan of about 10 days- replaced by differentiation of basal cells
where is the conscious awareness of taste
primary gustatory area of cerebral cortex (insula)
some axons cary taste signals also project to the limbic system (causes em and memory evoked responses)
where is the conscious awareness of smell
olfactory area in temporal lobe
olfactory epithelium has a total area of 5cm^2
covers the superior nasal cavity and cribriform plate which contains 10-100milliomn olfactory receptor cells
what is olfactory epithelium
contains receptor cells which are bipolar neurons which detect inhaled chemicals
extend from nasals cavity into olfactory bulb
odorants bind to receptors on the cells and trigger an electrical signal that travels thru the axon of the olfactory receptor neurones located in olfactory epithelium in superior nasal cavity
axons then converge to form the olfactory nerve, and passes thru small opening in cribriform plate, to then synapse with cells on the olfactory bulb, for processing of signals
signals then relayed and synapses via olfactory tract to reach certain regions of the brain
ethmoid bone is where olfactory receptors neurons pass thru before it reaches the bulb
how does the brain detect smell
conscious awareness of smell occurs in primary olfactory area of cerebral cortex (temp lobe)
axons of olfactory tract also project to the limbic system= abuses emo and memory evoked responses
what is the orbital cavity
eyes are protected from injury by bony orbital cavity
nerves and vessels transmitted thru ‘ spaces ‘ within the bone
made up of: frontal bone, maxilla, sphenoid bone, lacrimal bone, zygomatic bone, palatine bone and ethmoid bone
what are the accessory organs of sight
eyebrows
eyelids
extrinsic eye muscles
lacrimal apparatus
function of eyebrows and eyelids
eyebrows:
prevent sweat from running into eye
eyelids:
anterior protection of eyes
blink frequently
corneal reflex- eyelids close instantly in response to something touching the eye
eyelashes protect
lined by conjunctiva
function of extrinsic eye muscles
coordinate eye movements
arise from bony walls of orbit
attach to sclera
superior rectus (up)
inferior rectus (down)
medial rectus (inwards)
lateral rectus (outwards)
inferior oblique (up and outwards)
superior oblique (down and outwards)
function of lacrimal apparatus
lacrimal gland secrets lacrimal fluid (tears)- upper outer part of orbit
tears contain water, salts, mucus and lysozyme
movement of tears across the eye assisted by blinking
drains into nasolacrimal duct
- excess tears are drained into lacrimal sac via lacrimal canaliculi (on inner corner)
lacrimal sac temp hols the tears before it drains into nasolacrimal duct
nasolacrimal duct connects sac to nasal cavity
what are the layers of the eye
outer fibrous coat: sclera and cornea
middle vascular coat: choroid, ciliary body and iris
inner nervous coat: retina
what is the sclera and cornea
sclera:
dense CT
provides shape and protection
site of attachment for extrinsic muscles
extends along optic nerve posteriorly
cornea:
transparent
curved to focus light
avascular
continous with sclera
what is the choroid, ciliary body and iris
choroid:
lines interact surface of sclera
firmly attached in region of optic nerve
dense capillary network (provide nutrients to retina)
dark brown (melanocytes) to absorb stray light
ciliary body:
continuous with choroid
secrets aqueous humour (clear artery fluid to protect and provide nutrients)
contains smooth muscle
attached to lens by zonular fibres
alter shape of lens (change focus)
iris:
suspended by cornea and lens
attached to ciliary process
eye colour determined by levels of melanin in iris
contains circular and radial smooth muscle
regulates amount of light entering eye
functions of the retina
lines the choroid (posterior 3 quarters of eyeball)
contains specialised light sensing cells - rods and cones
macula: centre of posterior region of retina, resp for sharp, detailed vision
fovea: contains only cones and point of most accurate vision
optic disc: where optic nerve leaves the eye, blind spot because no photoreceptors
what are rods and cones
photosensitive pigments that cover light into nerve impulses
rods: process black and white and more sensitive so functions well in low light
cones: process colour and work best in bright light and concentrate in fovea
what are the optics nerves
leave orbital cavity thru the optic foramen
transmit visual info to the brain thru electrical impulses
medial division crosses over at the optic chiasm
what are the contents of the eyes
aqueous humour:
between lens and cornea
secreted by capillaries in ciliary body
supply nutrients to cornea and lens
lens:
elastic
suspended from ciliary body by suspensory ligament
vitreous humour:
jelly like, maintains shape of eye
helps keep the retina in contact with the choroid
what makes up the ear
external ear
middle ear
inner ear
what is the external ear
pinna:
upper elastic fibrocartilage
lower adipose and CT
external auditory canal:
2.5cm long
lies in temporal bone
tympanic membrane:
fibrous issue coated with epithelium
what is the middle ear
small air filled cavity
malleus
incus
stapes
joined by synovial joints
transmit vibrations of sound waves
connects with:
outer ear via tympanic membrane
inner ear via the oval and round windows
eustachian tube
what is the inner ear
semi circular canals: superior, lateral, posterior
provide balance and position
cochlea: hearing
vestibule: communicates via oval window with the middle ear
bony labyrinth:
series of cavities in temporal bone
filled with perilymph
membranous labyrinth:
series of epithelial sacs and tubes within the bony labyrinth
filled with endolymph
vestibular apparatus- equilibrium
orolith organs (utricle and saccule):
provide info on position and detecting linear acceleration/deceleration
contains macula
3 semicircular ducts:
detection of rotational acceleration/ deceleration
contains ampullae
macula and ampullae contain hair cells to detect movement
what does a change in head movement cause
causes movement of perilymph and endolymph
leads to movement of hair cells
resultant nerve impulses transmitted by vestibular nerve
combined with input from eyes and receptors within joint and muscles
