206 SSNS - Physiology Flashcards
Functions of skin (7)
Thermoregulation Blood reservoir Protection Cutaneous sensations Excretion Absorption Production of Vitamin D
What happens in the skin when there’s an increase in temperature?
Increase in temperature → sweat production
- Evaporation of sweat colls body
Increase heat loss - vasodilation
What happens in the skin when there’s a decrease in temperature?
Decrease in temperature → decrease sweat
Reduction in blood flow to dermal blood vessels - reduce heat loss
What happens to skin during shock?
Vasoconstriction of skin vessels occurs to divert blood to heart & brain; skin appears cold & pale
Keratin
Role in skin
Outermost layer of skin
Protects skin from abrasion, heat, chemicals
Tightly interlocked keratinocytes prevent entry of microbes
Oily sebum
Role in skin
Produced by sebaceous glands
Prevent drying of hair & skin
Contains bactericidal substances
Lipids
Role in skin
Prevent evaporation of water from skin surface & prevents dehydration
Also prevent entry of water into body during showers & swims
Acidic pH of sweat
Role in skin
Prevents growth of microbes
Melanin
Role in skin
Protects from damaging effects of UV rays
Epidermal and dermal macrophages
Role in skin
Phagocytose microbes that enter skin
What are the cutaneous sensations sensed by skin?
Touch Vibration Pressure Tickle Itch Pain Temperature
What can be absorbed through skin?
Fat soluble substances Acetone Carbon tetrachloride Salts of heavy metal Steroid Transdermal patches
How does UV light aid the production of vitamin D?
Activates precursors - conversion of 7-dehydrocholesterol to vitamin D3
Fill in the blanks:
Rods with ______ receptive field has ______ acuity.
larger; low
Fill in the blanks:
Cones with ______ receptive field has ______ acuity.
smaller; high
What is the mechanism of phototransduction?
- Rhodopsin activated by light
- 11-cis retinal absorbs light → all-trans retinal
- All-trans retinal dissociates from opsin (retinal bleaching)
- Activated opsins activates G protein transducin
- Transducin activates cGMP phosphodiesterase, converts cGMP → GMP
- cGMP levels ↓, closing Na+ channels
- ↓ entry of Na+ → photoreceptor hyperpolarized
What supplies the inner layer of retina?
Central retinal artery
What supplies the outer layer of retina?
Choroid vessels
In retinal detachment, ______ detaches from ______?
Retina; pigment layer
Why is it possible for a detached retina to survive for few days?
Diffusion from choroid vessels & supply by central retinal artery still occurs
Vision cycle
regeneration of visual pigment in rods
- Light absorbed by rhodopsin
- Rhodopsin decompose → all-trans retinal (instant change from cis form) & scotopsin (retinal bleaching)
- Isomerase reconvert all-trans → 11-cis
- 11-cis retinal binds with scotopsin to reform rhodopsin
How does vitamin A play a role in the vision cycle?
Vit A is present in cytoplasm of rods & pigment of retina
Hence is always available to form new retinal when needed
If excess retinal in retina, converted back to vit A
During darkness, the photoreceptors are ______.
Depolarized
During light, the photoreceptors are ______.
Hyperpolarized
What aids light & dark adaptation?
Pupil
Pigment
Neurons
Exposure to bright light ______ sensitivity to light.
Reduces
Exposure to darkness ______ formation of pigment; ______ sensitivity to light
increases; increases
What are the 3 types of cones?
Red cone
Green cone
Blue cone
How do we perceive color?
Depends on how much of each cones are activated
Lack of green cones is ______
Deuteranopia
Lack of red cones is ______
Protanopia
Lack of blue cones is ______
Tritanopia
What causes nyctalopia?
Lack of vitamin A - night blindness
Connections between photoreceptors & bipolar cells
Photoreceptors > Horizontal cells
Horizontal cells > Bipolar cells
Bipolar cells > Amacrine cells
Amacrine cells > Ganglion cells
P cell function
Parvocellular
Has smaller receptive field
Provides fine details about image like color
Project to parvocellular LGN
M cell function
Magnocellular
Sensitive to rapid movement visual signals
Sensitive to low contrast black and white stimuli
Project to magnocellular LGN
Lateral inhibition
Capacity of an excited neuron to reduce the activity of its neighbors
Visual pathway
1° bipolar cells on retina
2° ganglion cells of retina
3° neurons in the 6 layers of LGN
II, III, V - receives inputs from temporal retina of same side
I, IV, VI - receive inputs from nasal retina of opposite eyes
Which cells receive from magnocellular cells & which receive from parvocellular cells?
Magnocellular - I & II
Parvocellular - others
Visual cortex area #
17
Which fibre cross and which remain uncross in the visual pathway?
Nasal fibres cross, temporal fibres remain uncrossed
Mechanism of light reflex
- Light fall on retina carried to midbrain via optic nerve
- Reaches pretectal nucleus
- Impulses pass to Edinger-Westphal nucleus
- Preganglionic neurons reach ciliary ganglion
- Postganglionic neuron reach pupil
- Circular muscles contract
Mechanism of accomodation reflex
Contraction of ciliary muscle - increased refractive power - close object
Relaxation of ciliary muscle - decreased power - distant object
Refractive index
Speed of light in air / Speed of light in medium
Convex lens
Converges parallel light rays to a point
Focal length
Distance between focal point from centre of lens
Increase curvature of lens; ______ refractive power; ______ focal length
increase; decrease
Decrease curvature of lens; ______ refractive power; ______ focal length
decrease; increase
Power of lens
1 / focal length
Convex lens has ______ power
positive
Concave lens has ______ power
negative
Which surfaces of eye does refraction occurs?
Anterior & posterior surface of cornea
Anterior & posterior surface of lens
Reduced eye
Combining all refractive surfaces to form a single lens
59 diopters
Accommodation for near objects
Contraction of ciliary muscle
Relaxation of suspensory ligaments
Increase curvature & power of lens
3 things in accommodation reflex
Lens curvature increase
Eyeballs converge
Pupil becomes smaller
Hyperopia (hypermetropia)
Farsightedness 遠視
Image is focused behind retina when ciliary muscle is relaxed
Corrected with convex lens
Myopia
Near-sighted 近視
Distant object is focused in front of retina when ciliary muscle is relaxed
Corrected with concave lens
Astigmatism
散光
Image in one plane is focused at distance diff from plan right angles to it
Corrected using cylindrical lens
Where is vitreous humor found?
Found between lens & retina
No free flow
Where is aqueous humor found?
Found between lens & cornea
Free flowing
Formed from ciliary processes of ciliary body behind iris
Flow of aqueous humor
Posterior chamber → (through pupil) anterior chamber → trabeculae → canal of Schlemm → aqueous veins
Cause of Glaucoma
Blocking of drainage of aqueous humor
Treatment of glaucoma
Treated w drugs that reduce formation of aqueous humor
or drugs that increase drainage/absorption
How does external ear conduct sound to middle ear?
By causing vibrations of tympanic membrane
Handle of malleus attached to tympanic membrane → malleus connected to incus → incus connected to stapes → foot plate of stapes pushes on oval window
Which muscle keeps tympanic membrane tensed?
Tensor tympani
Stapedial reflex
Activated by loud sounds - stapes pulled out of oval window: protects cochlea
2 ways of sound conduction
Air conduction
Bone conduction
3 coiled tubes & 2 membranes in the cochlea
3 coiled tubes:
- Upper scala vestibuli
- Middle scala media
- Lower scala tympani
2 membranes:
- Reissner’s membrane (vestibular membrane)
- Basilar membrane
Where is organ of Corti located?
In the basilar membrane of cochlea
What happens when hair cells of organ of Corti vibrate?
Transduce sound vibration into electrical activity
How is sound waves transmitted in the cochlea?
- Vibration of tympanic membrane moves foot plate of stapes inward & outward
- Causing movement of fluid in scala vestibuli & media
- Causing vibration of basilar membrane
- Pushing of fluid at oval window causes bulging of membrane in round window
What regions of basilar membrane vibrate maximally at diff frequencies?
High - base of chochlea
Medium - middle
Low - tip
Movement of hair cells towards larger hair causing ______ of channel - ______
opening; depolarization
Movement of hair cells towards smaller hair causing ______ of channel - ______
closing; hyperpolarization
Stereocilia
Mechanosensing organelles of hair cells; increase in size away from modiolus
Endolymph
Fluid in scala media
Rich in K+
What is direction of sound determined by?
Difference in arrival of sound in both ears
Intensity of sound reaching both ears
Conductive deafness
Problems in tympanic membrane or ossicles
Air conduction affected
Rinne’s test: BC > AC
Weber test: sound lateralized to affected ear
Sensory neural deafness
Problem in cochlea, nerve, auditory pathway
Both air & bone conduction affected
Rinne’s test: both AC & BC affected, AC still > BC
Weber test: sound lateralized to normal ear
Weber test
Vibration tuning fork placed on top of head or forehead
Normal: vibrations perceived equally on both ears
Conductive deafness: sound lateralized to affected ear
Sensory neural deafness: sound lateralized to normal ear
Rinne’s test
Vibration tuning fork placed on mastoid
Once person stops perceiving vibrations, place in front of ear
Normal: hear sound - positive Rinne; AC > BC
Conductive deafness: BC > AC
Sensory neural deafness: both AC & BC affected, AC still > BC
Vestibular apparatus
For detecting sensations of equilibrium
Composed of membranous labyrinth
Membranous labyrinth
Membranous tubes & chambers
What’s the sense organ in utricle and saccule?
Macula
Utricle macula
Lies horizontally
Determine orientation when it’s upright
Stimulated by movement of head forwards & backwards
Saccule macula
Lies vertically
Determine orientation when lie down
Stimulated by vertical acceleration & deceleration
Statoconia
Calcium carbonate crystals in gelatinous layer
Kinocilium
Long hair cell in one side
Stereocilium
Other hair cells
3 semicircular ducts in inner ear
Anterior
Posterior
Lateral
Ampulla
Enlargement at one end of semicircular ducts
What does the duct & ampulla of the ear contain?
Endolymph (rich in K+)
What happens in the semicircular ducts when head rotates?
The fluid within remains stationary due to inertia → when movement stop fluid continues to move → bend hair in opposite direction
Medial longitudinal fasciculus
Links the 3 main nerves which control eye movements, i.e. the oculomotor, trochlear and the abducent nerves, & vestibulocochlear nerve.
Function to integrate movement of the eyes and head movements.
What are the 5 primary tastes?
Sour Salty Sweet Umami Bitter
3 types of papillae on tongue
- Circumvallate papilla - V shaped - posterior tongue
- Fungiform papillae - mushroom like - anterior surface of tongue
- Filiform papillae - thread like - lateral side of tongue
Mechanism of taste transduction
- Taste chemical bind to protein receptors
- Open ion channels → depolarization
Salt - Na+
Sour - H+
Sweet, bitter, umami - G-protein coupled receptor → activate second messenger
Taste pathway
1°
• Anterior 2/3 of tongue - supplied by lingual nerve → through chorda tympani into facial nerve → tractus solitarius (brainstem)
• Posterior 1/3 of tongue - glossopharyngeal nerve → tractus solitarius
• Base of tongue & pharynx - vagus nerve → tractus solitarius
2°
Synapse at nuclei of tractus solitarius → ventro posterior medial nucleus (thalamus)
3°
Thalamus → gustatory cortex (Brodmann area 43) = anterior insula + frontal operculum
Where is olfactory epithelium located?
Superior part of nostrils
Smell transduction
- Odorant molecule bind to receptor in olfactory cilia
- Activates G protein complex
- α subunit separates from β & γ subunits
- Activates adenyl cyclase
- Which converts ATP → cAMP
- cAMP activates/opens gated sodium channel → depolarization
- Action potential generated
Physical factors that affect degree of stimulation in smell
Volatile substance
Water soluble
Slightly lipid soluble
Olfactory pathway
1°
• Olfactory cells enter olfactory bulb (lie over cribriform plate) → glomerulus
2°
• Synapse with mitral or tufted cells in olfactory glomerulus
3°
• Medial pathway → hypothalamus - feeding & salvation
• Lateral olfactory pathway → limbic system (hippocampus) - olfactory memory
• New pathway → orbitofrontal cortex (by passing through dorsomedial nucleus of thalamus) - conscious analysis of odors
Ageusia
Lack of taste
- frontal lobe tumours, head injury
- can be due to injury to CN VII & IX
Hypogeusia
Reduced sensation of taste
- chewing tobacco
Dysgeusia
Abnormal taste sensation
Anosmia
Lack of smell
- COVID
- can be due to fracture of cribriform plate
Hyposmia
Reduced sensation of smell
- can be due to cold
Parosmia
Abnormal sensation of smell
What secretes endolymph?
Stria vascularis
