Sensory module Flashcards
Afferent
PNS
towards
Efferent
PNS
away
- somatic
- autonomic
somatic
voluntary
autonomic
involuntary
3 neuron classes
- afferent neurons - provide environmental info to CNS (towards)
- interneurons
- efferent neurons - carry instructions from CNS to effector organs (away)
patella tendon reflex
- patella gets stretched when tapped
- stretch detected in muscle spindles (afferent) sends input to CNS
- information integrated by interneuron
- sends info via efferent neurons to muscles which get extended and result is a knee kick
affarent nervous system
somatic
general: touch
special: vision, hearing, balance
autonomic
general: nociception (pain)
special: taste, smell
why do we need sensory system
- homeostasis
- perception of the world
- motor coordination
- conscioussness
sensory receptors
have low thresholds to specific stimulus types
- translate stimulus into electrical signal
= sensory transduction
mechanosensory ion channels
??
receptor potential
determines the rate and pattern of action potential firing in a sensory neuron - which is what determines if that stimulus gets sent to the brain
a graded depolarisation of the membrane by the relevant stimuli
separate receptor cell
example: taste bud
the pores of the taste bud detect the chemicals on food or whatever, and send signals to the sensory neurons which sends an action potentialse to the CNS
specialised afferent ending
olfactory epithelium
……
tonic receptors
adapt slowly or never
phasic receptors
adapt rapidly
e.g. pacinis corpsucle
univariance
regardless of the stimulus origin, receptors will always produce a given response type
lateral inhibition
improves acuity when the receptor fields overlap
sensory modality
type of sense
receptor types
photoreceptors - light
chemoreceptors - chemicals
mechanoreceptors - touch
osmoreceptors - body fluids
nociceptors - pain
thermoreceptors - heat and cold
sensory information
direction
location
intensity
timing
perception
conscious interpretation of external world
- what we perceive not real world
e.g. illusions
bottom-up
data-driven provided by photoreceptors
top down
expectations supplied by the CNS are used to interpret and modify data
(or based on previous experience)
e.g, determining handwriting. one word by itself is hard but in a sentence you could see it become one
cornea
- transparent
- mechanical protection (layered)
- most refractive power
- fixed focusing power
- 5 layers
lens
- layered
- fibres made of crystalline
- transparency depends on organisation
- adaptive focusing power
- damage accumulates (e.g. cateracs)
- focus light
(via accomodation) - UV filter
retina
receptor layer
- where we detect photons
very thin layer at the back of the eye
rods vs cones
….
fovea
adaptation
pupil:
- vision constriction (pupillary)
- parasympathetic stimulation of circular muscle
- sympathetic stimulation of radial muscle
phototransduction cascades
this is for rods (process same for cones)
visual pigments (opsins):
- light photon triggers isomerisation
- all-trans retinal doesn’t fit binding site
- opsin changes conformation
- transducins are activated
- PDE are activated
(PDE catayses cGMP to GMP)
- cGMP-gated cation channels close
- hyperpolarisation closes v-gated Ca channel
all these steps lead to a large amplification of the signal
when this conversion happens, it closes the channels and causes the .. to hypoerpolarise
2 different types of photoreceptors
rods and cones
they both have synaptic terminals and an inner segment with the nucleus and mitochondria etc
but specialised outer segments
visual pigments
protein opsin + retinal
in rods its called:
rhodopsin = scotopsin + retinal
retinal gives opsins their colours
photoreceptor hyperpolarisation
the base of the rod is depolarised
- cation channels continuously active
- inner segment leaks K+
- phototransduction hyperpolarise the rod
- the signal from 1 photon is above the noise
cones are less sensitive but are faster and dont saturate
walds cycle
note* need to regenerate cis-retinol so it can go again
