Lecture 5 : Sensory- Visual system
Sensory transduction :
● envi energy → neural signals
● Sensation = cognitive process
○ Central nervous system
○ Peripheral nervous system
● Sensory receptors
○ energy from envi trigger electrochemical signals that can be transmitted to the brain = sensory
transduction → limits of perception
○ nature of signals they sense :
■ photoreceptor
■ chemoreceptor
■ mechanoreceptor
■ thermal receptors
○ their vantage point in the body
■ exteroceptor
■ enteroreceptor
■ proprioreceptor
○ Telereceptor
■ specialized sense receptor
■ localized in
● eyes
● ears
● nose
○ Nociceptor
■ pain receptors
■ detect noxious agents both internally and externally
○ Optimized : lowest threshold for specific stimulus
○ Receptor specificity is ensured by their structure & position
■ univariance of sensory receptor → same response to all
○ Accessory structures
■ specific sensitivity of receptor
■ exclude unwanted stimuli
⇒ e.g lens of the eye
1
, ● Molecular signaling mechanisms for sensory transduction
○ Integral membrane proteins : G-protein- coupled receptors (GPCRs) for
■ vision/ olfaction/ some types of chemoreception
■ the 2nd-messenger pathways substances are the same one used for non-sensory
tasks in cells ( cyclic nucleotides, inositol phosphates, kinases)
○ Modified membrane ion channels
■ primary transduction process
■ mechanoreceptors
● Sensory stimulus
○ envi → effective response in a sensory receptor (biological transducer) → regulate Ca2+ into
the sensory cell -> transmitter release
○ triggers APs at a specific rate and pattern (neuronal firing)
● Sensory modalities :
○ general sensory modalities
■ seeing, hearing, touching, smelling, tasting, senses of pain, balance, body position,
mvm
○ complex sensations
■ combination of simpler sensations
○ affect
■ subjective perception of the sensory modality, influenced by previous experience and
learning
○ intricate sensory system
■ not conscious (interoceptors)
■ monitor the internal milieu (homeostasis)
■ body’s chemical and metabolic state
● Perception of sensory info involves encoding, transmission and decoding
○ encoding
■ AP
○ transmission to CNS
■ frequency modulated encoding, APs transmission
○ interpretation (decoding) of encoded and transmitted information into perception
■ neural pathway
■ Perception of the localization of cutaneous sensation to a particular part of the body
depends on the pathway it takes to the CNS
VISUAL SYSTEM
light-> cornea → pupil → lens → vitreous humor → Retina →
photoreceptor → Fovea
Outer layer of the eye :
● Tears
○ complex liquid (lipid, aqueous, mucoid layer)
○ allows O2 to diffuse from air to cornea cells
○ contains lysozyme & antibiotics
● Cornea
○ no blood vessels
○ most powerful eye lens
○ dioptric power is not variable
○ well innervated (pain), trigeminal nerve
● Sclera
○ continuation of the substantia propria of the cornea
○ tough CT coating, protective layer
Middle layer of the eye - uvea (uveal tract)= iris, ciliary body, choroid:
● Iris
○ Pupillary light reflex
2
Sensory transduction :
● envi energy → neural signals
● Sensation = cognitive process
○ Central nervous system
○ Peripheral nervous system
● Sensory receptors
○ energy from envi trigger electrochemical signals that can be transmitted to the brain = sensory
transduction → limits of perception
○ nature of signals they sense :
■ photoreceptor
■ chemoreceptor
■ mechanoreceptor
■ thermal receptors
○ their vantage point in the body
■ exteroceptor
■ enteroreceptor
■ proprioreceptor
○ Telereceptor
■ specialized sense receptor
■ localized in
● eyes
● ears
● nose
○ Nociceptor
■ pain receptors
■ detect noxious agents both internally and externally
○ Optimized : lowest threshold for specific stimulus
○ Receptor specificity is ensured by their structure & position
■ univariance of sensory receptor → same response to all
○ Accessory structures
■ specific sensitivity of receptor
■ exclude unwanted stimuli
⇒ e.g lens of the eye
1
, ● Molecular signaling mechanisms for sensory transduction
○ Integral membrane proteins : G-protein- coupled receptors (GPCRs) for
■ vision/ olfaction/ some types of chemoreception
■ the 2nd-messenger pathways substances are the same one used for non-sensory
tasks in cells ( cyclic nucleotides, inositol phosphates, kinases)
○ Modified membrane ion channels
■ primary transduction process
■ mechanoreceptors
● Sensory stimulus
○ envi → effective response in a sensory receptor (biological transducer) → regulate Ca2+ into
the sensory cell -> transmitter release
○ triggers APs at a specific rate and pattern (neuronal firing)
● Sensory modalities :
○ general sensory modalities
■ seeing, hearing, touching, smelling, tasting, senses of pain, balance, body position,
mvm
○ complex sensations
■ combination of simpler sensations
○ affect
■ subjective perception of the sensory modality, influenced by previous experience and
learning
○ intricate sensory system
■ not conscious (interoceptors)
■ monitor the internal milieu (homeostasis)
■ body’s chemical and metabolic state
● Perception of sensory info involves encoding, transmission and decoding
○ encoding
■ AP
○ transmission to CNS
■ frequency modulated encoding, APs transmission
○ interpretation (decoding) of encoded and transmitted information into perception
■ neural pathway
■ Perception of the localization of cutaneous sensation to a particular part of the body
depends on the pathway it takes to the CNS
VISUAL SYSTEM
light-> cornea → pupil → lens → vitreous humor → Retina →
photoreceptor → Fovea
Outer layer of the eye :
● Tears
○ complex liquid (lipid, aqueous, mucoid layer)
○ allows O2 to diffuse from air to cornea cells
○ contains lysozyme & antibiotics
● Cornea
○ no blood vessels
○ most powerful eye lens
○ dioptric power is not variable
○ well innervated (pain), trigeminal nerve
● Sclera
○ continuation of the substantia propria of the cornea
○ tough CT coating, protective layer
Middle layer of the eye - uvea (uveal tract)= iris, ciliary body, choroid:
● Iris
○ Pupillary light reflex
2
