BSC-2010 Lecture Notes - Lecture 3: Afferent Nerve Fiber, Ciliary Muscle, Transducin

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18 Nov 2016
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Sensory Mechanisms
sensory input (afferent pathways) —> integration —> motor output (efferent pathways)
stimuli:
chemicals - taste, smell, pheromones
mechanical - movement, touch, hearing
electromagnetic energy - visions (light)
thermal - heat/cold
pain
sensory receptors:
neuronal receptors - receptor is afferent neuron
stimulus —> afferent neuron —> sensory receptor —> CNS
non-neuronal receptors - receptor regulates afferent neuron
stimulus —> sensory receptor cell —> neurotransmitter released —> receptor protein of
afferent neuron —> CNS
sensory receptor: transduction, transmission, integration, perception, amplification, adaptation
Light Reception/Vision
specializations of insect vision:
compound eyes
extended wavelength sensitivity
can resolve more rapid changes
focusing in the mammalian eye
near vision (accommodation):
ciliary muscles contract, pulling border of choroid toward lens
suspensory ligaments relax
lens becomes thicker and rounder, focusing on nearby objects
distance vision:
ciliary muscles relax, and border of choroid moves away from lens
suspensory ligaments pull against lens
lens becomes flatter, focusing on distant objects
photoreceptor cells: rods & cones
rhodopsin: opsin (protein) + retinal (visual pigment)
light transduction in a rod cell: production of the receptor potential
light activates rhodopsin —> transducin binds to phosphodiesterase
transducin - a G-protein (activated when GTP replaces GDP)
phosphodiesterase (PDE) hydrolizes cGMP to GMP
light hyperpolarizes the rod cell
synaptic activity of rod cells in the dark vs light:
dark - rhodopsin inactive, Na+ channels open, rod depolarized, glutamate released
light - rhodopsin active, Na+ channels closed, rod hyperpolarized, no glutamate released
neural pathways for vision:
right visual field —> left eye —> optic nerve —> lateral geniculate nucleus —> primary
visual cortex
left visual field —> right eye
optic chiasm = where the two optic nerves cross over
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