Lecture 8 Afferent Division Flashcards
Stimulus
change detectable by the body
Sensory receptor cells
- have cell surface receptors; respond to internal and external stimuli
- can be an afferent neuron or communicate with afferent neuron
- stimuli induce change in membrane potential
Sensory transduction
process of converting a sensory signal to an electrical signal in the sensory neuron. The process of reception is dependent on the stimuli itself, the type of receptor, receptor specificity, and the receptive field, which can vary depending on the receptor type.
Acuity
- Influenced by receptive field (region of the skin surface surrounding the sensory neuron)
- Lateral inhibition-each activated pathway inhibits the pathway next to it.
Parts of the eye
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Sclera/cornea
Sclera-connective tissue, tough, white
Cornea- transparent, anterior
Choroid/Iris
Choroid-pigmented, blood vessels
Iris-ring of smooth muscle, pigmented
Retina
contains sensory receptor cells
Humors
Aqueous: in front of lens, thin, 5ml/day
Vitreous: behind lens jelly
Pupil
opening in center of iris
Iris
Thin, pigmented, smooth muscle
Circular Iris muscle
constrict pupil (PNS) (parasympathetic)
Radial Iris muscle
dilate pupil (SNS) (sympathetic)
Lens
- refracts incoming light
- Transparent, layered
- Shape determined by ciliary muscle and suspensory ligaments
- Shape determines where light is focused
Retinae and associated structures
Blind spot: Optic nerve, blood vessels
Macula lutea: surrounds fovea
Fovea: bipolar and ganglion cells pushed aside. light directly hits photoreceptor cells (many cones)
Photoreceptor cells
-Rods and cones
Outer segment: detects light
Inner segment: metabolism
Synaptic terminal: releases neurotransmitter to bipolar cells
Neurotransmitter release at synapse
- Signaling cell depolarizes; voltage gated Na+ channels open
- Depolarization opens voltage gated Ca2+ channels; Ca2+ is very low
- Ca2+ binds to NT-containing vesicles causing them to release
Rods
- 120 million cells, none in fovea
- One photopigment
- Gray; sensitive to dim light
Cones
- 6.5 million cells, concentrated in fovea
- Three photopigments
- Sensitive to bright light
- Greater acuity
Phototransduction
- Neurotransmitter release from rod/cone depends on conformation of pigment
- Pigment:
- Dark: 11-cis-retinal (bent)
- Light: all-trans-retinal (straight)
- Pigment conformation effects conformation of rhodopsin
In the dark…
- Na+ in, K+ out
- Guanylyl cyclase-converts GTP to cyclic GMP
Dark: phototransduction
- Retinal in 11-cis form
- High concentration of cGMP
- Keeps Na+ channels open
- Depolarization of photoreceptor (spreads to synaptic terminal)
- Opens Ca2+ channels in synaptic terminal
- Release of neurotransmitter
Light: phototransduction
- Retinal changes to all-trans form
- Activates transduction
- Activates phosphodiesterase
- Decreases concentration of cGMP
- Na+ channels close
- Photoreceptor hyperpolarizes (spreads to synaptic terminal)
- Ca2+ channels in synaptic terminal close
- Decreased release of neurotransmitter
Visual field
- Can be seen without moving
- Through Optic nerve (CN II)
Optic nerve CN II
Crosses at optic chiasm, to thalamus, visual cortex (also to higher brain=light levels)
Ear Structure
External: collects and funnels sound waves, creates vibrations
Middle: amplifies, transmits vibrations to inner ear
Inner: transduce vibrations into electrical signal (AP)
Pitch (tone):
depends on frequency; same loudness
Intensity (loudness):
depends on amplitude; same note
Pinna:
plays a role in sound localization
Tympanic membrane
vibrates in unison with sound waves
How sound is made:
- Vibrations at oval window make pressure waves in perilymph of scala vestibuli.
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