Visual System Physiology Flashcards
Direct targets of the retina: Superior colliculus
- Connects w/ tectospinal tract to send projections to cervical anterior horn cells (moves neck)
- Creates map of visual space to activate appropriate motor responses required to move eyes into intended position w/in orbits
- Specifies movement INTENTION rather than fixation of movement upon a target
Direct targets of the retina: Pretectum
-Pupillary light reflex: sends projections to Edinger-Westphal then on to ciliary ganglion –> pupillary constriction to light
Direct targets of the retina: Hypothalamus
- Small number of fibers branch off optic tract to form the retinohypothalamic tract and terminate in supraoptic, suprachiasmatic and paraventricular nuclei of hypothalamus
- Visual input to hypothalamus drives light-dark entrainment of neuroendocrine function and other circadian rhtyhms
Direct targets of the retina: Accessory optic nuclei
-Advanced visual processing, optokinetic nystagmus in response to prolonged large field motion
Direct targets of the retina: Lateral geniculate body/nucleus
- Controls motions of eyes to converge on point of interest
- Control focus of eyes based on distance
- Determine relative position of objects to map them in space
- Detect movement relative to an object by examining field around it
Function of V1 (primary visual cortex)
- Identify edges and contours of objects
- Decodes visual input to redirect info to other visual areas
Function of V2 (extrastriate cortex)
-Analyzes disparities b/w eyes to detect depth perception
Function of V3a
-Identification of motion (Is motion happening? Yes or no?)
Function of V4
- Complete processing of color inputs
- Lesions here cause achromatopsia in which color is faded/dull but can still see some color b/c color processing also occurs in V1 and retina
Function of Medial Temporal/V5
-Tracks motion across a scene in terms of directionality and context of background and foreground by containing neurons that selectively respond to direction of a moving edge (e.g. tracking a ball traveling through the air)
Melanopsin ganglion (MG) cells
- Directly sense light due to expression of blue-wavelength sensitive melanopsin which provides information for regulation of circadian rhythm
- Non-image forming light-responsive system
- MG cells project directly to hypothalamic suprachiasmatic nucleus (neuroendocrine effector in pineal gland which produces melatonin in rhythmic pattern)
- Blue light suppresses our body’s release of melatonin to keep us awake during the day by stimulating cognition and increasing alertness
Dorsal pathway from visual cortex
- Primary path associating vision w/ movement and completes motor acts based on visual input (“The WHERE pathway”)
- Arises from primary visual cortex and projects to parietal/frontal cortex (V1 –> V2,V3 –> V5/MT –> parietal lobe)
Ventral pathway from visual cortex
- Primarily involved in interpreting images (recognizing or copying shapes, forms, faces) and complex patterns (“The WHAT pathway”)
- Arises from primary visual cortex and projects to the inferior temporal cortex (V1 –> V2 –> V4 –> Inferior temporal lobe)
Where do the density of the rods and cones peak?
- Cones @ fovea
- Rods @ eccentricity of ~20 degree from fovea
How does glutamate act as an inhibitory NT when binding to bipolar cells?
-Glutamate binds the receptor mGluR6 which is a GPCR that CLOSES cGMP-gated Na+ channels
