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Questions and Answers
What is the molecule that interacts with light in visual pigments composed of a protein like rhodopsin or conopsin?
Chromophore
What type of cells are important for recycling retinal in rods and cones?
What is the distance between the lens and the retina called?
Focal length
The eye is mainly designed for near-sightedness.
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Match the following cells with their functions:
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What is the function of Vestibulo-ocular movements?
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What are the types of neurons in the visual cortex based on their response to light beam orientation in the retina?
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Perceptive agnosia refers to the inability to identify objects.
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____ pathway is involved in movement, spatial recognition, object localization, including Depth.
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Match the following types of agnosia with their definitions:
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Study Notes
Vision
- Vision involves the interaction of specific molecules with electromagnetic waves, and humans can only interact with a limited range of wavelengths (visible light spectrum).
Anatomy of the Eye
- The eye has different chambers and phases, and is highly mobile with three pairs of ocular muscles.
- Light must cross different structures to reach the retina, and the fovea is the point of maximal visual acuity.
- The pigmented epithelium absorbs light, and the dioptric power of the eye is measured in diopters.
Chromatic Vision
- Rods are achromatic (black and white), while cones are chromatic (color).
- Visual transduction is mediated by G-protein coupled receptors (GPCRs).
- The visual pigment is composed of a protein (rhodopsin/conopsin) associated with a chromophore (11-cis retinal), which interacts with light.
Signal Transduction
- Light induces changes in the visual pigment, leading to the activation of Gα and the closure of cGMP-gated channels.
- The Gβγ complex is important for signal amplification.
- The signal is terminated by the recovery of the chromophore, which requires the participation of the pigmented epithelium.
Photoreceptor Signaling
- In darkness, photoreceptors are depolarized due to the opening of cationic channels, and hyperpolarization occurs in the light due to the closure of cGMP-gated channels.
- Receptor deactivation involves rhodopsin phosphorylation, binding to arresting, and reduced calcium entry.
Retinal Processing
- Cones are concentrated in the fovea, allowing for maximal spatial discrimination (visual acuity).
- The retina has a complex organization, with different types of photoreceptors, bipolar cells, and ganglion cells.
ON and OFF Pathways
- ON and OFF axons are classified based on their response to light, and the concept is founded on the recording of ganglionar cell axons.
- The ON pathway is responsible for the transmission of visual information, while the OFF pathway is involved in the suppression of non-essential information.
Retinal Circuits
- Rod circuitry is phylogenetically more recent than cones, and cones have different types of bipolar cells.
- There are multiple circuits carrying specific information of different aspects of images to the CNS.
Visual Processing in the CNS
- Conscious information is relayed through the lateral geniculate nucleus (LGN) and then to the primary visual cortex (occipital cortex).
- There are different types of ganglionar cells, including P and M cells, which project to different layers of the LGN.
Visual Retinal Sensing
- Melanopsin-expressing ganglionar cells are sensitive to light intensity, and project to different CNS areas involved in circadian rhythms, pupillary reflex, and other responses.
Eye Movements and Accommodation
- Eye movements seek to focus the image on the retina despite object or head movements, and involve saccadic, smooth pursuit, and focusing movements.
Visual Cortex
- The visual cortex is organized in functional columns, with blobs for color information processing and layer IV divided into α and β layers.
- Visual processing becomes progressively more complex, with two main pathways: dorsal (WHERE) and ventral (WHAT).
Face and Object Recognition
- Face-recognizing neurons in primates are highly selective, and respond to complex images such as faces and objects.
- The ventral pathway is involved in object and face recognition, while the dorsal pathway is involved in movement and spatial recognition.
Tridimensional Perception
- Tridimensional perception is based on monocular vision, with cues such as prior knowledge of object size, occlusion, and convergence of parallel lines.
- Near sight tridimensional perception is also based on binocular (stereoscopic) vision.
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Description
Learn about the biology of vision, including the interaction of molecules with electromagnetic waves and the anatomy of the eye.
