In relation to other retinal ganglion cells, the M ganglion cells that make up the magnocellular pathway have A. a larger receptive field and a faster-conducting axon. B. a smaller receptive field, a slower-conducting axon, and transient responses. C. a faster-conducting axon, lower spatial resolution, and better color sensitivity. D. finer spatial resolution and better color sensitivity. E. All of the above are true F. Both A and C are true.
QUESTION 24
- In relation to other retinal ganglion cells, the M ganglion cells that make up the magnocellular pathway have
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A. |
a larger receptive field and a faster-conducting axon. |
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B. |
a smaller receptive field, a slower-conducting axon, and transient responses. |
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C. |
a faster-conducting axon, lower spatial resolution, and better color sensitivity. |
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D. |
finer spatial resolution and better color sensitivity. |
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E. |
All of the above are true |
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F. |
Both A and C are true. |
The nervous system in the human body is responsible for controlling all the body parts through transmission of nerve impulses. In humans, the nervous system contains two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The human central nervous system is mainly composed of the brain and the spinal cord. It regulates all the sensory and the motor working aspects of the body parts. The peripheral nervous system contains nerves which are responsible for connection of CNS to every other body part.
The specialized cells which make up the nervous system are the neurons and the glial cell. The neurons have a special ability to get excited via acting potential. The cell to cell communication between the neurons is achieved by the action potential. The glial cells provide nutrition to nerves and are responsible for formation of myelin sheath around axons which acts as an insulator during electrical nerve signal transmission.
The neurons situated at the inner surface of the retina of the eye are called retinal ganglion cells. A retinal ganglion cell is responsible for receiving visual information from the eye through other two types of neuron: bipolar cells and retina amacrine cells. The retinal ganglion cells are responsible for receiving image forming as well as non-image forming visual information from the retina of the eye. This visual information is received in the form of action potential and subsequently transported to thalamus, hypothalamus, and midbrain.
Retinal ganglion cells can be categorized into four types on the basis of their function and projection: M cells, P cells, bistratified cells, and photosensitive ganglion cells.
- M cells are the neurons which project to the magnocellular layers of the lateral geniculate nucleus. Hence, these cells form a part of the magnocellular pathway. Approximately 10% of all retinal ganglion cells are M cells. These neurons have much larger receptive fields, fast conduction velocity in axon, and can respond to low-contrast stimuli. However, they are but are not very sensitive to changes in color.
- P cells are the neurons which project to the parvocellular layers of the lateral geniculate nucleus. Hence, these cells form a part of the parvocellular pathway. Approximately 80% of all retinal ganglion cells are P cells. They have slow conduction velocity in the axon and are receptive to color changes.
- K cells are the neurons which project to the koniocellular layers of the lateral geniculate nucleus. Hence, these cells form a part of the koniocellular pathway. These cells receive inputs from intermediate numbers of rods and cones and have very large receptive fields.
- Photosensitive ganglion cells are the retinal ganglion cells which contain their own photopigment and melanopsin. Therefore, they respond directly to light even in the absence of rods and cones.
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