The key difference between bipolar cells and ganglion cells is that bipolar cells are interneurons present in the second layer of the retina which transform visual information from photoreceptors to ganglion cells while ganglion cells are retinal ganglion neurons in the third layer of the retina that carry the nerve impulses from bipolar cells to the first visual relay in the brain.
The retina is a thin layer of tissue located at the back of the eyeball. It is a light-sensitive layer. Hence, it captures light and sends signals to the brain. It is a nervous tissue composed of several layers. Nerve cells of retina receive and organize visual information. In fact, cells in the retina convert light energy into nerve impulses. Neurons in the retina are arranged in three layers. In the primary layer, there are photoreceptor cells. In the second layer, there are bipolar cells. In the third layer, ganglion cells are present. Within the retina, information travel from photoreceptors to bipolar cells to ganglion cells. Then ganglion cells transmit nerve impulses to the brain in order to create a visual image. These three neuron layers are separated by two intermediate layers.
CONTENTS
1. Overview and Key Difference
2. What are Bipolar Cells
3. What are Ganglion Cells
4. Similarities Between Bipolar Cells and Ganglion Cells
5. Side by Side Comparison – Bipolar Cells vs Ganglion Cells in Tabular Form
6. Summary
What are Bipolar Cells?
Bipolar cells are a type of nerve cells in the retina. They are interneurons which transfer visual information from photoreceptor cells in the deepest layer to ganglion cells in the third layer. Structurally, bipolar cells have a cell body that lies within the inner nuclear layer. Primary dendrites of bipolar cell extend to the outer plexiform layer. An axon of bipolar cell extends to the inner plexiform layer. There are multiple subtypes of bipolar cells that differ in their morphology, synaptic connectivity and response properties.
Figure 01: Bipolar Cells
Bipolar cells are not only present in the retina. They are also found in the vestibular nerve, spinal ganglia and cerebral cortex. Bipolar cells communicate via graded potential rather than action potentials.
What are Ganglion Cells?
Ganglion cells are a type of nerve cells found in the third layer or innermost layer of the retina. These cells receive signals from bipolar cells and retina amacrine cells. Then the ganglion cells transmit the visual information in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain.
Figure 02: Ganglion Cells
In our retina, there are about 0.7 to 1.5 million retinal ganglion cells. Basically, there are three classes of retinal ganglion cells in the human retina. They are W-ganglion, X-ganglion and Y-ganglion.
What are the Similarities Between Bipolar Cells and Ganglion Cells?
- Bipolar cells and ganglion cells are two types of nerve cells in the retina.
- Bipolar cells transfer visual information to ganglion cells in the retina.
- Signals must pass through the bipolar cells to reach the ganglion cells.
- Because of bipolar cells and ganglion cells, we are able to see things from our eyes.
- They are separated by an intermediate layer.
What is the Difference Between Bipolar Cells and Ganglion Cells?
Bipolar cells are nerve cells found in the second layer of the retina, while ganglion cells are the nerve cells found in the third or the innermost layer of the retina. So, this is the key difference between bipolar cells and ganglion cells. Functionally, the bipolar cells send signals from photoreceptors to ganglion cells, while the ganglion cells send information from bipolar cells to the brain. Moreover, bipolar cells send information in the form of gradient potential, while ganglion cells send information in the form of an action potential.
Below infographic shows more details of the difference between bipolar cells and ganglion cells as a side by side comparison.
Summary – Bipolar Cells vs Ganglion Cells
In the retina of the human eye, photoreceptors which are in the deepest layer respond to the light first. Then photoreceptors send signals to bipolar cells, which are the second nerve cells in the retina. Bipolar cells connect to the innermost layer of neurons, which are the ganglion cells. Hence, ganglion cells receive information from bipolar cells and send them to the brain. Bipolar cells transmit signals in the form of gradient potential, while ganglion cells transmit signals in the form of an action potential. Thus, this summarizes the difference between bipolar cells and ganglion cells.
Reference:
1. Euler, Thomas, et al. “Retinal Bipolar Cells: Elementary Building Blocks of Vision.” Nature News, Nature Publishing Group, 18 July 2014, Available here.
2. “Ganglion Cell Physiology by Ralph Nelson.” Webvision, Available here.
Image Courtesy:
1. “Retina-diagram” By Fig_retine.png: Ramón y Cajalderivative work Fig retine bended.png: Anka Friedrich (talk)derivative work: vectorisation by chris 論 – Fig_retine.pngFig retine bended.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Gray882” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body. Bartleby.com: Gray's Anatomy, Plate 882 (Public Domain) via Commons Wikimedia