Difference Between Rod Cells And Cone Cells [Notes & PDF]

What Are Rods/Rod Cells?

Rod cells are photoreceptor cells in the retina of the eye that function in less intense light conditions, they do not perceive color and fine details, a function performed by the other major type  of light-sensitive cell, the cone cell.  Rod cells are more sensitive to light and are almost entirely responsible for the night vision.

Rods can be described as specialized neurons that convert visual stimuli in the form of photons (particle of light) into chemical and electrical stimuli that can be interpreted by the central nervous system (CNS). Rods are often concentrated at the outer edges of the retina and are used in peripheral vision. Rod cells are stimulated by light over a wide range of intensities and are responsible for perceiving the size, shape and brightness of visual images. On average, the human retina contains approximately 120 million rods.

Rod cells have an elongated structure and consist of four distinct regions: The outer region, an inner segment, the cell body and the synaptic region.

• The outer region (contains phototransduction apparatus and a series of closely packed membrane disks that contain the photoreceptor molecule (rhodopsin).
• The synaptic region ( this is where the rod cell relays its information to intermediate neurons in the retina).
• Cell body (where neurons connect with ganglion neurons).

What You need To Know About Rods/ Rod Cells

1. Rods are a road-shaped, light-sensitive cell which lies on most peripheral parts of the retina in the vertebrate eye. Rods are located in the periphery of the retina.
2. Rod cells are cylindrical and comparatively longer than cone cells.
3. Rod cells help in scoptic vision (low light vision) and night vision.
4. The outer segments of rod cells contain rhodopsin as the visual pigment. Insufficiency of the rhodopsin causes night blindness.
5. Not less than 100 million rod cells are present in the retina of the human eye.
6. Rods contain more pigments. Consequently, they require light to detect images.
7. Rods are sensitive to both scattered and direct light.
8. Loss of rod cells results to night blindness.
9. In human eye, only a single type of rod cell is present.
10. The stacks of the membrane-enclosed disks are not attached directly to the rods.
11. Inner end of rods has a small knob.
12. Rods are arranged in functional units served by one bipolar neuron, hence provide less visual acuity.
13. Rod cells have very rapid regenerative power.
14. There is only one type of visual pigment present in rod cells.
15. Rod cells can be triggered even by a single photon of light.

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What Are Cones/Cone Cells?

Cone cells are photoreceptor cells in the retina of the eye which are responsible for color vision as well as color sensitivity. They work well in relatively bright light as opposed to rod cells that work best in dim light. Cone cells are also able to perceive finer details and more rapid changes in images because their response time to stimuli is faster than that of rods.

Cone cells are somehow shorter than rods, but wider and tapered and are much less numerous than rods in most part of the retina, but greatly outnumber rods in the fovea. Just like rods, every cone has a synaptic terminal, an inner segment and an outer segment as well as an interior nucleus and various mitochondria. The chemical changes that occur when light strikes the cones are ultimately relayed as impulses to optic-nerve fibres that enter the brain. The type of vision gained by cones is referred to as photopic vision.

On average, the human retina contains approximately 6 million cones. The cones contain pigments referred to as iodopsin, which is the violet colored pigment. The pigments are sensitive to the wavelength of approximately 420 nm, 534 nm and 563 nm and the sensitivity may rise to provide vision over the visible spectrum. Deficiency of the cones in the human eye may result to colorblindness and a person may be unable to distinguish among various colors.

What You Need To Know About Cones/Cone Cells

1. Cones are a type of photoreceptor in the retina which is responsible for the color vision at the daylight. They are located at the central part (fovea) of the retina.
2. Cone cells are comparatively shorter than rod cells.
3. Cone cells help in photopic vision (high light vision) daylight vision.
4. The outer segment of cones cell contain iodopsin as the visual pigment. Insufficiency of the iodopsin causes color blindness.
5. Averagely, about 6 million cone cells are present in the retina of human eye.
6. Cones contain lesser pigments than rods. Consequently, they require more light to detect images.
7. Cones are sensitive only to direct light.
8. Loss of cone cells result to legal blindness.
9. In human eye, three distinct types of cone cells are present based on their pattern of response to direct wavelength of light.
10. The disks are attached to the outer membrane.
11. The inner end of cones is branched.
12. Each cone is served by its own bipolar neuron, hence provide high visual acuity.
13. The cone cells have a very less regenerative power.
14. Three different distinct types of visual pigments are present in cone cells.
15. Cone cells requires large number of protons to be triggered.

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Difference Between Rods And Cones In Tabular Form

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What Are Some Of The Similarities Between Rods And Cones?

• In the retina, both rods and cones are photoreceptor cells.
• Both rods and cones contain visual pigments.
• The outer segment of both cells has membrane stacks that contain light absorbing pigments.
• Both rods and cone cells are modified nerve cells.
• Both cones and rods are triggered by photon.
• Both cells can be classified as types of secondary exteroreceptor cells.
• Cones and rods synapse have bipolar cells.