Date post: | 24-May-2015 |
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BY Muhammad Ramzan Ul Rehman Nistar ken 1
BY Muhammad Ramzan Ul Rehman Nistar ken
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PHYSIOLOGY OF EYE
BY Muhammad Ramzan Ul Rehman Nistar ken 3
NEURAL CIRCUITRY OF THE RETINA
BY Muhammad Ramzan Ul Rehman Nistar ken 4
NEURAL CIRCUITRY OF THE RETINA 1. The photoreceptors
themselves—the rods and cones—which transmit signals to the outer plexiform layer, where they synapse with bipolar cells and horizontal cells
BY Muhammad Ramzan Ul Rehman Nistar ken 5
NEURAL CIRCUITRY OF THE RETINA 2. The horizontal cells, which
transmit signals horizontally in the outer plexiform layer from the rods and cones to bipolar cells
BY Muhammad Ramzan Ul Rehman Nistar ken 6
NEURAL CIRCUITRY OF THE RETINA 3. The bipolar cells, which
transmit signals vertically from the rods, cones, and horizontal cells to the inner plexiform layer, where they synapse with ganglion cells and amacrine cells
BY Muhammad Ramzan Ul Rehman Nistar ken 7
NEURAL CIRCUITRY OF THE RETINA 4. The amacrine cells, which
transmit signals in two directions, either directly from bipolar cells to ganglion cells or horizontally within the inner plexiform layer from axons of the bipolar cells to dendrites of the ganglion cells or to other amacrine cells
BY Muhammad Ramzan Ul Rehman Nistar ken 8
NEURAL CIRCUITRY OF THE RETINA 5. The ganglion cells, which
transmit output signals from the retina through the optic nerve into the brain
BY Muhammad Ramzan Ul Rehman Nistar ken 9
THE VISUAL PATHWAY FROM THE CONES TO THE GANGLION CELLS FUNCTIONSDIFFERENTLY FROM THE ROD PATHWAY.
BY Muhammad Ramzan Ul Rehman Nistar ken 10
NEUROTRANSMITTERS RELEASED BY RETINAL NEURONS both the rods and the cones release glutamate at their synapses with the
bipolar cells. ***
amacrine cells secrete at least eight types of transmitter substances, including gamma-aminobutyric acid, glycine, dopamine, acetylcholine, and indolamine, all of which normally function as inhibitory transmitters.
The transmitters of the bipolar, horizontal, and interplexiform cells are unclear, but at least some of the horizontal cells release inhibitory transmitters.
BY Muhammad Ramzan Ul Rehman Nistar ken 11
TRANSMISSION OF MOST SIGNALS OCCURS IN THE RETINAL NEURONS BY ELECTROTONIC CONDUCTION, NOT BY ACTION POTENTIALS
BY Muhammad Ramzan Ul Rehman Nistar ken 12
LATERAL INHIBITION TO ENHANCE VISUAL CONTRAST—FUNCTION OF THE HORIZONTAL CELLS
BY Muhammad Ramzan Ul Rehman Nistar ken 13
LATERAL INHIBITION TO ENHANCE VISUAL CONTRAST—FUNCTION OF THE HORIZONTAL CELLS
BY Muhammad Ramzan Ul Rehman Nistar ken 14
EXCITATION OF SOME BIPOLAR CELLS ANDINHIBITION OF OTHERS—THE DEPOLARIZINGAND HYPERPOLARIZING BIPOLAR CELLS
BY Muhammad Ramzan Ul Rehman Nistar ken 15
EXCITATION OF SOME BIPOLAR CELLS ANDINHIBITION OF OTHERS—THE DEPOLARIZINGAND HYPERPOLARIZING BIPOLAR CELLS
There are two possible explanations for this difference. 1. One explanation is that the two bipolar cells are of entirely different types—
one responding by depolarizing in response to the glutamate neurotransmitter released by the rods and cones, and the other responding by hyperpolarizing.
2. The other possibility is that one of the bipolar cells receives direct excitation from the rods and cones, whereas the other receives its signal indirectly through a horizontal cell.
BY Muhammad Ramzan Ul Rehman Nistar ken 16
AMACRINE CELLS AND THEIR FUNCTIONS
BY Muhammad Ramzan Ul Rehman Nistar ken 17
FUNCTION OF AMACRINE CELLS About 30 different types Some involved in the direct pathway from rods to bipolar to amacrine to ganglion cells
Some amacrine cells respond strongly to the onset of the visual signal, some to the extinguishment of the signal
Some respond to movement of the light signal across the retina
Amacrine cells are a type of interneuron that aid in the beginning of visual signal analysis.
BY Muhammad Ramzan Ul Rehman Nistar ken 18
RODS, CONES AND GANGLION CELLSEach retina has 100 million rods and 3 million cones and 1.6 million ganglion cells.
60 rods and 2 cones for each ganglion cellAt the central fovea there are no rods and the ratio of cones to ganglion cells is 1:1.
May explain the high degree of visual acuity in the central retina
BY Muhammad Ramzan Ul Rehman Nistar ken 19
THREE TYPES OF GANGLION CELLS W cells (40%) receive most of their excitation from
rod cells. Large receptive field sensitive to directional movement in the visual field they are probably important for much of our crude rod vision under
dark conditions
X cells (55%) small receptive field, discrete retinal locations, may be responsible for the transmission of the visual image itself, always receives input from at least one cone, may be responsible for color transmission.
Y cells (5%) large receptive field respond to instantaneous changes in the visual field.
BY Muhammad Ramzan Ul Rehman Nistar ken 20
NEURAL ORGANIZATION OF THE RETINA
Direction of light Figure 50-11; Guyton & Hall
X cells ?W cells ?
BY Muhammad Ramzan Ul Rehman Nistar ken 21
EXCITATION OF GANGLION CELLSspontaneously active with continuous
action potentials (basic 5-40 AP per sec)
visual signals are superimposed on this background
many excited by changes in light intensity
respond to contrast borders, this is the way the pattern of the scene is transmitted to the brain
BY Muhammad Ramzan Ul Rehman Nistar ken 22
BY Muhammad Ramzan Ul Rehman Nistar ken 23
BY Muhammad Ramzan Ul Rehman Nistar ken 24
TRANSMISSION OF COLOR SIGNALS BY THEGANGLION CELLS
BY Muhammad Ramzan Ul Rehman Nistar ken 25
PROCESSING IN THE VISUAL CORTEX
separation of the signals from the two eyes is lost in the primary visual cortex
signals from one eye enter every other column, alternating with signals from the other eye
allows the cortex to decipher whether the two signals match
BY Muhammad Ramzan Ul Rehman Nistar ken 26
Connections in theVisual Cortex
In primary cortex Blobs receive lateral signals from adjacent columns respond to color vision
In secondary cortex color blobs Decipher higher meaning of color
BY Muhammad Ramzan Ul Rehman Nistar ken 27
ANALYSIS OF THE VISUAL IMAGEThe visual signal in the primary visual
cortex is concerned mainly with contrasts in the visual scene.
The greater the sharpness of the contrast, the greater the degree of stimulation.
Also detects the direction of orientation of each line and border. for each orientation of a line, a specific neuronal cell is stimulated.
BY Muhammad Ramzan Ul Rehman Nistar ken 28
VISUAL PERCEPTION IS A CREATIVE PROCESS
How the brain actually perceives a visual image is not understood well.
Visual perception is thought to be mediated by three parallel pathways–the process information on motion, depth and form, and color.
BY Muhammad Ramzan Ul Rehman Nistar ken
29 THANK YOU
By Muhammad Ramzan Ul Rehman