Human beings have five important senses: Vision Hearing Taste Smell & Touch In addition to touch, the skin contains senses for heat, cold, pain & pressure. Also, Kinesthesis (sense organs in the muscles, tendons & joints tell us about the position of our limbs & state of tension in the muscles) & Vestibular sense inform us about the movement & stationary position of the head. It plays key role in maintaining balance.
Human Eye Fig. 1
Fig. 3 ig. 2 The convex lens of the eye makes an inverted image fall on the retina.
Fig. 4 Fig. 5 Eye ball OPTIC NERVE carries visual information from retina to the brain. The point of exit of optic nerve (BLIND SPOT) has no photoreceptors.
Extraocular Muscles Fig. 6
Eye with schematic enlargement of retina Fig. 7
Retina It is the lightsensitive layer at the back of the eyeball which contains two types of photoreceptors- RODS CONES. & The yellow mark is blind spot. Fig. 8
Retina Vision begins with the electromagnetic radiation that objects emit. The visible spectrum extends from about 380-780 nanometers. Human retina contains about 120 million rods & 6 million cones. Human retina is actually rod-dominated numerically. Rods peak in density in a ring approximately 5mm (18 o ) from the center of the fovea.
To fall on the photoreceptors, light passes between the ganglion cells (M & P cells) and the bipolar neurons. Fig. 9 The bipolar neurons sends the sensory signal back to the ganglion cells.
Fig. 10 which carries the signal to the visual cortex. The axons of the ganglion cells together forms the optic nerve
A photomicrograph of rod and cone cells. Fig. 11
Retina o Pigment epithelium - Supporting cells for the neural portion of the retina (photo-pigment regeneration, blood) it is also dark with melanin which decreases light scatter within the eye. o Bacillary layer - Contains the outer segments and inner segments of the rod and cone photoreceptors. o Outer limiting membrane - o Outer Nuclear Layer (ONL) - Cell bodies of rods & cones. o Outer Plexiform Layer (OPL) rod and cone axons, horizontal cell dendrites, bipolar dendrites o Inner Nuclear Layer (INL) - Nuclei of horizontal, bipolar and amacrine cells o Inner Plexiform Layer (IPL) - Axons of bipolars (and amacrines), dendrites of ganglion cells. o Layer of Ganglion cells (GCL)- Nuclei of the ganglion cells and displaced amacrine cells o Layer of optic nerve fibers - Fibers from ganglion cells traversing the retina to leave the eyeball at the optic disk.
Visual Spectrum ig. 12
Transduction in Vision The rod & cone cells contain photosensitive pigments. Rhodopsin, the pigment in rods, exists in the cis-rhodopsin configuration when not excited. Excitation by light makes it to change to trans-rhodopsin configuration.
Rod photoreceptors and rodconnected nerve cells through the retina are responsible for pathways concerned with night vision and increased sensitivity of our visual system under what is called scotopic conditions (conditions of very little ambient light).
Fig. 13 Convergence of Rod cells The rod bipolar collects input from between 15 and 30 rod spherules in the outer plexiform layer.
Characteristics of Rods & Cones Number Approx. 120 million Approx. 8 million Response Lightness and darkness Lightness, darkness & colours Sensitivity More sensitive to light than cones Less sensitive to light than rods Best Operation Night time, darkness Daytime, bright light Location Not in fovea; Most dense just outside the fovea Neural connection Pooled connection to bipolar neurons Throughout the retina; Most dense in fovea One-to-one connection to bipolar neurons Dark adaptation time About 30 minutes About 10 minutes Light adaptation time About 1 minute About 1 minute
Visual Field & Pathway Fig. 14
Visual Pathway At OPTIC CHIASM some of the optic nerves from each eye cross to the other side of the brain. Fig. 15
Fig. 16 Human Visual Cortex
Frontal Eye Fields: Voluntary eye movement. Visual Sub-system Superoptic Nucleus: Controls daily rhythms (sleep, feeding, etc.) in response to day-night cycles. Pretectum Nucleus: Produces change in pupil size in response to light-intensity changes. Superior Colliculus: Head orientation, particularly to objects in peripheral visual fields. Pineal body: Long-term circadian rhythms. Accessory Optic Nucleus: Moves eye to compensate for head movements. Visual Cortex: Pattern perception, depth perception, colour vision & tracking moving objects.
Major Connections of the Visual System Geniculostriate System: Specialized for Pattern Analysis Eye Lateral Geniculate Nucleus Area 17 Secondary I Secondary II Lateral Posterior-Pulvinar Superior Colliculus Thalamic Complex Tectopulvinar System: Specialized for detection of & orientation to visual stimuli Accessory Optic Nucleus Pretectum Suprachiasmatic Nucleus Tertiary & Paralimbic
fmri of visual activation Fig. 17
Fig. 19 Structure of the Ear Fig. 18
The vibrations travel through the cochlea in the direction indicated by the arrow.
Fig. 20 Fig. 21 The Tympanic Membrane (eardrum) transforms sound into mechanical energy. The audible range lies between 20 20,000 Hertz (1 decible = 50 Hz.).
Fig. 22 Resonance Chamber The oscillation of the eardrum moves the three bones (Malleus, Incus & Stapes: Ossicles). The bones of the middle ear relay vibrations to the inner ear.
Fig. 23 Hearing Mechanism
The inner-ear sense organs are contained in a bony structure, Cochlea. It has three canals: Vestibular canal, Cochlear canal & Tympanic canal. Fig. 24
Oscillation of Stapes presses the oval window. Fig. 25 Waves in the cochlea reach the organ of corti, which lies on the basilar membrane. The organ of corti has numerous receptors- the hair cells.
The pressure of the waves stimulates the hair cells of the organ of corti. Fig. 26 If they bend by as much as 100-trillionth of a meter, the signal is sent through the auditory nerve.
Fig. 27
Fig. 28 Fig. 29 Hair cells Place Code: Nerve impulses arising from a given region of organ of corti are sensed as a particular pitch.
Stimulation of hair cells generate receptor potential as we saw in the second unit (Physiological Processes). Fig. 30
Fig. 31 Audible Range
Fig. 32 Auditory Pathway
Major Connections of the Auditory System Ear Eighth Nerve Cochlear Nucleus Inferior Colliculus Medial Geniculate (Dorsal) Medial Geniculate (Ventral) Area 41 Tertiary & Paralimbic Secondary 42, 22
Fig. 33
Section through Nose Fig. 34 Nasal gland produce odorant binding protein (OBP). The OBP gets sprayed in the tip of the nose when we breathe. The nasal membrane contains receptor cells for the odors. This membrane is called Olfactory Epithelium.
Fig. 35 OBP Operations in the Nose
Fig. 36 Olfactory epithelium has millions of receptor cells. Human nose has thousands of smell receptors. Each receptor specializes in identification of a particular smell. All together, ten thousand odors can be identified with the help of these receptors.
The large number of specific smell receptors (olfactory nerves) carry unique odor signal to the brain. Fig. 37
Fig. 38
Fig. 39 Axons of the olfactory receptors go to the olfactory bulb. Some recoding occurs at this stage. The recoded message then goes to the temporal lobe for conscious awareness. The impulses also go to amygdala & hippocampus where emotion and memory gets involved too.
Odor Recognition Frontal Cortex Motor Cortex Thalamus Limbic System Olfactory Cortex Olfactory Bulb Sniffing Command from the brain Receptors in Nose
Major Connections of the Olfactory System Nose Olfactory bulb Pyriform Cortex Lateral Hypothalamus Dorsal medial thalamus Orbitofrontal Cortex
The tongue has small bumps called Papillae that contain taste buds. The taste buds contain receptor cells that are spread at the tip, sides and back of the tongue. The total number of taste buds in an adult is approximately 10,000. Fig. 40 Tongue
Fig. 41 Sensitivity of the tongue: Tip- Sweet & Salty Back- Bitterness Sides- Sour
The chemical components of the food dissolve in saliva and goes down to the cervices between the papillae. The chemical interaction triggers the adjacent neurons. The impulses travel to the parietal lobe and the limbic system. Only sweet, sour, salty and bitter are detected by the tongue. Rest of the tastes are combinations of the them.
Fig. 42
Impulse Transmission for Taste Fig. 43
Major Connections of the Taste System Insular Taste Area? Ventral Posterior Medial Thalamus Tongue Solitary Tract SI Tongue Area 5,? Pontine Taste Nucleus Lateral Hypothalamus & Amygdala
In addition to 5 basic senses, i.e., vision, hearing, taste, smell & touch, Kinesthesis & Vestibular senses are also there. The visual & auditory systems are known as exteroceptive systems because they are sensitive to stimuli from external environment. The somatosensory exteroceptive function. system also has an
In addition, it is Proprioceptive, i.e., it provides information about the relative position of body segments to one another & the position of the body in space. It is also Interoceptive, i.e., it records internal bodily events.
Sensation - Hands Receptive fields of cortical neurons are smallest on the fingers and become larger on the hand and forearm.
Touch Meissner Corpuscle: Sensitive to pressure sense in hairless region of the body. Basket nerve endings: Sensitive to pressure sense in the roots of hairs. Pacinian Corpuscles: Sensitive to pressure.
Temperature The temperature of skin is usually 32-33º C. The temperature of blood beneath it is about 37 º C. A stimulus of 28-30 º C is definitely felt as cold. A stimulus of 34 º C is definitely felt as warm.
Somatosensory Cortex Fig. 44
Major Connections of the Somatosensory System Fine touch, Pressure & Kinesthesis Gracile & Cuneate Nuclei Ventrobasal Thalamus Area 3b Secondary (3a, 2, 1, 5, SI) Palm via dorsal column via lateral column Ventral basal, pulvinar & Lateral posterior thalamus Pain & Temperature Tertiary & Paralimbic
Sensation Perception is preceded by sensation. Sensation refers to the stimulations one receive from the sense modalities. For a sense modality to receive a stimulation, the stimulus should reach absolute threshold. Absolute Threshold refers to the minimum intensity of stimulus that can be detected fifty percent of the time.
Absolute Threshold of Different Sense Modalities (McBurney & Collings, 1984) Sense Vision Hearing Taste Smell Touch Threshold Candle flame visible from 50 km. on a clear dark night. Tick of a watch from 6 meters in silence. 1 gm. Table salt in 500 liters of water. 1 drop of perfume diffused in a 3-room apartment. A wing of bee falling on cheek from 1 cm. height.
Perception When we attach a meaning to what we have sensed, perception is said to have taken place. Hence, whatever we experience is our perception.
Perception Form Perception is dependent upon recognition of figure from the background. Visual Depth Perception depends on monocular (linear perspective, clearness, interposition, shadow pattern, texture gradients & relative movement) and binocular cues, (especially retinal disparity). Size, shape and brightness constancies play an important role in perception.
Objects (Available Information) Selection Perception (Attention) Modification Sampling Exploration (Activities) Direction Schema (Memory)
Attention Selection of certain inputs and retaining them in the conscious experience. In this process our field of experience is divided into focus and margin.
Fig. 1 www.webvision.med.utah.edu References Fig. 2 www.webvision.med.utah.edu Fig. 4 www.webvision.med.utah.edu Fig. 5 www.webvision.med.utah.edu Fig. 6 www.webvision.med.utah.edu Fig. 7 www.webvision.med.utah.edu Fig. 8 www.webvision.med.utah.edu Fig. 9 Morris, C.G. (1993). Understanding Psychology, 2 nd ed., Fig. 3-2, pp. 83. Fig. 10 Boycott, B.B. & Dowling, J.E. (1969). Organization of the primate retina: light microscopy. Phipos. Trans. R. Soc. Lond. B. Biol. Sci. 255: 109-194. Fig. 11 Morris, C.G. (1993). Understanding Psychology, 2 nd ed., Fig. 3-5, pp. 85. Fig. 12 www.colorado.edu Fig. 13 www.webvision.med.utah.edu Fig. 14 www.driesen.com Fig. 15 www.unn.ac.uk Fig. 16 www.webvision.med.utah.edu Fig. 17 Windhorst, U. & Johansoon, H. (Eds.) (1999). Modern techniques in neuroscience research. Pp. 1055-1082. Springer, Berlin. Fig. 18 http://tonydude.net Fig. 19 http://psych.athabscan.ca Fig. 20 www.meniett.com Fig. 21 www.mcg.edu Fig. 22 www1.omi.tulane.edu Fig. 23 www1.omi.tulane.edu Fig. 24 www1.omi.tulane.edu Fig. 25 www1.omi.tulane.edu
References Fig. 26 Fig. 27 Fig.28 www1.omi.tulane.edu www1.omi.tulane.edu www1.omi.tulane.edu Fig. 29 Morris, C.G. (1993). Understanding Psychology, 2 nd ed., Fig. 3-18, pp. 98. Fig. 30 www1.omi.tulane.edu Fig. 31 Morris, C.G. (1993). Understanding Psychology, 2 nd ed., Fig. 3-16, pp. 96. Fig. 32 http://psych.athabscan.ca Fig. 33 Morris, C.G. (1993). Understanding Psychology, 2 nd ed., Fig. 3-19, pp. 102. Fig. 34 Fig. 35 Fig. 36 Fig. 37 Fig. 38 Fig. 39 Fig. 40 Fig. 41 Fig. 42 Fig. 43 Fig. 44 www.cf.ac.uk www.cf.ac.uk www.cf.ac.uk www.leffingwell.com www.cf.ac.uk www.cf.ac.uk www.cf.ac.uk www.ecit.emory.edu www.cf.ac.uk www.cf.ac.uk www.socsci.uwosh.edu