Human Senses

BY : DR. ANWAR

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Human information system is quite sequential.

  Input Processed, Analyzed and decision output Input (Vision, Hearing, Smell, Taste, Skin) Afferent parts of Peripheral nervous system Output (muscles activity or organ activity) Efferent parts of peripheral nervous system.  Our body and computer are both machines but the difference is that computer is a machine which is abstract and mechanical, whereas our body is personal and have continual judging and feeling effects. 

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CPU in human body is Brain. It has two halves, Right and Left. Each has:  Fore Brain front 1/3  Mid Brain

mid 1/3  Hind Brain Back 1/3 

Anatomically = 4 parts 

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Cerebrum – concerned with voluntary neuromuscular activity.(Thinking, memory, hearing, consciousness, emotions) Basal Ganglia – semi voluntary (automatic movements of arms, while walking) Cerebellum – balance , Posture Medulla – Active control of Organs, for example Heart , Lungs

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Brain is made up of pulpy matter. Its outer half (Cortex), is thrown into heights called Sulci, and depth is called Gyri Brain is protected by the skull. 12 pairs of cranial nerves come out through small hole at the base of the skull. These control vision, eye movement, face muscles, smell, hearing, face sensation, tongue. Vision, eye movement2,3,4,6th Nerves Face muscles 7th Nerve Smell 1st Nerve Hearing 8th Nerve Face sensation 5th Nerve Tongue 9th Nerve

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Spinal cord is the continuation of brain stem, through a big hole at the bottom of the skull, “Foramen magnum”.Spinal nerves come out from sides of vertebral column. Mixed nerves, that is they carry both sensory & motor sensation from different parts of body. Each nerve supplies well defined area of skin, called Dermatome.

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Body Sensor:

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Information is received form a. Interior of body -Interoceptor b. Exterior -Exteroceptor   Interoceptor   1. Muscle spindle -Nerve filament wrapped Around muscle fibers Detect Stretch of muscle   2. Golgi Organs -attached with tendous Report (strength of) contraction of muscle   3. Ruffni Organs -With capsules of joints -Reports position of joints   4. Vestibulum -In the internal ear (Ear) Position of head in space & report sudden change in its attitude   5. Visceroceptor Internal organs -Reports pain, burning sensation and pressure

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External Receptor Gives information about interaction of body with outside a. Vision (Sight) Retina b. Hearing (Auditory) Inner Ear c. Taste (Gustation) Tongue d. Smell (Olfactory) Nose e. Touch (Taction) Skin Free nerve ending (Messiner Corpuscle-PaccinianCorpuscle) Temp are sensitive to Touch , Pressure & Determine direction & Pain strength of muscle activity. Vibration   Information  Sensory pathway  Brain (CNS) (Afferent pathway of Peripheral Nervous System)

 

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Brain Signals perceived in Context with the to Information stored  action decided organs/ glands (including no action) PNS)

Appropriate Action through motor pathway (effect or (efferent pathway of

Important thing is that nerve pathways from these nerve endings interconnect so freely that the sensations reported are not specific for that modality e.g. very hot or very cold sensation are associated with pain as well. Different technical devices are used to detect electrical activities of internal organs e.g. ECG to detect electrical activity in the heart EEG to detect electrical activity in the brain EMG to detect electrical activity in the muscles

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Human Senses Classical

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  Non Classical to electricity , pain, posture, motion   Body Sensors Receptors (act as converter) coverts the sensory pulses to electro-chem impulses  Brain   Brain (Stored Memory) information received, analysed and appropriate action (including no action)

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Vision Smelling Hearing Taste Taction

Appropiate action ordered to Target group of muscles or organs   Sensory threshold Minimal limits beyond which Maximal sensor do not react or Respond any more   Vision Wavelength (380-720 nm) Visible spectrum of light. Hearing (16000-20000 Hz)

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Retina- rods and cones These nerve cells convert light to electrical signals. They have pigments. Rods respond to low intensity light___ black, white and gray Cones respond to coloured bright___ mostly blue, green and red. Cones are concentrated at fovea, in the center of retina directly behind the pupil. The fovea along with it yellowish surrounding, the macula, is mostly needed for reading fine points.

Visual field: 

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An area measured in degrees, which can be seen by fixated eye in front. In each eye visual eye is limited Internally by - bridge of nose Above orbital bridge o 55 Below - cheek Externally ranges is > 90 Accommodation Action of focusing targets at various distances and when one moves from light to dark surroundings. Near point = point which can be focused at closet distance Far Point = point which can be focused at farthest distance.

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Some Important aspects: 1. Target at or near reading distance should be below eye level. 2. Low optical quality objects are difficult to be seen when eyes are fatigued or the person is under influence of drug. 3. Resting distance of accommodation (Dark Focus or Dark Vergence). Eye strains occur, when someone tries to focus at a target that is different from his minimal refractive state. This distance is different for different people, but constant for same person. -Myopic (near sightness) -can see near object better, difficult to see far objects, improves with age. -Hyperopic -can see far object clearly, cannot see near objects clearly, and deteriorate with age. -Astigmatism -Cornea is not uniformly curve, so light rays are not uniformly refracted on the retina. -Night blindness -vision is less than normal vision in dim light. -Color Weakness -can see all color but confuses especially in low illumination.

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Visual Stimuli

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Human eye can see from a range of 380-720nm.(i.e violet to red) Night vision capabilities deteriorate with decreasing O2 level -At 1300 m. altitude, it decreases by 5% -At 2000m. altitude, it decreases by 20% Heavy Smoker – upto 40% Amblyopia – sudden blindness may occur in heavy smokers. Adaptation from light to darkness take about 30 minutes. First, the cones are sensitive, then the rods. Even after adaptation, the sensitivity at forea(cones) is only 1/1000 that at periphery of Retina (Rod). Therefore, lights can be noticed at periphery of field of vision, but not of one direct gaze at them, when they are refracted at fovea. Adaptation from dark to light is quite fast with in few minutes.

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Visual Cavity:

Measurement is checked at a far point, 6 meter away  Measurement is made at near point, 0.4 meter.  Snellen Chart  Black Stumuli (letter) against contrasting white background.  Perfect Vision 20/20 6/6 At a distance of 6 meter, a person can read the 6th line from above on the Chart.  6/36 means, he can see the object at 6 meters, which others can at 36 meters  Legally Blind - if vision in the better eye, after correction is < 20/200. 

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External ear Middle ear Inner ear External Ear: Pinna and Auricle---- collects direct and augment sound waves onto Tympanic membrane (Eardrum). Sound is increased by 10-15 dB.   Middle Ear: Contains three bony ossicles Malleus Incus Stapes By a leverage action, they transmit the sound waves from eardrum to oval window in cochlea. The sound is increased by 25 dB. Middle ear is connected to back of nasal cavity by a channels (Eustachian Tube), which keep the middle ear at atmospheric pressure. Inner Ear: Has cochlea and semi circular canal. It is concerned with hearing and positioning of head in space. It has two parts 1. Auditory portion, 2. Vestibular. Vestibular System: respond to magnitude and direction of acceleration and gravity. Semicircular canals are sensitive to rotation of Head. Each canal function independently in spite that they share a common cavity at utricle. Each canal near its junction with utricle has widening (ampula), which contains a ridge, crista ampularis. This crista has sensory hair cells, which move with movement of Endolymph.

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Auditory Portion: Cochlea, makes 2-1/2 turns, has endolymph. Sound waves from ear drum conducted to oval window are transmitted into fluid waves. This fluid displacements deflect Basement members Sensory hair cells in organ of Corti on the membrane Transformed impules are transmitted along auditory nerves to brain.

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Therefore Soundwaves fluid waves(endolymph)

       

T.M

Sensory hair cell(organ of Corti)

Brain.

oval window

changed to

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Human hearing range Infants 16- 20000 Hz Old < 12000 Hz.   Air conduction better than bone conduction. Moving from atmospheric to non atmospheric and, Moving from gravity to non gravity as in space, or in water, changes the characters of sound transmission.   Imp: Velocity of sound in solid, liquid, and gases are different.   Music: Acoustic phenomenon, pleasant to the ear.   Noise: Unpleasant to ear Noise induced Hearing loss. (N.I.H.L) Noise can cause ---Temporary or permanent hearing loss. High intensity sound, whether one considers it pleasant but loud can cause permanent damage hearing ability. Short duration of high intensity sound, e.g., canon fire/ Bomb blast can damage any part of ear, but especially organ of Corti, which may be torn apart, which causes to severe , permanent hearing loss. Persistent noise of power tools, chain, saws, aero planes, automobiles, and music heard through loud speaker, concerts, or head phones, can cause hearing loss.