Sensing the environment

icer215's version from 2016-09-06 21:18


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Sensation Physical, electromagnetic, visual, vestibular, auditory, pain and other information from both the internal and external environments gets detected and translated into electrical signals in nervous system
Receptorsthe peripheral nervous system (PNS) sends the following information to the central nervous system (CNS) as action potentials and neurotransmitters
Sensation’s goalto detect stimuli from the surroundings
Perception’s goalcreate and interpret useful information of the surroundings
ThresholdsThe minimum amount of a stimulus required to cause action potential
Weber’s LawPhysiologist from Germany determined the sensory threshold


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Absolute thresholdThe minimum intensity of a stimulus that one can detect
Difference thresholdThe minimum difference in intensity between two stimuli that one can detect
ΔI/Intensity = kWeber discovered that there is a constant ratio between the change in stimulus to produce a difference threshold and the magnitude of the original stimulus
ΔIDifference in intensities
Iinitial intensity
Kweber fraction/constant = 1/50 = 2%


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Sensory receptorsRespond to stimuli ➙ electrical signals are triggered
Sensory pathwaysNerve endings or sensory cells receive stimulus ➙ carries the information through sensory ganglia ➙ arrives at central nervous system (CNS)
GangliaFound outside the CNS and Groups of neuron cell bodies
Projection areasIn the brain . Analyzes the sensory input
Types of sensory receptorsHair cells, Photoreceptors, Thermo receptors, Mechanoreceptors, Osmoreceptors, Nociceptors, Olfactory receptors, Taste receptors (chemoreceptors)
Hair cellsdetect the movement of fluid in the inner ear structures
Photoreceptorsrespond to electromagnetic waves in the visible spectrum
Thermo receptorsdetect the changes in temperature
Mechanoreceptorsrespond to physical force like pressure and stretch
Osmoreceptorsrespond to osmolarity of the blood
Nociceptorsdetect the painful or noxious stimuli
Olfactory receptorsrespond to volatile compounds
Taste receptors (chemoreceptors)respond to dissolved chemical compounds


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Signal Detection TheoryA theory that emphases on the changes in perception on both internal and external environment in uncertaint
Linked with response biasNonsensory factors that cause systemic response to a stimulus
Biasit is independent of sensitivity
Trials to test this theoryStimulus present vs. stimulus absent. e.g. e. Referred to as “noise”
Respond present vs. respond absent “Yes” to stimulus ➙ “hit”, “No” to stimulus ➙ “miss”, “Yes” to no stimulus ➙ “false alarm”, “No” to no stimulus ➙ “correct rejection”
Sensory AdaptationPhysiological (sensory) and a psychological (perceptual) component that decreases the response with repeated application of stimulus, so our bodies “get used to it”
Causes detection of stimulus to change over timee.g. Hearing, touch, smell, etc.
Allows us to differentiate meaningful information from the backgrounde.g. Unable to feel the clothes are on after dressed. e.g. No longer hearing people outside the house chattering


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ScleraWhite part of the eye, Thick layer, Does not cover cornea
Choroidal vesselsComplex blood vessels that supply nutrients to eyes. Between sclera and the retina
Retinal vesselsAlso provide nutrients to eyes
RetinaHas photoreceptors that translate light into electrical information for brain to process, Innermost layer of the eye, Consists of neutral components and blood vessels, Consists of 6 million cones + 120 million rods
Conesbest absorb bright light
Fovea only has conesvisual acuity, sensitivity to daylight vision
Rodshave a single pigment, rhodopsin, that allows night vision – sensation of light and dark. Not really for details and color vision
Amacrine and horizontal cellsBefore the information gets passed onto ganglion cells, they receive input from many retinal cells. Increase perception
Optic nerveIndirect connection between rods and cones
Bipolar cells connectsrods and cones ➙ synapses with ganglion cells ➙ group together forming optic nerve


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CorneaWhere light first passes through and Focuses on the entering light
Anterior chamberLocated in front of the iris
Posterior chamberLocated in between iris and the lens
IrisColor part of the eye
Composed of two musclesDilator pupillae and Constrictor pupillae
Dilator pupillaeunder sympathetic stimulation opens the pupil
Constrictor pupillaeunder parasympathetic stimulation constricts the pupil
ChoroidContinuous structure of iris along with Ciliary body
Choroid produces aqueous humorWashes frontal eye


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LensLocated behind the iris and Controls the refraction of entering light
Ciliary musclePart of ciliary body, Under Parasympathetic control contracts, As it contracts, pulls suspensory ligaments changing the shape of the lens, which is known as accommodation
Vitreous humorTransparent gel and Supports retina behind the lens
Visual ProcessingVisual pathways in the brain
Visual pathways in the brainPathway for visual information flow from physical anatomical connections between eyes and the brain
Optic chiasmFibers from nasal part of each retina intersects. Carry temporal visual field from each eye. Information goes from optic chiasm ➙ through optic tract to lateral geniculate nucleus (LGN) of the thalamus ➙ visual cortex in the occipital lobe
LGN neuronsrespond to stimulation of one eye only, center-surrounded receptive fields
Some input gets sent to superior colliculusfor controlled response to visual stimuli and reflexive eye movements
Right visual field ➙ projects onto the left half of each eye’s retina ➙ left side of the brain
Left visual field➙ projects onto the right half of each eye’s retina ➙ right side of the brain
Parallel processingSimultaneous analysis and combination of information, Information includes color, shape, depth, and motion, Allows determination of what is being viewed by comparing with stored memories, Correlated with feature detection (neuroscience)


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Feature detectionProcessed by specialized nerve cells in the brain
ColorDetected by cones
Shape3-D geometry of an object, Identify an object of interest from the background, Detected by parvocellular cells
Detected by parvocellular cellsHigh color spatial resolution ➙ can see small details of an object , But, low temporal resolution ➙ only for stationary or slow moving objects
MotionDetected by magnocellular cells
Detected by magnocellular cellsHigh temporal resolution ➙ can see moving objects. But, low spatial resolution ➙ not much detail will be seen (blurry)
Auditory ProcessingAuditory pathways in the brain
Auditory Processing Overview of the pathwaySound information gets received with auditory receptors in the cochlea, Causes synapses of vestibulocochlear nerve, The information is carried to cochlear nucleus, Then to superior olive, Superior olive projects up to the inferior colliculus, And medial geniculate nucleus (MGN) of the thalamus, Lastly, auditory cortex in the temporal lobe (sound processing occurs here) and inferior colliculus (vestibule-ocular reflex)


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Then to superior oliveCompares the difference in timing and loudness of the sound from each ear -> determines the direction of source of sound
Outer earPinna (or auricle)
Pinna (or auricle)Detects sound waves and channel them into the external auditory canal
Tympanic membrane (or eardrum)Extended from the end of the auditory canal, Separates the outer ear from the middle ear, Vibrates in phase with entering sound waves, Frequency of sound = vibration rate of tympanic membrane
Faster rate for high frequency
Slower for lower frequency
Intensity of sound = amplitude of the vibrationLouder the sound, greater the intensity (amplitude)
Middle earOssicles & Eustachian tube
OssiclesSmallest bones in the body. Function to transmit and amplify the vibration from eardrum to inner ear


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Eustachian tubeConnects middle ear to nasal cavity. Balance pressure between middle ear and the environment
Inner earBony labyrinth
Bony labyrinthComprises of cochlea, vestibule, and semicircular canals
CochleaSpiral-shaped cavity, Divided into 3 scalae – same length of cochlea, Middle scalae has hearing apparatus called organ of Corti that has thousands of hair cells
Translates the physical stimulus into an electrical signal and then vestibulocochlear nerve carries the information to CNS
VestibuleContains utricle and saccule, both covered with otoliths. Resists the motion
Senses linear accelerationDetects the orientation in 3D space
Semicircular canalsSenses rotational acceleration. Three of them, perpendicular to each other


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Membranous labyrinthContinuous structure of cochlea, vestibule, and semicircular, Has endolymph, a potassium-rich fluid, Also has perilymph which transmits vibration from the outside and cushions the inner ear structure
Hair CellsIn vertebrates, hair cells are sensory receptors in auditory and vestibular systems, Located within the organ of Corti on the basilar membrane in the cochlea of the inner ear, Epithelial cells, Cylindrical or flask-shaped, Rest on a basal lamina and are joined by tight junctions
Vibration reach the basilar membrane ➙ hair cells move back and forth à causes ion channels to open (K+ and Ca2+ ions enter the cell) ➙ producing receptor potential by depolarizing ➙ brain identifies the pitch of the sound
Damage of hair cellscauses hearing loss
SomatosensationComplex sensation system that includes pressure (mechanoception), position (proprioception), pain (nociception), and temperature (thermoception)
Types of receptors that are involvedFree nerve endings, Thermoreceptors, Meissner corpuscles, Pacinian corpuscles, Merkle disc, Ruffini endings
vestibular systemis associated with balance
Free nerve endingsfor pain and temperature
Thermoreceptorsfor temperatures
Meissner corpusclesfor light touch


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Pacinian corpusclesfor deep pressure and vibration
Merkle discfor deep pressure and texture
Ruffini endingsfor stretch
Stimuli gets sent to CNSto somatosensory cortex in the parietal lobe
Pain perceptionRelies on thresholds and varies by different individuals. Gate theory of pain
Gate theory of painMechanism that turns pain signals on or off, Involves spinal cord forwarding stimuli from variety of touch modalities like pressure and temperature to the brain, If non painful stimuli is detected ➙ “gate” closes ➙ no pain sensation gets sent to CNS
Taste buds/chemoreceptorsthat detect specific chemicals
Basic tastesSweet, sour, salty, bitter and savory (unami). Flavor is a more complex combination of taste and other sensation like mood, texture, smell, and color that affect the perception of food
ChemoreceptorsDetects dissolved compounds, Sodium ➙ alkali metals reaction = salty taste, Acidic reaction = sour taste, Receptors found in taste buds are found in papillae on the tongue


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Taste informationfrom the taste buds ➙ gets sent to brainstem ➙ and to thalamus’s taste center ➙ which signals to other parts in the brain
SmellOlfactory cells/chemoreceptors that detect specific chemicals
Olfactory chemoreceptors (olfactory nerves)Another sensory receptor that causes action potential by receiving chemical stimuli in the environment. Located in olfactory epithelium. Able to recognize differences between similar scents
PheromonesEffects on humans, Effects on animals for social and sexual behaviors, Once secreted and bounded with chemoreceptors they compel specific behaviors from others
Olfactory pathways in the brainOdor chemical molecules are inhaled into nasal passages ➙ reach olfactory nerves in the olfactory epithelium ➙ activate receptors cells ➙ olfactory bulb receives the signals ➙ sends information through olfactory tract to the brain (and limbic system)
Kinesthetic SenseAlso known as proprioception and Senses the body’s position in space(motion)
Senses the body’s position in spaceHand-eye coordination, Balance, Mobility
Receptors are located in muscle, ligaments, and jointsStretch receptors
Applicationse.g. Sobriety test- To test alcohol intoxication. Will fail to touch his/her nose with eyes close for those who are drunk