Y2 s1 sensory system final
Transcript of Y2 s1 sensory system final
![Page 1: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/1.jpg)
How brain receives information
Prof. Vajira Weerasinghe
Dept of Physiology
www.slideshare.net/vajira54
![Page 2: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/2.jpg)
Sensory functions
• Humans do not have receptor for every possible stimuli
• There are different sensory modalities that human brain can perceive
• Arrival of information is sensation
• Awareness of a sensation is perception
![Page 3: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/3.jpg)
Sensory Functions
• General SensationsPhysical (touch, pressure, vibration, stretch)TemperaturePain Chemical
• Special SensationsVisionHearingTasteSmell
![Page 4: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/4.jpg)
Modality specificity
• stimulation of a receptor usually produces only one sensationmodality specific
• But some receptors are stimulated by more than one sensory modality (polymodal)eg. free nerve endings
![Page 5: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/5.jpg)
Sensory pathway
• Once a receptor is stimulated
• impulse travels through a particular pathway
• known as sensory pathway or ascending pathway
• up to the brain
![Page 6: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/6.jpg)
Receptor
Sensory modality
Sensory nerve
Central Connections
Ascending Sensory pathway
Sensory area in the brain
Touch stimulus
AFFERENT
Sensory pathway
![Page 7: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/7.jpg)
Receptors
• Receptor cells are specific cells that are sensitive to different forms of energy from the environment
• These cells contain membrane receptors coupled to ion channels
• They transform the stimulus into electrical signals
![Page 8: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/8.jpg)
Classification of receptors
• Mechanoreceptors
• Thermoreceptors
• Nociceptorspain
• Chemoreceptorstaste, smell, visceral
• Electromagnetic receptorsvisual
Guyton p.496
![Page 9: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/9.jpg)
Mechanoreceptors
• Mainly cutaneousTouchPressureVibration
• Crude or Fine mechanosensations
• Others: auditory, vestibular, stretch, proprioceptors
![Page 10: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/10.jpg)
Cutaneous mechanoreceptors
• Pacinian corpuscle
• Meissner’s corpuscle
• Krause’s corpuscle
• Ruffini’s end organ
• Merkel’s disc
• Hair end organ
• Free nerve endings
![Page 11: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/11.jpg)
Mechanoreceptors
• Pacinian corpuscledeep, pressure sensitive, fast adapting, large receptive field
• Meissner’s corpusclesuperficial, sensitive to touch, small receptive field
• Ruffini’s end organdeep, tension sensitive, slow adapting, large receptive field
• Merkel’s discsuperficial, touch, pressure and texture sensitive, slowly
adapting, small receptive field
• Krause’s endingsvibration sensitive
![Page 12: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/12.jpg)
Mechanoreceptors
• Hair end organ
• Free nerve endingsCrude mechanosensations
![Page 13: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/13.jpg)
![Page 14: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/14.jpg)
![Page 15: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/15.jpg)
![Page 16: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/16.jpg)
Pacinian corpuscles
looks like onion, large receptive field, rapidly adapting
Hair follicle receptor
nerve endings around root of hair in hairy skin, small receptive field, either slowly or rapidly adapting
Ruffini's ending
looks like small Pacinian, large receptive fields, slowly adapting
Merkel's disks
small arrays of small disks which may have synapses to nerve endings, small receptive fields, slowly adapting
Meissner's corpuscles
hang under ridges of glabrous skin, small receptive fields, rapidly adapting
Krause end bulbs
look like knotted balls of string in skin in border between dry skin and mucous membrane in mouth, genitals, anus
![Page 17: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/17.jpg)
Pacinian Corpuscle
Capsule
Nerve fibre
![Page 18: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/18.jpg)
What happens inside a receptor?
• TRANSDUCTIONStimulus energy is converted to action potentials
Inside the nervous system signals are always action potentials
Language of the nervous system contains only 1 word: action potentials
• At the brain opposite happens in order to feel the sensationPERCEPTION
![Page 19: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/19.jpg)
Receptor potentials
• When a stimulus activate a receptor initially a “receptor potential” is generated
• This is also called “generator potential”
• This is a graded potential
• It does not follow “all-or-none law”
• Its amplitude depends on the strength of the stimulus
• When it reaches the threshold it triggers an “action potential”
![Page 20: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/20.jpg)
Transduction
Stimulus
Receptor potential(Generator potential)
Action potential
![Page 21: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/21.jpg)
Action Potentials
Threshold
RestingMembranePotential
-70
- 55
+30
StimulusReceptor potential
![Page 22: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/22.jpg)
Coding of sensory stimuli
• Stimulus strength is coded as the frequency of AP
• Higher the stimulus more frequent are the APs
• Amplitude of AP is constant
![Page 23: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/23.jpg)
Stimulus
Receptorpotentials
Action potentials
![Page 24: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/24.jpg)
Sensory coding
• A receptor must convey the type of information it is sending the kind of receptor activated determined the signal recognition by the brain
• It must convey the intensity of the stimulus the stronger the signals, the more frequent will be the APs
• It must send information about the location and receptive field, characteristic of the receptor
![Page 25: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/25.jpg)
Transduction in different receptors
• Different receptors have different ion channels
• Their opening causes receptor potential
![Page 26: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/26.jpg)
![Page 27: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/27.jpg)
Receptor potential generation in the Pacinian corpuscle
![Page 28: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/28.jpg)
Pacinian corpuscle
![Page 29: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/29.jpg)
Resting
![Page 30: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/30.jpg)
Physical Stimulus
Physical stimulus causing mechanical deformation on the capsule
![Page 31: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/31.jpg)
Physical Stimulus
Mechanical deformation is transmitted to the inside
Opens up mechanosensitive Na+ channel
Causes depolarisation and thus receptor potential
![Page 32: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/32.jpg)
Physical Stimulus
local current
Current flow through a local circuit
![Page 33: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/33.jpg)
Physical Stimulus
Action Potentialsare generated
Opening of voltage gated Na+ channels causes generation of action potentials
![Page 34: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/34.jpg)
Adaptation
• “getting used to”
• after a period of time sensory receptors adapt partially or completely
• different typesRapidly adapting receptorsslowly adapting receptors
![Page 35: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/35.jpg)
Adaptation
• after a period of time sensory receptors adapt partially or completely
• different typesfast adapting receptorsslowly adapting receptors
![Page 36: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/36.jpg)
Paciniancorpuscle
Musclespindle
Pain
Time
Imp
uls
es p
er s
eco
nd
![Page 37: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/37.jpg)
Mechanism of adaptation
• In the Pacinian corpusclemechanical deformation is transmitted throughout
the capsule and pressure redistributesNa+ channels inactivates after some time
![Page 38: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/38.jpg)
Impulse
Stimulus
Redistribution of pressure inside the capsule
NoImpulse
Stimulus
![Page 39: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/39.jpg)
• Rapidly adapting receptorsphasic or rate or movement receptors
detect changes in stimulus strengtheg. Pacinian corpuscle, hair end-organ
• Slowly adapting receptorstonic receptors
detect continuous stimulus strengtheg. muscle spindles, Golgi tendon organ, baroreceptors,
Ruffini endings and Merkel’s discs, pain receptors
![Page 40: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/40.jpg)
Classification of receptors
• Mechanoreceptors Cutaneous (touch, pressure, vibration) eg. Pacinian, Meissner’s corpuscle, free
nerve endings Proprioceptors (joint position receptors) eg. Muscle stretch receptors, tendon
organs Baroreceptors Auditory/vestibular hair cells
• Chemoreceptors Taste buds and smell receptors Visceral chemoreceptors sensitive to Pco2, pH, osmolality etc
• Thermoreceptors Cold and hot receptors
• Nociceptors (pain receptors)
• Other receptors: Visual (rods and cones): electromagnetic
![Page 41: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/41.jpg)
Two ascending pathways
• Dorsal column - medial lemniscus pathwayfast pathway
• Spinothalamic pathwayslow pathway
These two pathways come together at the level of thalamus
![Page 42: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/42.jpg)
Dorsal rootDorsal columns
Dorsal horn
Dorsal root ganglion
Spinothalamictracts
Posterior (dorsal)
Anterior (ventral)
![Page 43: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/43.jpg)
Dorsal column pathwaySpinothalamic pathway
Lateral Spinothalamic tract
AnteriorSpinothalamic tract
![Page 44: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/44.jpg)
Dorsal column pathway Spinothalamic pathway
• touch: fine degree
• highly localised touch sensations
• vibratory sensations
• sensations signalling movement
• position sense
• pressure: fine degree
• Pain
• Thermal sensations
• Crude touch & pressure
• crude localising sensations
• tickle & itch
• sexual sensations
![Page 45: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/45.jpg)
Dorsal column nuclei(cuneate & gracile nucleus)
Dorsal column
Medial lemniscus
thalamus
thalamocortical tracts
sensory cortex
internal capsule
1st order neuron
2nd order neuron
3rd order neuron
![Page 46: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/46.jpg)
dorsal column - medial lemniscus pathway
• after entering the spinal cordlateral branch: participates in spinal cord reflexesmedial branch: turns upwards
• forms the dorsal columns
• spatial orientation: medial: lower parts of the bodylateral: upper part of the body
![Page 47: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/47.jpg)
dorsal column - medial lemniscus pathway
• synapse in the dorsal column nucleinucleus cuneatus & nucleus gracilus
• 2nd order neuron cross over to the opposite side and ascends upwards as medial lemniscus
• as this travels along the brain stem fibres from head and neck are joined (trigeminal)
• ends in the thalamus (ventrobasal complex) ventral posterolateral nuclei
![Page 48: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/48.jpg)
dorsal column - medial lemniscus pathway
• spatial orientation in the thalamusmedial: upper part of the bodylateral: lower part of the body
![Page 49: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/49.jpg)
Spinothalamic tracts
thalamus
thalamocortical tracts
sensory cortex
internal capsule
1st order neuron
2nd order neuron
3rd order neuron
![Page 50: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/50.jpg)
spinothalamic pathway
• after entering the spinal cordsynapse in the dorsal horn
• cross over to the opposite side
• divide in to two tractslateral spinothalamic tract:
pain and temperature
anterior spinothalamic tractcrude touch
![Page 51: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/51.jpg)
spinothalamic pathway
• spatial orientation medial: upper part of the bodylateral: lower part of the body
![Page 52: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/52.jpg)
![Page 53: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/53.jpg)
Dorsal column pathwaySpinothalamic pathway
Lateral Spinothalamic tract
AnteriorSpinothalamic tract
![Page 54: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/54.jpg)
thalamocortical tracts
• from the thalamus 3rd order neuron ascends up through the internal capsule
• up to the sensory cortex
• thalamocortical radiationtracts diverge
![Page 55: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/55.jpg)
Sensory cortical areas
• parietal cortex
• a distinct spatial orientation exists
![Page 56: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/56.jpg)
![Page 57: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/57.jpg)
![Page 58: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/58.jpg)
![Page 59: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/59.jpg)
![Page 60: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/60.jpg)
![Page 61: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/61.jpg)
Sensory cortex
• different areas of the body are represented in different cortical areas in the sensory cortex
• sensory homunculussomatotopic representation not proportionate distorted mapupside down map
![Page 62: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/62.jpg)
Representation
•upside down•distorted
concept of homunculus
Map
![Page 63: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/63.jpg)
Sensory homunculus
![Page 64: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/64.jpg)
Brodmann areas
![Page 65: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/65.jpg)
Sensory cortical areas
• Primary somatosensory cortex (SI)postcentral gyrus(Brodmann areas 3a, 3b, 1, 2)
• Secondary somatosensory cortex and Somatosensory association cortex Posterior parietal areas(Brodmann areas 5, 7)
![Page 66: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/66.jpg)
Somatosensory cortex• Functions
To localise somatic sensationsTo judge critical degree of pressureTo identify objects by their weight, shape, form -
stereognosisTo judge texture of materialsTo localise pain & temperature
• Damage to the sensory cortex results in decreased sensory thresholdsinability to discriminate the properties of tactile stimuliInability to identify objects by touch (astereognosis)
![Page 67: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/67.jpg)
Secondary somatosensory cortex and Somatosensory association cortex
• Located directly posterior to the sensory cortex in the superior parietal lobes
• Consists of areas 5 and 7
• Receives synthesized connections from the primary and secondary sensory cortices
• Neurons respond to several types of inputs and are involved in complex associations
• Damage can cause Tactile agnosia
inability to recognize objects even though the objects can be felt
Spatial neglect This typically happens with non-dominant hemisphere lesions Neglect can be so severe that the individual even denies that their left side belongs to
them
![Page 68: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/68.jpg)
Receptive fields
• the receptor area which when stimulated results in a response of a particular sensory neuron
• Receptive fields of adjacent neurons overlap
![Page 69: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/69.jpg)
![Page 70: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/70.jpg)
Two-Point Discrimination
• Whether a stimulus feels like one sensation or two distinct sensations depends on the size of the receptive fields of the sensory receptors
• Different areas of the body have sensory receptors with different sized receptive fields
• Smaller receptive fields result in greater sensitivity
• Fingers are more sensitive than backs
![Page 71: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/71.jpg)
![Page 72: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/72.jpg)
Lateral Inhibition
• The capacity of an excited neuron to reduce the activity of its neighbors
• When the skin is touched by an object several sensory neurons in the skin next to one another are stimulated neurons that are firing suppress the stimulation of neighbouring neurons only the neurons that are most stimulated and least inhibited will fire so the firing pattern tends to concentrate at stimulus peaks
• Lateral inhibition increases the contrast and sharpness
• Weaker signals get weaker, stronger signals get stronger
• It is preset in the retina
![Page 73: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/73.jpg)
![Page 74: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/74.jpg)
Lateral inhibition improves 2-point discrimination
![Page 75: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/75.jpg)
Sensory abnormalities• Sensory loss
• Anaesthesiaabsence of sensation
• Paraesthesia (numbness or pins-needles-sensation)altered sensation
• Neuropathic pain
• HemianaesthesiaLoss of sensation of one half of the body
• Astereognosis
• Spatial neglect
![Page 76: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/76.jpg)
Localisation of the abnormality• Peripheral nerve
innervated area affected
• Rootsdermatomal pattern of sensory loss
• Spinal corda sensory level
• Internal capsuleone half of the body
• Cortical areasOther features
![Page 77: Y2 s1 sensory system final](https://reader035.fdocuments.net/reader035/viewer/2022062300/557d1561d8b42a4a498b486c/html5/thumbnails/77.jpg)
Examples of sensory lesions or sensory disorders
• Carpal tunnel syndrome median nerve lesion at the wrist
• Cervical radiculopathy Cervical root lesion
• Spinal cord lesion (cervical myelopathy)
• Sensory stroke Internal capsule lesion
• Dorsal column disease (eg. diabetes)
• Syringomyelia Spinal cord central canal lesion