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Sensory system
Sensory system
The sensory system is
composed of subsystems, each
transmitting specific information
to the central nervous system
Somatosensory system
The somatosensory system is the
body sensation. It monitors a
wide variety of stimuli from all
over the body from the activity
in receptors found in the skin,
and proprioceptors in the
muscle and the joints
The functions of the
Somatosensory system
- to monitor the contract of objects and
surface with the skin, particularly the
hands and feet
- to report the position of body segments
in space and in relation to each
other(body scheme)
- to initiate sensory activity for the
interpretation of harmful stimuli
The Somatic Sensory Cortex
- Primary somatosensory cortex(SⅠ)
: Brodmann's areas 1,2,3a and 3b
- Seconcary somatosensory
cortex(SⅡ)
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>20 types of receptors in skin: touc
h, temperature, stretch, etc
2 pathways to brain
 Dorsal columns
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Precise touch, joint angle, etc.
Crosses side at medulla
Antero-lateral Tract
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Coarse information regarding pain
and temperature
Convergence of information
Crosses side at entry in spinal colu
mn
Hierarchy of Sensory Fibers
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Specialized Receptors
Single Nerve Fiber
Sensory Fiber Bundle
Spinal Nerve
Dorsal Root Ganglia
Dorsal Column Nuclei
Spinal Motorneurons or Reticular Formation
Thalamus
Primary and Association Cortex (Parietal Lobe)
Organization
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Each tract mediates specific modalities
of sensation, somatotopic organization in
tracts and cortex
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Mechanoreceptive
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Thermoreceptive
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Mechanical displacement of nerve endings
Touch (fine and diffuse), pressure, vibration,
kinesthesia
Cold and Heat
Nociceptive
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Pain
Specialized Receptors
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Receptors specialize by type of stimulus
Adaptiveness: Reduction of response to sustained
stimuli
Basic Types of Sensory Receptors
Encapsulated Endings
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Free Nerve Endings (pain, temp, some tactile)
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Adapting (tactile)
 Pacinian corpuscle: deep pressure touch and high
frequency vibration.
 Meissner’s corpuscle: light touch, such as the fingertips,
palms, soles, lips, tongue, face
Nonadapting
Expanded Tip Endings (tactile, temp)
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Moderately adapting
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Primary Afferent Axons (Fibers)
1) Classified according to their diameters
2) The greater their diameter, the greater their conduction velocities
3) Peripheral nerve fibers show differences in the following functional
properties
Three neuron Organization
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1st Order
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2nd Order
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Dorsal Root Ganglion
Enter CNS at spinal cord or brainstem
Project to opposite side crossing midline to
thalamus
3rd Order
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Thalamus neurons which project to cortex
Anatomical Divisions
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Dorsal Column-Medial Lemniscal (or Epicritic
System)
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Fine discriminative touch, vibration, limb position,
kinesthesia & deep pressure
Position sense
 Proprioception - Awareness of limb position
 Kinesthesia - Awareness of limb movement
Anterolateral (or Protopathic System)
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Pain, temperature and diffuse touch
 Lateral spinothalamic tract
 Anterior spinothalamic tract
Dorsal Column-Medial
Lemniscal System
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Important for skilled movements
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Stereognosis - Fine touch discrimination
Graphesthesia - Recognizing numbers written on body
Two and multiple point touch
Deep touch
Receptors
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Meissner’s and Pacinian Corpuscles
 Encapsulated end receptors
 Highly sensitive and adaptable
Muscle Spindle Organs
 Kinesthesia
 Proprioception
Neural Pathways
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Neural Pathways
Fasciculus Gracilis
Fasciculus Cuneatus
Path
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Mediate discriminative
Touch from different
Body areas; follow
three-neuron
organization
Spinal Ganglion (1)
Gracilis or Cuneatus Nucleus (2)
Through Medial Lemniscus to Thalamus (3)
Thalamus to Cortex
Levels of Reception
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Fasciculus Gracilis
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Sacral to Midthoracic Level
Lower Body
Fasciculus Cuneatus
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Above Midthoracic Level
Upper Body
Pathway
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Spinal Cord
Brainstem Nuclei
Thalamus (N. Ventral Posterolateralis)
Thalamus through Internal Capsule to
Primary Sensory Parietal Cortex
Primary to Association Cortex
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Mapped spatially (homunculus)
Medial Lemniscal Pathway:
Mechanoreceptors & Proprioception
The homunculus
Anterolateral system
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Pain, Temperature, & Diffuse Touch
Three-tier neuron organization system
1.
2.
3.
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Enter at spinal ganglion (1st)
Cross in spinal tract (2nd order)
Ventral posterolateral n. of thalamus (3rd)
Two Tracts
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Lateral Spinothalamic
Anterospinothalamic
Pain and Temperature
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Anterolateral System
Cerebral Cortex
3
Thalmus
2
1
Brainstem/spinal cord
Spino-Thalamic Pathway:
Temperature & Pain
Lateral Spinothalamic Tract
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Receptors - Free Nerve Endings
Neural Pathway
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Nocioceptors (pain)
Dorsolateral spinal cord (up or down several segments)
 spinal cord entrance
Substantial Gelatinosa and Proprius
 Where 1st order neurons connect with 2nd order
neurons
Lateral Spinothalamic Tract
Cross Midline (2nd order)
Spinal Lemniscus (brainstem)
Thalamus (VPL) to Cortex
Collaterals to Subcortical structures
Anterospinothalamic Tract
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Discrimination of Diffuse touch
Receptors: All three types
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Neural Pathway
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Encapsulated endings
Free nerve endings
Expanded tip endings
Skin to ganglia (1st)
Dorsolateral spinal cord (up and down seg)
Proprius and Substantia Gelatinosa (2nd)
Go to spinothalamic tract to VPL (thalamus) to postcentral
gyrus
Collaterals to subcortical structures
Clinically, interruption causes no obvious deficit
Unconscious Proprioception
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Conscious proprioception by dorsal columnmedial lemniscal system
Unconscious involved in walking, articulating,
writing, swallowing, and eye movement.
Two order neural system
Tracts
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Dorsal Spinocerebellar
Cuneocerebellar
Ventral Spinocerebellar
Receptors
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Muscle spindles and Golgi tendon organs located in
muscles and limb joints
Ventral Spinocerebellar Tract
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Mediates unconscious proprioception
Lower limbs to bilateral cerebellum
Sacral and Lumbar levels through
ventrolateral Spinocerebellar tract to
opposite cerebellar hemisphere
Dorsal Spinocerebellar Tract
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Mediates unconscious
proprioception
Lower limbs and middle
regions of body to to
bilateral cerebellum
Spinal ganglion to
nucleus dorsalis of Clark
at third lumbar segment
Do not cross and enter
ipsilateral cerebellar
hemisphere
Cuneocerebellar Tract
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Mediates upper limbs and neck
Uncrossed fibers to ipsilateral external
cuneate nucleus to cerebellum
Clinical Considerations
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Romberg used to determine some function
Difficult to test clinically
Sensory abnormalities
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Cerebral cortex region
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conscious proprioception
two-point discrimination
stereognosis
touch & pain
Cerebellum region
- ataxia
Prerequisites of Treatment
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Normalising muscle tone
Suitable working positions
Stimulationg sensating without
increasing spasticity
Cooperation of patient
Allowing sufficient time
Consideration of other disabilities
Repetition of stimuli
Variation of stimuli
Adjustment of training intensity
Haptics