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)

>20 types of receptors in skin: touch, temperature, stretch, etc 2 pathways to brain Dorsal columns Precise touch, joint angle, etc. Crosses side at medulla Antero-lateral Tract Coarse information regarding pain and temperature Convergence of information Crosses side at entry in spinal column

Hierarchy of Sensory Fibers 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 Each tract mediates specific modalities of sensation, somatotopic organization in tracts and cortex Mechanoreceptive Mechanical displacement of nerve endings Touch (fine and diffuse), pressure, vibration, kinesthesia Thermoreceptive Cold and Heat Nociceptive Pain

Specialized Receptors Receptors specialize by type of stimulus Adaptiveness: Reduction of response to sustained stimuli Basic Types of Sensory Receptors Encapsulated Endings 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 Free Nerve Endings (pain, temp, some tactile) Nonadapting Expanded Tip Endings (tactile, temp) Moderately adapting

1) Classified according to their diameters ◆ 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 1st Order Dorsal Root Ganglion 2nd Order Enter CNS at spinal cord or brainstem Project to opposite side crossing midline to thalamus 3rd Order Thalamus neurons which project to cortex

Anatomical Divisions Dorsal Column-Medial Lemniscal (or Epicritic System) 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) Pain, temperature and diffuse touch Lateral spinothalamic tract Anterior spinothalamic tract

Dorsal Column-Medial Lemniscal System Important for skilled movements Stereognosis - Fine touch discrimination Graphesthesia - Recognizing numbers written on body Two and multiple point touch Deep touch Receptors Meissner’s and Pacinian Corpuscles Encapsulated end receptors Highly sensitive and adaptable Muscle Spindle Organs Kinesthesia Proprioception

Neural Pathways Neural Pathways Fasciculus Gracilis Fasciculus Cuneatus Path Spinal Ganglion (1) Gracilis or Cuneatus Nucleus (2) Through Medial Lemniscus to Thalamus (3) Thalamus to Cortex Mediate discriminative Touch from different Body areas; follow three-neuron organization

Levels of Reception Fasciculus Gracilis Fasciculus Cuneatus Sacral to Midthoracic Level Lower Body Fasciculus Cuneatus Above Midthoracic Level Upper Body

Pathway Spinal Cord Brainstem Nuclei Thalamus (N. Ventral Posterolateralis) Thalamus through Internal Capsule to Primary Sensory Parietal Cortex Primary to Association Cortex Mapped spatially (homunculus)

Medial Lemniscal Pathway: Mechanoreceptors & Proprioception

The homunculus

Anterolateral system Pain, Temperature, & Diffuse Touch Three-tier neuron organization system Enter at spinal ganglion (1st) Cross in spinal tract (2nd order) Ventral posterolateral n. of thalamus (3rd) Two Tracts Lateral Spinothalamic Anterospinothalamic

Pain and Temperature Cerebral Cortex 3 Thalmus 2 1 Anterolateral System Cerebral Cortex 3 Thalmus 2 1 Brainstem/spinal cord

Spino-Thalamic Pathway: Temperature & Pain

Lateral Spinothalamic Tract Receptors - Free Nerve Endings Neural Pathway 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 Discrimination of Diffuse touch Receptors: All three types Encapsulated endings Free nerve endings Expanded tip endings Neural Pathway 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 Conscious proprioception by dorsal column-medial lemniscal system Unconscious involved in walking, articulating, writing, swallowing, and eye movement. Two order neural system Tracts Dorsal Spinocerebellar Cuneocerebellar Ventral Spinocerebellar Receptors Muscle spindles and Golgi tendon organs located in muscles and limb joints

Ventral Spinocerebellar Tract Mediates unconscious proprioception Lower limbs to bilateral cerebellum Sacral and Lumbar levels through ventrolateral Spinocerebellar tract to opposite cerebellar hemisphere

Dorsal Spinocerebellar Tract 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 Mediates upper limbs and neck Uncrossed fibers to ipsilateral external cuneate nucleus to cerebellum Clinical Considerations Romberg used to determine some function Difficult to test clinically

Sensory abnormalities Cerebral cortex region - conscious proprioception - two-point discrimination - stereognosis - touch & pain Cerebellum region - ataxia

Prerequisites of Treatment 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