University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

101

Pages:

2
Author:

Mariam A. A.

• • The somatosensory system Complex system consisting of specialised sensory endings (mechanoreceptors, thermoreceptors, chemoreceptors and nociceptors) in the skin, muscles, tendons and joints that provide info about changes to the surface and internal state of the body Three subsystems: o Tactile system: mediates the sensation of fine touch, vibration and pressure from cutaneous mechanoreceptors o Proprioceptive system: mediates proprioception (sense of position and movement) from specialised receptors associated with muscles, tendons and joints o Nociception system: mediates the sense of pain and temperature Sensory transduction: converting energy of stimulus into an electrical signal (similar in all sensory afferents) • Stimulus alters the permeability of cation channels in the afferent (carrying inward) nerve endings, generating a depolarising current called receptor (generator) potential • Once the receptor potential passes the threshold, it leads to an AP that propagates along the axon to the dorsal roots of the spinal cord • Each spinal pathway has a sensory afferent and motor efferent that enter the spinal cord from a specific location along the vertebral column Dermatomes • Each segment of spinal cord receives cutaneous info from a single dorsal root → transduces info from a particular skin strip (dermatome) • Dermatomes are arranged segmentally • E.g. shingles is a viral disease that effects spinal nerves caused by reactivation of Varicella zoster virus → painful skin rash/blisters reveal spinal nerve effected by showing up as a dermatomic area • Axons of afferent sensory neurons can be classified by conduction velocity: >axon diameter, >velocity • Different sense modalities are mediated by morphologically distinct fibres • Sensory tactile information: conveyed by large, rapidly-conducting myelinated afferent sensory axons • Heat, pain info: usually conveyed by unmyelinated, slow-conducting afferent sensory axons Sensory pathways to the brain 1. Dorsal column-medial lemniscal pathway (DCML) – convey tactile info 2. Spinothalamic tract – convey crude touch, pain and temp