Sensory Pathways: Touch and Proprioception Flashcards
What receptors are responsible for the sensory modalities of touch and proprioception?
Mechanoreceptors
Describe the structure of mechanoreceptors involved in touch and proprioception.
Receptor is NOT a separate entity but is actually the peripheral terminal of the peripheral axon of the primary sensory neuron.
What is the difference between slow adapting and fast adapting receptors?
Slow: fire impulses for as long as stimulus is present
Fast: fire at start of stimulus + sometimes when stimulus switches off, but tend to fade in the middle
What type of receptors are mechanoreceptors?
Mixture of slow + fast adapting receptors
Describe how sensory neurons vary in their properties.
SIZE
CONDUCTION VELOCITY
What are the two classifications of axons?
Anatomical = based on axon diameter (LETTERS)
Physiological = based on conduction velocity (ROMAN NUMERALS)
Diameter + conduction velocity are related, there is a lot of overlap in the classifications
What is a receptive field?
A region on the skin which causes activation of a single sensory neurone when activated
What is the difference between small + large receptive fields?
Small: allow for detection of fine detail over a small area= precise perception
Large: allow cell to detect changes over a wider area= less precise perception
Describe how neurons can code for the intensity of a stimulus.
By FREQUENCY of the APs going down the sensory fibres
Which part of the spinal cord carries sensory axons for touch and proprioception?
Dorsal columns
What are the bundles of axons within the spinal cord that have come from above and below T6 called? Describe their spatial arrangement within the spinal cord.
Above: Cuneate Fasciculus (lateral in cord)
Below: Gracile Fasciculus (medial in cord)
Travel ipsilaterally, desiccate in medulla
Where do the fibres in the Gracile + Cuneate tracts have their 1st synapse?
In the medulla
Cuneate: Cuneate nucleus
Gracile: Gracile Nucleus
Describe what happens after the gracile + cuneate neurones synapse and the tract that they run in.
2nd order neurons decussate in the caudal medulla + continue up the brainstem in the contralateral MEDIAL LEMNISCUS tract
Which thalamic nucleus is responsible for relaying somatosensory information from the neck down?
Ventral Posterior-lateral nucleus (VPL)
Describe the passage of the 3rd order sensory neuron.
Project from VPL to the primary somatosensory cortex
What is the main sensory nerve of the face?
Trigeminal Nerve (CN V)
Where does the trigeminal nerve enter the brainstem and where does it synapse with a second order neuron?
Pons
It synapses at the trigeminal cranial nucleus
Describe the passage of this second order neuron (from the trigeminal nerve).
The 2nd order neuron decussates+ joins the medial part of the median lemniscus
Which thalamic nucleus is responsible for relaying sensory information from the face?
Ventral Postero-medial
What is lateral inhibition?
Lateral branches of primary axons stimulate interneurones that are inhibitory on neighbouring axons
Prevents the overlap of receptive fields, facilitating pinpoint accuracy in localisation of stimulus
Mediated by interneurones in dorsal horn
What is the purpose of lateral inhibition?
Facilitates enhanced sensory perception (discrimination)
Name the 3 parts of the somatosensory cortex.
Primary Somatosensory Cortex (SI)
Secondary Somatosensory Cortex (SII)
Posterior Parietal Cortex
What is the posterior parietal cortex mainly involved in?
Spatial relationships
Damage to the touch and proprioception pathway will halt sensory information going up to the primary somatosensory cortex. What effects will this have?
Anaesthesia (complete cessation of sensation)
Parasthesia (sensation is there but it isn’t normal)
