Neuro 7 - 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?
it is the peripheral termina of the peripheral axon of the primary sensory neuron
Not a separate entity
Describe the structure of Pacinian corpuscle and explain how the structure relates to its function.
Axonal ending in the middle, wrapped around concentric circles of epithelial cells
allows the receptor o be sensitive to vibration
What is the difference between slow and fast adapting receptors?
Slow - continue to fire impulses as long as the stimulus is present
Fast- - fire at start and end of stimulus
What type of receptors are mechanoreceptors - fast or slow adapting?
Mixture of both
Describe how sensory neurons vary in their properties.
vary in size and conduction velocity
What two ways can axons be classified?
based on diameter
based on conduction velocity
but these are also linked
larger diameter = faster conduction
Describe the general structure of sensory neurons that convey touch and proprioceptive information?
Large and have a fast conduction velocity
What is a receptive field?
An area of skin that is innervated by one sensory axon and its branches
Describe how the receptive fields in the lips and mouth vary from the receptive fields of the upper arm.
Lips and mouth - high density innervation with small receptive fields
Upper arm - low density innervation, with large receptive fields
Describe how neurons can code for intensity of a stimulus.
FREQUENCY
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 below/above the waist called?
Above waist = cuneate Fasciculus
Below waist = Gracile Fasciculus
Are axons from lower down packed more medially or more laterally?
Lower = medial Higher = lateral
Where do the cuneate and gracile fasciculus neurons synapse?
cuneate and gracile nuclei in the medulla
Where does decussation happen in the central pathway?
In the brainstem
Which thalamic nucleus is responsible for relaying somatosensory information from the neck down?
Ventero-postero lateral
Describe the passage of the third order sensory neuron.
Travels from the ventral postero lateral nucleus in the thalamus to the primary somatosensory cortex
What is the main sensory nerve of the face?
Trigeminal nerve
Where does the trigeminal nerve enter the brainstem and where does it synapse with the second order neuron?
Pons
synapses at the trigeminal cranial nucleus
Describe the passage of this second order neuron.
crosses the midline and join 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?
Each axons has lateral branches that are inhibitory on neighbouring axons
So each axon stimulates a second order neuron and inhibits neighbouring first order neurons
What is the point of lateral inhibition?
Improve the resolution of localising the stimulus
Name the three parts of the somatosensory cortex.
Primary somatosensory cortex
Secondary somatosensory cortex
Posterior parietal cortex
What is the posterior parietal cortex 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 loss of sensation
Paraesthesia - abnormal sensation
What is the most common cause of peripheral neuropathy?
Diabetes Mellitus
