3- Somatosensory System Flashcards
What classification can sensation be split into?
General (somatic and visceral)
Special sensation
What is a modality?
A basic unit of sensation e.g temperature or pain
What modalities does the spinothalamic system cover?
Temperature, pain, pressure/crude touch
What are the receptors called which detect pain?
Nociceptors
What receptors detect pressure?
Mechanoreceptors
Which modalities does the dorsal column medial lemiscus system cover?
Vibration, proprioception, two-point discrimination and fine touch
How will the strength of activation of a receptor affect frequency of action potentials in the primary sensory neurone?
Stronger receptor activation increases frequency of action potentials in primary sensory neurone
What feature of mechanoreceptors explains why you are not aware of your clothes on your skin after wearing them for a little while?
They are rapidly adapting receptors
What is an example of a type of receptor that would be slow adapting?
Nociceptors
Where are the cell bodies of primary sensory neurones located?
In the dorsal root ganglia
What is a receptive field?
The area of skin supplied by a single primary sensory neurone
Where does skin on the body have a relatively low sensory acuity?
Skin on the back and elbow
How does size of receptive field affect sensory acuity?
The smaller the receptive field the higher the acuity
Where are the cell bodies of second order sensory neurones of the spinothalamic pathway located?
In dorsal horn of spinal cord or medulla
Which of the sensory neurones in the somatosensory system decussate?
Second order sensory neurones
Where are the cell bodies of third order sensory neurones found?
In the thalamus
How does the organisation of information differ between the level of the spinal nerves compared to level of the thalamus and above?
Starts as dermatomal organisation and at thalamus and after there is a homuncular pattern
Through which tract do DCML system neurones from T7 and below travel up the spinal cord?
Gracile fasciculus
Through which tract do neurones of the DCML from the upper body travel up the spinal cord?
Cuneate fasciculus
Where are the second order neurone cell bodies of the DCML found?
Gracile nucleus and cuneate nucleus
Are axons are added to the dorsal columns from superior parts medially or laterally?
Axons from progressively superior body parts are added laterally to the dorsal columns
Where along the spinal cord do neurones of the spinothamalmic pathway decussate?
Around the level that they entered the spinal cord in ventral white commissure
What is the significance of Lissauer’s Tract?
It allows sensory neurones to ascend a few levels before crossing over
What effect do encephalinergic interneurones have on pain transmission?
These exert an inhibitory effect on the second sensory neurone receiving information from C fibres
Why does rub a sore area help to relieve the pain?
Inhibitory (encephalinergic) interneurones can be activated by impulses from incoming mechanoreceptors
Inputs from which higher centres act to activate encephalinergic interneurones and help with pain regulation?
Periaqueductal grey matter and nucleus raphe Magnus
