The sensory system Flashcards
Which modalities are carried by the dorsal columns?
Proprioception
2 point discrimination
Vibration
Which sensory modalities are carried by the spinothalamic tract?
Temperature
Pain
Pressure
Does strong receptor activation from a strong sensory stimulus give high frequency or low frequency action potentials?
High frequency
What is a rapidly adapting receptor?
They initially fire off a very high frequency of action potential that then slows down. Eg sitting down in a chair- at first you notice the chair pressing into your bum but then you become less aware of it.
What are slow adapting receptors? What is an example?
The frequency of action potentials doesnt reallt change so the stimulus is felt the same all the time.
Eg nociceptors (for pain)
If the region of skin supplied by a single neurone is small then how will this affect the sensory acuity ?
Sensory acuity will be very good as you will be able to tell one point from the other quite easily.
Where does the cell body of 1st order neurones lie?
In the dorsal root ganglion
Where does the cell body of 2nd order neurones lie?
In the dorsal horn/ medulla
Where does the cell body of tertiary order neurones lie?
In the thalamus.
In the dorsal column pathway where can fibres from the lower body be found?
Medially
In the spinothalamic tract where can the sensory fibres from the lower body be found?
Laterally
In the dorsal column medial lemniscus pathway where do 1st order neurones from the arms synapse with 2nd order neurones?
In the cuneate nucleus which is found in the floor of the 4th ventricle.
In the dorsal column medial lemniscus pathway where do 1st order neurones from the legs synapse with 2nd order neurones?
In the gracile nucleus which lies in the floor of the 4th ventricle.
Where does the medial lemniscus lie?
It is the pathway of sensory neurones from the dorsal columns travelling to the thalamus through the midbrain.
Where do fibres from the dorsal columns decussate?
In the medulla
Where do 2nd order neurones synapse with 3rd order neurones?
In the thalamus
Where in the primary sensory cortex located?
In the post central gryus which is a part of the parietal lobe.
Which parts of the body are represented most laterally on the sensory homunculus?
The face. The legs are most medial and the hand and arm lie inbetween.
Isolated lesions of the dorsal column pathway will lead to signs contralaterally or ipsilaterally below the lesion?
Ipsilaterally
Where do 1st order neurones synapse with 2nd order neurones in the spinothalamic tract?
In the dorsal horn
What is the pathway of the 2nd order neurones in the spinothalamic tract?
They cross the ventral white commisure and then ascend up the spinal cord and synapse with 3rd order neurones in the thalamus.
Isolated lesions of spinothalamic tract in the cord will lead to signs contralaterally or ipsilaterally below the lesion?
Contralaterally.
Which fibres carry impulses from mechanoreceptors in the skin?
A fibres
Which fibres carry pain from the skin to the spinal cord?
C fibres
Why does activation of mechanoreceptors alleviate pain?
It excites inhibitory enkephalinergic interneurones in the cord which inhibit C fibre transmission.