Sensory receptor 2 Flashcards
Why does the myelin sheath come in different sizes?
As the velocity of conduction is different in different axon sensation
Why is the position sensation the fastest?
- Before sending each motor signal, the brain needs to know the exact position of the muscles and tendons to send the precise motor signal for the next move.
- So, the position sensation must be fastest. Other sensations can arrive slightly later (because the brain can afford to send a delayed response)
What is meant by somatic sensations?
All of the signals that go to the brain
What are the types of sensation felt by the dorsal column medial lemniscus system?
1) Position of muscles
2) Position of tendons
3) Vibration
4) Refined touch (when something fine like a pin touches us)
What are the different sensations felt by the anterolateral spinothalamic tract?
1) Crude touch
2) Aching pain
3) Cold
4) Warmth
5) Deep pressure
6) Pricking pain
What are the types of dorsal column medial lemniscus system receptors?
Mechanoreceptors
What are the types of anterolateral spinothalamic tract receptors?
1) Thermoreceptors
2) Nociceptors
Which pathway is taken by photo & chemoreceptors?
They bypass the cranial nerves and go directly to the brain
How can we test the dorsal column medial lemniscus and the anterolateral pathways?
1) Anterolateral:
- Induce pain/temp sensation and ask the patient if he can feel it
2) Dorsal column medial lemniscus
We need two of
- Vision
- Vestibular system (we assume that it is correct)
- Proprioception
- Ask the patient to close his eyes and maintain his balance (if he doesn’t maintain his balance then the patient is probably suffering from DCML-Collapse)
When we touch our skin, why do we feel the touch sensation but not the movement of the skin?
1) Impulses come from the body to the thalamus
2) In the thalamus and before the brain the neurons are not directly connected to the brain but rather via interneurons that can either be excitatory or inhibitory, passing the signals from one area to another
3) each interneuron wants to pass its signal and inhibit the other interneurons in the thalamus, so in this case, the touch signal is the strongest enabling the neuron to inhibit any other signal at the thalamus level
- This is called lateral inhibition and only applies on each sensation alone (not heat + touch) only touch between it and its self
What is the purpose of lateral inhibition?
Precisely localizes the stimulus and defines its boundaries by providing contrast
What is meant by receptive field?
- It is an area of the body when stimulated it activates only one sensory neuron
- They can have 100s of receptors all supplied by one neuron
- For example the back of the torso compared to the fingertips, it has fewer receptor density while a bigger receptor field size
- A touch anywhere in the receptive field will stimulate the same neuron
- The Brain will feel the touch in the whole receptive field (including the untouched skin)
What will happen if a stimulus is constant?
The response will decrease gradually, due to reduction in receptor potential and thus neuronal firing rate
What will happen if a stimulus is increasing?
The proportional response is low but increasing, due to the increased opening of Na channels
- As the strength of a stimulus increases it either responds by increasing the firing rate “temporal summation” or increasing the number of active receptors “spatial summation”
What happens when the strength of a stimulus increases?
1) Receptor level-more sodium channels open
2) Receptor field- temporal summation and spatial summation seen
