4. Sensory System Flashcards
What does the quality of sensation depend on?
How the receptor is activated and the receptor subtypes.
What is the general pattern of primary/secondary/tertiary neurones?
Primary sensory neurone has cell body in PNS, collects information from receptor body in dorsal root ganglia then synapses with second order neurone in CNS. The secondary neurone decussates and ascends to the thalamus. It synapses with tertiary neurone here, this projects to sensory cortex.
What do phasic receptors transmit?
Pressure.
How do phasic receptors respond to ongoing pressure?
Adapt to condition so initially there are lots of action potential fired but then it lessens so the stimulus isn’t noticed.
What do tonic receptors transmit?
Pain.
How do tonic receptors respond to ongoing pain?
Don’t adapt to stimulus, the rate of action potential firing is constant so stay aware of pain.
How are acuity and size of receptive field linked?
Inversely proportional.
Why may damage to one receptive field by harder to locate?
Adjacent dermatomes overlap so afferent neurones from several dermatomes may supply that one receptive field.
Describe how lateral inhibition works on skin stimulated by a neuro tip.
Several primary neurones are depressed by the neurotip but the main neurone for that point has inhibitory interneurones that inhibit adjacent secondary neurones that are stimulated by other primary neurones in the area. This dampens down impulses from adjacent secondary neurones.
Why is topographical representation needed?
For efficiency, wastes less myelin and uses fewer axons. Means each part of the body has a primary neurone to the central nervous system.
What is the best way to test function of the dorsal column medial lemniscus pathway?
Steriognosis - put something in the patient’s hand and get them to recognise it by touch not sight.
What are the roles of the dorsal column medial lemniscus pathway?
Light touch, joint position sense, vibration, two-point discrimination.
What is the organisation of the neurones in the dorsal column medial lemniscus pathway?
Primary afferents are stimulated from spinal levels and have cell bodies in the dorsal root ganglia. They travel ipsilaterally up to the brainstem. They synapse with second order neurones in the pons, these decussate and travel up to the thalamus. Here they synapse with the third order neurones which project to the sensory cortex.
What is the topographical organisation of fibres in the dorsal column medial lemniscus pathway from different sections of the body?
Fibres from lower body travel closer to the midline. So medial to lateral is lower limbs, trunk, and cervical areas.
What are the roles of the spinothalamic pathway?
Pain, temperature, and crude touch.
