Sensory pathways: Touch and proprioception Flashcards
What is proprioception?
Awareness of position
What type of receptors detect all touch and proprioception?
Mechanoreceptors
What receptors detect temperature and pain?
Thermoceptors and nociceptors
What is a peritrichial ending?
When a nerve ending is wrapped around a hair
What is a pacinian corpuscle?
A pacinian corpuscle is when there is an axonal ending in the middle and it is wrapped around several concentric circles of epithelial cells- this allows the receptor to be very sensitive to vibration
What does it mean if a receptor has a high sensitivity
It has a low threshold of activation
What is the difference between slow and fast adapting receptors
Slow adapting- continue to fire impulses for as long as the impulse is present
Fast adapting- Tend to fire at the start of the stimulus and when it is switched off but they fade in the middle
What are the two methods of classifying axons?
One by anatomists is based on diameter of axons and one by physiologists is based on conduction velocity
Anatomical is labelled using letters and physiological is labelled using roman numerals
Why is there an overlap between the two classifications?
As axon diameter increases, conduction velocity increases
What are sensory neurones the convey touch and proprioception normally like?
Large and fast
What is a receptive field?
Area of skin that is innervated by one axon
In terms of receptive fields, what increases sensitivity?
Lots of innervation with small receptive fields
How do the neurones code for the intensity of a stimulus?
It is coded for by the frequency of action potentials going down the sensory fibres, it is nothing to do with amplitude
What route does sensory information in the leg take?
It comes in from the leg via the primary sensory neurone. As the axon goes into the dorsal horn, it passes straight into the white matter at the back of the spinal cord- dorsal columns
What is the arrangement of the dorsal columns
Fibres coming from the lowest parts will be the most medial and from the highest will be the most lateral
What are the two tracts of the axons in the dorsal column?
Cuneate fasciciulus- Waist up
Gracile fasciciulus- Waist down
What is a fasciculus?
Bundle of axons
What happens when the fasciculi reach the medulla?
In the medulla, the neurones synapse with two nuclei, cuneate and gracile, which then sends axons across the midline (at the decussation). After crossing the midline, the fibres head upwards and form a new pathway called the medial leminiscus
What happens to the medial leminiscus after this?
It maintains the same position until it reaches the thalamus where the axons relay with the third neurone in the chain- one of the thalamic nuclei: ventral postern-lateral nucleus. Through this, information is passed to the primary somatosensory cortex
What is the main sensory nerve of the face?
Trigeminal (CN V)
What is the route of sensory information from the face?
The trigeminal comes into the middle of the pons where it synapses with a second order neurone in the trigeminal cranial nucleus. The axon of this second cell crosses the midline and joins the medial end of the medial leminiscus
How does the dorsal column nuclei improve resolution of localising the stimuli?
Lateral inhibition- It takes place in the cuneate and gracile nuclei. Each axon doesn’t just activate the next nuclei but it also has lateral branches that are inhibitory to neighbouring axons.
What is the somatosensory cortex important for?
Analysing and using sensory information
What is the posterior parietal cortex involved in?
Spatial relationships
What happens if there is damage to the sensory pathway?
Information going upto the primary somatosensory cortex will be halted, this will lead to anaesthesia (loss of sensation) or paraesthesia (sensation is there but not normal)
What is peripheral neuropathy?
Disease of the peripheral nerves that tends start distally in hands and feet that progresses proximally
What is the most common cause of peripheral neuropathy?
Diabetes mellitus
