Sensation Flashcards
what detects sensation in the skin
free nerve ending - pain/temperature
Merkel endings - touch/pressure
meissner’s corpuscle - fine touch (esp concentrated in fingertips)
fibres travel proximally in nerves
what are peripheral nerves
a nerve contains many nerve fibres
some travel proximally (afferent), these are sensory pathways
others travel distally (efferent), these are motor pathways
some nerves are also autonomic
how does pain and temperature sensation travel in the body
unmyelinated C fibres, thinly myelinated Adelta fibres
how does proprioception travel through the body
large myelinated Aalpha fibres
how are major nerves formed
branches of individual nerves join together
how does sensory information travel
proximally towards spine
how do motor fibres travel
distally to innervate muscles
describe a plexi
nerves join together at plexi
enter spinal space via roots
the path taken by peripheral nerves (and hence the area innervated) is distinct from spinal nerves
describe roots
sensory fibres enter the spine via the dorsal roots
ganglion here contains the cell body but not the synapse
the level at which the spinal nerves enter (or exits for motor) is used to number the root
describe the spinothalamic tract
senses pain and temperature
1st order neurone synapses on entry
immediate decussation, 2nd order neuron ascends in spinothalamic tract
final synapse in thalamus, 3rd order neuron ascends to cortex
describe the pathway of touch, proprioception and vibration
1st order neuron enters cord, ascends via ipsilateral dorsal column pathway
synapses in medulla then decussate in medial lemniscus, ascend as 2nd order neurons
final synapse in thalamus, ascent to sensory cortex
what are dermatomes
cutaneous sensory innervation, numbered according to root levels
these differ from the peripheral nerve-innervated territories
clinical examination attempts to localise a root or spinal level
what is facial sensation innervated by
the trigeminal nerve (V), also innervates oral cavity, nostril, sclera and dura
also motor supply to masticatory muscles
what does the trigeminal nerve bracnh into
ophthalmic
maxillary
mandibular
the branches enter the skull separately then meet in the trigeminal ganglion and travel proximally to the brainstem
what is the sensory homunculus
somatosensory cortex
sensory information from specific body regions is transmitted to dedicated cortical areas
disproportinate space is given to key regions
