Types of nerves / axons Flashcards
what do Ia afferents innervate
all types of muscle spindles
- primarily dynamic bag type fibres
- primary endings
what do Ib afferents innervate
GTOs
what do II afferents innervate
secondary endings of muscle spindles
- nuclear chain type (static)
what info do A beta afferents carry
touch info
- from cutaneous receptors
what info do A delta and C afferents carry
pain and temp info
- from free nerve endings
- A delta = myelinated free nerve endings
- C = unmyelinated free nerve endings
what is the order of axon types from smallest to largest
A delta/C - pain + temp = smallest
A beta - touch = middle
Ia/Ib/II - muscle spindles + GTO = largest
what is the relation between axon size and conduction velocity
small axon = slow conduction velocity
large axon = fast conduction velocity
what is the order of axon types from fastest conduction velocity to slowest
fastest = Ia/Ib/II - muscle spindles + GTOs
middle = A beta - touch
slowest = A delta/C - pain + temp
what spinal tract do A beta axons travel up
DCML - cutaneous info
what spinal tract to A delta and C axons travel up
ventral (anterolateral) spinothalamic tracts
what is a renshaw cell
special type of interneuron
- activated by a collateral branch of a MN
- inhibits that MN and its neighbours
(example of a negative feedback loop)
how can we modulate renshaw cells
descending inputs can modulate
- sets an upper limit on MN firing rates (like car restrictor)
