Neuropathways Flashcards
describe a common unmyelinated nerve fiber
isolated axons are surounded by a schwann cell ad each axon has its own mesaxon
what is a mesaxon?
an opening for electricity to reach the nerve fiber
what is a node of ranvier?
pinch points in myelinated nerve fibers
what is saltatory conduction?
conduction that jumps from node to node
what is the epineurium?
dense connective tissue rich in collagen fibers and fibroblasts (outermost)
what is the perineurium?
several layers of flat cells tightly joined together to form a barrier to the penetration of the nerve by macromolecules (middle)
what is the endoneurium?
composed mainly of reticular fibers synthesized by schwann cells. (inner)
which fibers are myelinated?
A and B
Which fiber is fast, sharp well localized sensation?
A delta
What fibers are unmyelinated?
C fibers.
describe A alpha fiber
proprioception and motor
15 micrometers
100m/s conduction
describe A beta fibers
touch, pressure
10 micrometers
50 m/s conduction
describe A gamma fibers
muscle spindles
5 micrometers
25 m/s conduction
describe A delta fibers
pain (sharp), temperature
<5 micrometers
25 m/s conduction
Describe B fibers
preganglionic, autonomic
<3 micrometers
10 m/s conduction
Describe C dorsal root fibers
pain (dull) temperature
1 micrometers
1 m/s conduction
Describe C sympathetic fibers
postganglionic
1 micrometers
>1 m/s conduction
what is transduction?
noxious stimuli is translated into electrical activity at the sensory ending of nerves
what is transmission?
propagation of impulses thoughout the sensory nervous system
what is modulation?
efferent control of pain
pain fibers in the head are carried by?
trigeminal (V), facial (VII), glossopharyngeal (IX), and vagal (X)
what are first order neurons?
in the ganglia reach the spinal cord and synapse with the second order neuron
second order neurons
spinal cord gray matter divided into 10 lamina
I-VI dorsal horn
-receives all afferent neural activity
-represents the principle site for modulation of pain
lamina 1
responds to nocioceptive stimuli from cutaneous and deep somatic tissues
lamina 2 and 3
sunstantia gelatinosa
- containes many interneurons responsible for processing and modulation nocioceptive input from cutaneous tissue
- major site of action for opioids
lamina 1 and 5
contains visceral afferents
lamina 5
- responds to both noxious and non noxious stimuli
- receives both somatic an visceral inputs
spinothalmic tract
cross the midline to the level of the origin to the contralateral side of the spinal cord
-divided into lateral and medial
lateral spinothalmic tract
projects location, density, and duration of pain in the ventral posteriorlateral nucleus of the thalamus
medial spinothalmic tract
projects unpleasant emotional perception of pain in the medial thalamus
third order neurons
information transferred up to the thalamus
impulses then carried on the somatosensory cortex
modulation of pain
impulses arise in the periventricular/periaquaductal gray matter of brainstem
-impulses are transmitted through the raphe magnus to the substantia gelatinosa by way of the descending dorsolateral funiculus
enkelphins, substance P and pain
action potantials arriving at the substantia gelatinosa activate enkaphalin interneurons
- release of enkephalin decreases the release of substance P
- reduction in the number of pain impulses ascending in the lateral spinothalamic tract
- action potentials descending in the dorsolateral funiculus also hyperpolarize cell bodies of the second order neurons in the pain pathway
- reduction in the number of action potentials in the ascending lateral spinothalamic tract. The descending dorsolateral modulates pain
medication and pain
- IV opioids produce analgesia in part y initiating action potentials in the descending dorsolateral funiculus
- spinal analgenia, mediated by mu-2 receptors, occur when the number of pain impulses passing through the substantia gelatinosa is decreased
- IV opioids act in other sites in the brain (limbic, hypothalamus, and thalamus) produce supraspinal analgesia is mediated primarily by mu-1 receptors
- opioids act in complex fashion to decrease the perception of pain and decrease the response to pain
spinalreticular pain pathway
arousal and autonomic responses to pain
spinalmesencephalic pathway
anti-nocioceptive descending pathway because of its projections in the periductal gray area
pathway of fast-sharp pain
- A delta fibers enter and leave the tract of lissauer
- they then enter the dorsal horn and terminate at Rexed’s lamina 1, 5
- second order neurons leaving lamina 1 or 5 cross to the contralateral lateral spinothalamic tract and ascend to the brain
pathway of slow pain
the C fibers terminate primarily in lamina 2 (and 3) (substantia gelatinosa)
interneirons transmit C fiber impulses to lamina 5
neurons leaving 5 cross immediately to the contralateral lateral spinothalimic tract and ascend to the brain
primary neurotransmitters
A delta-glutamate
-binds to AMPA receptors on the postsynaptic membrane
C-fiber Substance P
-binds to NK-1 receptors on the postsynaptic membrane
tissue specific neurotransmitters
seratonin, histamine, prostaglandins, H+, K+
- arachidonic acid cascade
plasma specific neurotransmitters
kinins, histamine (platelets, basophils, granules of mast cells)
nerve terminal specific neurotransmitter
substance P
somatic pain
aching, often constant, possible dull or sharp, exacerbated with movement, well localized
visceral pain
constant/crampy, aching, poorly localized, referred
A-delta high threshold mechanoreceptors (HTMs)
noxious mechanical stimuli
A delta myelinated mechanothermal nocioceptors (MMTNs)
noxious heat and mechanical stimuli
C polymodal nocioceptors (CPNs)
noxious mechanical, thermal, chemical stimuli
muscle jints, faciae, other deep somatic structures C (group 4), A-delta (group 3) fibers
C afferent fibers, A-delta fibers
visceral
disease, inflammation, isometric contraction, ischemia, rapid distention
activated by noxious stimuli and allogenic substances
act as transducers
conducted to the dorsal horn or medulla
-influenced by intensity, duration, and microenvironment
muscle- skeletal/ cardiac transmission
- innervated by A delta and C fibers pain described as diffuse, poorly localized
- most intense during contraction, ischemia
- nocioceptors undergo sensitization in response to allogenic agents
Joint transmission
- innervated by A delta and C fibers
- respond only to extreme joint movement/ pressure
- can become sensitized with inflammation, leading to activation with normal movement, or developing background discharge
bone transmission
A delta and c fibers form a plexus around periosteum. Cortex/ marrow has no nocioceptive fibers has lowest threshold of deep somatic structures
visceral tissue transmission
A delta fibers, C fibers, not part of ANS
- insensitive to cutting, heating, pinching
- sensitive to twisting, distention
order of block
B, C and A delta, A gamma, A beta, A alpha
A alpha fibers A or E?
afferent and efferent fibers
A beta fibers A or E?
afferent and efferent fibers
A gamma fibers A or E?
efferent fibers
A delta fibers A or E?
afferent fibers
B fibers A or E?
efferent
C fibers A or E?
afferent
what does preganglionic autonomic mean?
from spinal cord to ganglion
Dorsal- afferent or efferent
afferent
ventral- afferent or efferent
efferent
what is the tract of lissaur
tract that carries signals a few levels up and down spine
if you stimulate enkelphalin receptors
with pain meds you stop the release of substance P
