PNS Revision Flashcards
what is a collection of nerve cell bodies known as in the CNS and PNS?
CNS = nucleus PNS = ganglion
dendrites vs axon?
dendrites = carry info towards the cell body axon = carries info away from the cell body, much longer
what does an axon connect to?
another neuron or an effector cell
Multipolar neuron?
- most common
- 2 or more dendrites
- all motor neurones of skeletal muscle and ANS
- cell body in CNS, axon in PNS
Unipolar neuron?
double process (aka pseudounipolar as technically have 2 processes but connect to a single point) involved in sensory function cell body in PNS
describe motor neurones?
efferent
impulse moves towards body wall, body cavity or organ
multipolar neuron
describe sensory neurone?
afferent
impulses moves towards the brain
unipolar
what are nerves?
collections of axons surrounded by connective tissue and blood vessels (called a tract in CNS)
single modality nerve?
all axons in the nerve carry the same one of - somatic motor, somatic sensory, special sensory, sympathetic, parasympathetic or visceral afferent
“tracts” in CNS tend to be single modality
mixed modality nerves?
somatic motor, somatic sensory and sympathetic all together in one nerve
(most nerves)
12 cranial nerves?
ophthalmic optic oculomotor trochlear trigeminal abducens facial vestibulocochlear glossopharyngeal vagus spinal accessory hypoglossal
cranial nerve modalities?
sensory sensory motor motor both motor both sensory both both motor motor
where do the cranial nerves attach to the CNS?
forebrain forebrain midbrain midbrain pons junction (P&Med) junction (P&Med) junction (P&Med) medulla medulla spinal cord medulla
in which direction are the cranial nerves named?
anterior to posterior and medial to lateral
what are the categories of spinal nerves?
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
where are the spinal nerves found?
only called a spinal nerve when in the intervertebral foramina
what do spinal nerves connect with?
structures of the soma via rami
the spinal cord segment of the same number via roots and rootlets
formation and divisions of spinal nerves?
anterior/posterior rootlets combine to form anterior/posterior roots
anterior/posterior roots combine to form the spinal nerve
spinal nerve then splits into anterior (large) and posterior (smaller) rami
what does the posterior rami supply?
posterior body wall
what does the anterior rami supply?
anterolateral body wall
spinal nerves/rami vs roots/rootlets?
roots/rootlets = only have one type of modality (anterior = motor, posterior = sensory)
spinal nerves/rami = all have mixed modality (somatic motor, somatic sensory and sympathetic innervation)
what is the dorsal root ganglion?
swelling in posterior root where cell bodies of primary afferent neurones are found
each spinal nerve pair supplies a body segment with what?
general sensory supply to all structures
somatic motor supply to skeletal muscles
sympathetic nerve supply to the skin and to the smooth muscle of arteries
what is a dermatome?
area of skin supplied with sensory innervation from a single spinal nerve which also supplies sensory innervation to deeper structures
is there any overlap in the sensory innervation of the skin of a dermatome?
yes innervation of skin is from adjacent spinal nerves
therefore if a dermatome is numb, more than one spinal nerve is damaged
what is a myotome?
the skeletal muscles supplied with motor innervation from a single spinal nerve
may be deep to the dermatome of the same spinal nerve, but not always
(T2 - T12 tend to have the same dermatome/myotome)
give an example of different dermatome/myotome?
C3,4,5
dermatome = shoulder and upper arm
myotome = diaphragm
dermatome landmarks?
nipple = T4 segment umbilicus = T10
dermatomes of posterior scalp, neck and shoulder?
C2-4
upper limb dermatomes?
C5-T1
lower limb, gluteal region and perineum dermatomes?
L2-Co1
what are nerve plexuses formed of?
intermingled ANTERIOR rami from a number of adjacent spinal nerves
what makes up the cervical plexus?
C1-C4
posterior scalp, neck and diaphragm
brachial plexus?
C5-T1
upper limb
lumbar plexus?
L1-L4
lower limb
sacral plexus?
L5-S4
lower limb, gluteal region and perineum
describe sympathetic outflow?
originates from control centres in the brain
passes down spinal cord and exits via T1 - L2
why can sympathetic outflow only exit via T1 - L2?
only they have lateral horns which contain cell bodies with presynaptic sympathetic axons
what is sympathetic innervation? what does this mean for outflow?
motor innervation
means it has to come from anterior roots/rootlets
what are the 4 possible routes of exit from the spinal cord for sympathetic outflow?
- ascend and then synapse
Synapse at level of entry - Descend then synapse
- Pass through sympathetic trunk without synapsing to enter an abdominopelvic splanchnic nerve
sympathetic innervation is present in all spinal nerves, true or false?
true
just takes different routes to get into the nerves
paravertebral ganglia?
sympathetic chain
Sympathetic outflow to the heart?
presynaptic axons synapse in T1 or cervical paravertebral ganglia
postsynaptic axons then pass in cardiopulmonary splanchnic nerves to the SA and AV nodes in myocardium
lungs sympathetic outflow?
presynaptic axons synapse in upper thoracic paravertebral ganglia
postsynaptic axons pass in cardiopulmonary splanchnic nerves to the bronchiolar smooth muscle and mucous glands
abdominopelvic organs sympathetic outflow?
presynaptic axons synapse in one of the prevertebral ganglia (outside of the spinal column)
adrenal medulla sympathetic outflow?
presynaptic axons pass through the aorticorenal ganglion to synapse directly onto the adrenaline/noradrenaline secreting cells of the adrenal medulla
describe parasympathetic outflow?
presynaptic axons leave the CNS via cranial nerves 3, 7, 9, 10 and sacral spinal nerves then travel via:
- ciliary ganglion (eye)
- parasympathetic ganglia in head (lacrimal/salivary glands)
- vagus nerve (organs between neck and mid-gut)
- sacral spinal nerves (hind-gut to perineum)
why do symptoms occur in horners syndrome?
no sympathetic innervation to the dilator pupillae = miosis
no innervation to LPS = droopy eyelid (ptosis)
no innervation to sweat glands = reduced sweating
reduced innervation to arterioles = dilation = increased warmth and redness
