Autonomic Nervous System Flashcards
What are the 2 types of nerve fibres in the PNS?
- somatic
- autonomic
What does the somatic nervous system supply?
motor supply to the voluntary striated skeletal muscle
aka lower motor neurons
conscious movement
What do the autonomic fibres supply?
aka the visceromotor
supply smooth muscle, cardiac muscle and contractile elements of glands
involuntary, self-regulating and predominantly subconscious
What controls the ANS?
descending impulses from the hypothalamus
ANS actions contribute to homeostasis
What is the structure of the somatic NS pathway/tract?
single (lower motor) neon between CNS and target structure
nerve cell body is in CNS
axon reaches target skeletal muscle via a peripheral nerve
What is the structure of the ANS pathway/tract?
2-neuron chain between CNS and target structure
preganglionic and postganglionic
and an intervening autonomic ganglion
What are the 2 plexus arrangements in the bowel?
- submucosal plexus of Meissener
- myenteric plexus of Auerbach
together this = enteric NS
Where are the cell bodies of pre-ganglionic sympathetic neurones located?
intermediolateral column of the spinal cord grey matter
[present only in the thoracic and upper 2-3 lumbar vertebrae of spinal cord T1 -L2/3)
= sympathetic outflow
Where do axons of the pre-ganglionic neurones leave the spinal cord?
via ventral (motor) root
here they join the mixed spinal nerve
then enter the sympathetic trunk (almost immediately)
What is the sympathetic trunk?
chain of autonomic ganglia
lies close to the spinal cord on either side of the vertebral column
sympathetic chain extends above and below into the cervical and lumbosacral regions
How do pre-ganglionic neurons enter the sympathetic chain?
via myelinated (white matter) communicating rami
What can a pre-ganglionic fibre do once it has entered the sympathetic chain?
- synapse on a post-ganglionic neurone at its own segment al level
- travel up the chain to synapse in a ganglion higher up
- travel down the chain to synapse in a ganglion lower down
- pass through the chain without synapsing and travel towards the gut
Where do most pre-ganglionic fibres synapse?
onto a post-ganglionic neuron at their own vertebral level
will rejoin the mixed spinal nerve via the unmyelinated (grey matter) communicating ramus
Where are white rami found?
White rami = myelinated neurones
between T1 and L3 only
Where are grey rami found?
grey rami = unmyelinated neurones
found at every vertebral level
[all spinal nerve roos receive post-ganglionic fibres from the sympathetic chain
Where do the lesser, greater and least splanchnic nerves originate?
As pre-ganglionic fibres that pass through the sympathetic chain w/o synapsing
arise from lower half of sympathetic chain
Where do the splanchnic nerves terminate?
[aka gut related]
terminate in 3x para-aortic ganglia
lie in front of the main abdo aortic branches (coeliac, SMA, IMA)
sympathetic axons enter arterial walls and are distributed via the blood vessels
What are the 3 ganglia present in the cervical portion of the sympathetic chain?
superior
middle
inferior
What is the stellate ganglion?
- star shaped
formed from the fusion of the inferior cervical and T1 ganglion?
Where does the sympathetic supply to the head arise?
T1
= highest level of sympathetic outflow
What is the course of the pre-ganglionic sympathetic fibres as they leave at T1?
ascend without synapsing to each supervisor cervical ganglion
most fibres then enter the internal carotid artery (= internal carotid sympathetic plexus)
What branches does the pre-sympathetic sympathetic fibres travelling in the internal carotid give rise to?
e.g
dilator pupillae muscle of eye
superior tarsal muscle (smooth muscle component of the eyelid elevator)
What allows for distribution of the fibres innervating the facial sweat glands?
external carotid artery
What is Horner’s syndrome?
loss of sympathetic innervation to one side of the face
What are the signs of clinical syndrome?
- a small, unreactive pupil (miosis)
- slight drooping of the eyelid (partial ptosis)
- loss of sweating on one side of the face (facial anhidrosis)
Why is enopthalmos not considered a true feature of Horner’s syndrome?
= posterior displacement of eye
sunken eyeball created by false impression by combo of narrow palpebral fissure and a small pupil
What does partial Horner’s syndrome feature?
occurs when sympathetic pathway is interrupted after the facial sweat gland fibres have left to join the external carotid artery
- may lack facial anhidrosis
What are the anatomical locations for the causes of Horner’s syndrome?
LATERAL MEDULLA
stroke, tumour
interrupts sympathetic control pathway from hypothalamus to T1
SPINAL CORD
traumatic transection
above T1
NERVE ROOT or BRACHIAL PLEXUS
trauma, infiltrating tumour
SYMPATHETIC TRUNK
as it passes near apex of lung
by a malignant tumour (Pancoast tumour)
WALL OF INTERNAL CAROTID
trauma, aneurysm, arterial dissection
What features may help to identify lesion causing Horner’s syndrome?
- presence/absence of facial anhidrosis (whether lesion/interruption is pre- or post-ganglionic
- cranial nerve
- cerebellar signs
(if causal lesion is part of the lateral medulla)
What is the sympathetic make-up of the adrenal gland?
large, modified sympathetic ganglion
contains post-ganglionic neurones that have lost their axons
What are the adrenal medullary cells innervated by?
pre-ganglionic sympathetic fibres
which secrete adrenaline directly into the bloodstream (therefore hormone not NT)
causes body-wide activation of adrenergic receptors [fight or flight response]
What kind of fibres are the majority of post-ganglionic sympathetic fibres?
noradrenergic (or adrenergic)
exception: fibres which innervate the skin of limbs and trunk
What is the nature of the sympathetic fibres which innervate the limb/trunk skin\?
use ACh rather than NA as neurotransmitter
supply sweat glands, piloerrector muscles and smooth muscle within dermal blood vessels
hence why there is sympathetic discharge during fight/flight response and in major trauma, MI
=> pale, clammy skin
=> goose bumps
What is the orgin of the parasympathetic nervous system?
craniosacral outflow
Which 4 cranial nerves carry PNS nerve fibres?
OCULOMOTOR
CN III
originates from the Edinger-Westphal nucleus
in midbrain
FACIAL
CN VII
originates from superior salivatory nucleus
in the pons
GLOSSOPHARYNGEAL
CN IX
originates from the inferior salivatory nucleus
in the medulla
VAGUS
CN X
originates from he dorsal motor nucleus of the vagus
in the medulla
What are the 4 types of autonomic ganglia?
- ciliary
- pterygopalatine
- otic
- submandibular
What is the course of PNS fibres supplying the head?
- cell bodies are in a cranial nerve nucleus
- pre-ganglionic axon travels with associated cranial nerve
- then synapses in one of the autonomic ganglia
How do fibres from the Edinger-Westphal nucleus reach the pupil constrictor muscle?
travel in the oculomotor nerve
via the ciliary ganglion
in orbit
What innervates the salivary and lacrimal glands?
facial (CN VII) and glossopharyngeal (CN IX) nerves
CN IX supplies the parotid gland
CN VII supplies remainder
What are the mural/intramural ganglia in the viscera of the thorax and abdomen?
PNS fibres originating from the vagus nerve
form autonomic plexuses which lie close to heart, lungs, stomach and intestines
often situated in or on walls of target organs
What is the PNS supply to the bowel and pelvic contents?
pelvic splanchnic nerves
arise from S2-S4
terminate in the hypogastric plexus
contribute to sexual function/continence
How is continence maintained by the bladder?
function of 2 sphincters, which are tonically-active muscles and lie inferior to bladder
INTERNAL URETHRAL SPHINCTER
contains smooth muscle
under sympathetic control
EXTERNAL URETHRAL SPHINCTER
composed of striated muscle
is tonically active but also can relaxed through voluntary control to enable voiding
Which higher centres control decision to void (bladder) belong infancy?
1) pontine micturition centre (brain stem)
2) cingulate gyrus (medial frontal region) - responds to pain and discomfort
What occurs in the filling cycle of the bladder?
bladder is empty
passively fills with urine
stretch receptors signal when bladder is half full (need to pass urine feeling)
as bladder fills more, stretch further increases (causing trigger of sacral parasympathetic reflex)
What is the neural pathway initiated after stretch receptors signal that bladder is half full?
sensation for needing to pass urine
ascending pathway
projects to brain
What is the function of the sacral parasympathetic reflex in the bladder?
causes detrusor (smooth) muscle to contract
accompanied by relaxation of internal urethral sphincter (reflex inhibition) of normal SNS tone
How is bladder voiding initiated?
conscious/voluntary action
projection from medial frontal lobe to pontine micturition centre
causes relaxation of the voluntary striated external urethral sphincter
passive bladder emptying occurs
assisted by detrusor muscle contraction + increase in intra-abdominal pressure
What are the hollow viscera sensitive to?
distension
twisting
ischaemia
[but not to cutting or burning]
Where are the sensory neurons for internal organs located?
these signal “visceral pain”
cell bodies located within the dorsal root ganglia
central processes enter the dorsal root of spinal cord to join the spinothalamic tract
What is the spinothalamic tract involved in?
temperature and pain
Where do visceral afferent fibres travel?
carry sensory info towards spinal cord
travel in the same nerve trunk that provides sympathetic innervation to the target organ
Where does the sympathetic innervation of the heart arise?
sympathetic: T1-T5
visceral afferents from heart trance along same nerve trunks (but different axons, and transmitting impulses in opposite direction)
Why are the visceral afferent fibres from the heart the ‘most silent’?
majority of people do not regularly experience pain of cardiac origin
(even in middle age or elderly)
What is the putative reason why the brain misinterprets nociception of visceral origin as somatic pain?
[not proven]
visceral and somatic sensory fibres might converge on the very same second order neurons (of spinothalamic tract) that convey temp. and pain sensations
What is the embryological explanation for other forms of referred pain?
same developmental origin of many far apart organs which may have retained the same innervation
e.g. gall bladder inflammation can lead to ipsilateral (RHS) shoulder pain (C4 dermatome)
caused by irritation of the diaphragm supplied by phrenic nerve
diaphragm, liver/gallbladder arise in the cervical region during development
but after development all structures all retain their original (cervical) nerve supply
Which type of nerve fibre innervates voluntary skeletal muscle?
somatomotor fibres
Where are the cell bodies of the first-order somatosensory neurons for the limb and trunk?
dorsal root ganglia
What is the main voluntary motor pathway of the CNS?
pyramidal tract
What do we call the orderly point-to-point arrangement of sensory fibres from different body parts (found in the somatic sensory pathways)?
somatotropic
Approximately how many axons (nerve fibres) are found in each corticospinal tract?
1 million
Which pathway provides voluntary motor control for movements of the jaw, face, tongue, larynx and pharynx?
corticobulbar
Stroke patients with spastic limbs can show
- marked upper limb flexion +
- lower limb extension
What is this characteristic postural pattern called?
pyramidal weakness
Where are Auberbach and Meissner’s plexuses located?
in the intestinal wall
Which major brain region is called the ‘gateway’ to the cerebral cortex?
thalamus
Where in the brain is the primary motor cortex (M1)?
Postcentral gyrus
At which vertebral level does the spinal cord normally terminate in the adult?
L1-2
Which major sensory pathway is the only one to enter the cerebral cortex directly?
e.g. w/o passing via a thalamic ‘relay’ nucleus
olfactory
Which white matter pathway contains the corticospinal (primary motor) tract?
Internal capsule
Which white matter pathway transmit somatosensory impulses for vibration and proprioception from the lower limbs?
Cuneate fasciculus
The sympathetic chain ganglia are innervated from which spinal cord levels?
T1-L2/3
Where in the brain is the primary somatosensory cortex (S1)?
Postcentral gyrus
Inflammation of the gallbladder might lead to referred pain in which dermatome?
C4
will cause referred pain in the shoulder (tip) which is innervated by the phrenic nerve (vertebral origin is C3-5)
Which of the following clinical signs could be produced by a UNILATERAL SPINAL CORD LESION affecting the corticospinal tract?
contralateral spasticity
Which NT has a pain-relieving (analgesic) effect in the spinal cord?
serotonin
If a patient has tremor and muscular rigidity, which part of the brain might be affected?
basal ganglia
What are the 3 groups of pre-ganglionic SNS fibres that pass straight through the sympathetic chain (w/o synapsing) to terminate in ganglia just in front of the aorta?
splanchnic nerves
Where does the corticospinal tract decussate?
at the junction between the brainstem and the spinal cord
Where is the brain’s micturition centre located?
in the Pons
What name is given to the most anterior part of the midbrain, which contains the corticospinal (primary motor) tract?
crus cerebri
Which nerves arise from S2-S4 and are important for penile erection in males?
Nervi erigentes
If a patient has a combo of muscle weakness, wasting and fasciculations PLUS hypertonia, spasticity and hyperreflexia, what is the probable Dx?
Motor neurone disease (MND)
Which PNS brain stem nucleus is responsible for pupillary constriction?
Edinger-Westphal nucleus
What is the best way to test the integrity of the dorsal columns of the spinal cord?
using a vibrating tuning fork
Interruption of the SNS supply to the head results in which syndrome?
Horner’s
In the dorsal column pathway, where is the cell body of the second order neurons?
medulla
Where are the cell bodies of ‘lower motor neurones’ for the trunk and limbs found?
ventral horn of the spinal cord
Which spinal cord reflex is responsible for normal muscle tone?
stretch reflex
What clinical sign is most suggestive of an upper motor lesion (rather than a lower motor lesion)?
clonus
Which NT is released by post-ganglionic SNS fibres that innervate sweat glands in the limbs and trunk?
ACh
In the somatosensory pathways, where is the cell body of the third order neuron found?
thalamus, ventral posterior (VP) nucleus
Damage at which anatomical site could be responsible for spasticity, hypertonia and increased tendon reflexes in the limbs?
precentral gyrus
In the spinothalamic tract, where are the cell bodies of the second order neurones?
dorsal horn of spinal cord
Which pathway is responsible for facial sensation?
trigeminothalamic
A lesion at which anatomical site could be responsible for weakness, wasting, reduced tone and fasciculations of the limbs?
anterior horn of the spinal cord
Which CN roots carry PNS fibres?
CN III (oculomotor) CN VII (facial) CN IX (glossopharyngeal) CN X (vagus)
