ANS and sympathetic blocks Flashcards
Which of the following statements regarding the autonomic nervous system is false?
a. They are not under voluntary control
b. Nerves may be myelinated or unmyelinated c. They help mainly by sensing danger
d. They respond to internal stimuli
C
Which of the following statements regarding the autonomic nervous system (ANS) is correct?
a. The sympathetic and parasympathetic nervous systems are independent of each other
b. Parasympathetic system is active during rest
c. The effects of acetylcholine are stimulatory
d. The effects of norepinephrine are inhibitory
B
Although most often, the two divisions of the autonomic nervous system have opposing actions, this is not always the case. Many organs have ‘dual innervation’, and the two divisions, sympathetic and parasympathetic, work synergistically to maintain homeostasis.
Parasympathetic division predominates in resting conditions, while the sympathetic division takes over during stress. While the former is usually inhibitory, the latter is usually stimulatory.
At preganglionic neurons, acetylcholine (ACh) is always stimulatory, while it can be either stimulatory or inhibitory at postganglionic neurons. Norepinephrine at postganglionic sympathetic terminals is usually stimulatory.
Which of the following organs lack a dual innervation from the ANS? a. Eye
b. Salivary glands
c. Liver
d. Lacrimal glands
D
Note: examples of single-organ innervations are:
parasympathetic only – lacrimal glands
sympathetic only – adrenal medulla, arterioles in skin, viscera and kidney.
Which one of the following statements correctly reflects the difference between sympathetic and parasympathetic nervous systems?
a. Sympathetic systems have long preganglionic neurons, while those of parasympathetic are short
b. Sympathetic systems have long postganglionic neurons, while those of parasympathetic are short
c. Sympathetic postganglionic neurons always release norepinephrine, while those of parasympathetic always release acetylcholine
d. Sympathetic postganglionic neurons sometimes release norepinephrine while those of parasympathetic always release acetylcholine.
B
Note: sometimes, the postganglionic neurons of the sympathetic system may
release ACh; for example, sweat glands and smooth muscles of skin and
blood vessels.
Regarding the organisation of the sympathetic nervous system, which of the following statements is false?
a. It originates from lateral grey horns of T1–L2 spinal segments
b. It is organised into two paraverterbral chains on either side of vertebrae
c. Each paraverterbral ganglia receives preganglionic fibres from the white ramus while it passes on the postganglionic fibres through the grey ramus d. Suprarenal medulla is a modified sympathetic ganglion
C The sympathetic division has the following organisational features:
Originates from thoracolumbar outflow, i.e. neurons in lateral grey horns of T1–L2. Their axons enter the ventral roots of spinal segments.
These axons may relay in:
Paravertebral (or lateral) ganglia: on either side of vertebral body. Three cervical (superior, middle and inferior), 12 thoracic, two to four lumbar, four to five sacral and one coccygeal (join in midline to form ganglion impar).
Prevertebral (or collateral) ganglia: coeliac, superior mesenteric and inferior mesenteric ganglia. They form their respective plexuses. Suprarenal medulla: modified sympathetic ganglia. The chromaffin cells (postganglionic neurons) do not have postganglionic fibres. They are neural crest derivatives.
Plexus: cardiac, pulmonary, oesophageal, hypogastric.
They receive preganglionic fibres from the white ramus while passing on the postganglionic fibres through the grey ramus. Since the outflow is received from T1–L2, only these spinal nerves have white ramus, while others do not. However, all spinal nerves have a grey ramus.
After entering the white ramus, preganglionic fibres of the sympathetic division of the ANS course along which of the following paths?
a. Synapse in the corresponding paraverterbral ganglia
b. Ascend or descend in the sympathetic chain to relay in other paraverterbral ganglia
c. Pass through paraverterbral ganglia without relaying to synapse in the peripheral ganglia
d. Any of the above
D After entering the white ramus, preganglionic fibres of the sympathetic division of ANS may course along any of the following paths:
Synapse in the corresponding paraverterbral ganglia. The postganglionic fibres join the spinal nerves through the grey ramus, to relay to the blood vessels of the skin and skeletal muscles, and in sweat glands.
Ascend or descend in the sympathetic chain to relay in other paraverterbral ganglia. This is the cause for the widespread action of the sympathetic division.
Pass through paraverterbral ganglia without relaying to synapse in the peripheral ganglia such as prevertebral ganglia or suprarenal glands.
Which of the following statements regarding the sympathetic nerve supply of body parts has both incorrect?
a. Head – C1–C4
b. Thoracic viscera – T1–T4
c. Abdominal viscera – T4–L2 d. Suprarenal medulla – T5–T8
A
Note: there is no craniosacral sympathetic outflow. Hence they derive sympathetic supply through nearest sympathetic ganglia. Cervical areas receive sympathetic supply through upper-thoracic segments, while the sacral
(pelvic) areas receive same through lower thoracolumbar segments.
Regarding the parasympathetic division of the ANS, which one of the following statements is false?
a. It is primarily craniosacral in origin
b. Preganglionic fibres are long, while the postganglionic fibres are short c. Most of its supply is distributed through the hypogastric plexus
d. Most of the parasympathetic ganglia are located peripherally
C The parasympathetic system originates in the brain stem (CNIII, VII,
IX, and X) and the sacral spinal segments (S2–S4 – nervi erigentes). Hence, it is often called the craniosacral outflow. The vagus nerve (CNX) carries 75% of the distribution of parasympathetic division. Unlike sympathetic ganglia, parasympathetic ganglia are quite distant from the brainstem and cord, often located directly on the effector organ itself. Thus the
preganglionic fibres are longer, while the postganglionic fibres are shorter.
Regarding the sensory nerve supply of the viscera (general visceral afferents), which of the following is incorrect?
a. Most are carried through the sympathetic division
b. They are not involved in referred pain
c. We are generally unaware of these afferent impulses
d. Visceral afferents conduct sensory information to higher centres, but do not relay in autonomic ganglia
B Sensory information from the viscera travels via GVA – general visceral afferents. They are fibres that use the ANS efferents as a conveyor belt to send sensory information from the viscera to higher centres. They mostly use the sympathetic efferents, but parasympathetic efferents are also used (CNIX, X, and sacral nerves). They do not relay in the peripheral ganglia. We are not aware of these sensations unless they cross the pain
threshold. This may then lead to referred pain.
Which of the following reflexes is mediated via the parasympathetic division of the ANS?
a. Direct light reflex
b. Cardioaccelerator reflex
c. Vasomotor reflex d. Pupillary reflex
A
Regarding the performance of stellate ganglion block, which one of the following statements is incorrect?
a. It is performed at C6 level
b. Carotid artery is pushed medially
c. Nasal congestion is an undesirable complication of the block d. Brachial plexus block may result
B
Cervical sympathetic ganglia are three in number: superior, middle and inferior. They communicate via grey rami with C1–C4, C5–C6 and C7– C8 spinal segments. They have no white rami. The inferior cervical ganglia are fused with upper thoracic (T1 usually) to form the stellate ganglia.
The stellate ganglia lie at the level of transverse process of the C7 vertebra. It lies in front of vertebral artery, brachial plexus sheath and neck of the first rib. Subclavian artery lies at or above it.
For a stellate ganglion block, the patient lies supine with the neck slightly extended. The Chassaignac tubercle (C6) is palpated between the sternocleidomastoid muscle and the trachea at cricoid level. The operator then pushes the carotid artery laterally. After raising a skin wheal, a 22-gauge, 5-cm needle with a 10-mL syringe attached is inserted perpendicularly until the tip contacts the C6 transverse process. The needle is then withdrawn 1–2 mm and is fixed. After careful aspiration, 10 mL of local anaesthetic solution is injected in 1- mL increments.
Signs of success: Horner syndrome, anhidrosis, injection of the conjunctiva, nasal congestion, vasodilatation and increased skin temperature.
Complications: haematoma, bleeding, pneumothorax, intravascular injections, seizures, spinal cord trauma, unintended nerve blocks (vagus, phrenic, brachial plexus, recurrent laryngeal), QTc alterations.
Note: stellate ganglion lies at C7 (or below), but is blocked at C6 as this is
safer. Vertebral artery and subclavian artery at lower levels may increase the
risk at C7. Hence a high-volume injection at C6 is expected to do the job!
Of the following, all are indications for stellate ganglion block except: a. Angina pain after recent myocardial infarction
b. Phantom limb pain
c. Frostbite
d. Raynaud’s disease
A
Regarding the coeliac plexus, the following are true except: a. It provides sympathetic supply to abdominal organs
b. It lies anterior to aorta at T12–L1 level
c. Block is performed mainly to block the sympathetic fibres
d. It receives parasympathetic supply through the vagus
C The thoracic organs are supplied by cardiac plexus, the abdominal organs by coeliac plexus, while the pelvic organs are supplied by the hypogastric plexus. Of these, the coeliac is the largest. It is also known as the solar plexus. It supplies all abdominal organs and intestines up to the splenic flexure. The coeliac ganglia are between two and 10 (average five) in number and lie anterior to the aorta at T12–L1 level on either side. The supra-renal glands lie lateral to celiac plexus while the stomach and pancreas are located anterior to it. The celiac plexus receives its sympathetic supply through the greater splanchnic nerve (T5–T6 to T9–T10), lesser splanchnic nerve (T10–T11) and least splanchnic nerve (T11–T12). The celiac plexus receives its parasympathetic supply from the left and right vagal trunks. The celiac plexus also transits the visceral afferents, which accounts for pain relief following celiac plexus block. The main indication for coeliac plexus block is pancreatic cancer pain.
Regarding the performance of coeliac ganglion block, which of the following is true?
a. Posterior retrocrural approach is inappropriate and hence least commonly practised
b. The solution is best deposited after hitting the transverse process
c. Transmitted aortic pulsations are a dangerous sign and needle should be redirected superficially
d. Landmarks can be the 11th or 12th rib
A Various approaches have been described for coeliac plexus:
posterior (most common) – retrocrural, transcrural or transaortic posterior paramedian
anterior approach
endoscopic approach
Posterior retrocrural approach: patient is given prone position, and a pillow under the abdomen is used to eliminate lumbar lordosis. Then lines connecting the T12 spine with points 7–8 cm lateral at the lower edges of the 12th ribs are drawn forming a flattened isosceles triangle. After raising a skin wheal, a 20-G, 10–15 cm needle is inserted on the left side at 45° angle toward the body of L1. Bony contact should be made at an average depth of 7–9 cm (superficial bony contact at 5–6 cm means hitting transverse process and should never be accepted). The needle is then withdrawn and redirected to slide off the tip past the vertebral body anterolaterally. It is then advanced 1.5–2 cm past this point to feel transmitted aortic pulsations along the needle (which allows the finger holding it to act as a pressure transducer). Once this depth is ascertained, the right-sided needle is inserted in a similar fashion to a depth of 1.0–1.5 cm farther than the left. After checking for blood, CSF and
urine, a test dose is given. The main dose is given after this incrementally.
Note: identifying the 11th rib instead of the 12th rib significantly increases the risk of pneumothorax!
Which of the following is not a complication of coeliac plexus block? a. Pneumothorax
b. Hypotension
c. Constipation
d. Kidney injury
C
Others:
infections
unopposed parasympathetic: diarrhoea alcohol intoxication or acetaldehyde syndrome.
Which one of the following blocks is correctly matched with the indication for its use?
a. Coeliac plexus block – lymphoedema
b. Hypogastric plexus block – pancreatic cancer pain
c. Ganglion impar block – coccydynia
d. Stellate ganglion block – hypohydrosis
C
