Autonomic Nervous System

Question 1

What does the overall arrangement of the ANS aim to do?

Answer 1

LOCALISE the autonomic output to certain areas for greater effect

CONVEY the correct autonomic neurotransmitters to receptors in target structures

DISTRIBUTE autonomic fibres to all parts of the body

Question 2

Autonomic vs Somatic NS

Answer 2

ANS
- chain of two motor neurons
~ preganglionic neuron
~ postganglionic neuron
- conduction is slower due to thinly or unmyelinated axons

SNS
- one motor neuron extends from the CNS to skeletal muscle
- axons are well myelinated, conduct impulses rapidly

Question 3

what does the lateral horn of the spinal cord contain?

Answer 3

cell bodies of sympathetic neurons

Question 4

Where is the lateral horn present?

Answer 4

the spinal cord between T1-L2/3

Question 5

What is THORACOLUMBAR outflow?

Answer 5

lateral horn (between T1-L2/3) and preganglionic sympathetic fibres that emerge from vertebral column at the same level

Question 6

What is SACRAL outflow?

Answer 6

Preganglionic parasympathetic fibres emerge from spinal nerves S2-4

Question 7

How do spinal nerves above T1-L2/3 receive their sympathetic fibres?

Answer 7

By making use of the paired sympathetic trunks lying on each side of the vertebral column from C1- Cc1

Question 8

What does the sympathetic trunk allow?

Answer 8

preganglionic sympathetic fibres to rejoin the spinal nerve at the same vertebral level

Question 9

How does the spinal nerve connect with the sympathetic trunk?

Answer 9

• WHITE rami communicans from spinal nerve to ST ganglion
• synapse in ST ganglion
• GREY rami communicans from ST back to spinal nerve
• Sympathetic fibres then distribute in ventral and dorsal rami of spinal nerve

Question 10

grey rami communications are…

Answer 10

unmyelinated, postganglionic

Question 11

Define mass sympathetic distribution

Answer 11

ST allows all spinal nerves from C1-Cc2 carry sympathetic fibres, meaning all parts of the body can receive sympathetic innervation

Question 12

What are splanchnic nerves?

Answer 12

sympathetic preganglionic fibres lying out with ST that supply the abdominal organs without synapsing in the ST

Question 13

What are the 3 options of sympathetic fibres emerging from the lateral horn in the sympathetic trunk?

Answer 13

1. they can synapse in the trunk at the SAME LEVEL as they originate in the spinal cord
2. they can run up or down the trunk and synapse at a HIGHER or LOWER level
3. they can PASS RIGHT THROUGH THE ST WITHOUT SYNAPSING there and instead synapse in a sympathetic ganglion lying OUTWITH ST

Question 14

Since ST starts at C1, how do structures in the face and head receive sympathetic supply?

Answer 14

After running up ST and synapsing in one of 3 cervical ST ganglia, the sympathetic fibres then utilise the blood vessels going to the face and head by ‘climbing’ up them

Question 15

Whats the name of the syndrome for when sympathetic fibres are stretched or damaged along their course to the face and head

Answer 15

Horner’s syndrome

Question 15

What is craniosacral outflow?

Answer 15

Parasympathetic nerve fibres arise from the CNS with the S2,S3 and S4 spinal nerves (and also from the 3rd, 7th, 9th and 10th (vagus) cranial nerves)

Question 16

What are the pelvic splanchnic nerves?

Answer 16

S2-S4 preganglionic parasympathetic fibres to pelvic organs