Introduction to the Autonomic Nervous System

Question 1

Describe the basic structure, characteristics, and function of the ANS.

Answer 1

• Connection between the central nervous system and the peripheral organs
• Largely outside of voluntary control
• Subdivided into two nervous systems (parasympathetic and sympathetic)
• Often has opposing effects on tissues

Question 2

What are ganglia? What do ganglia in the ANS have in common?

Answer 2

• GANGLIA are spaces between two adjacent neurons in the ANS
• All autonomic ganglia have ACh as their main neurotransmitter

Question 3

Compare and contrast the sympathetic nervous system and the parasympathetic nervous system.

Answer 3

SYMPATHETIC NERVOUS SYSTEM
- Thoraco-lumbar outflow
- The pre-ganglionic nerves are short, while the post-ganglionic nerves are long.
- Ganglia close to CNS
- ACh released at ganglia
- Postganglionic nerves release noradrenaline for most tissues e.g at the arteries and heart (exception is sweat glands - ACh is released instead)
- Post-ganglionic nerves are not myelinated
- Pre-ganglionic nerves are lightly myelinated

PARASYMPATHETIC NERVOUS SYSTEM
- Sacro-cranial outflow
- The pre-ganglionic nerves are long, while the post-ganglionic nerves are short.
- ACh released at ganglia
- Postganglionic nerves release ACh which bind to nAChRs on effectors
- Ganglia close to affected organ
- Post-ganglionic nerves are not myelinated
- Pre-ganglionic nerves are lightly myelinated

Question 4

Are there any nerves in the sympathetic nervous system that don’t use ganglia?

Answer 4

YES
- 1 lightly myelinated specialised nerve passing directly to adrenal gland - releases ACh and there are no ganglia

Question 5

List examples of parasympathetic nerves.

Answer 5

• CRANIAL NERVE III (OCULOMOTOR)
  Affects the pupil
• CRANIAL NERVE VII (FACIAL)
  Affects the lacrimal glands
• CRANIAL NERVE X (VAGUS)
  Affects the heart, kidneys, bronchi and the GI tract
• SACCRAL NERVE
  Affects rest of GI tract, bladder

Question 6

List examples of sympathetic nerves.

Answer 6

• SUPERIOR CERVICAL PARAVERTEBRAL GANGLIA
  Affects the pupil, facial glands and head circulation
• MIDDLE and INFERIOR PARAVERTEBRAL GANGLIA
  Affects the heart and lungs
• remaining PARAVERTEBRAL GANGLIA
  Affect the sweat glands, pilomotor (hair) muscles, blood vessels of the skeletal muscle and skin
• PREVERTEBRAL GANGLIA
  Affects the GI tract

Prevertebral ganglia lie between the paravertebral ganglia and the target organ.

Question 7

List three non-adrenergic, non-cholinergic (NANC) (non-sympathetic and non-parasympathetic) transmitters.

Answer 7

• ATP/NEUROPEPTIDE Y (NPY)
  Works on the post-ganglionic sympathetic neurone, and causes vasoconstriction
• VASOACTIVE INTESTINAL PEPTIDE (VIP)
  Works on the salivary glands or bronchial smooth muscle, and causes dilation
• NITRIC OXIDE (NO)
  Works on the parasympathetic pelvic nerves, and causes erection

Question 8

Explain the antagonistic effects of the two systems using the heart as an example.

Answer 8

• The heart is innervated by both the parasympathetic and sympathetic nervous system.
• When the parasympathetic nerves are stimulated, they induce a slower heart rate. When the sympathetic nerves are stimulated, they induce a faster heart rate.

Question 9

What is a single nerve tissue?

Answer 9

• Tissue controlled by ANS but without opposing effects
• Only governed by one division of the ANS (not both)

Question 10

Give some examples of single nerve tissues, and specify which autonomic nervous system governs the tissue.

Answer 10

• Bronchial smooth muscle
• Ciliary eye muscle
  These are governed by the parasympathetic system.
• Blood vessels
• Sweat glands
  These are governed by the sympathetic system.

Question 11

What are three characteristics of the somatic nervous system?

Answer 11

• Heavily myelinated
• ACh produced as neurotransmitter
• Work on skeletal muscle