ANS Physiology

Question 1

Describe the basic structure of the Autonomic Nervous System.

Answer 1

• it’s a connection between the central nervous system and the peripheral organs
• it’s largely outside of voluntary control
• it’s a two neurone system (parasympathetic and sympathetic)
• it often has opposing effects on tissues (BUT, some tissues may have a single nerve supply, meaning that the ANS will only affect it in one way, as opposed to normally having opposing effects)

Question 2

Describe the differences in the structure of nerves in the different parts of the sympathetic and the parasympathetic systems.

Answer 2

PARASYMPATHETIC:
The pre-ganglionic nerves are long, while the post-ganglionic nerves are short.
The pre-ganglionic nerves are lightly myelinated and release Acetylcholine. The post-ganglionic nerves are not myelinated and also release Acetylcholine.
It acts on the salivary gland, GI tract, heart and acid cells.

SYMPATHETIC:
The pre-ganglionic nerves are short, while the post-ganglionic nerves are long.

• In the arteries and the heart:
  The preganglionic nerves are lightly myelinated and release Acetylcholine. The post-ganglionic nerves are not myelinated and release Noradrenaline.
• In the sweat glands:
  The pre-ganglionic nerves are lightly myelinated and release Acetylcholine. The post-ganglionic nerves are not myelinated and release Acetylcholine.
• In the adrenal glands:
  There is only one nerve. It is lightly myelinated and releases Acetylcholine.

Question 3

List a few examples of parasympathetic nerves.

Answer 3

• CRANIAL NERVE III (OCULOMOTOR)
  affects the pupil
• CRANIAL NERVE VII (FACIAL)
  affects the sub-auxiliary, sublingual and lacrimal glands
• CRANIAL NERVE IX (GLOSSOPHARYNGEAL)
  affects parotid glands
• CRANIAL NERVE X (VAGUS)
  affects the heart, kidneys, bronchi and the GI tract to the colon
• SACRAL NERVES
  affects the remainder of the GI tract, bladder and genitalia

Question 4

List a few examples of sympathetic nerves.

Answer 4

• 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 5

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

Answer 5

The heart is innervated by both the parasympathetic and sympathetic nervous system.
The parasympathetic nerves (Cranial Nerve X, the Vagus Nerve) innervate the Sinoatrial Node and the Atrioventricular Node. The sympathetic nerves (Middle and Inferior Paravertebral Ganglia) are found throughout the atria (especially in the Sinoatrial Node) and ventricles.

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 6

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

Answer 6

• 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 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