Autonomic Nervous System

Question 1

Function of Autonomic Nervous System

Answer 1

Control involuntary types of muscle (cardiac and smooth) and gland activity.

Controls unconscious physiological responses

It involves neuronal control and ca act very rapidly e.g. heart rate can be doubled in 3-5 seconds.

Activities of the autonomic nerves can be controlled by centres of the brain stem and hypothalamus

Question 2

Characteristics of Autonomic Nerves

Answer 2

• Sympathetic and parasympathetic nerves reach the tissues they innervate via two neurones in series. The
  junction between these neurones is referred to as a ganglion, and therefore neurones carrying the signal to
  it are known as preganglionic neurones, and the neurones carrying the signal away are known as postganglionic neurones.
• The neurotransmitter released at the ganglion of both type of nerve is acetylcholine (Ach).
• Generally speaking
  the sympathetic postganglionic neurones release noradrenaline (NA), whereas the parasympathetic neurones release acetylcholine. As a result, sympathetic nerves can be referred to as noradrenergic nerves and parasympathetic nerves as cholinergic nerves.
• Noradrenaline activates adrenergic receptors, these may be of two main types α and β. Acetylcholine can act via nicotinic and muscarinic receptor types.
• The sympathetic nervous system often responds by mass discharge, i.e. when all portions of the sympathetic nervous system discharge simultaneously, this kind of response is called the alarm (fight or flight) response.
• In contrast, the parasympathetic nervous system usually causes specific localized responses.

Question 3

Autonomic Control of Visceral Functions - The Eye

Answer 3

For Radial muscle of Iris :
- Sympathetic - contraction (dilate pupil)
- Parasympathetic - no effect

For Circular muscle of Iris:
- Sympathetic - no effect
- Parasympathetic - Contraction (constrict pupil)

For Ciliary Muscles :
- Sympathetic - relaxed (thin lens)
- Parasympathetic - contracted (fat lens)

Question 4

Autonomic Control of Visceral Functions - The Integumentary System

Answer 4

Sweating - sympathetic

Hair raising - sympathetic

Question 5

Autonomic Control of Visceral Functions - The Cardiovascular System

Answer 5

Heart :
- Sympathetic effect - increased rate and increased force of contraction
- Parasympathetic - decreased rate and decreased force of contraction

Cardiac output :
- Sympathetic effect - increased
- Parasympathetic effect - decreased

Blood vessels of skin :
- Sympathetic effect - vasoconstriction
- Parasympathetic effect - vasodilation

Blood vessels of most viscera :
- Sympathetic effect - vasoconstriction
- Parasympathetic effect - vasodilation

Blood vessels of skeletal muscle :
- Sympathetic effect - vasodilation
- Parasympathetic effect - no effect

Mean Blood Pressure :
- Sympathetic effect - increased
- Parasympathetic effect - decreased

Question 6

Autonomic Control of Visceral Functions - The Respiratory System

Answer 6

For Bronchi and Bronchioles:
- Sympathetic effect - bronchodilation
- Parasympathetic effect - bronchoconstriction

Question 7

Autonomic Control of Visceral Functions - The Digestive System

Answer 7

For GI Motility :
- Sympathetic effect - decrease
- Parasympathetic effect - increase

For GI Secretion :
- Sympathetic effect - decrease
- Parasympathetic effect - increase

Sympathetic - thick saliva
Parasympathetic - thin saliva

Question 8

Autonomic Control of Visceral Functions - The Urinary System

Answer 8

Parasympathetic - detrusor muscle (+ve) and internal urethral sphincter (-ve)

Sympathetic - internal urethral sphincter (+ve)

Question 9

Sympathetic nerves and the Adrenal Medulla

Answer 9

The cells of the adrenal medulla are modified neuronal cells releasing noradrenaline and adrenaline. Therefore cells of the adrenal medulla therefore are essentially postganglionic sympathetic neurones.

During a fight or flight response the hypothalamus stimulates the release of noradrenaline and adrenaline from the adrenal gland, and they enter the blood stream (they are now known as hormones).

Since they are released at the same time as tissues are stimulated by sympathetic nerves, the tissues of the body are stimulated both directly by nerves and indirectly by circulating hormones during the fight or flight response.