AUTONOMIC FUNCTION

Question 1

Explain the combined action of pupil dilation and constriction

Answer 1

• Iris is smooth muscle and so autonomically innervated
• There is an inner band of smooth muscle
• Dilator Pupillae muscle is innervated by SNS and this results in pupil dilation
• Constrictor pupillae muscle is innervated by PNS and results in pupil constriction
• There is combined action
• Usually PNS is dominant

Question 2

Give an example of a structure that has single innervation

Answer 2

Blood vessels

Most blood vessels are only innervated by SNS. The level of vasoconstriction or vasodilation depends on the activity of the SNS

Increase in SNS –> Vasoconstriction
Decrease in SNS –> Vasodilation

Blood vessels that aren’t single innervation are in the head and reproductive system - they have Bothe SNS and PNS innervation

Question 3

Explain the dual innervation of the salivary gland

Answer 3

They have dual innervation where both the SNS and PNS work alongside each other - NOT antagonistic

Both the PNS and SNS stimulate secretory molecules to be released

Secretory molecules are delivered to the salivary gland from blood vessels. Increase in SNS means an increase in vasoconstriction of blood vessels and so less secretory molecules in the gland. PNS results in vasoconstriction and so more secretory molecules in the gland

PNS usually dominant

Question 4

Explain how SNS innervation can sometimes lead to vasodilation in some blood vessels

Answer 4

Most blood vessels have alpha receptors. These bind to noradrenaline produced by postganglionic neurones in the SNS. This binding results in vasoconstriction

Some blood vessels (e.g vessels of skeletal muscle) have beta receptors. SNS activity that is body-wide will stimulate the adrenal medulla and produce adrenaline. Beta receptors bind to adrenaline and causes vasodilation of blood vessels

Most receptors in the cardiac muscle are beta receptors

The expression will be somewhere in the middle

Question 5

Which nervous system is responsible for the male erection?

Answer 5

PNS (point)

Question 6

Which nervous system is responsible for the male ejaculation?

Answer 6

SNS