Lecture 12: Nerves I - Autonomic NS

Question 1

*Describe in detail the physiological functions of the ANS

Answer 1

The ANS controls smooth muscle (visceral
and vascular), exocrine (and some
endocrine) secretions, rate and force of the
heart and certain metabolic processes (e.g.
glucose utilisation).
Parasympathetic and sympathetic systems
have opposing actions in some situations
(control of heart rate, GI smooth muscle)
but not in others (salivary glands, ciliary
muscle).
Sympathetic activity increases in stress
(fight or flight) whereas parasympathetic
activity increases during satiation and
repose (rest and digest).
Both exert a continuous physiological control
of specific organs under normal conditions
when the body is at neither extreme.

Question 2

*Outline the role of the CNS in control of the ANS

Answer 2

Although the ANS is essentially a motor system, it does
require sensory input from peripheral structures to
provide information on the state of affairs of the body.
The feedback comes from streams of afferent impulses
originating in the viscera and other autonomically innervated structures that travel to integrating centres in the CNS (hypothalamus, medulla, spinal cord). These centres respond by sending out efferent reflex impulses via the ANS
1. Reflex arcs – most afferent impulses are converted into
reflex responses without involving consciousness. For
example a baroreceptor reflex arc is involved in
response to a drop in blood pressure.
2. Emotions – Stimuli that evoke strong emotion (rage,
fear, pleasure) can modify the activity of the ANS

Question 3

*Describe the general rules that apply to the neurotransmitters in the ANS

Answer 3

Neurotransmitters in the ANS
The 2 main neurotransmitters that operate in the ANS
are acetylcholine and noradrenaline
(norepinephrine). The following general rules apply:
1. All motor nerves leaving the CNS release
acetylcholine which acts on nicotinic acetylcholine
receptors.
2. All postganglionic parasympathetic fibres release
acetylcholine which acts on muscarinic acetylcholine
receptors.
3. All postganglionic sympathetic fibres (with one
exception) release noradrenaline which may act on
either α or β adrenoceptors.
4. The exception is sympathetic innervation of the
sweat glands where transmission is caused by
acetylcholine acting on muscarinic receptors.

Question 4

*Outline the differences between the production of adrenaline and noradrenaline

Answer 4

Noradrenaline and acetylcholine are
neurotransmitters because they are
synthesised, stored and released in
neurones.

Adrenaline is made in the adrenal medulla.
The adrenal medulla receives
preganglionic fibres from the sympathetic
system. The acetylcholine released from
these fibres promotes the release of
adrenaline (and some noradrenaline)
from the adrenal gland into the blood.

Question 5

*How do neurotransmitters exert their actions in the autonomic and somatic systems

Answer 5

g

Question 6

*Compare and contrast muscarinic and nicotinic acetylcholine receptor subtypes

Answer 6

g

Question 7

*Describe in detail the processes of synthesis and release of acetylcholine from the cholinergic neuron

Answer 7

g

Question 8

Function of the Endocrine System?

Answer 8

sends signals to target tissues by varying the levels of blood borne hormones