Autonomic physiology 1 & 2

Question 1

Describe the differences in anatomy of the somatic and the autonomic nervous system.

Answer 1

The somatic nervous system innervates skeletal muscle only (no ganglions)
The autonomic nervous system innervates smooth muscle, cardiac muscle, glands and GI neurons. It consists of a pre-ganglionic fibre (small myelinated) and a post-ganglionic fibre (unmyelinated). There is a ganglion between these fibres.

Question 2

Describe the junction of the autonomic nervous system.

Answer 2

The junction of the autonomic nervous system is a less specialised junction that contains metabotropic receptors and is capable of inhibiting and exciting a target.
Instead of pre-synaptic terminals (like within the somatic nervous system) there are bumps called varicoisities that release the neurotransmitter into the interstitial fluid where it eventually finds its receptor.

Question 3

Describe the diffuse action of the junction of the autonomic nervous system.

Answer 3

This diffuse action (possible because of varicosities) means that one post-ganglionic fibre can innervate a large area of tissue.

Question 4

Describe the anatomy of the sympathetic nervous system.

Answer 4

Sympathetic nervous system has a thoracolumbar outflow. (T1-L2)
They have short pre-ganglionic fibres indicating that their ganglia are very close the spinal cord. They have long post-ganglionic fibres.

Repsonsible for fight or flight.

Question 5

Describe the anatomy of the parasympathetic nervous system.

Answer 5

Parasympathetic nervous system has a cranialsacral outflow. They have long pre-ganglionic fibres and short post-ganglionic fibres. The fibres go everywhere in the body: heart, lungs, liver, stomach, intestines (small intestine and first 2/3 of the large intestine) and pancreas.

Responsible for rest and digest.

Question 6

Describe the neurotransmitters of the autonomic nervous system.

Answer 6

Acetylcholine:
Acts on cholinergic receptors.
-Nicotinic receptors (ionotropic)
-Muscarinic receptors (metabotropic)

Noradrenaline:
Acts on adrenergic receptors.
a-receptors (1&2)
B-receptors (1&2)

Question 7

Describe the pre-ganglionic fibres of the sympathetic and parasympathetic nervous system.

Answer 7

Parasympathetic and sympathetic preganglionic fibres release acetylcholine which acts on nicotinic cholinergic receptors.

Question 8

Describe parasympathetic post-ganglionic fibres.

Answer 8

Parasympathetic postganglionic fibres release acetylcholine which acts on muscarinic cholinergic receptors.

Question 9

Describe sympathetic postganglionic fibres.

Answer 9

Sympathetic postganglionic fibres release noradrenaline which acts on a or B adrenergic receptors.

Question 10

Describe the “hormonal component”

Answer 10

From the thoracic region, the fibres synapse onto the postganglionic cell (which has no axon) on the adrenal medulla, releasing the neurotransmitter (80% adrenaline, 20% noradrenaline) into the blood where it acts as a hormone and then finds it target, a or B adrenergic recpetors.

Question 11

Describe the complexity of sympathetic cholinergic fibres.

Answer 11

Sympathetic cholinergic fibres innervate sweat glands, however they are named sympathetic because they have a thoracolumbar outflow and have short preganglionic fibres. It synapses onto a long postganglionic fibre, acetylcholine is released (noradrenaline is expected)
Hence the name.

Question 12

Describe the complexity of postganglionic fibres that use NANC transmitters.

Answer 12

NANC = non-adrenergic non-cholinergic.
E.g. peptides.
These are sometimes co-released with the orthodox transmitter (acetylcholine/noradrenaline).

Question 13

Describe the effect of autonomic innervation on the heart (sympathetic NS)

Answer 13

The sympathetic nervous system activates Beta1 receptors on the pacemakers cells of the heart.
This increases the heart rate, which activates Beta1 receptors on the cardial myocytes. This increases strength of contraction.

Question 14

Describe the effect of autonomic innervation on the heart (parasympathetic NS)

Answer 14

The parasympathetic nervous system activates muscarinic receptors on pacemaker cells of the heart.
This decreases the heart rate, which has little effect on the cardial myocytes and therefore has little effect on contraction strength.

Question 15

Describe the effect of autonomic innervation on the lungs (sympathetic NS)

Answer 15

Activates muscarinic receptors, this makes smooth muscle contract and airways constrict.

Question 16

Describe the effect of autonomic innervation on the lungs (parasympathetic NS)

Answer 16

Noradrenaline and adrenaline activate Beta2 receptors on the smooth muscle of airways.
This makes smooth muscle relax & dilates the airways. (antagonistic action).

Question 17

Describe how the autonomic innervation of the lungs is therapeutically useful.

Answer 17

This can limit the side effects of some drugs (e.g. salbutamol - asthma, COPD)
The activation of the Beta2 agonists dilates airways, this has a limited effect on the heart as the lungs express a lot of Beta2 and the heart expresses a lot of Beta1.
The activation of the Beta2 antagonist decreases heart rate (by decreasing strength of contraction). This has a limited effect on the airways.

Question 18

Describe the effect of autonomic innervation on blood vessels (sympathetic)

Answer 18

The sympathetic nervous system activates alpha 1 receptors on the smooth muscle of blood vessels. This makes smooth muscle contract and blood flow decrease.
This activates Beta2 receptors on smooth muscle of vessels. This makes smooth muscle relax and the blood flow increases.
(dilation).

This is an example of the importance of tone in single innervation.

Question 19

Describe the effect of autonomic innervation on blood vessels (parasympathetic)

Answer 19

Usually no effect.

Question 20

Describe the effect of autonomic innervation on the bladder (sympathetic)

Answer 20

The sympathetic nervous system activates Beta2 receptors on smooth muscle of bladder wall, this relaxes smooth muscle and reduces pressure (on bladder).
This activates alpha receptors on smooth muscle of sphincter. Contracts smooth muscle and stops urination.

Question 21

Describe the effect of autonomic innervation on the bladder (parasympathetic)

Answer 21

The parasympathetic nervous system activates muscarinic receptors on the bladder wall. This contracts smooth muscle and increases pressure.
Which activates muscarinic receptors on sphincter and relaxes smooth muscle causing urination.

Question 22

Describe some autonomic reflexes.

Answer 22

Can be spinal (e.g. urination in babies)
Can have higher control (learned reflexes)

Question 23

Describe the central control reflex

Answer 23

Integrated in brain, mainly hypothalamus, thalamus and brainstem.

Question 24

Explain the baroreceptor complex as an example of central control reflex.

Answer 24

Baroreceptors detect changes in b.p.
Integrating centre processes information (in medulla obligata).
This coordinates a sympathetic and parasympathetic outflow to vary heart rate, strength of contraction and constriction of blood vessels accordingly.