Lectures 17-21: Autonomic Nervous System

Question 1

The motor part of the sympathetic nervous system is located in which region/s of the spinal cord?

Answer 1

1st thoracic to third lumbar segments (T1 to L3)

Question 2

The sympathetic preganglionic neuron is located in which region of a spinal cord segment?

Answer 2

Between the dorsal and ventral horn - in the intermediolateral cell column (IML)

Question 3

True or false:

Preganglionic neurons are unmyelinated.

Answer 3

False, postganglionic neurons are unmyelinated (transmission speed up to 1 m/s).
Preganglionic neurons are myelinated (transmission speed up to 30 m/s)

Question 4

True or false:

Preganglionic sympathetic neurons that are regulating the adrenal medulla project directly out to the adrenal gland

Answer 4

True, they do NOT synapse in the paravertebral/sympathetic chain.

Question 5

Mechanism of parasympathetic activation of erectile tissue

Answer 5

The parasympathetic nervous system postganglionic neurons release nitric oxide (NO) as their transmitter to affect the vascular smooth muscle.
NO activates guanylate cyclase, causing catalysis of GTP to cGMP which induces relaxation of the vascular smooth muscles and therefore dilation
Relaxation is switched off by the action of phosphodiesterase-5 which breaks down cGMP in the vascular smooth muscle of the erectile tissues leading to loss of dilation
Dilation of vasculature of erectile tissue leads to engorgement with blood

Question 6

Pupil dilation is caused by ___ nervous system

Answer 6

Sympathetic nervous system.

Parasympathetic nervous system causes pupil constriction, but acts on different set of muscles.

Question 7

The axons of sympathetic preganglionic neurons exit the spinal cord through the ____ horn

Answer 7

ventral

Question 8

True or false:

Erectile tissue only receives parasympathetic innervation.

Answer 8

False, erectile tissues receive both sympathetic and parasympathetic innervation.
Sympathetic innervation is involved with ejaculation.

Question 9

True or false,

The heart receives both sympathetic and parasympathetic innervation.

Answer 9

True. Rare case of the same cell receiving both inputs.

Question 10

Regulatory effects and mechanism of sympathetic innervation of the heart to regulate HR.

Answer 10

The sympathetic postganglionic neurons release noradrenaline acting on β1 adrenergic receptor that then via intracellular pathways involving cAMP leads to an increase in permeability to Na+ and Ca2+.
This increases the rate at which the cell comes back towards depolarisation.

Question 11

Regulatory effects and mechanism of parasympathetic innervation of the heart to regulate HR.

Answer 11

The parasympathetic nervous system releases acetylcholine which acts on M2 metabotropic receptor via its g protein subunit gαi which inhibits cAMP, decreasing permeability of Na+ and Ca2+ to decrease the rate of depolarisation
Furthermore, the M2 metabotropic receptor via the g protein subunit Gβγ which is physically connected to a K+ channel which it activates, hyperpolarising the cell after an action potential

Question 12

True or false:

Parasympathetic nervous system causes tonic constriction of blood vessels.

Answer 12

False,

Sympathetic nervous system causes tonic constriction of blood vessels via norepinephrine release onto alpha-receptors.

Question 13

Carotid sinus is filled with

Answer 13

sensory afferent neurons that sense the stretch of this part

Question 14

Carotid body detects

Answer 14

blood oxygenation and blood carbon dioxide levels

Question 15

C1 neurons are located in the

Answer 15

RVLM

Question 16

C1 neurons have the ability to synthesise

Answer 16

catecholamines

Question 17

Posterior pituitary contains the terminals of the neurons that exist in the ____ nucleus and _____ nucleus

Answer 17

supraoptic nucleus and the paraventricular nucleus

Question 18

The response of elevated HR and BP to mental stress involves activation of neurons within the

Answer 18

Dorsal medial hypothalamus

Question 19

Carotid sinus is filled with sensory afferent neurons that sense the stretch of this part that send their fibres up the ______ nerve

Answer 19

glossopharyngeal (IX cranial nerve)
Side note: There are also chemoreceptor bodies within the aortic arch and sensory afferents detecting stretch that send their fibres up the vagus nerve (X cranial)

Question 20

The glossopharyngeal (cranial nerve IX) synapses in the

Answer 20

nucleus tractus solitarii (NTS) located in the medulla

Question 21

Magnocellular neurons of the PVN project to the pituitary and release

Answer 21

vasopressin and oxytocin

*Vasopressin is a pituitary hormone which acts to promote the retention of water by the kidneys and increase blood pressure.