Review of the Sympathetic Nervous System

Question 1

where are the preganglionic motor neurones found for sympathetic NS?

where are the postganglionic neurones found for BV & sympatethic NS?

Answer 1

• The preganglionic motor neurones are in the lateral horn of the grey matter, leave the spinal cord the ventral roots

- Travel to the sympathetic ganglia via the white communicating ramus & synapse. Postganglionic neurones have their cell bodies in the sympathetic ganglia.

- sympathetic ganglia are connected by sympathetic trunk

• postganglionic fibres may return to spinal nerve in second branch, called the gray communicting ramus OR travel to target organs
• postgangloinic axons are unmyelinated: autonomic reflexes are slower

Question 2

label this xox

Answer 2

Question 3

what vertebral levels is sympathetic chain?

Answer 3

sympathetic division has thoracolumbar outflow, meaning that the neurons begin at the thoracic and lumbar (T1–L2)

Question 4

how many ganglia do the sympathetic chains have?

sympathetic NS exhibits both what?

Answer 4

25 :)

divergence (pre-ganglionic fibres branch and connect to postg neurons at different levels) and convergence (post ganglionic neuron can receive synapses from many pre-ganglionic fibres)
= coordinated action at many sites

Question 5

which sympathetic ganglia do we find in the neck / cervical ganglia? (3)

what innervation does the largest of ^ supply?

how do thes sympathetic post. g fibres exist / get to the head?

Answer 5

Superior Cervical Ganglion (largest)

Middle Cervical Ganglion

Inferior Cervical Ganglion

The superior cervical ganglions supply sympathetic nerves to the head; this includes innervation of the iris of the eye, skin of the face and the salivary glands

sympathetic post. g fibres in the head:
Form nerve plexi around the carotid arteries and enter the skull together with the carotids. The fibres reach the eye, skin etc. as plexuses around the arteries supplying these tissues: dilate pupil, thicken saliva, can increase or decrease blushing

Question 6

why does dilation of the pupil occur due to SNS?

Answer 6

• makes vision worse!
• *- why occur?**
  i) non-verbal signal of sympathetic arousal: if pupils are dilate = clear sign of mutual attraction
  ii) BUT: also dilate when scared / fight or flight

= ambigious response

Question 7

how is the efferent sympathetic NS different to the somatic NS?

Answer 7

sympathetic: efferent system has two neurones between spinal cord and muscle

somatic: single neuron

Question 8

what do, in both para and sym, the preganglionic neurones relese to activate post. g neuron?

what type of receptors

Answer 8

The SNS & PNS preganglionic neurones release acetylcholine in the ganglion to activate the postganglionic neurone.

All autonomic ganglia (both sympathetic and parasympathetic) ganglionic receptors are of the cholinergic nicotinic type

Question 9

in sympathetic NS, what type of myelination are the preganglionic neurones and postganglionic neurons?

Answer 9

preganglionic neurones: Type Ab axons - small myelination
postganglionic neurons: Type C axons - unmyelinated

Question 10

The transmitter released from the postganglionic sympathetic fibres is what?

explain how sympathetic NS causes vasoconstricntion?

Answer 10

noradrenaline

vasoconstriction

• The postganglionic sympathetic neurones project to smooth muscle in arterioles (small arteries) and produce vasoconstriction
• The postganglionic neurone releases noradrenaline on to the arterial smooth muscle to make it contract via an action on alpha 1 adrenoceptors.

Question 11

which sympathetic ganglia innervates
i) the heart ii) the lungs?

what is the efferent and afferent sympathetic fibres for heart innervation?

Answer 11

cardiac plexus innervates the heart
- sympathetic efferent fibres: Cardiac nerves from the lower cervical and upper thoracic ganglia
-sympathetic afferent fibres: toupper thoracic and lower cervical ganglia

pulmonary plexus innervates the lungs

Question 12

what do the coeliac plexus, superior mesenteric plexus and inferior mesenteric plexus provide innervation for?

Answer 12

The Coeliac Plexus supplies sympathetic (vasoconstrictor) nerve fibres to the liver, pancreas stomach and initial parts of the small intestine

The Superior Mesenteric Plexus supplies sympathetic innervations to the rest of the gut, (large intestine and colon)

The Inferior Mesenteric Plexus supplies sympathetic innervation to the bladder, kidney, rectum and reproductive organs

all primarily sympathetic innervation !

Question 13

which sympathetic pre-ganglionic neurones DO NOT stop at ganglia and go directly to a gland?

Answer 13

Sympathetic innervation to the adrenal medulla is via myelinated pre-synaptic fibres, mainly from the T10 to L1 spinal cord segments.

Question 14

at which sympathetic post ganglionic fibre does NOT release noradrenaline? what does it release instead?

Answer 14

sweat glands (triggered by sympathetic NS)

uses acetylcholine on post-ganglionic fibres

• *- acetylcholine** triggers nitric oxide release from the **vascular endothelium.
• Thisrelaxesanddilatesthevesselsand thusincreases**their blood flow
• Sodium concentrationis high in theextravascularspace, and thiscauses watertopass outof thebloodand into theglands to besecreted as sweat**

Question 15

explain mechanism of sweat being secreted after Ach is released on post ganglionic fibres?

Answer 15

Ach released from sweat glands (bc the sweat glands use Ach as NT):

• acetylcholine triggers nitric oxide release from the vascular endothelium.
• This relaxes and dilates the vessels and thus increases their blood flow
• Sodium concentration is high in the extravascular space, and this causes water to pass out of the blood and into the glands to be secreted as sweat

Question 16

what does adrenal gland secreted ?

Answer 16

adrenal gland secretes: adrenaline from the medulla

Question 17

what does the sympathetic NS normally do to the arterioles of the vascular bed?
what is a consequence of this ^?

what is postural hypotension?

Answer 17

• normally keeps all the arterioles of the vascular beds in the body slightly constricted
• causes a _**resting level of sympathetic nervous output in the healthy resting man
• **_

postural hypotension:
The body is unable to increase vasoconstrictor tone in leg muscles when you stand up. Thus, blood pressure drops and you faint.

Question 18

what happens to sympathetic activity during exercise?

(action on resp centre, from adrenaline and HR?)

Answer 18

• start of exercise, the sympathetic nerve centres in the brainstem stimulate the respiratory centres (which are also in the brainstem) and stimulate an increased rate and depth of breathing
• Adrenaline, released into the blood by sympathetic stimulation of the chromaffin cells in the adrenal medulla, relaxes the smooth muscle around lung airways, which allows them to dilate, thus reducing airflow resistance and improving air delivery to the alveoli.

- Sympathetic nerves to the heart increase the heart rate and adrenaline in the cardiac arteries increases the force of contraction of the heart muscle

• *-** adrenaline causes:
  i) liver and non-active muscles to release glucose into the blood stream to provide energy for the active muscles.
  ii) stimulates lipolysis which releases free fatty acids into the blood: these can be used as fuel by the active muscles.

Question 19

what happens to blood vessels during exercise?

Answer 19

- chemical vasodilators (adenosine and nitric oxide) are released from the exercising muscle(s) and enter the local blood vessels

• dilate the blood vessels in the active muscles and thus increase the local blood flow so that more oxygen can be delivered

Question 20

what is a consequence of exercising muscles having vasodilation?

how does the body get around to solving this?

Answer 20

• vasodilation in the active muscles reduces total peripheral resistance and would, if not compensated for, cause a drop in blood pressure.

SO

• at the start of exercise the sympathetic outflow increases.
• This produces a **general vasoconstriction in the non-exercising muscles and the digestive tract
• The result is that thedecrease in vascular resistance in the exercising muscles is compensated by an increase in vascular resistance in the nonactive muscles**

Question 21

what happens to blood flow in the coronary arteries during exercise?

what happens to blood flow in the brain during exercise?

Answer 21

coronary arteries
blood flow through the coronary arteries of the heart increases as the cardiac muscle works harder and faster to increases blood flow to the exercising muscles

brain
brain blood flow during exercise does not change significantly, but the distribution of the blood to different areas of the brain may alter (eg increased flow to the motor and premotor cortices, decreased flow to less active regions)

Question 22

what are adrenoreceptors?
what are the two type?

Answer 22

• adrenoreceptors: receptors for adrenaline and noradrenaline
• two main types: alpha and beta

Question 23

out of noradrenaline and adrenaline, which acts on alpha receptors?
what are the two types of alpha adrenoreceptors?

Answer 23

noradrelanine acts on alpha receptors

• *Alpha 1**
• location: main receptor on **vascular smooth muscle
• function: Acts toincrease contraction**

Alpha 2
-location: presynaptic sympathetic nerve terminals & varicosities
- function: reduce noradrenaline release by negative feedback:
(i) they reduce calcium inflow into the terminal during an action potential
ii) thus reduce vesicle fusion with the synaptic membrane)

Question 24

whats an example of an alpha 1 antagonist? what does it do?

whats an example of an alpha 2 agonist? what does it do?

Answer 24

Alpha 1 -antagonists- eg prazosin -are given to reduce blood pressure

Alpha 2 agonists-eg clonidine- can be given to lower blood pressure as they inhibit noradrenaline release.

Question 25

how many types of beta receptors are there?
what do each beta receptor do / found?

Answer 25

3 types of betareceptor

Beta 1 receptor:

location: heart
function: increase force and rate of contraction of myocardium

Beta 2 receptor
location: bronchial smooth muscle
​function: primarily relaxes ^
further functions:

1. Decreased motility of the GI tract
2. Lipolysis in adipose tissue
3. Relaxation of detrusor urinae muscle of bladder wall
4. Glycogenolysis and gluconeogenesis
5. Stimulation of insulin secretion
6. Thickened secretions from saliva
7. Inhibition of histamine release from mast cells

Beta 3 receptor - unclear function
location: adipose tissue cells
​function: stimulates lipolysis

Question 26

what do beta 2 agonists do?
what are the two types of beta 2 agonists? can u name an e.g. of each?

what do beta 2 receptors d?

Answer 26

beta 2 agonists: relax smooth bronchial smooth muscle in asthmatics

SABAs (short acting beta agonists)
- e.g. salbutamol & fenoterol

• *LABAs**
• e.g. clenbuterol

Question 27

what effect do alpha 1, beta 1 and beta 2 adrenoreceptors have in exercise?

Answer 27

alpha 1 receptors: constrict vessels in the non-active muscles and gut and so r_edistribute the blood to the active exercising muscles._

beta 1 receptors: increase the rate and force of cardiac contraction and thus increase cardiac output

• *beta 2 receptors:
  i) ** relax bronchial smooth muscle to decrease airway resistance and increase oxygen uptake.
• *ii)** increase glucose supply to exercising muscle by glycogenolysis (breakdown of glycogen) and gluconeogenesis (formation of glucose)

Question 28

what role does sympathetic NS have when haemorhages occur?

how?

Answer 28

maintains BP when haemorrhage occurs:
(HOW?) :O

- venous smooth muscle contraction via alpha receptors: because of their large size act as reservoirs for blood

- Constricting the veins increases venous return which will compensate for blood lost by haemorrhage

Question 29

explain mechisnm with SNS in severe haemorrhage?

Answer 29

• blood loss is severe:
• arterial vasoconstriction of vessels in non-essential organs like the gut and skin reduces their blood flow and helps maintain blood pressure and perfusion of vital organs like heart, brain and kidney
• renin released from kidney maintains BP by formation of angiotensin
• Stimulation of antidiuretic hormone release will reduce urine flow and thus reduce fluid loss.
• *- Adrenaline** stimulates release of megakaryocytes and platelets from bone marrow; this increases the clotting ability of the blood to reduce blood loss.
• Adrenaline also increases the oxygen carrying capacity of the blood by increasing the release of erythrocytes from bone marrow.

Question 30

how does stress work on the Symapathetic NS?
for awareness!

Answer 30

“HPA” or hypothalamo-pituitary-adrenal axis is activated by stress

• (This HPA system releases ACTH (adrencorticotrophic hormone) which) stimulates cortisol release from the adrenal cortex*
• Cortisol (acts on several target tissues but one important action is to) stimulates adrenaline and noradrenaline synthesis*

BUT

• If cortisol production is lowered the sympathetic nervous system becomes progressively weaker*
• therefore: prolonged stress damages your ability to cope with stress and a ‘vicious circle’ can be created leading to psychological depression.*

Question 31

what does hypogastric ganglia do?

Answer 31

sympathetic innervation: It is responsible for the emission of semen into the posterior urethra.

Question 32

Answer 32

Question 33

complete this xoxx

Answer 33

Question 34

where do you find chromaffin cells in the adrenal glands? what is secreted from them?

Answer 34

in the medulla: secretes adrenaline