Basic Autonomic Functioning

Question 1

Whats the difference between the effectors innervated by the ANS compared to the Somatic nervous system?

Answer 1

ANS = smooth muscle, cardiac muscle, and glands
not under conscious control

SNS= skeletal muscle
under conscious control

Question 2

What are the divisions of the ANS

Answer 2

Sympathetic
Parasympathetic
Enteric

Question 3

What is the difference between neurotransmission in somatic nervous system compared with the autonomic nervous system at the effector

Answer 3

SNS it is discrete can control specific muscle fibres (on off switch) released via synapse at NMJ

ANS= Post ganglionic neurone NT realised from varicosities on effect (small swellings)
many varicosities leads to large scale realises of NT over many cells therefore is said to be diffuse

Question 4

What is the difference between the SNS and the PNS in terms of function?

Why is this not always the best?

Answer 4

SNS alert and active
(in extreme situations freight flight fight response) but is active all the time in normal conditions

PNS rest and digest (energy conservation)

Very general classification doesn’t quite fit for things like male sex organs

Question 5

What is a difference between the PNS and SNS in terms of there anatomical strucutre

Answer 5

SNS =
short preganglioninc neurone cell body of preganglionicn neurone thoracicolumbar origin (T1-L2)
Ganglia located in Sympathetic chain close to spinal cord
Long postganglioninc neurone

PNS
long preganglionic neurone
Cell bodies originate from craniosacral origin (CN’s III, VII, IX, X and then S2-S4)
Ganglia located very close to target organ or in the walls of it!
Short postganglionic neurone

Question 6

What is the difference between the PNS and SNS in terms of neurotransmission

Answer 6

SNS:
Preganglionic neurone releases ACh binds to nAChR’s on postganglionic neuron
Postganglioninc neurone releases Noradrenaline acts on mainly alpha adrenergic receptors

PNS:
Preganglionic neurone releases ACh that acts on nAChR’s on the postganglioinc neurone
Postganglioninc neurone releases ACh too that binds to muscarinic AChR’s on target tissue

Question 7

What is special about the sweat glands

Answer 7

Receive SNS innervation only
Postganglioninc neurone releases ACh instead of Noradrenaline like you would expect (is still SNS though due to embryological origin)

Question 8

What is special about the adrenal medulla?

Why is it significant?

Answer 8

Only directly receives preganglioninc SNS innervation
synapse with chromaffin (neuroendocrine) cells derived from neural crest that produce mainly adrenaline but also some noradrenaline

Adrenaline and noradrenaline in this case are therefore hormones and act on non-innervated receptors e.g. smooth muscle in bronchioles and in walls of blood vessels

Question 9

Describe the effect ANS innervation on the heart

Answer 9

SNS innervation increases the contractility of the heart and increases the heart rate

PNS innervation decreases the heart rate and the contractility of the heart

Question 10

What type of innervation do most organs have

Answer 10

Dual innervation PNS and SNS

Question 11

Describe the innervation of the GI tract in terms of PNS and SNS

Answer 11

PNS and SNS can also influence the Gi tract not just enteric

SNS decreases motility (peristalsis) and decreases secretions
Decreased blood flow to Gi tract

PNS increases motility (peristalsis) and increases the amount of secretions released to digest food
increase blood flow to the Gi tract to allow for absorption

Question 12

how is pupil diameter controlled?

Answer 12

PNS and SNS work antagonistically

SNS fibres innervate radial muscle (dillator pupillae) causing contraction and pupil dilation

PNS fibres innervate circular muscles (sphincter pupillae) causing contraction and constriction

Diameter is controlled by a interplay between SNS and PNS action

Question 13

Give two examples of single innervation in the ANS

Answer 13

Sweat glands only SNS innervation

MOST blood vessels SNS only

Question 14

What is the case in most blood vessels?

Answer 14

Only have SNS innervation

Increased SNS activity results in contraction of smooth muscle –> vasoconstriction

Decreased SNS activity vasodilation

Question 15

What is significant about blood vessels in the head and neck

Answer 15

They have dual innervation
SNS causes vasoconstriction
PNS causes vasodilation

Question 16

What is significant about the exocrine glands of the head and neck e.g salivary glands?
How do the salivary glands work?
What is the normal level of saliva production?

Answer 16

Receive both PNS and SNS innervation however it is not antagonistic

SNS and PNS innervation both promote production of saliva

Blood vessels supplying the head and neck region have both PNS and SNS innervation

SNS innervation causes vasoconstriction of blood vessels supplying the salivary gland –> this results in less raw components getting to the gland therefore meaning there is less saliva production and the saliva that is produced is thick and sticky (leads to people saying I have a dry mouth when doing speeches)

PNS innervation of blood vessels supplying the salivary gland causes vasodilation
increased amount of raw materials can get to gland leading to increased production of very watery saliva

Normally the PNS dominates over the SNS effect so there is an average quantity of reasonably watery saliva produced
Go on a run decreases
eat something increases

Question 17

Why is it that blood vessels supplying the heart brain and skeletal muscles vasodillate?
how does this occur

Answer 17

SNS activity body wide results in vasoconstriction of most blood vessels (through release of NA acting primarily on alpha adrenergic receptors on smooth muscle)

Inc SNS activity body wide results in increased activation of neuroendocrine cells in adrenal medulla resulting in increased production of mainly adrenaline but also a smaller amount (20%) NA

Adrenaline binds also binds to alpha adrenergic but preferentially binds to beta adrenergic receptors which are found in high quantities in the smooth muscle of blood vessels supplying the heart and SK muscles
Binding results in vasodilation

Question 18

Give an important example of where the SNS and PNS work together

Answer 18

Male sex organs
PNS results in erection (point)
SNS results in ejaculation (shoot)

Question 19

What is the body response to cold and example of

Answer 19

Somatic and ANS working together

Cold SNS causes vasoconstriction of blood vessels supplying the skin

Somatic nervous system increased activity of SK muscles causing shivering to generate heat