ANS Flashcards
What does ANS do?
Controls all involuntary functions (eg heart rate, blood pressure, GI motility, iris diameter)
ANS vs Somatic (voluntary) motor nervous system
They are separate
Afferent vs Efferent neurons
Afferent = sensory
Efferent = motor
Is the ANS Efferent or Afferent
Autonomic nervous system is entirely efferent (away from CNS) but regulated by afferent inputs
Two divisions of ANS
Parasympathetic
Sympathetic
Sympathetic system purpose
- Responds to stressful situations
- Fight or flight
increase HR, force of contraction, blood pressure
Parasympathetic function
- Rest and digest
- Regulates basal body activities (eg resting heart rate)
Where is sympathetic system located?
Thoracic and Lumbar regions of the spinal cord
(The Last Straw)
Thoracic
Lumbar
Sympathetic
Where does parasympathetic system come from?
Medullary/cranial and
Sacral region of the spinal cord
Important parasympathetic nerve
Cranial nerve 10 = Vagus nerve
Which ganglions are myelinated? What does this mean for transmission?
Pre ganglionic
parasympathetic faster transmission as more preganglionic
Parasympathetic vs sympathetic structure
Para:
long preganglionic
short post ganglionic (mAchR)
Sympathetic: short preganglionic (synapse in sympathetic chain) long postganglionic (Adrenoreceptors)
1) What are all preganglionic neurones like?
2) So what neurotransmitter is used for all of them?
1)Cholinergic
2)So Acetylcholine is released from all of them
Describe the release of neurotransmitters in the parasympathetic and sympathetic NS (for the preganglionic neurone)
In both the parasympathetic and sympathetic nervous system:
- Ach is released from pre-ganglionic neurone
- This activates post ganglionic nAchR
Type of channel nAchR
Ligand gated ion channels
allow influx of +ve ions Na+ mostly (causing depolarisation and transmitting the signal)
What are the Postganglionic neurones in the parasympathetic vs sympathetic nervous system like? Describe the transmission
1) Parasympathetic - cholinergic
- They release Acetylcholine which acts on muscarinic ACh receptors in the target (effector) tissue
- Muscarinic ACh receptors are GPCRs
2) Most Sympathetic postganglionic neurones- noradrenergic or adrenergic
- They release noradrenaline
- Which acts on 2 major classes of adrenoreceptors
- Alpha adrenoreceptors
- Beta adrenal receptors (which can further be divided into a1, a2,b1,b2,b3 subtypes)
Type of receptor mAchR and adrenoreceptors
G protein coupled
What are the subtypes for:
1) Muscarinic acetylcholine receptors
2) Adrenoreceptors
1) M1-M5
2) Alpha 1 and alpha 2 adrenoreceptors
Beta 1, beta 2, beta 3 adrenorecepors
Describe the exceptions to sympathetic nervous system transmission
How would you describe these responses?
- Although most postganglionic neurones in the sympathetic NS are noradrenergic and act on adrenoreceptors , some are cholinergic and release Ach that acts on mAchR
- Such as those that innervate sweat glands, hair follicles - ( piloerection)
- These are sympathetic responses mediated by acetylcholine
- Adrenal medulla is another exception
1) Name the Other transmitter in the ANS
2) When are they usually released?
Non-adrenergic, non-cholinergic (NANC) transmitters
Usually Co released with NA with or Ach
NANC examples (4)
Nitric oxide
ATP
Serotonin
Neuropeptides
Adrenal gland sympathetic system explained (6)
- Noradrenaline is the neuronal component of the sympathetic fight or flight response
- Adrenaline is the hormonal component of the sympathetic fight or flight response:
- Preganglionic
neurones synapse at adrenal medulla - The adrenal medulla is effectively a whole bunch of post ganglionic neurones (specifically the chromaffin cells) that receives a myelinated nicotinic input from the preganglionic fibres.
- Chromaffin cells (in the adrenal medulla) are postganglionic neurones
- When sympathetically stimulated, release adrenaline into bloodstream
Describe the parasympathetic release of Ach in the heart?
What does it act on?
(Ach activates M2 Muscarinic receptors to cause:
- Bradycardia (SA node)
- Reduced conduction velocity (AV node)
Describe the parasympathetic Ach release in smooth muscle (5 + 1)
ACh acts on M3 muscarinic receptors to cause:
- Bronchiolar contraction in lungs - Increased intestine secretion/mobility in GI Tract - Bladder contraction and relaxation in GU (genitourinary tract) - Penile erection in GU tract - Iris and cillary muscle sphincter contraction in eye
ACh also increases NO (nitric oxide) generation, which causes a local vasodilation
NO CONSTRICTION
