Flashcards in ANS Deck (59)
What are some of the major functions of the ANS?
- maintain homeostasis
- coordinate response to external stimuli (fight or flight)
- specific regulatory functions
what are some of the specific functions of the ANS?
- contraction and relaxation of the vascular and visceral smooth muscle
- CVS reflexes
- all exocrine and endocrine secretions
- energy metabolism, particularly in liver and skeletal muscle
What are the divisions of the ANS? what do they do?
- dominates during stress and emergency situations
- expenditure of energy
- increase in BGL, heart activity and BP
- conserve energy
- reduce HR
- increase GI and secretions
- comprises the intrinsic nerve plexuses of GI tract
What are some of the responses of the SNS?
- increased HR
- vasoconstriction and increased BP
- skeletal muscle vasodilation and tremor
- pupil dilation, adjusting for far vision
- glycogenolysis, gluconeogenesi, lipolysis, thermogenesis
- release of adrenaline
What are some responses of the PNS?
- decrease HR to resting
- digestion and secretion of waste products, increased Gi motility, gastric acid secretion, defecation, urination
- pupil constriction, accommodation for near vision, lacrimation
What are autonomic efferent pathways made of?
- Preganglionic neurons
- autonomic ganglia (contains nerve endings of preganglionioc and cell bodies of postganglionic)
- post ganglionic neurons
What are the main neurotransmitters in the ANS?
Acetylcholine and noradrenaline
How do cholinergic nerves function?
Using Acetycholine on:
ALL preganglioninc nerves
ALL post ganglionic nerves in the PNS
ACTS on nicotininc and muscurain
How do noradrenergic nerves function?
Use noradrenaline on:
most post ganglionic nerves in the SNS
Describe the neurons and their actions in the PNS
Preganglionic neurons release Ach which acts on nicotinic receptors in the cell body of the postganglionic neuron
Postganglionic neurons release AcH which acts on the muscarinic receptors on the effector tissue
What is cholinergic transmission?
Nerve transmission mediated by acetylcholine
What are the functions of acetylcholine in the CNS and PNS?
CNS: arousal, learning, memory and motor control
- ANS: involuntary control of many structures
- enteric: involuntary control of the GIS
- somatic: voluntary control of skeletal muscles
Describe the steps in cholinergic transmission
1. Uptake of choline
2. Synthesis of AcH
3. Uptake of transmitter into synaptic vesicles
4. degradation of surplus AcH
5. depolarisation by propagated action potential
6. opening of voltage gated Ca2+ channels
7. release of transmitter by exocytosis
8. diffusion to postsynaptic membrane
9. binding to postsynaptic receptors
10. inactivation of ACh by ACHE
11. reuptake of transmitter or degradation products by nerve terminal
12. uptake of ACh by non-neuronal cells
13. Binding with presynaptic receptors
What is the nicotinic receptor?
a cholinergic receptor activated by acetycholine.
Ligand gated ion channel with two Ach binding sites.
What happens when ach binds to a nicotinic receptor?
the channel opens and Na+ enters, causing membrane depolarisation
Where are nicotinic receptors located and what do they do?
Skeletal muscle: cause contraction
Autonomic ganglia: allow transmission between pre and post ganglionic neurons
adrenal medulla: cause release of adrenaline
What is the muscarinic receptor?
A GPCR activated by acetylcholine. It passes on a message within the cell that generates a cellular response
What are the types of muscarinic receptors and their general functions?
M3: glandular/smooth muscle
M4/M5: mostly CNS
What is the role of M1 receptors and where are they located?
Found mainly on CNS and peripehral neurons and gastric parietal cells, M1 receptor activation has excitatory effects
What is the role of M2 receptors and where are they located?
Found mainly on the heart, M2 receptor activation has inhibitory effects
What is the role of M3 receptors and where are they located?
Located mainly on smooth muscle and glands, receptor activation has excitatory effects
What is the role of M4/M5 receptors and where are they located?
Mainly in the CNS. Function is not well understood
What is the mechanism of the M1 receptor? What is the result?
Gq: activates phospolipase C
= increased IP3 and DAG
= increased Ca2+
RESULT: neuronal excitation
What is the mechanism of the M2 receptor? What is the result?
Gi: inhibitis adenylate cyclase
= decreased cAMP
= decreases PKA
= decreased opening of Ca2+ channels
RESULT: reduce HR and contractility
What is the mechanism of the M3 receptor? What is the result?
Gq: activates phospholipase C
= increased IP3 and DAG
RESULT: contraction of visceral smooth muscle. secretion of exocrine glands.
CAN cause relaxation of some smooth muscles, mainly vascular, via the release of nitric oxide from neighbouring endothelial cells (not innveravted by PNS but respond to circulating muscarinic agonists)
What are the PNS effects of M2 on the heart?
decreased rate and force of contraction
What are the PNS effects of M3 on the blood vessels?
generally none as there is no PNS innervation.
exception: erectile tissue which has mediated vasodilation via nitric oxide. dilated by exogenous muscarinic agonsts
PNS effects of M3 on smooth muscle (incl. bronchi, GI and bladder)?
PNS effects of M3 on the eye?
Contraction of the pupil = miosis
contraction of the ciliary muscle = near vision