Autonomic Nervous System (textbook) Flashcards
What does the autonomic nervous system consist of and what does it control?
The autonomic nervous system consists of the sympathetic and parasympathetic nervous systems and controls various systems of the body.
What transmitter is released at the sympathetic nerve end?
Noradrenaline/norepinephrine is released at the sympathetic nerve end.
What receptors do noradrenaline and norepinephrine target?
Norepinephrine and noradrenaline target the alpha, beta 1 and beta 2 adrenoceptors.
Whats the difference in nerve fibres between sympathetic snd parasympathetic fibres?
Sympathetic fibres arise from the thoracolumbar region of the spinal cord (T1-L3) whereas the parasympathetic fibres leave via cranial nerves especially ( III, VII, IX and X) and sacral spinal roots.
What neurotransmitter are released by the parasympathetic nerves?
Postganglionic parasympathetic nerve fibres release acetylcholine.
What receptors does acetylcholine bind to?
Acetylcholine acts on muscarinic receptors.
Explain the difference in the inactivation of norepinephrine and acetylcholiine.
Norepinephrine is largely inactivated largely by reuptake into the nerve terminals. Acetylcholine is inactivated by the enzyme acetylcholinesterase.
What hormone mimics most sympathetic effects?
Adrenaline
What are the effects of sympathetic stimulation?
Sympathetic stimulation can be thought of fight or flight responses:
- Pupillary dilation (allows more light into the retina)
- Bronchiolar dilation ( facilitates increased ventilation)
- Heart rate and force are increased; blood pressure rises (more blood for increased activity of skeletal muscles).
- Vasoconstriction in skin and viscera and vasodilation to skeletal muscle (appropriate redistribution of blood go skeletal muscle
- To provide extra energy, glycogenolysis is activated snd the blood glucose level increases. The gastrointestinal tract and bladder relax
The ANS consists of motor neurons that:
- Innervate smooth muscle, cardiac muscle and glands
- Make adjustments to ensure optimal support for body activities
- Operate via subconscious control
What are drug designed to target ANS do?
Drugs in this group are designed to either enhance or mimic the actions of the ANS or to block the effects of the neurotransmitter at the receptor sites
Describe the basic anatomy of a parasympathetic neuron.
A parasympathetic neuron consists of both pre and post ganglionic neurons
Describe the basic anatomy of a preganglionic neuron
A preganglionic neuron:
Cell body in the brain or spinal cord.
Axon is a myelinated type B fiber that extends to autonomic ganglion
Describe the basic anatomy of a post ganglionic neuron
A post ganglionic neuron
The cell body lies outside the CNS in an autonomic ganglion
The axon is an unmyelinated type C fiber that terminates in a visceral recptor
Explain how neurotransmitters are released.
- Action potential arrives at the axon terminal
- This causes calcium to enter the terminal via voltage gated calcium channels
- This causes the neurotransmitter to be releaesd
- The neurotransmitter diffuses across the synaptic cleft to ehich it binds to receptors on postsynaptic target cell membranes
Name the different ANS neurotransmitters 7
- Acetylcholine
- Norepinephrine
- Dopamine
- 5HT
- GABA
- Glutamate
- Histamine
What receptors do norepinephrine and epinephrine bind to?
Norepinephrine binds to adrenergic receptors such as alpha, beta dopaminergic receptors
What receptors do acetylcholine bind to?
Acetylcholine binds to muscarinic and nicotinic receptors.
Acetylcholine is a parasympathetic neurotransmitter. Describe how it is made, broken down and remade.
- Acetylcholine is made up of choline and acetyl coA
- In the synaptic cleft, acetylcholine is rapidly broken down by the enzyme acteylcholinesterase.
- Choline is transported back into the nerve terminal where it is used to make more Ach
Why does Acetylcholine lack therapeutic importance?
Ach lacks therapeutic importance because of it’s multiplicity of actions and its rapid inactivation by acetylcholine esterase.
What are the actions of Ach?
- Decrease in heart rate
- Decreased cardiac output
- Decreased blood pressure (vasodilation)
- Increased salivation
- Increased sweating
- Increased intestinal secretions
- Increased motility
- Miosis (pupil constriction)
- Increased urination
- Increased bronchial secretions
How are parasympathetic drugs classified?
Parasympathetic drugs can be classified as either:
- Direct acting (muscarinic agonists)
- Indirect acting (reversible/ irreversible acetylcholineesterase inhibitors)
Name a direct acting muscarinic agonist
Pilocarpine
Name the reversible acetylcholine esterase inhibitors: 4
- Neostigmine
- Pyridostigmine
- Physostigmine
- Edrophonium
What are the irreversible acetylcholine esterase inhibitors? 3
- Organophosphates
- Parathion
- Malathion