The automatic nervous system Flashcards
What makes up the nervous system?
The central nervous system (brain and spinal chord)
The peripheral nervous system (nerve cells carrying info to or from CNS)
What are the 2 branches of the peripheral nervous system?
The somatic and autonomic nervous system.
What are the 2 branches of the autonomic nervous system?
The sympathetic and parasympathetic systems.
What is the input of the autonomic nervous system?
They get their input from autonomic sensory neurons (associated with interoceptors such as chemoreceptors and thermoreceptors).
What is the output of the autonomic nervous system?
Output via autonomic motor neurons to cardiac muscle, smooth muscle and glands.
Main actions of autonomic nervous system?
In the heart, sympathetic stimulation= heart rate and force increased, parasympathetic= heart rate and force decreased.
In the iris, sympathetic= pupil dilation, parasympathetic= pupil constriction.
What is the meaning of dual innervation?
The organ receives both sympathetic and parasympathetic impulses (most organs have this).
Both sympathetic and parasympathetic are 2 neuron systems.
What is the sympathetic system?
Cell bodies in lateral horns of grey matter in spinal cord of: 12 thoracic segments, first 2-3 lumbar segments of the thoracolumbar division.
What is the parasympathetic system?
Cell bodies in nuclei of: 4 cranial nerves (III, VII, IX and X), lateral horns of 2-4 sacral segments, craniosacral division.
What is the length of preganglionic neurons in sympathetic?
These are short.
(close to spinal cord, not far to go)
What is the length of postganglionic neurons?
These are long.
(go far to reach effectors).
Where are the sympathetic ganglia?
These lie in a vertical row alongside vertebrae from the skull to coccyx (sympathetic chain).
Found closer to spinal cord.
What are the features of the collateral (pre vertebral) ganglia?
These lie in front of the vertebral column alongside the abdominal arteries (celiac ganglion, superior mesenteric ganglion and inferior mesenteric ganglion).
Where are the parasympathetic ganglia?
These are located close to the effector organs.
(The preganglionic axons are longer than the sympathetic axons.)
What are some examples are neurotransmitters in the ANS?
Acetylcholine and noradrenaline.
Which neurons release acetylcholine (ACh) ?
Both the parasympathetic and sympathetic preganglionic neurons.
Also, parasympathetic postganglionic neurons (sympathetic postganglionic neurons that innervate sweat glands).
What are the 2 types of acetylcholine receptors?
-Nicotinic receptors
-Muscarinic receptors
What are nicotinic receptors?
The sympathetic and parasympathetic ganglia.
What are muscarinic receptors?
-Plasma membranes of effector organs inverted by parasympathetic NS
-Membrane of sweat glands inverted by sympathetic postganglionic neurons.
How is ACh broken down?
It is broken down by the action of acetylcholinesterase.
What is noradrenaline released by?
Released by sympathetic postganglionic neurons.
What are the features of noradrenaline?
Acts at adrenergic receptors at effector organs.
2 main groups of adrenergic receptors (alpha -1 and 2 and beta-1,2 and 3).
How is noradrenaline broken down?
Broken down by catechol-O-methyltransferase (COMT).
Function of alpha 1 adrenergic receptor?
Located at vascular smooth muscle and increased vascular smooth muscle contraction.
Function of alpha 2 adrenergic receptor?
Located at CNS and decreases sympathetic outflow.
Function of beta 1 adrenergic receptor?
Located at cardiac cells and increase heart rate, contractility and renin release.
Function of beta 2 adrenergic receptor?
Located at bronchiole smooth muscle and vascular smooth muscle. They account for bronchodilation and vasodilation.
Function of beta 3 adrenergic receptor?
Located at adipose tissue, bladder and gall bladder and increase lipolysis and relaxation of bladder.
What is the impact on bronchi if you have asthma?
The muscles wrapped around the tube tighten and cause the bronchial tube lining to become inflamed (excess mucus).
What does a bronchodilator do?
This is medication that helps people with asthma breathe easier as it relaxes the muscles and widens the airways.
What is the mechanism for bronchodilation in beta 2 receptors?
Beta-2 Receptor Agonists (Adrenergic)
* Work on sympathetic nervous system
* Drug (eg Salbutamol) binds to receptor
* Receptor stimulates G-Protein to activate adenyl cyclase
* Adenyl cyclase converts ATP to cAMP
* cAMP relaxes smooth muscle by:
* Inhibits release of calcium from sarcoplasmic reticulum
* Activates Protein Kinase A
* Protein Kinase A inactivates myosin light chain kinase ( thus prevents
actin-myosin interaction)
* Smooth muscle relaxation
What is the bronchodilator mechanism at muscarninc receptors?
- Acetylcholine binds to muscarinic receptors
- Receptor stimulates G-Protein to activate Phospholipase C
- Phospholipase C stimulates production of Inositol Phosphate (IP3)
- IP3 binds to sarcoplasmic reticulum and stimulates release of calcium
(contraction) - Phospholipase C also leads to activation of myosin light chain kinase which
causes contraction
What does the sympathetic system do?
Enables fight or flight (stress).
What does the parasympathetic system do?
Rest and digest (conserving energy).
Where are the nerve fibres of the sympathetic system?
In the thoracolumbar area (between thoracic and lumbar vertebrae).
Where are the nerve fibres of the parasympathetic system?
Above and below sympathetic.
Craniosacral (base of brain and just superior to tailbone).
What are ganglia?
These are clusters of neuron cell bodies that house millions of synapses.
What are preganglionic cells?
These are neurons before the ganglion.
What are postganglionic cells?
These are neurons after the ganglion.
