Autonomic Nervous System Flashcards
What is the autonomic nervous system?
Sub-section of peripheral nervous system that regulates involuntary processes from CNS to peripheral organs e.g. heart rate, digestion, respiration
What are the 3 divisions of the ANS?
- Sympathetic - links CNS to peripheral organs
- Parasympathetic - links CNS to peripheral organs
- Enteric nervous system- controls GI tract
What is the autonomic nervous system comprised of?
- 2 efferent (transmit away from CNS) neurones
- Pregranglionic neurons which synapse onto Postganglionic neurons- these innervate target organs
Describe the parasympathetic nerves
- Have long pre-ganglionic fibre, short post- ganglionic fibre
Where do the parasympathetic pre-ganglionic fibres arise from?
- Cranial nerves 3,7,9 and 10 and the sacral spinal cord 2,3,4
Where do the parasympathetic preganglionic fibres synapse with postganglionic fibres?
- At the head or near the wall of an organ supplied by vagus or sacral nerves
- The vagus nerve contains about 75% of all parasympathetic fibres
What do the parasympathetic pre-ganglionic fibres release, and where does the neurotransmitter act?
- ACh, which acts at nicotinic (Nic) receptors
What do the parasympathetic post-ganglionic fibres release and where does the neurotransmitter act?
- ACh which acts at muscarinic (Mus) receptors
- Exception is non-adrenergic-non-cholinergic (NANC) nerves which use chemicals such as nitric acid (NO)
What are the functions of the parasympathetic nervous system?
- Slows heart rate and lowers blood pressure
- Vasodilates gut and stimulate gut motility and secretions
- Constricts pupil and contracts ciliary muscles to allow closer focus
- Increase secretion from salivary glands
What are some of the organs ONLY innervated by parasympathetic nerves?
- Pancreas
- Secretory cells of stomach
- Lungs (though airways contian Beta adrenoceptors, modulate by circulating adrenaline released by sympathetic adrenal glands)
Describe the sympathetic nerves?
- Short pre-ganglionic fibre, long post-ganglionic fibre
Where do the sympathetic pre-ganglionic fibre arise from?
- Lateral horns of grey matter from T1-L2/3
Where do the Sympathetic preganglionic fibres synapse with postganglionic fibres?
At paravertebral or pre vertebral ganglia. They directly synapse onto chromatin cells of adrenal medulla
What do the sympathetic pre-ganglionic fibres release and where does the neurotransmitter act?
- ACh, which acts at nicotinic receptors (Nic).
What do the sympathetic post-ganglionic fibres release and where does the neurotransmitter act? What is the exception?
- NA (noradrenaline), which acts at alpha or beta adrenoceptors
- Exception is sweat glands, where the nerves release ACH which acts at muscarinic receptors (Mus)