15. Autonomic Nervous System Flashcards
What does the ANS do?
Controls all involuntary functions
E.g. heart rate, blood pressure, GI motility, iris diameter
Entirely efferent but is regulated by afferent inputs
What are the anatomical divisions of the brain stem and spinal cord?
Medullary Cranial Thoracic Lumbar Sacral
Which divisions control the parasympathetic nervous system?
Medullary and sacral
Describe parasympathetic nerves
Originate in lateral horn of medulla and sacral spinal cord
Have long myelinated postganglionic fibres
Have short unmyelinated postganglionic fibres
Ganglia are located within innervated tissues
Have actions that oppose sympathetic nervous system
Describe sympathetic nerves
Originate in lateral horn of lumbar and thoracic spinal cord
Have short myelinated preganglionic fibres
Have long unmyelinated postganglionic fibres
Ganglia are located in paravertebral chain close to spinal cord
Have actions that oppose the parasympathetic nervous system
What are the principal neurotransmitters in the ANS?
Acetylcholine
Noradrenaline
Which neurotransmitter is used in pre-ganglionic neurons?
ACh
Which neurotransmitter is used in parasympathetic post-ganglion is neurons?
ACh - acts on muscarinic ACh receptors in target tissue
What type of receptors are mACh receptors?
G-protein coupled receptors
M1, M2, M3, M4, M5
What is the neurotransmitter of most sympathetic post-ganglionic neurons?
Noradrenaline
What neurotransmitter do some specialised sympathetic post-ganglionic neurons use?
E.g. sweat glands, hair follicles
ACh (not noradrenaline like others)
What is the third division of the ANS?
Enteric nervous system - controls GI system
How are sympathetic postganglionic neurons in the adrenal glands different?
They differentiate to form neurosecretory chromaffin cells
What are chromaffin cells?
Can be considered as postganglionic sympathetic neurons that do not project to a target tissue
They release adrenaline into the blood stream
Present in adrenal medulla
What is the M2 ACh receptor function?
Bradycardia - SAN
Reduced cardiac conduction velocity - AVN
