Lecture 10 - ANS Physiology Flashcards
ANS functions (5)
- Cardiac output must increase.
- Blood diverted to skeletal muscle (quads etc).
- Body temperature rises so sweating must increase.
- Peripheral vasodilatation to allow heat loss.
- Metabolism of fuel stress to provide glucose.
ANS overview (6)
- Connection between the central nervous system and peripheral organs.
- Largely outside of voluntary control.
- Two neurone systems.
- Two nervous systems= Sympathetic & Parasympathetic.
- Often have opposing effects on a tissue.
- BUT some tissues have a single nerve supply.
Somatic system (1)
Rapid impulse, ACh is released, single nerve process.
Sympathetic nerves (3,4)
• Chain of ganglia near spinal cord. thoracic and lumbar spinal.
• Paravertebral chain of ganglia (~25).
• Prevertebral ganglia near aorta.
Other 4 marks on sheet.
Parasympathetic nerves (5)
On sheet
Properties of ANS (4)
- Sympathetic and parasympathetic produce the opposite actions in the same organs. e.g. heart – ANTAGONISTIC EFFECT.
- Sympathetic - increases heart rate
- Parasympathetic - decreases heart rate
- So, heart rate is controlled by a balance between the sym/parasym
- Sympathetic and parasympathetic produce the same effect in the same organ. e.g. both increase secretions from salivary gland.
- Some organs are only innervated by sympathetic. e.g. kidney, sweat glands, blood vessels (last two are single input tissues).
- Some organs are only innervated by parasympathetic. e.g. lungs (Bronchiole smooth muscle) (but airways do contain β-adrenoceptors and are modulated by circulating adrenaline). Ciliary muscle of the eye and penile artery - that’s how erections work (all single input tissues).
Non-adrenergic non-cholinergic transmitters (NANC) (3)
• ATP / neuropeptide Y (NPY)
Post-ganglionic sympathetic neurone = vasoconstriction
• Vasoactive intestinal peptide (VIP)
Salivary glands or bronchial smooth muscle = dilatation
• Nitric oxide (NO)
Parasympathetic pelvic nerves = erection. Erectile tissue innervated by NANC parasympathetic nerves release nitric oxide.
Homeostasis (3)
- ANS contains both afferents and efferent fibres.
- ANS is of primary importance in mediating homeostatic involuntary mechanisms – achieved through feedback systems
- Example: Responses to a decrease in blood pressure
- Drop in blood pressure
- Sensed by baroreceptors (aortic arch)
- Change in firing of sensory nerves (afferents) to CNS
- Sensory information processed by CNS
- Signals are sent out via sympathetic nerves (efferent) to the heart, blood vessels, kidney to increase in blood pressure.
Sympathetic system (13)
FFF - Fear, fight, flight
Short pre ganglionic fibres
Long post ganglionic fibres
Increases BP/HR/O2 intake
Ganglion next to spine - paraventricular
Thoraco-lumbar outflow
NICOTINIC receptors always at autonomic ganglia.
SN release NA/ACh.
NA - a/B adrenoreceptors. Main terminal messenger/post ganglionic axons.
Sweat glands - releases ACh at MUSCARINIC receptors.
Adrenal glands - Have diff ganglion.
First nerve in PNS/SNS always releases ACh.
• Stimulation of pre-ganglionic sympathetic fibres release adrenaline (80%) and noradrenaline (20%) from adrenal glands.
• Exception - post-ganglionic fibres are NOT involved.
Parasympathetic system (11)
• RD – Rest and Digest.
• Decrease in heart rate and pupil diameter.
• Increase in GI secretions, glucose uptake.
• Made up of two nerves.
• Long pre-ganglionic fibres, short post ganglionic fibres.
• Ganglia are close to or on the effector organs innervated- found in target organs.
• Acetylcholine is the main terminal messenger/ postganglionic axons.
• ACh in PNS will interact with the neuronal form on nicotinic acid receptor–> rapid depolarisation of the post ganglionic fibre.
First nerve in PNS/SNS always releases ACh.
• Pre-ganglionic sympathetic/parasympathetic nerves release ACh. Acts at nicotinic receptors (NIC) at ALL autonomic ganglia.
• Post-ganglionic parasympathetic nerves release ACh Acts at muscarinic receptors (Mus).
