Autonomic nervous system Flashcards
What is the autonomic nervous system used for?
Involuntary control:
- Regulates operation of the internal organs
- Maintains internal environment
- Innervates smooth muscle, cardiac muscle, glands
Describe the sympathetic system
Fight, flight, fright
Maximises use of metabolic resources
Describe the parasympathetic system
Opposite to sympathetic division
Switched on during resting
Increases/conserves metabolic resources
Which divisions work to control the internal environment?
Both sympathetic and parasympathetic
Where is the parasympathetic function found?
Brainstem
S2 to S4 of spinal cord
Where is the sympathetic division found?
T1 to L2 spinal cord
Describe the axons of the autonomic nervous system
Do not pass directly to effector organs
Form disynaptic pathways
Myelinated Ganglia unmyelinated effector organ
Within autonomic ganglia which is the main neurotransmitter?
Acetylcholine
Where does acetylcholine bind?
Nicotinic receptors on postganglionic neurons
Ionotropic ligand gated (fast influx of Ca2+ and Na+ causing depolarisation)
Within postganglionic sympathetic neurons which is the main neurotransmitter?
Noradrenaline
Where does noradrenaline bind?
Adrenergic receptors on effector organ
Metabotropic G protein coupled
What is prazosin?
Alpha 1 antagonist used in hypertension
What is atenolol?
Beta 1 antagonist used in hypertension
What is salbutamol?
Beta 2 agonist used in asthma
Within the adrenal medulla which neurotransmitter is present?
Acetylcholine
Where does acetylcholine bind in adrenal medulla?
Nicotinic receptors on chromaffin cells
Causes release of adrenalin/noradrenalin
Direct activation of sympathetic organs
Which neurotransmitter is used in postganglionic parasympathetic neurons?
Acetylcholine
What is atropine?
cholinergic-muscarinic antagonist (Lowers parasympathetic activity)
Used to treat bradycardia, dilate pupils, reduce glandular secretions
Which parts of the body use the sympathetic system?
Cardiac muscle
Bronchi of lungs
Sweat glands
Hair follicles
Blood vessels
Abdomino-pelvic viscera
Eye
Describe the sympathetic trunk/chain
Interconnected paravertebral ganglia
Extends from cervical to sacral levels
Where do preganglionic fibres enter the sympathetic trunk?
Preganglionic fibres enter sympathetic trunk through white rami communicans
On entering the trunk, preganglionic fibres either:
Synapse in ganglion (same level or travel to another level)
Pass through ganglion in splanchnic nerves to synapse in prevertebral ganglia
From sympathetic trunk, postganglionic fibres follow one of two routes:
To the periphery (sweat glands, hair follicles, blood vessels)
- Via grey rami communicans back into spinal nerves
To the viscera (heart, lungs, head)
- Via medial branches/plexus
From prevertebral ganglia, postganglionic fibres form
plexus around viscera
Describe the cervical sympathetic
3 ganglia in cervical sympathetic trunk
- Superior/middle/inferior cervical ganglia
[Stellate ganglion = fused inferior cervical and T1 ganglia]
Where do the postganglionic fibres exit?
Via gray rami communicans to spinal nerves (sympathetic supply to upper limbs)
Piggy back down common carotid artery to the heart (sympathetic supply to the heart)
“Piggy back” up internal/external carotid artery to head (internal carotid plexus - to eye (dilates pupil,smooth muscle of eyelid and to lacrimal gland (inhibits secretions) or external carotid plexus (to submandibular and parotid plexus (inhibits secretions))
What is horner’s syndrome?
Disruption of the sympathetic supply to head
Any part of pathway - hypothalamus to preganglionic neurons
E.g. Lesions within brainstem/cervical spinal cord (in MS or apical lung tumours)
(Affecting descending autonomic regulatory pathways)
Affecting pupil (Miosis - constriction of pupil), eyelid (Ptosis - drooping of eyelid) or skin to the face (Anhidrosis - lack of sweating)
Describe the thoracic sympathetic
12 thoracic sympathetic trunk ganglia
Postganglionic fibres exit via:
Grey rami communicans to spinal nerves
Medial branches to heart and lungs
Preganglionic fibres exit via:
Thoracic splanchnic nerves to abdomen
Greater, lesser and least to prevertebral ganglia
Where do the thoracic splanchnic nerves synapse?
In prevertebral ganglia Celiac ganglion - Stomach/duodenum Superior mesenteric ganglion - Small intestine Aorticorenal ganglion - Kidney
Where are the ganglia located?
Close to abdominal aorta
Describe the lumbar sympathetic
4 lumbar sympathetic trunk ganglia
Where do postganglionc fibres of the lumbar sympathetic exit?
Via Grey rami communicans to spinal nerves
Where do preganglionic fibres of lumbar sympathetic exit?
Lumbar splanchnic nerves to pelvis
Describe the sacral sympathetic
4 sacral sympathetic trunk ganglia
Where do Postganglionic fibres of the sacral sympathetic exit?
Grey rami communicans to spinal nerves (lower limb)
Sacral splanchnic nerves to pelvic organs
Describe the parasympathetic system
Smaller division
Cardiac muscle - decreases pacemaker activity and contractile force
Bronchi of lungs - bronchoconstriction
Sweat glands - None
Hair follicles - None
Blood vessels - None
Abdominopelvic viscera - stimulates peristalsis and release of gastric secretions
Eye - constrict
Salivary and lacrimal glands - Increase secretions
Describe the parasympathetic preganglionic fibres
Preganglionic neurons within:
Brainstem
Grey matter spinal cord (part that forms S2 – S4 spinal nerves)
All ganglia located close to target organ
Describe the cranial parasympathetic neuronal cell bodies
Preganglionic neuronal cell bodies in cranial nerve nuclei
Cranial nerve 3, 7, 9 and 10
Describe the cranial parasympathetic preganglionic axons
Preganglionic axons pass through cranial nerves to ganglia
Cranial nerve 3 (to ciliary ganglion), 7 (to pterygopalatine ganglion and submandibular ganglion) and 9 (to otic ganglion)
Where does the vagus nerve pass to?
Heart
Lungs
Abdomen
Describe the sacral parasympathetic system
From sacral spinal cord
Preganglionic fibres exit via:
Pelvic splanchnic nerves to pelvic organs
Form pelvic plexus over viscera
Preganglionic fibres synapse in walls of target organs
List the functions of the sacral parasympathetic division
Bladder (urination)
Contraction of bladder wall
Inhibition to bladder sphincter
Rectum (defecation)
Inhibition of rectal sphincter
Sexual function
Vasodilation in erectile tissues
Describe the enteric nervous system
In walls of gastrointestinal tract
2 very complicated plexi:
Auerbach’s – Regulates muscle contraction - between muscle wall
Meissner’s – Regulates glandular secretions - On inside wall
Contains 10-100 billion neurons
Very unusual – retains functions after all central connections severed
Truly autonomic
