T2 L6 Autonomic nervous system Flashcards
What is the function of the ANS?
Involuntary control
Regulates operation of internal organs
Maintains internal environment
Innervates smooth muscle, cardiac muscle, glands
What are the 3 divisions of the ANS?
Sympathetic
Parasympathetic
Enteric
What is the function of the sympathetic nervous system?
Fight, flight or fright
Maximise use of metabolic resources
What is the function of the parasympathetic nervous system?
Switched on during resting
Increase / conserve metabolic resources
Where is parasympathetic located?
Brainstem
S2-S4
Where is sympathetic located?
T1 to L2
What happens when acetylcholine binds to nicotinic receptors on postganglionic neurons?
Ionotropic ligand gated (fast)
Acetylcholine opens pore
Influx of calcium & sodium leading to depolarisation
What is the main neurotransmitter in the sympathetic postganglionic neurons?
Noradrenaline
Except for sweat glands which use acetylcholine
What are the 3 adrenergic subtypes?
Alpha 1
Beta 1
Beta 2
Where is alpha 1 found?
Smooth muscle of blood vessel
Prazosin is an alpha 1 antagonist used to treat hypertension
Where is beta 1 found?
On the heart
Atenolol is B1 antagonist used to treat hypertension
Where is beta 2 found?
On smooth muscle in bronchial
Salbutamol is beta 2 agonist used to treat asthma
Describe the sympathetic neurons within adrenal medulla
Acetylcholine is main neurotransmitter
Binds to nicotinic receptors on chromatin cells leading to release of adrenaline / NA into circulation
Describe postganglionic parasympathetic neurons
Acetylcholine is main neurotransmitter
Binds to muscarinic receptors on effector organ
Metabotropic G-protein coupled (slow)
What is atropine?
Cholinergic muscarinic antagonist which lowers parasympathetic activity
Treat bradycardia, dilate pupils, reduce glandular secretions
Describe the effects of the sympathetic system
Larger system
Cardiac muscle –> increases pacemaker activity & contractile force
Bronchi of lungs –> bronchodilator
Sweat glands –> sweat secretion
Hair follicles –> piloerection
Blood vessels –> vasoconstriction in skin, vasodilation in skeletal muscle
Abdomino-pelvic viscera –> inhibit peristalsis & gastric secretions. Stimulates glucagon secretion. Stimulates adrenaline secretion from adrenal medulla
Eye –> dilates pupils
What is the sympathetic trunk?
Interconnected paravertebral ganglion
Extends from cervical to sacral levels
Preganglionic fibres enter sympathetic trunk through white rami communications (from T1-L2 spinal nerves only)
What happens to preganglionic fibres once they have entered sympathetic trunk?
Synapse in ganglia at same level or travel to another level
OR
Pass through ganglion into splanchnic nerves to synapse in prevertebral ganglion
Describe postganglionic sympathetic fibres
More numerous than preganglionic
From sympathetic trunk they go to periphery or visceral
From the pre vertebral ganglion they form plexus around viscera
Describe the path of postganglionic sympathetic fibres to the periphery
Via grey rami communicans back into spinal nerves
Sweat glands, hair follicles, blood vessels
Describe the path of postganglionic sympathetic fibres to the viscera
Via medial branches / plexus
Heart, lungs, head
What are the 3 ganglia in the sympathetic trunk?
Superior ganglia
Middle ganglia
Inferior ganglia
What happens to the inferior cervical ganglia in sympathetic trunk?
Fuses with T1 to form stellate ganglion
Describe the exit of postganglionic fibres from the cervical sympathetic trunk
Exit via grey rami communicans to spinal nerves for sympathetic supply to upper limbs
Piggy back down common carotid to heart
Piggy back up internal / external carotid artery to head
What does the sympathetic internal carotid plexus do?
To eye to dilate pupil, smooth muscle of eyelid
To lacrimal gland to inhibit secretion
What does sympathetic external carotid plexus do?
To submandibular & parotid glands to inhibit secretions
What is horner’s syndrome?
Disruption of sympathetic supply t head Any part of pathway Pupil --> mitosis Eyelid --> ptosis Skin of face --> anhidrosis
Describe 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 to prevertebral ganglia
Describe thoracic splanchnic nerves
Pierce diaphragm
Synapse in pre vertebral ganglia
Ganglia located close to abdominal aorta
Postganglionic fibres form pre vertebral plexus around viscera
Were does celiac ganglion innervated?
Stomach / duodenum
Where does superior mesenteric ganglion innervate?
Small intestine
Where does aorticorenal ganglion innervate?
Kidney
Describe lumbar sympathetic
4 lumbar sympathetic trunk ganglia
Postganglionic fibres exit via grey rami communicans to spinal nerves
Preganglionic fibres exit via lumbar splanchnic nerves to perlves
Inferior mesenteric ganglia goes to large intestine
Describe sacral sympathetic
4 sacral sympathetic trunk ganglia
Postganglionic fibres exit via grey rami communicans to spinal nerves or sacral splanchnic nerves to pelvic organs
Describe parasympathetic system
Smaller division
Cardiac muscle –> decreases pacemaker activity & contractile force
Bronchi of lungs –> bronchoconstriction
Sweat glands –> none
Hair follicles –> none
Blood vessels –> none except male erectile tissue / salivary glands which dilate
Abdomino-pelvic viscera –> stimulates peristalsis & gastric secretions
Eye –> constricts pupil
Salivary & lacrimal glands –> secretion of watery saliva & tears
Where are preganglionic parasympathetic fibres found?
Within brainstem –> cranial nerves –> head, heart, lungs, abdomen
Grey matter spinal cord –> pelvic splanchnic nerves –> pelvic organs
All ganglia located close to target organ
Describe cranial parasympathetic
Preganglionic axons pass through cranial nerves to ganglia
Oculomotor nerve –> sphincter pupillae (constriction)
Facial nerve –> lacrimal gland (tears) & submandibular gland (water saliva)
Vagus nerve to heart, lungs, abdominal viscera
Describe sacral parasympathetic
From sacral spinal cord
Preganglionic fibres exit via pelvic splanchnic nerves tp pelvis organs
Form pelvic plexus over viscera
What is the function of sacral parasympathetic?
Bladder (urination): contraction of bladder wall, inhibition of bladder sphincter
Rectum (defecation): inhibition of rectal sphincter
Sexual function: vasodilation in erectile tissue
Describe the 2 plexi of the enteric nervous system
Auerbach’s - regulate muscle contraction
Meissners - regulate glandular secretion
Contains 10-100 billion neurons
Retains function after all central connections are severed
