ANS Flashcards
Describe the map of the ANS
Sympathetic is sandwiched between the parasympathetic
Brainstem and S2-S4 region of spinal cord are parasympathetic and T1-L2 region is parasympathetic
Briefly describe the ANS as part of the nervous system, include its action in involuntary control and its divisions
Part of peripheral NS
Involuntarily control:
- Regulates operation of the internal organs
- Maintains internal environment
- Innervates smooth muscle, cardiac muscle and glands
Divisions: sympathetic, parasympathetic and enteric
What are disynaptic pathways?
They describe the way in which ANS neurons synapse as their axons do not pass directly to effector organs.
Cranial nerve nuclei/grey matter of spinal cord along with its myelinated preganglionic axon synapse at symp/parasymp ganglion. Postganglionic axon (unmyelinated) synapse with effector organ (smooth muscle, cardiac muscle, glands0
EXCEPTION: Sympathetic innervation of the adrenal medulla (they pass through ganglion into splanchnic nerves to synapse in prevertebral ganglia)
What is the function of the sympathetic and parasympathetic NS?
SYMPATHETIC FUNCTION
Fight, flight, fright
Maximises use of metabolic resources
PARASYMPATHETIC FUNCTION
Opposite to sympathetic division (Rest and digest)
Switched on during resting
Increases/conserves metabolic resources
WORK TOGETHER TO CONTROL THE INTERNAL ENVIRONMENT
Consider the neurotransmission. Describe it within autonomic ganglia
ACh is main neurotransmitter
Binds to nicotinic receptors on postganglionic neuron
- Ionotropic ligand-gated (fast): ACh opens pore, depolarises neuron
Consider the neurotransmission. Describe it within postganglionic sympathetic neurons
Noradrenaline is main neurotransmitter (sweat glands use ACh)
Binds to adrenergic receptors of effector organ
- Metabotropic G-protein coupled (slow)
State, with examples, the subtypes of the adrenergic receptors on effector organs
Give drugs which effect such receptors
a1- blood vessel smooth muscle
Prazosin is an antagonist used to treat hypertension
b1- on heart
Atenolol is an antagonist used to treat hypertension
b2- on bronchial smooth muscle
Salbutamol is an agonist used to treat asthma
The sympathetic system is a huge system. State where it has its effects
Cardiac muscle Bronchi of lungs Sweat glands Hair follicles Blood vessels Abdomino-pelvic viscera Eye
Consider the neurotransmission. Describe it within the adrenal medulla
ACh is main neurotransmitter
Binds to nicotinic receptors on chromaffin cells
Causes release of adrenline/noradrenaline into circulation
- DIRECT activation of sympathetic effector organs
Describe the sympathetic trunk/chain
Interconnected paravertebral ganglia
Extends from cervical to sacral levels
Preganglionic fibres enter sympathetic trunk through white rami communicans (from T1-L2)
ANATOMY:
Lateral horn- cell bodies of preganglionic neurons
White ramus communicans- myelinated preganglionic axons
Grey ramus communicans- unmyelinates postganglionic axons
symp trunk
Consider the neurotransmission. Describe it within postganglionic parasympathetic neurons
Give an exampled of an antagonistic drug
ACh is main neurotransmitter
Binds to muscarinic receptors to the effector organs
- Metabotropic G-protein coupled (slow)
Atropine- cholinergic-muscarinic anatagonist (lowers parasympathetic activity) used to treat bradycardia, dilate pupils, reduce glandular secretions
Describe the cervical sympathetic trunk
3 ganglia in cervical sympathetic trunk
-Superior/middle/inferior (Stellate ganglion= fused inferior cervical and T1 ganglia, exists in 80%)
Postganglionic fibres exit via grey rami communicans to spinal nerves (sympathetic supply to upper limbs)
“Piggy back” DOWN common carotid artery to heart (sympathetic supply to heart)
“Piggy back” UP internal/external carotid artery to head
- Internal carotid plexus: to eye (dilation, eye lid move) and to lacrimal gland (inhibits secretion)
- External carotid plexus: to submandibular and parotid glands (inhibits secretions)
What is the ratio of postganglionic fibres to preganglionic?
What type of responses are sympathetic ?
Postganglionic fibres much more numerous than preganglionic
1:10 ratio
Sympathetic responses are mass responses
Allows coordinated activity at multiple levels
What is the distribution os postganglionic fibres from sympathetic trunk and from prevertebral ganglia?
FROM SYMP TRUNK:
- 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
What is Horner’s syndrome?
Disruption of the sympathetic supply to the head
Any party of pathway- hypothalamus to preganglionic neurons e.g. lesions with brainstem/ cervical spinal cord (in MS)
Pupil
Eyelid
Skin of face
Describe the fibres involved in the thoracic sympathetic chain
Preganglionic fibres exit via thoracic splanchnic nerves, by piercing diaphragm, to abdomen (Greater>Lesser>Least>to prevertebral ganglia)
Celiac ganglion- stomach/duodenum
Superior mesenteric ganglion- SI
Aorticorenal ganglion- kidney
Ganglia close to abdominal aorta
12 thoracic sympathetic trunk ganglia
Postganglionic fibres exit via grey rami communicans to spinal nerves and medial branches to heart and lungs
Postganglionic fibres form prevertebral plexus around viscera
Describe the lumbar sympathetic fibres
4 lumbar sympathetic trunk ganglia
Postganglionic fibres exit via grey rami communicans to spinal nerves
Preganglionic fibres exit via lumbar splanchnic nerves to pelvis
Synapse in prevertebral ganglia. Inferior mesenteric ganglia- large intestine
Describe the sacral sympathetic fibres
4 Sacral sympathetic trunk ganglia
Postganglionic fibres exit via:
- Grey rami communicans to spinal nerves (lower limb)
- Sacral splanchnic nerves to pelvic organs
The parasympathetic system is a small(er) system. State where it has its effects
Cardiac muscle Bronchi of lungs Sweat glands Hair follicles Blood vessels Abdomino-pelvic viscera Eye Salivary and lacrimal glands
Consider the cranial parasympathetic system. Describe the nerves involved.
Preganglionic neuronal cell bodies in cranial nerve nuclei
MIDBRAIN
CN3- Oculomotor nerve (Edinger-Westphal nucleus)
PONS
CN7- Facial nerve (Superior salivatory nucleus)
MEDULLA
CN9- Glossopharyngeal nerve (Inf. salivatory nucleus)
CN10- Vagus nerve (Nucleus ambiguous, dorsal motor nucleus), passes to heart, lungs and abdominal viscera
Consider the cranial parasympathetic system. State the ganglia that oculomotor , facial and glossopharnygeal nerve pass through and their effector organ
What is special about the location of the ganglia and effector organ?
Oculomotor nerve synapses at the ciliary ganglion and sphincter pupillae for pupil constriction
Facial nerve synapses at the pterygopalatine ganglion and lacrimal gland for tears. Alternatively, it can synapse at the submandibular ganglion and submandibular gland for watery saliva.
Glossopharyngeal nerve synapses at the optic ganglion and the parotid gland for watery saliva
! Close proximity of ganglia to effector organ
Describe parasympathetic preganglionic fibres
Neurons within brainstem or grey matter of spinal cord (forms S2-S4 spinal nerves)
All ganglia located close to target organ
Brainstem - cranial nerves - short postgang fibre- head, heart, lungs, abdomen
Spinal cord - pelvic splanchnic nerves - short postgang fibre- pelvic organs
Describe the sacral parasympathetic fibres
From sacral spinal cord
Preganglionic fibres exit via pelvic splanchnic nerves to pelvic organs
From pelvic plexus over viscera
Preganglionic fibres synapse in walls of target organs
Describe the enteric nervous system
(from most superficial to least)
Longitudinal muscle
Auerbach’s plexus - regulates muscle contraction
Circular muscle
Meissner’s plexus- regulates glandular secretions
Mucosa
Contains 10-100 billion neurons
Retains functions after all central connections severed
TRULY AUTONOMIC
Describe the sacral parasympathetic function
Urination form bladder
- contraction of bladder wall
- inhibition to bladder sphincter
Defecation from rectum
-inhibition of rectal sphincter
Sexual function
-vasodilation in erectile tissues (example of balance between parasympathetic and sympathetic divisions)
Outline the control of the ANS
Cerebral cortex (involuntary response ie blushing and pallor in fear) THEN
Hypothalamus -autonomic regulation Autonomic centres in brain Preganglionic neurons Postganglionic neurons Effector organs Sensory ganglia Autonomic centres in brain Hypothalamus -autonomic regulation
