Week 1.07 ANS Flashcards
What is the PNS
Cranial nerves and spinal nerves. Connects CNS to all receptors and effectors
Sensory division
Receptors —> CNS
Afferent
Motor division
CNS —> effectors
Efferent
Somatic nervous systems
Supplies skin and muscoskeletal system - voluntary
Autonomic system
Automatic - digestion, control of heart rate
The autonomic nervous system is divided into
Parasympathetic and sympathetic
Sympathetic
Increase pupil size
fight or flight’ – responds to stress will increase your heart rate and blood flow. Can also decrease flow of blood to organs not required for their flight or fight
parasympathetic
Decrease pupil size
rest and digest’ – decrease heart rate and increase blood supply to the gastrointestinal blood vessels aiding the digestive system
Where is the ganglion in both sympathetic and para sympathetic
In sympathetic ganglion is closer to the CNS and pre ganglion pathway is shorter
And the other ways around in parasympathetic
What’s the parasympathetic pathways
Oculomotor nerve —(Ach)—> ciliary ganglion —-> ciliary muscle and sphincter muscle (Ach)
Sympathetic pathway b
Spinal cord —(Ach)—> superior cervical ganglion —-(NA)—> dilator muscle
Neurotransmitter
A chemical substance that allows impulse to pass across a synapse in a nerve
What is the neuroeffector junction
The junction between the end of the nerve and the muscle cell
What are the different types if neurotransmitter we use
- Acetylene choline (has a cholinergic receptor)
o Neurotransmitter for the ganglia of both sympathetic and parasympathetic branches
o Neurotransmitter at the neuro-effector junction of parasympathetic branch - Noradrenaline ((has an adrenergic receptor)
o The neurotransmitter at the neuro-effector junction of the sympathetic branch of ANS
Acetylcholinesterase
Enzyme that catalyses breakdown of acetylcholine and is mainly found at neuroeffector junctions and synapses
- Hydrolyses acetylcholine into choline and acetic acid
- Main job is to terminate transmission of the signal that acetylcholine is propagating
What are 5 methods by which a drug can affect the neuro-effector junction
- Interfere with release of nt
- Induce nt release - to turn on contraction of the effector muscle
- Interfere with destruction of nt - prolong stimulation of effector muscle
- Agonistic action - mimicking action of nt
- Antagonistic - blocking action of nt
Parasympathetic innervation
- Responsible for accommodation
- Responsible for contraction of pupil
- Originates at the edinger-westphal nucleus
- Leaves the midbrain via the third nerve
- Just before the orbit the third nerve splits, carries on the inferior division
- Synapse at the ciliary ganglion
- From here, travel into the eye with the short ciliary nerves
- Supply the ciliary muscle and pupil sphincter muscle
Sympathetic innervation:
- Originates at the hypothalamus
- Run downwards, exiting the cord via T1, T2, T3 to the thoracic ganglion
- From here, head to superior cervical ganglion (neck)
- Follow the internal carotid artery, enters cavernous sinus
- Joins ophthalmic division of the trigeminal
- Reaches pupil dilator via long ciliary nerves
What are the the 5 classes of drugs that affect the ANS
• Parasympathomimetics
• Anticholinesterases
• Antimuscarins
• Sympathomimetics
• Adrenergic blocking drugs
Parasympathomimetics
- stimulate parasympathetic system
- mimics acetylcholine at muscarinic receptors
- induces mitosis
If below 40 - dv blur
E.g. pilocarpine
Agonistic drug as mimics action of nt
Acetylcholinesterase
Inhibits cholinesterase (enzyme that turns off acetylcholine)
- causes accumulation of acetylcholine released into synaptic cleft - prolongs parasympathetic activity
- can induce mitosis
E.g. physostigmine
Antimuscrinic
- blocks acetylcholine at muscarinic receptors
- occupies the muscarinic receptions antagonistic effect
- produces mydriasis and cycloplegia
E.g. atropine, cyclopentolate, tropicamide
Sympathomimetics
- stimulate the sympathetic system - mimics effect of noradrenaline
- causes mydriasis
E.g. phenylephrine
Adrenergic blocking drugs
- blocks the action sympathetic system causing pupils to reduce in diameter
E.g. thymoxamine
