The Autonomic nervous system Flashcards
Difference between central nervous system & peripheral nervous system
Central Nervous system = brain and spinal cord
Peripheral nervous system = ganglion and nerve
Cephalisation
Cerebral Cortex (telencephalon) = memory, attention, thought language consciousness.
Thalamus and hypothalamus (diencephalon) = metabolism, autonomic nervous system.
Midbrain (mesencephalon) = motor behaviour, alertness, temp and regulation
Pons and cerebellum (metencephalon) = sleep, respiration, equilibrium taste
Roles of the hypothalamus
- control of autonomic nervous system
- controls the pituitary gland which releases hormones
- control eating and drinking
- control of body temp
- regulation of circadian rhythm
Chemical transmission
- communication between neurons is mediated by chemical transmission at synapses.
- synapses release neurotransmitters which act on receptors.
STEPS IN CHEMICAL TRANSMITTERS :
- TRANSMITTER SYNTHESIS
- TRANSMITTER STORAGE
- TRANSMITTER RELEASE
- TRANSMITTER BINDING TO AND ACTIVATION OF RECEPTOR
- TRANSMITTER ACTIVATION
Process of chemical transmission
- transport of metabolite/molecule into presynaptic button
- biochemical processing of metabolite into the neurotransmitter
- uptake of the neurotransmitter into vesicles
- action potential reaches the presynaptic area
- calcium influx is triggered. calcium mobilises neurotransmitter vesicles towards the presynaptic membrane
6.neurotransmitter is released in the synaptic cleft - neurotransmitter binds to receptors on the postsynaptic membrane
- this triggers a response in the synaptic neuron/cell
- neurotransmitter is inactivated and processed into its original precursor
- neurotransmitter reuptake into the neuron
Peripheral nervous system
composed of :
- somatic efferent system = innervates skeletal muscle
- sympathetic system
- parasympathetic nervous system
SYMPATHETIC AND PARASYMPATHETIC MAKES UP THE AUTONOMIC NERVOUS SYSTEM
MAIN NEUROTRANSMITTERS ARE ACH AND NORADRENALINE
SUMMARY OF SYMPHATEITC ( FIGHT OR FLIGHT RESPONSE) NEURONS AND SYNAPSES
PREGANGLIONIC NEURONS
- short
- synapse with postganglionic neurons near spinal cord
- release ACH to activate nicotinic receptors on postganglionic neurons
POSTGANGLIONIC NEURONS
- long
- synapse on the target organ
- release norepinephrine activate adrenergic receptors on target organs
SUYMMARY OF PARASYMPATHETIC ( REST AND DIGEST) AND SYNAPSES
PREGANGLIONIC NEURONS
- long
- synapses with postganglionic neurons at or near organ
-release ACH to activate nicotinic receptors on postganglionic neurons
POSTGANGLIONIC NEURONS
- short
synapse on the target organ
- release ACH to activate muscarinic receptors on the target organ
SYMPATHETIC SYSTEM
- liver releases glucose into blood to increase energy supply
- increased heart rate, blood pressure, respiration
- increased blood flow to skeletal muscles, heart, brain
- decrease GI activity
PARASYMPATHETIC SYSTEM
- decreased heart rate, blood pressure, respiration
- increased GI activity facilitates digestion
Choline transport
most choline is derived of ACh in synaptic cleft.
choline is transported is inhibited by :
- hemicholinium
- triethylcholine
What are the two subtypes of cholinergic receptors
- nicotinic = ligand gated ion channels
- muscarinic = G protein coupled receptors
Ligand gated ion channels
- ion channels is integral part of receptor
- generally composed of 4-5 protein sub-units
- agonist binding has direct effect on ion channel function.
Nicotinic receptors
categorised into three classes based on location :
- muscle = skeletal neuromuscular junction
- ganglia = autonomic nervous system
- brain = synapses between neurons
Muscarinic receptors
categorised into classes based on difference in location :
-M1 ( neural ) = nervous system, ganglia, gastric parietal cells
M2 ( cardiac ) = heart, auto receptors on presynaptic terminals
M3 ( GLANDULAR ) = glands, visceral and vascular smooth muscle
Drugs affecting cholinergic transmission
mAChR agonists = also known as parasympathomimetic - few in clinical use but include bethanechol used to treat urinary retention
mAChR antagonists - Darifenacin = M3 selective , relaxes bladder contraction, used in treatment of urinary incontinence
Activators of the sympathetic nervous system
- stress
- trauma and fear
- hypoglycaemia
- cold
- excercise
CATECHOLAMINES (CA)
- sympathomimetic amines with a 3,4 - dihydroxy benzene group
ORIGINS OF CA :
- noradrenaline
- adrenaline
- dopamine
- isoprenaline
REUPTAKE
UPTAKE 1 = high efficiency system more specific for NA located in neuronal membrane
UPTAKE 2 = less specific for NA - located in smooth muscle/cardiac muscle
Metabolism of catecholamines
MONO AMINE OXIDASE
- intracellular bound to mitochondrial membrane
- present in NA terminals and liver/intestine
- MAO are used as antidepressants
CATECHOL-O-METHYL-TRANSFERASE ( COMT )
- neuronal and non neuronal tissue
- acts on catecholamines and by-products
VMA levels are diagnostic for tumours
SUBGROUPS OF ADRENO RECEPTORS
- alpha 1 = blood pressure
- alpha 2 - NA release
- beta 1 = myocardial contraction
- beta 2 = uterine relaxation
- beta 3 = lipolysis
Subdivision of alpha - adrenoreceptors
alpha 1 and alpha 2
majority of alpha 1 receptors are situated post synaptically
the majority of adrenergic alpha 2 type are situated pre-synaptically
Presynaptic receptors
Two types = auto and hetero
Auto receptor interaction = neurotransmitter affects the nerve terminals from which it is being released
Heteroreceptor interaction = a neurotransmitter affects the release of another
Beta- adrenoreceptors
beta 1 are found in the heart, stimulation results in increased rate and contractility
beta 2 are widely distributed on smooth muscle tissue, stimulation causes relaxation
beta 3 are found in adipose tissue, stimulation results in lipolysis
Adrenoceptor agonists : clinical uses
- the heart : cardiac arrest (B1)
- blood vessels : hypertension, migraine profylax (A2)
- the lungs : asthma (B2)
- mucous membranes : Decongestant (A1)
- small blood vessels : addition to local anaesthetics (A1) : reduction of superficial bleeding (A1)
- mixed indications : anaphylactic shock (B1,B2) Premature labour (B2) Intraocular pressure (A1) Obesity (B3)
