Autonomic nervous system Flashcards
List the three different divisions of the ANS
- PARASYMPATHETIC
- SYMPATHETIC
- ADRENAL SYMPATHETIC/ ENTERIC
parasympathetic pathway
CNS –> long axon preganglionic neuron –> nicotinic receptor at the ganglion –> short postganglionic neuron –> muscarinic receptor close to target
- preganglionic neuron is a long distance from the CNS
- nicotinic receptor at the ganglion is ionotropic and a cholinergic signalling
- autonomic targets : smooth/cardiac muscles; endocrine/exocrine glands; adipose tissue
- ACh binds to the muscarinic receptor (metabotropic)
sympathetic pathway
CNS –> short axon preganglionic neuron –> nicotinic receptor at the ganglion –> long postganglionic neuron –> adrenergic receptor at target
- postganglionic neuron is a long distance from the CNS, far from target
- nicotinic receptor at the ganglion is ionotropic and a cholinergic signalling
- autonomic targets : smooth/cardiac muscles; endocrine/exocrine glands; adipose tissue
- noradrenaline binds to the alpha adrenergic receptors (metabotropic)
adrenal sympathetic
efferent neurone–> adrenal glands –> chromaffin cells in the adrenal cortex produces adrenaline –> adrenaline enters the circulation/bloodstream –> targets a whole plethora of organs
- no secondary neuron like the para and sympathetic pathway
- synpases at the adrenal gland instead of the autonomic ganglia
integration of autonomic function
pons, medulla and hypothalamus : receives sensory input from hypothalamic sensors (senses internal stimulus –> temp, salt levels)
* response: autonomic, endocrine, behavioural response
limbic system, cerebral cortex : receives sensory input from somatic and visceral sensory neurons (external sensory output == photons/light)
–> limbic system and cerebral cortex are the emotional influence
* response: behavioural response
hypothalamus role in the autonomic nervous system
thermoreceptors send signal for temperature control
osmoreceptors send signal for water balance
eating behaviour
pons and medulla role in the autonomic nervous system
urinary bladder control
secondary respiratory center
blood pressure control
respiratory center
difference between para and sympathetic pathway
site of origin of preganglionic neurones + autonomic ganglia
para: sacral & brainstem (cranial nerves) = top and bottom region of spine
–> long pre-ganglionic neurons
–> close to target organs
sympathetic: thoracic & lumbar regions = middle region of spine
–> short pre-ganglionic neurons (close to spinal cords)
–> close to spinal cord
difference in sympathetic and para responses
pupil of eye
sympathetic : dilates (for more light to come in during fight/flight) = a receptor
para : constricts –> relaxation
heart
sympathetic : increases rate and force of contraction = B1 receptor
para : slows rate –> relaxation
lungs
sympathetic : bronchioles dilate (more volume of air) = B2 receptor
para : bronchioles constrict –> relaxation
digestive tract
sympathetic : decreases motility and secretion = a/B2 receptor
para : increases motility and secretion –> relaxation
peripher nervous system
two branches : somatic and autonomic NS
somatic = voluntary
autonomic = involuntary
autonomic –> para (increase energy) + sym (decrease energy)
differences in the para and sym pathways
both pre ganglionic neurons have nicotinic ACh (ACh) receptors and ACh binds to it (ACh)
at target tissue with post ganglionic neuron :
para : ACh binds to muscarinic ACh receptors (just uses ACh)
sym : noradrenaline to adrenergeric receptors (noradrenaline)
varicosities at neuroeffector junctions
unlike NMJ, synpase doesn’t contain clusters of receptors
post ganglionic axons contain varicosities (swollen areas full of neurotransmitter)
varicosities also contain mitochondria as exocytosis of neurotransmitter is a high energy requiring active process
neurotransmitters are synthesised in the axons and diffuses through interstitial fluid
=> slower signalling
=> slower to initiate response
=> slower to terminate neurotransmitter
BUT –> affects a larger area
neuromuscular vs neuroeffector junctions
NMJ : synpase contains clusters of receptors –> quick responses to fire neurons
=》 termination : acetylcholinesterase breaks down ACh
NEJ : contain varicosities (swollen areas full of neurotransmitter) –> doesn’t need rapid info transmission
=》 termination : monoamine oxidase breaks down noradrenaline
transmission of neuroeffector junction
- action potential arrives at varicosities and propagated by voltage gated sodium channels
- depolarisation opens voltage gated Ca2+ channels
- Ca2+ entry triggers exocytosis of synaptic vesicles
- noradrenaline binds to adrenergic receptor on target
- noradrenaline is removed from synapse by diffusing away into bloodstream or and actively taken back by synpase to be recycled and receptor activation ceases
- noradrenaline taken back into synapse vesicles for rerelease or metabolised by monoamine oxidase (MAO) in mitochondria
neurotransmitter receptors
sympathetic uses adrenergic:
Two subtypes: α and β
α most common, responds strongly to noradrenaline (NA)
β has 3 subtypes (β1 , β2 , β3 ), different
sensitivities to NA vs adrenaline
All are G protein-coupled receptors but trigger
different 2 nd messenger pathways
Parasympathetic pathways use muscarinic ACh receptors
5 subtypes, all G protein coupled receptors
