Autonomic Nervous System II Flashcards
Describe how the ANS differs from the somatic NS
Effectors, Efferent pathways, Target organ responses
Describe the effectors of the somatic NS and ANS
SNS: Skeletal muscles
ANS: Cardiac, smooth muscles and glands
Describe the efferent pathways of the Somatic NS
Motor neuron cell bodies in CNS/axons extend in spinal/cranial nerves all the way to skeletal muscles they activate
Describe the structure of somatic motor fibres
Usually large diameter, heavily myelinated fibres that conduct impulses rapidly
Describe the efferent pathways of the ANS
Use 2-neuron chain to its effectors
Usually conduct nerve impulses more slowly than somatic nerves
Describe the target organ response of the somatic NS and ANS
Somatic - Always excitatory on NMJ through nAChr
Autonomic - Excitatory/Inhibitory responses of target tissue
Describe autonomic NTs
ANS only has 2 main NTs: ACh, Noradrenaline
What is the main enzyme involved in synthesis via ACh and NA?
ACh: Cholineacetyltransferase
NA: Dopamine-b-monooxgenase
What is the main enzyme involved in breakdown via ACh and NA?
ACh: Cholinesterase enzymes
NA: Monoamine oxidase
What is the site of breakdown via ACh and NA?
ACh: Extracellular - Metabolism at synaptic cleft
NA: Intracellular - Metabolism inside neurons
Describe the preganglionic neurons of ANS NTs
Always ACh and excitatory
Describe the postganglionic neurons of ANS NTs in terms of PS/S
PS: ACh, Cholinergic neurons, Excitatory or inhibitory effects
S: Primarily NA, Adrenergic neurons, Excitatory/Inhibitory effects
Describe the adrenal medulla
Preganglionic sympathetic neurons innervate adrenal medulla cells (cholingeric neurons)
Stimulation of AMCs cause release of A/NA into bloodstream
Activation occurs in emergencies
Describe the signal transduction processes in cholinergic receptors - nAChR
In all autonomic ganglia (postgang)
LG ion channel - Stimulation causes cation flow to postgang neuron (excitatory)
Describe the signal transduction processes in cholingeric receptors - Muscarinic
On all target organs innervated by PSNS
G-Protein coupled receptors
5 main subtypes (M1-5_
Diversity of effects - Relax cardiac muscle, contracts smooth muscle)
Describe the differences of nicotinic and muscarinic receptors
N: Ionotropic, Fast excitatory signalling (ms)
M: Slower signalling (secs), Effects depend on signalling pathway
Describe adrenergic receptors - alpha/beta receptors
On target organs innervated by SNS
2 subtypes of adrenegic receptors (a/b receptors)
Both subtypes are GPCRs - Activation linked to second messenger pathways
Describe the differences between alpha and beta receptors
A: High affinity for NA, Mediate excitatory effects
B: Binds NA/A, Mediate relaxation/dec activity (except on cardiac tissue its excitatory)
Describe ANS functional rules
S/PSNS produce opposite effects in GI smooth muscle, heart rate, bladder
Sweat glands/blood vessels only regulated by S innervation
Bronchial smooth muscle only has PS innervation
Ciliary muscle of eye only regulated by PS innervation
Salivary glands innervated by both S/PS to produce similar effect
Describe the changes caused by fight or flight response
Heart rate increase Heart contractility increased BP increased Long sight vision increased O2 delivery to muscles inc Energy stores activated Skeletal muscle activity inc
Describe what studies on the PSNS show
Studies shows PSNS exhibits dominant activity during non-REM sleep
Describe the visceral reflex - The baroreceptor reflex
Carotid artery pressure falls, baroreceptor firing rate in wall falls
Afferent neuron firing dec
Vagal PS firing to heart dec
Heart rate inc, systemic bp rises, brain oxygenated maintained (postural hypotension avoided)
What is the ANS vital for?
Short term body homeostasis
How is the autonomic function finely controlled?
Using distinct transmitter and receptor systems
