Lecture 9: The nervous system part 1: The autonomic nervous system Flashcards
What are the two divisions of the peripheral nervous system?
Afferent and efferent
What information does the afferent division of the PNS transmit via action potentials?
Information from the sensory receptors and visceral stimuli
What are the two divisions of the efferent nervous system?
Somatic nervous system and autonomic nervous system
What is the somatic nervous system?
Voluntary control of skeletal muscles
What makes the autonomic nervous system special?
It does not require conscious regulation
What does the autonomic nervous system do?
Regulates activity of the internal organs (smooth muscle, cardiac muscle and glands)
What is another major function of the autonomic nervous system?
Homeostasis
What can the autonomic nervous system be divided into?
Sympathetic (flight or fight)
Parasympathetic (rest and digest)
What nerves are associated with the parasympathetic division of the autonomic nervous system?
Cranial nerves
Sacral nerves
What nerves are associated with the sympathetic division of the autonomic nervous system?
Thoracic and lumbar nerves
What do lumbar nerves of the sympathetic nervous system do?
Makes kidney secrete epinephrine/norepinephrine, relaxes bladder, inhibits sex organs
The ANS does not usually have single neurons connecting the CNS to organs. Instead…
There is usually an autonomic ganglion in between
What are the two ganglions in the ANS?
Neurons from the CNS to ganglia are preganglionic
Distal ones are postganglionic
In autonomic ganglia, preganglionic nerves are ________ and postganglionic fibres are ________
Myelinated
Unmyelinated
Where are sympathetic ganglia located?
Close to the CNS
Where are parasympathetic ganglia located?
Close to the target organ, or embedded in it
How many cell bodies do sympathetic preganglionic axons innervate?
> 20
How many cell bodies do parasympathetic preganglionic axons innervate?
<4
How are sympathetic ganglia arranged?
In a row on each side of the spinal cord (Paravertebral ganglia)
Further away called prevertebral ganglia
What is the neurotransmitter for the preganglionic neurons of both divisions (para and sympathetic) of the ANS?
Acetylcholine
What is the postganglionic neurotransmitter of the sympathetic nervous system?
Norepinephrine
What is the postganglionic neurotransmitter of the parasympathetic nervous system?
Acetylcholine
Where is ACh broken down after being secreted from the preganglionic neurons?
Synaptic cleft
What enzyme breaks down ACh?
Acetylcholineterase
What happens once ACh is broken down?
Choline is transported back into the axon terminal and is used to make more ACh
What are the two types of ACh receptors?
Nicotinic
Muscarinic
What happens when ACh (or nicotine) binds to nicotinic receptors?
They open and allow ions to flow (Na+ in and K+ out)
What is the effect of ACh binding to nicotinic receptors and ions flowing?
Ionotropic (the binding of the ligand DIRECTLY alters permeability of the channel_
What are two features of ionotropic receptors?
- Fast synaptic transmission
- Often stimulatory
What happens when ACh (or mucarine) binds to muscarinic receptors?
They release G proteins which begin a cascade of information
What is the effect of ACh binding to muscarinic receptors causing G protein cascade?
Metabotropic: binding of the ligand to the channel INDIRECTLY alters permeability of ion channels
What are two features of metabotropic receptors?
- Several types
- May be stimulatory or inhibitory
In ANS, where are muscarinic receptors found?
Only in the post ganglionic parasympathetic nervous system
Where are nicotinic receptors found within the body?
Neuromuscular junctions, ganglionic neurons and adrenal medulla
What is the second messenger pathway of nicotinic vs. muscarinic receptors?
Ion influx
G protein coupled
What do epinephrine and norepinephrine bind to?
Adrenoreceptors
What happens when adrenoreceptors bind with nor/epinephrine?
They release G proteins, which begin a cascade of information
What are the two subtypes of adrenoreceptors?
Alpha and beta (both metabotropic)
Epinephrine and norepinephrine are both what type of molecule?
Catecholamines
Where are alpha 1 receptors found?
Blood vessels of skin, gut, kidneys and salivary glands
What is the effect of alpha 1 receptors in humans?
Vasocontriction
Where are beta 1 receptors found?
Heart
What is the effect on beta 1 receptors in humans?
Increases heart rate and strength
Where are beta 2 receptors found in humans?
Lungs
What is the effect of beta 2 receptors in humans?
Dilates bronchial passages
What is the first reason for the number of different types of receptors in humans?
Evolution is messy
What is the second reason for the number of different types of receptors in humans?
Different needs in different tissues: different combinations gives large range of responses
