Lecture 4 Flashcards
What is the central nervous system composed of?
Brain and spinal cord
What is the peripheral nervous system composed of?
All nerves outside the brain and spinal cord
What are the three domains of the PNS and what are their targets?
- Somatic= skeletal muscle - autonomic= all targets except skeletal muscle - enteric= gut
What is the autonomic nervous system composed of?
- Sympathetic nervous system - Parasympathetic nervous system
What is the sympathetic nervous system responsible for?
Fight or flight response
What is the parasympathetic nervous system responsible for?
Rest and digest
What is the role of afferent fibres?
Carry sensory information to the CNS
What is the role of efferent fibres?
Carry signals from the CNS to the periphery
Outline the sensory reflex arc
Sensory receptors > afferent fibres in dorsal root > interneurone > efferent fibres in ventral root > effector cell
Role of the dorsal horn?
Receives sensory input
What is found in the lateral horn?
Spinal preganglionic neurones
What is found in the ventral horn?
Somatic motor neurones
What is the structure of the synapse?
- presynaptic terminal - mitochondrion - synaptic vesicles - active zone - synaptic cleft - postsynaptic density - postsynaptic structure
Stages of neurotransmission
1) synthesis 2) storage 3) release 4) activation 5) inactivation
What is the purpose of storing a neurotransmitter in a vesicle?
- protection - packaging (quanta)
What happens in neurotransmitter release?
- docking of a vesicle - Ca2+ entry - exocytosis - endocytosis (recycling)
What is the neurotransmitter released at the somatic nervous system synapse?
Acetylcholine
What is the synapse called in the somatic nervous system?
Neuromuscular junction/endplate
What are the two neurones found in most efferent autonomic pathways?
- preganglionic neurones - postganglionic neurones
Where do postganglionic neurones synapse with?
- visceral smooth muscle - cardiac muscle - vascular smooth muscle - exocrine glands
What is the neurotransmitter released from preganglionic autonomic neurones?
Acetylcholine
Where are transmitters released from in the autonomic synapse?
Varicosities
What is the neurotransmitter released from postganglionic parasympathetic neurones?
Acetylcholine
What is the neurotransmitter released from the majority of postganglionic sympathetic neurones?
Noradrenaline
What neurotransmitter is released from sympathetic postganglionic neurones innervating sweat glands?
Acetylcholine
What is released from the chromaffin cells of the adrenal medulla and what is its target?
Adrenaline is released into blood vessels
What are cholinoceptors?
Receptors upon which ACh acts
What are the two classes of cholinoceptor?
- nicotinic - muscarinic
What are adrenoceptors?
Receptors upon which noradrenaline acts
What are the two classes of adrenoceptor?
- š¼ - Ī²
What type of receptors are nicotinic receptors?
ligand-gated ion channels (ionotropic)
What type of receptors are muscarinic receptors?
GPCRs (metabotropic)
What type of receptors are adrenoceptors?
GPCRs (metabotropic)
How many subunits do nicotinic receptors have?
5 (pentameric)
What are the types of subunits found in nicotinic receptors?
- š¼ - Ī² - šæ - š¾
Why does the composition of receptor subunits matter?
Determines - structure - function - ion permeability
Why is the M2 region important in ionotropic receptors?
Amino acid residue determines the acetyl activity of receptors of particular ions
What happens once the ionotropic receptor is agonised?
Induced conformational change allowing ions to flow in/out
What is an appropriate analogy for a nicotinic receptor- colander or pore?
Colander
Why is a colander an appropriate analogy for a nicotinic receptor
Ions repelled by the high positive charge at the bottom of the vestibule flow in/out of fenestrations
What are the steps of GPCR activation?
1) agonist binding induces conformational change in receptor 2) receptor interacts with š¼ G protein subunit 3) GTP displaces GDP 4) Gš¼ subunit interacts with target protein 5) Gš¼ containing GTPase hydrolyses GTP= inactivation
What differentiates the receptor subtypes from one another e.g. M1 and M2?
The ligand binding pocket differs between subtypes
How does GĪ²š¾ interact with GIRKs?
After separating from Gš¼, GĪ²š¾ induces opening of GIRKs= K+ ions leave the cell
Name an example of where nAChRs are found
Skeletal muscle
Names examples of where mAChRs are found
Salivary and sweat glands
Name an example of where adrenoceptors are found
Blood vessels
What happens to organs innervated by the parasympathetic NS?
- pupils= contract - tears= stimulated - salivation= stimulated - bronchi= constricted - bronchi secretions= stimulated - heart= slowed - gallbladder= constricted - gut motility= increased
What happens to organs innervated by the sympathetic nervous system?
- blood vessels= constricted - sweat glands= stimulated - pupils= dilated - bronchi= dilated - heart rate and contractility= increased - gut motility= slowed - stimulates production of adrenaline
