4. Autonomic Nervous System Flashcards
Compare control of SNS and ANS
SNS: voluntary
ANS: involuntary
Compare number of neurons in pathway of SNS and ANS
SNS: single motorneuron
ANS: a preganglionic and postganglionic neuron
Compare cell body location of SNS and ANS
SNS: CNS
ANS: CNS for preganglionic and autonomic ganglion for post ganglionic
Compare effectors of SNS and ANS
SNS: skeletal muscle
ANS: cardiac muscle, smooth muscle, glands
Compare NTs and receptors of SNS and ANS
SNS: ACh/AChR
ANS: Preganglionic neuron: ACh/nAChR; postganglionic neuron: ACh/mAChR and NE/a1, a1, b1, b2
Divisions of autonomic nervous system
Sympathetic: ‘fight or flight’ (e.g. the body responds to fear, a difficult exam, a burning house, or an attacker)
Parasympathetic: ‘rest-and-digest’ (e.g. sexal arousal, salivation, lacrimation, urination, digestion, and defecation)
Describe the two neurons in series that connect the spinal cord and effector organs of the sympathetic division
Cell bodies of preganglionic sympathetic neurons are in thoracic and lumbar regions of spinal cord (T1-L3)
Thoracolumbar
Cell bodies of postganglionic sympathetic neurons are in:
-Paravertebral ganglia (sympathetic chain)
-Prevertebral/collateral ganglia (celiac, superior and inferior mesenteric ganglia)
Length of axons: short pre-ganglionic and long post-ganglionic
Adrenal gland
A speicalized sympathetic ganglion
Cell bodies of preganglionic located in thoracic spinal cord (T5-T9)
The axon of preganglionic neurons pass through the sympathetic chain and the celiac ganglion without synapsing, and travel to adrenal medulla, where they synapse on chromaffin cells
Endogenous analgesia system
Includes the secretion by the brain of endorphins in response to the central perception of pain.
Opioids and serotonin/catecholamines come from adrenal gland
Describe two neurons in series that connect the spinal cord and effector organ in the parasympathetic division
Cell bodies of preganglionic parasympathetic neurons are in nuclei of cranial nerves (III, VII, IX, X) and sacral region of spinal cord (S2-S4).
Craniosacral
Cell bodies of postganglionic parasympathetic neurons are within or very close to effector organs.
Length of axons: long pre-ganglionic axon; short post-ganglionic axon.
Sympathetic vs parasympathetic: origin of preganglionic nerve
Sympathetic=thoracolumbar
Parasymapthetic=craniosacral
Sympathetic vs parasympathetic: location of ganglia
Sympathetic=far from effector organs
Parasymapthetic=near or within effector organs
Sympathetic vs parasympathetic: length of preganglionic nerve
Sympathetic=short
Parasymapthetic=long
Sympathetic vs parasympathetic: length of post ganglionic nerve
Sympathetic=long
Parasymapthetic=short
Neuromuscular junction
The junction between motoneuron and its effectors (skeletal muscle fibers)
Motor end plate
Nerve terminals
Neuroeffector function
The junction between postganglionic autonomic neurons and its effectors (target tissues)
Branching networks
Varicosities
Neuroeffector junction vs. Neuromuscular junction: arrangement
neuroeffector junction = diffuse, branching networks
neuromuscular junction= discrete, organized structure called motor end plate
Neuroeffector junction vs. Neuromuscular junction: innervation
neuroeffector junction = target tissues may be innervated by many postganglionic neurons
neuromuscular junction= a skeletal muscle fiber is innervated by a single motorneuron
Neuroeffector junction vs. Neuromuscular junction: NT storage sites
neuroeffector junction = varicosities
neuromuscular junction= nerve terminals
Neuroeffector junction vs. Neuromuscular junction: postsynaptic receptors
neuroeffector junction = postsynaptic receptors are widely distributed on the target tissue
neuromuscular junction= postsynaptic receptors are located in the specialized motor end plate
Adrenergic neurons
Synthesize and release norepinephrine
Adrenoreceptors
a1, a2, b1, b2; activated by NE or epinephrine
Cholinergic neurons
neurons that synthesize and release ACh
Cholinoreceptors
Nicotinic AChR, muscarinic AChR; activated by ACh
Similarities of ACh in both ANS divisions
Preganglionic neurons release ACh that activates nAChR on postganglonic neurons in both sympathetic and parasympathetic divisions.
A substantial amount of nicotine (nAChR agonist) will cause…
Increase parasympathetic AND sympathetic response.
Non-classic neurotransmitters in parasympathetic division
VIP (vasoactive intestinal peptide)
NO (nitric oxide)
Non-classic neurotransmitters in sympathetic division
ATP
Neuropeptide Y
In the ganglia, which transmitters and receptors are used in the parasympathetic, sympathetic and adrenal medulla?
ACh = transmitter
nAChR=receptor
In the effector organs, which transmitters and receptors are used in the parasympathetic, sympathetic, and adrenal medulla
Parasympathetic:
ACh (VIP, NO) = transmitter
mAChR=receptor
Sympathetic:
NE, ACh (ATP, neuropeptide Y) = transmitter
a1, a2, b1, b2, mAChR =receptor
Adrenal medulla:
NE and epinephrine = transmitter
a1, a2, b1, b2=receptor
G protein linked receptors
Activate G proteins (GDP to GTP)
Seven TM domains
Ex: adrenoreceptors (a1, a2, b1, b2) mAChRR
G protein
Guanosine nucleotide-binding proteins
Heterotrimer (a, b, g)
Molecular switches: GTP (active) / GDP (inactive)
Activated by G protein-linked receptors
Steps of G protein activation
- Inactive state
- Ligand binding
- Nucleotide exchange
- Active state
- Ligand-dissociation GTP hydrolysis
Downsteam effects of G protein activation
Gs, Gi: activates or inhibits Adenylyl cyclase (AC) → cAMP↑ or ↓ → PKA ↑ or ↓
Gq: activates Phospholipase C (PLC) → inositol-1,4,5-triphosphate (IP3) ↑, diacylglycerol (DAG) ↑ → Ca2+↑ and PKC ↑
Direct alters the function of ion channels: mAChR → Gi → K+ channels of the sinoatrial node
A1 receptor location
Vascular smooth muscle of the skin, skeletal muscle, and the splanchnic region
Sphincters of the gastrointestinal tract and bladder
Radial muscle of the iris.
A1 receptor function
Activation leads to contraction
A2 receptors and G protein
Adenylyl cyclase, but activates Gi protein, causes inhibitory effect – relaxation
A1 receptors and G protein
Gq activates phospholipase C upon norepinephrine binding (alpha subunit with GTP binding lead to activation of phospholipase C) – skin and skeletal muscle, cause tissue contraction
B1/B2 receptors and G protein
Norepinephrine binding, beta receptor activated… - in sinoatrial node and atrioventricular, increase heart rate, conduction velocity and contractility of heart muscle, increase lipolysis, saliva (beta1)
B1 location
Sinoatrial (SA) node, atrioventricular (AV) node, and ventricular muscle of the heart
Salivary glands, kidney, and adipose tissue
B2 location
Vascular smooth muscle of skeletal muscle
Walls of the gastrointestinal tract and bladder
Bronchioles
B1 receptor function
Increase heart rate, conduction velocity, and contractility
Increase secretion of saliva, renin, and lipolysis
B2 receptor function
Relaxation or dilation
A2 receptor location
Vascular smooth muscle of certain blood vessels
Gastrointestinal tract
A2 receptor function
Relaxation
Autoreceptors
Present on sympathetic presynaptic regions
Inhibits further release of norepinephrine from the same terminals
Negative feedback
Are presynaptic a2 receptors
Heteroreceptors
Present on parasympathetic presynaptic regions
Inhibits release of acetylcholine from the parasympathetic postganglionic nerve terminals.
Are presynaptic a2 receptors
Why does Curare (nAChR blocker) cause relaxation of skeletal muscle?
Curare blocks nAChR that is required for the initiation of action potential and muscle contraction.
Why does Atropine (mAChR blocker) increases heart rate?
Atropine inhibits mAChR and parasympathetic division, countering the “rest and digest” activity.
Action of a1 adrenoreceptors
Stimulation of phospholipase C → ↑ IP3 → ↑ intracellular [Ca2+]
Action of a2 adrenoreceptors
Inhibition of adenylyl cyclase → ↓ cAMP
Action of b1 adrenoreceptors
Stimulation of adenylyl cyclase → ↑ cAMP
Action of b2 adrenoreceptors
Stimulation of adenylyl cyclase → ↑ cAMP
Action of nictotinic cholinoreceptors
Opening Na+ and K+ channels → depolarization
Action of muscarinic cholinoreceptors
Stimulation of phospholipase C → ↑ IP3 → ↑ intracellular [Ca2+]
Dual innervation by sympathetic and parasympathetic divisions
Most organs are dual innervated.
Usually antagonistic but often complementary
Overall function
Sympathetic: ‘fight or flight’
Parasympathetic: ‘rest or digest’
Only sympathetic innervation: sweat glands, adrenal medulla, blood vessels
Pupil in bright light
Parasympathetic: constrictor/sphincter muscles contract
Increased ACh release and mAChR activity in pupillary constrictor (sphincter) muscle → sphincter muscle constricts → constricts pupil (miosis)
Pupil in dim light
Symmapethetic: dilator/radial muscles contract
Increased NE release and a1 receptors activity in pupillary dilator (radial) muscle → radial muscle constricts→ dilates pupil (mydriasis)
What is the pathophysiology of Horner’s syndrome (typical symptoms - miosis, and anhidrosis)?
Interruption of the sympathetic innervation of the head and neck.
Autonomic functions of hypothalamus
Temperature
Food intake
Water balance
Autonomic functions of brain stem
Micturition Breathing Cardiovascular function Swallowing Coughing Vomiting
Servomechanism
A control system uses a negative feedback mechanism to operate another system
Ex: vasomotor center in blood pressure regulation
Temperature regulation
Central thermoreceptors in the anterior hypothalamus
What is the mechanism of fever?
Pyrogens increase the temperature regulation set point in the hypothalamus
Glucoreceptors
In the hypothalamus, regulate food intake
Osmoreceptors
In the hypothalamus, regulate water intake
Diversity as a determinant of physiologic functions
- Different transmitters, different functions
The same effector cells (e.g., smooth muscle cells) may respond differently depending on whether it receives cholinergic or adrenergic input. - Different receptors, different functions
The same effector cells (e.g., smooth muscle cells) may respond differently when receiving adrenergic input depending on the types of adrenergic receptor.
Specificity as a determinant of physiologic functions
Same transmitter/receptor, but different functions
Tissue-specific and cell type-specific
- b1 activation in the sinoatrial (SA) node: increase heart rate
- b1 activation in the atrioventricular (AV) node: increase conduction velocity
- b1 activation in the ventricular muscle: increase contractility
- b1 activation salivary gland: increase secretion
- b1 activation kidney: secrete renin
Table of effects of ANS and organ function
Go look at it and study it HAHAHHA
