Autonomic nervous system Flashcards
Which component of the nervous system is the autonomic system a part of?
Visceral efferent
Function of the autonomic nervous system
Controls involuntary activities of smooth muscle (e.g. vasoconstriction/dilation), cardiac muscle, glands (salivary, GI, sweat), and metabolism.
2 divisions of the autonomic nervous system
Sympathetic and parasympathetic nervous system
Where in the CNS are the cell bodies of preganglionic parasympathetic neurons located?
Brainstem and sacral spinal cord (S 2-4)
Which parasympathetic preganglionic neurons have their cell bodies in the brainstem?
Oculomotor (CN III), Facial (CN VII), Glossopharyngeal (CN IX) nerves that control head structures, and the Vagus nerve (CN X) that controls thoracic and abdominal viscera.
Which parasympathetic pre-ganglionic neurons have their cell bodies in the spinal cord?
S 2, 3, 4 which control the pelvic organs
Where are the cell bodies of sympathetic pre-ganglionic neurons found?
Thoracic and lumbar regions of the spinal cord (T1-L2)
Which division of the ANS is the adrenal medulla a part of?
Sympathetic NS
What is a ganglion?
A collection of neuron cell bodies in the PNS where the preganglionic nerve synapses with the postganglionic nerve.
Difference of ganglion location in parasympathetic and sympathetic NS
In the parasympathetic NS, the ganglion is closer to / in the target/effector.
Structure of the ANS
The preganglionic neuron has its cell body in the CNS and synapses with the postganglionic neuron (or adrenal medulla) at the ganglion in the PNS. The impulse then travels to the effector/target.
How is the ANS structured when the adrenal medulla is involved?
The sympathetic neuron has its cell body in the CNS and travels to the adrenal medulla, triggering the release of a hormone which is transported in the blood to the effector/target.
Comparison of preganglionic and postganglionic neuron lengths in the parasympathetic NS
Preganglionic neuron is longer than the postganglionic neuron (because the ganglion is close to / in effector organ)
Comparison of preganglionic and postganglionic neuron length in sympathetic NS
Both similar in length
Where do sympathetic pre and postganglionic neurons synapse?
In the sympathetic chain or in one of the collateral ganglia or adrenal medulla
Which 2 neurons is the ANS composed of?
Preganglionic and postganglionic neurons
Effector organs innervated by the ANS
Smooth muscle, cardiac muscle, glands
2 groups of ganglia
Sensory ganglia (transmit info from periphery to CNS) and autonomic ganglia (transmit info from CNS to periphery)
Function of parasympathetic NS
Acts on single organs in the body core (e.g. salivary glands, heart, iris and ciliary muscles, bronchi, GIT…). Conserves energy and has anabolic effects such as storing energy (digestion), reducing heart rate.
Which nerves are part of the parasympathetic NS?
Oculomotor (CN III), Facial (CN VII), Glossopharyngeal (CN IX), Vagus (CN X), and sacral nerves S2-4.
Function of sympathetic NS
Often affects whole body - homeostasis (blood pressure, thermoregulation), fight or flight response (adrenaline, meet energy demands, dental anxiety).
Which nerves are part of the sympathetic NS?
Thoracic and lumbar (thoracolumbar) nerves T1-L2 (14 total)
What is the sympathetic chain/trunk / paravertebral ganglia?
Site where preganglionic and postganglionic nerves synapse along the entire length of the vertebral column on either side forming 2 sympathetic chains.
Is breathing controlled by the ANS?
No - skeletal muscle therefore it is controlled by the somatic NS (e.g. phrenic nerve). ANS can affect bronchodilation.
Which head structures are affected by the ANS?
Muscles: iris and ciliary. Blood vessels.
Glands: salivary, lacrimal, nasal.
How does the parasympathetic NS affect salivary secretions?
Increases quantity and more watery (digestion)
How does the sympathetic NS affect salivary secretions?
Reduces volume and more viscous.
Which neurotransmitter is released by the parasympathetic preganglionic neuron at the ganglion?
Acetylcholine
Which neurotransmitter is released by the postganglionic parasympathetic neuron at the effector?
Acetylcholine
Which neurotransmitter is released by the sympathetic preganglionic neuron at the ganglion?
Acetylcholine
Which neurotransmitter is released at the sympathetic postganglionic effector?
Noradrenaline
Which neurotransmitter is released by the sympathetic nerve at the adrenal medulla?
Acetylcholine (adrenal medulla then releases adrenaline)
Alternative name for noradrenaline
norepinephrine
Alternative name for adrenaline
epinephrine
What feature causes variations in the effects of a neurotransmitter?
Type of receptor
Effect of noradrenaline binding to alpha (a) receptor
Vasoconstriction (contraction of SM in blood vessels)
Effect of noradrenaline binding to beta receptor
Bronchodilation (relaxation of bronchial SM)
Effect of adrenaline binding to adrenergic alpha (a) receptors
Contraction of smooth muscle (e.g. vasoconstriction, pylorus contraction)
Effect of adrenaline binding to adrenergic beta 1 (B-1) receptors
Increase heart rate and force of contraction
Effect of adrenaline binding to adrenergic beta-2 (B-2) receptors
Relaxation of smooth muscle (e.g. bronchodilation, vasodilation)
How is the action of beta blockers restricted to the heart?
Beta blockers only block B-1 receptors
Why do many local anaesthetics contain adrenaline?
Adrenaline is used as a vasoconstrictor (prolongs effect as adrenaline not transported elsewhere, and reduces bleeding)
Types of adrenergic receptors (bind to adenaline)
a-1, B-1, B-2
Types of cholinergic receptors (bind to ACh)
Muscarinic and nicotinic receptors
How are different types of cholinergic receptors distinguished?
By action of drugs e.g. muscarinic receptors are blocked by atropine.
Where are muscarinic receptors located?
post-ganglionic, neuro-effector junctions
Which drug blocks muscarinic receptors (prevents ACh binding)?
Atropine
Where are nicotinic receptors located?
ganglion synapse, neuromuscular junction
Which part of the ANS do blood vessels and glands in the periphery (e.g. skin, muscle) only receive signals from?
Blood vessels and glands in the periphery only receive sympathetic supply.
How is control of blood vessels and glands in the periphery received?
By varying amount of activity in the sympathetic neurons (parasympathetic neurons do not supply the periphery - single controls). increased activity leads to vasoconstriction, decreased activity leads to vasodilation.
Sympathetic and parasympathetic nerves have opposing effects except from which organs?
Genitalia
Example of the dual control of heart rate
Parasympathetic (vagus) nerve releases ACh at the SAN which decreases heart rate, while sympathetic nerve (accelerans) releases noradrenaline at SAN which increases the heart rate.
