Autonomic nervous system Flashcards
What is the nervous system broken down into?
- Central nervous system
- Peripheral nervous system
What is the central nervous system composed of?
- Brain
- Spinal cord
What is the peripheral nervous system broken down into?
- Autonomic nervous system
- Somatic nervous system
To what does the autonomic nervous system communicate?
- Internal organs
- Glands
To what does the somatic nervous system communicate?
- Sense organs
- Voluntary muscles
What is the autonomic nervous system broken down into?
- Sympathetic division
- Parasympathetic division
What is the function of the sympathetic division?
Arousing
What is the function of the parasympathetic division?
Calming
What is the somatic nervous system broken down into?
- Sensory (afferent) nervous system
- Motor (efferent) nervous system
What is the function of the sensory nervous system?
For sensory input
What is the function of the motor nervous system?
For motor output
Describe the communication link between afferent visceral/sensory input to CNS integration and effector function
Afferent visceral/sensory input is sent in to the CNS, to be processed then depending on the information (electrical conduction / chemical transmission) will be sent into the A.N.S or the S.N.S and then onto effector function.
What type of control is the A.N.S usually involved in?
Subconscious and involuntary
What type of control is the S.N.S usually involved in?
Conscious and voluntary
Give three examples of control areas of the A.N.S
- Mobility - cardiac and smooth muscle
- Secretory glands
- Metabolic - liver and adipose tissue
Give an examples of a control muscle of the S.N.S
Skeletal muscle
What is the function of the efferent division of the P.N.S
It is communication link by which the CNS controls muscles and glands, the effector organs that carry out intended effects or actions
How does CNS regulate the effectors?
By initiating action potentials in the cell bodies of efferent neurons whose axons terminate on these organs
What does the A.N.S regulate? ( x 4 systems)
- Cardiovascular
- Renal
- Gastrointestinal
- Thermoregulatory
Why is A.N.S regulation so important?
To enable the body to meet the continual and ever-changing stresses to which it is exposed.
What innervates cardiac, smooth muscle and glands?
Autonomic nerve fibres
What does the ANS play a role in regulating thanks to autonomic nerve fibres? (9)
(1) Blood pressure and flow,
(2) Gastrointestinal movements and secretions
(3) Body temperature,
(4) Bronchial dilation,
(5) Blood glucose levels,
(6) Metabolism,
(7) Micturition and defecation,
(8) Pupillary light and accommodation reflexes,
(9) Glandular secretions
What is a muscle or gland innervated by autonomic fibres is called?
An effector organ
What happens if the autonomic nerve fibres to an effector organ are cut?
The organ may continue to function, but will lack the capability of adjusting to changing conditions
What are the two functional parts of the ANS?
- Sympathetic nervous system
- Parasympathetic nervous system
When is the sympathetic system involved?
When there is an emergency or where there is stress involved - flight or fight
What is the parasympathetic system involved in (and allows us to do)?
In nonemergencies - allows us to unwind and conserve energy and to “rest and digest”
What are ANS inputs called?
Visceral afferents
What are ANS efferent pathways formed by?
A two neuron chain
What is the direction of impulse in the ANS efferent pathway?
CNS → Preganglionic fibre → autonomic ganglion → Preganglionic neurotransmitter → Postganglionic fibre → Postganglionic neurotransmitter → Effector organ
What do myelinated preganglionic fibres exit the spinal cord via?
Ventral roots
Which fibres are often unmyelinated (C-fibres)?
Postganglionic fibres
Give three points about the preganglionic neuron
- Cell body in brain / spinal cord (lateral horn)
- Axon is myelinated
- Synapses in ganglion
Give three points about the postganglionic neuron
- Cell body is autonomic ganglion
- Axon is unmyelinated
- Synapses on visceral effector
Autonomic nerves pathway
Spinal cord → Preganglionic neuron (myelinated) →Autonomic ganglion → Postganglionic neuron (unmyelinated) → Effectors
Where do sympathetic nerves arise from?
From the lateral horn of the thoracic & lumbar regions of the spinal cord
What size is the axon of preganglionic cell?
Short
Where is the 1st synapse of the sympathetic nervous system?
It’s near the spinal cord within sympathetic chain ganglia
What does the sympathetic system use at the 1st synapse in the ganglion?
Acetylcholine
What does the sympathetic system release at the 2nd synapse in the ganglion?
Noradrenaline
Why is adrenal medulla an exception?
As it’s directly innervated by the preganglionic sympathetic neurons
What is released at the adrenal gland?
Epinephrine released into blood
Where do parasympathethic nerves arise form?
From cranial (brain) & sacral (lower region of spinal cord)
What size (vague) are the axons of preganglionic neuron?
Very long
Where do parasympathetic nerves synapse?
Near their endpoint - muscles/glands
What does the parasympathetic system use at the 1st synapse in the ganglion
Acetylcholine
What does the 2nd synapse of the parasympathetic system release?
Acetylcholine
What is the difference between the preganglionic neuron of the parasympathetic and sympathetic systems?
Para - Soma is usually in the brain-stem or sacral spinal cord
Sym - Soma is usually in the spine
What is the difference between the postganglionic neuron of the parasympathetic and sympathetic systems?
Para - Soma is usually in a ganglion near the target organ
Sym - Soma is in a sympathetic ganglion, located next to spinal cord
What is the difference in the neurotransmitters release from postganglionic synapse in parasympathetic and sympatic systems?
Para - Acetylcholine or nitric oxide
Sym - Norepinephrine
What response is sent to target organ in the parasympathetic nervous system?
‘Rest and digest’
What response is sent to target organ in the sympathetic nervous system?
‘Fight or flight’
What is the neurotransmitter released from the preganglionic synapse is the parasympathetic and sympathetic nervous systems?
Acetylcholine
What is adrenal medulla?
A modified sympathetic ganglion
What is the adrenal gland apart of?
The endocrine system
What do the sympathetic pre-ganglionic fibres do?
They directly stimulate the adrenal medulla (neuroendocrine chromaffin cells)
What do chromaffin cells do in response to stimulation?
They synthesise adrenaline from tyrosine
What is the difference and similarity between adrenaline and noradrenaline?
Adrenaline gives rise to similar effects to noradrenaline except via the bloodstream
Why are chemical signals required?
To integrate a multitude of finally tuned responses
How many main neurotransmitters are there in the autonomic neurotransmitters?
2
What are the main neurotransmitters in the autonomic neurotransmitters?
- Acetylcholine
- Noradrenaline
What is the neurotransmitter affinity of a nicotinic receptor?
- ACh from autonomic preganglionic fibres
- ACh from motor neurons
What is the effectors with a nicotinic receptor?
- All autonomic postganglionic cell bodies; adrenal medulla
- Motor end plates of skeletal muscle fibres
What is the mechanism of action at the nicotinic receptor?
- Opens nonspecific cation receptor-channels
- Opens nonspecific cation receptor-channels
What is the effect on effector of the nicotinic receptor?
Excitatory
What is the effect on effector of the nicotinic receptor?
Excitatory
What is the neurotransmitter affinity of the muscarinic receptor?
ACh from parasympathetic postganglionic fibres
What is the neurotransmitter affinity of the alpha-2 muscarinic receptor?
Greater affinity for NE than for E
What is the neurotransmitter affinity of the beta-1 muscarinic receptor?
Equal affinity for NE and for E
What is the neurotransmitter affinity of the beta-2 muscarinic receptor?
Affinity for E only
What is the neurotransmitter affinity of the alpha-1 muscarinic receptor?
Greater affinity for NE (from sympathetic postganglionic fibres than for E (from the adrenal medulla)
What are the effector(s) with the alpha-1 muscarinic receptor?
Most sympathetic target tissues
What are the effector(s) with the muscarinic receptor?
Cardiac muscle, smooth muscle, glands
What are the effector(s) with the alpha-2 muscarinic receptor?
Digestive organs
What are the effector(s) with the beta-1 muscarinic receptor?
Heart
What are the effector(s) with the beta-2 muscarinic receptor?
Smooth muscles of arterioles and bronchioles
What is the mechanism of action at the muscarinic receptor?
Activates various G-protein-coupled receptor pathways depending on effector
What is the mechanism of action at the alpha-1 muscarinic receptor?
Activates IP3-Ca2+ second-messenger pathway
What is the mechanism of action at the alpha-2 muscarinic receptor?
Inhibits cAMP
What is the mechanism of action at the beta-1 muscarinic receptor?
Activates cAMP
What is the mechanism of action at the beta-2 muscarinic receptor?
Activates cAMP
What is the effect on effector of the muscarinic receptor?
Excitatory or inhibitory, depend on effector
What is the effect on effector of the alpha-1 muscarinic receptor?
Excitatory
What is the effect on effector of the alpha-2 muscarinic receptor?
Inhibitory
What is the effect on effector of the beta-1 muscarinic receptor?
Excitatory
What is the effect on effector of the beta-2 muscarinic receptor?
Inhibitory
What are the two classes of alpha-adrenergic receptors?
alpha-1 and alpha-2
What does alpha-1 adrenergic receptors activate?
The calcium second messenger
What is the effect of the calcium second messenger?
Excitatory
What is the calcium second messenger important for?
The peripheral vasoconstriction
What does the alpha-2 adrenergic receptor cause?
A blockade of cAMP second messenger
What is the effect of the alpha-2 adrenergic receptor?
Inhibitory
What is the effect of the blockade of cAMP second messenger?
Decreased digestive tract activity
What are the two classes of Beta-adrenergic receptors?
Beta-1 and Beta-2
Where does beta-1 adrenergic receptors principally act?
On the cardiac muscle
What is the effect on cardiac muscle of the beta-1 adrenergic receptor?
Increases rate and force of contraction (B-blockers)
What does beta-2 adrenergic receptor utilise?
cAMP second messenger system
What is the effect beta-2 adrenergic receptor usually?
Primarily inhibitory (salbutamol - agonist)
What is an example of the use of the beta-2 adrenergic receptor?
For bronchiolar dilation
What is the affinity of alpha-adrenergic receptors?
Binds NA with greater affinity than A
What is the affinity of beta-1 adrenergic receptors?
NA and A equal affinity
How many types of alpha-1 adrenergic receptors are there?
Three types (A,B,D)
What is the purpose of all of the alpha-1 adrenergic receptors?
- All increase PKC and Ca2+
- Increase smooth muscle contraction - arteriolae
How may types of alpha-2 adrenergic receptors are there?
Three - (A,B,C)
What is the purpose of all of the types of alpha-2 adrenergic receptors?
- Decrease cAMP and Ca2+
- Decrease secretory activity
What is always the response of alpha-2 adrenergic receptors?
Inhibitory
Where are alpha-2 adrenergic receptors present?
GI tract - endocrine and exocrine glands
How many types of beta adrenergic receptors are there?
Two types - 1 & 2
What is the function of the beta-1 adrenergic receptor?
- Increase Ca2+
- Increase heart rate and force
What is the function of the beta-2 adrenergic receptor?
- Decrease Ca2+
- Smooth muscle relaxation e.g. bronchiolar dilation
What does the binding of nicotinic cause?
It stimulates inward cation flow in postganglionic cell (ionotropic)
Where is muscarinic present?
On effector cell membranes
What is muscarinic innervated by?
By the parasympathetic branch
What are muscarinic receptors bound to?
G proteins
What system is linked in muscarinic receptors?
Second messenger system is linked
How many classes of muscarinic receptors are there?
Five - M1 to M5
Give two samples of the effects of muscarinic receptors
- Relaxation of cardiac muscle
- Contraction of smooth muscle
What are most organs activated by?
Both sympathetic and parasympathetic systems
What do sympathetic and parasympathetic system usually cause in the organ?
Cause opposite effects on the same organ
What does dual innervation by both branches of the autonomic nervous system allow?
Allows more precise control over the organ and to keep it running smoothly, enabling homeostasis
What needs to be increased as a parameter requirement in an emergency situation?
- Heart rate
- Heart contractility
- Blood pressure
- Oxygen delivery
- Vision
In an emergency situation what are the sympathetic effects?
- Increase in SA node firing frequency
- Increase calcium entry
- Peripheral vasoconstriction
- Maximal airway opening
- Dilation of pupil - long-sight
What is the effect of atropine?
Selective antagonist of ACh at muscarinic receptors
What is the indication of atropine?
Suppression of salivary and bronchial secretion during surgery
What is the effect of salbutamol?
Selective activation of the β2 adrenergic receptor
What is the indication of salbutamol?
Bronchiolar dilatation in asthma
What is the origin of the sympathetic nervous system?
Thoracic / lumbar
What is the origin of the parasympathetic nervous system?
Craniosacral
What is the structure of the sympathetic nervous system?
- Short pre-ganglionic
- Long post-ganglionic
What is the structure of the parasympathetic nervous system?
- Long pre-ganglionic
- Short post-ganglionic
What is the ganglia location of the sympathetic nervous system?
- Paravertebral
- Collateral
What is the ganglia location of the parasympathetic nervous system?
Terminal (at or very near organ)
Why are resistance vessels (arteriolae) exceptions to dual innervation effect rule?
As they receive only direct sympathetic input
What is an exception to the above exception and why?
Penis and clitoris as they receive input from both systems
Why are sweat glands exceptions to dual innervation effect rule?
As they receive sympathetic cholinergic input
Why is the salivary gland an exception to dual innervation effect rule?
As secretion is increased by both sympathetic and parasympathetic (qualitative differences in resultant saliva due to balance of inputs)
What are the effectors of the somatic nervous system?
Skeletal muscle
What are the effectors of the autonomic nervous system?
Cardiac and smooth muscle
What are the neuron characteristics of the somatic nervous system?
Thick, heavily myelinated conduct impulses rapidly
What are the neuron characteristics of the autonomic nervous system?
- Preganglionic = thin, lightly myelinated
- Postganglionic = even thinner, no myelin
What are the efferent pathways of the somatic nervous system?
Motor neuron cell bodies in CNS: axons extend in spinal or cranial nerves
What are the efferent pathways of the autonomic nervous system?
- Preganglionic in brain or spinal cord
- Postganglionic cell body outside CNS, axon extends to effector
What are the neurotransmitters of the somatic nervous system?
Acetylcholine (ACh)
What are the neurotransmitters of the autonomic nervous system?
- Norepinephrine (NE)
- Acetylcholine (ACh)
What are the effects of the somatic nervous system?
Stimulatory
What are the effects of the autonomic nervous system?
Stimulatory or Inhibitory
