N26- Autonomic nervous system Flashcards
what can the entire nervous system be divided into?
- CNS
- PNS
what are the 2 components of the autonomic nervous system?
- central
- peripheral
what are the divisions of the autonomic nervous system?
- enteric
- sympathetic divison
- parasympathetic divison
what is the overall functions of the ANS?
The motor autonomic nervous system (ANS) mediates output from the CNS to the whole of the body, with the exception of skeletal (voluntary) muscle
what is output of the ANS modulated by?
external and internal sensory input, often via reflexes involving negative feedback loops within PNS and the CNS
what does the ANS regulate?
functions essential to human health and life that do not require conscious effort (e.g. whilst asleep) and that are largely involuntary
Name some of these function that do not require conscious effort.
- contraction and relaxation of vascular and visceral smooth muscle
- the heartbeat (including rate and force)
- all exocrine and certain endocrine secretions
- aspects of metabolism (particularly in liver and skeletal muscle)
- modulation of the processes of the immune system
- is subdivided anatomically into sympathetic and parasympathetic divisions (and, debatably, the enteric nervous system also)
What is an example of a function with a degree of conscious influence?
training allows a degree of conscious influence over the execution of some ANS reflexes i.e urination
what is the motor (efferent) component comprised of?
two neurone in series: preganglionic and postganglionic fibres
where is the autonomic ganglionic located?
outside CNS
what happens between the preganglionic neurone and the autonomic ganglion?
chemical synaptic transmission in the ganglia
what happens between the postganglionic neurone and the effector cells?
Chemical transmission at the neuroeffector junction
how do the sympathetic and parasympathetic divisions of the ANS work ?
simultaneously in a reciprocal and complementary manner maintaining homeostasis
what is the role of the sympathetic ANS?
orchestrates the stress response and energy consumption associated with ‘fight or flight’ reactions, but also has very important ongoing activity
what is the role of the parasympathetic ANS?
regulates many functions, some of which are restorative and energy conserving ‘rest and digest’
what is the transmitter of the preganglionic neurones in sympathetic and parasympathetic system?
acetylcholine
what does the acytelcholine act via?
excitatory nicotinic cholinoceptors
what is the classical transmitter of the postganglionic neurone in the sympathetic system?
noradrenaline
what is the classical transmitter of the postganglionic neurone in the parasympathetic system?
acetylcholine
what is the outflow of the sympathetic division?
thoracolumbar outflow from spinal cord (T1-L2/3)
what is the outflow of the parasympathetic division?
craniosacral outflow from brainstem and spinal cord
what receptors are in the effecter cells of the sympathetic division?
adrenoreceptors
what receptors are in the effecter cells of the parasympathetic division?
cholinoceptors
where do the sympathetic preganglionic neurones synapses with postganglionic neurone? (2)
-paravertrebal ganglia (close to spinal cord)
OR
-prevertebral ganglia ( distance from spinal cord)
what is the length of axons fibres in sympathetic system from preganglionic to postganglionic neurones?
typically short
what is the length of axons fibres in sympathetic system from postganglionic neurones to effector cells in organs distant to the sympathetic ganglia?
generally long
where do sympathetic preganglionic fibres branch to?
to synapse with many postganglionic neurones located in one, or several, pre- or para-vertebral ganglia
where do parasympathetic preganglionic neurones synapse with postganglionic neurones?
terminal ganglia -distant to the CNS and often located in the walls of the target organ
what is the length of parasympathetic postganglionic neurones ?
short
which of the neurones are myelinated?
both sympathetic and parasympathetic preganglionic
what appearance are the myelinated preganglionic fibres?
white
which of the neurones are unmyelinated?
postganglionic fibres
what appearance are the unmyelinated postganglioic fibres?
grey and termed motor C-fibres
what regulates sympathetic outflow?
higher centres in the brainstem
what gland innervation does not follow the rule and why?
- adrenal gland
- innervation is pre ganglionic and the transmitter is ACh and not NA
what does the adrenal gland release as hormones?
adrenaline and NA
what cranial nerves have a parasympathetic outflow?
CN III, VII, IX and X
where is parasympathetic usually?
in the target organs (discrete ganglia in head and neck and some plexuses in the pelvis)
Describe the chemical transmission in the sympathetic division.
- action potential originates in the CNS
- travels to the presynaptic terminal of the preganglionic neurone triggering Ca2+ entry through voltage-gated, calcium selective, ion channels and the release of ACh by exocytosis
- ACh binds to and opens ligand-gated ion channels (nicotinic ACh receptors) in the postganglionic neurone, causing depolarization and the initiation of action potentials that propagate to the presynaptic terminal of the neurone, triggering Ca2+ entry and the release, usually, of noradrenaline
- noradrenaline activates G-protein-coupled adrenoceptors in the effector cell membrane to cause a cellular response via ion channels/enzymes
Describe the chemical transmission in the parasympathetic division.
- The process is very similar to that described for the sympathetic division, with the important exceptions that
- ACh is always the classical transmitter used by postganglionic neurones
- ACh activates G-protein- coupled muscarinic acetylcholine receptors in the effector cell membrane to cause a cellular response via ion channels/ enzymes
what is it when a transmitter is neither NA, nor ACh?
non-adrenergic, non-cholinergic (NANC) transmission
what are the common NANC substances?
- Adenosine triphosphate (ATP) and neuropeptide Y (NPY) from sympathetic fibres
- nitric oxide (NO) and vasoactive intestinal peptide (VIP) from parasympathetic
what transmitters produce a rapid response?
Sympathetic - ATP
Parasympathetic - ACh
what transmitters produce an intermediate response?
sympathetic- NA
parasympathetic - NO
what transmitter produce a slow response?
sympathetic - NPY
parasympathetic - VIP
Describe electrical stimulation of postganglionic sympathetic fibre to vessel (tension of vascular smooth muscle/time).
- ATP produces a fast contraction of the smooth muscle
- Noradrenaline produces a moderately fast response
- Neuropeptide Y produces a slow response
Describe electrical stimulation of postganglionic parasympathetic fibre to vessel (tension of vascular smooth muscle/time).
- Acetylcholine and nitric oxide produce a rapid relaxation
2. Vasoactive intestinal peptide can produce a slow, delayed response
what is ACh an endogenous agonist of?
cholinoceptors that are nicotinic, or muscarinic
what are nicotinic Ash receptors of the ganglia?
- Ligand-gated ion channels (LGICs), selectively activated by the plant alkaloid, nicotine
- Structurally and pharmacologically distinct from nicotinic receptors at the skeletal neuromuscular junction, or in the CNS
what are muscarinic ACh receptors of the effector cells?
- G-protein-coupled receptors (GPCRs), selectively activated by the plant alkaloid, muscarine
- Structurally and pharmacologically defined as five subtypes: M1, M2, M3, M4 and M5 that are differentially expressed across tissues/organs, M1-3 being most important in the ANS
what are NA and adrenaline (A) endogenous agonists of?
family of adrenoreceptors that are all GPCRs
how are these adrenorecptors classified?
originally on the basis of the rank order of potency of agonists, as α-, or β-adrenoceptors
what are subclasses of adrenoreceptors , with differing tissue locations characterised ?
characterised structurally and pharmacologically as α1, α2, β1, β2 and β3, all of which are selectively targeted by current therapeutic agents
what affect does stimulation of S and P have on the heart?
S-Increases heart rate (β1)
Increases force of contraction in atria and ventricles (β1)
P-Decreases heart rate (M2) and force (M2) in atria
what affect does stimulation of S and P have on the lungs?
S-Relaxes bronchi (β2)
Decreases mucus production (β2) (decreases airway resistance)
P-Constricts bronchi (M3)
Stimulates mucus production (M3) (increase airway resistance)
what affect does stimulation of S and P have on the intestines?
S-Reduces intestinal motility (α1, α2, β2) Constricts sphincters (α1, α2, β2) P-Increases intestinal motility and secretions (M3) Relaxes sphincters (NO, M3)
what affect does stimulation of S and P have on vasculature ?
S-Constricts vasculature in most locations (α1), but relaxes in skeletal muscle (β2)
P-Largely no effect, but relaxes vasculature in a few locations (e.g. penis, salivary glands, pancreas (NO, M3)
what affect does stimulation of S and P have on the adrenal gland?
S-Release of adrenaline from adrenal medulla (nicotinic AChR)
P-No effect
what affect does stimulation of S and P have on the bladder?
S-Relaxes wall (detrusor) of bladder (β2/β3), constricts internal urethral sphincter (α1)
P-Contracts wall of bladder (M3), relaxes internal urethral sphincter (NO)
what affect does stimulation of S and P have on the penis?
S- ejaculation (α1)
P- erection (NO, M3)