Autonomic Physiology Flashcards
The autonomic nervous system exists to
control the things we don’t want to think about.
the somatic nervous system sends signals
directly to skeletal muscle
the autonomic nervous system sends signals
from pre ganglionic fibre (small myelinated) to ganglion to post ganglionic fibre (unmylinated) and finally to smooth muscle, glands, cardiac muscle, GI neurons
ganglion =
nerve cell cluster, typically linked by synapses, located in autonomic nervous system
the somatic nervous system has
- specialised neuromuscular junction
- ionotropic receptors
- always excites target
the autonomic nervous system has
- less specialised junction
- metabotropic receptors
- may excite or inhibit target
sympathetic response causes
flight or fight response
- dilated pupils to see into distance
- increased heart rate
- shallow rapid breathing
- release of catecholeamines which includes adrenaline and noradrenaline
- tense muscles
parasympathetic response causes
rest and digest response
- slows heart rate
- conserves energy
- increases intestinal and gland activity
- relaxes sphincter muscles in GI tract
Sympathetic nervous system exists from
spinal cord in thoracic (T1 - T12) and lumbar (L1 - L2) regions.
short pre-ganglionic chain and then long post-ganglionic chain to target
Ganglia lie close to spinal cord in the sympathetic trunk (paravertebral ganglia), or in collateral ganglia (prevertebral ganglia = celiac, mesenteric
Sympathetic nervous system exists from
spinal cord in thoracic (T1 - T12) and lumbar (L1 - L2) regions.
short pre-ganglionic chain and then long post-ganglionic chain to target
in the sympathetic nervous system,
Ganglia lie close to
spinal cord in the sympathetic trunk (paravertebral ganglia), or in collateral (prevertebral ganglia = celiac, mesenteric) ganglia
in sympathetic nervous system what is the difference between grey and white ramus
White ramus (preganglionic fibre) vs Grey ramus (postganglionic fibres)
Convergence and divergence lead to “mass activation”
Parasympathetic targets =
cranio-sacral. Cranial outflow to head & neck (mainly, look at that vagus go!), sacral to bladder and genitals
Long preganglionic fibre, short postganglionic fibre. Ganglion is in, or close to, target.
sympathetic targets =
= thoraco-lumbar.
Ganglia close to spinal cord in sympathetic trunk (aka para-vetebral ganglia). Note this extends further than outflow into these cervical ganglia.
Usually preganglionic fibre enters
sympathetic trunk, makes synapse there, and then along postganglionic fibre.
But some go straight through and make synapse in prevertebral(= collateral) ganglia, ie celiac & mesenteric ganglia, then postganglionic fibre carries on.
Odd ones go to adrenal gland and have no postganglionic fibre. They do have cell body there and that releases the transmitter, as a hormone, into to the blood.
Parasympathetic targets =
cranio-sacral. Cranial outflow to head & neck (mainly, look at that vagus go!), sacral to bladder and genitals
Long preganglionic fibre, short postganglionic fibre. Ganglion is in, or close to, target.
Autonomic neurotransmitters
Acetylcholine
- Acts on cholinergic receptors
- Nicotinic receptors
- Muscarinic receptors
Noradrenaline (& adrenaline)
- Acts on adrenergic receptors
- alpha receptors
- beta receptors
what are the big differences in autonomic nervous system and somatic nervous system
anatomy
neurotransmitters used
Sympathetic nervous system
Preganglionic fibres release acetylcholine
- acts on nicotinic cholinergic receptors*
Postganglionic fibres release noradrenaline
- acts on alpha or beta adrenergic receptors
These are different from those at the neuromuscular junction
sympathetic nervous system,
Postganglionic cells of adrenal medulla
have no axons, but release adrenaline & noradrenaline (approx 80%/20%) into the blood
Parasympathetic nervous system exits from
spinal cord in cranial (3, 7, 9, 10) & sacral (S2-4) regions
Long preganglionic fibre, short postganglionic fibre. Ganglion is in, or close to, target.
In Parasympathetic nervous system, ganglia lie
close to, or within, the target
Parasympathetic nervous system neurotransmitters
Preganglionic fibres release acetylcholine
- acts on nicotinic cholinergic receptors
Postganglionic fibres release acetylcholine
- acts on muscarinic cholinergic receptors
Some postganglionic fibres release non-adrenergic non-cholinergic (NANC) transmitters
eg peptides or Nitric Oxide
Sympathetic cholinergic fibres can also
innervate sweat glands
differences in sympathetic and parasympathetic nervous system
- outflow from CNS
- Location of ganglia
- transmitters and receptors used
Sympathetic main points
- Thoraco-lumbar
- Ganglia usually close to spinal cord (except collateral ganglia)
- Pre-ganglionic cells release ACh
- Acts on nicotinic receptors - Post-ganglionic cells usually release noradrenaline (norepinephrine)
- Acts on alpha or beta receptors - Hormonal component (adrenaline (epinephrine) from adrenal medula)
- Produces co-ordinated effects
- Fight-or-flight response
Parasympathetic main points
- Cranio-sacral
- Ganglia close to, or within, the target tissue
- Pre-ganglionic cells release ACh
- Acts on nicotinic receptors - Post-ganglionic cells usually release ACh
- Acts on muscarinic receptors - No hormonal component
- Produces independent effects
- Rest-and-digest response
Sympathetic Homer
- airways dilate
- heart beats faster and stronger
- blood diverts to muscle and gut motility decreases
- enzyme secretion in gut generally inhibited
- stored energy is released
- pupils dilate and eye focus far way
- hair stands on end
- mouth gets dry
Parasympathetic Homer
- airways constrict
- heart beats slower and weaker
- blood diverts to gut and gut motility increases
- enzyme secretion in gut generally stimulated
- energy is stored
- pupils constrict and eyes focus close up
- hair lies flat
- mouth starts drooling
difference in parasympathetic and sympathetic nervous system depends on
the neurotransmitter released and what receptor it acts on.
Noradrenaline (and adrenaline) act on alpha and beta receptors.
acetylcholine acts on nicotinic and muscarinic receptors
when radial muscle contracts
pupils dilate
when circular sphincter muscle contracts
pupil constricts
when the ciliary muscle relaxes
eye focuses far away
when ciliary muscle contracts
eye focuses close up
The eye:
Sympathetic system
Activates beta 2 receptors on ciliary muscle round lens
- Ciliary muscle relaxes & eye focuses far away
Activates alpha 1 receptors on radial muscle of iris
- Radial muscle contracts & makes pupil larger
The eye:
Parasympathetic system
Activates muscarinic receptors on ciliary muscle
- Ciliary muscle contracts & eye focuses close up
Activates muscarinic receptors on sphincter muscle
- Contracts sphincter muscle & makes pupil smaller
The heart:
Sympathetic system
Activates beta 1 receptors on pacemaker cells
- Increases heart rate
Activates (mainly) beta 1 receptors on myocytes
- Increases strength of contraction
The heart:
Parasympathetic system
Activates muscarinic receptors on pacemaker cells
- Decreases heart rate
Little effect on myocytes
- Little effect on strength of contraction
The lungs:
Sympathetic system
Activates beta 2 receptors on smooth muscle of airways
- Makes smooth muscle relax & dilates airways
The lungs:
Parasympathetic system
Activates muscarinic receptors
- Makes smooth muscle contract & constricts airways
The lungs:
Therapeutically useful
beta 2 agonist (eg salbutamol)
- dilates airways, but does not affect the heart
beta 1 antagonist (eg atenolol)
- decreases heart rate, but does not affect airways
Blood vessels:
Sympathetic system
Activates alpha 1 receptors on smooth muscle of vessels
- Makes smooth muscle contract & blood flow
decreases
Activates beta 2 receptors on smooth muscle of vessels
- Makes smooth muscle relax & blood flow increases
Blood vessels:
Parasympathetic system
usually no effect
The gut:
Sympathetic system
Activates alpha or beta receptors on smooth muscle of gut
- Decreases gut motility
Activates alpha receptors in pancreas
- Inhibits secretion of enzymes
The gut:
Parasympathetic system
Activates muscarinic receptors on smooth muscle of gut
- Increases gut motility
Activates muscarinic receptors in pancreas
- Increases secretion
Energy stores:
Sympathetic system
Activates alpha or beta receptors on liver cells (hepatocytes)
- Stimulates glycogenolyis & gluconeogenesis
Activates alpha or beta receptors on fat cells (lipocytes)
- Increases lipolysis
Energy stores:
Parasympathetic system
no effect
Salivary glands:
Sympathetic system
Activates beta receptors
- Stimulates thick secretion rich in enzymes
Salivary glands:
Parasympathetic system
Activates muscarinic receptors
- Stimulates profuse watery secretion
An example of antagonistic actions
the eye and its relationship with parasympathetic and sympathetic system
An example of dual innervation with non-antagonistic actions
Salivary glands and its relationship with parasympathetic and sympathetic system
Example of single innervation
Energy stores and its relationship with sympathetic system
An example of dual innervation with non-antagonistic actions
Salivary glands and its relationship with parasympathetic and sympathetic system
The bladder:
Sympathetic system
Activates beta 2 receps on smooth muscle of bladder wall
- Relaxes smooth muscle and reduces pressure
Activates alpha 1 receptors on smooth muscle of sphincter
- Contracts smooth muscle and stops urination
The bladder:
Parasympathetic system
Activates muscarinic receptors on bladder wall
- Contracts smooth muscle and increases pressure
Activates muscarinic receptors on sphincter
- Relaxes smooth muscle and causes urination
The bladder:
Parasympathetic system
Activates muscarinic receptors on bladder wall
- Contracts smooth muscle and increases pressure
Activates muscarinic receptors on sphincter
- Relaxes smooth muscle and causes urination
Reproductive tract:
Sympathetic system
Activates alpha 1 receptors on smooth muscle of urethra
- Contracts smooth muscle and causes ejaculation
Reproductive tract:
Parasympathetic system
Activates muscarinic receptors on smooth muscle of corpus cavernosum
- Relaxes smooth muscle & causes erection
An example dual innervation with complementary effects
Reproductive tract and its relationship with parasympathetic and sympathetic system
What controls this autonomic nervous system
Autonomic reflexes
- eg baroreceptor reflex - baroreceptors detect blood pressure
Plus central control
- from the hypothalamus
- co-ordinates autonomic, somatic and endocrine
activity,
- eg defence response
Complications in autonomic nervous system
Some neurones release non-adrenergic non-cholinergic (NANC) transmitters
- eg nitric oxide (NO), ATP, VIP
Neurones may co-release transmitters
- eg ACh plus a peptide
Some autonomic neurones are odd
- eg sympathetic post-ganglionic fibres innervating
sweat glands release ACh
dual innervation effects may be
antagonistic or complimentary.
many tissues have this
single intnervation is controlled by
varying tone.
some tissues have this
sympathetic is always
noradrenaline or adrenaline acting on alpha or beta receptors
parasympathetic is always
acetylcholine acting on muscarinic receptors
