Lecture 5: Autonomic System Flashcards
E.g homeostasis
Heart
Sympathetic: increase rate and strength of contractions, inhibits effect of parasympathetic system to allow blood vessels to dilate
Parasympathetic: decrease rate and strength of contractions, constricts coronary vessels in accordance with decreased demand
E.g of homeostasis
Eye
Parasympathetic: constrict pupil, contract ciliary muscles to allow lens to thicken for near vision
Sympathetic: dilate pupil
E.g homeostasis
Genital organs
Sympathetic: ejaculation and constriction causing remission of erection
Parasympathetic: produces engorgement of erectile tissue
Autonomic nerves
All sympathetic and parasympathetic nerves contain BOTH general visceral sensory and general visceral motor fibres
General visceral sensory (afferent)
Usually parasympathetic
Visceral reflexes (gag reflex)
Organic sensation
Pain only accompany sympathetic nerves e.g heart attack
Sympathetic comes from what region?
Thoracolumbar region
Parasympathetic comes from what region?
Craniosacral region
Sympathetic ganglia are located where?
Close to spinal cord in a chain
Parasympathetic ganglia are located where?
Close to target organ
Sympathetic post ganglionic fibres are what length in general?
Long
Parasympathetic post ganglionic fibres are what length in general?
Short
Sympathetic branching?
Lots of branching so that more than one organ can be targeted at once
Parasympathetic branching?
Not much branching
Sympathetic nerve system pre-synaptic fibres are located where?
in lateral horn of grey matter of T1-L2.
Para vertebral ganglia of sympathetic system are located where?
sympathetic trunk
Prevertebral ganglia sympathetic nerve system are located where?
plexuses on abdominal aorta.
Sympathetic activity
- Dilates pupil.
- Reduces secretions from lacrimal and salivary glands.
- Increased viscosity of saliva.
- Increases heart rate and CO.
- Relaxes bronchial muscles.
- Dilates or constricts skeletal muscle.
- Constricts arteries to skin and viscera.
- Reduced gut motility and secretions.
- Sphincters contract.
- Relaxes gallbladder.
- Increases secretion from sweat glands
Interomediolateral cell column
Interomediolateral cell column contains pre-ganglionic sympathetic neurons for the entire body.
Lies between segments T1-L2 (“thoracolumbar outflow”).
Courses of sympathetic motor fibres
Axons leave spinal cord through anterior (motor) root.
• Enter anterior rami of spinal nerves (T1-L2).
• Enter into WHITE rami communicantes and pass into sympathetic trunk.
4 pathways:
1. Ascend and then synapse
2. Synapse at same level
3. Descend and then synapse
4. Pass through and continue on through abdomino-pelvic
splanchnic nerve.
Synapse in paravertebral or prevertebral ganglia.
• Exit via GREY rami communicantes.
• Enter all branches of all 31 pairs of spinal nerves
(to reach all blood vessels, sweat glands etc).
Pathways of sympathetic neurons: C1-C8 levels
Cell body of pre-synaptic sympathetic neuron in interomediolateral cell column of T1-L2 spinal cord.
Pre-synaptic sympathetic neurons ASCEND to cervical level and
synapse in one of three cervical ganglia.
Post-synaptic neuron leaves sympathetic trunk and enters grey
rami communicante before entering anterior and posterior
rami of spinal nerves.
Note: no white rami in cervical region
Pathways of sympathetic neurons: T1-L2 levels
Cell body of pre-ganglionic sympathetic neuron in interomediolateral cell column of T1-L2.
Myelinated axon leaves spinal cord via anterior (motor) root and enters white rami communicante.
Synapses in sympathetic trunk (splanchnic nerves synapse in prevertebral ganglia instead)
Post-ganglionic unmyelinated neuron leaves via grey rami communicante and enters anterior and posterior rami of spinal nerves.
Note: both white and grey rami communicante in thoracic region
Pathways of sympathetic neurons: L3-Co levels
Cell body of pre-ganglionic sympathetic neuron in interomediolateral cell column of T1-L2.
Myelinated pre-synaptic sympathetic neuron axon descends in sympathetic trunk and synapses with post-ganglionic neuron in the ganglia of the trunk.
Post-ganglionic unmyelinated neuron leaves the sympathetic trunk via grey rami communicante and enters anterior and
posterior rami of spinal nerves.
Note: no white ramicommunicante in lumbar or sacral region
Sympathetic fibres always leave through grey rami, why?
Post-synaptic sympathetic neurons pass out of sympathetic chain via the grey rami communicantes.
This way they can reach virtually all areas of the body to innervate
blood vessels, sweat glands and visceral structures.
Splanchnic nerves
Convey visceral motor and visceral sensory fibres from autonomic system to and from viscera of the body cavities (pericardial, pleural and peritoneal)
Splanchnic nerves for peritoneal, plural and pericardial cavities
- Thoracic (pericardial + pleural) cavity = cadiopulmonary splanchnic => cardiac, pulmonary and oesophageal plexuses.
- Peritoneal cavity = abdominopelvic splanchnic (greater, lesser, least & lumbar splanchnics).
Abdominopelvic splanchnic nerves from peritoneal cavity
• All pre-synaptic sympathetic fibres of abdominopelvic splanchnic nerves (except those going to adrenal gland) synapse in prevertebral ganglia.
Abdominopelvic splanchnic nerves
ARE ALL SYMPATHETIC
• Myelinated pre-ganglionic fibres passing through the sympathetic trunk without synapsing.
- Greater splanchnic nerve: T5-T9
- Lesser splanchnic nerve: T10-T11
- Least (lower) splanchnic nerve: T12
Pelvic splanchnic
not related to the sympathetic trunk and carry parasympathetic fibres! s2 s3 s4
Paravertebral and prevertebral ganglia
Paravertebral ganglia: adjacent to vertebral column
Prevertebral ganglia: on anterior surface of abdominal aorta
surrounding branches of major blood vessels.
Sympathetic division summary
Pre-ganglionic neurons: short, myelinated, cell bodies in lateral horns of gray matter in spinal cord from T1-L2 (Thoraco-lumbar outflow).
• Ganglionic neurons: Sympathetic chain or collateral ganglia on abdominal aorta.
• Post-ganglionic neurons: long, exit sympathetic trunk in gray rami
spinal nerve
effector
organs.
Parasympathetic divison
- “Rest and digest”
- Pre-ganglionic neurons: brain stem and S2, S3, S4 (cranio-sacral outflow).
- Pre-ganglionic fibres are long, myelinated, travel through cranial nerves III, VII, IX and X plus spinal nerves S2-S4. (3,7,9,10)
- Synapse with short post-ganglionic fibres that are very close to, or directly on, effector organs.
- Restricted distribution: head, viscera of trunk, erectile tissues of genitalia.
• Not part of spinal nerves (except anterior rami
S2-S4).
Parasympathetic outflow
• CN III – Oculomotor nerves
• => pupil constriction, lenses bulge.
• CN VII – Facial nerves
• => increased secretions from nasal, lacrimal and
salivary glands.
• CN IX – Glossopharyngeal nerves
• => increased secretion from parotid salivary
glands.
• CN X – Vagus nerves
• => slows HR, contracts bronchioles, dilates
visceral arteries, increases gut motility and
secretions.
Vagus nerve/ pelvic splanchnic
Vagus nerve provides all parasympathetic stimulation to viscera of thorax and abdomen up to left colic (splenic) flexure.
Pelvic splanchnic nerves provide PS to distal GIT and
repro organs.
Visceral afferent fibres of pain are carries how?
- Most visceral reflex sensation and some pain travel in visceral afferent fibres travelling with parasympathetic fibres back to brain.
- Most visceral pain impulses (from heart & most organs of peritoneal cavity) travel centrally along visceral afferent fibres accompanying sympathetic fibres.
What is referred pain?
• Feeling of pain at a location other than the site of origin of the stimulus but in an area supplied by same or adjacent segments of spinal cord.
Referred abdominal pain
Pain from abdominal viscera follow sympathetic splanchnic nerves back to spinal cord (T5-L2).
• Sensory fibres synapse in dorsal root ganglia.
Pain and somatic sensory afferents( sensory of skeletal muscle) synapse in same location = confuses brain!
Angina pectoris
- Painful impulses from myocardium (caused by ischaemia) projected via GVA to dorsal horn of T1-T4.
- Dorsal horn of T1-T4 also receives cutaneous sensory info from corresponding dermatomes.
•Painful impulses projected to brain via spinothalamic
tract and misperceived as coming from nociceptors in dermatomes (T1-T4).
Carotid sinus
• To maintain homeostasis, the ANS must receive sensory
information from the body (via visceral AFFERENT fibres).
The carotid artery in the neck, for example, has receptors (called
baroreceptors,in the carotid sinus) that sense blood pressure.
These receptors send high blood pressure signals via the vagus nerve to the nucleus of the solitary tract (NST).
The NST projects to the nucleus ambiguus and vagal nucleus, which release acetylcholine as part of the parasympathetic system to slow down the heart.
Hypothalamus
- Controls all autonomic functions of body.
- Anterior hypothalamus => excitatory effect on parasympathetic nervous system.
- Posterior hypothalamus => excitatory effect on sympathetic nervous system
- Hypothalamospinal tract => conveys descending autonomic fibres that influence sympathetic Neurons in IML cell column and preganglionic neurons of sacral parasympathetic nucleus.
- Lesion above T1 : Horner Syndrome.
Horner’s syndrome
• Due to lesion in pathway of sympathetic fibres travelling to
the head.
• Clinical signs:
• Ptosis: drooping of upper eyelid due to paralysis of superior tarsal smooth muscle.
• Miosis: pupillary constriction due to paralysis of pupillary
dilator smooth muscle.
• Anhidrosis: Loss of sweating due to loss of sweat gland
innervation by sympathetic fibres.
• Flushed, warm dry skin: vasodilation of subcutaneous
arteries due to lack of vascular tone and sweat gland innervation.
