Autonomic NS Flashcards
3 divisions of the autonomic ns?
Sympathetic
Parasympathetic
Enteric
Where are the somatic afferents?
Towards the CNS
Dorsal horn
Dorsal root
Synapse with CNS cell bodies
Where are the somatic efferents?
Away from the CNS
Cell bodies- Ventral horn
Axons - Ventral root
Where is the lateral horn present?
Thoracic and lumbar regions
Anterolateral horn is present in sacral segments
What do the lateral horns contain?
Pre-ganglionic sympathetic neuronal cell bodies
What cell bodies are found in the anterolateral horn of a sacral segments?
Pre-ganglionic cell bodies of pelvic splanchnic nerves (parasympathetic)
Characteristics of the autonomic ns:
- involuntary control
- maintains homeostasis
- works continuously
- sympathetic, parasympathetic and enteric divisions
Structure of nerve pathway in autonomic ns?
- Pre-ganglionic fibre
Myelinated
Primary nt is ACh - Ganglion in PNS
Synapse - Post-ganglionic fibre
Unmyelinated
Target tissue or organ
Primary nt ACh or NA
Cholinergic fibres?
ACh nt
Adrenergic fibres?
Catecholamine NT (secreted from adrenal medulla)
Adrenaline/ noradrenaline
How do general visceral afferent fibres send sensory into back to the CNS?
Via the dorsal root and horn
visceral/ autonomic afferent fibres travel in the same way as somatic afferent fibres? True/ false
True
Where are autonomic neuronal cell bodies located
In specific sensory nerve ganglia of
1. Cranial nerves (brain stem) and Sacral spinal cord (parasympathetic)
2. Anterolateral horn of thoracic lumbar regions (sympathetic)
What are dermatomes?
Maps out the region of skin innervated by a particular spinal nerve
Overlap between cutaneous innervation and spinal segments
Difference btw somatic and autonomic efferent fibres ?
Somatic efferent: single neurone which synapses with skeletal muscle
General visceral (autonomic) efferent: two neurone pathways
-Pre-ganglionic fibres synapse with ganglia
-Post-ganglionic fibres synapse smooth and cardiac muscle/ gland cells
Myotomes?
Efferent fibres from spinal nerves supply innervation to skeletal muscles within specific compartments
(Myotomes are the similar to dermatomes)
Most skeletal muscles are innervated by nerves derived from several spinal cord levels
Difference btw myotome and dermatomes?
Myotome: group of muscles innervated by motor fibre from a specific nerve root
Dermatome: area of the skin innervated by sensory fibres that stem from specific nerve root
Role of sympathetic ns?
Fight or flight response
Areas of autonomic innervation of the sympathetic ns:
- head
- neck
- thorax
- abdomen
- pelvis
- blood vessels
Where are the pre-ganglionic cell bodies of sympathetic ns located?
In lateral horn btw T1-L2
Where are sympathetic ganglion found?
In sympathetic chain or near target organ
Length of pre ganglionic and post ganglionic neurones in Sympathetic ns?
Pre: short
Post: long
What are the exceptions of the sympathetic ns?
- Direct innervation from sympathetic pre ganglionic neurones to the adrenal medulla (chromaffin cells) for adrenaline production (no post ganglionic neurone)
- ACh secreted by post ganglionic sudomotor motor neurones (innervating sweat glands and are tortilla muscles of skin)
Key sympathetic ganglia?
Sympathetic chain
Pre aortic/ prevertebral
Difference btw autonomic and somatic ns?
Autonomic: has two neurones thats synapse at ganglion
Somatic: direct neurone to target
Difference btw paravertebral (sympathetic chain) ganglia and prevertebral (pre aortic) ganglia?
Para: sympathetic chain on each side of vertebral column
Pre: ganglia closer to target organs. On aorta.
3 types of cervical ganglia and whether SNS or PNS
SNS:
- Superior cervical ganglia
- Middle cervical ganglia
- Inferior cervical ganglia
Where are the cervical Ganglia?
On either side of the neck
Superior cervical ganglia (C2/C3 level) control:
Pupil dilation and inhibition of saliva
Middle cervical (C6 level) ganglia innervate:
Thyroid gland
Trachea
Oesophagus
Heart
Inferior cervical (C7/T1 level) ganglia innervate:
Upper limb
Types of thoracic splanchnic nerves:
Greater T5-T9
Lesser T9-T10
Least T12
3 types of pre vertebral (pre aortic) ganglia?
- Coeliac
- Superior mesenteric
- Inferior mesenteric
How is abdominal and pelvic viscera innervated?
Via thoracic splanchnic nerves
That synapse at pre vertebral ganglia
Via parasympathetic splanchnic nerves
Intramural synapse
Lower Abdominopelvic region
What does the meningeal ramus supply?
The dura
The pathway of sympathetic innervation:
Cell body in lateral horn
Preganglionic fibre passes through ventral root
Enters sympathetic chain via white ramus communicantes
Synapse at sympathetic ganglion
Post ganglionic fibres depart via grey ramus communicantes
Then travel through dorsal ramus, ventral ramus, meningeal ramus
Routes in sympathetic chain:
Divergence: one pre ganglionic neurone projects to several post ganglionic neurones
Convergence: one post ganglionic neurone receives input from several pre ganglionic neurones
Occurs via inter ganglionic nerves connecting the ganglia
Main function of parasympathetic ns
Rest and digest
Where does parasympathetic ns provide autonomic innervation to?
Head
Neck
Thorax
Abdomen
Pelvis
Blood vessels
Where are the pre ganglionic cell bodies of parasympathetic ns located?
- cranial nerve nuclei (brain stem) - innervates head, neck, thorax, upper abdomen
- lateral horn of sacral segments from S2-S4 - lower abdomen, pelvis
Where are parasympathetic ganglion for post ganglionic fibres found?
Intramural - within walls of target organs
In named ganglion of the head
The lengths of parasympathetic neurones?
Long pre ganglionic fires
Short post ganglionic fibres
4 Parasympathetic ganglia on either side of head
- Ciliary
- Pterygopalatine
- Submandibular
- Otic
What are the Parasympathetic cranial nerves?
Oculomotor nerve III - ciliary ganglion - pupil
Facial nerve - pterygopalatine ganglion - lacrimal gland
Facial nerve - submandibular ganglion - submandibular and sublingual glands
Glossopharyngeal nerve - otic ganglion - parotid gland
Vagus nerve
Parasympathetic vagus nerve innervation?
• CN X →Cardiac plexus → SAN and AVN
• CN X → Pulmonary Plexus → Bronchi
• CN X → Intramural Ganglia → Foregut (Stomach and Pancreas)
• CN X → Intramural Ganglia → Midgut (Small intestines)
Parasympathetic pelvic splanchnic innervate these organs:
- bladder
- rectum
- prostate
- vagina
- erectile tissue of penis
- clitoris
Where are parasympathetic pelvic splanchnic nerves?
In anterolateral horn of s2-s4
And synapse at intramural ganglia
Sympathetic and parasympathetic innervation of the gut:
Parasympathetic:
- Vagus nerve (foregut and midgut)
- Pelvic splanchnic nerves (hindgut)
Sympathetic:
- thoracic and lumbar splanchnic nerves
Pre aortic ganglion
- coeliac ganglion (foregut)
- superior mesenteric ganglion (midgut)
- inferior mesenteric ganglion (hindgut)
Parasympathetic nerves from brain stem innervate:
Head
Neck
Thorax
Upper abdomen
Parasympathetic nerves from lateral horn of S2-S4 innervate:
(Splanchnic nerves)
Lower abdomen
Pelvis
Where is sympathetic outflow?
Thoracolumbar T1-L2
Where is parasympathetic outflow?
Craniosacral
Cranial nerves: 3, 7, 9, 10
Sacral segments: S2-S4
Ganglia of the parasympathetic ns:
- Ganglia of the head
- Intramural ganglia (within the walls of the target organ)
Enteric ns regulates:
Peristalsis
Glandular secretion
What are 3 features of autonomic ns that are different from somatic?
- Effector innervated
- No. Neurones between CNS and Effector
- Neurotransmission
- the type NT used
- NT released
What are the splanchnic nerves?
Paired autonomic nerves that carry both
- sympathetic visceral fibres
- sensory fibres
Except pelvic splanchnic nerves that carry parasympathetic fibres
Are the CNS and PNS continuous
Yes they are not separate or distinct
Through which organ system does the autonomic ns maintain homeostasis
Cardiovascular
Respiratory
Digestive
Thermos-regulative apparatus (37C)
Effectors of the ANS
- Smooth muscle
In walls of blood vessel
In tube of GI tract - Cardiac muscle
- Secretary glands
How do the SNS and PNS differ anatomically
Innervate different effectors
Have different receptors
Use different NT
Number of neurones btw effector and CNS
What are the receptors of the ANS
- Visceral e.g. baroreceptors
Not consciously perceived. Responsible for internal monitoring. - Somatosensory/ external environment
E.g. vision, hearing, touch and detection of joints and limbs
Can sensory information produce both ANS and somatic NS outflow?
Yes
Examples of interaction of autonomic and somatic nervous system
- Focusing eyes on near objects
ANS - pupil lense adjustments
Somatic - eye movements to look at object - Response to cold
ANS - vasoconstriction vessels near skin
Somatic - shivering
Why is somatic innervation said to be discrete
One single uninterrupted neurone from cell body in CNS to effector
Innervate specific skeletal muscle fibres
Precise coordination over a small area
What is the advantage of preganglionic fibres branching to innervate multiple post ganglionic fibres
Synchronised and Wide spread effect
Activation of many different cell types (cardiac and smooth)
What is the advantage of ANS having diffuse release of NT
Diffuse over a large area via branching network
NT released at multiple sites
- Small number of post ganglionic neurones can influence a large number of effector cells
- High level of coordination btw smooth muscle cells
- In an organ we can organise the change in activity through activation of a small number of post ganglionic neurones
How can a drug target SNS and PNS
Target cholinergic transmission
NT of the SNS
Pre ganglionic - ACh and nAChR
Post ganglionic - noradrenaline and adrenoceptors
NT of the PNS
Pre ganglionic - ACh and nAChR
Post ganglionic - ACh and mAChR (muscarinic)
Advantage of catecholamines being directly secreted from adrenal medulla
Catecholamines can activate non innervated receptors (Adrenergic receptors)
Distant from nerve terminals
Receptors activated by circulating catecholamines
Adrenergic receptors located in smooth muscle of bronchioles and some blood vessels
Why is adrenal medulla known as neuroendocrine organ
Medulla cells are neuroendocrine cells because they release adrenaline and NAd into the blood
What is the role of SNS
Alert and active
Active in maintaining homeostasis
Active when emergency
What is the role of PNS
Rest and digest
Energy conservation when sleeping/ relaxing
Gaining energy through digestion
Emptying (bowel/ bladder)
How does the heart use dual innervation that work antagonistically
SNS increases HR
PNS decreases HR
How does the GIT use dual innervation that work antagonistically
SNS decreases motility
PNS increases motility
Via action of NS on the smooth muscle cells of GIT
An example of antagonistic dual functional control with different muscles
Smooth muscles surrounding pupil of eye
Smooth muscle cells arrange in 2 bands (inner and outer)
Outer band = constrictor (circular muscle)
Inner band = dilator (radial muscle)
How is pupil constriction caused?
PNS innervates circular muscle (sphincter pupillae)
Contraction of circular muscle
How is pupil dilation caused?
SNS innervates radial muscles (dilator pupillae)
Contraction of radial muscle
Examples of single innervation
Sweat glands only have SNS input
Smooth muscles of most blood vessels have SNS only
Lens adjustments by PNS
What is vasomotor tone?
In most blood vessels
Only SNS input but degree of input varies
Increase in SNS activity - vasoconstriction
Decrease in SNS activity - vasodilation
Contrasts with somatic ns which is more on and off (skeletal muscle either contracts or relaxes)
Which blood vessels receive dual innervation
PNS and SNS input
Head
Neck
Reproductive organs
Antagonistic effect:
SNS vasoconstriction
PNS vasodilation
Example of dual innervation thats not antagonistic
Exocrine glands in the head and neck e.g. salivary glands
Male sex organs:
PNS innervation: erection “point”
SNS Innervation: ejaculation “shoot”
Need erection before ejaculation
What is the SNS input to salivary glands
Production of low volume, sticky, viscous saliva
SNS causes vasoconstriction in head/ neck blood vessels
Reduces blood flow to salivary gland
Less raw product (fluids, ions) delivered to gland
Why do we get dry mouth when anxious
SNS is alerted
Mouth is less wet with thick and sticky saliva
PNS>SNS when at rest
How does PNS effect salivary gland
Promotes secretion of watery and more saliva
PNS input to blood vessels of head and neck cause vasodilation
More raw material to salivary glands
Saliva lubricates food before goes into GIT
How does SNS activity cause vasoconstriction and vasodilation
Vasoconstriction:
Innervation of skin blood vessels
Cause NAd release from SNS
NAd acts on alpha receptors
Smooth muscle of vessels constricts
Vasodilation:
SNS innervates adrenal medulla so adrenaline released
Adrenal binds to beta receptors
Relaxation of smooth muscle of vessels
Work in combination simultaneously
What is the most common receptor in most blood vessels
Alpha receptors
Hence more vasoconstriction
Receptors in blood vessels that supply skeletal and cardiac muscle
Beta and alpha receptors
So vasodilation and vasoconstriction
How SNS and PNS work together not antagonistically
Exocrine glands of head and neck - salivary and sweat
Male sex organs
PNS erection
SNS ejaculation
What are the 4 parasympathetic ganglion of the head
Ciliary
Pterygopalatine
Submandibular
Otic
3 types of pre aortic ganglia
Coeliac
Superior mesenteric
Inferior mesenteric
What do ANS fibres follow
Blood vessels
What does the ventral and dorsal ramus supply
Dorsal - back
Ventral - anterior body and limbs
