Wk8 Anatomy Of The ANS Flashcards
What is the ANS responsible for?
Fight/flight sympathetic THE Fs - fight - flight - fright
Rest/digest parasympathetic NON-Fs - rest - digest - energy storage
The autonomic nervous system is in a state of equilibrium during normal activity
Overview of ANS
Somatic motor ▪ Spinal cord ▪ Single neuron pathway ▪ Voluntary: Skeletal muscle
ANS motor ▪ Spinal cord ▪ 2 neuron pathway ▪ Involuntary: • Cardiac muscle • Smooth muscle • Glands
ANS general principles
Pre-ganglionic fibre releases ACh
Synapse - ganglion in PNS
Post-ganglionic fibre - ACh or noradrenaline (target organ or tissue)
Sympathetic nerves - key facts
- Thoracolumbar outflow (T1 – L2/L3 spinal level)
- ACh secreted by pre-ganglionic fibres
- NA secreted by post-ganglionic adrenergic fibres
Cell body in lateral horn of T1-L2 spinal cord
Ganglion in sympathetic chain or near target organ
- Head & neck Thorax • Abdomen
- Pelvis
- Blood vessels
Sympathetic nerves exceptions
No ganglion to suprarenal gland
Direct innervation from sympathetic preganglionic neurons to adrenal medulla (chromaffin cells) for production of adrenaline
- Skin - sweat glands
- Skin – arrector pili
ACh secreted by postganglionic ‘sudomotor’ neurons (innervating sweat glands and arrector pili muscle of skin)
Parasympathetic nerves summary
- Cell body in brain stem (CNIII or CNX)—> ganglion near target organ —> head and neck, thorax, upper abdomen
- Cell body in sacral spinal cord (S2-S4) —> ganglion near target organ —> lower abdomen and pelvis
Craniosacral outflow with acetylcholine (ACh) as primary neurotransmitter for both pre-ganglionic and post-ganglionic neurons
The spinal cord
▪ Dorsal horn with dorsal root.
(somatic afferents synapse with CNS cell bodies)
▪ Ventral horn with ventral root (somatic efferent cell bodies and axons)
▪ Lateral horn (T1-L2 spinal cord segments) (pre-ganglionic sympathetic cell bodies)
Remember: Spinal cord to peripheral nervous system:
Horn → Root → Mixed spinal nerve → Dorsal/ventral ramus…
What is the lateral horn?
pre- ganglionic sympathetic neuronal cell bodies
Summary of the ANS
▪ The ANS is tonically activated and maintains homeostasis.
• Involuntary control of cardiac, smooth muscle and glands.
▪ Sympathetic outflow is thoracolumbar (T1-L2).
• Increase sympathetic activity in response to stress (fight/flight).
• Pre-ganglionic from the lateral horn of spinal cord = ACh
• Post ganglionic = NA (ACh for sweat glands and arrector pili).
▪ Parasympathetic outflow is craniosacral (cranial nerves and S2-S4).
• Increase parasympathetic activity in response to consumption of food.
• Pre- and post-ganglionic release ACh
Actions of sympathetic ANS
Dilate pupil Increase HR Constrict blood vessels Dilate bronchial smooth muscle Inhibit digestion Inhibit salivation Secretion of adrenaline Orgasm shoot
Actions of parasympathetic ANS
Constrict pupil Decrease HR Constrict bronchial smooth muscle Increase peristalsis Stimulate salivation Erection - point
Sympathetic ganglia
On either side of the neck
Superior cervical ganglia (C2/C3 level) Middle (C6 level) cervical ganglia innervate
thyroid gland, trachea, oesophagus, heart
Inferior cervical ganglia (C7/T1 level (AKA stellate ganglia) innervate upper limb
Abdominal autonomic ganglia
▪ Via thoracic splanchnic nerves Greater/lesser/least ▪ Pre-aortic (pre-vertebral) ganglia Coeliac Superior mesenteric Inferior mesenteric ▪ ANS fibres follow the blood vessels.
▪ ANS fibres follow the blood vessels.
▪ Visceral efferent = ANS motor
▪ Visceral afferent = visceral sensory
Parasympathetic ganglia
▪ Parasympathetic pre- ganglionic fibres synapse on post ganglionic fibres at:
• Named ganglia in the head.
• OR in the wall of their target organ.
▪ 4parasympathetic ganglia (on either side of head): Ciliary Otic Pterygopalatine Submandibular COPS
▪ Ganglia are in wall of target organ (intramural). ▪ X Vagus • Foregut and midgut organs ▪ Pelvic splanchnic nerves • S2–S4 • Wall of hindgut or pelvic organs
Enteric nervous system
Myenteric plexus
▪ Peristalsis
Submucosal plexus
▪ Glandular secretion
Hirschprung’s disease
Congenital absence of myenteric and submucosal plexus neurons (ganglion cells) in parts of intestine
Autonomic nerve supply to the gut
Parasympathetic
▪ Vagus nerve to distal third of transverse colon (splenic flexure)
▪ Pelvic splanchnic nerves (from S2 – S4) to hindgut and pelvic organs
Parasympathetic
▪ Vagus nerve
▪ Pelvic splanchnic nerves (S2 – S4)
Sympathetic (thoracic + lumbar splanchnic nerves)
▪ Celiac ganglion (foregut)
▪ Superior mesenteric ganglion (midgut)
▪ Inferior mesenteric ganglion (hindgut)
Form autonomic nerve plexi around arteries.
▪ Autonomic nerves follow blood vessels to reach target organ
Sympathetic nervous stem
1) Pre-ganglionic neurones depart the lateral horn (T1 –L2)
2) Pass through the ventral root
3) Enters the sympathetic chain via the white ramus communicans (myelinated)
4) Synapse at sympathetic ganglion
5) Post-ganglionic neurons depart via the grey ramus communicans (unmyelinated)
6) The dorsal ramus will supply the back, the ventral ramus will supply the anterior body and limbs
Routes in the sympathetic chain
Superior Cervical Ganglion
- Pupil Dilation
- Inhibit Salivation
ABDOMEN (pre-vertebral/pre-aortic ganglia)
- Coeliac Ganglion
- Superior Mesenteric Ganglion
- Inferior Mesenteric Ganglion
Horner’s syndrome - left side
Constricted pupil (miosis)
Partial ptosis
Anhydrosis (reduced sweating on same side)
Some potential causes are:
• Trauma (e.g. blunt or surgical trauma in the root of the neck)
• Tumour (e.g. lung, thyroid)
• Multiple sclerosis and spinal cord lesions
• Cervical rib (impinging on sympathetic chain)
Pupillary constriction
Miosis
Sphincter pupillae muscle contracts: pupil size decreases
Parasympathetic
Mydriasis
Dilator pupillae muscle contracts: pupil size increases
Sympathetic
Stellate block
▪ Local anaesthetic at stellate ganglion
• Sympathetic paralysis in head, neck and upper limb on same side.
▪ Successful stellate block is demonstrated by
1. a warm, dry hand;
2. Horner syndrome, a constricted pupil (pupillary constrictor is unopposed by
dilator pupillae;
3. ptosis (drooping) of the upper eyelid because of paralysis of smooth muscle fibres within the levator muscle of the upper eyelid
Summary
▪ The sympathetic chain allows pre-ganglionic neurons to synapse, ascend or descend or to pass through to other sympathetic ganglia.
▪ The route taken by the pre-ganglionic fibre is:
• Lateral horn – Ventral root, spinal nerve, white ramus communicans –
sympathetic chain/through to pre-aortic ganglia
The route taken by the post-ganglionic fibre is:
• Sympathetic chain – grey ramus communicans – spinal nerve – dorsal/ventral ramus to body.
▪ Horner’s syndrome is a paralysis of the sympathetic neurons in the head, neck and upper limb. Characterised by pupillary constriction, warm skin/anhidrosis, partial ptosis
▪ The adrenal gland is directly innervated by pre-ganglionic fibres. Chromaffin cells secrete adrenaline into the blood.
What can sympathetic pregangionic neurones do?
▪ Synapse with a postganglionic neuron in a sympathetic ganglion at the same spinal level
▪ OR ascend the sympathetic chain to synapse with a postganglionic neuron in a higher sympathetic ganglion
▪ OR descend the sympathetic chain to synapse with a
postganglionic neuron in a lower sympathetic ganglion
▪ OR pass through the sympathetic ganglion to reach a splanchnic nerve and travel to the thoracic/abdominal organs
Key themes
▪ Resolve the paradox that, despite an outflow restricted to 14 or 15 ventral roots,
all 31 spinal nerve trunks acquire sympathetic fibres.
▪ Appreciate that the sympathetic ganglia along the abdominal aorta are activated
by preganglionic fibres, as is the adrenal medulla.
▪ Pay special attention to the autonomic innervation of the eye, discussed both
here and in Chapter 23 .
▪ Appreciate that the four parasympathetic ganglia in the head are functionally
similar to intramural ganglia elsewhere.
▪ Be aware that the pelvic ganglia are mixed autonomic ganglia.
▪ Realise that the preganglionic neurons of both divisions are cholinergic and that
the target receptors in all of the autonomic ganglia are nicotinic.
▪ Appreciate that visceral afferents utilise autonomic pathways to gain access to
the nervous system. They are especially important in the context of thoracic and abdominal pain.