Week 8 Flashcards
What are the autonomic sensory components
Receptors:
Viscera- not consciously perceived e.g. baroreceptors which detect blood pressure
Somatosensory/external environment- somatic and autonomic integration
Autonomic motor components
Different to somatic:
Effectors innervated
Number of neurones between CNS and effector
Neurotransmission
Efferent (motor) neurones and their effector cells
Somatic neurones— skeletal muscle
Sympathetic and parasympathetic (autonomic) neurones —— smooth and cardiac muscle and glands
Somatic neurones
Alpha-motoneurone, cell body in spinal cord, direct synapse to skeletal muscle, precise control of effector cells
Autonomic neurones
Single pre-ganglionic neurone synapses in ganglia outside CNS to post ganglionic neurone/neurones
Effect a large proportion of effector, widespread control
Neurotransmitter release in somatic neurones
Discrete
Very precisely match up motoneurone and muscle cell, accurate degree of functional control
Neurotransmitter release in autonomic neurones
Covering a larger area
Loads of neurotransmitter release sites from one post ganglionic neurone, can affect a large number of effector cells
Sympathetic neurotransmitters
ACh released by pre-ganglionic neurone in ganglia, noradrenaline (NA) released by postganglionic neurone
Except for sweat glands which are sympathetic but both neurones release ACh
Parasympathetic neurotransmitters
ACh released by both neurones no NA
Adrenal medulla, exception
Preganglionic neurone form synapse with cells in the medulla, release ACh
Adrenal medulla- neuroendocrine organ
Cells then produce hormone, adrenaline and noradrenaline into the bloodstream
Adrenaline— non-innervated receptors, e.g. smooth muscle of bronchioles/ blood vessels
What do the SNS and PNS do
Homeostasis + vision, reproduction
SNS- alert and active: always working, emergency -defence response (flight or fight)
PNS- rest and digest, energy conservation, digestion, emptying bowel and bladder
How do the SNS and PNS work
Most organs have dual innervation, antagonistic
Heart: SNS increase heart rate, PNS decrease
GIT: SNS decrease motility and PNS increase
Pupil: pupil dilation is SNS (contraction of radial muscle, dilator pupillae). Pupil constriction is PNS (contraction of circular muscle, constrictor pupillae)
Combine action, most active one dominates
SNS and PNS different types of innervation
Dual innervation and not antagonistic, exocrine glands e.g. salivary. SNS and PNS work together
Single innervation e.g. sweat glands is SNS only. most blood vessels SNS only, vasomotor tone increase in SNS=vasoconstriction, decrease SNS=vasodilation
Other cases of blood vessels with SNS and PNS
Blood vessels of head and reproductive organs
SNS= vasoconstriction
PNS= vasodilation
Exocrine glands in head and neck
SNS and PNS not antagonistic, doing same thing
Exocrine gland gets substance from blood vessel
SNS causes vasoconstriction so reduced flow and raw material to blood vessel supplying gland, but SNS increases substance in gland , small quantity of substance released from gland
PNS causes vasodilation, increased raw material and PNS increases substance in gland so lots substance released from gland
PNS> SNS effect
SNS body wide activation can cause vasodilation
Blood vessels of skeletal muscle and heart
Most vessels- an increase in SNS activity, noradrenaline produced to alpha receptors . Vasoconstriction
Vessels of skeletal muscle, smooth muscle cells in these vessels have more beta receptors so an increase in SNS produces adrenaline to beta receptors causing vasodilation
SNS and PNS working together
Male sex organs
PNS-erection, p for point
SNS- ejaculation
Interaction of autonomic and somatic systems
E.g. focusing eye on near object:
ANS- pupil/ lens adjustments
Somatic- eye movement
E.g. response to cold:
ANS-vasoconstriction in skin
Somatic- shivering
What is the enteric nervous system
3rd division of ANS sometimes classed as parasympathetic
Targets smooth muscles and secretory cells associated with digestive system
Intramural plexus in GIT
Intrinsic innervation of GIT - oesophagus to rectum, pancreas and biliary system
Contains lots of types of neurotransmitter
Where is enteric nervous system
Two major plexuses of ganglion cells and their fibre bundles
Submucosal (Meissner’s ) plexus - stomach and intestines only
Myenteric (Auerbach’s) plexus- full length of GIT, extensively interconnected
Wall of GIT
Wall of GIT
Longitudinal muscle
Myenteric plexus
Circular muscle
Submucosal plexus
Submucosa
Mucosa
Lumen
Types of neurones in ENS
Afferent: mechanoreceptors and chemoreceptors
Interneurons: excitatory and inhibitory
Efferent (secretomotor) neurones: excitatory or inhibitory, many neurotransmitters including ACh, various peptides
Effectors: motor and secretory- short reflex
What do enteric reflexes do
Control: motility, secretion, blood flow to the gut
Motor reflex- Myenteric plexus- synapse with both smooth muscle layers
E.g. peristalsis
ENS- Myenteric plexus
Peristalsis
One stimulus
To move bolus along need coordination of contraction and relaxation of smooth muscle
Contraction behind bolus and dilation in front(relaxation)
Mucosal stimulation, distension , Myenteric plexus
Secretory reflex- submucosal plexus
Both plexuses are connected together, interneurons process info
Reflex arc: food-> sensory receptors (mechano, chemo) -> ENS(submucosal plexus) -> secretory neurones-> increase secretion (mucus, enzymes, acid) -> food
Right type of secretion varies depending on where you are in GIT
Blood flow ENS
Myenteric/ submucosal plexus
Vasoactive neurotransmitters
Affect smooth muscle in blood vessels, efferent neurones within short reflex not innervating smooth muscle in wall of GIT but are in the wall of blood vessels in submucosal layer. Affect blood flow locally
Integration of ENS with CNS
ENS <-> SNS/PNS <-> CNS
Long reflex
CNS influence varies along GIT
What dysfunction/ diseases are associated with ENS
Age in number/ function
Disease: pathology, ENS specific or NS generally, function
Chaga’s disease: trypanosome parasite, toxin leads to neurone death, problems with nutrition, growth and development
Achalasia: oesophagus/ sphincter, may be autoimmune, most often seen in elderly, difficulty swallowing and food moving down oesophagus, leads to malnutrition, food avoidance
Hirschprung’s disease
Also known as mega colon
Congenital absence of ENS neurones, distal colon manifests itself soon after birth
Peristaltic wave halts at the section missing ENS neurones, stasis in faeces movement, distension, colitis
Abolition of rectoanalreflex, abnormal defaecation, treatment- surgery, colostomy
General neurological conditions association with ENS
Parkinson’s- enteric neurones often badly affected, often have gut dysfunction can be prior to motor symptoms
Peripheral neuropathies- can include enteric neurones
Myasthenia Gravis- autoimmune condition, antibodies against nicotinic receptors on skeletal muscle, nicotinic receptors on neurones, ACh transmission in enteric, some people produce antibodies that affect receptors on muscle and neurones, can affect transmission on ENS
Gut brain axis
Irritable bowel syndrome IBS
Different from inflammatory bowel disease IBD
Doesn’t appear to be anything wrong histologically, dysfunctional interactions between ENS and CNS
Drug therapies can help mange symptoms
Mental health: microbiome that lives in the gut, bacteria can change and influence ENS function which can influence brain function
ENS neurotransmission
Many drug targets
Endogenous opioids ( not really found anywhere in PNS other than ENS, lots in CNS) and receptors
Opioid peptides in normal enteric transmission so there’s opioid receptors
The good: anti-diarrhoeal medication, targets opioid transmission in gut
The bad: analgesia e.g. morphine, codeine- causes constipation. Opioid often used for serious conditions, extreme pain
The nervous systems
CNS and PNS (anatomical difference- whether nervous tissue is surrounded by meninges)
Afferent and efferent
Somatic and autonomic
Autonomic= sympathetic, parasympathetic and enteric
CNS and PNS are continuum not separate or distinct can have a neurone who’s cell body is located in PNS but its axon extends into CNS
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
Spinal cord to PNS: horn-> root-> mixed spinal nerve-> dorsal/ventral ramus
Within lateral horn of thoracic and lumbar regions contains pre-ganglionic sympathetic neuronal cell bodies
Pre-ganglionic cell bodies of pelvic splanchnic nerves (parasympathetic) found in lateral (anterolateral) horn of sacral segments S2-4
The autonomic nervous system
Innervation of visceral organs, smooth muscle and secretory glands
Involuntary control
Responsible for maintaining homeostasis. Cardiovascular, respiratory, digestive, thermos-regulative apparatus, excretory
Works continuously
Divided into sympathetic (involved in constriction of cutaneous arteries, redirects blood to important organs) and parasympathetic (results in decrease HR, increase in glandular secretion and peristalsis in gut)
Both divisions are functionally antagonistic maintaining homeostasis, integrate with each other
How does ANS work
Cell body in CNS-> preganglionic fibre-> ganglion in PNS (collection of neuronal cell bodies) -> post ganglionic fibre-> target organ or tissue
Pre-ganglionic fibre= myelinated, primary neurotransmitter is ACh (cholinergic fibres), synapse in ganglion. Axon crosses meninges and enters PNS
Post-ganglionic fibre= unmyelinated, primary neurotransmitters is either ACh or NA(adrenergic fibres), axon supplies effector organ directly
Effector organs of ANS
Muscles of body that generate own electrical activity- myogenic
Smooth muscle- walls of blood vessels, tube of GIT
Cardiac muscle
Secretory glands
afferent fibres
General visceral afferent GVA fibres (not ANS) send sensory info back to CNS via dorsal root and horn
Visceral or autonomic afferent fibres travel in same way as somatic afferent fibres
The neuronal cell bodies are located in specific sensory nerve ganglia or cranial nerves or dorsal root ganglia
Visceral afferents involved in nociception, excessive tension in smooth muscle and some pathological conditions produce visceral pain
Viscera insensitive to crushing, cutting and burning
Dermatomes
Afferent fibres from spinal nerves supply cutaneous innervation to a specific region of skin
Dermatome maps map out the region of skin innervated by a particular spinal nerve
Theres considerable overlap between cutaneous innervation and spinal segments
Visceral or referred pain- pain in visceral organs interpreted in a region innervated by same spinal segment
E.g. irritation of peritoneum on inferior surface of diaphragm, which is innervated by phrenic nerve can be referred to skin on top of shoulder which is innervated by other nerves from same spinal level
Efferent fibres
Somatic efferent fibres consist of a single neurone which synapses with skeletal muscle
General visceral efferent GVE fibres or autonomic efferent fibres consist of 2 neurone pathway
Preganglionic fibres synapse within ganglia, postganglionic synapse with cardiac or smooth muscle cells or with gland cells
Myotomes
Efferent fibres from spinal nerves supply innervation to skeletal muscles within a specific compartment
Most skeletal muscles are innervated by nerves derived from several spinal cord levels
Sympathetic nervous system
Acts in sympathy, accordance with emotions
Provides autonomic innervation to the head, neck, thorax, abdomen, pelvis and blood vessels
Preganglionic cell bodies located in lateral horn between t1-l2 Thoracolumbar outflow
Ganglion is found in the sympathetic chain or near target organ
Short Preganglionic neurone, long post ganglionic neurone
SNS exception innervation of suprarenal gland
Cell body in lateral horn of T1-L2 spinal cord
No ganglion
ACh
Direct innervation from sympathetic preganglionic neurone to adrenal medulla chromaffin cells for production of adrenaline
SNS exception innervation of sweat glands
Cell body in lateral horn T1-L2
Ganglion in sympathetic chain or near target organ
ACh secreted by postganglionic ‘sudomotor’ neurones innervtaing sweat glands and arrector pili muscle of skin
No NA produced only ACh
Sympathetic ganglia
Sympathetic chain, paravertebral chain, found in thoracic cavity
Pre-aortic ganglia found in aorta
Cervical ganglia -sympathetic ganglia
Found behind carotid sheath, nerve synapsing with these ganglia dont originate from cervical part, come from T1-T3/5 ascend upwards
Superior cervical ganglia C2-3= pupil dilation and inhibition of salivation. Supplies nerves C1-4, largest
Middle C6 cervical ganglia= innervate thyroid + parathyroid gland, trachea, oesophagus, heart. Smallest ganglion, supplies nerves C5-6, sometimes not present
Inferior cervical ganglia C7-T1 level (Stellate ganglia) innervates upper limb, supplies C7, C8, T1 sometimes C6 if middle ganglia present
Abdominal ganglia
Receive innervation via splanchnic nerve , dont synapse with sympathetic chain
Greater (T5-9)/ lesser(T9-10), least (T11-12)
Pre-aortic (pre-vertebral) ganglia:
Celiac = all nerves,found in abdominal aorta, pain and sensation from foregut
Superior mesenteric = found where superior mesenteric artery leaves abdominal aorta, lesser nerve
Inferior mesenteric= receives innervation from lumbar splanchnic
Sympathetic innervation
Pre-ganglionic neurones depart lateral horn (T1-L2)
Pass through ventral root
Enter sympathetic chain via white ramus communicantes (myelinated)
Synapse at sympathetic ganglion
Post ganglionic neurones depart via grey ramus communicantes (unmyelinated)
Dorsal ramus will supply back, ventral ramus supplies anterior body and limbs
Meningeal ramus supplies dura mater
Routes in sympathetic chain
Can either synapse with ganglion on same level or ascend or descend or pass medially and synapse with ganglion not in sympathetic trunk
divergence= one Preganglionic neurone projects to several post ganglionic neurones
Convergence= one postganglionic neurone receives innervation from several pre ganglionic neurones
Occurs via the inter ganglionic nerves connecting ganglia
Allows widespread effects on target organs
Parasympathetic nervous system
Counterbalances affect of sympathetic
Provides autonomic innervation to head, neck , thorax, pelvis, abdomen, blood vessels
Preganglionic cell bodies located in cranial nerve nuclei (CNIII, VII, IX, X) and lateral horn of sacral segments S2-4 Craniosacral outflow
Ganglion is found near target organ or within walls of tissue intramural
Long pre ganglionic, short post ganglionic
Both ACh
PNS innervation
CN nuclei (CNIII, VII, IX, X)= cell body in brainstem, ganglion near target organ, head neck, thorax , upper abdomen
Lateral horn of S2-4= cell body in sacral spinal cord, ganglion, lower abdomen and pelvis
Craniosacral outflow with ACh as primary neurotransmitter for both preganglionic and post ganglionic neurons
Parasympathetic ganglia in head
Ciliary- Oculomotor nerve CNIII, synapse in ciliary ganglion, post ganglionic fibres innervate sphincter of pupil and ciliary muscle, both muscles act to produce accommodation reflex
Pterygopalatine - facial nerve CNVII, innervates lacrimal gland and nasal gland, increased secretion
Submandibular -facial nerve CNVII, innervates submandibular and sublingual glands
Otic- glossopharyngeal nerve CNIX, innervates parotid gland, increased secretion
Parasympathetic vagus nerve
Long pre-ganglionic fibre
CNX-> cardiac plexus-> SAN, AVN
CNX-> pulmonary plexus-> bronchi
CNX-> intramural ganglia-> foregut (stomach and pancreas)
CNX-> intramural ganglia-> midgut (small intestines)
Contraction of smooth muscles,increases gastric secretion, increase motility and peristalsis
Parasympathetic pelvic splanchnic
Anterolateral horn S2-4
Intramural ganglia
Innervate bladder, rectum, prostrate or vagina and erectile tissue of penis and clitoris
S2- second half perineum (enteric) and bladder sphincter
S3- colon
S4- erectile tissue of penis/clitoris
Plexuses of enteric
Myenteric= peristalsis
Submucosal= glandular secretion
Autonomic innervation of gut
Parasympathetic: vagus nerve (foregut and midgut), pelvic splanchnic nerves S2-4 (hindgut)
Sympathetic: thoracic and lumber splanchnic nerves T1-L2/3, celiac ganglion (foregut), superior mesenteric ganglion (midgut), inferior mesenteric ganglion (hindgut)
From autonomic plexuses around arteries and follow blood vessels to reach target organ
