Autonomic Nervous System Flashcards
Subdivisions of nervous system
Recap of somatic NS division
- Voluntary action
- Somatic motor = efferent fibres to striated (skeletal) muscles
- Somatic sensory = afferent fibres from receptors (e.g. skin receptors)
- All within 31 pairs of segmental spinal nerves (or cranial nerves)
How do somatic sensory fibres enter the spinal cord?
Via the dorsal root ganglion
What does the ANS control?
Contrals internal activities of organs and glands
ANS recap
- Largely involuntary
- Monitors conditions in the internal environment to maintain homeostasis
- Influenced rostrally by the hypothalamus
Where do autonomic (visceral) motor fibres go to?
Efferent fibres to smooth muscles, cardiac muscle or glands
Where do autonomic (visceral) sensory fibres come from?
afferent fibres from sensory receptors in an internal organ
Where do visceral efferent fibres have their cell bodies?
- Lateral grey horn of spinal cord –> only found in T1-L2 and S2-S4
- Use ventral root to exit the spinal cord
Where do autonomic visceral afferent fibres have their cell bodies?
Dorsal root ganglion then use dorsal root to enter spinal cord
Where do autonomic fibres (either afferent or efferent) only exist?
Segemental spinal nerves at either T1-L2 or S2-S4 OR specific cranial nerves
Autonomic (visceral) afferents recap:
- Autonomic (visceral) sensory = afferent fibres from sensory receptors in an internal organ, glands and blood vessels
- Conduct sensory impulses from viscera to CNS
- Responsible for referred pain
Which division of the NS is responsible for referred pain?
Autonomic (visceral) afferent
What is referred pain?
Pain sensations from visceral organs often perceived as regions of the body surface innervated by the same spinal nerves.
E.g. MI pain is referred to upper chest and limb
Referred pain explained
- Somatic afferent fibres (e.g. from skin T1-T4) use dorsal root to enter cord
- Visceral afferent fibres (e.g. from heart) follow same pathway and use dorsal root to enter cord
- Heart is innervated by afferent fibres between T1-T4
- Brain interprets pain as if its coming from T1-T4 regions of skin
- The pain is usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse.
Describe the 2 neuron chain for autonomic (visceral) efferents
- Preganglionic neuron in CNS
- Cell body in CNS (brainstem or spain cord)
- Pre and postganglionic neurons synapse at an autonomic ganglion in the PNS
- Postganglionic neuron in PNS
- Travels to target organ/tissue
The ANS: summary
- Innervates smooth muscle (organs), cardiac muscle (heart) and glands (e.g. salivary, lacrimal, sweat, etc)
- Visceral motor efferents and visceral afferents
- Two divisions, exert antagonistic effects
- Sympathetic –> Produces effects most apparent during stress or excitement: fright/flight/fight
- Parasympathetic –> Conserves and restores energy: rest and digest
- Most visceral organs receive both sympathetic and parasympathetic
Difference between the outflow of parasympathetic vs sympathetic information
Properties of the SNS and PSNS preganglionic neurons differ with respect to the spinal cord exit points:
- Sympathetic:
- Has thoracolumbar outflow, meaning that the neurons begin at the thoracic and lumbar (T1–L2) portions of the spinal cord.
- Parasympathetic:
- Has craniosacral outflow, meaning that the neurons begin at the cranial nerves (CN3, CN7, CN9, CN10) and sacral (S2–S4) spinal cord.
Sympathetic outflow summary
Thoracolumbar outflow –> T1-L2
Parasympathetic outflow summary
Craniosacral outflow:
- Brainstem CN III, VII, IX, X
- S2-S4
Difference between the ganglia of the sympathetic and parasympathetic NS
- Sympathetic:
- Organised ganglia in sympathetic chain/paravertebral chain
- Series of ganglia that extends whole length of spinal cord
- Prevertebral and paravertebral ganglia
- Parasympathetic:
- Ganglia located near the effector organ
Is the effect of the parasympathetic and sympathetic system widespread or localised?
Sympathetic –> widespread
Parasympathetic –> localised
Route of parasympathetic division; cranium and sacral origin
- Cranio-sacral origin (brainstem and S2-S4)
- Axons of preganglionic neurons from brainstem leave via cranial nerves III, VII, IX or X
- Axons of preganglionic neurons from sacral cord leave spinal cord via S2-S4 spinal nerve
- Synapse with postganglionic fibre in PNS (autonomic ganglia)
- Sends axon to effector organ
All preganglionic fibres of the ANS use what as their neurotransmitter?
Acetylcholine –> all fibres are cholinergic and are myelinated for faster transmission
What do the postganglionic fibres of the ANS use as their neurotransmitter?
Sympathetic division –> use noradrenaline so are adrenergic
Parasympathetic division –> use acetylcholine so are cholinergic
Describe the length of the preganglionic and postganglionic fibres of the parasympathetic division
2 neuron chain:
- Preganglionic fibre has long axon
- Postganglionic fibre has relatively short axon
- Autonomic ganglion (where these 2 synapse) is located close to effector organ
Parasympathetic fibres run within which 4 cranial nerves? Where do each of these cranial nerves travel to? What is the effect?
- CN III
- Travels to pupil
- Causes dilation of pupil
- CN VII
- Travels to salivary and lacrimal glands
- Increases salivary secretions / tears
- CN IX
- Travels to salivary glands
- Increases salivary secretions
- CN X
- Travels to cardiac, pulmonary and digestive systems
- Decreases heart rate
- Constricts bronchi
- Increases digestion
What is the main parasympathetic nerve of the viscera of the trunk?
Vagus nerve
Origin of the vagus nerve?
Medulla oblongata of brainstem –> posterolateral sulcus
how does the vagus nerve innervate target organs?
Via organ plexuses
What do S2-S4 parasympathetic fibres leave the spinal cord as? Effect on organs?
As pelvic splanchnic nerves
- Control over bladder and distal part of colon and erectile tissue
- Allows urination and defecation as well as erection