W7: Anatomy Of ANS Flashcards
Afferent nervous system
Nerves that carry information from the body to the brain (sensory). Does not split any further
Efferent nervous system
Nerves that carry info from brain to body, motor system. Split into somatic and autonomic.
Somatic nervous system
Under voluntary control - supplies skeletal muscles. No split, just somatic efferents
Autonomic nervous system
Not under voluntary control - supplies smooth muscles, glands, and cardiac muscles. Split into sympathetic, parasympathetic, and enteric.
General actions of the ANS
- establishes and maintains homeostasis or internal environment in the body - through regulation of various systems of the body: cardiovascular, respiratory, digestive, thermo-regularise apparatus. Constantly working
- promotes excretory mechanisms of the body as and when necessary and appropriate. Intermittent.
General layout of the ANS
- neurone with the cell body in the CNS and neurone with the cell body in the PNS connected in series
- CNS neurone’s axon crosses the boundary of the meninges to end up being in the PNS
- in the PNS, the neurone terminates to make contact with a cell body of another neurone in the PNS
- this neurone then has an axon that comes out to supply the effector organ
What makes up a ganglion?
The cell bodies collected in the PNS constitute a ganglion.
What does pre-ganglionic mean?
A neurone that occurs and terminates in the ganglion. Does not supply effector organs directly.
What does post-ganglionic mean?
A neurone who’s axon terminates outside the ganglion. These communicate with the effectors. Relies on pre-synaptic neurone for drive. Terminate directly on effector organs.
Sympathetic pre and post ganglionic neurotransmitter and receptors
Preganglionic = ACh acting via nicotinic receptors Postganglionic = noradrenaline or adrenaline acting via alpha or beta adrenoceptors (respectively)
Where are sympathetic nuclei found and what do they command?
High brain structures. These command only spinal cord systems. Then to paravertebral chain and to the effector organs.
What do sympathetic fibres form?
Paravertebral chain or pre-vertebral ganglia.
Parasympathetic pre and postganglionic neurotransmitters
Preganglionic = ACh acting via nicotinic receptors Postganglionic = ACh acting via muscarinic receptors
Where are parasympathetic fibres found?
Found in walls of effector organ or near branches of CNV.
Where are parasympathetic nuclei found and what do they command?
High brain structures. These command brainstem/spinal cord systems. Then to the wall of the effector organ and then to the effector organ.
Autonomic innervation of organs
- most have dual innervation from the sympathetic and parasympathetic and have reciprocal actions
- autonomic tone is determined by the balance of outputs of SNS and PNS
- sweat glands receive sympathetic drive only
Where do autonomic fibres originate from?
Cranial-sacral sources and thoraco-lumbar sources
Describe the autonomic fibres originating from cranial-sacral sources
- parasympathetic in function
- cell bodies/somata found in specific named cranial nuclei and S2,3,4 segments of the spinal cord
- axons of cranial nuclei reach periphery by hitch-hiking on fibres of cranial nerves III, VII, IX, X
Describe autonomic fibres originating from thoraco-lumbar sources
- sympathetic in function
- all neural segments of spinal cord between T1 and L2
What might lesions of the CNS cause?
Imbalances of autonomic outflow to visceral organs
Unbalanced autonomic outflow leading to disturbed autonomic reflexes
Death if not managed expertly
Output of CNIII, CNVII, IX
- head region only
- output of pre-ganglionic neurones terminate on discrete ganglia which are in the head region
- these ganglia occur in relation to the branches of the trigeminal nerve CNV
Output of CNX
- distribution to rest of body - visceral organs excluding the head region, and some head region
- cranial nerve course: specific cranial nuclei including vagal nuclei
- spinal nerve source: S2-S4
- pre-ganglionic neurones are found in either dorsal vagal motor nucleus or spinal segmental nerves of S2-S4 segments
Where does all sympathetic outflow originate from?
Thoracic level of the spinal cord. T1-L2.
What does the dorsal horn do?
Largely involved in sensory processing of information in the spinal cord - SOMATIC NOT AUTONOMIC
What does the ventral horn do?
Largely contains cell bodies of commands or actions which will lead to effector organs - SOMATIC NOT AUTONOMIC
Where is lateral horn found and what is it?
In thoracic and lumbar segments
In the grey matter produced by collections of cell bodies or preganglionic sympathetic neurones
Seen in S2-S4
Layout of sympathetic pre-ganglionic neurones
- all PNS outflow from CNS to peripheral target is entirely spinal
- T1-L2/3 innervates almost all organs of the body
- axons of all pre-ganglionic neurones either: terminate immediately in the paravertebral sympathetic chain of ganglia (sympathetic trunk) OR pass through it
What are the 3 possible modes of termination of sympathetic pre-ganglionic neurones?
White rami communicans, gray rami communicans, splanchnic nerves
Effector organs of the ANS
Muscles that generate their own electrical activity - smooth muscles and cardiac muscles
Secretory glands
