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Organisation Of The Autonomic Nervous System Notes

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Organisation of the autonomic nervous system
-all of the peripherial autonomic nervous system derives from the neural crest cels
-as neural plate folds meet, the neural crest forms at the interface between neuroectoderm and ectoderm.
-first cells of the neural crest migrate away from neural tube and ectoderm to form the enteric nervous system
-next wave of neural crest cells migrate through the somitic mesoderm to form the segmental sympathetic chain ganglia
-outflow from the sympathetic chain ganglia is arranged segmentally, neural crest migrates through the rostral half of each somite. The caudal half has inhibitory molecules ephrins that prevent neural crest migration- forms segmental sympathetic chain ganglia
-parasympathetic ganglia and the prevertebral sympathetic ganglia are neural crest derived.
-preganglionic fibres of the ANS are CNS neurons lie in the intermediate part of the spinal cord and are patterned by SHH signalling notochord.
-motor neurones come from CNS not from neural crest. Function of the ANS
-involuntary control of body functions maintains the body's homeostasis Symapthetic- fight/flight response Parasympathetic - rest/digest Enteric- Intrinisic nerves in the gut wall
-output from the CNS travels along 2 anatomically functionally distinct pathways
-somatic motor neurones that innervate striated skeletal muscle
-autonomic motor neurones- innervate smooth muscle, cardiac muscle, secretory epithelia and glands Organisation of the ANSArise in the CNS and innervate target tissue by a 2 synapse pathway. Preganglionic neurones have cell bodies that lie within the CNS and neurones found in coloumns of cells in the brainstem and spinal cord. Axons come out from the CNS and make synapses with post ganglionic neurones

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Post ganglionic neurones- found in the peripheral ganglia and the axons from these neurones project to their targets.

Both the sympathetic and parasympathetic are independent to each other and work synergistically to regulate visceral activity
-increase output from the sympathetic nervous system occurs under stress/anxiety/fear/excitement/physical
-increase output from the parasympathetic nervous system occurs during sedentary activity such as eating/ vegetative behaviour
-the enteric nervous system- system of afferent neurons, interneurones, motor neurones that forms network of neurones called plexuses. These surround the GI tract and are controlled by the CNS through sympathetic and parasympathetic fibres Organisation of the sympathetic chain ganglia
-Preganglionic neurones-cell bodies of preganglionic sympathetic motor neurones are in the thoracic and upper lumbar spinal cord. T1-L3.
-Axons leave through the ventral roots along with the axons of the somatic motor neurones. After they enter the spinal nerve, Sympathetic motor neurones diverge from the somatic motor neurones and enter the white rami communicantes (preganglionic motor neurones are myelinated)
-paravertebral ganglia
-axons from the preganglionic neurones enter the sympathetic paravertebral ganglion through a white ramus. This ganglia lies adjacent to the vertebral coloumn and extend from the the upper part of the neck to the coccyx. One ganglion is positioned at level of each spinal root, some adjacent ganglia are fused
-superior cervical ganglion (fusion of C1-C4) supplies the head, neck- dilates the pupil, elevates the eyelid, innervates cilary body, stimulates salivation
-middle cervical ganglion (fusion of C5-C6), Stellate ganglia (C7,C8,T1)- innervate heart, lungs, bronchi
-throacic chain ganglia innervates all other organs in a segmental fashion
-after entering the paravertebral ganglia the preganglionic sympathetic axon has three fates
-synapse within that segmental paravertebral ganglion

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