L17 - autonomic nervous system Flashcards
somatic motor fibres
efferent fibres to skeletal muscles which leave via ventral root
somatic sensory fibres
afferent fibres from receptors to spinal cord which enter via dorsal root
how many segmental spinal nerves are there
31
autonomic motor
efferent fibres to small muscles, cardiac muscles or glands
autonomic sensory
afferent fibres from sensory receptors in an internal organ
where are autonomic fibres carried
within segmental spinal nerves T1-L2 and S2-S4 or specific cranial nerves
function of autonomic sensory neurones
- conduct sensory impulses from viscera to CNS
- tells CNS about state of organ
- responsible for referred pain
referred pain
pain sensations from visceral organs which are often perceived as regions of the body surface innervated by the same spinal nerves
how does refereed pain work (theory)
somatic afferent fibres from skin and visceral afferent fibres (autonomic sensory) follow the same pathway as they enter the CNS so the brain interprets information as if pain is coming from skin rather than the organ
location of preganglionic neurone
cell body in CNS
location of postganglionic neurones
cell body in PNS
sympathetic
fight or flight
parasympathetic
rest and digest
outflow in sympathetic NS
thoracolumbar (T1-L2)
outflow in parasympathetic NS
craniosacral
- brainstem (CN3, 7, 9, 10)
- S2-S4
organisation in sympathetic NS
highly organised in sympathetic chain
- paravertebral
- prevertebral / collateral ganglia
paravertebral meaning
chain is parallel to spinal cord
prevertebral meaning
lie outside the chain
organisation in the parasympathetic NS
ganglia are located near the effector organ
effect of sympathetic NS
widespread
effect of parasympathetic NS
localised
comparison of outflow in sympathetic NS and parasympathetic NS
sympathetic:
- thoracolumbar (T1-L2)
parasympathetic:
- craniosacral (brainstem and S2-S4)
comparison of organisation in sympathetic NS and parasympathetic NS
sympathetic:
- highly organised
parasympathetic:
- ganglia located near effector organ
comparison of effect in sympathetic NS and parasympathetic NS
sympathetic:
- widespread
parasympathetic:
- localised
neurotransmitter in the parasympathetic division
acetylcholine
length of axons in parasympathetic division
preganglionic neurones are long but postganglionic axons are short as are located near effector organ
route of parasympathetic division
- axons leave brainstem using CN3, 7, 9, 10 and S2-S4
- synapse in the ganglion
- Ach released by preganglionic neurones to stimulate postganglionic neurones
- sends axons towards target organ
main parasympathetic nerve of the viscera of the trunk
vagus nerve
CN10
route of vagus nerve in parasympathetic stimulation
- leaves from medulla oblongata
- descends into thorax and abdomen
- synapse near target organ
- proves parasympathetic supply to these organs
preganglionic neurotransmitter in sympathetic NS
acetylcholine
postganglionic neurotransmitter in sympathetic NS
noradrenaline (apart from sweat glands)
types of widespread effects in sympathetic nervous system
- neuronal divergence
- adrenal medulla
neuronal divergence
one preganglionic fibre can synapse with many postganglionic neurones
adrenal medulla in the widespread effect of sympathetic nervous system
- Some preganglionic fibres travel directly to the adrenal medulla (modified postganglionic) cells
- Do not synapse with any ganglion
- Cells of medulla are analogous to postganglionic cells
- Release norepinephrine and epinephrine into the bloodstream
where do sympathetic fibres run through
- sympathetic chain
- prevertebral / collateral ganglia
sympathetic trunk / chain
interconnected chain of autonomic ganglia located on either side of the entire vertebral column (paravertebral)
routes of sympathetic outflow
- synapse at level of entry - paravertebral ganglia
- pass through trunk without synapsing to synapse in collateral ganglia or adrenal medulla
- ascend or descend in the trunk to synapse with another ganglion
white rams communicans
- Contains myelinated preganglionic sympathetic fibres
- Only between T1-L2
gray rami communicant
- Contains unmyelinated postganglionic fibres
- All levels of the cord
rami communicantes
additional structures in the sympathetic division which are communicating branches
sympathetic effects in autonomic control of heart rate
- Preganglionic fibres leave cord from T2-4 levels of thoracic cord
- Find a postganglionic neuron in different levels of sympathetic chain
- Sympathetic chain travels towards the heart via cardiac plexus
- heart contraction is stimulated
- heart rate increases
sympathetic effects in autonomic control of respiratory volume
- Preganglionic fibres leave cord from T2-4 levels of thoracic cord
- Find a postganglionic neuron in different levels of sympathetic chain
- Sympathetic chain travels towards the lungs via the pulmonary plexus
- Short pre and long post ganglionic neurone
- dilation of bronchi stimulated
- increase oxygen to produce more energy
parasympathetic control on heart rate and respiratory volume
- Chief parasympathetic nerve to thoracic organs is vagus nerve which leaves from medulla oblongata (posterolateral sulcus)
- Associated parasympathetic nucleus in brainstem contains preganglionic cell bodies and axons leave via long vagus nerve and descend to the thorax to reach the target organs
- Synapse occurs here
- inhibits contraction to decrease heart rate
- constriction of bronchi to reduce air flow to lungs
glossopharyngeal afferent fibres
- carotid body and the carotid sinus are structures close to the bifurcation of the internal and external carotid arteries
- constantly monitor BP and oxygen levels
- fibres travel from glossopharyngeal nerve from medulla to give information to from brain about these levels
sympathetic control on defecation
- prevents rectum emptying
- collateral ganglion
- postganglionic fibres travel towards colon and rectum
- prevent peristalsis and emptying of rectum
parasympathetic control on defecation
- fibres leave via S2,3
- innervations induce peristalsis and emptying of rectum
- stimulated by stretch receptors in rectum which senses levels of distention by increases levels of stools
pudendal nerve
- Pudendal nerve is always inducing contraction of external anal sphincter, preventing defecation most of the time
- When we voluntary want to go to the toilet, there is a voluntary inhibition of the contraction of the external anal sphincter
why do infants not have control over their rectum
no pudendal nerve present
hypothalamus and ANS
hypothalamus exerts overall control on ANS
