M2 Topic 8: Autonomic Nervous System Flashcards
(15 cards)
Autonomic nervous system (ANS)
Involuntary or unconscious
- Works with endocrine and behavioural state systems to maintain homeostasis
Composed of two divisions
- Sympathetic (fight-or-flight)
- Parasympathetic (rest-and-digest)
How does the CNS control the ANS?
Starts at hypothalamus and through to the brainstem (pons and medulla) where it initiates autonomic, endocrine and behavioural responses
Hypothalamus…
- Receives sensory info about body, activates hypothalamic neurons to control temps, thirst, hunger
- Activates neurons in pons to control need for urination, helps maintain respiration
- Activates medulla, critical in maintaining blood pressure and breathing
Sympathetic nervous system
Fight-or-flight
- Dilation of pupils
- Secretion of mucus & enzymes
- Increase of heart rate and contractility
- Relaxing of airways
- Inhibits digestion
- Decreases enzymes and insulin
- Increases renin secretion
- Relaxes bladder
- Induces ejaculation
- Stimulates contraction
Where do the sympathetic neurons in the spinal cord exit?
Exit via the spinal nerves along spinal cord from T1 to L2, covering 14 vertebrae in total
Peripheral ganglia
Parasympathetic/Sympathetic neurons synapse in ganglion before going to innervate target organs and glands
Sympathetic chain ganglia
Sympathetic ganglia linked together and running alongside spinal cord
- Nerve fibres exiting from one level of spinal cord can innervate organs associated with other levels
What can fibres do in the ganglia chain?
- Ascend the chain and synapse
- Synapse at the level of entry
- Pass through and synapse elsewhere
- Descent the chain and synapse
Parasympathetic nervous system
Rest-and-digest
- Pupil constricts
- Watery secretion of salivary glands
- Slow heart rate
- Constricts airways
- Increase bile secretion
- Increase motility and secretion
- Release enzymes and insulin
- Adrenal medulla secretes catecholamines
- Release of urine
- Induces erection
- Engorgement and secretions
Parasympathetic neurons
Mainly located in brainstem and exit CNS via cranial nerves = most important of which is Vagus (X)
- Innervation of the viscera mainly via Vagus (X)
- Innervation of the sex organs is via the sacral cord
Organisation of ANS pathways
- Preganglionic neurons
- Autonomic ganglion
- Postganglionic neurons
- Synapse
- Target tissue
What two neurotransmitters does the ANS use?
- Acetylcholine (ACh)
- Noradrenaline/Norepinephrine
Autonomic ganglion
Peripheral cluster of neuronal cell bodies (e.g. sympathetic chain ganglia)
Preganglionic neuron
Central neuron that projects to ganglion
- Arise before the ganglia (coming from the spinal cord)
Postganglionic neuron
Peripheral neuron that projects to target tissue (organ)
- Arise after the ganglia (fibres leaving the ganglia)
ANS pathway
- Preganglionic neurons (ALL sympathetic and parasympathetic) release ACh onto the autonomic ganglion receptors
- Postganglionic SYMPATHETIC neurons release noradrenaline on target tissue to synapse
- Postganglionic PARASYMPATHETIC neurons release ACh on target tissue to synapse
