L16 Autonomic Nervous System Flashcards
Describe the divisions of the peripheral nervous system.
Peripheral NS: peripheral sensory NS + autonomic NS
Autonomic NS: sympathetic, parasympathetic and enteric NS
What is the overall function of the ANS?
Contributes to homeostasis, operates without our awareness, we have no conscious control over the ANS.
What is the function of the sympathetic NS?
- Fight or flight
- Prepares the body for active/stressful situations
- E.g. increases heart rate, dilates pupils and bronchioles, diverts blood flow from viscera towards striated muscle
What is the function of the parasympathetic NS?
- Rest and digest
- Passive, prepares body for maintenance/rest
- E.g. decreases heart rate, pupillary and bronchiolar constriction, blood diverted to viscera, increased gut motility
What is the function of the enteric NS?
- Self-contained, embedded in the lining of the gastrointestinal system
- Regulated gut motility and secretion of mucous and digestive enzymes
Describe the anatomy of the sympathetic NS.
- 2-neuron relay
- Pre-ganglionic sympathetic neurons with cell bodies in the spinal cord, post-ganglionic sympathetic neurons in the peripheral ganglion
- Post-ganglionic project axons to target tissues
Describe the preganglionic neurons of the sympathetic NS.
- Neurons found in a column in the intermediolateral horn of the spinal cord
- Short, lightly myelinated axons
- Realease acetylcholine as their neurotransmitter
- Make connections with postganglionic neurons in the sympathetic ganglia
Describe the postganglionic neurons of the sympathetic NS
- Found in the sympathetic ganglia
- Long, non-myelinated axons which project to target tissue, normally smooth muscle, cardiac muscle or glands
- 90% release noradrenaline
- 10% release acetylcholine
What are the sympathetic ganglia?
Paravertebral or prevertebral sympathetic ganglion.
3 main types of prevertebral ganglia: celiac, superior mesenteric, inferior mesenteric
Describe the anatomy of the parasympathetic NS.
- 2 neuron relay
- Preganglionic neurons are loacted in visceral efferent motor nuclei of cranial nerves, or in the sacral region of the spinal cord
- Postganglionic neurons found in ganglia close to target organs
Describe the preganglionic neurons of the parasympathetic NS.
- Either found in visceral efferent motor nuclei of cranial nerves or sacral region of spinal cord
- Long and lightly-myelinated axons
- Release acetylcholine
Describe the postganglionic neurons of the parasympathetic NS.
- Found in loose plexi embedded in target organs
- Short, non-myelinated axons
- Release acetylcholine
Describe the 3 routes of sympathetic outflow from the spinal cord.
- Preganglionic axons project through ventral root to white ramus, make synaptic contact with postganglionic neuron in 1st paravertebral sympathetic ganglion, postganglionic neuron joins the segmental spinal nerve
- Preganglionic neuron projects up or down the sympathetic chain, makes contact with postganlgionic neuron in paravertebral sympathetic ganglion at different level of spinal cord
- Preganglionic neuron passes straight through the paravertebral sympathetic chain and enter the splanchnic nerves where they make synaptic contact with a postganglionic neuron in the prevertebral sympathetic ganglia
Describe some of the actions of the sympathetic NS on target organs.
- Pupil dilation
- Increases heart rate
- Increases saliva viscosity
- Bronchodilation
- Inhibits digestion
- Anal sphincter contraction
- Stimulates release of adrenaline and noradrenaline from adrenal medulla
- Reduces kidney blood flow, increase water and sodium
- Bladder relaxation
- Vasoconstriction
- Increased sweating
- Stimulates orgasm, vaginal contraction
Describe some of the actions of the parasympathetic NS on target organs.
- Pupil constriction
- Reduced heart rate
- Secretion of saliva
- Bronchial constriction
- Increased peristaltic movement
- Secretion of insulin and digestive enzymes
- Bladder contraction
- Secretion of tears
