Lecture 17- Autonomic Nervous System Flashcards
What does the autonomic nervous system do?
- Perform sub-conscious functions to help maintain a constant internal environment (homeostasis), so is continually active
- Modulate function of various organs in response to external stimuli
What types of neurons is the autonomic nervous system made of?
Collection of central and peripheral neurons, with peripheral
neurons mostly organized into ganglia
What are the broad subdivisions of the autonomic nervous system?
- Sympathetic (fight or flight)
- Parasympathetic (rest and digest)
- Enteric (located within the wall of the GI tract)
What does the autonomic nervous system receive input from and what does it output to?
- Receives input from somatic, visceral, & special senses, and endocrine system
- Delivers output to autonomic motor and endocrine system
How many motor neurons does the output (sympathetic and parasympathetic) of the autonomic nervous system have and what are these called?
2 neurons:
-Preganglionic neuron cell body in CNS, postganglionic neuron in
peripheral ganglia
-Postganglionics synapse on target organs (eg cardiac & smooth muscle & glands)
Summarize the sympathetic output….
- Preganglionic neurons in thoracic & upper lumbar spinal cord
- Postganglionic neurons in paravertebral (“sympathetic chain”) or prevertebral ganglia (Celiac & mesenteric ganglia in abdomen)
- Because sympathetic ganglia are (mostly) remote from target, symp. postganglionic neurons have relatively long axons (short then long)
- Use acetylcholine at the preganglionic synapse and noradrenaline at the post ganglionic synapse.
What are the actions of the sympathetic output?
Typically prepares the body for action eg. Incr blood pressure, incr heart rate, decr GI activity, incr. blood flow to lungs & muscles etc
Do preganglionic neurons in the sympathetic branch of the autonomic nervous system project to the same side or different side? What is the exception to the rule?
Most preganglionic project to ganglia on same side of body & control function ipsilaterally (not intestines)
What’s special about the adrenal medulla in the sympathetic division of the autonomic nervous system?
Adrenal medulla directly innervated by preganglionic fibres, target cells (chromaffin cells) have no axon & release their neurotransmitter directly into bloodstream
Summarize the parasympathetic division of the autonomic nervous system…
-Preganglionic neurons in cranial nerve nuclei in brainstem, and
sacral spinal cord
-Postganglionic neurons in cranial ganglia (ciliary, submandibular, otic ganglia) and in ganglia in or near visceral organs
-Because parasymp ganglia are near target, postganglionic axons are short (long then short)
-Acetylcholine at both preganglionic synapse and postsynaptic synapse
What are the actions of the parasympathetic division of the nervous system?
Activation balances & opposes actions of symp system (eg decr. heart rate, incr activity of digestive tract, salivation)
Contrast distribution of the sympathetic and parasympathetic divisions….
- Sympathetic: Widely distributed: salivary glands, eyes, skin, viscera, smooth & cardiac muscles
- Parasympathetic: Distributed less widely than symp. Many axons carried in vagus nerve
What neurotransmitter is released by all preganglionic autonomic neurons?
AcetylCholine
How does the receptor type for acetylcholine differ and different parts of the autonomic nervous system/ different branches?
-Nicotinic ACh receptors (nAChR) in peripheral ganglia and adrenal
medulla
-Parasympathetic postganglionic neurons release ACh onto Muscarinic AChR
What receptor is used by the sympathetic nervous system due to release of noradrenaline by postganglionic neurons?
Sympathetic postganglionics release Noradrenaline onto adrenergic
receptors (several receptor subtypes, capable of triggering opposing actions)
How do nicotinic acetylcholine receptors and muscarinic acetylcholine receptors differ? i.e what type of receptor is each?
Nicotinic= ion channel Muscarinic= G-protein receptor (trigger downstream effects)
Explain what happens when beta adrenergic receptors are stimulated? How does this differ according to type?
- Beta receptor activated when noradrenaline/epinephrine binds. This activates a G protein
- The G protein causes adenylyl cyclase to convert ATP to cyclic AMP
- If beta 1 effect is cardiac muscle stimulation and increased tissue metabolism
- If beta 2 effect is the relaxation of smooth muscle in the respiratory passages and in the blood vessels of skeletal muscle
- If beta 3 effect is release of fatty acids and adipose tissue for metabolic use in other tissues
Why does ANS trigger a variety of functions?
As a consequence of different transmitter/ receptor combinations
What is the result of norprenphrine interaction with an alpha receptor? How does this differ under different receptor types?
- G protein is activated
- If a1 receptor then secondary messengers are activated and there is the release of calcium from the ER leading to smooth muscle contraction and gland cell secretion
- If its an a2 receptor then reduced levels of cAMP is the result and there is the inhibition of the cell.
What is the main CNS center invovled in autonomic control?
The hypothalamus= coordinates sensory information and then output (not at level of consciousness usually)
What are long reflexes?
- Autonomic nervous system makes use of them
- Goes within the spinal chord but not above
- Involves interneuron
- Organization similar to somatic reflexes
What is the enteric nervous system + its role?
- Can operate independently of symp & parasymp, but is typically modulated by them
- Has own network of sympathetic and parasympathetic fibres (embedded in layers of GI tract)
- Generates GI activity patterns (peristalsis, segmentation) to propel and mix food thru the GIT
- Regulates secretion of GI hormones (eg gastrin, secretin)
What receptors/ transmitters does the enteric nervous system make use of? (Give some examples)
Multiple transmitters & receptors (eg. ACh, VIP, 5-HT, substance P)
What are the roles of the different plexus’ in the enteritic nervous system?
- Submucosal plexus: has sensory & motor neurons, innervates mucosal epithelium & muscle
- Myenteric plexus: includes sensory chemoreceptors & mechanoreceptors and drives GI smooth muscle
What type of reflexes does the enteric nervous system make use of?
-”short reflexes”: involves ENS sensory & motor neurons whose
cell bodies are in peripheral structure (eg intestine)
- Used in simple, localized reflex actions
- Allow ENS to operate independently of CNS
