Autonomic Nervous System (L2) Flashcards
What is the central nervous system?
A central processing center for integration, processing, and reactions occur. The response is conveyed by the peripheral nervous system.
What are sensory nerve fibers?
Afferent fibers; they bring information to the CNS.
What are motor nerve fibers?
Efferent fibers; they bring information from the CNS to the periphery to affect target organs. This conveys the command from the control center (CNS)
What are the 3 branches of the Autonomic Nervous System (ANS)?
Sympathetic
Parasympathetic
Enteric (gut brain; can further be modified by SNS and PSNS)
5 autonomic centers in the brain (that she mentioned)
Medulla*, pons*, hypothalamus*, amygdala, cortex
Medulla function within ANS
Respiratory and water control
Pons function within ANS
Respiratory and urinary control
**Hypothalamus function within ANS
Four F’s (fighting, fleeing, fucking, and feeding)
Known as the master gland
Amygdala function within ANS
Emotional center; we can have learned responses of fear
Does the ANS control skeletal, or smooth muscle?
Smooth muscle. Skeletal muscle is under somatic control (we can modulate it voluntarily).
Sympathetic nervous system purpose and location in body (cervical, thorax, lumbar, sacral, coccygial, some kind of combination?)
Thoracolumbar location
Excitatotry/ flight or flight division
Parasympathetic nervous system overarching role and location in body (ex. cervical, lumbar, thoracic, etc, some kind of combo?)
Craniosacral ; rest and digest;
Enteric nervous system (structure/location, function)
Large network of billions of neurons in the gut, that function as a “gut brain” to coordinate digestion. It can be controlled further by parasympathetic and sympathetic stimulation but is largely autonomous.
What is the overall goal of the autonomic nervous system, with regard to the body’s “balance” state?
The ANS’s goal is to maintain homeostasis, so changes made are meant to drive the body back toward that. Receptors receive a signal (ex. light, pain), and transmit it to the CNS for processing, and then a response is sent back out to modulate what cells are doing to compensate/respond.
Describe the two-neuron system
The two-neuron system is how our body acts as a relay, with regard to passing information from the CNS to the visceral organ systems. A pre-ganglionic neuron, whose dendritic end is in the CNS, will pass a signal through its white communicating ramus to synapse in a ganglion. It synapses with a post-ganglionic neuron (dendrite is in ganglion) that then reaches out through its gray communicating ramus to synapse with an organ elsewhere in the body.
Are neuronal synapses at visceral organs and smooth muscle clear defined synapses or are they more flimsy
They’re more flimsy and called en passant meaning in passing. The axon is filled with varicosities that deposit neurotransmitter. This is in contrast to neuronal or skeletal muscle junctions that are very defined.
Neurotransmitters released from ANS efferent fibers, pre-and-post ganglionic
NT released from ALL ANS efferent PRE-GANGLIONIC: Acetylcholine onto nicotinic receptors
NT released from SNS post-ganglionic: Epinephrine
NT released from PSNS post-ganglionic: Acetylcholine onto muscarinic receptors
Adrergic Neurotransmission
Norepinephrine is released from varicosities onto the target visceral organ where it can bind to adrenergic receptors. It is then going to be degraded by COMT (catechol-o-methyl-transferase) / MAO in mitochondria for NE that is just reuptaken. NE that is not degraded when taken up by presynaptic cell can then be re-packaged into vesicles of future signaling.
Fresh norepinephrine is derived from tyrosine
Cholinergic neurotransmission, and how can this be modulated by drugs?
Acetylcholine is released from the presynaptic cell, where it then binds to muscarinic acetylcholine receptors. Excess acetylcholine will be degraded by acetylcholine esterases. Choline will be taken up into the cell and used to generate new acetylcholine for future cycles.
This process can be blocked by atropine (muscarinic blocker). The process can be forced to continue by sarin gas (blocks acetylcholine esterases).
If you are trying to stimulate vasoconstriction (symapthetic) through SNS nerve activity, but you are also trying to vasodilate that same region (via vascular endothelial cells generating nitric oxide (NO)), what signal will win?
The local signal
How are SNS and PSNS distinct, with regard to ganglionic length?
In the SNS the ganglia is relatively close to the spinal cord, but in PSNS the ganglia are distant from the spinal cord, meaning there is a very short path from the post-ganglionic neuron to the target organ .
Do ALL SNS nerve fibers release norepinephrine?
No. Sweat glands are hit by acetylcholine to stimulate them.
Describe the SNS pathway to the adrenal gland
There is a pre-ganglionic neuron that synapses right on the adrenal gland. The cells in the adrenal gland will dump epinephrine / NE into the bloodstream directly, so there is no true post-ganglionic neuron in this system. This is good, because we want a fight/flight response to occur as quickly as possible and dumping epinephrine into the blood stream gets it through the systemic circulation quickly.
Baroreceptor reflex
Aortic arch senses blood pressure drop and sends signal though vagus nerve (Cranial nerve X); carotid sinus senses blood pressure spike and sends signal through glossopharangyeal nerve (Cranial nerve IX) via mechanoreceptor channels whose open status is altered by the change in pressure. This signal, when sent to the CNS (medulla oblongata) sends a signal back to parasympathetically to say “hey, maybe stop”. This involves M2 receptors on the heart. This then leads to decreased SNS activity on heart (b1) and vasculature (a1).
Intrinsic innervation of the gut
Myenteric and submucosal Plexi (locations are in the name)
Extrinsic innervation of the gut
PSNS and SNS (pelvic and vagal nerve; Celiac, superior and inferior mesenteric vertebral ganglion respectively)
Description of the intrinsic innervation of the gut
past the mucosal layer of the gut there is a layer of nerves (submucosal; meissner’s). This is between the mucosal and inner smooth muscle layer.
The two extrinsic most layers of muscle are a longitudinal layer (outermost) and a circular smooth muscle layer (second-outermost). between those is the myenteric (auerbach’s) plexus.
Peristaltic reflex
The bolus of food takes up space, so as it moves through the small intestine it causes distentions where it is. This leads to stretch receptors in the area being activated. Seritonin is going to be released to aid in the process. Behind the bolus (we call this upstream) there is going to be a release of Ach and substance P from these neurons to cause contraction of the circular smooth muscle layer, and also an inhibitory neuron will release VIP and NO to the longitudinal layer of smooth muscle. This will lead to overall contraction.
Downstream of the food bolus we have the opposite occuring. We have NO and VIP being released from a descending inhibitory neuron to relax the circular smooth muscle, and Ach and substance P will be released from a descending excitatory neuron to contract the longitudinal layer. This will overall increase the cavity and allow food to be pushed in that direction. The cycle will then repeat.
