ANS Revision Flashcards
In the autonomic nervous system (ANS), nerve fibers that connect the central nervous system to ganglia are known as ___?
Preganglionic fibres
All preganglionic fibres of the ANS are cholinergic. What 2 features does this mean they have?
- They use acetylcholine as their neurotransmitter
- They are myelinated for faster transmission
Differences between sympathetic and parasympatheic preganglionic fibers regarding a) length b) number of synapses
a) sympathetic preganglionic fibers tend to be shorter than parasympathetic fibers
b) sympathetic fibers tend to form more synapses than parasympathetic fibers
The parasympathetic division (craniosacral outflow) consists of cell bodies from one of two locations. What are these?
- Brainstem (cranial nerves III, IV, IX and X)
- Sarcal spinal cord (S2, S3 and S4)
Location of cell bodies of the sympathetic divison (thoracolumbar outflow)? What type of cell bodies are these?
- In the lateral horn of the spinal cord (intermediolateral cell columns) from T1 to L2.
- These cell bodies are GVE (general visceral efferent) neurons and are the preganglionic neurons
Define ‘cholinergic’
Pertaining to, activated by, producing, or having the same function as acetylcholine
Define ‘postsynaptic neuron’
The nerve cell that bears receptors for neurotransmitters released into the synaptic cleft by the presynaptic neuron.
Define ‘preganglionic fibre’
In the autonomic nervous system, fibers from the CNS to the ganglion are known as preganglionic fibers.
Define ‘ganglion’
A cluster of interconnecting nerve cells outside the brain.
Define ‘preganglionic neuron’
The nerve fibers that supply a ganglion.
What do all preganglionic fibres of the ANS use as their neurotransmitter?
Acetylcholine
Are all preganglionic fibres of the ANS myelinated or unmyelinated?
Myelinated
How many neurons are involved in the efferent pathways of the ANS?
2; the preganglionic neuron must first cross a synapse onto a postganglionic neuron before innervating the target organ
Why do sympathetic preganglionic fibers tend to be shorter than parasympathetic preganglionic fibers?
Because sympathetic ganglia are often closer to the spinal cord while parasympathetic preganglionic fibers tend to project to and synapse with the postganglionic fiber close to the target organ.
Spinal cord exit point of sympathetic division of ANS vs parasympathetic division?
SNS: thoracolumbar outflow (T1-L2)
PSNS: craniosacral outflow (CN III, VII, IX, X, S2-S4)
There are several locations where preganglionic neurons of the sympathetic NS create synapses with their postganglionic neurons. What are the 3 main locations?
- The paravertebral ganglia of the sympathetic chain –> these run either side of the vertebral bodies;
- Cervical ganglia
- Thoracic ganglia
- Rostral lumbar ganglia
- Caudal lumbar ganglia
- Pelvic ganglia
- The prevertebral ganglia –> lie between the paravertebral ganglia and their target organ;
- Celiac ganglion
- Aorticorenal ganglion
- Superior mesenteric ganglion
- Inferior mesenteric ganglion
- The chromaffin cells of the adrenal medulla –> This is the one exception to the two-neuron pathway rule as they create a synapse directly onto the target cell bodies.
What are the 6 main locations where the preganglionic neurons synapse with the postganglionic neurons of the parasympathetic nervous system?
Parasympathetic ganglia of the head:
- Ciliary (CN III)
- Submandibular (CN VII)
- Pterygopalatine (CN VII).
- Otic (CN IX).
- In or near the wall of an organ innervated by the vagus (CN X)
- In or near the wall of an organ innervated by the sacral nerves (S2, S3, S4).
Define ‘divergence’ regarding neurons
the number of postsynaptic fibers a single preganglionic fiber creates a synapse with
Divergence factor of parasympathetic division vs in the sympathetic division
Para –> 1:4
Symp –> 1:20
What is a dorsal root ganglion?
A nodule on a dorsal root of the spine that contains the cell bodies of nerve cells that carry signals from sensory organs to the appropriate integration center.
Which division of the ANS is responsible for the fight-or-flight response?
Sympathetic - sympathetic ganglia deliver information to the body about stress and impending danger,
Where are sympathetic ganglia located?
located close to and on either side of the spinal cord in long chains
What are the axons of dorsal root ganglion neurons known as?
Afferents
In the PNS, what do ‘afferents’ refer to?
axons that relay sensory information into the central nervous system (i.e., the brain and the spinal cord)
Define ‘sympathetic ganglion’
The ganglia of the sympathetic nervous system. They deliver information to the body about stress and impending danger, and are responsible for the familiar fight-or-flight response.
Define ‘parasympathetic ganglion’
The autonomic ganglia of the parasympathetic nervous system. Most are small terminal ganglia or intramural ganglia, so named because they lie near or within (respectively) the organs they innervate.
What are ‘autonomic ganglia’
- Can be classified as either sympathetic ganglia and parasympathetic ganglia
- Clusters of neuron cell bodies that transmit signals from the periphery to the integration centers in the CNS/from the CNS to the periphery \
I.e. They are essentially a junction between autonomic nerves originating from the CNS and autonomic nerves innervating their target organs in the periphery.
Where do the dorsal root ganglia develop from in the embryo?
From neural crest cells, NOT neural tube –> can be regarded as gray matter of the spinal cord that became translocated to the periphery
Is the ciliary ganglion sympathetic or parasympathetic?
Parasympathetic
Function of ciliary ganglion?
Involved in pupil constriction and accommodation
What are the 4 parasympathetic ganglia of the head and neck?
- Ciliary
- Pterygopalatine
- Otic
- Submandibular
What type of neurons are dorsal root ganglion neurons?
Pseudo-unipolar –> they have an axon with two branches that act as a single axon; a distal process and a proximal process
How does an action potential pass along a dorsal root ganglion neuron?
Unlike the majority of neurons found in the CNS, an action potential in a dorsal root ganglion neuron may initiate in the distal process in the periphery, bypass the cell body, and continue to propagate along the proximal process until reaching the synaptic terminal in the dorsal horn of the spinal cord
The distal section of the axon of the dorsal root ganglion neuron may be 1 of 2 types. What are these 2 types?
- Bare nerve ending
- Encapsulated by a structure that helps relay specific information to a nerve.
The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors. What are these activated by?
mechanical, thermal, chemical, and noxious stimuli
A Meissner’s corpuscle or Pacinian corpuscle may encapsulate the dorsal root ganglion nerve ending. What are these sensitive to?
Mechanical stimulation, such as stroking or vibration, respectively
What is a neuroblastoma?
A cancer that develops from immature nerve cells found in several areas of the body
Which tissue do neuroblastoma tumors arise from?
Sympathetic ganglia
What are the bilateral symmetric sympathetic chain ganglia also called?
Paravertebral ganglia
Where are paravertebral ganglia located?
Located just ventral and lateral to the spinal cord. The chain extends from the upper neck down to the coccyx (forming the unpaired coccygeal ganglion).
Regarding the paravertebral sympathetic ganglia;
a) where do the preganglionic nerves from the spinal cord create a synapse?
b) where do the postganglionic fibres extend to?
a) create a synapse end at one of the chain ganglia
b) extends to an effector (typically a visceral organ in the thoracic cavity)
How many pairs of paravertebral ganglia are there?
There are usually 21 or 23 pairs of these ganglia: three in the cervical region, 12 in the thoracic region, four in the lumbar region, four in the sacral region and a single, unpaired ganglion lying in front of the coccyx called the ganglion impar.
What are pervertebral ganglia also called?
Collateral ganglia
Which nerves do the prevertebral ganglia receive input from?
Receive input from the splanchnic nerves and innervate organs of the abdominal and pelvic region.
What are the 4 main prevertebral ganglia?
- celiac ganglia
- aortic–renal ganglia
- superior mesenteric ganglia
- inferior mesenteric ganglia.
Most parasympathetic ganglia are small terminal ganglia or intramural ganglia, so named because they lie near or within (respectively) the organs they innervate. What are the 4 exceptions to this?
The four paired parasympathetic ganglia of the head and neck; ciliary, pterygopalatine, otic, submandibular
Describe the 2 neuron pathway of efferent parasympathetic nerves
Preganglionic:
- Its cell body sits in the CNS
- Its axon usually extends to a ganglion somewhere else in the body, where it synapses with the dendrites of the second neuron in the chain.
- Postganglion:*
- The axons extend from the CNS into a ganglion that is either very close to or embedded in their target organ.
In the autonomic nervous system, fibers from the ganglion to the effector organ are called ___?
Postganglionic fibres
Postganglionic fibers in the sympathetic division are adrenergic. What does this mean?
Use noradrenaline as their neurotransmitter
Compare the postganglionic fibres of the SNS and PSNS
SNS:
- Adrenergic
- Noradrenaline as neurotransmitter
PSNS:
- Cholinergic
- Acetylcholine as neurotransmitter
Postganglionic fibers in the sympathetic division are adrenergic. What is the one exception to this?
The postganglionic neurons of sweat glands
What neurotransmitter do the postganglionic neurons of sweat glands release? Why?
Release acetylcholine for the activation of muscarinic receptors.
What are chromaffin cells of the adrenal medulla analogous to?
Post-ganglionic neurons (the adrenal medulla develops in tandem with the sympathetic nervous system and acts as a modified sympathetic ganglion)
In the sympathic nervous system, presynaptic nerves’ axons terminate in which 3 locations?
- Prevertebral ganglia
- Paravertebral ganglia
- Adrenal medulla
Define adrenergic
Containing or releasing adrenaline.
At the synapses within the ganglia, the preganglionic neurons of the SNS release what? Onto what receptors?
Release acetylcholine, a neurotransmitter that activates nicotinic acetylcholine receptors on postganglionic neurons.
In response to ACh, what do postganglionic neurons of the SNS release? What receptors does this activate on peripheral target tissues?
Release noradrenaline –> activates adrenergic receptors on the peripheral target tissues. The activation of target tissue receptors causes the effects associated with the sympathetic system.
In response to ACh, postganglionic neurons of the SNS release noradrenaline. What are the 2 exceptions to this?
- The postganglionic neurons of sweat glands
- The chromaffin cells of the adrenal medulla
What do the postganglionic neurons of sweat glands release?
acetylcholine for the activation of muscarinic receptors
Within the adrenal medulla (an endocrine gland), the pre-ganglionic neurons create synapses with chromaffin cells and stimulate the chromaffin cells to release what?
Adrenaline and noradrenaline directly into the blood
Whether synapsing in them or not, all presynaptic axons of the SNS enter the paravertebral ganglion. At what level do they enter?
The axon enters the paravertebral ganglion at the level of its originating spinal nerve.
After the presynaptic nerve axon of the SNS enters the paravertebral ganglion, what are its 4 options?
- create a synapse in this ganglion
- ascend to a more superior paravertebral ganglion and synapse there
- descend to a more inferior paravertebral ganglion and synapse there
- pass through to a prevertebral ganglion and synapse there
Why are presynaptic neurons of the SNS generally much shorter than their postsynaptic counterparts?
Because paravertebral and prevertebral ganglia are relatively close to the spinal cord, presynaptic neurons are generally much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.
In the cranium, preganglionic fibers of the parasympathetic NS (cranial nerves III, VII, and IX) usually arise from specific nuclei in the CNS. Where do they create a synapse?
Create a synapse at one of four parasympathetic ganglia of the head: ciliary, pterygopalatine, otic, or submandibular.
From these four parasympathetic ganglia of the head, how do the the postsynaptic fibers complete their journey to target tissues?
Via cranial nerve V (trigeminal)
Which parasympathetic cranial nerve does NOT participate in the parasympathetic ganglia of the head? Why?
Vagus nerve (CN X) –> as most of its fibers are destined for a broad array of ganglia on or near the thoracic viscera (esophagus, trachea, heart, lungs) and the abdominal viscera (stomach, pancreas, liver, kidneys).
Where do the pelvic splanchnic efferent preganglionic nerve cell bodies reside?
In the lateral grey horn of the spinal cord at the S2-S4 spinal levels.
Where do the pelvic splanchnic efferent preganglionic nerve axons synapse?
Their axons continue away from the CNS to synapse at an autonomic ganglion close to the organ of innervation.
How do synapses between pre- and post-ganglionic efferent nerves differ between SNS and PSNS?
SNS: synapses between pre- and post-ganglionic efferent nerves in general occur at ganglia that are farther away from the target organ.
PSNS: synapse at an autonomic ganglion close to the organ of innervation
What 2 types of receptors can ACh act on?
- muscarinic cholinergic receptors
- nicotinic cholinergic receptors
When stimulated, the parasympathetic preganglionic nerve releases what? What does this act on?
releases ACh at the ganglion, which acts on the nicotinic receptors of the postganglionic neurons
When stimulated, what does the parasympathetic postganglionic fibre release? What does this act on?
releases ACh to stimulate the muscarinic receptors of the target organ.
Location of muscarinic vs nicotinic receptors?
Muscarinic receptors predominate at higher levels of the central nervous system, while nicotinic receptors, which are much faster acting, are more prevalent at neurons of the spinal cord and at neuromuscular junctions in skeletal muscle.
How does an autonomic plexus differ from an autonomic ganglion?
Ganglion: cluster of nerve cell bodies, either sympathetic or parasympathetic
Plexus: formed from sympathetic and parasympathetic fibers that innervate and regulate the overall activity of visceral organs
What are the 5 autonomic plexuses?
- Cardiac plexus
- Pulmonary plexus
- Oesophageal plexus
- Abdonimal aortic plexus
- Superior and inferior hypogastric plexuses
What are autonomic plexuses formed from?
Autonomic plexuses are formed from sympathetic postganglionic axons, parasympathetic preganglionic axons, and some visceral sensory axons.
What do autonomic plexuses provide?
Plexuses provide a complex innervation pattern to the target organs, since most organs are innervated by both divisions of the autonomic nervous system.
What fibres form the pulmonary plexus?
The pulmonary plexus is an autonomic plexus formed from pulmonary branches of vagus nerve and the sympathetic trunk.
What type of parasympathetic fibres form autonomic plexuses? Sympathetic fibres? Visceral fibres?
Parasympathetic –> preganglionic
Sympathetic –> postganglionic
Visceral –> sensory
Do the different fibres (e.g. para, symp, visceral) of the autonomic plexuses interact or synpase together?
The nerves in the each plexus are close to each other but typically do not interact or synpase together.
What is the cardiac plexus?
The cardiac plexus is an autonomic plexus of nerves situated at the base of the heart that innervates the heart.
Each parasympathetic ganglion has 3 roots. What are these?
- a motor root
- a sympathetic root
- a sensory root
What is the ‘lacrimal gland’
One of a pair almond-shaped glands, one for each eye, that secrete the aqueous layer of the tear film.
How does a sympathetic fibre pass through a parasympathetic autonomic ganglion?
Postsynaptic sympathetic fibers that traverse the ganglion without crossing a synapse.
Describe the sympathetic root in the parasympathetic ganglion
This carries postsynaptic sympathetic fibers that traverse the ganglion without crossing a synapse.
Describe the motor root of the parasympathetic ganglion
This carries presynaptic parasympathetic nerve fibers that terminate in the ganglion and create synapses for the postsynaptic fibers to travel to their target organs.
Describe the sensory root of the parasympathetic ganglion
The proximal end of a dorsal afferent nerve that is attached to the spinal cord.
Most parasympathetic ganglia are small terminal ganglia or intramural ganglia, so named because they lie near or within (respectively) the organs they innervate.
What are the exceptions to this?
The exceptions are the four paired parasympathetic ganglia of the head and neck.
What parasympathetic innervation does the ciliary ganglion supply?
spincter pupillae, ciliary muscle
What parasympathetic innervation does the pterygopalatine ganglion supply?
lacrimal gland, glands of nasal cavity
What parasympathetic innervation does the submandibular ganglion supply?
submandibular and sublingual glands
What parasympathetic innervation does the otic ganglion supply?
parotid
Each parasympathetic ganglia of the head has three roots entering the ganglion (motor, sympathetic, and sensory roots) and a variable number of exiting branches. Describe these 3 roots
- The motor root carries presynaptic parasympathetic nerve fibers (general visceral efferent fibers) that terminate in the ganglion by creating a synapse for the postsynaptic fibers traveling to target organs.
- The sympathetic root carries postsynaptic sympathetic fibers (general visceral efferent fibers) that traverse the ganglion without creating a synapse.
- The sensory root carries general sensory fibers (general somatic afferent fibers) that also do not create a synapse in the ganglion.
What is a reflex arc? What are the 2 types?
A neural pathway that controls an action reflex. There are two types of reflex arcs:
- the autonomic reflex arc that affects the inner organs
- the somatic reflex arc that affects muscles
Define somatic
Part of, or relating to, the body of an organism.
Within the brain, where is the ANS located?
In the medulla oblongata
What are the major ANS functions of the medulla?
respiration (the respiratory control center, or RCC), cardiac regulation (the cardiac control center, or CCC), vasomotor activity (the vasomotor center or VMC), and certain reflex actions (such as coughing, sneezing, vomiting and swallowing).
