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