lecture 12 Flashcards
the motor subdivisions of the PNS are:
somatic (voluntary) and autonomic (involuntary)
what do the motor subdivisions of the PNS innervate?
smooth muscle, cardiac muscle, glands
the somatic nervous system has ___ neuron(s):
1
the autonomic nervous system has ___ neuron(s):
2
describe autonomic nervous system’s pathway for motor output
- one preganglionic and one postganglionic neuron (one is short and one is long)
- pre has its cell body in the CNS
- pre = B fibre (faster)
- pre synapses on ganglion
- post has its cell body outside the CNS
- post = C fibre (slower)
- post synapses on target tissue
what are the divisions of the autonomic nervous system?
sympathetic and parasympathetic
what is the origin of the sympathetic ns?
lateral gray horns of the sc segements T1-L2 (thoracolumbar division)
is the sympathetic ns widely distributed to many parts of the body or more limited?
widely distributed to many parts of the body (divergent)
why are the effects of the sympathetic ns widely spread?
- because one pregang fiber can synapse with many postgang fibers
- also medulla of adrenal gland releases sympthatheic NTs epinephrine and norepinephrine which travel through the blood across most of the body
generally, what is the sympathetic ns responsible for?
situations in which energy needs to be expended (fight or flight)
what is the origin of the parasympathetic ns?
brainstem and sc segements S2,3,4 (craniosacral division)
is the parasympathetic ns widely distributed to many parts of the body or more limited?
more limited in distribution to target organs (convergent)
why are the effects of the parasympathetic ns more limited?
- pregang fibers on only a few postgang neurons
- no comparable organ to the medulla of adrenal gland
generally, what is the parasympathetic ns responsible for?
enhances energy storage and conserves energy (rest and digest)
describe the sympathetic efferent pathway up to the ganglia
- myelinated pregang neurons from lateral horn leave the sc via the ventral nerve root
- pass through the spinal nerve and then leave via ramus to sympathetic trunk (paravertebral ganglia)
the preganglionic neuron has three options at the ganglia, what are they?
(1) synapse, then unmyelinated postgang neurons pass through the ramus to enter the spinal nerve and then onward to the target site
(2) pregang neurons can travel up or down the sympathetic trunk to synapse in another paravertebral ganglia, then postgang neurons pass through the ramus to enter the spinal nerve and then onward to target site
(3) pregang neurons can pass through the sympathetic trunk without synapsing, to form the splanchnic nerves
what are the splanchnic nerves?
- greater splanchnic
- lesser splanchnic
- least splanchnic
where is the greater splanchnic nerve?
T5-T9 thoracic ganglia
where is the lesser splanchnic nerve?
T10-T11 thoracic ganglia
where is the least splanchnic nerve?
(T12-L2 thoracic and lumbar ganglia)
describe the pathway and function of splanchnic nerves
these nerves synapse in prevertebral ganglia which then sends postgang neurons to abdominal and pelvic viscera
a few pregang fibers in the greater splanchnic nerve end directly on cells in the:
adrenal medulla
describe sympathetic preganglionic neurons
unmyelinated, shorter than postganglionic, and relatively slow comducting B fibers
describe the sympathetic afferent pathway
travels from viscera to the dorsal root ganglia
do sympathetic afferent fibers synapse along the way to the sc?
no
how do parasympathetic preganglionic neurons leave the brainstem?
through the nuclei of cranial nerves III, VII, IX and X
what is the preganglionic nucleus for CN III?
Edinger-Westphal nucleus
what is the preganglionic nucleus for CN VII?
superior salivatory and lacrimatory nuclei
what is the preganglionic nucleus for CN IX?
inferior salivatory nucleus
what is the preganglionic nucleus for CN X?
dorsal nucleus
how do parasympathetic preganglionic neurons leave the gray matter of the sc?
through sacral nerves 2, 3, 4, and the spalnchnic nerves
where parasympathetic preganglionic fibers synapse?
in ganglia close to viscera
what are the cranial parasympathetic ganglia?
- ciliary (CN III)
- pterygopalatine (CN VII)
- submandibular (CN VII)
- otic (CN IX)
what are the parasympathetic plexuses?
- cardiac and pulmonary (CN X)
- celiac (CN X)
- hypogastric (CN X)
what are the sacral parasympathetic ganglia?
pelvic splancnic nerves synapse in ganglia of the hypogastric plexus
describe the parasympathetic postganglionic neurons
short, unmyelinated, smaller than preganglionic and slower conducting C fibers
what do postganglionic neurons from CNs III, VII, and IX supply?
head
what do postganglionic neurons from CN X supply?
thorax and descending colon
what do postganglionic neurons from S2,3,4 supply?
terminal gut and pelvic vicsera (bladder/repro organs)
describe the parasympathetic afferent pathway
myelinated fibers travel from the vicera to their cell bodies located in the sensory ganglia of cranial nerves or in the dorsal root ganglia of the sacral spinal nerves
how are sympathetic postganglionic neurons activated? what are the receptors involved?
ach (nicotinic receptors)
how are parasympathetic postganglionic neurons activated? what are the receptors involved?
ach (nicotinic receptors)
what do sympathetic postganglionic neurons release? what are the receptors involved?
norepinephrine (a/b receptors)
what do parasympathetic postganglionic neurons release? what are the receptors involved?
ach (muscarinic receptors)
are there any exceptions to NT activation/release?
yes - sympathetic postganglionic neurons that end on cells of sweat glands release Ach (cholinergic receptors)
what are the levels of autonomic control?
- hypothalamus (regulation btwn two systems)
- pons, medulla (regulation of autonomic functions)
- cortex, limbic system (motor arises, sensory arrives)
compare neuron length for pre/postganglionic neurons in the sympathetic and parasympathetic ns’s
symp: short pre, long post
para: long pre, short post
