ans Flashcards
Innervates skin (sensory) and skeletal mm fibers (motor)
Peripheral distribution is done directly by spinal and cranial nerves and (usually) a single neuron connects the CNS with the organ
This part is mainly involved w/ receiving impulses from external environments and responding accordingly
SOMATIC PART
Somatic connects to target via one neuron
- Deals with Collecting Information from the outside world: Pain, touch temperature vibration.. (receptors are primarily housed in the skin)
Source for sensory inputs is the skin from the outside world.
Creates motor impulses which will be conveyed to your skeletal muscles.
When the somatic nervous system reaches it’s target it does that only through one single neuron.
Only one neuron connects the system to the target. Intrinsic muscles of the hand (thenar Muscles)
Each Thenar muscle receive motor impulses through the axon of a motor neuron.
Which sit at the anterior horn of the spinal cord. At the level of C8 Spinal Segment.
There is a motor neuron. The axon goes all the way to the thenar muscles. There is no interruption in this axon. One single neuron is controlling that musc
Internal organ systems, smooth/cardiac mm fibers,glandular tissues (sweat, mammary, salivary)
Basically involved in receiving information from internal milieu (environment) and initiating appropriate response (homeostasis)
Peripheral distribution of this part is done by autonomic (sympathetic and parasympathetic) nerves and there are 2 neurons between CNS and the target organ
After travelling to CNS, a motor impulse is sent out
VISCERAL (AUTONOMIC) PART
Connects to target via second neuron after the ganglion
innervates internal organ systems, smooth muscles, and glandular tissues.
Analyzes information and initiates motor impulses. Directed towards three tissues: Smooth muscle Tissue, Cardiac Tissue, and glandular tissue.
A neuron which ONLY sits in the lateral horn L2,-L4 (s2-s4)of the spinal cord. These axons will never reach to the target organ directly.
Ex. An autonomic neuron sits on the lateral horn of the spinal cord at the level of L2 Segment. This gives rise to an axon that tries to reach to the bladder.. But it will never directly reach to the bladder because it has to stop at a point known as the ganglia. It passes it to a 2nd neuron which then can pass to the bladder.
So ANS/VNS - Indirectly reaches its way to the destination with two neurons.. These points of connection are known as ganglions. There is only ever one extra ganglion.
It is hard to find any visceral nerves that are not associated with ganglion.
2 TYPES OF CLASSIFICATIONS of ans
STRUCTURAL:
CNS (central)
PNS (peripheral)
FUNCTIONAL:
Somatic
autonomic
Why does the ANS need two neurons?
- Less time needed to check to ensure that the nerve impulse.
ANS SUBDIVISION
SYMPATHETIC DIVISION:
Fight or flight
Catabolic
Mobilize energy storage
PARASYMPATHETIC DIVISION:
Rest and repose
Anabolic
Growth, tissue repair/maintenance
Sympathetic vs. Parasympathetic
Differ in 2 major ways: Groups of ganglia on either side of the column (paravertebral ganglia)
Origin of nerve cell bodies:
thoracic + lumbar = sympathetic
sacral + cranial = parasympathetic
1st synapse (connection with 2nd nerve):
Close to CNS = sympathetic
Close to the target organ = parasympathetic
Black dots in spinal cord is the center for sympathetic nervous system in lateral horn
sits in T1-L2 spinal segments
Black dots in brainstem and lateral horn of spinal cord @ level of S2-S4 segments are
parasympathetic
First exit spinal cord as presynaptic or pre-ganglionic fibers reach para-vertebral ganglion : leads to head and neck, upper limb, thorax, and lower limb become postganglionic or postsynaptic fibers after synapsing
Sometimes can bypass paravertebral ganglion and synapse @ pre-vertebral ganglion (in front of vertebral column)
Only in abdomen
Sphlanchnicus = Intestine
are in 2 long chains lateral to the spinal cord (3 in cervical, 5 in sacral, 12 in thoracic, 5 in lumbar and 1 in coccygeal – join together by coccyx
Paravertebral ganglion
t/f/
If synapse in pre-vertebral ganglion chances are zero that they will supply anything other than abdominopelvic
true
Pre-ganglionic fibers use dorsal rami
Sympathetic Distribution
Sympathetic fibers arising from spinal cord at the level of T1 – L2 may have one of the following faiths:
- They may enter the para-vertebral ganglia, via the white ramus communicans, and after synapsing with second neuron re-enters the spinal nerve, via the gray ramus communicans. Then they will be distributed by the spinal nerves to the periphery (eg. sweat gland) or may directly target the thoracic viscera (eg. Heart). In this latter case, the postganglionic fibers do not return to the spinal nerves.
- Pre-ganglionic sympathetic nerve fibers may enter the para-vertebral ganglia and then ascend or descend to other levels to synapse with second neuron and finally re-enter the spinal nerves at higher or lower levels to be distributed by them. They may also synapse at the same level but then the post-ganglionic fiber ascends or descends to other levels and enters the spinal nerves.
- Some of the pre-ganglionic sympathetic fibers enter the para-vertebral ganglia to only by pass them to get to the pre-vertebral ganglia (in front of abdominal aorta).
These fibers are known as splanchnic nerves. greater (T5 – T9) lesser (T10 – T11) least (T12)lumbar (L1 – L2) and sacral (L2) splanchnics.
These nerves synapse in pre-vertebral ganglia, and the post-ganglionic fibers will supply the abdominal / pelvic viscera.
Sympathetic Distribution
Fibers arising from spinal cord @ T1-T2 level can have one of the following faiths:
- Pre-Ganglionic nerve fibres enter para-vertebral ganglia via white ramus communicans (bridge between spinal nerve and para-vertebral ganglia) and after synapsing w/ second neuron, re-enters the spinal n (via gray ramus communicans).
- Then will be distributed by spinal n’s to periphery (eg. Sweat gland, erector pili muscles) or may directly target thoracic viscera (eg. Heart).
- In the latter case, postganglionic fibers do not return to spinal nerves - Pre-ganglionic sympathetic fibers may enter para-vertebral ganglia and then ascend or descend to other levels (sympathetic chain) to synapse w/ second neuron.
- Finally re-enter the spinal nerves @ higher or lower levels to be distributed by them
- May also synapse @ same level but then post-ganglionic fiber ascends or descends to other levels & enters the spinal nerves - Some of pre-ganglionic sympathetic fibers enter para-vertebral ganglia (chain) to only bypass them to get to pre-vertebral ganglia (in front of abdominal aorta)
These fibers are known as splanchnic nerves: greater (T5-T9), lesser (T10-T11), least (T12), lumbar (L1-L2) & sacral (L2) splanchnic.
These nerves synapse in pre-vertebral ganglia, and the post-ganglionic fibers will supply the abdominal/pelvis viscera.
T1 to T4 - exit sympathetic chain and go directly supply heart, lung, esophagus.
- presynaptic sympathetic fibers which reach to abdominal viscera after synapsing in prevertebral ganglia
Splanchnic nerve
There are certain Nuclei that are classified as parasympathetic nuclei.
One group of pre-ganglionic parasympathetic fibers arise from the brain stem, they find their target and when they get close to their target they pass the information to the second neuron giving rise to a very short postganglionic parasympathetic fiber which will innervate the heart.
Parasympathetic nervous system is associated with certain ganglia. They are known as: Visceral Ganglia exclusively associated with parasympathetic fibers. Indicating the location of this ganglia.
4 cranial nerves that carry parasympathetic fibers: 3, 7, 9, and 10
Parasympathetic Component: On each side.
Highest level of the spinal cord that can hold sympathetic fibers is T1. However the nerves can climb up to the cervical region and connect to the lip and eyebrows
