Download T3 - Neurology

T3 - Neurology
Oct. 17, 2003
Dr. Laura McNeilly
Autonomic Nervous System (ANS)



Involuntary actions in the body
Autonomous – self governing
Referred to as ‘Reptilian Brain’
Refers to 2 main situations in life:
1. Fight or Flight
 Sympathetic NS
2. Rest and Digest
 Parasympathetic NS
3. Freeze (fyi only, not testable) “Waking the Tiger”
ANS: prepares us physiologically for appropriate response to threat, as well as facilitating
appropriate recovery and regeneration.



Primarily efferent (motor)
Motor innervation to: smooth muscles (digestive, blood vessels, lungs), cardiac muscles,
glands (sweat, salivary)
Maintains our “vital signs”: pulse, blood pressure, respiratory rate, temperature.
1. body temperature rises: dt infection, inflammation, exercise, sauna (external
environment).
ANS  shuttles blood from internal organs to skin
2. body temp. drops: dt under active thyroid, endocrine glands fluctuations, environmental
cold.
ANS  shuttle blood from skin to internal organs.
3. need for oxygen or metabolism increases: dt hemorrhage, dehydration, exercise,
pathology, altitude.
ANS  makes heart beast faster, lungs breathe faster
4. BP falls: dt dehydration, loss of blood, standing up too quickly. ANS  narrows arteries,
forcing BP up.
** Anxiety and Panic are emotional states which can lead the ANS to believe that life threatening
scenarios are taking place when they are not. Sympathetics are in a fight or flight state constantly
leading to huge problems.
Organization





Motor neurons of the ANS do not travel directly to their effector organs
There are 2 neurons per spinal segment involved in the innervation
Cell bodies of primary neurons are located in either:
1. Brainstem in association with CN 10, 3, 9, 7. (Cranial)
 All 4 carry ANS and parasympathetic.
2. In the Anterolateral horn of the SC at levels T1 – L2 and S2 – S4
(Thoracolumbar, Sacral)
ANS nerves travel w/motor nerves from the SC
Primary neuron leaves CNS w/motor portions of CN’s OR w/the Anterior root of a spinal N




They synapse on a Secondary neuron
Cell bodies of primary neurons form the autonomic ganglia.
Their axons run from the ganglia to the effector organ
At each synapse there is a neurotransmitter released
Summary

Primary neuron is called Preganglionic Neuron

Secondary neuron is called Postganglionic Neuron

Based on the location of origin of the Preganglionic neuron, the ANS is divided into the
1. Cranial portion
2. Thoracolumbar portion
3. Sacral portion

Based on the NT released, the synapses are
1. Cholinergic (Ach – acetylcholine)
2. Adrenergic (Adrenaline aka: norephinephrine)

Based on the function mediated by the neurons the ANS is divided into
1. Sympathetic
2. Parasympathetic

Majority of autonomic responses are due to segmental reflexes
Sympathetic NS

Can be influenced by higher centers including:
1. Brainstem – CV, resp. control centers
2. Hypothalamus – fight, flight, feed, fornicate
3. Frontal lobe – conscious influence
Preganglionic Neurons







Cell bodies form the Anterolateral horns of spinal segments T1 – L2
= Thoracolumbar flow
Axons exit w/anterior root (motor neuron) and travel a short distance w/the mixed spinal
nerve.
Splits to post and ant ramus, it travels w/ant ramus then branches off
All sympathetic fibers branch off the ant ramus and enter the Sympathetic chain or trunk
Sympathetic chain = a chain of ganglia (C1 – Co) on the lateral boarders of vertebral
column
Because these preganglion neurons are myelinated, this connecting branch btwn the ant
ramus and sympathetic chain is called the White ramus.
Once entering the sympathetic ganglion, preganglions have 4 options:
1. can synapse in the associated ganglion at that level
2. can enter sympathetic chain, NOT SYNAPSE, travel to another ganglion ABOVE and
synapse there, 2, 3, 4 levels.
3. can enter the chain, NOT SYNAPSE, travel to another ganglion BELOW, and synapse
there, 2, 3, 4 levels
4. travel through chain and synapse on a different set of ganglia  Prevertebral ganglia



above T1, there are no preganglionic neurons exiting the SC, therefore all fibers found
above T1 in the chain come from ganglia at or below T1.
Same w/fibers below L2, ie: from at or above L2.
Only T1 – L2 have WHITE RAMI
4 Segment rule:
 Anything above T1 receives fibers from T1 – T4
 Anything below L2 receives fibers from T11 – L2
 Everything above the Diaphragm (heart, thorax) receives fibers from T1 –T4
Quiz next Friday, everything up to here.