Part 2: Autonomic Nervous System Flashcards
The Autonomic Nervous System (ANS) is responsible for:
- monitoring and regulating visceral functions.
- ANS carries signals to and from viscera, blood vessels and glands via visceral motor (efferent) and visceral sensory (afferent) neurons.
Two divisions of the ANS:
sympathetic and parasympathetic
Sympathetic ANS is primarily responsible for:
- motor innervation of smooth muscle lining blood vessels, cardiac muscle and sweat glands and sensory innervation of viscera.
Sympathetic ANS nerve fibers are distributed with:
spinal nerves and blood vessels.
Parasympathetic ANS is primarily responsible for:
- motor innervation of smooth muscle lining digestive tract, cardiac muscle and salivary glands and sensory innervation of viscera.
Parasympathetic nerve fibers are distributed with:
cranial nerves and pelvic autonomic nerves.
Somatic Motor (efferent) nervous system:
- single neuron pathway from CNS to skeletal (voluntary) muscle.
- cell bodies multipolar and located in ventral (motor) horn.
Visceral Motor (efferent) nervous system (ANS):
- two neuron pathway from CNS to smooth muscle, cardiac muscle and glands.
- preganglionic and postganglionic components
Structure of Visceral Motor (efferent) nervous system (ANS):
- two neuron pathway
- cell bodies of the first motor neuron (preganglionic) are located in the CNS.
- cell bodies of the second motor neuron (postganglionic) are located in ganglia in the PNS.
postganglionic neurons directly innervate visceral structures.
Preganglionic neurons only innervate:
- postganglionic neurons.
- postganglionic neurons directly innervate visceral structures.
The Sympathetic Motor and Parasympathetic Motor Nervous Systems of the ANS both use:
- a two neuron pathway with the first neuron located in the CNS and the second neuron in the PNS.
Location of Preganglionic Cell Bodies in Sympathetic Motor Nervous System:
- Lateral horn of spinal cord segments T1-L2.
- Referred to as thoracolumbar outflow.
Location of Preganglionic Cell Bodies in Parasympathetic Motor Nervous System:
- Brainstem nuclei and lateral horn of spinal cord segments S2-S4.
- Referred to as craniosacral outflow.
Location of Postganglionic Cell Bodies in Sympathetic Motor Nervous System:
Paravertebral and Prevertebral Ganglia
Location of Postganglionic Cell Bodies in Paraympathetic Motor Nervous System:
- 4 discrete ganglia of the head and enteric ganglia of the gut.
Length of preganglionic and postganglionic axons in sympathetic motor versus parasympathetic motor nervous sytems:
- Sympathetic:
- short preganglionic, long postganglionic
- Parasympathetic:
- long preganglionic, short postganglionic
Lateral Horn:
- Location of sympathetic preganglionic cell bodies found only from T1-L2 spinal cord segments.
Ventral Root:
- Carries preganglionic sympathetic axons to spinal nerve.
- Also carries somatic motor axons.
Spinal Nerve:
- All spinal nerves carry somatic motor axons, somatic sensory fibers, and postganglionic sympathetic axons.
- Spinal nerves from T1-L2 carry all of those fibers plus visceral sensory and preganglionic sympathetic axons.
Ventral Ramus:
- Carries pre- and postganglionic sympathetic axons.
- Also carries somatic motor and sensory fibers and visceral sensory fibers.
White Ramus Communicans:
- Connects ventral rami of spinal nerves T1-L2 with paravertebral ganglia.
- Carries preganglionic sympathetic axons.
- Also carries visceral sensory fibers.
“ENTRANCE RAMP TO PARAVERTEBRAL GANGLIA”
Gray Ramus Communicans:
- Connects ventral rami of all spinal nerves with paravertebral ganglia.
- Carries postganglionic sympathetic axons that are distributed to somatic structures.
“EXIT RAMP FROM PARAVERTEBRAL GANGLIA”
Paravertebral Ganglia:
- Sympathetic chain of ganglia located alongside the vertebral column.
- Contain postganglionic cell bodies.
Prevertebral Ganglia:
- Contain postganglionic cell bodies whose axons are distributed to abdominopelvic viscera.
Spinal nerves T1-L2 provide innervation primarily to:
- the trunk
Pathway of how sympathetic motor neurons are distributed to the T2 portion of the trunk from the spinal cord:
- Preganglionic cell body located in lateral horn of spinal cord segment T2.
- Preganglionic axon exits the cord via the T2 ventral root.
- Preganglionic axon runs in the T2 spinal nerve to the T2 ventral ramus.
- Preganglionic axon passes through the T2 white ramus communicans to enter the T2 paravertebral ganglion.
- Preganglionic axon synapses on postganglionic cell bodies located in the paravertebral ganglion.
- Postganglionic axon exits T2 paravertebral ganglion via gray ramus communicans.
- Postganglionic axon joins the T2 ventral ramus and is distributed to sweat glands supplied by T2 ventral ramus.
Pathway of how sympathetic motor neurons are distributed to the L5 portion of the lower limbs from the spinal cord:
- Preganglionic cell body located in lateral horn of segment L1.
- Preganglionic axon exits the cord via the L1 ventral root.
- Preganglionic axon runs in the L1 spinal nerve to the L1 ventral ramus.
- Preganglionic axon passes through the L1 white ramus communicans to enter the L1 paravertebral ganglion.
- Preganglionic axon does not synapse in L1 ganglion, but descends the chain.
- Preganglionic axon synapses on a postganglionic neuron in the paravertebral
- ganglion attached to the L5 ventral ramus.
- Postganglionic axon exits the L5 paravertebral ganglion via gray ramus communicans.
- Postganglionic axon joins the L5 ventral ramus and is distributed to lower limb supplied by L5 ventral ramus.
