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
The preganglionic sympathetic neuronal cell bodies are restricted to:
- lateral horn of spinal cord segments T1-L2
Before being distributed, all preganglionic sympathetic fibers enter paravertebral ganglia from T1-L2
via:
white rami communicans
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.
Preganglionic sympathetic axons are only carried through which spinal nerves?
spinal nerves T1-L2
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”
White Ramus Communicans are only located on and between what spinal nerves?
T1-L2
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.
Splanchnic Nerve:
- Connects paravertebral and prevertebral ganglia.
- Carries preganglionic sympathetic axons.
- Also carries visceral sensory fibers.
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.
What spinal nerves supply the upper limb?
C5-T1
What spinal nerves supply the lower limb?
L2-S4
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.
Sensations conveyed by Somatic Sensory Neurons:
Pain, Temperature, Touch, Proprioception
Location of Somatic Sensory Neuron Cell Bodies:
Dorsal Root Ganglia from C2-Coccyx
Sensations conveyed by Visceral Sensory Neurons:
Distension, Nausea, Hunger
Location of Visceral Sensory Neuron Cell Bodies:
Dorsal Root Ganglia from T1-L2.
How many neurons are involved in both the somatic and visceral sensory pathways?
- one neuron
- only visceral motor pathways (ANS) require two neurons
Pathway of how visceral afferent neurons (ANS sensory) reach the spinal cord from the heart:
SAME, BUT OPPOSITE PATH AS SYMPATHETIC MOTOR NEURON
- Sensory fiber axons from receptors in heart enter visceral nerve.
- Axons enter superior cervical ganglion and descend the chain to T2 paravertebral ganglion.
- Axons exit via white ramus communicans to reach the T2 ventral ramus.
- Axons travel back to T2 spinal nerve via T2 ventral ramus.
- Axons enter T2 dorsal root to their cell body located in the T2 dorsal root ganglion.
- Axon continues through the T2 dorsal root to the dorsal horn of the T2 spinal cord segment where it will synapse.
Referred pain occurs because:
- visceral afferent fibers synapse on the same neurons in the dorsal horn of spinal cord segments T1-L2 as the somatic afferent fibers.
- Ex: pain stimulus coming from a visceral organ (i.e. heart) is perceived as having come from the arm and interpreted as coming from that region.
