HS2-1 ANS in the Neck Flashcards
What are the target tissues of the autonomic nervous system? (3)
cardiac muscle
smooth muscle
glandular epithelium (glands)
(T/F) The nerves of the autonomic nervous system are the only source of innervation for smooth muscle, cardiac muscle, and glandular epithelium.
True. The ANS is the only source of innervation for these tissues.
What are general visceral afferent nerves?
afferent (as opposed to efferent) nerves that travel with the peripheral components of the ANS
What are the three divisions of the ANS?
sympathetic
parasympathetic
enteric
Draw a diagram showing the synaptic organization of the ANS. Label the sympathetic and parasympathetic divisions, along with their associated neurotransmitters.
The terms “presynaptic” and “synaptic” are commonly used to describe the organization of the ANS in an anatomical context. What is the preferred terminology for clinicians?
preganglionic (presynaptic) = neurons from CNS to peripheral ganglia
postganglionic (postsynaptic) = neurons from peripheral ganglia to target organs
Define ganglia.
collections of neuronal cell bodies outside CNS
Describe the length of the fibers in the sympathetic division.
preganglionic = short
postganglionic = long
Describe the length of the fibers in the parasympathetic division.
preganglionic = long
postganglionic = short
Differentiate between the sympathetic and parasympathetic divisions in terms of neurotransmitter usage.
sympathetic = acetylcholine at ganglion, then norepinephrine at target organ
parasympathetic = acetylcholine at both ganglion and target organ
Where are the preganglionic neurons for the sympathetic division located?
thoracolumbar spinal cord (T1-L2)
Where are the preganglionic neurons for the parasympathetic division located? (2)
brainstem (carried through CN III, VII, IX, X)
sacral spinal cord (S2-S4)
What are paravertebral ganglia?
paired sympathetic ganglia extending from cranial cervical ganglion to coccyx
How are paravertebral ganglia connected to each other?
connected superiorly and inferiorly by sympathetic trunk
The sympathetic trunk primarily consists of
axons of preganglionic neurons
The sympathetic trunk acts as the distribution system for which nerve fibers?
acts as distribution system for preganglionic fibers from thoracolumbar spinal cord to sympathetic ganglia
Why is the number of ganglia lower than the number of spinal nerves supplying the sympathetic trunk?
Because the ganglia fuse at various levels — e.g. 3 cervical ganglia, though all cervical spinal nerves carry sympathetic fibers
What are the white rami communicantes?
structures through which preganglionic fibers from the thoracolumbar spinal cord pass
Preganglionic fibers from the thoracolumbar spinal cord are carried through what structure(s)?
carried through white rami communicantes
Why are white rami only found in the thoracic and upper lumbar regions?
because the other regions (cervical, lower lumbar, sacral, coccygeal) do not give rise to preganglionic fibers
What is the function of gray rami communicantes?
carry postganglionic outflow from paravertebral ganglia to spinal nerves
Where are the cell bodies of motor neurons located?
anterior horn of spinal cord
List the pathway taken by sympathetic motor fibers.
axon leaves spinal cord through ventral root → spinal nerve → reaches skeletal muscle via ventral or dorsal primary ramus
Where are the cell bodies of sensory neurons located?
dorsal root ganglion
Describe how sensory afferent fibers transmit signals to the spinal nerve.
reach spinal nerve via ventral or dorsal primary ramus → cell bodies in dorsal root ganglion → fibers enter dorsal horn of spinal cord through dorsal root w/ out being synapsed in dorsal root ganglion
Where is the first preganglionic neuron of the sympathetic pathway located?
lateral horn of spinal cord at T1-T2 to L1-L3 level
What is another name for the lateral horn of the spinal cord?
intermediolateral cell column (IML)
Describe the pathway of the first preganglionic neuron of the sympathetic pathway. (7)
axon exits spinal cord through ventral root → enters spinal nerve → leaves through white rami communicans → enters paravertebral ganglion → synapses with postganglionic neuron → leaves through gray rami communicans → reaches effector
After exiting the gray rami communicans, how does the postganglionic sympathetic fiber reach its effectors? (2)
(1) for smooth muscle of blood vessels/hair follicles/sweat glands → through ventral/dorsal primary rami
(2) for cardiac muscle/smooth muscle of viscera/other glands → directly
List the targets of sympathetic fibers in neck, body wall, and limbs. (3)
(1) vasomotor smooth muscle = regulation of vessel diameter and therefore blood supply
(2) pilomotor smooth muscle = associated with hair follicles
(3) sudomotor = associated with sweat glands of skin
Define piloerection.
goose bumps
When paravertebral ganglia are connected, what structure do they form?
sympathetic trunk
(T/F) In the thoracolumbar region, sympathetic ganglia are fused, meaning that each spinal nerve is not associated with its own sympathetic ganglion.
False. In the thoracolumbar region, each spinal nerve is associated with one sympathetic ganglion. The scenario described applies to the cervical region.
Describe the organization of cervical sympathetic ganglia.
ganglia from various spinal levels are merged, resulting in fewer sympathetic ganglia and less regular distribution of ganglia
Where does the preganglionic output for cervical sympathetic ganglia come from?
preganglionic neurons at superior thoracic level of spinal cord
Describe the pathway of neurons to the cervical sympathetic ganglia.
preganglionic fibers enter sympathetic trunk via white rami communicans
travel superiorly in sympathetic trunk
synapse with cervical sympathetic ganglia
After synapsing with the cervical sympathetic ganglia, how do postganglionic fibers from the cervical sympathetic ganglia exit? (2)
exit ganglia either:
(1) directly to form cardiac/pulmonary plexus
(2) by entering gray ramus communicans to join a spinal nerve
What are the three cervical sympathetic ganglia?
superior
middle
inferior
Describe the location of the superior cervical sympathetic ganglia.
fused ganglia from levels C1-C4
What is the function of the superior cervical sympathetic ganglia? (3)
(1) postganglionic fibers provide sympathetic innervation of structures in head by following common carotid artery
(2) postganglionic fibers distributed via spinal nerves C1-C4 to supply smooth muscle + sweat glands in neck
(3) postganglionic fibers form cardiac nerves for sympathetic contribution to cardiac/pulmonary plexus
[tip: HNC = head, neck, cardiac]
Describe the location of the middle cervical sympathetic ganglia.
fused ganglia from levels C5-C6
What is the function of the middle cervical sympathetic ganglia? (2)
(1) postganglionic fibers distributed via spinal nerves C5/C6 to supply smooth muscles + sweat glands in neck and UEs
(2) postganglionic fibers form cardiac nerves to contribute to cardiac/pulmonary plexus
Describe the location of the inferior cervical sympathetic ganglia. (2)
fused ganglia from levels C7 and C8
ganglion often fused with first thoracic sympathetic ganglion = cervicothoracic (stellate) ganglion
What is the function of the inferior cervical sympathetic ganglia? (3)
(1) postganglionic fibers distributed via spinal nerves C7/C8 to supply smooth muscles + sweat glands in neck and UEs
(2) cervicothoracic ganglion supplies T1 of brachial plexus + intercostal space
(3) postganglionic fibers form cardiac nerves to contribute to cardiac/pulmonary plexus
(T/F) The somatic structures of the neck, body wall, and limbs do not receive parasympathetic innervation.
True.
What is the only parasympathetic structure visible in the neck?
vagus nerve (CN X)
How does the vagus nerve travel through the neck?
within the carotid sheath
The vagus nerve provides innervation to
viscera in thorax and abdomen
[note: does not provide parasympathetic innervation to neck/body wall/limb structures]
