Pain - Anatomy

Question 1

Describe the organization of the nervous system, in regards to Somatic, Visceral (Splanchnic nerves, paired visceral), and Branchial arches, and how influences how pain is perceived.

Answer 1

1. Somatic structures (skin, muscles, bones of body walls, and their parietal membranes) are innervated by the spinal nerves (segmental and non-segmental). It senses all modalities: pain, temperature, touch, chemo; thus pain is sharp, well localized.
2. Visceral structures (organs, glands, blood vessels - smooth muscle, and visceral membranes) are innervated by the autonomic nervous system. Motor supply by the sympathetic branch (T₁-L₂) and Parasympathetic (CN III, VII, IX, X and S₂₃₄). Sensory visceral afferents travel with sympathetics + vagus (X); respond to stretch + ischemia. Pain is dull, vague, ill-focused.
3. Branchial arches are the head and neck structures. Innervated by the Cranial Nerves.

Question 2

Describe the spinal nerves, what they innervate and how many are there?

Answer 2

31 pairs of spinal nerves innervating somatic structures (skin, skeletal muscle, bone, parietal membranes). Then become cutaneous to supply dermatomes.

VM DS (virtual machine, DS - nintendo)

Ventral Horn - Motor neuron leaves spinal cord.

Dorsal horn - Sensory dorsal root ganglion enters.

Both motor and sensory combine into the spinal nerve and these split into the Dorsal (1⁰) ramus (means branch) and Ventral (1⁰) ramus.

All dorsal rami are segmental, ventral rami only T₁- T₁₂ are segmental.

Question 3

What is a dermatome, which areas are segmental, and name the landmark dermatomes?

Answer 3

A band of skin with its own sensory innervation (from segmental spinal nerves).

The thorax and abdomen remain segmental. There are also non-segmental arrangement of the dermatomes on the extremities.

Some landmarks at:

T₂ - sternal angle

T₄ - nipple

T₇ - xiphoid

T₁₀ - umbilicus

L₁ - suprapubic

Question 4

What are plexuses? What are the 4 main Plexuses?

Answer 4

Part of the somatic innervation. Plexesus are intermixing of spinal nerves.

Cervial, Brachial, Lumbar and Sacral. (Lumbar and Sacral form sciatic nerve).

Recall the dorsal rami are segmental, but the ventral are only segmental from T₁-T₁₂. Intercostal nerves from T₁-T₁₁.

Above and below T₁ and T₁₂ on the Ventral Rami are Plexuses.

Question 5

Describe the sympathetic (motor) and parasympathetic (motor) supply:

Answer 5

Sympathetic: T₁-L₂ = Thoracolumbar outflow - “Fright, Flight, Fight” response. Innervates the skin (none for parasympathetic).

T₁ to T₅ synapse in paravertebral chain, then postganglionic.

T₅ to L₂ don’t synapse in the chain. Are called splanchnic nerves, 3 ganglia for foregut, midgut and hindgut.

Parasympathetic: CN III (oculomotor), VII (facial), IX (glossopharyngeal), X and S₂₃₄ (heart, lungs, GI, Repro, kidney) = Craniosacral outflow - “Rest, Relax, Regenerate” response. Long preganglionic neurons.

Question 6

Which level are the Sympathetic motor nerve fibers, and which part of the spinal cord to they leave, and what do they supply?

Answer 6

T₁ to L₂ leave the laternal horn of spinal cord, and leave the ventral root to join the spinal nerve.

Supply arterioles (muscles and skin), sweat glands, and arrector pili (hair) muscles.

Question 7

What is the difference in neurons for somatic vs visceral (autonomic) motor system?

Answer 7

Somatic - only a single neuron, leaves the ventral horn and root of spinal cord.

Autonomic - two neuron system. Preganglionic neuron leaves lateral horn to ventral root of spinal cord to synapse on a ganglion. Postganglionic neuron continues the signal.

Question 8

What can sympathetic motor neurons do (5 options)?

Answer 8

1. Synapse on sympathetic chain ganglion, post ganglionic travel with spinal nerve.
2. Synapse in chain, postganglionic ascend/descend and travel with spinal nerve.

Above the diaphragm T1-T5 only:

3. Synapse in chain, postganglionic goes to heart.
4. Preganglionic travel up chain, synpase on superior cervical ganglion (SCG) and go to head and neck structures.

T5-L2

5. Skips the chain, goes to a ganglion close to the organ (Splanchnic Nerves!)

Question 9

Describe why we get referred pain:

Answer 9

Sympathetic T5 - L2 preganglionic motor don’t synapse in the paravertebral chain ganglion, but close to the organs.

Visceral afferents (sensory) travel in the opposite direction of they sympathetic motor (thus from T5-L2 bundle up into ganglia closer to the organs) and have their ganglia also in the dorsal root (same as the somatic afferent nerve). Now when the brain receives the pain input, it assumes it was from the level of the somatic afferent nerve and attributes it to its corresponding dermatome.

Question 10

What kind of referred pain can you get?

Answer 10

Somatic referred pain due to 1) Embryological displacement or 2) projected referred pain (anytime you injure a nerve along its length, its projected to the end of that nerve)

Visceral referred pain by stretch, ischemia & chemoreception. Conducted by visceral afferent fibers arising from certain spinal levels that supply that organ, but is perceived as arising from somatic structures supplied by those same spinal levels.