Referred Pain

• It is a type of pain, which is felt away from its original site.

• It is most frequent with visceral pain and deep somatic pain but Cutaneous pain is not referred.

Mechanism of referred pain 1• Referred pain is explained by Conversion

Projection Mechanism where the afferent pain-conducting fibers from the viscera converge with afferent pain-conducting fibers from the skin on one central neuron of the paleospinothalamic tract.

• In these way impulses viscera travel in the same central pathway as pain impulses from the skin to reach the same final sensory neuron in the brain.

Mechanism of referred pain 2

• The final sensory neuron projects pain sensation to the skin as the skin in the place from which it usually receives pain signals.

• This means that the pain signals from the viscera converge to the same final sensory neuron as the signals from the skin, the brain projects any pain sensation from the viscera to the skin.

Examples• Pain of Cholecystitis It is usually referred to the

tip of right shoulder.

• Cardiac pain: It is usually referred to the left shoulder and inner side of the left arm.

• Renal pain: Pain in the kidneys and ureters is referred to the testicular region.

• Appendix pain: Pain from inflamed appendix is referred to the other area around the umbilicus.

• Gastric pain: Is referred to abdominal structures above the umbilicus.

Somatic Sensations from the HeadTwo pathways conduct somatic sensations from the head area:1) From Back of head: cervical nerves 2, 3 2) From the face: Trigeminal nerve

The Trigeminal pathway• Sensory signals are collected from the face and upper

part of the head by the three divisions of the Trigeminal nerve. Then the signals travel through Trigeminal pathway in 3 order neurons:-

• 1- 1st order neurons:• These are the central branches of unipolar nerve cells

located in the trigeminal ganglion, they enter the pons and divided into 2 groups:-

• A) Ascending fibers:• Carry touch sensation, vibration sense, sense of position

and sense of passive movement. These fibers end in main sensory nucleus of the trigeminal nerve which corresponds to the gracile & cuneate nuclei.

• B) Descending fibers:• These transmit pain and temperature. They terminate in

spinal trigeminal nucleus.

The Trigeminal pathway• 2- 2nd order neuron:• These starts at the sensory,

mesencephalic and spinal nuclei, cross to opposite side, and ascend as the trigeminal lemniscus → which terminate at the thalamic vertebral posteromedial nucleus (VPMN).

• 3- 3rd order neuron:• These start at the thalamic nuclei (VPMN)

→ pass in the sensory radiation → and terminate in the cortical sensory areas.

Trigeminal pathway

Lesions in the trigeminal pathway 1

• Trigeminal neuralgia

Is a painful condition which affects the face.

The pain of trigeminal neuralgia is felt in the territory of one or more branches of this nerve.

It usually occurs on one side of the face; in rare cases it can affect both sides at the same time.

Lesions in the trigeminal pathway 2

• Trigeminal nerve injury = Trigeminal anesthesia.

• Lesion of trigeminal ganglion = Ipsilateral.

• Lesion of trigeminal leminscus = Contralateral.

• Lesion of sensation from eyes = leads to corneal inflammation & ulceration in sever cases.

HeadacheIt is a painful sensation at the head.It may be referred from other structures.It may be either intracranial or extracranial.

• Extracranial causes of headache:

• - Eye disease • Errors of refraction.• - Sinusitis.

• - Toothache.• -Otitis media and Otitis

externa. • - Emotions and tension.• - Spasm of head and

neck muscle.

• Intracranial causes of headache:

• 1- Meningeal irritation:• - Alcohol headache.• - Space occupying lesion.• - Constipation headache.• - Meningitis headache.• - Lumber puncture headache.• 2- Arterial distention:• Hypertension headache.• Migraine headache.

Somatic Sensory areas of the cerebral cortex

• All sensations of the body reach the thalamus of the opposite side except the olfactory sensation.

• The thalamus sends its impulses to the sensory areas of the cerebral cortex.

• These include the primary somatic sensory areas and The association somatic sensory areas

Brain areas

Somatic sensory areas

• Primary Somatic Sensory areas:

• Somatic Sensory Area I.

• Somatic Sensory Area II.

• Somatic Sensory Area I(SI):

• It lies in the postcentral gyrus immediately behind the central sulcus in the parietal lobe.

Functions of Somatic Sensory Area I

1- It receives the following sensations:

2- Fine touch sensations (T.L.– T.D. – Stereognosis – Texture of material).

3- Discrimination of weight.

4- Vibration sense.

5- Discrimination of various grades of temperature.

Somatic Sensory Area I(SI):It lies in the postcentral gyrus immediately behind the central sulcus in the parietal lobe.

• It is characterized by:• It receives sensations from the opposite side of

the body i.e. crossed representation. • The body is represented in an inverted manner.

The head is represented in the lower part of postcentral gyrus, while the area of the leg lies in the upper part of the sensory area.

• The area of representation of each part is proportional to the number of receptors in this part, not to size.

Somatic Sensory Area II (SII):

• It is a small area that lies posterior and inferior to the lower end of postcentral gyrus.

• Body representation:

Bilateral representation with poor topographic representation.

The head area is gradually in the anterior part and the leg area is in the posterior.

• Functions: – SII is a potentiator to SI.

- It cannot work independent of S1.