48 Somatic Sensations:

II. Pain, Headache,and Thermal Sensations

Dr. A.R. Jamshidi Fard2011

Types of Pain• Fast Pain

– sharp pain– pricking pain – acute pain – electric pain

• Slow Pain– Burning pain– Aching pain– Throbbing pain– Nauseous pain– Chronic pain

• Three Types of Stimuli Excite Pain Receptors:

» Mechanical» Thermal» ChemicalBradykinin, Serotonin, Histamine, Potassium, Ions, Acids, Acetylcholine,

Proteolytic enzymes. + ( Prostaglandins - Substance P)

Threshold of Thermal Stimuli

to Excite Pain Receptors

Other causes of Pain

Tissue DamageTissue IschemiaMuscle Spasm

Dual Pathways for Transmission of Pain Signals into the Central Nervous System

Capability of Pain Signals to Arouse Overall Brain Excitability

Pain Suppression (“Analgesia”) System in the Brain and Spinal Cord

periaqueaductalgray matterpons - medulla area seretonin releasing neuronenkephaline releasing neuronpainfiber

pre-synaptic inhibitionoccurs here via the release ofenkephaline, which blocksCa channels, subsequentlypreventing the release of acetylcholine+ +

ascending anteriolateralpain neuron going to the sensory cortex

spinal cord

free nerve ending

enkephaline releasing neuron

periaqueaductalgray matterpons - medulla area seretonin releasing neuronenkephaline releasing neuronpainfiber

pre-synaptic inhibitionoccurs here via the release ofenkephaline, which blocksCa channels, subsequentlypreventing the release of acetylcholine+ +

ascending anteriolateralpain neuron going to the sensory cortex

spinal cord

free nerve ending

enkephaline releasing neuron

periaqueaducta lgray m atter

pons - m edu lla

area

seretonin re leasing neuron

enkephaline re leasing neuron

pa infiber

pre -synaptic inh ib itionoccurs here v ia the re lease o fenkephaline , w h ich b locksC a channels, subsequentlypreventing the re lease o f acetylcholine

+ +

ascending an terio la tera lpa in neuron go ing to the sensory cortex

spina l cord

free nerve end ing

enkephaline re leasing neuron

Visceral Pain

True Visceral Pain- Ischemia - Chemical Stimuli- Spasm of a Hollow Viscus(cramps)- Overdistention of a Hollow Viscus

“Parietal Pain” Caused byVisceral Disease

Referred Pain

Some Clinical Abnormalities of Pain and Other Somatic Sensations

• Herpes Zoster (Shingles)

• Hyperalgesia

• Tic Douloureux

• Brown-Séquard Syndrome

Some Clinical Abnormalities of Pain and Other Somatic Sensations

• Herpes Zoster (Shingles)

• Hyperalgesia

• Tic Douloureux

• Brown-Séquard Syndrome

Some Clinical Abnormalities of Pain and Other Somatic Sensations

• Herpes Zoster (Shingles)

• Hyperalgesia

• Tic Douloureux

• Brown-Séquard Syndrome

Some Clinical Abnormalities of Pain and Other Somatic Sensations

• Herpes Zoster (Shingles)

• Hyperalgesia

• Tic Douloureux

• Brown-Séquard Syndrome

Headache• Headache of Intracranial Origin

– Meningitis - Low Cerebrospinal Fluid Pressure – Migraine – Alcohol –Constipation

• Extracranial Types of Headache– Muscle Spasm - Irritation of Nasal and Accessory Nasal Structures - Eye Disorders

Areas of the Head to Which Intracranial Headache Is Referred.

Inhibition of Pain Transmission by Simultaneous Tactile Sensory Signals

TENS

ranscutaneus

electrical

erve

timulation

Thermal Sensations

Receptors: - Cold receptors- Warmth receptors-Pain receptors “freezing cold” “burning hot”

Centers:-Reticular areas of the brain stem -Ventrobasal complex of the thalamus