﴿و ما أوتيتم من العلم إلا قليلا﴾ بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

Assist. Prof. of Medical Physiology Sensory System By Dr. Abdel Aziz M. Hussein Assist. Prof. of Medical Physiology Member of American Society of Physiology

Reaction to pain includes all the following, except :- a- increased heart rate b- depression c- withdrawal reflexes d- depressed transmission of pain impulses along sensory pain fibers

Pain receptors :- a- become more sensitive with prolonged stimulation b- are stimulated by prostaglandins c- are more numerous in viscera than other tissues d- include different morphological types

Pain Control System

Pain Control System 1) Def, System which control pain transmission in CNS or inhibit pain transmission i.e. endogenous analgesia system N.B The activity of this system differs from one person to another and from time to time in the same person.

2) Components : 1. Periventricular hypothalamic area 2. Periaqueductal area (PAG) 3. Nucleus reticularis paragigantocellularis (NRPG) 3. Nucleus raphe magnus (NRM) 4. Pain Inhibitory Complex (PIC)

Mechanism of action of Pain Control System

Posterior horn of spinal cord Ascending pathway 1st order neuron of pain Glutamate Substance P Posterior horn of spinal cord

Posterior horn of spinal cord Limbic system RF Hypothalamus Cerebral cortex PAG Severe stress Strong emotions Encephalin ++ NRM NRPGC Serotonin ++ Noradrenaline ++ Ascending pathway 1st order neuron of pain Encephalins -- Glutamate Substance P Posterior horn of spinal cord

Action of encephalins at PIC

Endogenous Opioid Peptides

Endogenous opioid peptides Natural peptide substances produced inside the body and have the ability to bind the opioids receptors (morphine receptors) and produce analgesia. Types: are 3 groups; Enkephalins: Derived from proenkephalins Present in high conc. in brain stem and spinal cord Are 2 main types: leu-enkephalin and met enkephalin. 2. Endorphins: Derived from pre-opio-melanocortin “POMC” Present mainly in anterior pituitary and hypothalamus. Most common type is -endorphins. 3. Dynorphins: same sites of encephalins

Opiate Receptors Are receptors which respond to opiates and endogenous opioids Types: are 4 subtypes; Delta receptors () respond to enkephalins. Kappa receptors (K) respond to dynorphins Mu receptors (µ) respond to endorphins. Sigma receptors () respond to (4-phenyl-1-(4-phenylbutyl) piperidine) (4-PPBP) N.B. Neurons in PAG and Raphi nuclei contain opioids receptors which stimulated by exogenous or endogenous opioids→ pain suppression

Stimulation of thick myelinated N.F (Abeta) Stimulation of A delta NF. Other Mechanisms for Pain Control and inhibition Stimulation of thick myelinated N.F (Abeta) Stimulation of A delta NF. Acupuncture Rubbing method

Pain Control by Rubbing Interneuron Rubbing of the skin A beta fibers Pain C fiber Painful stimuli

Acupuncture Interneuron A delta fibers Pain C fiber Painful stimuli

Acupuncture Mechanism: Acupuncture has been practiced in China for more than 4000 years as a method for pain relief. Mechanism: 1- Needles in appropriate body regions are thought to excite certain sensory neural pathways which feed into the brain stem centers (such as the PAG) involved in the pain control system, with release of endogenous opioid peptides. 2- Simultaneous suppression of pain transmission at the spinal pain-gate by acupuncture

Gate Control Theory

Gate Theory of Pain Sites: The sites of synapses along the pain pathway are considered as gates through which pain transmission can be; Facilitated (if the gate is open) or Blocked (if the gate is closed). Sites: The main pain gates are: 1- Spinal gate: at the SGR. 2- Brain stem gate: at the nuclei of reticular formation. 3- Thalamic gate: At neurons of PVLNT & intalaminar thalamic nuclei.

3 2 1

Spinal Gate At spinal gate pain transmission is blocked by; Supraspinal pathways through the pain control system activating enkephalin-secreting interneuron Spinal inhibition: through; Stimulation of A beta (A beta) by skin rubbing Stimulation of A delta by acupuncture and counter irritants 3. Cortico-fugal fibers (as during thinking the pain is ).

Gate Theory of Pain

Applications of Gate Control Theory This theory provides basis for various methods of pain relief Massaging a painful area Applying irritable substances to a painful area (counter-irritation) Transcutaneous Electrical Nerve Stimulation (TENS) Acupuncture

TENS

Itching and tickling

Itching and tickling Are examples for cutaneous pain. Itching sense is the sense of desire to scratch the skin usually accompanying the allergic diseases. Tickling sense is the sense of something crawling through the skin leading to itching sense (e.g.) in case of scabies. The receptors of both belong to the free nerve endings. Both senses are transmitted by type C-non-myelinated nerve fibers along the anterolateral system.

Somatic Sensations from Head

Trigeminal Pathway A) 1st order neuron: Afferents from face (ophthalmic N. from upper 1/3 of face, maxillary N. from middle 1/3 of face, mandibular from lower 1/3 of face) → to trunk of trigeminal N. → mother cell in Gasserian Ganglia → central branches divide into 2 branches Ascending branch end in sensory nucleus (carry touch and proprioception) and mesencephalic nucleus (proprioception) Descending branch end in spinal nucleus (carry pain and temperature)

Trigeminal Pathway B) 2nd order neuron: From both sensory and spinal nuclei → cross to opposite side and ascend as trigeminal leminiscus End in medial part of PVNT C) 3rd order neuron: From PVNT of thalamus → sensory radiations → primary somatic sensory area

Trigeminal leminiscus Area 3,1,2 Sensory radiations PVNMT Trigeminal leminiscus

Trigeminal Pathway It carries the cutaneous sensations from the face, forehead, and anterior part of the scalp, conjunctiva, cornea and nasal mucosa Also, it carries the proprioceptive sensations from the mandibular ms

Headache

Headache Def: Pain felt in the head region It is an example of referred pain from deep structures of head Pain sensitive structures in the head Extracranial structures All structures in the scalp , covering skull including skin, fasciae, ms, arteries and nerves Eyes Paranasal sinuses Teeth

Headache Pain sensitive structures in the head B) Intracranial structures Brain is insensitive to pain Some structures are sensitive to pain e.g. Arteries e.g. middle meninegial arteries Venous sinuses Parts of dura covering skull base Cranial nerves carrying pain V,IX, X

Headache Site of referral of intracranial headache : A) Frontal headache: Due to stimulation of pain receptors above tentorium (referred by trigeminal nerve) B) Occipital headache: Due to stimulation of pain receptors below tentorium (referred by 2nd cervical nerve)

Headache Mechanism: Irritation of pain sensitive structures e.g. in case of meningitis Pressure or traction on pain sensitive structures e.g. in brain tumors Dilatation of pain sensitive structures e.g. arterial dilatation and brain tumors Spasm of ms e.g. spasm of neck and head ms

Headache Causes of Extracranial headache: Due to stimulation of pain receptors in extracranial structures by; Spasm of head and neck ms due to emotional tension (psychogenic headache). Sinusitis: inflammation of nasal sinuses Eye diseases: Glaucoma →increased intraocular pressure Errors of refraction e.g. astigmatism and myopia 4. Oral causes: e.g. teeth caries.

Headache Causes of Intracranial headache: Meningeal irritation e.g. meningitis, trauma, alcoholics and constipation (absorption of toxins from rectum which cause meningeal irritation) Brain tumours cause pressure, traction, or dilatation of intracranial pain sensitive structures. Changes in CSF pressure: a) ↓ CSF pressure → compensatory dilatation of blood vessels

Headache Causes of intracranial headache: 3) Changes in CSF pressure: b) ↑ CSF pressure → pressure and traction on pain sensitive structures e.g. in hydrocephalus 4) Dilatation of intracranial arteries → pulsation of arteries and severe headache as in migraine (due to release of histamine) Hypertension also leads to dilatation of cerebral vessels and headache

THANKS