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- Slow pain
- Polymodal nociceptors (high-intensity persisting mechanical, thermal or chemical stimuli)
- C fiber (group IV)
- Peripheral fibers terminate in the spinal cord almost entirely in laminae II and III of the dorsal horns, which together are called the substantia gelatinosa
- Enters mainly lamina V, also in the dorsal horn
- Join the fibers from the fast pain pathway, passing first through the anterior commissure to the opposite side of the cord, then upward to the brain in the anterolateral pathway

Paleospinothalamic tract


- Loss of sensation and motor function paralysis and ataxia caused by the lateral hemisection (cutting) of the spinal cord
- Pain, temperature sensations lost on the opposite side of the body(Spinothalamic pathway)
- Kinesthetic, position, vibration, discrete localization and two-point discrimination lost on the side of the transection (Dorsal column)
- Crude touch retained

Brown Sequard syndrome


- Chronic disease of the spinal cord characterized by the presence of fluid-filled cavities and leading to spasticity and sensory disturbances
- Generally in the cervical region, with resulting neurologic defects; thoracic scoliosis is often present



Parenchymatous neurosyphilis marked by degeneration of the posterior columns and posterior roots and ganglion of the spinal cord

- muscular incoordination
- paroxysms of intense pain
- visceral crises
- disturbances of sensation
- Trophic disturbances, especially of bones and joints(tabes-wasting)

Tabes dorsalis


- Selective suppression of pain without effects on consciousness or other sensations
- Descending pathways selectively inhibit the transmission of information originating in nociceptors -> release certain endogenous opioids -> inhibit the propagation of input through the higher levels of the pain system e.g. morphine



- “Transmission” – turns on gate for pain
- “Inhibitory” cells –shut the gate
- Perception of pain is subject to modulation

Gating Theory of Pain modulation


Analgesia system: Pain suppression in the brain and spinal cord

-- Periaqueductal gray and periventricular area of mesencephalon and upper pons
-- Raphe magnus nuclei, nucleus reticullaris pargigantocellular
-- Dorsal horn of SC – pain inhibitory complex
-- Stimulation of higher brain centers that suppress periaqueductal gray area can also suppress pain:
- Periventricular nuclei in the hypothalamus
-Medial forebrain bundle
-- Transmitters involved in the Analgesia system:
- Enkephalin – presynaptic and postsynaptic inhibition of type Adelta and C fibers
- Serotonin


- painful site itself or the nerves leading from it are stimulated by electrodes placed on the of the skin
- stimulation of non-pain, low threshold afferent fibers (touch receptor fibers) leads to the inhibition of neurons in the pain pathways

Transcutaneous Electric Nerve Stimulation (TENS)


- Needles are introduced into specific parts of the body to stimulate afferent fibers, and this causes analgesia
- Endogenous opioid neurotransmitters are involved in acupuncture analgesia



Analgesic drugs

Aspirin - inhibits the synthesis of prostaglandins and slows the transmission of pain signals from the site of injury

Opiates (endogenous opioids: endorphins & enkephalins) - act directly on opioid receptors in the brain, which activate descending pathways that inhibit incoming pain signals


Sensory Pathways for Pain

- Paleospinothalamic tract
- Neospinothalamic tract


Most important Opiate-like substances - stimulate inhibitory neuron so that pain will be less
- Met and leu-enkephalin
- β-endorphin
- Dynorphin

Opiate system


- portion of anterior end of diencephalon that lies below the hypothalamic sulcus and in front of the interpeduncular nuclei
- divided into a variety of nuclei and nuclear areas
- links the nervous system to the endocrine system via the pituitary gland



• portion of anterior end of diencephalon that lies below the hypothalamic sulcus and in front of the interpeduncular nuclei
• divided into a variety of nuclei and nuclear areas
• links the nervous system to the endocrine system via the pituitary gland



Important Functions of the Hypothalamus

• Endocrine Functions
• Autonomic Functions
• Limbic Functions


___ hypothalamus increase BP and HR

posterior and lateral


part of hypothalamus that decreases BP and HR

preoptic area


- hypothalamus controls the set-point of human body temperature
- controlled by neurons in the preoptic area
- signal appropriate cells to activate body temperature-lowering or temper-ature-elevating mechanisms

Body Temperature Regulation


thirst center of the hypothalamus is the __

lateral hypothalamus


__ release antidiuretic hormone (ADH) into posterior pituitary; controls urinary excretion of water; acts on cortical collecting duct of the kidneys to cause water reabsorption

magnocellular cells in supraoptic nuclei


___ release OXYTOCIN causes contraction of the smooth mus-cle of the uterus and milk let down

magnocellular cells in paraventricular nuclei


______ is responsible for hunger; lesions result in starvation; inhibited by leptin

lateral hypothalamus


___ is the satiety center; activity produces a “stop eating” signal; lesions cause uncontrolled voracious appetite; stimulated by leptin

ventromedial nucleus


__ are involved in reflexes related to food intake like lip licking and swallowing

mamillary nuclei


- hypothalamus elaborates releasing and inhibitory factors that modulate ante-rior pituitary function
- subserved by periventricular zone, ar-cuate nucleus and ventromedial nucle-us

Anterior Pituitary Gland Regulation


Hypothalamus is the __________ of autonomic nervous system; stimulation of the hypothalamus produces autonomic responses

head ganglion


Autonomic Functions of the Hypothalamus

sympathetic: posterior hypothalamus - has a warming function

parasympathetic: anterior hypothalamus - has a cooling function


• stimulation of hypothalamus affects behavioral control functions

Limbic Functions of the Hypothalamus


__ hypothalamus causes increased general level of activity leading to rage and aggression



__ causes sense of tranquility, pleasure and reward

ventromedial nucleus