Reasons for thinking so, according to von Frey:
The experiment consisted of sticking a pig bristle against the eye. Even with fairly light contact, the bristle was painful...... and a warm and cold bristle elicited the same response -- pain, rather than a sense of warmth or cold.
It contains several other kinds of endings, and when properly tested, it can sense light touch, vibration and temperature. Also, it is now known that the ear lobe contains only free nerve endings, but it can sense all submodalities of skin sensation.
However, Iggo (mid 30s) found that about 30% of small, unmyelinated axons began firing at the point where the stimulus was judged to be painful. This is the kind of axon which generally innervates the skin as a free nerve ending. Also, after WWII, Waddell studied pain syndromes after battlefield injuries.
lowered threshold to pain e.g. can trigger with light touch pain spreads to other skin areas normal dermatome denervated dermatome
Classical view -- through the ventrolateral sector of the spinal cord on the contralateral side, or the ipsilateral, or both.
mid 60s But Melzack and Wall formulated a new concept of the method for pain transmission from the spinal cord.
It is common for amputees, such as war veterans, to suffer severe pain.
Note motor effects
Even transecting the entire spinal cord did not provide permanent relief from pain. Melzack and Wall argued that a new concept was needed for how pain could be transmitted to the brain.
The theory which they offered was known as the They argued that pain and other skin sensations interact at a common junction, and then are sent by various routes to higher brain areas.
to brain A fiber excitatory inhibitory SG T c fiber SG: substantia gelatinosa T: transmission cell There are various ways of diagramming their concept, so don t worry about details.
to brain SG T Pain The basic concept is that a pain message will cause a high firing rate in a common transmission pathway.
to brain SG T SG T
Their theory spurred a lot of research, and pain gates were found to exist at at least two locations: Electrodes implanted into these sites (in humans) is now being used to treat chronic pain.
The intralaminar nuclei connect to the frontal lobes. Patients with frontal lobotomy often are less sensitive to pain, i.e. it doesn t bother them.
Just a few words about... -- short chain polypeptides -- used as neural transmitters to gate pain at various sites -- protein, released by the pituitary gland and at synapses -- carried by blood to many pain-relay sites (likely mimicking enkephalins)
to brain pain gate enkephalin substance P pain message
Ch. 48 Pain Sensations (Reading Homework) Purpose of pain: protection of body Types of pain: fast pain and slow pain Pain receptors are free nerve endings Three types of stimuli excite pain receptors: mechanical, thermal, and chemical Pain receptors are non-adapting Fig. 48-3: pain pathways Pain suppression ( analgesia ) system in the brain and spinal cord Analgesia system: Fig. 48-4 Inhibition of pain signals Enkephalin-secreting neurons Morphine Opiates: morphine-like agents Typical opiate substances: endorphine & enkephalin