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+## Sensory systems
+
+* The CNS consists of discrete systems for each of the modalities of sensation (touch, vision, hearing, taste, smell)
+* Each functional system involves several CNS regions that carry out different types of information processing
+* Identifiable pathways link the components of a functional system
+* Each part of the brain projects in an orderly fashion onto the next, thereby creating topographic maps. Neural maps not only reflect the position of receptors on a sensory surface, but also their density
+* Functional systems on one side of the body generally control the other side of the body
+
+Note:
+
+
+
+---
+
+## Parallel processing of sensory information
+
+
+
+Note:
+
+Totally fascinating to think out how all this works. Talk about which ones we will go over, common principles, all can get linked together.
+
+---
+
+## Somatic sensory system
+
+* Touch, vibration, pressure, position of limbs (sense of self), pain, temperature.
+* Monitors the external and internal forces acting on the body at any moment.
+* Leads to the ability to identify shapes and textures of objects.
+* Detects potentially harmful circumstances.
+
+Note:
+
+Today we will focus on the somatic sensory system also called the somatosensory system.
+
+
+
+Responsible for a bunch of fairly important things including touch or tactile discrimination, vibration, pressure, limb positioning or proprioception, pain, temperature.
+
+
+
+Monitors external and internal forces acting on the body— e.g. touch is external, proprioception/self positioning is internal.
+
+
+
+Gives rise to our ability to identify objects, also called stereognosis.
+
+
+
+And of course helps us become alarmed to potentially dangerous environments.
+
+
+
+
+
+
+
+soma
+
+: the parts of an organism other than the reproductive cells
+
+: the body as distinct from the soul, mind, psyche
+
+
+
+---
+
+## Overview of somatic sensory system
+
+* Specific receptor neurons located in skin or joints receive stimuli.
+* Information is carried to brain via the spinal cord, brainstem, thalamus, to the post central gyrus of the parietal lobe, which in turn project to higher order cortical areas.
+* Projections are topographic with respect to body region, and the amount of cortical space allocated to various body parts is proportional to the density of sensory receptors in that area.
+
+Note:
+
+
+
+---
+
+## Somatosensory pathway– from somatic sensory neuron to cortex
+
+Touch and pain have different
+
+routes to the brain.
+
+
+
+Note:
+
+We’ve already become aware that the dorsal root ganglia contain sensory neurons that act as sensory receptors for the body with the cell body located in the ganglion and processes extending to the sensory periphery— e.g. this mechanosensory afferent fiber connected to your index finger, or a proprioceptive neuron sensing internal muscle stretch connected to your knee joint for the myotactic reflex that we’ve discussed previously.
+
+
+
+In this inset you see both mechanosensory and pain sensitive fibers connected to the finger— notice that these are coming from two different neurons (red and blue) and the ascending process from the DRG neurons course through the spinal cord to higher brain regions through different routes. More on this later.
+
+
+
+anterolateral tract vs dorsal column
+
+
+
+---
+
+## Somatosensory receptors
+
+
+
+Note:
+
+The sensation of touch, pain, or temperature all starts with specialized receptors and nerve endings in the skin. In all cases ion channels open on the receptor neuron ending that can depolarize and initiate an AP with a sufficiently strong stimulus.
+
+
+
+
+
+[from: http://www.ncbi.nlm.nih.gov/gene/63895](http://www.ncbi.nlm.nih.gov/gene/63895)
+
+-piezo type mechanosensitive ion channel component 2
+
+-protein encoded by this gene contains more than thirty transmembrane domains and likely functions as part of mechanically-activated (MA) cation channels
+
+-channels serve to connect mechanical forces to biological signals
+
+-piezo greek for push.
+
+>Piezoelectric Effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress
+
+-reversible: mechanical stress <–> electricity
+
+-gass stoves, cigarette lighters,
+
+
+
+
+
+---
+
+## There are many types of somatic sensory receptors
+
+* Have different functions– pain, temperature, touch, and proprioception.
+* Different morphologies– free nerve endings or encapsulated.
+* Different conduction velocities– fast vs. slow
+* Differ locations– skin, muscle, tendon, hair
+* Different rates of adaptation– slow vs. fast
+
+Note:
+
+Variety of somatosensory receptors.
+
+---
+
+## Types of somatosensory afferents
+
+
+
+Note:
+
+This table summarizes the somatosensory afferents types, and variety in their functions, morphologies, and AP conduction velocities.
+
+
+
+The fastest ones are…
+
+
+
+The slowest ones are…
+
+
+
+
+
+---
+
+## Slowly adapting and rapidly adapting mechanoreceptors respond differently to stimulation
+
+
+
+Note:
+
+Another type of somatosensory afferent variability I mentioned was rate of adaptation– this figure highlights this difference where if we were performing extracellular electrode recordings close to somatic sensory we find that some types adapt slowly, with sustained spiking as a stimulus stays on, whereas others adapt rapidly with their spiking activity strong at the beginning of the stimulus but quiet as the stimulus is maintained.
+
+---
+
+## General properties of sensory receptors
+
+* Stimuli applied to skin, deforms or changes the nerve endings, produces a receptor potential that triggers an action potential
+* Quality of stimulus (what it represents and where it is) is determined by the relevant receptor and the afferent neuron’s targets in the brain.
+* Quantity or strength of stimulus is determined by the rate of action potential discharge.
+
+Note:
+
+
+
+---
+
+## Skin harbors morphologically distinct mechanoreceptors
+
+Neuroscience 5e Fig. 9.5
+
+
+
+Note:
+
+So here are 5 types of morphologically different somatic sensory receptors—
+
+
+
+
+
+---
+
+## Low threshold (or high sensitivity) mechanoreceptors
+
+* Provide information about touch, pressure, vibration, and cutaneous tension.
+* Four major types of encapsulated mechanoreceptors:
+* Meissner’s corpuscle,
+* Pacinian corpuscles,
+* Merkel’s disks
+* Ruffini’s corpuscles.
+* Called low-threshold mechanoreceptors because even weak stimulation causes them to fire action potentials. Innervated by large myelinated axons (type Aβ fast).
+
+Note:
+
+
+
+---
+
+## Meissner corpuscle
+
+* Located in the superficial layers of the skin, between the dermal papillae just beneath the epidermis.
+* Generate rapidly adapting action potentials after minimal stimulation. Adapt fast.
+* Have small receptive fields
+* Account for 40% of the sensory innervation of the human hand. Particularly good in transuding info about low-frequency vibrations.
+* Detects movement of textures across the skin
+
+Note:
+
+
+
+---
+
+## Merkel’s disks
+
+* Located in epidermis, precisely aligned with the ridges (finger print part of fingers).
+* 25% of the mechanoreceptors in the hand.
+* Are particularly dense in finger tips, lips, and genitalia.
+* Slow adapting, selective stimulation leads to the feeling of light pressure.
+* Have small receptive fields.
+
+Note:
+
+
+
+
+
+
+
+[from: http://www.ncbi.nlm.nih.gov/gene/63895](http://www.ncbi.nlm.nih.gov/gene/63895)
+
+-piezo type mechanosensitive ion channel component 2
+
+-protein encoded by this gene contains more than thirty transmembrane domains and likely functions as part of mechanically-activated (MA) cation channels
+
+-channels serve to connect mechanical forces to biological signals
+
+[-http://www.nature.com/nature/journal/v509/n7502/full/nature13251.html 2014](http://www.nature.com/nature/journal/v509/n7502/full/nature13251.html)
+
+[-http://www.ncbi.nlm.nih.gov/pubmed/25471886 2014](http://www.ncbi.nlm.nih.gov/pubmed/25471886)
+
+
+
+
+
+
+
+---
+
+## Ruffini’s corpuscles
+
+*
+
+* Lie parallel to the skin
+* Large receptive fields
+* Detect cutaneous stretching produced by digit or limb movements
+* 20% of receptors in hand
+* Slow adapting
+
+Note:
+
+
+
+---
+
+## Pacinian corpuscles
+
+* Have large encapsulated endings located in subcutaneous tissue.
+* The onion-like capsule acts like a filter allowing in only high frequency stimulation.
+* Adapts more rapidly than Meissner’s and has a lower response threshold.
+* Has large receptive fields.
+* Stimulation induces a sense of vibration or tickle.
+* Involved in the discrimination of fine surface textures.
+* 10-15% of cutaneous receptors in the hand
+
+Note:
+
+
+
+---
+
+## Properties of afferent systems
+
+
+
+Note:
+
+
+
+---
+
+## Cutaneous mechanoreceptors
+
+
+
+Note:
+
+
+
+---
+
+## Simulated activity patterns in different mechanosensory afferents as Braille is read
+
+Neuroscience 5e Fig. 9.6
+
+
+
+Note:
+
+
+
+
+
+Each dot represents an action potential recorded in a single mechanosensory afferent fiber.
+
+
+
+Horizontal line of dots in the raster plot represents the pattern of activity in the afferent when moving the pattern across the finger. The pattern position is then displaced slightly by a small distance and then the pattern is moved again and the spike pattern is displayed on the next row.
+
+
+
+Individual Braille dots can be distinguished in the pattern of Merkel afferent neural activity
+
+
+
+---
+
+## Differences in mechanosensory discrimination across the body surface
+
+* The accuracy of our sense of touch is not the same all over the body.
+* Can use two-point discrimination tests to show this.
+* Fingers can distinguish things 2 mm apart, forearms 40 mm apart.
+* Mechanosensory receptors are more numerous in finger tips and have smaller receptive fields.
+* Doesn‘t explain everything about ability to discriminate two points. The CNS is also involved with discrimination. Two point thresholds vary with practice, and depend on the stimulus.
+
+Note:
+
+
+
+---
+
+## Sensitivity of tactile discrimination varies with location on the body surface
+
+Neuroscience 5e Fig. 9.3
+
+
+
+
+
+Note:
+
+
+
+---
+
+## Receptive field
+
+* Receptive field (RF)– the area in the periphery within which sensory stimulus can modulate the firing of the sensory neuron.
+* Spatial resolution of the RF:
+* Size– smaller RF, higher resolution
+* Density– higher density, higher resolution
+* “Two-point discrimination test”
+
+
+
+Note:
+
+
+
+---
+
+## Discrimination can also be at the level of
+
+## the primary or secondary sensory neuron
+
+
+
+
+
+Note:
+
+
+
+---
+
+## Title Text
+
+
+
+Note:
+
+[from: http://physiologyonline.physiology.org/content/28/3/142](http://physiologyonline.physiology.org/content/28/3/142)
+
+
+
+---
+
+## Title Text
+
+
+
+Note:
+
+[from D. Ginty, Science: http://science.sciencemag.org/content/346/6212/950](http://science.sciencemag.org/content/346/6212/950)
+
+
+
+---
+
+## Title Text
+
+
+
+Note:
+
+[from: http://www.nature.com/nrn/journal/v12/n3/fig_tab/nrn2993_F1.html#close](http://www.nature.com/nrn/journal/v12/n3/fig_tab/nrn2993_F1.html#close)
+
+
+
+---
+
+## Discrimination can also be at the level of
+
+## the secondary sensory neuron
+
+
+
+Note:
+
+
+
+---
+
+## Receptive fields can be direction selective
+
+* Crickets sense of touch comes from air currents moving sensory hairs.
+* Left: Specific hairs only fire if blown a certain direction.
+* Right: summation of recordings from a single neuron whose hair has been blown from every direction. It only fires an AP when it is moved in a certain direction.
+
+
+
+
+
+Note:
+
+
+
+---
+
+## Lateral inhibition to make discreet borders
+
+
+
+Note:
+
+
+
+---
+
+## Mechanoreceptors specialized in proprioception
+
+* Some sensory receptor’s job is to relay information of self. Where are my limbs and other body parts?
+* Muscle spindles: Are located in most muscles. Contain specialized muscle fibers encapsulated by connective tissue.
+* Axons from sensory neurons wrap around this connective tissue and fire depending on muscle length.
+* Feeds back to γ motor neurons that change spindle length to compensate as needed.
+* Golgi tendon organs do a similar thing but with tendons.
+
+Note:
+
+Proprioception are stimuli that are produced and perceived within an organism, such as the positioning and movement of the body
+
+
+
+---
+
+## Proprioceptors provide information about the position of body parts
+
+Neuroscience 5e Fig. 9.7
+
+
+
+Note:
+
+
+
+---
+
+## Pathways for sensory information
+
+* The cell somas of mechanosensory axons are located in the dorsal root ganglion (DRG). One on each side of the spinal cord, one for each segmental spinal nerve.
+* DRG neurons called first-order because they initiate the sensory process.
+* All sensory axons cross the midline one time.
+* All map to primary somatic sensory cortex, located in the postcentral gyrus.
+* Mechanoreceptors and proprioception receptors use the Dorsal-column-medial lemniscus pathway to get to brain.
+* Pain and temperature use spinothalamic (anterolateral pathway).
+
+Note:
+
+
+
+---
+
+## Dorsal column-medial lemniscus system
+
+* DRG neurons– first order, initiate process
+* Contains info from mechanoreceptors concerned with tactile discrimination and proprioception.
+* Upon entering spinal cord, axons bifurcate into ascending and descending branches, which in turn send out collateral branches to several spinal segments.
+* Some branches go to ventral horn of the cord and synapse on neurons that are part of the reflex system
+
+Note:
+
+
+
+---
+
+## Dorsal column-medial lemniscus system
+
+
+
+Note:
+
+
+
+---
+
+## 2nd order neurons
+
+* The major branches of DRG neurons are ascending and go up the dorsal columns of the spinal cord ipsilaterally.
+* They terminate in the gracile and cuneate nuclei (dorsal column nuclei) in the caudal (posterior) medulla.
+* Axons are organized such that lower limbs are mapped medially (gracile nucleus) and the upper limbs, trunk, and neck in the cuneate nucleus.
+* Axons from both nuclei cross the midline in the medulla and send projections to the somatic sensory portion of the thalamus, the ventral posterior lateral nucleus, VPL. Cuneate axons medial, gracile projections lateral.
+
+Note:
+
+
+
+---
+
+## Mechanosensory pathways
+
+cross in the medulla
+
+upper and lower body
+
+use slightly different pathways.
+
+Neuroscience 5e Fig. 9.8
+
+
+
+Note:
+
+
+
+---
+
+## Trigeminal tract
+
+* Information about the face takes a different route to the thalamus.
+* Trigeminal nerve (cranial nerve 5, three subdivisions, ophthalmic, maxillary, and mandibular).
+* Enters the brainstem at the level of the pons and terminates in the trigeminal brainstem complex. This complex has two main components, the principal nucleus (mechanosensory stimuli) and the spinal nucleus (pain and temp).
+* Crosses midline in the pons and ascends to thalamus.
+
+Note:
+
+
+
+---
+
+## Trigeminal pathway
+
+Info from head and face
+
+mid-pons
+
+midbrain
+
+
+
+Note:
+
+
+
+---
+
+## The somatic sensory components of the thalamus
+
+* Ventral posterior complex (VPC)–
+* Ventral posterior lateral nucleus (VPL) receives projections from the medial lemniscus carrying all somatic sensory information from the body and posterior head.
+* Ventral posterior medial nucleus (VPM) receives axons from the trigeminal info from the face.
+* VPC contains a complete representation of the body.
+
+Note:
+
+
+
+---
+
+## VPL and VPM location in human thalamus
+
+
+
+Note:
+
+
+
+---
+
+## Somatic sensory cortex
+
+* All axons from ventral posterior complex project primarily to layer IV of the somatic sensory cortex.
+* Located in parietal lobe, post-central gyrus
+* Divided into regions, Broadmann’s areas 3a, 3b, 1 and 2– primary somatic sensory area, SI.
+
+Note:
+
+
+
+---
+
+## Brodmann’s cytoarchitectural map
+
+
+
+Note:
+
+
+
+---
+
+## Somatic sensory portions of the thalamus and cortical targets
+
+
+
+Note:
+
+Cross section view shows that there are really 4 subdivisions of primary somatosensory cortex
+
+
+
+In VP complex, Upper body medial, Lower body lateral
+
+---
+
+## Receptive fields of somatosensory cortical neurons
+
+* Area 3b and 1– cutaneous stimuli
+* 3a– proprioceptive stimuli
+* 2– tactile and proprioceptive stimuli
+* SI is organized in columns, by receptive field, and modality. Stick an electrode vertically, all neurons share same region of body.
+
+Note:
+
+
+
+---
+
+## Somatotopic order in the human primary somatosensory cortex
+
+
+
+Note:
+
+
+
+---
+
+## Somatotopic order in the human primary somatosensory cortex
+
+somatotopy
+
+areas of high receptor density
+
+get more cortical space
+
+
+
+
+
+Note:
+
+
+
+---
+
+## More cortical space for body areas with higher somatic receptor density
+
+
+
+
+
+Note:
+
+
+
+---
+
+## More cortical space for body areas with higher somatic receptor density
+
+
+
+
+
+Note:
+
+
+
+---
+
+## Whisker ‘barrels’ in rodent cortex
+
+
+
+Note:
+
+
+
+---
+
+## The ‘homunculus’ reflects sensory receptor density
+
+
+
+Note:
+
+
+
+---
+
+## Magnified cortical representations of sensory apparatus
+
+
+
+
+
+Note:
+
+
+
+
+
+
+
+[from: http://www.pnas.org/content/109/Supplement_1/10647/F3.expansion.html](http://www.pnas.org/content/109/Supplement_1/10647/F3.expansion.html)
+
+
+
+---
+
+## Higher order processing
+
+* SI sends out projections to other areas of cortex.
+* SII, adjacent to SI. Receives info from all 4 SI areas and sends it to amygdala and hippocampus. Plays roles in fear conditioning and tactile learning and memory.
+
+Note:
+
+
+
+---
+
+## Higher order processing
+
+
+
+Note:
+
+
+
+---
+
+## Pain
+
+* Submodality of the sense of touch, warns of injury and things that should be avoided.
+* More subjective than the other senses. The same stimulus can produce different responses in different individuals, or in the same individual in different circumstances.
+
+[http://www.youtube.com/watch?v=s28fCIQKJTA](http://www.youtube.com/watch?v=s28fCIQKJTA)
+
+Congenital insensitivity to pain:
+
+Note:
+
+
+
+Congenital insensitivity to pain
+
+[from: http://ghr.nlm.nih.gov/condition/congenital-insensitivity-to-pain](http://ghr.nlm.nih.gov/condition/congenital-insensitivity-to-pain)
+
+>20 cases have been reported in the scientific literature
+
+>Mutations in the SCN9A gene cause congenital insensitivity to pain. The SCN9A gene provides instructions for making one part (the alpha subunit) of a sodium channel called NaV1.7.
+
+>NaV1.7 sodium channels are found in nerve cells called nociceptors that transmit pain signals to the spinal cord and brain. The NaV1.7 channel is also found in olfactory sensory neurons, which are nerve cells in the nasal cavity that transmit smell-related signals to the brain.
+
+>The SCN9A gene mutations that cause congenital insensitivity to pain result in the production of nonfunctional alpha subunits that cannot be incorporated into NaV1.7 channels. As a result, the channels cannot be formed.
+
+>autosomal recessive pattern
+
+
+
+
+
+---
+
+## Pain involves specialized neurons not just extrastimulation of touch receptors.
+
+* Scheme for transcutaneous nerve recording.
+* Nociceptor doesn’t fire until pain is felt. Other thermoreceptors fire at all temps and at about the same frequency
+
+
+
+Note:
+
+
+
+---
+
+## How do we detect pain?
+
+* A family of ion channel receptors have been found that open in response to heat as well as capsaicin called TRP (transient receptor potential) channels.
+* Structurally resemble voltage-gated K⁺ channels, having 6 transmembrane domains that make a pore.
+* When open allows Ca²⁺ and Na⁺ across membrane to generate a receptor potential.
+
+Note:
+
+
+
+---
+
+## Heat gated ion channels
+
+* Capsaicin receptors are nonselective cation channels opened by heat, low pH, and capsaicin (the hot in hot peppers).
+* Mice without TRPV1 (VR1) have impaired sensitivity to pain. Can drink capsaicin as if it were water.
+
+
+
+
+
+Note:
+
+
+
+
+
+transient receptor potential cation channel subfamily V member 1 (TrpV1), also known as the capsaicin receptor or the vanilloid receptor 1 (VR1)
+
+
+
+function of TRPV1 is detection and regulation of body temperature. In addition, TRPV1 provides a sensation of scalding heat and pain (nociception).
+
+
+
+
+
+43ºC threshold (110ºF)
+
+
+
+---
+
+## Heat gated ion channels
+
+* Capsaicin receptors are nonselective cation channels opened by heat, low pH, and capsaicin (the hot in hot peppers).
+* Mice without VR1 have impaired sensitivity to pain. Can drink capsaicin as if it were water.
+
+
+
+Note:
+
+
+
+---
+
+## Nociceptors
+
+* This figure compares the activation of VR1 channels by pure capsaicin and extracts of various peppers.
+
+Nature 1997 Oct 23;389(6653):816-24
+
+
+
+Note:
+
+
+
+---
+
+## Nociceptors
+
+* Transfer information about pain.
+* Three major classes of nociceptors: Aδ mechanosensitive nociceptors, Aδ thermal nociceptors, and polymodal nociceptors.
+* Aδ mechanosensitive nociceptors-activated by intense pressure, are lightly myelinated and have speeds of 5-30 m/s.
+* Aδ thermal nociceptors are activated by very hot or very cold temperatures. Are lightly myelinated.
+* Polymodal nociceptors (C fibers) respond to temperature, pressure, or chemicals, are unmyelinated and conduct at speeds of 1m/s.
+* Aδ and C fibers have cold temperature gated ion channels. When they fire they are perceived as pain.
+* Pain receptor receptive fields are generally pretty large, presumably because the detection of pain is more important than its exact location.
+
+Note:
+
+
+
+---
+
+## Two categories of pain perception
+
+* first pain (sharp), Aδ fibers
+* second pain (dull, longer lasting) C-fibers
+
+selective block of either Aδ or C fibers
+
+
+
+
+
+
+
+Note:
+
+
+
+---
+
+## Hyperalgesia
+
+* Enhanced sensitivity and response to stimulation of the area around the damaged tissue. Stimuli that would not ordinarily be perceived as pain now is. For example after a sunburn a normal shower now feels painful.
+* Due to the release of stuff from the damaged cells, such as prostaglandins, bradykinin, histamine, serotonin, ATP, can increase the sensitivity of nociceptors by interacting with the channel (directly or indirectly) and making it open easier, or by interacting with other receptors on nociceptive fibers to potentiate activity of TRP channels.
+* Aspirin and ibuprofen inhibit cyclooxygenases (COX-2 inhibitors), necessary for prostaglandin synthesis.
+* Shows that pain and injury are inter-related
+
+Note:
+
+
+
+---
+
+## Hyperalgesia
+
+Correlation between the perception of pain in a human subject and impulse
+
+firing in a monkey C multimodal heat receptor under normal conditions and during hyperalgesia.
+
+
+
+Note:
+
+
+
+---
+
+## Inflammatory response to tissue damage
+
+
+
+Note:
+
+Another type of peripheral sensitization can occur due to substances released within damaged tissues can modulate the response of nociceptive fibers. A host of molecules that can augment the activity of free nerve endings like…
+
+
+
+Most interact directly with the receptors or ion channels of the nociceptive fibers. e.g. TRPV1 capacin receptor can be potentiated form the channels direct interactions with extracellular protons that are released by immune cells or through indirect interaction with other enzyme receptors like TrkA for NGF or bradykinin receptors.
+
+
+
+>a peptide that causes blood vessels to dilate (enlarge), and therefore causes blood pressure to fall
+
+
+
+
+
+
+
+
+
+nociceptive
+
+: of or related to pain arising from stimulation of nerve fibers
+
+---
+
+## Pain pathways
+
+* Spinothalamic tract
+* Cell bodies found in the most lateral parts of the dorsal root ganglia, but not discretely localized.
+* Innervate neurons in the dorsal horn of the spinal cord. Some of these neurons project within the spinal cord. These are important for reflex behaviors.
+* Others project axons cross the midline in the same segment and then go up to the brain.
+
+Note:
+
+
+
+---
+
+## Major pathways for pain (and temperature) sensation
+
+
+
+Note:
+
+
+
+
+
+nociceptive projections into dorsal horn branch into ascending and descending collaterals forming the dorsolateral tract of Lissauer (named after 19th c. German neurologist).
+
+C fibers (slow pain) terminate in layer 1 (Rexed’s laminae, named after anatomist who first described spinal gray matter layers in 1950s) of dorsal horn.
+
+Adelta (fast pain) terminate in layer 5 of dorsal horn where Abeta mechanosensory terminals innervate.
+
+---
+
+## Pathways for pain (and temperature) sensation of the face
+
+
+
+Note:
+
+
+
+---
+
+## Nociceptive component in the VP nuclei in the thalamus
+
+* Pain and temp go to VPM and VPL nuclei just like the mechanosensory axons.
+* VPM from the face, VPL from the body
+* Presumably responsible for our ability to locate a pain with respect to body position.
+
+Upper body medial
+
+Lower body lateral
+
+
+
+Note:
+
+
+
+---
+
+## Cortex
+
+* VPM and VPL neurons project to primary somatosensory cortex. These thalamic neurons have small receptive fields and are likely used to locate where the pain is, but are not responsible for dull aches that are associated with chronic pain as ablation does not reduce pain.
+* There are also direct projections to the reticular formation (in medulla), and the midline thalamic nuclei. These neurons project to areas of the limbic system and are responsible for the emotional aspects of pain.
+
+Note:
+
+
+
+---
+
+## The anterolateral system sends information to different parts of the brainstem/forebrain
+
+
+
+Note:
+
+
+
+---
+
+## Pain vs touch
+
+* 2nd order mechanosensory axons cross at the level of the medulla but 2nd order pain axons cross at about the segment their cell bodies are in.
+* If there is a damage on one side of the spinal cord, below the injury site, there would be no sense of touch on the same side and no sense of pain on the contralateral side.
+
+Note:
+
+
+
+---
+
+## Spinothalamic tract
+
+* Also called anterolateral column part of the ventral column
+* Note where axons cross over the midline.
+* Touch and pain are on opposite sides below medulla
+* Touch and pain are on the same side above medulla
+
+
+
+Note:
+
+
+
+---
+
+## The anterolateral and dorsal column-medial leminiscal systems cross the midline at different sites
+
+
+
+Note:
+
+nociceptive and mechanosensory pathways
+
+---
+
+## Referred pain
+
+* Few if any neurons in dorsal horn are specialized solely for the transmission of visceral pain.
+* It is conveyed to brain via dorsal horn neurons that also get inputs from skin.
+* Therefore a person may feel pain at a site completely different than its source.
+
+
+
+Note:
+
+
+
+anginal pain which is pain arising from heart muscle that is not being adequately perfused with blood. Referred to the upper chest wall, with radiation into the left arm and hand.
+
+
+
+Innervation of same neuron in the dorsal horn of the spinal cord.
+
+---
+
+## Pain perception is subjective
+
+* Rubbing the site of injury can make pain less severe.
+* Pain is somewhat subjective. Depends on context. Soldiers wounded in battle feel less pain than if one gets the same injury at home.
+* There is a descending pain pathway that can impinge on the dorsal horn to quiet neurons.
+
+Note:
+
+
+
+---
+
+## Direct electrical stimulation of the brain produces analgesia
+
+* The observation is that stimulation of periaqueductal grey (in midbrain) or rostral medulla reduces pain.
+* Stimulation only reduces pain sensation, animal/person still responds to touch, temp etc, just feels less pain.
+* These areas are part of a descending pathway that modulates pain. Cortex and hypothalamus project to periaqueductal gray which then projects to nuclei in the medulla (Raphe nuclei, reticular formation), projects to dorsal horn, where they can inhibit ascending pain fibers.
+
+Note:
+
+
+
+---
+
+## Modulation of ascending pain signal transmission
+
+* Axons from neurons with mechanoreceptors can synapse onto inhibitory interneurons in spine to dampen pain response.
+* Descending pathways from the brainstem can dampen pain response.
+
+
+
+Note:
+
+
+
+
+
+enkephalins, endorphins, dynorphins— present in the periacq. gray matter, ventral medulla, and in spinal cord regions in dorsal horn.
+
+
+
+Also CB1 and endocannabinoids work similiarly here in the dorsal horn.
+
+
+
+
+
+
+
+---
+
+## Descending systems modulate the transmission of ascending pain signals
+
+* Descending pathways from cortex and hypothalamus
+
+
+
+Note:
+
+
+
+---
+
+## Descending systems modulate the transmission of ascending pain signals
+
+* Through periaqueductal gray rostral medulla reduce activity in spinothalamic tract.
+* Reduction of activity in the spinothalamic tract.
+
+
+
+Note:
+
+
+
+---
+
+## Opioids
+
+* Opioid receptors (metabotropic) are expressed in the areas of descending pain pathway (also expressed in other areas, such as muscles of the bowel and anal sphincter).
+* Ligands– enkephalins, endorphins, and dynorphin. Found in all descending pain areas.
+* Opioids decrease the chance that a nociceptor will fire, cause inhibition.
+* Opiate antagonist naloxone blocks stimulation produced analgesia as well as morphine-induced analgesia. Suggests that they are the same thing.
+
+Note:
+
+
+
+---
+
+## Endogenous opioids
+
+
+
+Note:
+
+
+
+---
+
+## Endogenous opioids dampen pain signal transmission
+
+
+
+Note:
+
+
+
+---
+
+## Placebo effect
+
+* Sugar pills can reduce perception of pain.
+* The effect can be blocked by naloxone, a competitive antagonist of opioid receptors.
+* The placebo effect is based on a biochemical change in the brain, as are all perceptions.
+
+Note:
+
+
+
+
+
+-mind separate from body. No– this highlights something that neuroscientists already widely accept, that you cannot separate the mind from the body, the mind is body and vice versa.
+
+-what is or is not reality philosophers
+
+
+
+-highlights descending control and higher order processing of pain.
+
+
+
+endogenous opioid
+
+
+
+---
+
+## Phantom limbs and phantom pain
+
+
+
+Note:
+
+Phantom limbs can be another fascinating clue to higher order processing of somatic sensation. This stems from the fact that for amputees, almost have an illusion that the missing limb is present.
+
+
+
+It’s been proposed that there is an internal mismatch between the brain’s representation of the body and the pattern of peripheral tactile input that results in the illusory sensation.
+
+
+
+
+
+R. Melzack 1989 Can Psychol Phantom limbs
+
+TINS 1990
+
+
+
+
+
+[http://www.youtube.com/watch?v=Esgl1q73wP8](http://www.youtube.com/watch?v=Esgl1q73wP8)
+
+---
+
+---
+
