Chapter 2 Notes PDF

Ch. 2.1 Peripheral Somatosensory System Overview Periphery allows us to sense thing such as: temperature, pain, pressure or stretch These signals to the brain allows the body to perform appropriate responses to the signals Nervous system Peripheral nervous system Autonomic Somatic nervous syste...

Ch. 2.1 Peripheral Somatosensory System Overview Periphery allows us to sense thing such as: temperature, pain, pressure or stretch These signals to the brain allows the body to perform appropriate responses to the signals Nervous system Peripheral nervous system Autonomic Somatic nervous system Central nervous system Visceral nervous nervous system system Peripheral Somatosensory System (PSS) Sensory stimuli PNS (Peripheral) CNS Central Visceral stimuli ↳ Afferent Neurons L Brain + Spinal Cord ↳ Skeletal muscle > Somatic efferents Autonomic efferents - Sympathetic nervous system - 7 - Parasympathetic nervous system Smooth muscle + glands Nervous system works on three-order neuronal pathway for signal to be sent to periphery ex: hand up to cerebral cortex Cerebral cortex 1st order works out in periphery activated by receptors receiving a signal such as touch or temp & It then sends signal to neuron located in spinal cord or brainstem & Neuron is pseudo-unipolar w a distal axon out to receptor (in this case the hand) Proximal axon signaling to 2nd order neuron (either in SC or brainstem) 2nd order neuron then sends signal to 3rd order neuron 3rd order is in the thalamus and communicates to the cerebral cortex M ⑨ O ⑧ Note: pathway for different sensations like pain and temp vs discriminate touch (ex: vibrations) differs, HOWEVER the 3 neurons in the pathway DO NOT ⭐ ⭐ Main difference bw them is where paths cross the midline in order to reach the contralateral thalamus So that cerebral hemisphere receives signals to opposite of body PSS: Receptors Receptors aware the same as the ANS: mechanical receptors Chemoreceptors Nociceptors Thermoreceptors Can also be classified as: tonic or phasic Tonic receptors send a signal as long as a stimulus continues to be present and DOES NOT ease or fatigue w time - gives you constant info that the stimulus is ongoing Phasic receptors will quickly adapt to a signal that is being send and WILL fatigue or stop responding despite the presence of an ongoing stimulus Ex: walking into a bakery and smelling fresh cookies -overtime signal fades the longer you’re there w said smell PSS: Cutaneous Innervation 1. Free nerve endings 2. Meissner’s corpuscle 3. Pacinian corpuscle =characteristics 4. Ruffini’s ending 5. Merkel’s disk Free nerve endings: sense coarse touch, pain and temperature It’s freaking hot and it freaking hurts -small-diameter, unmyelinated or lightly myelinated, fibers w slow conduction velocity -the rest of receptors are mechanical and are encapsulated w the primary fxn of sensing various types of light touch Meissner’s Corpuscle: sense fine touch, low-frequency vibration my fine self Pacinian corpuscles: respond to deep pressure & high frequency vibration Ruffini’s ending: positioned to sense stretch she’s stretchy Merkel’s disk: feel fine details of touch like: surface texture, shapes and edges *Both are found heavily on hand and less on torso area* Notes: each of these receptors and afferent signals have different thresholds for activation and level of adaption to the signal. Could either be tonic or phasic and each has varied receptive field sizes PSS: Receptive Field Receptive Field: area of skin innervated by a single secondary neuron Degree of sensation based on size of receptive field and density of receptors per secondary sensory neuron • no matter how many receptors are activated by stimuli in a particular part of skin, the ability of feel sensation is dependent on the # of primary n’s converging on that secondary neuron LARGE RECEPTIVE FIELD Primary neuron Primary neuron — body is unable to detect Secondary neuron stimulus as 2 distinct point Small receptive field Primary neuron Primary neuron Secondary neuron = Secondary neuron points brain is able to identify two separate contact Note: receptive fields in the hands are smaller than those in the torso PSS: Neural FIber Classification (Diameter) Peripheral somatosensory nerves can also be classified by diameter and speed of signal transmission A (alpha) neurons: largest in diameter w fastest speed Size decreases as you go down to A-beta, A-delta and C axons Also be classified using 1-4 system 1. A-alpha: 1a and 1b 2. A-beta: 2 3. A-delta: 3 4. C: 4 Summary: The PSS conveys important sensory feedback to the CNS 1. Relies on diff types of sensors and sizes of neural axons, each w its own fxn and signal speed 2. Sensitivity toward these signals based on the receptive field and density Ch. 2.2 Dermatome vs. Peripheral Nerve Distribution PSS Nerve Innervation Two categories: 1. dermatome 2. cutaneous nerve distribution Note: neuroscience stand point- tend to focus more on dermatomes, particularly when discussing spinal cord injuries - both however are essentially for differential diagnosis and understand pathologies Sensory innervation- Anterior Posterior Can better see S1-S5 from post view *important for spinal cord injuries General locations: T4- nipple helpful to estimate other thoracic dermatomes T10- umbilicus Notes: In lecture she says to focus on regions of C5-T1, L2-S2, T5 and T10!! It is important for a PT to know dermatomes and cutaneous distributions so we can use them while testing someone’s ability to sense things. This will help find normal and abnormal sensation to better figure out where the lesion or problem is in the body Dermatome vs. Cutaneous Innervation 1. Differential diagnosis 2. Impairment testing based on diagnosis Ex: someone w abnormal sensation at digit 3 or 4 may have an issue at C7 or 8 If you also find that the person as an issue at digit 5, then we know more than likely the issue is C8 Another ex: if someone has issues w sensation at digit 2,3&4 on the volar (palm) side of hand, we should instead think it could be median n issues like carpal tunnel Pls refer to the pic below for these examples Sensory Nerve Conduction Studies 1. Distal latency 2. Amplitude of evokes potential 3. Sensory n conduction studies are used to understand how fast the sensory signal goes from one peripheral location up to the recording site.. sooo from point A to B or C Conduction velocity Distal latency: time it takes the depolarization caused by the stimulus to reach the distal recording site Amplitude of evokes potential: indicates the strength of the signal sent and the # of axons sending a signal in response to a stimulus Conduction velocity: simply the distance the signal travelled over the latency, or time it took to travel that distance Note: oftentimes a nerve is tested at two locations to better locate the area of a nerve problem they compare the conduction velocity from the stimulus to site 1 vs site 2 (She said we will learn more later) Summary: Regional sensation can be based on Dermatome or cutaneous distribution, a key concept for differential diagnosis Nerve conduction studies can help w differential diagnosis, analyzing the delay, size and speed of sensory signal 👛 💪 2.3 Musculoskeletal Innervation 3 components of sensory Innervation to musculoskeletal system: 1. Muscle spindle 2 Golgi tendon organ 3. Joint receptors Muscle spindle: sensory organ embedded w the skeletal muscle Fxn: provide information of overall length of muscle and rate of change • Basically… how fast a muscle is being lengthened or stretched it can also initiate an automatic reflex w/in the spinal cord to change the length in response to sensory signals Muscle spindle is made of 3 parts: 1. Muscle fibers 2. Sensory nerve endings Muscle spindle is wound up around muscles fibers Breakdown muscle spindle: 3. Motor nerve endings • intrafusal vs extrafusal Muscle fibers - Intrafusal muscle fibers: if muscle fibers are wound inside coil considered nuclear chain or bag fibers • chain fibers • - Extrafusal: surrounding muscle fibers Nuclear bag vs nuclear Primary endings vs secondary endings parallel to muscle fibers, lack nerve coils Nuclear chain: (chain fibers) have the cell nuclei in a line, forming a chain Bag fibers: contain nuclei that come together centrally Muscle spindles also have 2 kinds of sensory nerve endings 1. Type 1A 2. Type 2 Type 1A- coiled around the center of each of the intrafusal fibers provide both phasic and tonic information Type 2: found at the end of each spindle Both detect changes in length provide tonic signals Muscle Spindle Activation • co-activation of intrafusal and extrafusal muscle spindles by alpha and gamma motor neurons in norms Primarily in a muscle stretch: sensory ending of the muscle spindle detect change in length and the signal is sent out to the spinal cord Neuron in the spinal cord: 2 things are able to occur in a normal system 1. Cortical spinal neuron is able to activate both gamma and alpha motor neurons to signal a contraction this means BOTH the intrafusal and extrafusal muscle fibers contract at the same time and rate = muscle spindle resets in length Note: if gamma motor neurons are unable to contract at the same time, the alpha motor neurons are able to contract the extrafusal muscle fibers, but the intrafusal muscle fibers remain lengthened or slack and are unable to accurately detect further stretch in an abnormal system Golgi Tendon Organs (Second type of sensory feed back from musculoskeletal system) Located in muscle tendons Sensitive to active contraction and passive stretch Signals from these nerve endings are sent via 1B afferent axons to the spinal cord Joint Receptors 4 types: 1. Paciniform corpuscles 2. Ruffini’s endings 3. Free nerve endings 4. Ligament receptors Paciniform corpuscles: in joint, respond to joint mvmt and are NOT activated when a joint maintains the same position Ruffini’s endings: play an active role in detecting extreme end range of motion, when it is most stretched passively Free nerve endings: are scattered throughout the capsule sense joint capsule irritation, such as inflammation Ligament receptors: sense tension in the ligaments surrounding the joint capsule, such as the LCL Signal Overload ask: explain chart bc these are definitions of different receptors not joint receptors Note: Integration & signals coming from muscle spindles, Golgi tendon organs, joint receptors and other somatorysensory signals provide great information to the brain for awareness of joint position and mvmt, muscle length, & rate of length change, pressure, pain and temp • signals arrive in the CNS in a large variety of axons, which range in conduction velocity and size Intact system: sensory overload provided ample information for the body to react properly to excessive stretch, contracting muscles to counter that stretch (stretch reflex), and adapting stretch w/in a muscle for continued detection - w/out said sensory information to the muscle and joint or the skin; the body would be more prone to sprains, strains, among other types of injuries Summary: The musculoskeletal system is innervated by various sensory endings and nerves to coordinate movement and prevent injury 1. Muscle spindles 2. Golgi tendon organs 3. Joint receptors 4. Free nerve endings Ch. 2.4 Central Somatosensory System Overview one stimuli from the environment is detected by the receptors in the periphery, the afferent signals are sent • to the spinal cord for processing PSS to CSS • receptive field • Homunculus on primary somatosensory cortex Homonculus: somatotopic map of the brain of sensory information in relation to different body parts Little man In relation to the homunculus, areas that have smaller receptive fields would have MORE coverage on the cerebral cortex, rather than larger receptive fields Hands and face are LARGE on the homunculus Legs and feet= small portion PSS to CSS pt 2 peripheral system is formed by different cutaneous and musculoskeletal system receptors and its efferent nerves -once the signal hits the spinal cord, we enter the central nervous system The two main pathways that a sensory signal will fall under once it reaches the spinal cord are: 1. Dorsal column system 2. spinothalamic system Somatosensory System Pathways • each tract is considered either conscious relay, divergent, or nonconscious Conscious relay paths carry information to the cerebral cortex on the location and type of sensory stimulation Info is considered high fidelity and discriminative details on stimulus and precision of location of said stimulus arrives at the brain Relay pads carry information on light touch, proprioception, pain and temperature Divergent paths carry information toward the brainstem and cerebrum uses wider network of neurons and pathways (A) BCD Information can be conscious or nonconscious nonconscious relay pathways carry only nonconscious proprioceptive information of the cerebellum, Note: we can distinguish each by the type of sensory information conveyed, the fidelity of said information, or the accuracy of information, the target w/in the CNS and location of the second order neuron cell body Summary: • peripheral signals are sent to the brain in a 3-neuron pathway in various pathways based on the conveyed information- conscious, divergent, or non-conscious • Each pathway is distinct, w specific signals, fidelity, anatomical target in the CNS and location of the 2nd neural body • A homunculus depicts the somatotropin arrangement of sensory information 🦵 ⭐ 2.5 Light Touch & Conscious Proprioception (DCML) *remember* when investigating pathways we need to keep 4 things in mind 1. Type of information conveyed 2. Fidelity or accuracy of that information 3. Anatomical target in the CNS 4. Location of the second neuronal body Dorsal Column-Medial Lemniscus Tract: The Traffic Contains signals for -light touch -conscious proprioception vibration • -stereognosis Stereognosis: describes the ability to coordinate light touch and proprioception to correctly identify an object by Jimmy Fallon game touch and not by sight or any other sensations Dorsal Column- Medial Lemniscus Tract: The Tollbooths 1. Dorsal root ganglion from either the trunk and the lower limb or the trunk and upper limb -cell body’s axon then enters the spinal cord and ascends along the dorsal column 2. Ipsilateral nucleus cuneatus or gracilis if signals are coming from the lower trunk or legs -nucleus cuneatus- if signals are coming from the upper trunk and the upper limb Both of these nuclei are located ipsilateral to incoming signals w/in the lower medulla 3. Contralateral VPL nucleus of thalamus -here is where the signals decussate or cross the midline and head towards the third cell body in the contralateral VPL (ventral posterolateral) nucleus of the thalamus Dorsal Column-Medial Lemniscus Tract: The Highway 1. Peripheral nerve; body signal sent from either the lower and upper body and is sent to the dorsal ganglion of that spinal Innervation level 2. Dorsal column; Fasciculus Cuneatus or Gracilis -if signal is from the legs , it travels up the dorsal column medially in the fasciculus gracilis tract -if signal is from upper body or arms , it travels up the dorsal column, but more lateral to the fasciculus gracilis along the fasciculus cuneatus tracts -both gracilis and cuneatus tracts convey information on discriminative touch and pressure. -brig travel up the dorsal column to their respective nuclei in the lower medulla, ipsilateral to the signals. 3. Detour to contralateral medial lemniscus-midbrain 4. Contralateral VPL of thalamus from the second cell body, these signals then decussate in the medial lemniscus to target the contralateral VPL nucleus of the thamalus 5. Contralateral primary somatosensory cortex -from the thalamus, the signal is then sent out to the primary somatosensory cortex, contralateral to original stimulus Summary: The road trip highlights of this dorsal column-medial lemniscus system are that it conveys high fidelity information on light touch and conscious proprioception The final target of the signal is the contralateral primary somatosensory cortex, w the second order neuron body located in the ipsilateral nucleus cuneatus for the upper trunk and limbs or the nucleus gracilis for the lower trunk and limb 2.6 Conscious Nociception, Temperature, Crude Touch (ATL) Anterolateral Column Conscious Ray -spinothalamic tract Divergent -spinomesencephalic -spinoreticular -spino-emotional Spinothalamic tract: located more laterally, where as Divergent tracts : located more medially w/in the spinal cord -have diffused projections throughout the CNS Conscious relay tracts: tend to have a more direct target in the cerebral cortex Spinothalamic tract: The Traffic Can be split further into 1. Lateral spinothalamic tract 2. Anterior spinothalamic tract These pain signals travel quickly to the CNS Anterior spinothalamic tract: carries information on crude touch Lateral spinothalamic tract: carries information on discriminative pain and temperature Spinothalamic tract: the tollbooths L Tollbooths or site of neural cell bodies are the same 1. Dorsal root ganglion: spinal level innervating the periphery 2. Dorsal horn of spinal cord signals then travel up two or three spinal levels to a neural body located in the dorsal horn of SC 3. Contralateral VPL nucleus of thalamus 3rd cell body found here Note: important to remember that the signal from the dorsal root ganglion does not immediately cross midline nor traveled up to the brainstem before decussating Spinothalamic Tract: The Highway 1. Signal comes into the dorsal root ganglion in the SC then into the dorsal horn of the SC v 2. Signal then travels either up or down the SC a few levels through the dorsal horns of C3,4 or down to C6 along lissauer’s tract or the dorsolateral tract towards a second neuronal body v 3. The axon from second order neuron will decussate over the anterior commisure of the contralateral spinothalamic tract Y 4. The signal Will then ascend up to the SC and connect to the contralateral VPL nucleus of the thalamus 5. Third order cell body in the thalamus, will then relay the signal to the primary somatosensory cortex on the SAME side as the VPL nucleus, and therefore contralateral to the side of the sensory stimulus- parietal lobe Spinothalamic tract: Road Trip Highlights Divergent tracts (or pathways) in the anterior lateral system are -spinomesencephallic - spinoreticular -spino-emotional They convert pain signals w low fidelity and speed -targets include various areas in the cortex, such as the prefrontal cortex, parietal vortices and the insula, along w the anterior cingulate cortex and the medial thalamic nuclei Spino-emotional tract: integrated pain signals w the brains emotional, motivational, autonomic and personality systems Spinomesencephalic tract: target periaqueductal gray and superior follicular on the midbrain to draw our eyes and head towards the painful stimulus Spinoreticular tract: terminates in the reticular fxn of the midbrain. Slow pain signals interact w the area of the brain responsible for attention, arousal and our sleep-wake cycles • all three of these pathways convey signals for slow, vague, pain sensations, which have low fidelity • Target various parts of the contralateral brain including the cortex, thalamus and midbrain and also travel up the SC along the anterolateral column along w the spinal thalamic tract Note: important to remember is that these divergent pathways do not all follow a three-order neuronal signaling pathway the spinomesencephalic and spinoreticular tracts only have two, whereas the spino-emotional tract, which does • not go out to the cerebral cortex, does have three Summary: • the anterolateral column contains sensory information for conscious relay and divergent systems • The spinothalamic tract conveys information on discriminate pain and temp to the contralateral primary somatosensory cortex, w signals fairly immediately decussate w the spinal cord • Three divergent tracts in the system: spinoemotinal, spinomesencephalic and spinoreticular tracts, carry vague pain sensations to various parts of the cortex and the midbrain 🧍 2.7 Other Somatosensory Pathways The Pain Matrix -includes the nervous system structures that involved in pain signaling, processing and regulation • structures include 1. the cerebral cortices 2. amygdala, 3. thalamus 4. brainstem 5. spinal cord 6. Afferent signaling induced by the painful stimulus Pain signals are sent upwards to the brain through the medial divergent pain pathways and the spinothalamic tract located more laterally w/in the system It is then processed in the brainstem and brain to provide the actual experience of said pain • experience of that pain is primarily mediated by the medial pain or divergent pathway of pain signals Pain matrix is the integration of information to generate either an antinociception or pronociception response Antinociception: the top-down inhibition of pain signals Pronocoception: top down amplification of those signals Both can alter the actual pain experienced The Puzzle of Pain • pain signals are dispersed throughout the CNS, integrating w the somatosensory cortex, the emotional and motivational areas of the cortices, such as the insula, amygdala, and anterior cingulate cortex and the cognition areas in the prefrontal cortex • All the areas of the brain can light up or become active in response to a single painful stimulus, and then alter or regulate the pain experienced the human body’s experience of said pain is impacted by the chemical environment of the body, previous exposure and type of exposure to that painful stimulus, along w any memories or feelings associated w that prior exposure Tame the Pain Counterirritant Theory -built upon gate theory of pain There are interneurons in the dorsal horn; they connect the signals coming from the mechanical receptors and the C fibers detecting the pain -signals coming from these mechanical receptors can interact with the interneurons to release enkephalin, a neurotransmitter Enkephalin then is able to inhibit the transmission of the nociceptive signals into the spinothalamic tract Ex: you jam your finger in a doorway and immediately go to squeeze that finger in, perhaps, an ability to try to decrease the pain -Added pressure stimulated the mechanical receptors in the same area, activating the interneurons to inhibit said painful stimulus being sent from jammed finger Pain Processing in the Dorsal Horn ☹ 1. Normal 2. Suppressed 3. Sensitized 4. Reorganized • regulation of a pain stimulus in the dorsal horn of the SC is impacted by the state of neural activity in that region if an area of the SC is altered or injured, the integration and regulation of signals would NOT be optimal or normal With suppressed nociception, there is a reduced experience of a painful stimulus -pain is still present at the same level, but it is not experienced in the same fashion Sensitized state: opposite occurs stimulus is likely to induce a pain response where normally is does. This is termed allodynia, or it can also induce an excessive response to pain termed hyperalgesia Reorganized same type of response may also occur in a reorganized state of the dorsal horn, so some degree of neuro plasticity occurring after an injury Levels of Antinociception Occur at multiple levels - Peripheral - Dorsal horn drugs such as aspirin can prevent the activation of the nociceptors throughout the body where modalities such as heat and transcutaneous electrical stimulation can facilitate the release of enkephalin through the interneurons - Fast acting neuronal pathway - Hormonal - cerebral cortex/amygdala where higher level regulation can occur. Use of hormones controlled by hypothalamus and mediation of the pain sensation by the emotional and motivational systems in the cerebral cortex The Puzzle of Pain Part 2 • the distributed responsibility of the cortex when it comes to pain regulation The insula, somatosensory association cortex, ventrolateral orbitofrontal cortex, VPL thalamus, and the tracts w/in SC can all intensify the experience of pain input Summary: • the experience of pain variable, with regulation coming from different sites of the nervous system • The experience of pain is influenced by motivation, emotion, and cognition, and has topdown regulation to enhance or inhibit pain signals • Initially, pain stimulus is processed in the dorsal horn via interneurons with regulation, perhaps guided by the counterirritant theory. From there, pathways ascend to higher centers in the brain, and they can be considered antinociceptive or pronociceptive pathways.