Physio PDF - Central Nervous System & Sensory Receptors

Central Nervous System Synaptic transmission By Abeer El-Emam Prof. of Medical Physiology Alexandria Faculty of Medicine  ILOs By the end of this lecture, the student should be able to: 1. Define synapse and list their types 2. Ex...

Central Nervous System Synaptic transmission By Abeer El-Emam Prof. of Medical Physiology Alexandria Faculty of Medicine  ILOs By the end of this lecture, the student should be able to: 1. Define synapse and list their types 2. Explain the types of synaptic transmission 3. Explain types of post synaptic potentials 4. Differentiate different mechanisms of synaptic inhibition 5. Describe the properties of synaptic transmission  How can you transfer information to another person, place, or group?? The brain uses precise and specific pathways to communicate. Synaptic Transmission  SYNAPTIC TRANSMISSION Synapses are highly specialized contacts between nerve cells that transmit signals from the presynaptic neuron to the postsynaptic cell. between the axon or other portion of the presynaptic cell to the dendrites, cell body or axon of another neuron (postsynaptic), or in some cases a muscle or gland cell along which transmission of electrical messages takes place. Electrical & Chemical synapse Synaptic transmission  Each presynaptic neuron typically releases only one neurotransmitter Recent evidence suggests, however, that in some cases two different neurotransmitters can be released simultaneously from a single axon terminal. On binding with their subsynaptic receptor-channels, different neurotransmitters cause different ion permeability changes. excitatory synapses and inhibitory synapses.  How can NT produce their action By binding to specific receptors binding of a neurotransmitter with its appropriate subsynaptic receptor-channels always leads to change in permeability and resultant change in potential of the postsynaptic membrane. Excitatory postsynaptic potential Inhibitory postsynaptic potential  Types of NT INHIBITORY NT EXCITATORY NT Acetylcholine GABA Glutamate Glycine Norepinephrine Dopamine Serotonin Histamine SUMMATION OF POSTSYNAPTIC POTENTIAL  DIRECT & INDIRECT INHIBITION Inhibition in the CNS can be postsynaptic or presynaptic. Postsynaptic inhibition during the course of an IPSP is called direct inhibition. There are various forms of indirect inhibition, which is inhibition due to the effects of previous postsynaptic neuron discharge.  Presynaptic inhibition Mechanisms that suppress release of neurotransmitters from axon terminals or varicosities. Involves axo-axonal transmission where release of a neurotransmitter from one axon acts at receptors on another axon to suppress release of transmitter from the second axon. The increase in Cl- conductance or K efflux reduces transmitter release by inactivation of voltage- gated Na+ and Ca2+ channels Figure 4  lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception. Figure 5  The vast majority of drugs that influence the nervous system function by altering synaptic mechanisms. Synaptic drugs may block an undesirable effect or enhance a desirable effect Properties of synaptic transmission Effect of alkalosis or acidosis Effect of drugs Stimulants: caffeine, theophylline (found in coffee-tea) Inhibitory: anaesthetics  Synaptic plasticity Synaptic plasticity is the ability of the synapse, between two neurons to change in strength in response to either use or disuse of transmission over synaptic pathway, i.e., synaptic conduction can be strengthened or weakened on the basis of past experience.  Post- tetanic facilitation increase in neurotransmitter release after a brief, high-frequency train of action potentials The successive stimulation causes Ca++ to accumulate in the presynaptic neuron; the elevated Ca++ level causes more and more vesicle to release their transmitter producing a greater response of the postsynaptic neuron. may last for minutes and sometimes hours THANK YOU  SENSORY RECEPTORS By Abeer El-Emam Prof. of Physiology Alexandria Faculty of Medicine  ILOs By the end of this lecture, the student should be able to: 1. Define sensory receptors. 2. Classify receptors according to the type of the stimulus. 3. Explain the properties of sensory receptors. 4. Describe receptor potential 5. Explain receptor adaptation. 6. Describe coding for sensory information  SOMATIC SENSATIONS The somatosensory system tells us what the body what’s going on in the “environment” by providing information about bodily sensations, such as touch, temperature, pain, position in space, and movement of the joints. It is distributed throughout the entire body. Sensory receptors are the specialized structures that carry information about external and internal environment to different levels of the nervous system  SENSORY RECEPTORS Sensory receptor is a sensory nerve ending that recognizes a stimulus in the internal or external environment of an organism and responds to it by creating an action potentials in the same cell or in an adjacent cell. (1) a specialized ending of the afferent neuron or (2) a separate receptor cell closely associated with the peripheral ending of the neuron WHAT DISTINGUISH THE SENSORY RECEPTORS  ADEQUATE STIMULUS Each type of receptor is specialized to respond to one type of stimulus, (ADEQUATE STIMULUS). But can respond to another form of energy provided the intensity of stimulation is sufficiently high but will still be giving its own specific modality of sensation. e.g. stimulation of retina of eye mechanically, it still respond by producing a sensation of a flash of light.  Muller's law Each receptor is most sensitive to one specific type of stimulus called its adequate stimulus giving rise to one type of sensation regardless of the method of stimulation because the sensation perceived depends on the area in the brain ultimately activated. (specific projection). ACCORDING TO THEIR ADEQUATE STIMULUS  SOMATIC SENSATION These are sensations from the skin and deeper structures (muscles, bones, tendons and joints). TACTILE- PROPRIOCEPTIVE MECHANORECEPTIVE (KINAESTHETIC) THERMORECEPTIVE SENSATIONS: SENSATIONS SENSATIONS Touch sensation, position or NOCICEPTIVE Pressure sensation, movement of a body SENSATIONS Vibration sense part. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore.  MECHANORECEPTORS They relay extracellular stimulus to intracellular signal transduction through mechanically gated ion channels. The external stimuli are touch, pressure, stretching, sound waves, and motion There are four major categories of tactile mechanoreceptors: Merkel’s disks, Meissner’s corpuscles, Ruffini endings, and Pacinian corpuscles. Upon mechanical disruption of the receptor, ions can flow in or out of the cell, causing electrical depolarization and generation of action potentials **Touch ,pressure and vibration receptors (in the skin) **Proprioceptors (muscle, tendon, joint)  THERMORECEPTORS Stimulated by thermal form of energy Cutaneous thermoreceptors are specialized free nerve endings, found with highest density in the skin of the hands and face. Thermoreceptors include cold receptors and warmth receptors. Cold receptors or cool receptors are on dendritic endings of Aδ fibers and C fibers, whereas warmth receptors are on C fibers The skin has discrete cold-sensitive and heat-sensitive spots. There are 4–10 times as many cold-sensitive as heat-sensitive spots.  THERMORECEPTORS The threshold for activation of warmth receptors is around 30°C, and they increase their firing rate as the skin temperature increases to 46°C. However, warmth receptors are unresponsive to hot temperatures above 50°C. At these high temperatures human perceive heat pain rather than sensations of warmth. Cold receptors are inactive at temperatures of 40°C, but then steadily increase their firing rate as skin temperature falls to about 24°C. As skin temperature further decreases, the firing rate of cold receptors decreases until the temperature reaches 10°C.  CHEMORECEPTORS Stimulated by chemical forms of energy and include: Taste receptors, smell receptors  NOCICEPTORS *Respond to tissue damage They are present in the skin and viscera  ELECTROMAGNETIC RECEPTORS Respond to electromagnetic waves of light They include: the rods and cones in the retina of the eye  RECEPTOR POTENTIAL The receptors able to respond to stimuli and generate a receptor potential The generator potential normally leads to the formation of action potential provided it is large enough to bring the membrane potential of the fiber to the critical firing level CHARACTERISTICS OF RECEPTOR POTENTIALS 1 2 3 4 It does NOT It is NOT It is a local If a receptor unpropagated obey to all followed by potential is potential or none law, Refractory large enough, Its duration (more so it can be period so it than 5 msc) is it may trigger graded can be longer than the an action summated duration of potential AP(about 2msc)  RECEPTOR ADAPTATION Adaptation is decrease in the depolarization of the receptor (frequency of action potential) despite the sustained stimulation BY Adaptation; receptors are classified into: Tonic receptors : slowly adapting to stimuli and continue to produce action potentials over the duration of the stimulus.. These receptors are important in situations where it is important to maintain information about a stimulus Some tonic receptors are permanently active and don't adapt to stimuli as pain receptors, and muscle stretch receptors Phasic receptors: Rapidly adapting to stimuli, Their response diminish very quickly and then stops, such as touch receptors, CODING OF SENSORY INFORMATION Sensory coding is the process of converting a receptor stimulus to a recognizable sensation. All sensory systems code for several attributes of a stimulus: MODALITY, LOCATION, INTENSITY.  (1) MODALITY DISCRIMINATION - The “Labeled Line” Principle is the type of energy transmitted by the stimulus. Determination of stimulus modality is based on the adequate stimulus of the receptors and on the area of the brain ultimately activated The specific sensory pathways from the receptor to the cerebral cortex are discrete and are called labelled lines.  LAW OF SPECIFIC NERVE ENERGIES When the nerve pathways from a particular sense organ are stimulated, the sensation evoked is that for which the receptor is specialized no matter how or where along the pathway the activity is initiated Müller discovered that sensory organs always “report” their own sense no matter how they are stimulated. for example, applying pressure with your finger to your eyes results in a visual experience  (2) LOCALLITY DISCRIMINATION - The “law of projection” The site on the body or space where the stimulus originated ultimately reach specific area on the cortex. Each specific region of the body surface supplied by a particular spinal nerve is called a dermatome Each somatosensory neuron responds to stimulus information only within a circumscribed region of the skin surface surrounding it (Receptive field). The size of a receptive field varies inversely with the density of receptors in the region  (2) LOCALLITY DISCRIMINATION - The “law of projection” - Depends on the fact that each receptor has a specific pathway to the sensory cortex where different parts of the body are represented. Therefore, Stimulation of a sensory pathway anywhere along its course to the sensory cortex produces sensation referred to the location of the receptor.  (3) INTENSITY DISCRIMINATION is signaled by the frequency of action potential generation which is related to the amplitude of the stimulus applied to the receptor. As a greater pressure is applied to the skin, the receptor potential in the mechanoreceptor increases and the frequency of the action potentials in a single axon transmitting information to the CNS is also increased.  CHANGES IN FREQUENCY OF FIRING OF RECEPTORS Action potentials 'obey' the All-or-None law , the strength of the stimulus cannot be encoded by varying the amplitude of the action potentials (= amplitude modulation). Instead, the receptor varies the frequency of action potentials sent to the brain. This encoding method is termed frequency modulation, and it the only way that receptors can inform the brain about the strength of the stimulus  Ascending tracts They are the nervous pathway convey sensory information to the higher levels of the CNS. By Abeer El-Emam Prof. of Medical Physiology Alexandria Faculty of Medicine ILOs 1. Classify sensations according to the modality 2. Describe different types of somatic sensations 3. Categorize different somatosensory pathways 4. Explain the pathway and function of ascending sensory tracts 5. Explain sensory ataxia 6. Compare conscious and subconscious proprioception 7. Describe sensations from the head and neck  General rules - All sensory inputs enter the spinal cord via spinal dorsal root or trigeminal root. - Asecnding tracts have 2 or 4 order neurons - The first order neuron for all sensations is the dorsal root ganglia or the ganglia of cranial nerves.  General rules - All sensory pathway cross to the opposite side at different levels along their course. - All somatosensory pathways include a thalamic nucleus. - Most somatosensory pathways terminate in the parietal lobe of the cerebral cortex. - Each somatosensory pathway is named after a major tract or nucleus in the pathway.  General rules Somatosensory neurons are topographically (i.e., spatially) organized so that adjacent neurons represent neighboring regions of the body or face. This organization is preserved by a precise somatotopic pattern of connections from the spinal cord and brain stem to the thalamus and cortex. Consequently, within each somatosensory pathway there is a complete map (spatial representation) of the body or face in each of the somatosensory nuclei, tracts, and cortex  Segmental Organization of the Spinal Cord. The 30 spinal segments are divided into four groups, and each segment is named after the vertebra adjacent to where the nerves originate: cervical (C) 1–8, thoracic (T) 1–12, lumbar (L) 1– 5, and sacral (S) 1–5. columns. Each half of the spinal gray matter is divided into a dorsal horn, an intermediate zone, and a ventral horn  Segmental Organization of the Spinal Cord. Each spinal nerve is composed of nerve fibers that are related to the region of the muscles and skin that develops from one body somite (segment). A spinal segment is defined by dorsal roots entering and ventral roots exiting the cord, (i.e., a spinal cord section that gives rise to one spinal nerve is considered as a segment.)  Dorsal Horn The dorsal horns are divided laminae I–VII, with I is being the most superficial and VII the deepest. Lamina VII receives afferents from both sides of the body, whereas the other laminae receive only unilateral input.  Gray Matter and Spinal Roots Dorsal ramus Ventral ramus Rami communicantes Figure 12.31b Dorsal column medial lemniscal pathway carries general somatic afferent (general sensory) information about  Discriminative touch  Vibration sense.  Proprioceptive sensations. First order neuron (dorsal root ganglion) Their fibers are thick, myelinated rapidly conducting Aβ Second order neuron (gracilis and cuneate nuclei) Third order neuron ventral posterolateral nucleus of the thalamus terminate in the sensory area of the cerebral cortex in postcentral gyrus. The fasciculus gracilis, which carries information from the lower limb and trunk (up to and including T6) The fasciculus cuneatus, which carries information from the trunk and upper limb (above T6). The gracile and cuneate fasciculi are collectively called the posterior funiculus or posterior column. Ascends the spinal cord in the posterior funiculus up to the medulla without synapsing or decussating (i.e., without crossing the midline to the contralateral half of the spinal cord). This somatotopic organization continues as the fibers reach the medulla, where they synapse on their respective second-order neurons located in the nucleus gracilis and nucleus cuneatus. Axons from these second-order neurons cross the midline as the internal arcuate fibers and ascend bundled as the medial lemniscus to the contralateral ventral posterolateral (VPL) nucleus of the thalamus above the level of the gracile and cuneate nuclei, each half of the body is represented contralaterally (e.g., left half of body in right medial lemniscus) within the medial lemniscal pathway The axons of the dorsal column nuclei ascend within a white matter tract called the medial lemniscus. The medial lemniscus rises through the medulla, pons, and midbrain, and its axons synapse upon neurons of the ventral posterior (VP) nucleus of the thalamus. Thalamic neurons of the VP nucleus then relay the information through the posterior limb of the internal capsule and corona radiata to specific regions of primary somatosensory cortex, or S1.  Diseases of the dorsal columns produce: Sensory ataxia Subacute combined degeneration of the spinal cord (SCD) resulting from severe vitamin B12 deficiency. (paraesthesia, loss of vibratory sensation, and proprioception). Cut of the dorsal column lemniscus in the right side of the spinal cord is associated with: a. Loss of tactile discrimination on the right side of the body b. Loss of pain and temperature sensations on the right side of the body. c. Loss of vibration sense on the left side of the body. d. Loss of tactile localization on left side of the body. a  Ventrolateral (Anterolateral)system Ventral spinothalamic tract Transmits the following sensations: Pressure sense Itch and tickle  Dorsal and ventral spino-cerebellar tract Relay information unconscious proprioception to the cerebellum. Proprioception can be divided into conscious and unconscious proprioception. The spinocerebellar tract is a set of axonal fibers originating in the spinal cord and terminating in the ipsilateral cerebellum. Proprioceptive information is obtained by Golgi tendon organs and muscle spindles. Axons from muscle and joint receptors are thick myelinated Aß fibres All of these neurons are "first order" or "primary" and are sensory (and thus have their cell bodies in the dorsal root ganglion).  Pathway for dorsal spinocerebellar tracts The sensory neurons synapse in an area known as Clarke's nucleus or "Clarke's column". This is a column of relay neuron cell bodies within the medial gray matter within the spinal cord in layer VII (just beneath the dorsal horn), specifically between T1-L3. These neurons then send axons up the spinal cord, and project ipsilaterally to medial zones of the cerebellum through the inferior cerebellar peduncle.  The cuneocerebellar tract The cuneocerebellar tract has functions analogous to the posterior spinocerebellar tract but carries information about the upper limb to the cerebellum.  The ventral spinocerebellar tract The axons of these neurons cross the midline and ascend as the anterior spinocerebellar tract to the cerebellum, where the majority of the fibers cross again terminating on the side of the cerebellum ipsilateral to the original peripheral input Inform the cerebellum about future movements plan. the postural stability of the lower limb,  Lesions of the spinocerebellar tracts lead to ataxias, or loss of muscle coordination, due to a loss of proprioceptive input to the cerebellum. Clinically, however, the spinocerebellar tracts are rarely, if ever, damaged in isolation.  SOAMTOSENSORY TRACT OF THE HEAD AND NECK Trigeminal nerve is the main sensory nerve which convey sensory information from the head and neck, fibres relay in the trigeminal ganglia and relay in 3 nuclei in the brainstem: main sensory nucleus (touch, proprioception from the head), spinal trigeminal nucleus (Pain, temperature) mesencephalic nucleus (proprioception from teeth and jaw). Fibers then decussate and ascend to the contralateral ventral posteromedial nucleus of the thalamus then somatosensory cortex  Other ascending tracts Spino olivary tract: ascends from the spinal cord to the inferior olivary nucleus in the medulla. Its function is motor learning and modifying motor actions. Spino tectal: Runs from the cervical cord to the tectum of the midbrain. Its function is integration of spinal (head /neck reflexes) with visual and auditory stimuli.  PHYSIOLOGY OF PAIN SENSATION Prof. Maha Hegazi 9/18/2024 Prof Maha Hegazi 1  ILOS 1. List the general criteria of pain 2. Describe pain receptors 3. Explain the mechanism of pain 4. Distinguish pathways for pain sensations 5. Describe different types of pain 6. Compare rapid and slow pain sensation 7. Explain types of hyperalgesia 8. Compare characteristics of all types of pain 9/18/2024 Prof Maha Hegazi 2  Pain characterized by the following: 1. Has a protective value 2. Is accompanied by somatic emotional and autonomic manifestations 3. Is widely-distributed (particularly in the skin). 4. Its adequate stimulus is not specific. 5. Requires a high threshold of stimulation. 6. Is almost a non-adapting sensation. 7. Is perceived at both the cortical level as well as the thalamic level. 9/18/2024 Prof Maha Hegazi  Types of pain 1. NOCICEPTIVE PAIN a. Somatic (cutaneous) pain ; (can be fast or slow pain) b. Muscle (deep) pain c. Visceral pain It is pain due to stimulation of pain receptors Pain receptors = Nociceptors: Nociceptors are specific free nerve endings situated on Aδ myelinated and C- unmyelinated fibres, with their adequate stimulus being tissue damage. 2. NEUROPATHIC PAIN (pain due to disease of peripheral, cranial nerve or CNS) 9/18/2024 Prof Maha Hegazi  Mechanism of stimulation of pain receptors 9/18/2024 Prof Maha Hegazi 9/18/2024 Prof Maha Hegazi 6  Prof Maha Hegazi 9/18/2024 Types of pain receptors: 1.Mechanosensitive pain receptors: Stimulated by intensive pressure applied to the skin. 2.Thermosensitive pain receptors: Stimulated by extremes of temperature. These are cold-pain receptors (stimulated by temperature between 0 and 10°C) and hot pain receptors, (stimulated by temperature above 45°C). 3.Polymodal pain receptors: stimulated by high intensity mechanical, thermal (hot and cold) or chemical stimuli. These chemical stimuli are pain producing substances liberated from damaged tissues, such as: histamine, bradykinins, proteolytic enzymes, serotonin, lactic acid prostaglandins. a. Somatic pain: 1. cutaneous if produced by stimulation of pain receptors in the skin and subcutaneous tissues 2. deep ----------stimulation of pain receptors in muscles, ligaments, tendons and periosteum Deep pain is poorly localized, dull aching and commonly associated with autonomic parasympathetic effects such as bradycardia, hypotension, nausea and vomiting. 9/18/2024 Prof Maha Hegazi Types of somatic pain Somatic pain is conducted from pain receptors through two types of afferent fibers, A delta fiber (group III fibers) C fibers (group IV fibers) This gives double pain sensation a. A fast-pricking immediate pain b. A slow burning or dull aching delayed pain 9/18/2024 Prof: Maha Hegazi 9 9/18/2024 Prof: Maha Hegazi 10 9/18/2024 Prof: Maha Hegazi 11 9/18/2024 Prof: Maha Hegazi 12 Somatic pain is transmitted by the lateral tract of the ventrolateral ascending tract (which transmits also thermal sensations). Different ascending pathways are concerned with pain transmission: Spinothalamic tract (STT) Spinoreticular tract (SRT) Spinomesencephalic Spinobulbar tracts. the ascending tracts shows somatotopical character 9/18/2024 Prof Maha Hegazi 9/18/2024 Prof: Maha Hegazi 14 9/18/2024 Prof: Maha Hegazi 15  lateral sensory-discriminative pathway of the anterolateral system “The neospinothalamic tract It is the for fast pain, its location, severity and duration of injury Fibers from the S.C. terminates in the specific thalamic nucleus “ventral posterolateral (VPL) nucleus of the thalamus Fibers from the trigeminal system project to the ventral posteromedial [VPM] nucleus of the thalamus. From the thalamus, fibers project to the 9/18/2024 Prof: Maha Hegazi 16 primary somatosensory cortex.  Medial affective-motivational pathways Projections to the reticular formation, midbrain, thalamus, hypothalamus, and limbic system Influence the emotional and visceral responses to pain as well as the descending modulation of pain Transmit dull, throbbing poorly localized type of pain. It contain 1. Periaqueductal gray (PAG) (spinomesencephalic) It stimulates noradrenergic neurones in the locus coeruleus, and thus decreases the pain transmission by activating the descending pain modulating systems 2. reticular formation (spinoreticular tract) to the whole cortex for arousal an alertness associated with pain. 3. Paleospinothalamic tract: to limbic system for emotional components of pain 9/18/2024 Prof: Maha Hegazi 17 9/18/2024 Prof: Maha Hegazi 18  Reactions (effects) of somatic pain Somatic reflexes: Autonomic effects Emotional effects Cutaneous hyperalgesia (tenderness) This is pathological hypersensitivity to pain that commonly accompanies skin injuries, inflammation, burns & overexposure to sun rays. 9/18/2024 Prof Maha Hegazi  Cutaneous hyperalgesia 9/18/2024 Prof Maha Hegazi DEEP PAIN slow pain conducted by C nerve fibers. diffuse (i.e. poorly-localized) and dull aching associated with parasymp. effects. initiates reflex contraction of the near muscles. 9/18/2024 Prof Maha Hegazi  Causes of deep pain 1- Trauma to the deep structures. 2- Bone fractures & inflammation (bone itself is pain- insensitive). 3- Arthritis (= joint inflammation). 4- Severe muscle spasm e.g. in tetany 5- Muscle ischaemia 9/18/2024 Prof Maha Hegazi  VISCERAL PAIN Prof. Maha Hegazi 9/20/2024 Prof: Maha Hegazi 1 ILOs List the causes of visceral pain Explain the characters of visceral pain Interpret referred pain Explain neuropathic pain 9/20/2024 Prof: Maha Hegazi 2  VISCERAL PAIN 1) Slow pain transmitted via the paleospinothalamic pathway. 2) Diffuse (i.E. Poorly-localized). 3) Dull aching, may be spasmodic (colic). 4) Often referred to somatic structures 5) Often associated with sweating, nausea & vomiting as well as parasympathetic effects e.G. Bradycardia and hypotension, so it is frequently described as a “sickening pain”. 6) Often causes somatic reflexes e.G. Contraction of the abdominal muscles (which is known as guarding rigidity). 7) Some 9/20/2024 are referred Prof Maha Hegazi  Visceral afferent nerves Autonomic nerves 9/20/2024 Prof Maha Hegazi  Causes Of Visceral Pain 1. Mechanical stimuli (Spasmodic contraction) or Overdistension ischemia 2. Thrombosis of blood vessels supplying the viscus ischemic pain (coronary thrombosis) 3. Visceral inflammatory processes and ulcerations as gastric ulcer result in chemical irritation and pain 9/20/2024 Prof Maha Hegazi  Prof Maha Hegazi REFERRED PAIN DEFINITION: Visceral pain may be felt not only in the diseased viscus but also at a somatic structure sharing that viscera the same dermatomal origin. The pain in the skin area may be a distance away from the diseased viscus. 9/20/2024  Prof Maha Hegazi 9/20/2024 MECHANISM OF REFERRED PAIN based on 2 facts: 1. The brain is used to receive painful stimuli from the skin, so it is almost unaware of the viscera. 2. There is a considerable convergence of various afferent neurons on the spinothalamic neurons.  Mechanisms: 9/20/2024 Prof Maha Hegazi 9/20/2024 Prof Maha Hegazi 9  EXAMPLES OF REFERRED PAIN 1. Cardiac pain is referred mainly to the retrosternal region, as well as to the left shoulder and inner side of the left arm. 2. Gall bladder pain is referred to the tip of the right shoulder and right scapula. 3. Renal pain is referred to the inguinal region and testicles 4. In the early stages of inflamed appendix , pain is produced around the umbilicus, later when the parietal peritoneum is irritated, pain becomes localized to the Prof Maha Hegazi 9/20/2024 9/20/2024 Prof: Maha Hegazi 11 9/20/2024 Prof: Maha Hegazi 12  NEUROPATHIC PAIN Neuropathic pain is pain resulting from disease or damage to the peripheral or central nervous system. The pain may persist even in the absence of initial injury, commonly, it is severe and difficult to treat. Common qualities include burning or, "pins and needles" sensations, numbness and itching. Somatic pain, by contrast, is more commonly described as aching. Prof Maha Hegazi 9/20/2024 Features of neuropathic pain Abnormal pain quality—burning, stabbing. Pain is poorly localized and diffuse Pain intensity altered by emotion and fatigue Onset of pain is immediate or delayed after injury Sympathetic nervous system dysfunction may be present, vasomotor (regulation of blood vessels) and sudomotor (stimulation of sweat glands) changes 9/20/2024 Prof: Maha Hegazi 14 Peripheral neuropathic pain Causes Diabetic neuropathy Herpes zoster infection, HIV-related neuropathies, Nutritional deficiencies, toxins, Remote manifestations of malignancies 9/20/2024 Prof: Maha Hegazi 15 9/20/2024 Prof Maha Hegazi Central neuropathic pain Causes Spinal cord lesion, Multiple sclerosis and some strokes, and thalamic syndrome Mechanism: Central sensitization. Hypoactivity of the descending anti-nociceptive systems or loss of descending inhibition. 9/20/2024 Prof: Maha Hegazi 17  HEADACHEAND ENDOGENOUS PAIN CONTROL SYSTEM Prof. Maha Hegazi 9/21/2024 Prof Maha Hegazi 1 ILOs Explain headache Explain the endogenous control of pain sensations Describe stress analgesia Evaluate the significances of endogens pain control system 9/21/2024 Prof Maha Hegazi 2  DEFINITION: A headache is pain anywhere in the region of the head or neck. The brain tissue lacks pain receptors. pain is caused by stimulation of pain- sensitive structures around the brain. 9/21/2024 Prof Maha Hegazi 3  PAIN SENSITIVE STRUCTURES OF THE HEAD AND NECK Intra Cranial Cranium (the periostium of the skull) Meninges Nerves Arteries and veins 9/21/2024 Prof Maha Hegazi 4  PAIN SENSITIVE STRUCTURES OF THE HEAD AND NECK Extra Cranial Subcutaneous tissues Muscles Eyes Ears Sinuses Mucous membranes 9/21/2024 Prof Maha Hegazi 5 HEADACHE A. Primary B. secondary 9/21/2024 Prof Maha Hegazi 6  A. PRIMARY HEADACHES Types 1. Tension-type (muscular contraction) headache 2. Migraine (vascular) headache 3. Cluster headache 9/21/2024 Prof Maha Hegazi 7  TENSION-TYPE HEADACHES: account for nearly 90% of all headaches Caused by stress, overexertion, and loud noise described as if the head were being squeezed. The pain is frequently bilateral. It is a chronic neurological disorder characterized by: moderate to severe headache, and nausea. 3 times more common in women than in men. 9/21/2024 Prof Maha Hegazi 8 CAUSES OF TENSION HEADACHE Stress: Sleep deprivations Uncomfortable stressful position and/or bad posture Irregular mealtime Eyestrain Caffeine withdrawal Dehydration 9/21/2024 Prof Maha Hegazi 9  2. MIGRAINE. 9/21/2024 Prof Maha Hegazi 10  MIGRAINE Is unilateral pulsating in nature lasting from four to 72 hours It occurs secondary to prolonged tension or emotions. Accompanied by nausea, vomiting, and phonophobia and increased sensitivity to sound One-third of patients have an aura—”transient visual, sensory, language, or motor disturbances” Food items, such as chocolate, and aged cheeses trigger it. More common in women, occur at specific points in the menstrual cycle, with use of oral contraceptives, or the use of hormone replacement therapy after menopause. 9/21/2024 Prof Maha Hegazi 11 MECHANISM Reflex V.C. of the cerebral arteries, then ischemia, followed by rebound of the dilatation of the blood vessels and activation of the perivascular nociceptive nerves. 9/21/2024 Prof Maha Hegazi 12 CLUSTER HEADACHES 9/21/2024 Prof Maha Hegazi 13  The worst pain that humans experience. Crushing, or shooting pain The pain may be around the eye area and may also be a pain within the back of the eye. Occur periodically: Spontaneous remissions the cause is currently unknown More in men Unilateral headaches of extreme intensity. Duration ranges from 15 minutes to three hours The onset is rapid, and without the preliminary signs that are characteristic of the migraine 9/21/2024 Prof Maha Hegazi 14 Suicidal Electric shocks, headache Starts10/10 of intensity 9/21/2024 Prof Maha Hegazi 15 MECHANISM OF CLUSTER HEADACHE Vascular headaches ----- vasodilation that causes pressure on the trigeminal nerve. the cause is not known but recently testosterone low level is accused Hypothalamus “it has a biological clock function----- and cluster headache is strike around the same time each day, and during a particular season 9/21/2024 Prof Maha Hegazi 16  B. SECONDARY HEADACHE CAUSES & SYMPTOMS 9/21/2024 Prof Maha Hegazi 17  Secondary headaches may result from 1. Contraction of the muscles of the scalp, face or neck 2. Dilation of the blood vessels in the head 3. Brain swelling that stretches the brain's coverings. 4. Involvement of specific nerves of the face and head 5. Sinus inflammation is a common cause of headache. people who suffer from chronic headaches or severe headaches have lower levels of endorphins compared to people who do not complain of headaches. 9/21/2024 Prof Maha Hegazi 18  Extracranial causes of headache 1. Eye diseases and error of refraction 2. Teeth and gum diseases (toothache). 3. Sinusitis: 4. Otitis media and otitis externa. 5. Emotions & tension (psychogenic headache). This causes headache due to spasm of the head muscles. 9/21/2024 Prof Maha Hegazi 19  Intracranial causes of headache Irritation of the suprs-tentorial pain-sensitive structures initiates signals that are transmitted by the trigeminal nerve (leading to frontal headache) Irritation of the infra-tentorial structures initiates signals that are transmitted by the 2nd cervical nerve (leading to occipital headache). 9/21/2024 Prof Maha Hegazi 20 The commonest causes of intracranial headache include the following 1. Meningeal irritation “meningitis, brain tumors, alcohol and constipation” 1. Lowering of CSF pressure: only 20 ml removal is compensated by vascular dilation leads to pain 1. Distension of the intracranial arteries e.g. due to fevers, lowering of the CSF pressure hypertension (which causes throbbing headache) 9/21/2024 Prof Maha Hegazi 21  X The gate theory of I P pain P I control X 9/21/2024 Prof Maha Hegazi 22 At the spinal cord level A: pain inhibition + the inhibitory interneurons are stimulated by rapidly conducted sensation and + inhibited by slow one such as pain X X 9/21/2024 Prof Maha Hegazi 23 At the spinal cord level B. Pain stimulation X X X X + + 9/21/2024 Prof Maha Hegazi 24  Supraspinal (descending) analgesia built-in pain-suppressing or analgesic system Areas of the brainstem that are involved are The periaqueductal gray (PAG) The nucleus raphe magnus PAG in mid brain has (NRM) enkephalin-rich neurons The locus coeruleus (LC). opiate system which binds with opiate Stimulation pf raphe nuclei receptors that excite the produces serotonin release and NRM and/or LC neurons. activates the inhibitory interneurons and thus blocks pain transmission 9/21/2024 Prof Maha Hegazi 25 9/21/2024 Prof Maha Hegazi 26  The descending serotonergic NRM “ and noradrenergic LC axons release enkephalin from DHC interneurons as well as activating inhibitory GABAergic interneurons. Enkephalin from the dorsal-horn inhibitory interneuron inhibits release of substance P from the afferent pain-fiber either presynaptic or post-synaptic by causing hyperpolarization and opening potassium channels, thereby blocking further transmission of the pain signal. 9/21/2024 Prof Maha Hegazi 27  Supraspinal inhibition (central pathway of pain inhibition) No perception of pain Periagueductal To thalamus gray matter Opiate Reticular receptor formation Noxious stimulus Endogenous opiate Transmission of pain impulses to brain blocked Afferent pain fiber Substance P Nociceptor 9/21/2024 Prof Maha Hegazi 28  Stress analgesia Aqua puncture 9/21/2024 Prof Maha Hegazi 29  Mechanism: stress stimulates SNS. which activate the slow pain pathways then activate NArgic cells in the LC. Noradrenergic axons project to the spinal cord and block pain transmission through different inhibitory interneurons pre or post synaptic. Activity from autonomic brain areas such as the hypothalamus or the 9/21/2024 Prof Maha Hegazi amygdala30 stimulates the PAG 3 1 Thank you 9/21/2024 Prof Maha Hegazi  SOMATOSENSORY CORTEX Prof. Maha Hegazi 9/22/2024 Prof: Maha Hegazi 1  Cerebral Cortex Motor and Sensory cortex prof. Maha Hegazi 9/22/2024 prof Maha Hegazi 2 ILOs Classify the functional parts of the cerebral cortex Describe the functional areas of the sensory cortex Compare their functions Expect the consequences of their lesions 9/22/2024 prof Maha Hegazi 3 9/22/2024 prof Maha Hegazi 4 9/22/2024 prof Maha Hegazi 5  Cerebral Cortex 9/22/2024 prof Maha Hegazi 6  Cerebral Cortex 9/22/2024 prof Maha Hegazi 7  Lateral surface of the cerebral cortex.  Cerebral cortex Areas for Sensory areas Motor areas integrative functions - Primary motor area - Primary sensory areas I,II - Prefrontal association - Premotor area area - Sensory association areas - Supplementary (secondary, tertiary) - language areas motor 9/22/2024 prof Maha Hegazi 9 9/22/2024 prof Maha Hegazi 10 9/22/2024 prof Maha Hegazi 11  Sensory areas of the cerebral cortex 1. Primary somatic sensory area I: It occupies the post central gyrus in (Broadmann areas 1,2,3) 9/22/2024 prof Maha Hegazi 12   Crossed.  Inverted. 9/22/2024 prof Maha Hegazi 13 CHARACTERS 1. It receives sensations opposite side of the body (however, there is a very small amount of sensory information from the same side of the face). 2. The body is inverted but the face is not inverted. 3. The area of representation of each part is proportionate to the number of receptors in this part and not to its size 4. The areas of representation are changeable 5. It shows modality orientation e.g. the posterior part is concerned with pressure & tactile sensations, while the anterior part is concerned with proprioceptive sensations. prof Maha Hegazi 9/22/2024 14  AREAS OF REPRESENTATION ARE UNEQUAL. 9/22/2024 prof Maha Hegazi 15  16 SI cortex is necessary for the conscious Function of awareness that a stimulus has occurred, and of its quality, location, intensity and duration. Somatosensory It is a center for perception of Fine touch, area I. Tactile discrimination, vibration, Pressure, all grades of temperature and proprioception (conscious kinesthesia). 9/22/2024 prof Maha Hegazi  Lesion  it does not result in a complete loss of sensory perception, but rather in a deficit in the awareness of sensory input and poor localization of sensory stimuli from the opposite side of the body. its destruction causes deficits in all aspects of discriminative touch and proprioception on the opposite side of the body. 9/22/2024 prof Maha Hegazi 17 2. Primary somatic sensory area II Site: This is a small area that lies posterior to the lower end of the postcentral gyrus. Character: The representation of the different parts of the body in this area is much less sharp than in somatosensory area I. 9/22/2024 prof Maha Hegazi 18 9/22/2024  Lesion Difficulty in learning new features of objects based on shape or texture. 9/22/2024 prof Maha Hegazi 20  3. Somatic sensory association area (Brodmann’s areas 5 and 7) Site: It receives afferent fibres from primary somatic sensory areas I and II from the thalamic association nuclei. from the visual system and other systems involved in attention and motivation. 9/22/2024 prof Maha Hegazi 21 9/22/2024  Effect of Damage: this leads to inability to recognize objects by touch (tactile agnosia) (astereognosis) and failure to perceive complex sensations though the simple sensory skills are normal. 9/22/2024 prof Maha Hegazi 23  Large lesions involving the posterior parietal cortex and the adjoining superior temporal gyrus may result in an attentional deficit called “neglect”, The patient is described as ignoring the contralesional half of her/his body and space. The perception of a "whole" body is lost, and the body parts affected may be considered to belong to someone else. 9/22/2024 Prof: Maha Hegazi 24  Motor Cortex & Cortical Control of Motor Function Passainte Saber Professor of Medical Physiology 1  OBJECTIVES By the end of this lecture students should be able to: 1. List the cortical motor areas (primary, premotor, supplementary), their characteristics, functions & the effects of their lesions. 2. Explain the importance of the related cortical structures located within the motor area 6 & their specific functions. 3. Describe Prefrontal association area and list its functions. 4. Describe the cortical control over the motor function. 5. Describe cortical plasticity. 2  Cerebral cortex Areas for Sensory areas Motor areas integrative functions - Primary motor area - Primary sensory areas I,II - Prefrontal association area - Premotor area - Sensory association areas - Language areas - Supplementary motor (secondary, tertiary) 3 Cortical motor areas 4 Cortical motor areas 5  1- Motor area 4 (primary motor cortex) Site: Precentral gyrus in frontal lobe. 6  1- Motor area 4 (primary motor cortex) Topographical representation: Inverted (head down and legs up). Size of presentation coincide with the complexity of movement and not its size stylised reconstruction of the body in the motor cortex Crossed. Area of representation is proportional to the skilled movement produced. 7  1- Motor area 4 Functions: (primary motor cortex) 1- Initiation of fine discrete movements of the opposite side of the body e.g. fingers. 8  1- Motor area 4 (primary motor cortex) Functions: 2- Necessary for superficial reflexes (abdominal, cremastric and plantar reflex). 9  2- Motor area 4 (primary motor cortex) Effects of lesion: 1- Loss of fine movements of opposite side of body in the form of monoplegia (localized). 2- Loss of abdominal and cremastric reflex. 3- Partial Babiniski’s sign: dorsiflexion of the big toe on scratching lateral aspect of the foot. 10  2- Motor area 6 (Premotor area) Site: in front of motor area 4 on lateral aspect of frontal lobe (part of prefrontal cortex). Topographical representation: is inverted and crossed. 11  2- Motor area 6 (Premotor area) Functions: 1- Controls gross movements of the opposite side of body (big joints and limbs). 12  2- Motor area 6 (Premotor area) Functions: 2- It deals with learned motor activities of a complex and sequential nature, by coordinating contractions of specific groups of muscles 13  2- Motor area 6 (Premotor area) Functions: 3-contain the (mirror neurons) for Sensory motor association are a class of neuron that modulate their activity both when an individual executes a specific motor act and when they observe the same or similar act performed by another individual 14  2- Motor area 4 (primary motor cortex) Effects of lesion: 1- Paresis i.e weakness of voluntary movements But not paralysis. 15  Specialized areas in premotor cortex 1- Motor speech area (Broca’s area) 2- Eye movement area 3- Head rotation area 4- Hand skills area 16  Motor speech area (Broca’s area) Site: Word formation area (area 44) It lies immediately anterior to the primary motor cortex and immediately above the sylvian fissure 17  Motor speech area (Broca’s area) Word formation area (area 44) Function: It is involved in the formation of words by controlling muscles associated with speech, including those in the mouth, tongue and larynx It stores the complex sequence of orders for vocalization. 18  Motor speech area (Broca’s area) Word formation area (area 44) Effects of lesion: It doesn’t prevent the person from vocalization but makes it impossible for the person to speak the whole words or an occasional simple word like (no) or (yes) 19  Eye movement area (area 8) Frontal eye field area Site: In the premotor area immediately above Broca’s area 20  Eye movement area (area 8) Frontal eye field area Function: Gives origin to the corticonuclear tract of both sides It is responsible for voluntary conjugate deviation of both eyes to opposite side. 21  Eye movement area (area 8) Frontal eye field area Effect of lesion: Transient inability to produce conjugate eye movement. The tectospinal tract from the superior colliculus compensates and the reflex of eye movement returns 22  Head rotation area Site: In the premotor area immediately above area 8 23  Head rotation area Functions: It directs the head towards different objects Lesions: Inability to rotate the head towards different objects 24  Hand Skills area Site: In the premotor area anterior to the primary motor cortex for the hands and fingers. 25  Hand Skills area Function: It controls complex skilled movements e.g.: sharpening of pencil and drawing figures Lesions: Agraphia and motor apraxia. Damage of this area makes hand movements uncoordinated and non- purposeful 26  3. Supplementary motor area Site: Medial surface of premotor cortex (superior to area 6). 27  3. Supplementary motor area Functions: - 1- It supplements (helps) area 6 in the control of voluntary movements of the proximal parts of the body (gross movements) as a background for fine hand or feet movements. 28  3. Supplementary motor area Functions: - 2- It plays a role in planning of movements before they start especially complex and bilateral movements 3- It is active during “mental rehearsal” for a movement. 29  MENTAL REHEARSAL OF MOVEMENTS Executing a skill and practices the skill in their mind  3. Supplementary motor area Functions: - 4- This area functions in concert with the premotor area to provide body-wide attitudinal movements, positional movements of the head and eyes, as background for the fine motor control of the arms and hands by the premotor area and primary motor cortex. 31  Damage to the PM or SMA APRAXIA N.B.: Apraxia is the loss of ability to carry out familiar learned purposeful movements, in the absence of sensory or motor impairment. 32  The prefrontal association area (Anterior association area) Site: It lies in frontal lobe anterior to premotor area. It is divided into: a- Dorsolateral prefrontal cortex (Executive functions) B- Ventromedial prefrontal cortex (orbitofrontal cortex) (Controlling behavior) 33  The prefrontal association area (Anterior association area) Functions: 1. Elaboration of thoughts and ideas. 34  The prefrontal association area (Anterior association area) Functions: 2. Because of its close association with the motor cortex, it shares in planning complex patterns and sequences of motor movements. 35  The prefrontal association area (Anterior association area) Functions: 3. Due to its connection to hippocampus, it is involved in recent memory. 4. Due to its connection with the limbic system, it shares in the control of emotional behavior. 36 The prefrontal association area (Anterior association area) 37 Cortical control over the motor function (MOTOR HIERARCHY) 38 The control of movement by the central nervous system is a complicated process that involves multiple regions of the brain: 1. Generation of idea occurs in the prefrontal cortex. 2. Awareness of the surrounding environment and position in space. This information is generated through somatosensory, visual and auditory sensory inputs to the posterior parietal cortex. 3. Motivation and memories regulating the behavior takes place either rewarding or stopping the desire in the limbic system. 39 40 The control of movement by the central nervous system is a complicated process that involves multiple regions of the brain: 4. Plan or program performed in the basal ganglia, Cerebellum, Premotor cortex (PMC) Supplementary motor areas 41 The control of movement by the central nervous system is a complicated process that involves multiple regions of the brain: 5. Execution of motor orders through the cortex is relayed via the corticospinal tracts and corticobulbar tracts to motor neurons. 42  Cortical plasticity The motor cortex shows cortical plasticity, , the maps of the motor cortex are not immutable, and they change with experience. - The finger areas of the contralateral motor cortex enlarge as a pattern of rapid finger movement is learned with the fingers of one hand. this change is detectable at 1 week and maximal at 4 weeks. 43  Cortical plasticity - When a limb is amputated, its area of representation in the brain become not useless, but expansion of the neighboring area representing other body parts to this area occur. 44 MCQs 45 The area of the motor cortex that is devoted to a particular region of the body is proportional to the : A) size of the body area. B) distance of the body area from the brain. C) degree of precision of movement in this area. D) type of receptors in the area of the body. ANSWER C 46 Supplementary motor area is involved in which of the following functions? a) Adjusting posture. b) Working memory. c) Coordinating Bilateral movements. d) Coordinating fine movements ANSWER C 47 Thank you 9/22/2024 copyright 2006 www.brainybetty.com 48 Descending Motor Tracts By Abeer El-Eman Prof. of Medical Physiology Alexandria Faculty of Medicine ILOs 1. Explain the physiological significances of the descending motor tracts (Corticospinal tract, and Corticobulbar tracts) 2. Differentiate between medial and lateral descending brain stem pathways involved in motor control. 3. Describe physiological role of medial descending system: pontine and medullary reticulospinal, vestibulospinal, and tectospinal in motor control 4. Describe physiological role of Lateral descending system in motor control 5. Explain the mechanism of cortical control on axial and distal muscles.  How does the brain communicate with motor neurons of the spinal cord??? Through axons descend from the brain through the spinal cord along several pathways (DESCENDING SPINAL TRACTS) They are the tracts that deliver efferent impulses from the brain to AHC in the spinal cord or motor cranial nerve nuclei.  The motor system can be divided into upper and lower motor neurons Upper motor Lower motor neurons neurons Are those in the Refer to the spinal cerebral cortex and cranial motor and brain stem neurons that that activate the directly innervate lower motor skeletal muscles. neurons. Their axons Their axons proceed through constitute the the peripheral descending motor somatic nerves to pathways. innervate skeletal muscles  Descending motor pathways are organized into two major groups: 1.Lateral pathways control distal muscles and are responsible for most voluntary movements of arms and legs. They include the 1. Lateral corticospinal tract 2. Rubrospinal tract 2.Medial pathways terminates at neurons in the medial or ventral portions of the anterior horn of the spinal cord. control axial muscles and are responsible for posture, balance, and coarse control of axial and proximal muscles. They include the 1. Vestibulospinal tracts (both lateral and medial) 2. Reticulospinal tracts (both pontine and medullary) 3. Tectospinal tract 4. Ventral corticospinal tract Descending motor pathways are organized into two major groups: Descending motor pathways are organized into two major groups:  Corticospinal tracts Originate from area 4,6,SMA,Somatosensory cortex Pass through the posterior limb of internal capsule- Midbrain-pons and form tract at the base of the medulla.(medullary pyramid) At the junction of the medulla and spinal cord, 80% of the fibers crosses or decussates ; PYRAMIDAL DECUSSATION Descend in the lateral column of the spinal cord to terminate in the anterior horn cells of the opposite side directly on the anterior motor neurons that cause muscle contraction , making monosynaptic connections to spinal motor neurons. LATERAL CORTICOSPINAL TRACT  Corticospinal tracts Functions Control of voluntary movement of distal muscles on the opposite side of the body It inhibits Babinski sign.  Corticospinal tracts The remaining 20% of the axons that do not cross at the caudal medulla constitute the ventral corticospinal tract, as they continue down the spinal cord in the anterior column where axons synapse on spinal interneurons prior to motor neurons and then cross at the level of the spinal cord to terminate on the anterior horn cells of the opposite side. Ventral corticospinal tract is concerned with Postural adjustments. Control of the proximal musculature. Facilitation of muscle tone.  Corticospinal tracts Effect of lesion Loss of fine movements on the contralateral side of the body. (the person can sit upright and stand with normal posture but unable perform movements with distal muscles) Lesions of the ventral corticospinal tract produce axial muscle deficits that cause difficulty with balance, standing and walking.  Corticobulbar tracts It originates as axons of the pyramidal neurons in the cerebral corte pass from motor cortex axons through the genu of the internal capsule,the cerebral peduncle (medial to corticospinal tract neurons), to descend with corticospinal tract fibers in the pons and medulla. terminates in brain stem on motor neurons V,VII,X, XI,XII. Corticobulbar fibers end either directly on the cranial nerve nuclei or on interneurons within the brain stem  Corticobulbar tracts Corticobulbar tract from one side of the brain terminates mostly in the cranial motor nuclei of both sides of the brain stem. EXCEPT the lower part of the facial nerve nucleus, and the hypoglossal nerve nucleus receive only contralateral innervation from the cerebral cortex. Coticobulbar tract intiatie the voluntry movements of head, neck, face and tongue muscles.  Corticonuclear tracts Controls LMNs of cranial nerves supplying extra-ocular muscles of the eye (III, IV, VI).  Somatotopic arrangement Throughout its course, the corticospinal tract features a somatotopic arrangement of fibers from medial to lateral: arm, trunk, leg. In the cortex, this somatotopy results in a cortical map of motor representation of the body, known as a motor homunculus