Physiology Notes Dr.Turki PDF

‫ال تنسوني من صالح دعائكم‬ ‫‪Physiology‬‬ ‫‪Dr.Turki’s Notes‬‬ ‫قال ﷺ "من سلك طريقا يلتمس فيه علما سلك ال به طريقا إلى اجلنة "‬ Check out my channal on Telegram @DrTurkiNotes Le...

‫ال تنسوني من صالح دعائكم‬ ‫‪Physiology‬‬ ‫‪Dr.Turki’s Notes‬‬ ‫قال ﷺ "من سلك طريقا يلتمس فيه علما سلك ال به طريقا إلى اجلنة "‬ Check out my channal on Telegram @DrTurkiNotes Lecture Page Physiology of synapses & receptors 2 Physiology of Reflexes 5 Sensory Physiology 8 Motor Physiology 11 Physiology of Brainstem 13 Physiology of Sleep 15 Physiology of Sympathitic & 17 Parasympathitic Physiology of Hearing 20 Physiology of Eye 23 Vision Phototransduction Light & Dark 27 Physiology of Taste & Smell 30 1 Check out my channal on Telegram @DrTurkiNotes Lec1: Physiology of synapses & receptors Types of Synapses: 1. Nerve-to-nerve synapse: A junction where the axon of a neuron terminates on a part of another neuron: a. Dendrites (axo-dendritic) b. Soma (axo-somatic) c. Axon (axo-axonic) 2. Nerve to muscle - neuromuscular junction 3. Nerve to gland – neuro-glandular junction A. Electrical Synapses: Communication via current flowing through gap junctions. No gap junctions delay transmission. Can be unidirectional or bidirectional. Locations: Cell membrane to cell membrane protein interconnection. Rare in the brain, used in attention, emotion, and memory. B. Chemical Synapses: Communication via secretion of neurotransmitters (NTs). Input is converted to a nerve impulse (AP) at the axon hillock. Output signal (AP) travels via a single axon leaving the neuron. Synaptic vesicles contain (NTs). Each vesicle contains only one type of (NTs), but different vesicles containing different types of NTs can be found in a single synaptic terminal. Synaptotagmin and SNAREs are proteins involved in vesicle fusion. Neurotransmitters are divided into two groups depending on the rate of action: A. Small-molecule transmitters: Rapidly acting (open ion channels). 1. Acetylcholine 2. Amines 3. Amino acids B. Neuropeptides: Action is slow (act on DNA or through second messenger systems) and are released in small quantities but have a potent effect. 1. Opioids 2. GI peptides 3. Hypothalamic and pituitary peptides 2 Check out my channal on Telegram @DrTurkiNotes Oxytocin Somatostatin Vasopressin Neurokinin Substance P Receptors: There are two types of receptor proteins (NT receptors) on membranes of postsynaptic neurons: 1. Ionotropic receptors: These directly gate ion channels (ligand-gated ion channels). Contain two functional domains: 1. An extracellular site that binds NTs (binding site). 2. A membrane-spanning domain that forms an ion channel. a. Cation channels (mainly Na+, but also K+ and Ca2+). b. Anion channels (Cl-). 2. Metabotropic receptors: These act through second messenger systems. NT can be excitatory or inhibitory depending on the receptor it binds to. Metabotropic receptors: Physically separated from the ion channel. Proteins with an extracellular domain binds NTs and an intracellular domain binds to a G-protein. Activate channels indirectly through intermediate molecules (G-proteins). Postsynaptic potentials: Ionotropic receptors mediate rapid post-synaptic potentials (PSPs) lasting 10-30 ms or less. PSPs (EPSPs or IPSPs) develop within 1-2 ms after an AP reaches the presynaptic terminal. Metabotropic receptors mediate slower PSPs, which can last from hundreds of milliseconds to minutes or longer. This slowness is due to second messenger leading to the opening of ion channels. Neurotransmitter fate: a. After dissociation neurotransmitter can undergo one of three fates: 1. Enzymatic degradation: Part is inactivated by enzymes at the postsynaptic membrane. 2. Reuptake by the presynaptic neuron for reuse. 3. Diffusion into the bloodstream. At rest (-65 mV), resting membrane potential is uniform throughout the cell. At excitatory synapses: Na+ influx causes depolarization (EPSP) (~20 mV change, to -45mV). At inhibitory synapses: K+ efflux or Cl- influx causes hyperpolarization (IPSP) (~5 mV change). 3 Check out my channal on Telegram @DrTurkiNotes Summation: Spatial summation: Summation of stimuli from two different presynaptic elements arriving at the same time. Temporal summation: Summation of stimuli from a single or different presynaptic impulses arriving one after the other. Dale’s Phenomenon: Only one type of neurotransmitter is released from all terminals of a single neuron at a time. Bell-Magendie Law: One-way conduction in nerves. Synaptic delay: Time taken for synaptic transmission. Occlusion and subliminal fringe: Overlapping or non-overlapping neural networks. Synaptic fatigue: Exhaustion of neurotransmitter stores. Convergence and divergence: Convergence: Multiple presynaptic inputs converge on a single postsynaptic neuron. Divergence: One presynaptic neuron branches to multiple postsynaptic neurons. Drugs and synaptic transmission: Drugs can influence synaptic transmission by: Altering neurotransmitter synthesis, storage, or release. Modifying interaction with postsynaptic receptors. Affecting reuptake or destruction of neurotransmitters. Examples of drug effects: Cocaine: Blocks dopamine reuptake, prolonging the activation of the pleasure pathway. Strychnine: Competes with glycine, blocking glycine receptors and preventing IPSPs. Prozac (SSRI): Blocks serotonin reuptake, used to treat depression by increasing serotonin levels. Parkinson’s disease: Caused by dopamine deficiency in the substantia nigra (responsible for complex movements). Symptoms: Tremors, muscle rigidity. Treatment: , a dopamine precursor that crosses the blood-brain barrier and converts into dopamine in the brain. Other factors affecting neurons: Alkalosis: Increases neuronal excitability (can cause cerebral epileptic seizures). Acidosis: Depresses neuronal excitability (pH ~7.0 can cause coma). Caffeine: Increases excitability by lowering the excitation threshold. 4 Check out my channal on Telegram @DrTurkiNotes Lec2: Physiology of Reflexes Spinal Cord Organization: White Matter: Outer layer containing ascending (sensory) and descending (motor) tracts, divided into: a) Dorsal (Posterior) Column b) Lateral Column c) Ventral (Anterior) Column Gray Matter: Inner H-shaped region divided into: a) Dorsal Horn: Contains sensory neurons. b) Lateral Horn: Contains autonomic neurons (in certain segments). c) Ventral Horn: Contains motor neurons. Basic Functions of the Spinal Cord: Acts as a two-way communication channel between the brain and the body. Processes sensory signals and motor commands. Houses centers for important spinal reflexes. Reflex Arc Components: 1. Stimulus 3. Sensory Neuron 5. Motor Neuron (Afferent) (Efferent) 2. Receptor 4. Center: Processing 6. Effector: Organ that center. responds 5 Check out my channal on Telegram @DrTurkiNotes Types of Reflexes: a. Classification Based on Receptor Site: Deep Reflexes Visceral Reflexes Superficial Reflexes Micturition Reflex: Polysynaptic visceral reflex involving stretch receptors in the bladder. Superficial Reflexes: Abdominal Reflex: Tested by gentle skin stroke causing movement of the umbilicus. Plantar Reflex: Tested by stroking the sole, resulting in plantar flexion (Babinski’s sign indicates upper motor neuron lesion). Polysynaptic Reflexes: Involves multiple interneurons, often à reciprocal inhibition and longer-lasting motor responses. Withdrawal Reflex: A protective reflex that withdraws a body part from harmful stimuli. A. Crossed Extensor Reflex: A withdrawal reflex where one leg flexes while the opposite extends to maintain balance. Stretch Reflex: Stimulus: Muscle stretch. Receptor: Muscle spindle. 6 Check out my channal on Telegram @DrTurkiNotes Afferent: Sensory fibers (Type Ia & II). Effector: Extrafusal muscle fibers. Center: Anterior horn cells. Response: Muscle contraction. Efferent: Alpha motor neurons. Muscle Spindle Stimulation: 1. Resting state: Some impulses are present. 2. Stretching: Increases impulses. 3. Contraction: Stops impulses. 4. Gamma efferent stimulation: Leads to peripheral contraction of intrafusal fibers. Mechanisms and Functions of Reflexes: Gamma Efferent Discharge: Function: Enhances muscle contraction through alpha-gamma coactivation. Muscle Tone: Caused by static stretch reflex, allowing muscles to resist gravity without causing fatigue. Types of Stretch Reflexes: Dynamic Stretch Reflex: Sudden stretch leads to contraction. Static Stretch Reflex: Steady stretch leads to maintained contraction. Negative Stretch Reflex: Muscle shortening leads to relaxation. Inverse Stretch Reflex: Overstretching activates the Golgi tendon organs, causing relaxation. Deep Reflexes (Tendon Jerks): Based on dynamic stretch reflex. Commonly examined in biceps, triceps, knee, and ankle reflexes. 7 Check out my channal on Telegram @DrTurkiNotes Lec3: Sensory Physiology 1. Organization of the Nervous System: Sensory Receptors: specialized cells or nerve endings that detect stimuli from the environment (internal or external). Reflexes: Involuntary, immediate movements in response to a stimulus. Neuronal Circuits: Networks of neurons that process sensory input & motor output. 2. Types of Somatic Sensations: General Sensations: Include touch, pressure, vibration, temperature, and pain. Special Sensations: Include vision, hearing, taste, and smell. 3. Nerve Fiber Diameter and Myelination: The myelination (fatty covering of axons) of afferent (sensory neurons) affect the speed at which nerve impulses are conducted. Larger & more myelinated fibers conduct signals faster. 4. Dorsal Column-Medial Lemniscus vs. Spinothalamic Systems: a. Dorsal Column-Medial Lemniscus System: Carries fine touch, vibration, and proprioception (position sense) information. Neurons decussate (cross to the opposite side) at the medulla. b. Spinothalamic System: Carries pain, temperature, crude touch, and pressure. Neurons decussate earlier, at the level of the spinal cord. 5. Topographic Representation of the Body in the Somatosensory Cortex: The somatosensory cortex has a map (homunculus) of the body, where each body part is represented according to the number of sensory receptors it has. 8 Check out my channal on Telegram @DrTurkiNotes Sensory System Overview: Receptors Tracts Sensory Cortex Afferents Types of Receptors: 1. Mechanoreceptors: Sense touch, pressure, vibration, and position. 2. Thermoreceptors: Sense heat and cold. 3. Nociceptors: Sense pain, activated by tissue damage. Sensory Pathway (Transduction & Conduction): Transduction: conversion of a stimulus into an electrical signal (AP). Impulse Conduction: transmission of the AP to the CNS. Classification of Nerve Fibers: (Aα, Aβ, Aδ, C) varying functions & conduction speeds. Dorsal Root Ganglia: where the cell bodies of sensory neurons are located. Spinal Cord Processing: Sensory fibers enter dorsal horn, and divided into laminae based on fiber types. Ascending Tracts (Sensory Pathways) sensory informationà brain: 1. Dorsal Column Tract: Carries fine touch, proprioception, and vibration. 2. Anterior Spinothalamic Tract: Carries crude touch and pressure. 3. Lateral Spinothalamic Tract: Carries pain and temperature. 4. Spinocerebellar Tracts: Carry proprioceptive information to the cerebellum (balance and movement coordination). 5. Spino-olivary, Spinotectal, Spinoreticular, Spinopontine Tracts: have sensory processing and modulation. Dorsal Column-Medial Lemniscus Pathway (Detailed): 1. 1st Order Neurons: Start in the periphery and enter the spinal cord through the dorsal root ganglia, running ipsilaterally and synapsing in the nucleus gracilis (for lower limbs) or nucleus cuneatus (for upper limbs) in the medulla. 2. 2nd Order Neurons: Decussate in the medulla and ascend through the medial lemniscus to the thalamus. 3. 3rd Order Neurons: Project from the thalamus to the somatosensory cortex (S1) in the parietal lobe. Spinal Cord Lesions: 9 Check out my channal on Telegram @DrTurkiNotes Dorsal Column Injuries ( B12 deficiency, Tabes dorsalis) result in ipsilateral loss of fine touch, proprioception, and vibration below the lesion. Anterolateral System Injuries result in contralateral loss of pain and temperature sensation. Anterolateral System (Spinothalamic Tract) Pathway: 1. 1st Order Neurons: Enter the spinal cord and synapse with 2nd order neurons. 2. 2nd Order Neurons: Decussate in the spinal cord and ascend through the ventral or lateral tracts to the thalamus. 3. 3rd Order Neurons: Project from the thalamus to the somatosensory cortex. Lateral spinothalamic tract carries pain and temperature sensations. Anterior spinothalamic tract carries crude touch and pressure. Speed of Pain Fibers: Aδ fibers: Myelinated, fast pain conduction. C fibers: Unmyelinated, slow pain conduction. Sensory Cortex Representation: The area of the cortex devoted to a body part depends on the density of sensory receptors in that region (e.g., hands and face have more representation than the back). 10 Check out my channal on Telegram @DrTurkiNotes Lec4: Motor Physiology Motor Pathways Overview: 1. Upper Motor Neurons (UMNs): A. Definition: Neurons with cell bodies in higher motor centers (motor cortex) whose axons project to the brainstem and spinal cord to activate LMNs. B. Function: UMNs influence the activity of LMNs and control voluntary muscle movements. 2. Lower Motor Neurons (LMNs): A. Definition: Neurons located in the brainstem and spinal cord directly innervate skeletal muscles. B. Function: LMNs directly stimulate muscles to contract. Types of Motor Pathways: 1. Pyramidal Tracts: Corticospinal Tract: a. Origin: Primary motor cortex (M-I), premotor area, supplementary motor area, and somatic sensory areas. b. Course: Fibers descend through the corona radiata, internal capsule, midbrain, and pons. About 80% decussate in the medulla and descend as the lateral corticospinal tract; 20% descend ipsilaterally as the ventral corticospinal tract. c. Functions: Controls fine motor skills of the limbs and digits, posture, and muscle tone. 2. Corticobulbar Tract: a. Origin: Primary motor cortex. b. Course: Descends to cranial nerve nuclei in the brainstem. c. Functions: Controls facial expression, mastication, swallowing, and movements of the face & neck. 3. Extrapyramidal Tracts: Rubrospinal Tract: o Origin: Red nucleus in the midbrain. o Course: Descends in the lateral columns of the spinal cord. o Functions: Facilitates motor control of distal limb muscles, particularly flexors, and is involved in fine motor control. Reticulospinal Tracts: Medial Reticulospinal Tract: 11 Check out my channal on Telegram @DrTurkiNotes o Origin: Pontine reticular formation. o Course: Descends to all levels of the spinal cord. o Functions: Facilitates α- and γ-motor neurons for antigravity muscles and extensor muscles of the lower limbs. Lateral Reticulospinal Tract: o Origin: Medullary reticular formation. o Course: Descends to all levels of the spinal cord. o Functions: Inhibits α- and γ-motor neurons for antigravity muscles, facilitates flexor muscles. Vestibulospinal Tract: o Origin: Vestibular nuclei in the pons. o Course: Descends in the spinal cord. o Functions: Controls balance and posture by regulating muscle tone and helping with body position adjustments. Tectospinal Tract: o Origin: Superior colliculus in the midbrain. o Course: Descends to the cervical spinal cord. o Functions: Coordinates head and neck movements in response to visual stimuli. Olivospinal Tract: o Origin: Inferior olivary nucleus in the medulla. o Course: Found only in the cervical region of the spinal cord. o Functions: Involved in proprioception and regulation of muscle tone. Motor Cortex Areas: Primary Motor Cortex (M-I): Located in the pre-central gyrus; contains Betz cells and controls contralateral muscle movements. Damage results in paralysis on the opposite side of the body. Premotor Cortex: Lies in front of the primary motor cortex and is involved in planning and coordinating complex movements. Supplementary Motor Area (SMA): Works with premotor cortex to initiate and coordinate complex movements. Broca’s Area: Responsible for speech production, located in the frontal lobe. Frontal Eye Field: Controls voluntary eye movements toward different visual objects. Head Rotation Area: Directs head movements toward visual objects. Area for Hand Skills: Responsible for bilateral grasping movements and motor programs for axial muscles. 12 Check out my channal on Telegram @DrTurkiNotes Lec5: Physiology of Brainstem 1. Introduction to the Brainstem Components: Midbrain Pons Medulla Connections: The cerebellum connects to the brainstem via the superior, middle, and inferior cerebellar peduncles, linking to the midbrain, pons, and medulla, respectively. 2. Importance of the Brainstem Functions: Conduit Functions: Transmits information between the brain and body. Cranial Nerve Origins: Cranial nerves III-XII originate here. Integrative Functions: Coordinates sensory and motor functions. Conjugate Eye Movements: Controls coordinated eye movements. 3. Motor and Sensory Pathways Ascending (Sensory) Tracts: Spino-thalamic Tract: Transmits pain and temperature sensations. Dorsal Column Tracts: Fasciculus Gracilis: Touch, proprioception, and pressure sensations. Fasciculus Cuneatus: Same as above but from upper body. Descending (Motor) Tracts: Corticospinal Tract: Originates in the cerebral cortex. Other UMNs: Originate from vestibular nucleus, red nucleus, and reticular nuclei and descend to synapse in the spinal cord. 4. Cranial Nerves Overview Cranial Nerves Originating in the Brainstem: 13 Check out my channal on Telegram @DrTurkiNotes Midbrain: III (Oculomotor), IV (Trochlear) Pons: V (Trigeminal), VI (Abducens), VII (Facial), VIII (Vestibulocochlear) Medulla: IX (Glossopharyngeal), X (Vagus), XI (Accessory), XII (Hypoglossal) Functions of Cranial Nerves: 1. I (Olfactory): Smell 8. VIII (Vestibulocochlear): Hearing, equilibrium 2. II (Optic): Vision 9. IX (Glossopharyngeal): Taste, carotid blood pressure 3. III (Oculomotor): Eyelid & eyeball movement 10. X (Vagus): Aortic blood pressure, heart rate, digestive 4. IV (Trochlear): Innervates superior oblique; turns eye organs, taste downward and laterally 11. XI (Accessory): Trapezius & sternocleidomastoid 5. V (Trigeminal): Chewing, face & mouth touch and pain control, swallowing movements 6. VI (Abducens): Turns eye laterally 12. XII (Hypoglossal): Tongue movements 7. VII (Facial): Facial expressions, tears, saliva, taste 5. Functions of the Brainstem Reflex Centers Balance Maintenance: Via vestibular nuclei. Pain Sensitivity Control: Periaqueductal grey matter modulates painful stimuli. Autonomic Regulation: Cardiovascular Center: Controls myocardial contractility, HR, BP, and BV diameter. Respiratory Centers: Medulla: DRG (Inspiratory center), VRG (Expiratory center) Pons: Apneustic center, Pneumotaxic center Other Functions: Controls tone, posture, equilibrium, and respiration, circulation, and digestion. 6. Reticular Formation and RAS Reticular Formation: Diffuse mass of neurons and nerve fibers within the brainstem. Reticular Activation System (RAS): Ascending RAS: Modifies thalamic and cortical functions. Descending RAS: Regulates muscle tone, posture, voluntary movements, and reflexes. Functions: Maintains alertness, consciousness, and attention; influences motivation, emotional reactions, learning, and motor coordination. 7. Clinical Correlations Decerebrate Rigidity: when brainstem is sectioned below the mesencephalon level, causing spastic rigidity in antigravity muscles due to blocked inputs from cerebral cortex, red nuclei, and basal ganglia. Brain Death: Complete and irreversible cessation of all brain functions, including brainstem functions. Legal definition of death in many jurisdictions, distinct from biological death. Resuscitative measures may maintain respiration and circulation temporarily. 8. Differentiating Brain Death Distinguishing from Other States: Important to differentiate from conditions like barbiturate overdose, alcohol intoxication, sedative overdose, hypothermia, hypoglycemia, coma, and chronic vegetative states. Transplantation Implications: Continuing function of vital organs in brain-dead individuals with life support provides opportunities for organ transplantation. 14 Check out my channal on Telegram @DrTurkiNotes Lec6: Physiology of Sleep Why We Sleep? Physical and Mental Rest: Essential for recuperation. Replenish Brain Glycogen: Restores energy reserves. Decreasing Metabolism: Reduces metabolic rate during sleep. Memory Consolidation: Enhances learning and memory retention. Consequences of Sleep Deprivation Memory Deficits: Impaired cognitive functions. Diminished Cognitive Function: Reduced ability to think clearly. Mood Swings & Hallucinations: Emotional instability and altered perceptions. Fatal Familial Insomnia: rare disorder leading to death within several years due to lack of sleep. Normal Sleep Duration and Requirements Sleep Requirements Change with Age: Different stages and needs over a lifetime. Sleep Cycle: 4-6 cycles per night. Each cycle lasts 90-110 minutes. Composed of 80% NREM 20% REM sleep. Sleep Stages NREM Sleep: Stage I: Stage II: Slow Stages III & IV: Drowsiness. wave sleep. Deep sleep (Very slow wave). Electrophysiological Sleep Assessment EEG (Electroencephalogram): Records brain activity. EOG (Electrooculogram): Monitors eye movements. EMG (Electromyogram): Measures neck muscle activity. EEG Changes During Sleep Awake: High frequency, low amplitude beta waves. Stage I (NREM): Alpha rhythm. Stage II (NREM): Theta waves with sleep spindles. Stages III & IV (NREM): Delta waves, highest amplitude, and lowest frequency. REM Sleep: Beta rhythm similar to the awake state, paradoxical sleep. 15 Check out my channal on Telegram @DrTurkiNotes Comparison of Sleep Stages IMP Mechanisms of Sleep NREM Sleep: 1) Serotonin: Produced by the Raphe Nuclei in the pons and medulla. 2) Effects: Stimulation induces slow-wave sleep (SWS). Destruction causes prolonged sleeplessness. Serotonin-secreting Raphe fibers inhibit the (RAS) to induce sleep. REM Sleep: Cholinergic Neurons: Located in the Pontine Reticular Formation. Mechanism: Spikes in the PRF spread to the Lateral Geniculate Nucleus (LGN) and Occipital Cortex, known as Ponto-Geniculo-Occipital (PGO) spikes, initiating REM sleep. Sleep-Wake Cycles and Circadian Rhythm Melatonin: Secreted (Pineal Gland) in darkness, inhibiting the RAS and inducing NREM sleep. Suprachiasmatic Nucleus (SCN): Responds to daylight, inhibiting melatonin secretion and promoting wakefulness. Sleep vs. Coma Sleep: Unconscious state from which a person can be aroused by sensory stimuli, characterized by distinct EEG patterns. Coma: Loss of consciousness not responsive to sensory stimuli, primarily showing slow waves on EEG. Sleep Disorders Transient Sleep Disorders: Jet lag, shift work disruptions, illness. Insomnia: Lack of sleep due to stress, anxiety, or depression. Sleep Apnea: Associated with obesity; characterized by slow respiratory rate and weak pharyngeal muscles, leading to disrupted sleep and daytime sleepiness. 16 Check out my channal on Telegram @DrTurkiNotes Lec6: Physiology of Sympathitic & Parasympathitic Somatic Nervous System (SNS) Function: Involved in voluntary actions. Control: Manages skeletal muscles (e.g., writing your name). Autonomic Nervous System (ANS) Function: Controls involuntary functions. Control: Regulates blood vessels, glands, and internal organs (e.g., bladder, stomach, heart). Divisions of the Autonomic Nervous System Sympathetic Nervous System (SNS): Thoracolumbar outflow (T1 to L3). Parasympathetic Nervous System (PNS): Craniosacral outflow (III, VII, IX, X; S2 to S4). Functions of the Autonomic Nervous System Sympathetic Nervous System (During Stress): Dilates pupils. Contracts the splenic capsule. Increases heart rate and contractility. Stimulates adrenal medulla to secrete Dilates bronchioles. adrenaline & noradrenaline. Constricts skin blood vessels. Enhances mental alertness. Redirects blood flow to heart, CNS, and Increases sweating. skeletal muscles. Stimulates the reticular formation via Increases glycogenolysis in the liver. catecholamines. Elevates blood glucose and free fatty acid levels. Parasympathetic Nervous System (During Rest): Pupillary constriction and Constriction of bronchioles. accommodation. Secretion of tears. Stimulation of GI secretion and Stimulates emptying of the rectum & peristalsis. urinary bladder. Secretion of watery saliva. Contributes to sexual arousal. Decreases heart rate and contractility. 17 Check out my channal on Telegram @DrTurkiNotes Autonomic Reflex Arcs Sympathetic Reflex Arc: Receptor: Mostly in viscera. Efferent: Two neurons, relay in Afferent: Identical to parasympathetic. autonomic ganglia outside the CNS. Center: Lateral horn cells. Effector Organs: Smooth and cardiac muscles. Somatic Reflex Arc: Receptor: Mostly in skin. Efferent: One neuron, directly supplies Afferent: Identical to sympathetic. the effector organ. Center: Anterior horn cells. Effector Organs: Skeletal muscles. Neurotransmitters and Receptors Preganglionic Fibers: Release (ACh) (cholinergic). Parasympathetic Postganglionic Fibers: Release ACh. Most Sympathetic Postganglionic Fibers: Release norepinephrine (adrenergic); exceptions include sweat glands and some blood vessels in skeletal muscles where ACh is released. Cholinergic Receptors Muscarinic (M1, M2, M3, M4, M5): G-protein coupled receptors. Nicotinic: Ligand-gated receptors. Blocker: Atropine blocks M receptors, used to inhibit salivary and bronchial secretions before surgery. Adrenergic Receptors α1-Receptors: Usually produce excitation (target tissues). α2-Receptors: Usually produce inhibition (digestive organs). β1-Receptors: Excitatory response, mainly in the heart. β2-Receptors: Inhibitory response (B.V, airways). 18 Check out my channal on Telegram @DrTurkiNotes β3-Receptors: Functions not fully detailed. Functions of Adrenergic Receptors Alpha (α-) Receptor: Vasoconstriction, iris dilation, intestinal and bladder sphincter contraction, pilomotor contraction. Beta (β-) Receptor: Vasodilation (β2), cardioacceleration (β1), increased myocardial strength (β1), glycogenolysis (β2). Adrenal Medullae Function Response to Sympathetic Activation: Releases large quantities of epinephrine (80%) and norepinephrine (20%) into the blood, affecting various tissues. Differences Between Epinephrine and Norepinephrine: Epinephrine has a greater effect on cardiac stimulation. Epinephrine causes weaker constriction of blood vessels compared to norepinephrine. Epinephrine has a more significant metabolic effect, increasing metabolic rate and glycogenolysis. Sympathetic and Parasympathetic Tone Sympathetic Tone: Controls blood pressure, maintains partial constriction of blood vessels. Sympathetic activation leads to prolonged effects due to slower inactivation of norepinephrine and the presence of epinephrine in the blood. Parasympathetic Tone: Slows the heart and regulates normal digestive and urinary activity. Can be overridden by sympathetic responses during stress. CNS Control of the ANS Negative Feedback Control: Regulates autonomic functions to maintain homeostasis. Effects of Sympathetic and Parasympathetic Stimulation Detailed effects on specific organs and systems. 19 Check out my channal on Telegram @DrTurkiNotes Lec8: Physiology of Hearing Sound and Its Characteristics Sound is a mechanical wave, a traveling vibration of air. IT waves consist of alternating regions of compression and rarefaction of air molecules. Sound intensity (loudness) is measured in decibels (dB). Noise Levels and Effects Anatomy of the Ear 1. External Ear: Pinna provides clues about the location of sound. It gathers and focuses sound energy on the tympanic membrane (ear drum). 2. Middle Ear: Ossicles (Malleus, Incus, Stapes) amplify vibrations from the tympanic membrane to the oval window. This amplification is necessary for sound waves to move through the fluid of the inner ear. 3. Inner Ear (Cochlea): Cochlea is a snail-like, fluid-filled structure deep in the temporal bone. It contains the Organ of Corti, the hearing sensory organ. Vestibular membrane separates the scala media from scala vestibuli. Basilar membrane separates the scala media from scala tympani. Tectorial membrane is attached to the stereocilia of hair cells. Organ of Corti Located on the basilar membrane in the scala media. It contains two types of receptor cells called hair cells: Inner hair cells: Responsible for detecting sound vibrations. Outer hair cells: Modify their length in response to sound vibrations to enhance sensitivity. 20 Check out my channal on Telegram @DrTurkiNotes Stereocilia protrude from the surface of each hair cell and are bathed in endolymph, while the body of the hair cells is bathed in perilymph. Cochlear Fluids: Perilymph (found in scala vestibuli and scala tympani) has a composition similar to extracellular fluid. Endolymph (found in scala media) has a unique composition, very rich in potassium (150 mM) and poor in sodium (1 mM). Mechanism of Hearing 1. Sound waves cause vibration of the tympanic membrane. 2. Ossicles amplify sound vibrations to the oval window. 3. Vibrations produce pressure waves in the perilymph of the cochlea. 4. Waves travel through the vestibular canal and return through the tympanic canal. 5. This motion causes the basilar membrane to vibrate. 6. Hair cells in the Organ of Corti are stimulated by this vibration. 7. Fluid waves dissipate when they strike the round window (reset). Inner Hair Cell Activation Vibrations of the basilar membrane cause stereocilia to move toward the tallest hair. This stretches tip links, causing the opening of mechanically gated K+ channels. K+ influx leads to depolarization of hair cells. Depolarization causes Ca2+ influx, triggering neurotransmitter release. Neurotransmission: Inner hair cells release glutamate at synapses with spiral ganglion neurons (1st-order neurons). The axons of these neurons form the auditory nerve (VIII), transmits signals to the brain. Auditory Pathway 1. Spiral ganglion neurons (Cochlea). 2. Cochlear nerve (VIII). 3. Cochlear nuclei (Medulla). 4. Superior olivary complex (Pons). 5. Lateral lemniscus. 6. Inferior colliculus (Midbrain). 7. Medial geniculate nucleus (Thalamus). 8. Primary auditory cortex (Temporal lobe). 21 Check out my channal on Telegram @DrTurkiNotes Auditory Cortex: The primary auditory cortex is tonotopically organized; specific tones activate specific regions of the cortex. Secondary auditory cortex (Wernicke’s area) is responsible for detecting language sounds. Types of Hearing Loss 1. Conductive Hearing Loss: Cause: Inadequate transmission of sound through the external or middle ear. Examples: Blocked ear canal (wax, fluid), perforated eardrum, otitis media, ossicular immobility. Effect: Bone conduction is better than air conduction. 2. Sensory Neural (Nerve) Deafness: Cause: Damage anywhere from hair cells to the auditory cortex. Examples: Loss of hair cells (due to noise exposure or aging), damage to the vestibulocochlear nerve (VIII), or central auditory pathways. Weber’s Test: Lateralization to the better ear indicates sensory neural hearing loss. Other Considerations Cochlear Implants are available to help individuals with sensory neural deafness, but they do not restore normal hearing. 22 Check out my channal on Telegram @DrTurkiNotes Lec9: Physiology of Eye Physiological Anatomy of the Eye Outer Fibrous Layer Cornea: The anterior 1/6 of this layer. Transparent, allowing light to pass through. Sclera: The posterior 5/6. Opaque, not transmitting light. It is where extraocular muscles attach. Middle Vascular Layer Choroid: The posterior 5/6, highly vascularized and pigmented, providing nutrients to other layers. Ciliary Body: Contains the ciliary muscle, processes, and suspensory ligament for lens control. Iris: Colored part of the eye, controlling the size of the pupil and light entry. Inner Nervous Layer (Retina) Photoreceptors (Rods & Cones): Located in the retina, responsible for detecting light. Optic Disc: Where the optic nerve exits, creating a physiological blind spot. Macula Lutea: A yellow spot 3mm lateral to the optic disc; central area for detailed vision. Fovea Centralis: The most sensitive area in the macula, composed solely of cones. Tear Film & Corneal Transparency Tear Film: Prevents dryness and consists of three layers: 1. Lipid layer from oil glands. 2. Aqueous solution from lacrimal glands, containing lysozymes for infection protection. 3. Mucous layer from the conjunctiva. Corneal Transparency: Maintained by the regular arrangement of collagen fibers and the absence of blood vessels. Internal Structures of the Eye Crystalline Lens A transparent, biconvex structure behind the iris. Suspended by the suspensory ligament. Provides about 30% of the diopteric power and assists in focusing light on the retina. The lens also absorbs ultraviolet waves to protect the retina. 23 Check out my channal on Telegram @DrTurkiNotes Aqueous Humor A clear, watery fluid in the anterior chamber of the eye. Functions: 1. Nourishes the cornea, iris, and lens. 2. Removes waste products. 3. Maintains (IOP). Formation: Sodium is actively secreted by Na+/K+ ATPase, followed by passive diffusion of chloride and bicarbonate, which draws water via osmosis. Drainage: Flows through the pupil into the anterior chamber, then into the trabecular meshwork (Spaces of Fontana) and finally exits through the canal of Schlemm into extraocular veins. Vitreous Humor Gel-like substance located behind the lens, filling the posterior segment of the eye. Intraocular Pressure (IOP) Normal Value: 15 mmHg (12-20). Measurement: tonometer. Functions: 1. Keeps tension in the suspensory ligaments, allowing for proper focusing. 2. Maintains the shape and positioning of (lens, retina, iris). Regulation: constant when the rate of aqueous humor formation matches the rate of drainage. Glaucoma Definition: Increased IOP primarily due to impaired aqueous drainage. Effects: Can lead to severe eye pain, headaches, and even blindness due to retinal and optic nerve damage. Treatment: 1. Carbonic anhydrase inhibitors (e.g., Diamox) to reduce aqueous formation. 2. Parasympathomimetics (e.g., pilocarpine) to constrict the pupil and open drainage pathways. 3. Surgery to enhance drainage. 24 Check out my channal on Telegram @DrTurkiNotes Refractive Media & Dioptric Power of the Eye Refractive Media: Cornea, aqueous humor, lens, and vitreous humor all contribute to refraction. Total Diopteric Power: 60-75 diopters (cornea provides 70%, lens 30%). Refractive Power of the Lens The lens’ refractive power changes from 20 diopters at rest to up to 34 diopters during full accommodation (focusing on near objects). Refractive Errors 1. Emmetropic Eye A normal eye where parallel rays focus directly on the retina without accommodation. 2. Ammetropic Eye Eyes in which parallel rays do not converge on the retina, causing blurred vision. 3. Myopia (Nearsightedness) Cause: Eyes are too long, or the cornea is too curved, leading to convergence of light in front of the retina. Effect: Distant objects appear blurry; near objects are clear. 4. Hypermetropia (Farsightedness) Cause: Eyes are too short, or the lens is too weak, causing convergence behind the retina. Effect: Difficulty seeing near objects; far objects are seen clearly. 5. Presbyopia Definition: Age-related decline in the eye’s ability to accommodate, starting around 45 years old. Cause: Gradual loss of lens elasticity. Effect: Difficulty focusing on near objects. 6. Astigmatism Definition: A refractive error where the curvature of the cornea or lens is uneven, causing light to focus on multiple points. 25 Check out my channal on Telegram @DrTurkiNotes Accommodation Definition: The ability of the lens to increase its refractive power to focus on near objects. Mechanism: During accommodation, the ciliary muscles contract, reducing tension in the suspensory ligaments, allowing the lens to become more spherical, increasing its refractive power. Power of Accommodation: Decreases with age from 10 diopters at age 20 to 1 diopter by age 60. Near Point: The closest distance at which the eye can focus on an object, about 10 cm in young adults and 80 cm by age 60. Near Response When focusing on near objects, the eye undergoes three changes: 1. Miosis: Pupil constricts to reduce excess light. 2. Convergence: Both eyes move inward by contracting the medial recti muscles. 3. Accommodation of the Lens: Increased curvature of the lens to focus the image on the retina. Near Response Pathway Stimulus: Blurred image of a near object. Afferent Pathway: Visual pathway from the retina to the cerebral cortex. Efferent Pathway: Oculomotor nerve innervates the constrictor pupillae muscle, ciliary muscle, and medial recti muscles to enable near vision. Errors of Refraction: Summary 1. Myopia (Nearsightedness): Light focuses in front of the retina, requiring concave lenses for correction. 2. Hypermetropia (Farsightedness): Light focuses behind the retina, corrected by convex lenses. 3. Astigmatism: Irregular curvature of the cornea, corrected by cylindrical lenses. 4. Presbyopia: Age-related loss of accommodation, corrected by reading glasses. 26 Check out my channal on Telegram @DrTurkiNotes Lec10: Vision Phototransduction Light and Dark Structure of the Retina: Pigmented Epithelium: The outermost layer, imp for absorbing stray light & maintaining the health of photoreceptors. Photoreceptors (Rods and Cones): Detect light & convert it into electrical signals. Bipolar Cells: Transmit signals from photoreceptors à ganglion cells. Ganglion Cells: Their axons form the optic nerve, which transmits visual information to the brain. Path of Light: Light enters through the lens, passes through the vitreous body, & reaches the photoreceptors (rods and cones) in the retina. Fovea Centralis: Small, specialized area located at the center of the retina. Is the visual center of the eye & is responsible for sharp, detailed vision. Contains only cones, which are responsible for color vision & high visual acuity. There is no convergence. Each cone is directly connected to a single bipolar cell, which in turn connects to a single ganglion cell, forming one optic nerve fiber. This direct ensures the highest visual precision. Other layers of the retina (bipolar & ganglionic layers) are displaced to the side, leaving the fovea free of obstruction, allowing light to reach the cones without interference. Accommodation mechanisms of the eye always try to focus the light rays precisely on the fovea for the clearest image. This region is essential for tasks requiring sharp vision, like reading and recognizing faces. Photoreceptor Function: Rods: Highly sensitive to light; responsible for vision in low-light conditions (scotopic vision). 27 Check out my channal on Telegram @DrTurkiNotes Cones: Responsible for color vision & function best in bright light (photopic vision). Photoreceptor Mechanism: Photoreceptors contain photopigments made of opsin (protein) & retinal (derived from vitamin A). When light hits the photoreceptors, a process (bleaching) occurs, where opsin & retinal separate, forming metarhodopsin II. Metarhodopsin II triggers electrical changes, à hyperpolarization of the photoreceptors, à transmission of signals to the bipolar cells. Electrical Changes: In dark conditions, Na+ channels are open, à depolarized state, which releases glutamate. In light conditions, Na+ channels close due to the breakdown of cGMP, causing hyperpolarization & reducing glutamate release. This leads to the excitation of ganglion cells, creating an AP that is transmitted via the optic nerve. 28 Check out my channal on Telegram @DrTurkiNotes Retinal Adaptation: Light Adaptation: moving from a dark area à bright light, there is initial discomfort, but the retina adjusts, allowing normal vision. Dark Adaptation: moving from a bright area à darkness, the retina gradually increases its sensitivity, allowing the detection of objects in the dark. The retinal sensitivity is markedly increased in the dark. While, it decreases on exposure to the light.did Scotopic vs. Photopic Vision: Scotopic Vision: Vision in dim light, mediated by rods, which do not provide color vision. Photopic Vision: Vision in bright light, mediated by cones, which allow color perception. Lec11: Physiology of Taste & Smell 29  Check out my channal on Telegram @DrTurkiNotes Primary Sensations of Taste 1. Sweet: Sugars 2. Sour: Acids (free H ions) 3. Bitter: Alkaloids and other substances 4. Salty: Chemical salts (NaCl) 5. Umami: Glutamate (meaty taste) Taste Buds Structure: Taste buds are barrel-shaped structures containing taste receptors. They are mainly found in the tongue mucosa, soft palate, inner surface of the cheeks, pharynx, and epiglottis. Types of Papillae: 1. Foliate 3. Fungiform 2. Circumvallate 4. Filiform (no taste buds) Taste Bud Cells Taste Receptor Cells: 50-150 receptor cells are arranged like segments of an orange. These cells are modified epithelial cells with microvilli (hairs) but are not neurons. 1. Basal Cells: Precursors to taste receptor cells, which are replaced every 10-14 days. 2. Supporting Cells: Provide structural support to the taste buds. Taste Transduction Salty taste transduction: 1. Na+ from salty food enters cells through Na+ channels. 2. Depolarization opens voltage-gated Ca2+ channels. 3. Ca2+ influx causes neurotransmitter release, transmitting signals to afferent neurons. Gustatory Pathway Cranial Nerves: Anterior 2/3 of the Posterior 1/3 of the Base of the tongue and tongue: CN VII (Facial) tongue: CN IX other parts: CN X (Glossopharyngeal) (Vagus) 30 Check out my channal on Telegram @DrTurkiNotes Nucleus of Tractus Solitarius (TS): 1st order synapse in the TS in the medulla. Thalamus: 2nd-order cross the midline and ascend to the VPM of the thalamus. Cortex: 3rd-order project to the gustatory cerebral cortex. Taste Disorders Ageusia: Complete loss of taste. Dysgeusia: Disturbed or bad taste. Hypergeusia: Heightened taste. Hypogeusia: Reduced ability to taste, often caused by diseases or drugs like penicillamine. Olfaction (Sense of Smell) A powerful stimulant for emotions and can warn of dangers (gas leaks, spoiled food). Odorants: Airborne molecules that must be volatile to give off vapors. More vapors are emitted when heated. Olfactory Epithelium Located in the roof of the nasal cavity, near the septum. Contains: 1. Olfactory Sensory Neurons: Bipolar nerve cells. 2. Bowman’s Glands. 3. Basal Stem Cells. Olfactory receptors are specialized endings of afferent neurons that detect gaseous chemicals and convert them into nerve impulses. Olfactory Transduction Process 1. Odorant Diffusion: Odorants diffuse into the mucus. 2. Binding and Activation: Odorants bind to receptor proteins, activating G-protein complexes. 3. Adenyl Cyclase Activation: This enzyme converts ATP into cAMP. 4. Depolarization: cAMP opens sodium ion channels, depolarizing the neuron and transmitting signals to the CNS. 31 Check out my channal on Telegram @DrTurkiNotes Olfactory Pathway 1. Olfactory receptor cells pass through the cribriform plate of the ethmoid bone to synapse in the olfactory bulb. 2. Mitral cells in the olfactory bulb carry signals along the olfactory tract to the cortex and limbic system. 3. Glomeruli in the olfactory bulb: Axons of receptor cells synapse with mitral cells here. 4. Mitral cells project to the olfactory cortex and other brain areas, including the amygdala, hippocampus, and hypothalamus. Olfactory Adaptation Adaptation occurs about 50% in the first second and continues slowly thereafter. CNS mechanisms also contribute to adaptation, with feedback inhibition from granule cells suppressing the relay of smell signals. Olfactory Disorders Anosmia: Loss of smell. Hyposmia: Reduced ability to smell (e.g., due to Vitamin A deficiency). Dysosmia: Distorted smell identification (e.g., parosmia and phantosmia). Agnosia: Inability to classify odors. Hyperosmia: Increased sensitivity to smell. Causes of Smell Disorders 1. Aging. 2. Respiratory infections. 3. Smoking. 4. Nasal cavity growths. 5. Head injury. 6. Hormonal disturbances. 7. Exposure to chemicals (e.g., insecticides). 8. Neurological diseases (e.g., Parkinson’s, Alzheimer’s). Note: - If you like this and want to see more, check out my channal on Telegram @DrTurkiNotes - See you soon future doctors 32