Nervous System Physiology Quiz
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Questions and Answers

Which type of receptors is classified as rapidly adapting?

  • Muscle spindle
  • Pain receptors
  • Baroreceptors
  • Hair end-organ (correct)

    • What is a characteristic of slowly adapting receptors?

  • They detect the strength of a continuous stimulus. (correct)
  • They transmit impulses only when stimuli change.
  • They have a rapid response to sudden pressures.
  • They adapt completely to continuous stimuli.

    • How do rods and cones in the eye adapt to changes in stimulus?

  • By increasing the conduction velocity.
  • By changing the level of light-sensitive chemicals. (correct)
  • By altering the temperature of the surrounding environment.
  • By reducing the number of impulses sent to the CNS.

    • What mechanism is used to encode stimulus intensity in the CNS?

    <p>Increasing the frequency of impulses induced by the receptor.</p> Signup and view all the answers

    What defines the conduction velocity of a stimulus in nerve fibers?

    <p>The diameter of the nerve fibers and myelination.</p> Signup and view all the answers

    When pressure is applied to the pacinian corpuscle, what is its response characteristic?

    <p>It is excited briefly before it stops responding.</p> Signup and view all the answers

    What is the approximate conduction velocity of an Aδ fiber for a stimulus applied to the fingertip?

    <p>25 m/sec</p> Signup and view all the answers

    Which of the following nerves has the slowest conduction velocity?

    <p>C fiber</p> Signup and view all the answers

    What type of sensation is associated with mechanoreceptive somatic senses?

    <p>Touch and vibration</p> Signup and view all the answers

    Which classification of sensations relates to sensations felt at the surface of the body?

    <p>Exteroreceptive sensations</p> Signup and view all the answers

    Which of the following describes specialized receptor cells?

    <p>They constitute a sensory unit with axonal branches</p> Signup and view all the answers

    What is a characteristic of receptor potentials?

    <p>They can vary in amplitude</p> Signup and view all the answers

    Which of the following is an example of a proprioceptive sensation?

    <p>Position awareness of limbs</p> Signup and view all the answers

    What is primarily involved in the neural adaptation process?

    <p>Decline in receptor responsiveness over time</p> Signup and view all the answers

    Which of the following statements about pain sense or nociception is true?

    <p>It can be mediated by specialized receptors and free nerve endings</p> Signup and view all the answers

    Which type of sensation includes deep pressure and vibration?

    <p>Deep sensations</p> Signup and view all the answers

    What primarily characterizes receptor potentials in sensory transduction?

    <p>They are graded potentials that vary with stimulus intensity.</p> Signup and view all the answers

    Which of the following best describes the role of ion channels in sensory receptors?

    <p>Ion channels can be influenced by mechanical, chemical, thermal, and electromagnetic changes.</p> Signup and view all the answers

    The maximum amplitude of a receptor potential is approximately how many millivolts?

    <p>100mV</p> Signup and view all the answers

    What occurs if a receptor potential surpasses the threshold in the attached nerve fiber?

    <p>Action potentials are generated and transmitted.</p> Signup and view all the answers

    What type of receptor is characterized by having concentric capsule layers and responding to mechanical deformation?

    <p>Pacinian corpuscles</p> Signup and view all the answers

    How does the amplitude and duration of receptor potential relate to the stimulus applied?

    <p>They directly depend on both amplitude and duration of the stimulus.</p> Signup and view all the answers

    What is true about the relationship between receptor potentials and action potentials?

    <p>Receptor potentials can trigger action potentials when thresholds are met.</p> Signup and view all the answers

    What kind of sensory adaptation occurs during the constant presence of a stimulus?

    <p>Decreased responsiveness to a constant stimulus over time.</p> Signup and view all the answers

    What initiates the opening of ion channels in sensory receptors?

    <p>Mechanical deformation of the receptor membrane</p> Signup and view all the answers

    Which of the following statements best describes the nature of receptor potentials?

    <p>They are graded potentials dependent on stimulus intensity.</p> Signup and view all the answers

    What happens when a receptor potential reaches the threshold level in a nerve fiber?

    <p>Action potentials are generated and transmitted.</p> Signup and view all the answers

    Which factor does NOT influence the amplitude and duration of receptor potentials?

    <p>Previous stimuli experienced by the receptor</p> Signup and view all the answers

    How does the receptor potential of a pacinian corpuscle respond to mechanical pressure?

    <p>It results in the opening of Na+ channels and depolarization.</p> Signup and view all the answers

    What defines the maximum receptor potential amplitude?

    <p>It is approximately 100mV.</p> Signup and view all the answers

    What type of sensations does mechanoreceptive somatic sense include?

    <p>Tactile and position sensations</p> Signup and view all the answers

    What are exteroceptive sensations primarily associated with?

    <p>Sensations from the surface of the body</p> Signup and view all the answers

    Which of the following best describes the relationship between receptor potentials and action potentials?

    <p>Receptor potentials are graded, while action potentials are all-or-none.</p> Signup and view all the answers

    What role does electromagnetic radiation play in sensory transduction?

    <p>It stimulates the receptor membrane and opens ion channels.</p> Signup and view all the answers

    How can somatic sensations be classified physiologically?

    <p>As mechanoreceptive, nociceptive, and others</p> Signup and view all the answers

    Which type of sensory receptor would be found on the cellular membrane or in the cytoplasm?

    <p>Specialized receptors</p> Signup and view all the answers

    What physiological classification includes sensations related to the physical state of the body?

    <p>Proprioceptive sensations</p> Signup and view all the answers

    Which of the following describes deep sensations?

    <p>Pain, deep pressure, and vibration</p> Signup and view all the answers

    What constitutes a sensory unit?

    <p>A single sensory axon and its peripheral branches</p> Signup and view all the answers

    Which type of receptors are capable of detecting nociceptive sensations?

    <p>Nociceptors</p> Signup and view all the answers

    What is the function of rapidly adapting receptors?

    <p>Detect changes in stimulus strength</p> Signup and view all the answers

    How do slowly adapting receptors respond to a continuous stimulus?

    <p>They transmit impulses continuously as long as the stimulus is present</p> Signup and view all the answers

    What role does the frequency of impulses play in perceiving stimulus intensity?

    <p>Higher frequency corresponds to a stronger stimulus</p> Signup and view all the answers

    Which statement accurately describes the conduction velocity of nerve fibers?

    <p>Conduction velocity can range from 0.5 to 120 m/sec based on fiber diameter</p> Signup and view all the answers

    What distinguishes tonic receptors from phasic receptors?

    <p>Tonic receptors provide continuous signaling in response to stimuli</p> Signup and view all the answers

    What adaptation mechanism do rods and cones in the eye utilize?

    <p>Adjustment of light-sensitive chemical levels</p> Signup and view all the answers

    Which of the following fibers has the fastest conduction velocity?

    <p>Aα fibers</p> Signup and view all the answers

    What physiological change is observed when stimulus intensity increases?

    <p>Increase in the amplitude of the receptor potential</p> Signup and view all the answers

    What does the labeled line principle explain in sensory perception?

    <p>Different sensory modalities are transmitted by separate nerve impulses.</p> Signup and view all the answers

    What sensation is commonly associated with phantom limb syndrome?

    <p>Feeling of pain or discomfort in an amputated limb.</p> Signup and view all the answers

    What causes the sensation of seeing stars when pressure is applied to the eyes?

    <p>High-intensity nonspecific stimuli activating photoreceptors.</p> Signup and view all the answers

    What is the consequence of irritation in severed nerve endings?

    <p>It causes the brain to misinterpret signals as pain.</p> Signup and view all the answers

    In terms of sensory receptors, what does the term 'modality' refer to?

    <p>The specific type of energy that stimulates a receptor.</p> Signup and view all the answers

    What does the law of projection imply regarding sensory pathways?

    <p>Specific local sensory impulses are interpreted in exact corresponding brain regions.</p> Signup and view all the answers

    How do different sensory receptors recognize specific stimuli?

    <p>By being sensitive to distinct forms of energy related to their function.</p> Signup and view all the answers

    What phenomenon describes the process where neighboring sensory fibers may misproject sensations?

    <p>Neighbor projection effect.</p> Signup and view all the answers

    Which somatic sensation includes the detection of touch, pressure, and vibration?

    <p>Mechanoreceptive somatic sense</p> Signup and view all the answers

    What classification of somatic sensations is related to sensory information from the surface of the body?

    <p>Exteroceptive sensations</p> Signup and view all the answers

    What type of receptor is characterized by having specialized receptor cells?

    <p>Cellular receptors</p> Signup and view all the answers

    Which classification of somatic sensations pertains to the physical state of the body, including muscle and tendon sensations?

    <p>Proprioceptive sensations</p> Signup and view all the answers

    What type of sensation does nociception primarily relate to?

    <p>Pain sense</p> Signup and view all the answers

    Which type of receptors are free nerve endings primarily responsible for detecting?

    <p>Temperature sensations</p> Signup and view all the answers

    Deep sensations include the detection of which of the following?

    <p>Vibration from deep tissues</p> Signup and view all the answers

    What best describes the role of sensory units in the context of receptors?

    <p>Sensory units include a single sensory axon and all its peripheral branches.</p> Signup and view all the answers

    What is the primary function of sensory receptors?

    <p>To transform stimuli into electrical impulses</p> Signup and view all the answers

    How does the labeled line principle operate in sensory perception?

    <p>Modalities of sensation are transmitted through distinct nerve tracts</p> Signup and view all the answers

    What causes phantom limb sensations?

    <p>Irritation of severed nerve endings</p> Signup and view all the answers

    What sensory phenomenon might occur when excessive pressure is applied to a receptor?

    <p>Perception of light flashes</p> Signup and view all the answers

    What is the law of projection in sensory physiology?

    <p>It states that sensations are perceived based on brain location</p> Signup and view all the answers

    Which statement best describes how receptors recognize different sensory stimuli?

    <p>Each receptor is tuned to a specific form of energy</p> Signup and view all the answers

    What is the primary significance of receptor potentials in sensory transduction?

    <p>They are graded potentials based on stimulus intensity.</p> Signup and view all the answers

    What is primarily responsible for sending pain signals to the brain in amputated limbs?

    <p>Neuromas formed in the severed nerve endings</p> Signup and view all the answers

    What percentage of individuals with an amputation typically experience phantom sensations?

    <p>70%</p> Signup and view all the answers

    How does the amplitude and duration of the receptor potential vary?

    <p>They depend on the amplitude and duration of the applied stimuli.</p> Signup and view all the answers

    What happens when the receptor potential exceeds the threshold in the nerve fiber?

    <p>Action potentials are generated and transmitted to the CNS.</p> Signup and view all the answers

    In the pacinian corpuscle, what initiates the receptor potential?

    <p>The deformation of the central fiber which opens Na+ channels.</p> Signup and view all the answers

    Which characteristic differentiates receptor potentials from action potentials?

    <p>Receptor potentials are graded and depend on stimulus intensity.</p> Signup and view all the answers

    What defines the maximum amplitude of a receptor potential?

    <p>It is approximately 100mV and depends on stimulus intensity.</p> Signup and view all the answers

    What occurs during the transduction phase in sensory receptors?

    <p>Local potential changes due to ion channel opening.</p> Signup and view all the answers

    Which form of stimulation can lead to the opening of ion channels in sensory receptors?

    <p>Chemical, mechanical, thermal, and electromagnetic stimulation.</p> Signup and view all the answers

    What differentiates slowly adapting receptors from rapidly adapting receptors?

    <p>Slowly adapting receptors do not adapt completely to the stimulus.</p> Signup and view all the answers

    Which type of receptor would be primarily responsible for transmitting the sensation of deep pressure?

    <p>Pacinian corpuscle</p> Signup and view all the answers

    How does the frequency of action potentials relate to stimulus intensity?

    <p>Frequency increases with the amplitude of the receptor potential.</p> Signup and view all the answers

    What factor is NOT a determinant of conduction velocity in nerve fibers?

    <p>Type of receptor activated</p> Signup and view all the answers

    In the classification of nerve fibers, which characteristic is true of C fibers?

    <p>They are unmyelinated and conduct slowly.</p> Signup and view all the answers

    What is the primary reason for the decrease in receptor response when a continuous stimulus is applied?

    <p>Adaptation at the receptor level occurs.</p> Signup and view all the answers

    Which describes the conduction velocity of Aδ fibers when a stimulus is applied?

    <p>They conduct at approximately 25 m/sec.</p> Signup and view all the answers

    What distinguishes the response of the Pacinian corpuscle to mechanical pressure?

    <p>It adapts quickly and stops responding after a brief moment.</p> Signup and view all the answers

    Study Notes

    Nervous System Physiology

    • Study of nervous system functions
    • Sensory Physiology, sensory receptors, and receptor potentials

    Sensory Receptors

    • List of receptor types
    • Description of receptor potential
    • Classification of fiber types
    • Classification of somatic sensation
    • Description of receptor functions
    • Explanation of receptor adaptation

    Somatic Sensations

    • Senses classified as special senses (vision, hearing, smell, taste, equilibrium)
    • Physiological classification of somatic senses: mechanoreceptive senses detect tactile & position sensations
      • Tactile sensations (touch, pressure, vibration, itch)
      • Position sensations (proprioception, equilibrium)
    • Pain sense, nociception
    • Other classifications:
      • Exteroreceptive sensations (from the surface of the body)
      • Proprioceptive sensations (physical state of the body: position, tendon & muscle sensations, pressure sensations from the bottom of the feet)
      • Visceral sensations (from viscera of the body)
      • Deep sensations (from deep tissues like fascia, muscles, & bone: deep pressure, pain, & vibration)

    Types of Sensory Receptors

    • Mechanoreceptors, detect tactile & position sensations (skin tactile sensibilities, expanded tips, Merkel's discs, spray endings, Ruffini's endings, encapsulated endings, Meissner's corpuscles, etc.)
    • Thermoreceptors, detect temperature (cold receptors, warmth receptors)
    • Nociceptors, detect pain (free nerve endings)
    • Electromagnetic Receptors, detect light (rods & cones)
    • Chemoreceptors, detect chemicals (taste receptors, olfactory epithelium, receptors of aortic and carotid bodies, receptors in hypothalamus)

    Modality of Sensation: Labeled Line Principle

    • Each principal type of sensation (pain, touch) is a modality of sensation
    • Nerve fibers transmit only impulses
    • Each nerve tract terminates at a specific point in the CNS
    • Stimulus (e.g., electricity, overheating, crushing) is interpreted as the respective modality of sensation
    • Phantom limb: sensation that an amputated part is still connected to the body (~70% of people), often felt in distorted & painful positions
    • Mechanism of phantom limb sensations (irration & inflamed nerve endings called neuromas)
    • Law of projection: local signals sent via a specific pathway are interpreted as pain in that location.
    • Receptor recognizes specific stimuli through special forms of energy (intensity/amplitude)

    Transduction of Sensory Stimuli

    • Receptor potentials (different receptors can be excited by mechanical deformation, chemicals & electromagnetic radiation)
    • Different processes: mechanical deformation, chemical application, and temperature changes alter permeability, electromagnetic radiation
    • The receptor potential depends on stimulus amplitude/duration
    • Transduction phase: stimulus causes change in local potential (receptor potential)
    • The action potential phase: if the threshold is reached action potentials are transmitted.

    Adaptation of Receptors

    • Rapidly adapting (phasic): Meissner corpuscle end-organs, Pacinian corpuscle end-organs, hair end-organ
    • Slowly adapting (tonic): Baroreceptors, chemoreceptors, muscle spindle, golgi tendon organ, Merkel cell end-organ, Ruffini corpuscle, joint capsule, & pain receptors

    Encoding Stimulus Intensity

    • CNS perceives stimulus intensity by changing frequency of impulses induced by receptor
    • Amplitude of receptor potential increases as stimulus intensity increases, increasing the rate of action potentials in nerve fibers.

    Classification of Fibers

    • Nerve fiber diameter & conduction velocity affect signal transmission time
    • Different fiber types (Aα, Aβ, Aγ, Aδ, C) have different functions & conduction velocities.
    • A fibers (large myelinated fibers); B myelinated fibers, & C (small unmyelinated) - sensory fiber & postganglionic autonomic fiber

    Somatic Sensations - Tactile and Position Senses

    • Tactile sensations (touch, pressure and vibration) are detected by various receptors like Meissner corpuscles, Pacinian corpuscles, Ruffini's corpuscles, & Merkel's discs
    • Hair end-organs adapt readily, detecting movement of objects and initial contact.
    • Ruffini endings adapt slowly, signaling sustained pressure.
    • Tactile location correlates to the number of receptors
    • Types of sensory receptors: Tactile receptors, deep receptors near the joints, individual joint receptors

    Receptors for Position Senses (Proprioception)

    • Mechanoreceptors located in joints (e.g., Ruffini endings).
    • Mechanoreceptors in the skin
    • Muscle spindle receptors, Golgi tendon organs

    Transmission of Tactile Signals

    • Different fiber types (Aβ, Aδ, C) carry tactile signals with varying speeds, affecting the type of sensation perceived
    • Location and intensity of touch are determined by rapidly-conducting fibers.

    Transmission of Tactile Signals - Detection of Vibration

    • Pacinian corpuscles detect higher-frequency vibrations.
    • Meissner's corpuscles detect lower-frequency vibrations.

    Transmission of Tactile Signals - Tickle & Itch

    • Primarily transmitted by small, unmyelinated C fibers.

    Dorsal Root, Ventral Root

    • Afferent fibers carrying sensory signals enter the spinal cord through the dorsal root
    • Sensory afferent fibers are the projections of dorsal root ganglia (DRG) cells.
    • Ventral root contains efferent axons (motor neurons) and pre-ganglionic autonomic axons

    Sensory Pathways for Transmitting Signals into CNS (Dorsal Column-Medial Lemniscal System)

    • Nerve fibers: large & myelinated, ~30-110 m/sec
    • Fine touch, tactile sensations, requiring high degrees of localization, intensity, and judgment of pressure.

    A. Dorsal Column-Medial Lemniscal System

    • Functions of afferent neurons stimulated by sensory stimuli in spinal cord:
      • Going to the brain in dorsal column
      • Function in local spinal cord reflexes
      • Participates in spinocerebellar pathways
    • Soma of the first order neuron is located in DRG
    • One peripheral branch functions like a dendrite; one central branch functions like an axon.
    • This is a pathway for sensory information (pressure, fine touch, proprioception) from the trunk and limbs

    B. The Anterolateral Pathway (Spinothalamic Tract)

    • Characterized by slower transmission (8-40 m/sec)
    • Less sensitive to spatial localization and intensity gradients
    • Responsible for pain, temperature, crude touch and pressure senses

    Function of the Thalamus in Somatic Sensation

    • Primary relay station for sensory information coming into the cerebral cortex
    • Although damage can reduce tactile sensibility, some crude sensibility returns.
    • Pain sensation is affected moderately, and temperature sensation also affected
    • The thalamus (and other lower centers) can discriminate tactile sensations

    Cortical Control of Sensory Sensitivity (Corticofugal signals

    • Corticofugal signals are transmitted from the cerebral cortex to lower sensory relay stations in the thalamus, medulla, & spinal cord
    • Regulate the intensity of sensory input

    Dermatomes

    • Each spinal nerve innervates a segmental area of skin.
    • Used to identify levels of spinal cord injury

    Neural Lesions: Peripheral Lesions

    • Dorsal root lesions prevent sensory signal transmission while ventral root lesions cause weakness in innervated muscles
    • Affecting different parts of the body (pain, motor function)

    Abnormalities Brown-Séquard Syndrome

    • If the spinal cord is lesioned on one side, this syndrome occurs.
    • All motor functions are blocked on the side of the transection.
    • Pain, temperature, and crude touch sensations are lost on opposite side.
    • The kinesthetic, position and vibration senses, discrete localization, and two- point discrimination are lost on same side.

    Pain

    • Pain is a protective mechanism activated by tissue damage.
    • Nociceptors (free nerve endings) detect pain, responding to mechanical, thermal, or chemical stimuli.
    • Chemical pain stimuli include extreme temperatures, trauma, & various chemicals.
    • Chemicals that stimulate pain include bradykinin, serotonin, histamine, proteolytic enzymes, potassium ions, and acids
    • If damage sustained. slow chronic pain begins after about 1s & increasing intensity
    • Tissue destruction lead to prolonged unbearable suffering

    Pain Sensation

    • Nociceptors convert thermal, mechanical, and chemical stimuli into receptor potential using TRP channels
    • TRPV1, TRPV2, TRPV3, TRPV4, & TRPA1 are types of TRP channels that detect variations in temperature, pressure, and chemicals

    Pathways for Transmission of Pain Signals

    • Fast pain signals: The neospinothalamic pathway - Fast, sharp, localized pain
    • Slow pain signals: The paleospinothalamic pathway - Slow, burning, poorly localized
    • Anterolateral system: contains both neospinothalamic and paleospinothalamic tracts; it transmits pain signals to different brain regions

    Surgical Interruption of Pain Pathways

    • Anterolateral cordotomy interrupts pain fibers but may not always be effective (issues with incomplete crossing)
    • Cauterizing specific pain areas in the intralaminar nuclei of the thalamus can sometimes relieve severe pain, without impacting perception/awareness.
    • Prefrontal lobotomies interrupt frontal lobe connections, which can help some but are now rarely performed.

    Pain Suppression (Analgesia) System

    • The brain has systems to suppress pain (analgesia).
    • These systems involve the periaqueductal gray (PAG) and other brain stem areas.
    • These areas release enkephalins and other peptides that inhibit pain signals
    • The brain's opiate system - receptors for these naturally occurring neurotransmitters.

    Projected Pain

    • Pain felt in areas other than the tissue source of injury due to synapse in similar locations in the spinal cord causing a felt sensation.
    • Neuralgia: sever pain attributed to irritated/damaged nerve.
    • Examples: Trigeminal neuralgia, involving the trigeminal nerve in the face.

    Referred Pain

    • Visceral pain being felt in a different part of the body.
    • Visceral pain fibers synapse in the spinal cord on the same 2nd-order neuron from a different part of the body
    • This causes pain in the skin over the organ from similar signaling in the spinal cord, causing the sensation of pain in the skin instead of the organ

    Visceral Pain Causes

    • Ischemia (reduced blood flow)
    • Chemical stimuli (e.g., from GI tract or organ damage)
    • Spasms of hollow viscera
    • Overdistention (severe swelling) of organs.

    Poor Localization of Visceral Pain

    • Difficulty localizing pain due to varied nerve connections and brain's lack of direct sensory organ awareness & lack of understanding of the different organs' differences between each other

    Abnormalities of Pain: Hyperalgesia

    • Excessive sensitivity to pain; can be primary (increased sensitivity in nociceptors themselves) or secondary (increased sensory transmission) due to tissue chemicals, etc.

    Abnormalities of Pain: Herpes Zoster (Shingles)

    • Painful rash caused by reactivation of latent herpes virus affecting segmental (dermatomal) regions of the body.

    Headache of Intracranial Origin

    • Brain tissue is immune to pain, but pressure, trauma, stretching, or damage to blood vessels & meninges elicits pain sensation.
    • Several headaches of intracranial origin include inflammation, cerebrospinal fluid pressure drops, alcohol or constipation.

    Headache — Migraine Headaches

    • Mechanisms are not fully understood, but there seems to be a genetic predisposition to migraines.
    • Various triggers such as smells, noise, light, sleep loss, caffeine, hormonal fluctuations, and medications can evoke them
    • The prodrome, aura, pain, and postdrome phases are common features of a migraine attack and often can include nausea, vomiting, or sensory disturbances.

    Headache — Theories of Mechanisms

    • Vasospasm theory: changes in or constriction of blood vessels due to emotion /tension cause discomfort
    • Migraine center theory: trigger factor increases the excitability of the cerebral cortex and activates the migraine center which is located in the brain stem.

    Extracranial Headaches

    • Muscle spasm
    • Nasal and accessory nasal structures

    Thermal Sensations

    • Receptors (free nerve endings) with TRPM8 (stimulated by menthol) and TRPA1 are responsible for cold sensations
    • TRPM8 activates below 25°C - feels cool and cold
    • TRPA1 activates below 17°C - cold and freezing sensation occurs
    • Cold receptors are predominantly type Aδ, but some are type C.
    • Warm receptors are largely type C fibers (slow) in range 0.8 - 2m/sec

    Motor Functions of the Spinal Cord — Cord Reflexes

    • Study of spinal reflexes (involuntary, unlearned movements)

    Organization of the Spinal Cord for Motor Functions

    • Afferent neurons enter the spinal cord through dorsal roots or cranial nerves to the CNS
    • Efferent fibers exit through ventral roots or cranial nerves; fibers are related to their nuclei (somatic, visceral)

    Functional Anatomy of Spinal Cord

    • Dorsal (posterior) roots are afferent; ventral (anterior) roots are efferent
    • Dorsal root ganglia house cell bodies of sensory neurons
    • Ventral horn cells house motor neurons

    Functional Anatomy of Spinal Cord - Sources of Afferent Spinal Nerves

    • Somatic sensory receptors
    • Visceral sensory receptors

    Functional Anatomy of Spinal Cord - Efferent Spinal Nerves

    • Somatic, innervating skeletal muscles
    • Visceral, innervating smooth muscles, cardiac muscles, and glands

    Functional Anatomy of Spinal Cord - Gray Matter

    • Integrative area for cord reflexes, initiating local segmental reflexes and also signal relay for higher CNS processing and response

    Spinal Nerves

    • There are 31 pairs of spinal nerves originating from the cord
    • Each segment corresponds to a vertebra

    Spinal Cord Ascending & Descending Tracts

    • Different tracts in the spinal cord have different functions relaying sensory or motor info.
    • Sensory: Pain, temperature, touch, vibration, proprioception are relayed in numerous pathways via the spinal cord
    • Motor: Voluntary and postural movements, use pyramidal and extrapyramidal tracts

    Spinal Cord, Neurons

    • Include sensory relay neurons, motor neurons (alpha and gamma), and interneurons
    • Motor neurons innervate skeletal muscles
    • Interneurons are the most numerous in the spinal cord, facilitating complex integration

    Interneurons Multisegmental Connections

    • Provide pathways for multisegmental reflexes through branching from one cord segment to another

    Interneurons Renshaw Cell Inhibitory System

    • Axonal collaterals of anterior motor neurons synapse with Renshaw cells
    • Renshaw cells inhibit adjacent motor neurons, producing subtle or greater regulation over motor patterns

    Locomotor Pattern Generators in Spinal Cord

    • Neural circuit localizing in the spinal cord that produces coordinated, sequential movements for locomotion

    Reflexes

    • Involuntary, unlearned motor responses to stimuli
    • Components of a reflex arc include receptors, afferent pathways, integrating centers, efferent pathways, and effectors.
    • Classification of reflexes include monosynaptic, disynaptic, and polysynaptic.
    • Examples include the stretch reflex, Golgi tendon reflex & flexor-withdrawal reflexes

    Monosynaptic Reflexes Stretch Reflex

    • Stretch of the muscle triggers a contraction to resist and oppose sudden stretching,
    • Muscle spindle and Golgi tendon organ involved
    • The knee-jerk reflex is a typical example (monosynaptic pathway).
    • Gamma motor neurons adjust muscle spindle tension, contributing to reflex dynamics

    Muscle Sensory Receptors, Muscle Spindles & Golgi Tendon Organs

    • Muscle Control; the importance of continuous feedback needed to fine tune movements and regulate muscle tension.
    • Muscle spindle - a type of proprioceptor, sensitive to muscle length and rate of change of length
    • Golgi tendon organ - a type of proprioceptor, sensitive to muscle tension and rate of change of tension; important for protecting muscles from overexertion

    Muscle Spindle

    • Extrafusal muscle fibers
    • Intrafusal muscle fibers
    • Motor end plates
    • Sensory endings (Ia & II fibers).
    • Gamma motor neurons

    Muscle Spindle Sensory Endings

    • Primary ending (Ia fibers) - middle of the muscle spindle
    • Secondary ending (II fibers) - sides of the muscle spindle

    Muscle Spindle Sensory Endings - Stimulation

    Muscle Stretch Reflex

    Muscle Spindle in Voluntary Motor Activity

    • Co-activation of alpha and gamma motor neurons
    • Maintaining precise muscle posture
    • Prevent jerky, oscillatory movements

    Brain Areas for Control of the Gamma Motor System

    • Bulboreticular facilitatory area plays a crucial role in activating gamma neurons for postural control.
    • Other brain regions, including the cerebellum, basal ganglia, and cerebral cortex, contribute to the control of gamma motor neuron activity.

    Clinical Applications of the Stretch Reflex

    • Assessing the state of spinal cord and motor control centers
    • Observing the appropriate reflexes for age
    • Observing and understanding some clinical abnormalities in spinal cord and/or brain stem

    Monosynaptic Reflexes and Disorders

    • Hyperactive reflexes suggest interruption of inhibitory pathways (e.g., lesions in brain motor areas)
    • Hypoactive reflexes suggest a problem in any part of the reflex arc pathway; there may be a problem with the muscle spindle, afferent nerve fibers to the quadriceps muscle.

    Clinical Applications of Clonus

    • Assessing the stretch reflex, looking for oscillations with rapid stretching, a sign of facilitated impulses

    Stretch Reflex in Clinics: Babinski Reflex

    • Normal plantar response is the toes fanning downward
    • Abnormal is the toes fanning upward, suggesting pyramidal pathway problems

    Golgi Tendon Organ

    • Detects muscle tension & inhibiting contraction of the same muscle to prevent overexertion or tearing of the muscle.

    Flexor Reflex & Withdrawal Reflexes

    • Painful stimulus trigger this reflex to withdraw from the painful stimulus
    • This can happen on the same or opposite side because the brain is trying to stabilize the posture of the body

    Reciprocal Inhibition & Reciprocal Innervation

    • When one muscle group is excited, the antagonist muscle group is inhibited, allowing coordinated movement

    Role of the Motor Cortex & Brain Stem

    • Motor Function Control (Motor cortex responsible for the initiation and planning, and brainstem responsible for more complex or fine-tuned movements).

    Cranial Nerves

    • Olfactory (I) - smell
    • Optic (II) - vision
    • Oculomotor (III) - eye movement, pupil size, lens shape - Parasympathetic (accommodation, near vision)
    • Trochlear (IV) - superior oblique muscle
    • Trigeminal (V) - facial sensation, chewing, jaw muscles - 3 divisions (Ophthalmic, Maxillary, and Mandibular) sensory and motor functions
    • Abducens (VI) - lateral rectus muscle, eye movements
    • Facial (VII) - facial expression, taste (anterior 2/3 of tongue), secretions (tears, saliva)
    • Vestibulocochlear (VIII) - hearing & balance
    • Glossopharyngeal (IX) - taste (posterior 1/3 of tongue), swallowing, and salivary gland control
    • Vagus (X) - parasympathetic function for organ regulation in thorax & abdomen
    • Accessory (XI)- head & neck movement (trapezius & sternocleidomastoid muscles)
    • Hypoglossal (XII) - tongue movements

    Cerebellum

    • Its function: Motor coordination, timing, and balance
    • Divisions: Posterior lobe, Anterior lobe, & Flocculonodular lobe
    • Deep nuclei: Dentate, Interposed, & Fastigial
    • Many pathways input into the cerebellum for fine-tuning of movement including cortical and brainstem inputs

    Cerebellum - Input Pathways

    • Cortico-ponto-cerebellar pathway - from motor, premotor & somatosensory cortical areas
    • Olivocerebellar tract - from inferior olive to cerebellum
    • Vestibulo-cerebellar fibers - from vestibular apparatus to cerebellar nuclei.
    • Reticulo-cerebellar fibers - from reticular formation to vermis
    • Other peripheral pathways transmit signals that provide sensory info. about muscle length, tension, and movement to cerebellum

    Cerebellum - Output Pathways

    • Output of cerebellum through projections to deep cerebellar nuclei, and back through numerous pathways to various parts of the brain

    Cerebellum - Functions (in different lobes)

    • Vestibulocerebellum - balance and eye movements
    • Spinocerebellum - muscle coordination and movement; receives information from proprioceptors and sensory receptors
    • Cerebrocerebellum - planning and executing complex movements, based on higher cortical input; receives information from cortex; involved in timing & extramotor abilities

    Cerebellum - Clinical Abnormalities

    • Dysmetria - overshooting movement targets
    • Ataxia - uncoordinated movements
    • Intension tremor - wavering movement towards target, caused by movement overshoots
    • Nystagmus - involuntary, rhythmic eye movements & suggests a problem with flocculonodular lobe
    • Hypotonia - reduced muscle tone.

    Basal Ganglia & Motor Control

    Basal Ganglia - Structure

    • Caudate nucleus, Putamen, Globus pallidus (internal & external segments), Substantia nigra (compacta & reticulata), & Subthalamic nucleus (STN).

    Basal Ganglia - Circuitry

    • Putamen circuit - involved in learned & subconscious movements (e.g. writing, hammering nails, etc.)
    • Caudate circuit - involved in initiating and planning complex &/or instinctive movements (e.g. choosing one action over another, etc.).

    Basal Ganglia - Pathways

    • Two major pathways; direct & indirect.
    • Direct pathway is used for initiating movement; indirect for inhibiting incorrect & inappropriate movements.
    • Dopamine is critical in modulating these pathways to regulate motor function smoothly.

    Basal Ganglia - Diseases

    • Parkinson’s disease: decreased dopamine production → difficulty initiating and controlling movements (characteristic symptom: tremor).
    • Huntington’s chorea: inappropriate, uncontrollable movements, caused by loss of many GABAergic neurons.

    Stroke

    • Interruption of blood flow in a specific artery to a region in the brain.
    • Causes: rupture of a blood vessel or thrombosis (blockage due to a clot)
    • Types: hemorrhagic (rupture) or ischemic (blockage)

    Upper Motor Neuron Lesions

    • Lesion above anterior horn cell: Spastic paralysis, hyperactive deep tendon reflexes; Babinski sign

    Lower Motor Neuron Lesions

    • Lesion in the anterior horn cell/nerve to specific muscle: hypotonicity (reduced muscle tone) &/or atrophy (muscle loss).

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    NeuroPhysiology_B PDF Notes

    Description

    Test your knowledge on the physiology of the nervous system, focusing on sensory receptors and somatic sensations. This quiz will cover various types of sensory receptors, their functions, and the classification of sensations. Understand how the nervous system processes different sensory information.

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