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Questions and Answers
What are the primary cell types found in the olfactory bulb?
What are the primary cell types found in the olfactory bulb?
Which statement accurately describes the olfactory pathway?
Which statement accurately describes the olfactory pathway?
What is the significance of the spatial map established by olfactory receptor neurons?
What is the significance of the spatial map established by olfactory receptor neurons?
Which factors can lead to disorders of olfaction?
Which factors can lead to disorders of olfaction?
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How do odorant molecules trigger the generation of action potentials in olfactory receptor neurons?
How do odorant molecules trigger the generation of action potentials in olfactory receptor neurons?
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What role do low threshold mechanoreceptors play in relation to vibration?
What role do low threshold mechanoreceptors play in relation to vibration?
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Which of the following body areas is likely to exhibit the highest two-point discrimination?
Which of the following body areas is likely to exhibit the highest two-point discrimination?
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Which structure is primarily responsible for transmitting fine touch information from the lower limbs?
Which structure is primarily responsible for transmitting fine touch information from the lower limbs?
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Where do second-order neurons for fine touch information synapse onto third-order neurons?
Where do second-order neurons for fine touch information synapse onto third-order neurons?
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What is the significance of decussations in the fine touch pathway?
What is the significance of decussations in the fine touch pathway?
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Which thalamic relay nucleus is responsible for receiving information from the face and head?
Which thalamic relay nucleus is responsible for receiving information from the face and head?
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How does the cuneate funiculus differ from the gracile funiculus?
How does the cuneate funiculus differ from the gracile funiculus?
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Which of these areas of the body is associated with a less precise two-point discrimination?
Which of these areas of the body is associated with a less precise two-point discrimination?
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What is the primary signal molecule secreted by taste cells?
What is the primary signal molecule secreted by taste cells?
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Which type of taste cell is mainly responsible for the salty taste?
Which type of taste cell is mainly responsible for the salty taste?
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Which type of cells primarily detect sweet, bitter, and umami tastes?
Which type of cells primarily detect sweet, bitter, and umami tastes?
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How do Type III taste cells activate sensory neurons?
How do Type III taste cells activate sensory neurons?
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What kind of channels do salty and sour tastants primarily use for transduction?
What kind of channels do salty and sour tastants primarily use for transduction?
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What key role does calcium play in Type II taste cells?
What key role does calcium play in Type II taste cells?
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Which receptors are most relevant in the Type II cells for ATP sensitivity?
Which receptors are most relevant in the Type II cells for ATP sensitivity?
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What process allows taste buds to regenerate their receptors?
What process allows taste buds to regenerate their receptors?
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What is the role of NTPDase2 in Type I taste cells?
What is the role of NTPDase2 in Type I taste cells?
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Which component directly contributes to the internal depolarization of Type III taste cells?
Which component directly contributes to the internal depolarization of Type III taste cells?
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What is primarily demonstrated by the Rubber Hand Illusion?
What is primarily demonstrated by the Rubber Hand Illusion?
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Which brain structure is responsible for processing sensory information related to the body?
Which brain structure is responsible for processing sensory information related to the body?
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What distinguishes the myotactic reflex from other reflexes?
What distinguishes the myotactic reflex from other reflexes?
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How does the brain react to threats to a convincingly integrated fake hand?
How does the brain react to threats to a convincingly integrated fake hand?
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What condition might lead to phantom limb sensations?
What condition might lead to phantom limb sensations?
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Which component of the body is primarily influenced by the homunculus in the primary somatosensory cortex?
Which component of the body is primarily influenced by the homunculus in the primary somatosensory cortex?
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What happens to the reaction to a fake limb if it is placed in an unnatural position?
What happens to the reaction to a fake limb if it is placed in an unnatural position?
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What is the role of muscle spindles in the myotactic reflex?
What is the role of muscle spindles in the myotactic reflex?
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What is the main feedback mechanism used in mirror box therapy?
What is the main feedback mechanism used in mirror box therapy?
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Which of the following characteristics describes the autogenic aspect of the myotactic reflex?
Which of the following characteristics describes the autogenic aspect of the myotactic reflex?
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What does the medial portion of the homunculus represent?
What does the medial portion of the homunculus represent?
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How does plasticity of the somatosensory cortex manifest after losing sensory input?
How does plasticity of the somatosensory cortex manifest after losing sensory input?
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What phenomenon occurs when individuals feel sensations in a missing limb after amputation?
What phenomenon occurs when individuals feel sensations in a missing limb after amputation?
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What is the purpose of mirror box therapy?
What is the purpose of mirror box therapy?
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What does medial stimulation in the primary somatosensory cortex activate?
What does medial stimulation in the primary somatosensory cortex activate?
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What happens to the sensory representation in the brain when a limb is amputated?
What happens to the sensory representation in the brain when a limb is amputated?
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What regions does the central portion of the homunculus represent?
What regions does the central portion of the homunculus represent?
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Which process describes the ability of the brain to change its representation based on sensory input?
Which process describes the ability of the brain to change its representation based on sensory input?
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What type of sensation may patients experience in a missing limb that has been amputated?
What type of sensation may patients experience in a missing limb that has been amputated?
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Which statement about the homunculus is true?
Which statement about the homunculus is true?
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Which brain regions receive projections from mitral and tufted cells in the olfactory bulb?
Which brain regions receive projections from mitral and tufted cells in the olfactory bulb?
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What is the primary mechanism by which odorant molecules lead to depolarization in olfactory receptor neurons?
What is the primary mechanism by which odorant molecules lead to depolarization in olfactory receptor neurons?
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Which type of fiber is characterized by large diameter, thick myelination, and fast conduction?
Which type of fiber is characterized by large diameter, thick myelination, and fast conduction?
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Which receptors are specifically responsible for proprioception?
Which receptors are specifically responsible for proprioception?
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What role does the olfactory bulb play in the processing of odorants?
What role does the olfactory bulb play in the processing of odorants?
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Which condition is primarily associated with disruptions in the sense of smell, impacting taste perception?
Which condition is primarily associated with disruptions in the sense of smell, impacting taste perception?
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What type of fibers are found in the contractile portions of the intrafusal fibers?
What type of fibers are found in the contractile portions of the intrafusal fibers?
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What is the primary function of the A-alpha sensory fibers in muscle spindles?
What is the primary function of the A-alpha sensory fibers in muscle spindles?
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How do olfactory signals differ from those of other sensory systems in their initial processing?
How do olfactory signals differ from those of other sensory systems in their initial processing?
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Which statement accurately describes C-fibers?
Which statement accurately describes C-fibers?
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The gain of the motor system is primarily set by which component?
The gain of the motor system is primarily set by which component?
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What is true about A-delta fibers compared to A-beta fibers?
What is true about A-delta fibers compared to A-beta fibers?
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Which of the following best describes the central portion of muscle spindles?
Which of the following best describes the central portion of muscle spindles?
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What is the main function of A-alpha and A-beta fibres in the spinal cord?
What is the main function of A-alpha and A-beta fibres in the spinal cord?
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Where are the cell bodies of the sensory axons found in the spinal cord?
Where are the cell bodies of the sensory axons found in the spinal cord?
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What does the gracile funiculus primarily carry information about?
What does the gracile funiculus primarily carry information about?
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What role do the axon collaterals play in the dorsal columns of the spinal cord?
What role do the axon collaterals play in the dorsal columns of the spinal cord?
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Which statement accurately reflects the organization of information within the gracile funiculus?
Which statement accurately reflects the organization of information within the gracile funiculus?
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At which spinal level is the cuneate funiculus present?
At which spinal level is the cuneate funiculus present?
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What characterizes first-order afferent neurons in the spinal cord?
What characterizes first-order afferent neurons in the spinal cord?
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How do the structures of the spinal cord change along its length?
How do the structures of the spinal cord change along its length?
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What happens to A-alpha and A-beta fibers after synapsing at the dorsal root ganglia?
What happens to A-alpha and A-beta fibers after synapsing at the dorsal root ganglia?
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What is the primary function of sweet taste perception?
What is the primary function of sweet taste perception?
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Which type of papillae contain taste buds and are scattered across the tongue?
Which type of papillae contain taste buds and are scattered across the tongue?
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What role does saliva play in taste perception?
What role does saliva play in taste perception?
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Which taste is generally considered an aversive stimulus signaling potential toxins?
Which taste is generally considered an aversive stimulus signaling potential toxins?
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Which of the following statements about filiform papillae is true?
Which of the following statements about filiform papillae is true?
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What distinguishes umami from other taste sensations?
What distinguishes umami from other taste sensations?
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What is a consequence of consuming food with high concentrations of sour and bitter flavors?
What is a consequence of consuming food with high concentrations of sour and bitter flavors?
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How many taste receptor cells are typically found in a single taste bud?
How many taste receptor cells are typically found in a single taste bud?
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Which structure extracts tastants from saliva and facilitates taste perception?
Which structure extracts tastants from saliva and facilitates taste perception?
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What is the primary reason humans are attracted to sweet tastes?
What is the primary reason humans are attracted to sweet tastes?
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What characteristic differentiates myotactic reflexes from other reflexes?
What characteristic differentiates myotactic reflexes from other reflexes?
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How does the brain respond when a convincingly integrated fake hand is threatened?
How does the brain respond when a convincingly integrated fake hand is threatened?
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What is the function of muscle spindles in the myotactic reflex?
What is the function of muscle spindles in the myotactic reflex?
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What occurs if a fake limb is positioned unnaturally during the Rubber Hand Illusion?
What occurs if a fake limb is positioned unnaturally during the Rubber Hand Illusion?
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What does phantom limb sensation illustrate about the brain's sensory map?
What does phantom limb sensation illustrate about the brain's sensory map?
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Which aspect of the homunculus is dynamic and can change over time?
Which aspect of the homunculus is dynamic and can change over time?
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Which structure is primarily responsible for integrating visual and tactile information during the Rubber Hand Illusion?
Which structure is primarily responsible for integrating visual and tactile information during the Rubber Hand Illusion?
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What is the primary mechanism behind mirror box therapy?
What is the primary mechanism behind mirror box therapy?
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In what way does the thalamus contribute to sensory processing?
In what way does the thalamus contribute to sensory processing?
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Which ventricles are fluid-filled cavities located within the brain?
Which ventricles are fluid-filled cavities located within the brain?
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Study Notes
Vibration and Touch:
- Vibration is information about movement or life.
- Low threshold mechanoreceptors are abundant in hands, feet, lips, and tongue.
- Two-point discrimination is used to measure tactile acuity.
- The thumb and lips exhibit high precision in two-point discrimination.
- In the thigh and upper back, stimuli closer than 40mm are perceived as a single point.
Central Nervous System Pathways
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Fine Touch System: Information travels through the dorsal column system.
- Primary Afferent Pathway: Dorsal column nuclei in the medulla, crosses midline, ascends via medial lemniscus to the thalamus.
- Thalamic Relay: VPM (face and head) and VPL (body surface).
- The dorsal columns (gracile and cuneate funiculi) terminate in the medulla, with the gracile carrying information from the lower limbs and the cuneate from the upper limbs.
- Second-order neurons cross the midline at decussations and synapse onto third-order neurons in the VPM and VPL thalamus.
- The VPM relays information from the face and head, while the VPL relays information from the body surface.
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Internal Capsule: A white matter bundle connecting the thalamus and cortex.
Mapping the Body on the Brain (Homunculus)
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Somatotopic Map: The primary somatosensory cortex is organized as a body map, the homunculus.
- Medial portion: Represents legs and feet.
- Central portion: Represents arms and hands.
- Lateral portion: Represents face and oropharynx.
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In Vivo Intercortical Recordings: Electrodes stimulate or record activity in different cortical regions to determine body part representation.
Dynamic Nature of the Homunculus
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Plasticity of the Somatosensory Cortex: The homunculus is dynamic and can change throughout life.
- When sensory input from a body part is lost, adjacent brain areas can take over its representation.
- For example, if the hand's sensory input is lost, the face and other adjacent regions may expand to cover the hand's representation.
- When sensory input from a body part is lost, adjacent brain areas can take over its representation.
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Phantom Limb Sensation: Sensations are felt in a missing limb after amputation.
- Occurs due to the brain's persistent representation of the limb, which can be activated by stimulating adjacent cortical areas.
- It can be described as residual sensation, where sensations associated with the fingers and hands are felt along the face even though the forelimb is missing.
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Mirror Box Therapy: A mirror creates a visual illusion of the missing limb, reducing pain and discomfort by moving the intact hand while looking at its reflection.
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Rubber Hand Illusion: Visual and tactile information integration allows the brain to adopt a fake hand into its body map. When a fake hand is stroked while the real hand is hidden and stroked simultaneously, the person may feel that the fake hand is part of their own body.
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Illusory Third Arm: If a fake hand is convincingly integrated into a person's body map, the person may react to threats to the fake hand as if it were their own. This reaction disappears if the fake limb is placed in an unnatural position.
Summary of Key Brain Structures:
- Thalamus: Processes sensory information (VPM for face, VPL for body).
- Ventricles: Fluid-filled cavities (third and lateral ventricles).
- Primary somatosensory cortex: Located in the post-central gyrus, organized as a body map (homunculus).
- Central sulcus: Landmark dividing the frontal and parietal lobes.
- Internal capsule: White matter connecting the thalamus and cortex.
- Homunculus: A dynamic, plastic body map in the brain. Representation of body parts can change based on sensory input.
- Phantom limb sensation: Sensations in missing limbs due to reorganization of the brain's sensory map.
- Mirror box therapy: Visual feedback can help reduce phantom limb pain.
- Rubber hand illusion: The brain can adopt a fake hand into its body map.
- Illusory third arm: Demonstrates real-time body map updates in the brain.
Major Clinical Proprioceptive Reflexes
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Myotactic (Stretch) Reflexes: Examples include the patellar tendon reflex and ankle tendon reflex.
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Characteristics:
- Monosynaptic: Involves only one synapse between the sensory neuron and the motor neuron.
- ** Autogenic:** The muscle being stretched is the same muscle that contracts.
- Ipsilateral: The reflex action occurs on the same side of the body as the stimulation.
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Characteristics:
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Mechanism of the Patellar Tendon Reflex:
- Stimulus: Tapping the patella with a reflex hammer stretches the quadriceps muscle.
- Muscle Spindle Activation: When the muscle stretches, the muscle spindle detects changes in muscle length and is activated. This sends a signal to the spinal cord.
- Signal Pathway: The sensory neuron splits and synapses with the motor neuron responsible for controlling the quadriceps muscle. The motor neuron transmits a signal, causing the quadriceps muscle to contract, resulting in the leg extension.
Taste System
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Type I (Glial-like) Taste Cells: Contribute to salty taste through ion channels that process sodium.
- Contain K+ channels for K+ secretion.
- Express NTPDase2, an enzyme that processes ATP as a transmitter signal.
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Type II (Receptor) Taste Cells: The most common type, detect sweet, bitter, and umami tastes through G-protein coupled receptors.
- Use Panx family receptors for ATP release.
- Possess receptors (P2X and P2Y) that are sensitive to ATP.
- Utilize TRP channels for environmental signal sensing.
- Internal calcium depolarization stimulates ATP release.
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Type III (Presynaptic) Taste Cells: Most neuronal-like, directly activating sensory neurons through neurotransmitters.
- Release neurotransmitters (serotonin, CCK, and NPY) in response to sour tastants.
- Undergo internal calcium depolarization and membrane depolarization via ATP secreted from Type II cells.
- Calcium stimulates neurotransmitter release alongside P2Y channel activation by Type II cell-secreted ATP.
Transduction Pathways for Tastant Types
- Salty and Sour: Utilize direct ion channels.
Olfactory System
- Olfactory Receptor Neurons (ORNs): Express specific odorant receptors for smell detection.
- Olfactory Bulb: The first brain region that processes olfactory information, contains mitral and tufted cells.
- Glomeruli: Structures in the olfactory bulb that receive input from ORNs, create an organizational map based on odorant types.
- Labelled Line Code: Specific olfactory receptor neurons project to distinct glomeruli, forming a spatial map of the olfactory bulb.
Olfactory Pathway and Memory
- Central Olfactory Pathway: Olfactory signals bypass the thalamus initially and project directly to the limbic cortex and primary olfactory cortex.
- Memory Association: Olfactory signals strongly trigger long-term memories, allowing smells to evoke memory recall even in individuals with memory loss.
Disorders of Olfaction
- Taste disorders are often olfactory disorders.
- Anosmia: Loss of smell.
- Dysosmia: Distorted smell.
- Causes of Olfactory Disorders: Environmental toxins, diseases, and aging.
- Effects: Affect quality of life and safety (e.g., detecting fire or fumes).
Odorant Transduction
- Odorant molecules bind to receptors on cilia, activating a G- protein (Golf).
- This triggers cAMP production, opening ion channels and causing depolarization.
- Chloride efflux further depolarizes the cell, generating action potentials.
Central Olfactory Pathways
- ORNs project to glomeruli in the olfactory bulb.
- Mitral and tufted cells in the olfactory bulb project to:
- Piriform cortex (primary olfactory cortex).
- Amygdala (emotional processing).
- Entorhinal cortex (memory processing).
Olfactory Coding
- Each type of ORN projects to specific glomeruli, creating a spatial map of odorant types.
- This map differentiates between thousands of odorants.
Fiber Types
- A-alpha Fibers: Large diameter, low internal resistance, fast conduction, thick myelination, and use saltatory conduction
- A-beta Fibers: Slightly smaller, strong myelination, and rapid conduction
- A-delta Fibers: Narrower, lightly myelinated, and slow conduction
- C-fibres: Smallest diameter, high internal resistance, limited conduction capacity, unmyelinated, very slow conduction, and no saltatory conduction
Proprioception
- Ability to sense body and limb position in space.
- Receptors: Muscle spindles are embedded in skeletal muscles and act as sensors to measure muscle stretch and muscle length
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Intrafusal muscle fibres: Three segments:
- Central non-contractile portion with annulo-spiral endings
- Contractile portions on either end with gamma motor fibres
- The large extrafusal skeletal muscle fibres are innervated by alpha motor neurons
- Intrafusal Fibre Types: Nuclear chain fibres and nuclear bag fibres
Proprioception Innervation
- Central Non-Contractile Portion: A-alpha sensory fibers
- Contractile Portions: Gamma motor fibers
- Extrafusal muscle fibres: Alpha motor neurons
Proprioception Function
- Encode muscle stretch and length, provide proprioceptive feedback
Spinal Cord & Structures
- Dorsal root ganglia: Cell bodies of A-alpha and A-beta fibres, found in the dorsal portion of the spinal nerve.
- Dorsal columns: Carry proprioception and fine touch mechanoreception information to the medulla.
- Axon collaterals: Allow information about muscle stretch to be processed at the level of the spinal cord.
Histology of the Dorsal Columns
- Gracile funiculus: Extends from the fifth sacral vertebrae to the seventh thoracic vertebra, carrying information from the legs and feet.
- Cuneate funiculus: Located at C5, carrying information from the upper limbs.
Medial Lemniscus
- First-Order Neurons: Carry fine touch and proprioception information from the peripheral nervous system to the central nervous system.
Rubber Hand Illusion
- A person sees a fake hand being stroked while their own hand is hidden and simultaneously stroked.
- The brain can integrate visual and tactile information and update the body map.
Illusory Third Arm
- A fake hand is convincingly integrated into a person's body map and the person reacts to threats to the fake hand as if it were their own.
- The fake limb must be in a natural position for this to work.
Summary
- Thalamus: Processes sensory information
- Ventricles: Fluid-filled cavities
- Primary somatosensory cortex: Organized as a body map
- Central sulcus: Landmark dividing the frontal and parietal lobes
- Internal capsule: White matter connecting thalamus and cortex
- Homunculus: Dynamic, plastic map of the body in the brain
- Phantom limb sensation: Sensations in missing limbs
- Mirror box therapy: Can help reduce phantom limb pain
Major Clinical Reflexes
-
Myotactic (Stretch) Reflexes:
- Examples: Patellar tendon reflex and ankle tendon reflex
- Characteristics: Monosynaptic, autogenic, and ipsilateral
-
Mechanism of the patellar tendon reflex:
- 1. Stimulus: Tapping the patella stretches the quadriceps muscle.
- 2. Muscle Spindle Activation: The muscle spindle detects changes in muscle length and is activated.
- 3. Signal Pathway: Sensory neuron splits and sends a signal via type 1A sensory neurons to the spinal cord.
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Description
Explore the mechanisms of vibration and touch perception, including the role of low threshold mechanoreceptors and the fine touch system. Understand two-point discrimination and the central nervous system pathways involved in tactile acuity. This quiz highlights the pathways from afferent receptors to the thalamic relay for fine touch information.
