Vibration and Touch: Central Nervous System

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Questions and Answers

What are the primary cell types found in the olfactory bulb?

Bipolar cells and amacrine cells

Mitral cells and tufted cells (correct)

Purkinje cells and Golgi cells

Pyramidal cells and granule cells

Which statement accurately describes the olfactory pathway?

Olfactory signals always pass through the thalamus before reaching the olfactory cortex.

Olfactory signals have direct projections to the limbic cortex and primary olfactory cortex. (correct)

Olfactory signals are integrated in the brainstem before reaching the olfactory cortex.

Olfactory information is first routed to the sensory motor cortex.

What is the significance of the spatial map established by olfactory receptor neurons?

It prevents olfactory fatigue during continuous exposure to scents.

It regulates dopamine levels in the olfactory bulb.

It allows for the precise detection of changes in temperature.

It creates a labelled line code for odorant types. (correct)

Which factors can lead to disorders of olfaction?

Environmental toxins, diseases, and aging Signup and view all the answers

How do odorant molecules trigger the generation of action potentials in olfactory receptor neurons?

By activating a G-protein that leads to an increase in cAMP, causing ion channels to open. Signup and view all the answers

What role do low threshold mechanoreceptors play in relation to vibration?

They help determine if an object is living or moving. Signup and view all the answers

Which of the following body areas is likely to exhibit the highest two-point discrimination?

Thumb Signup and view all the answers

Which structure is primarily responsible for transmitting fine touch information from the lower limbs?

Gracile funiculus Signup and view all the answers

Where do second-order neurons for fine touch information synapse onto third-order neurons?

Thalamus Signup and view all the answers

What is the significance of decussations in the fine touch pathway?

They enable contralateral projection of sensory information. Signup and view all the answers

Which thalamic relay nucleus is responsible for receiving information from the face and head?

VPM Signup and view all the answers

How does the cuneate funiculus differ from the gracile funiculus?

It is located more laterally in the spinal cord. Signup and view all the answers

Which of these areas of the body is associated with a less precise two-point discrimination?

Thigh Signup and view all the answers

What is the primary signal molecule secreted by taste cells?

ATP Signup and view all the answers

Which type of taste cell is mainly responsible for the salty taste?

Type I (Glial-like) Signup and view all the answers

Which type of cells primarily detect sweet, bitter, and umami tastes?

Type II (Receptor Cells) Signup and view all the answers

How do Type III taste cells activate sensory neurons?

By releasing neurotransmitters like serotonin and CCK Signup and view all the answers

What kind of channels do salty and sour tastants primarily use for transduction?

Direct ion channels Signup and view all the answers

What key role does calcium play in Type II taste cells?

Stimulating ATP release Signup and view all the answers

Which receptors are most relevant in the Type II cells for ATP sensitivity?

P2X and P2Y Signup and view all the answers

What process allows taste buds to regenerate their receptors?

Presence of associated stem cells Signup and view all the answers

What is the role of NTPDase2 in Type I taste cells?

Processing secreted ATP Signup and view all the answers

Which component directly contributes to the internal depolarization of Type III taste cells?

Calcium ions Signup and view all the answers

What is primarily demonstrated by the Rubber Hand Illusion?

The integration of visual and tactile information Signup and view all the answers

Which brain structure is responsible for processing sensory information related to the body?

Thalamus Signup and view all the answers

What distinguishes the myotactic reflex from other reflexes?

It is a monosynaptic reflex Signup and view all the answers

How does the brain react to threats to a convincingly integrated fake hand?

It reacts as if the fake hand is real Signup and view all the answers

What condition might lead to phantom limb sensations?

Reorganization of the brain's sensory map Signup and view all the answers

Which component of the body is primarily influenced by the homunculus in the primary somatosensory cortex?

Body parts in terms of sensory input Signup and view all the answers

What happens to the reaction to a fake limb if it is placed in an unnatural position?

The reaction disappears Signup and view all the answers

What is the role of muscle spindles in the myotactic reflex?

To detect changes in muscle length Signup and view all the answers

What is the main feedback mechanism used in mirror box therapy?

Visual feedback Signup and view all the answers

Which of the following characteristics describes the autogenic aspect of the myotactic reflex?

The same muscle that is stretched contracts Signup and view all the answers

What does the medial portion of the homunculus represent?

Legs and feet Signup and view all the answers

How does plasticity of the somatosensory cortex manifest after losing sensory input?

Adjacent brain areas can take over the lost representation Signup and view all the answers

What phenomenon occurs when individuals feel sensations in a missing limb after amputation?

Phantom limb sensation Signup and view all the answers

What is the purpose of mirror box therapy?

To create a visual illusion of movement in a missing limb Signup and view all the answers

What does medial stimulation in the primary somatosensory cortex activate?

Neurons corresponding to the legs Signup and view all the answers

What happens to the sensory representation in the brain when a limb is amputated?

Adjacent areas may expand to compensate for the loss Signup and view all the answers

What regions does the central portion of the homunculus represent?

Arms and hands Signup and view all the answers

Which process describes the ability of the brain to change its representation based on sensory input?

Neuroplasticity Signup and view all the answers

What type of sensation may patients experience in a missing limb that has been amputated?

Phantom limb sensation Signup and view all the answers

Which statement about the homunculus is true?

It can adjust based on experience and loss of limbs Signup and view all the answers

Which brain regions receive projections from mitral and tufted cells in the olfactory bulb?

Amygdala, piriform cortex, and entorhinal cortex Signup and view all the answers

What is the primary mechanism by which odorant molecules lead to depolarization in olfactory receptor neurons?

Binding to receptors activating a G-protein and opening ion channels Signup and view all the answers

Which type of fiber is characterized by large diameter, thick myelination, and fast conduction?

A-alpha Fibers Signup and view all the answers

Which receptors are specifically responsible for proprioception?

Muscle spindles Signup and view all the answers

What role does the olfactory bulb play in the processing of odorants?

Creates a spatial map based on odorant types Signup and view all the answers

Which condition is primarily associated with disruptions in the sense of smell, impacting taste perception?

Anosmia Signup and view all the answers

What type of fibers are found in the contractile portions of the intrafusal fibers?

Gamma motor fibers Signup and view all the answers

What is the primary function of the A-alpha sensory fibers in muscle spindles?

To encode muscle stretch Signup and view all the answers

How do olfactory signals differ from those of other sensory systems in their initial processing?

They bypass the thalamus and have direct projections to limbic and olfactory cortices. Signup and view all the answers

Which statement accurately describes C-fibers?

They are unmyelinated and conduct signals very slowly. Signup and view all the answers

The gain of the motor system is primarily set by which component?

Fusimotor systems Signup and view all the answers

What is true about A-delta fibers compared to A-beta fibers?

A-delta fibers are lightly myelinated and slower. Signup and view all the answers

Which of the following best describes the central portion of muscle spindles?

It is bounded by contractile muscle portions. Signup and view all the answers

What is the main function of A-alpha and A-beta fibres in the spinal cord?

They transmit proprioceptive and fine touch mechanoreception information. Signup and view all the answers

Where are the cell bodies of the sensory axons found in the spinal cord?

In the dorsal root ganglia. Signup and view all the answers

What does the gracile funiculus primarily carry information about?

Fine touch and proprioception from the legs and feet. Signup and view all the answers

What role do the axon collaterals play in the dorsal columns of the spinal cord?

They allow information about muscle stretch to be processed locally at the spinal cord level. Signup and view all the answers

Which statement accurately reflects the organization of information within the gracile funiculus?

Fine touch from the feet is medial while that from the hands is lateral. Signup and view all the answers

At which spinal level is the cuneate funiculus present?

At L2 and above. Signup and view all the answers

What characterizes first-order afferent neurons in the spinal cord?

They carry sensory information from the peripheral nervous system to the central nervous system. Signup and view all the answers

How do the structures of the spinal cord change along its length?

The presence or absence of gracile and cuneate funiculi varies with sensory input. Signup and view all the answers

What happens to A-alpha and A-beta fibers after synapsing at the dorsal root ganglia?

They bypass the cell body and extend up to the dorsal columns. Signup and view all the answers

What is the primary function of sweet taste perception?

To indicate energy-rich nutrients Signup and view all the answers

Which type of papillae contain taste buds and are scattered across the tongue?

Fungiform Signup and view all the answers

What role does saliva play in taste perception?

It solubilizes food compounds and distributes tastants. Signup and view all the answers

Which taste is generally considered an aversive stimulus signaling potential toxins?

Bitter Signup and view all the answers

Which of the following statements about filiform papillae is true?

They are the most numerous papillae. Signup and view all the answers

What distinguishes umami from other taste sensations?

It indicates protein-rich foods, particularly from amino acids. Signup and view all the answers

What is a consequence of consuming food with high concentrations of sour and bitter flavors?

Nausea and vomiting. Signup and view all the answers

How many taste receptor cells are typically found in a single taste bud?

50 to 150 Signup and view all the answers

Which structure extracts tastants from saliva and facilitates taste perception?

Taste pore Signup and view all the answers

What is the primary reason humans are attracted to sweet tastes?

To seek energy-rich nutrients. Signup and view all the answers

What characteristic differentiates myotactic reflexes from other reflexes?

They involve only one synapse between sensory and motor neurons. Signup and view all the answers

How does the brain respond when a convincingly integrated fake hand is threatened?

It reacts to the fake hand as if it were part of the real body. Signup and view all the answers

What is the function of muscle spindles in the myotactic reflex?

To detect changes in muscle length. Signup and view all the answers

What occurs if a fake limb is positioned unnaturally during the Rubber Hand Illusion?

The reaction to threats to the fake limb disappears. Signup and view all the answers

What does phantom limb sensation illustrate about the brain's sensory map?

It undergoes reorganization after losing a limb. Signup and view all the answers

Which aspect of the homunculus is dynamic and can change over time?

The representation of body parts. Signup and view all the answers

Which structure is primarily responsible for integrating visual and tactile information during the Rubber Hand Illusion?

Primary somatosensory cortex. Signup and view all the answers

What is the primary mechanism behind mirror box therapy?

Visual feedback of the reflection of the intact limb. Signup and view all the answers

In what way does the thalamus contribute to sensory processing?

It relays sensory information to the appropriate cortical areas. Signup and view all the answers

Which ventricles are fluid-filled cavities located within the brain?

Lateral and third ventricles. Signup and view all the answers

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

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.
Internal Capsule: A white matter bundle connecting the thalamus and cortex.

Mapping the Body on the Brain (Homunculus)

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.
In Vivo Intercortical Recordings: Electrodes stimulate or record activity in different cortical regions to determine body part representation.

Dynamic Nature of the Homunculus

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.
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.
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.
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.
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

Myotactic (Stretch) Reflexes: Examples include the patellar tendon reflex and ankle tendon reflex.
- 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.
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

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.
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.
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
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.