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Questions and Answers
What is the immediate response of somatic sensory receptors to a stimulus?
What is the immediate response of somatic sensory receptors to a stimulus?
What role do interneurons play in the somatic nervous system?
What role do interneurons play in the somatic nervous system?
What type of neurons transmit information from somatic sensory receptors to the central nervous system?
What type of neurons transmit information from somatic sensory receptors to the central nervous system?
Which of the following is the most accurate description of the process that follows the generation of an action potential in a sensory neuron?
Which of the following is the most accurate description of the process that follows the generation of an action potential in a sensory neuron?
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What is the primary function of the somatic sensory system?
What is the primary function of the somatic sensory system?
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Which type of nerve fibers are associated with relaying slow pain sensations, such as burning or aching?
Which type of nerve fibers are associated with relaying slow pain sensations, such as burning or aching?
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Which of the following locations does NOT contain thermoreceptors?
Which of the following locations does NOT contain thermoreceptors?
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What is the primary function of baroreceptors?
What is the primary function of baroreceptors?
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What characteristic distinguishes fine touch and pressure receptors from crude touch and pressure receptors?
What characteristic distinguishes fine touch and pressure receptors from crude touch and pressure receptors?
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Which type of tactile receptor is best suited for detecting initial contact with the skin and subsequent movements?
Which type of tactile receptor is best suited for detecting initial contact with the skin and subsequent movements?
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Which of the following describes the Iggo dome receptor?
Which of the following describes the Iggo dome receptor?
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Where are Meissner's corpuscles primarily located?
Where are Meissner's corpuscles primarily located?
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What is the primary difference between touch and pressure sensations based on their stimulation?
What is the primary difference between touch and pressure sensations based on their stimulation?
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Which tactile receptor is responsible for detecting low-frequency vibrations?
Which tactile receptor is responsible for detecting low-frequency vibrations?
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Which of the following are classified as mechanoreceptors?
Which of the following are classified as mechanoreceptors?
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Which of the following is NOT a characteristic of Pacinian corpuscles?
Which of the following is NOT a characteristic of Pacinian corpuscles?
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Which of the following is NOT a type of proprioceptor?
Which of the following is NOT a type of proprioceptor?
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Which of the following best describes the role of chemoreceptors in the carotid bodies?
Which of the following best describes the role of chemoreceptors in the carotid bodies?
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What is the primary function of muscle spindles?
What is the primary function of muscle spindles?
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Which of the following is TRUE regarding static position sense?
Which of the following is TRUE regarding static position sense?
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What is the function of Golgi tendon organs?
What is the function of Golgi tendon organs?
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Which of the following is a characteristic of Ruffini's corpuscles?
Which of the following is a characteristic of Ruffini's corpuscles?
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Where are the chemoreceptors that monitor blood pH, carbon dioxide, and oxygen levels located?
Where are the chemoreceptors that monitor blood pH, carbon dioxide, and oxygen levels located?
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What occurs during sensory transduction?
What occurs during sensory transduction?
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Which of the following best describes tonic receptors?
Which of the following best describes tonic receptors?
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What characterizes phasic receptors?
What characterizes phasic receptors?
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What is meant by adaptation in sensory receptors?
What is meant by adaptation in sensory receptors?
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What happens when a Pacinian corpuscle is stimulated?
What happens when a Pacinian corpuscle is stimulated?
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What characteristic of tactile receptors allows for rapid adaptation to stimuli?
What characteristic of tactile receptors allows for rapid adaptation to stimuli?
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What is the function of lateral inhibition in sensory pathways?
What is the function of lateral inhibition in sensory pathways?
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Which of the following statements best describes the relationship between receptive field size and acuity?
Which of the following statements best describes the relationship between receptive field size and acuity?
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What role does the thalamus play in sensory perception?
What role does the thalamus play in sensory perception?
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How quickly can the dorsal column recognize changing stimuli?
How quickly can the dorsal column recognize changing stimuli?
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Which part of the body is represented with a larger area on the sensory homunculus?
Which part of the body is represented with a larger area on the sensory homunculus?
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What type of sensations are recognized by the dorsal column at high frequencies?
What type of sensations are recognized by the dorsal column at high frequencies?
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Which statement about the perception of stimuli is correct?
Which statement about the perception of stimuli is correct?
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What is the main function of motor neurons?
What is the main function of motor neurons?
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Where are the cell bodies of first order neurons located?
Where are the cell bodies of first order neurons located?
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What distinguishes the primary motor cortex within the cerebral cortex?
What distinguishes the primary motor cortex within the cerebral cortex?
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What occurs in the somatosensory cortex when a sensory signal is received?
What occurs in the somatosensory cortex when a sensory signal is received?
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What is a primary role of the premotor cortex?
What is a primary role of the premotor cortex?
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Which of the following statements about third order neurons is correct?
Which of the following statements about third order neurons is correct?
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What consequence results from damage to the premotor cortex?
What consequence results from damage to the premotor cortex?
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What would be the outcome of bilateral excision of the somatosensory area I?
What would be the outcome of bilateral excision of the somatosensory area I?
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What characterizes the layers of the somatosensory cortex?
What characterizes the layers of the somatosensory cortex?
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What is the function of the sensory areas in the cerebral cortex?
What is the function of the sensory areas in the cerebral cortex?
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Flashcards
Somatic Nervous System
Somatic Nervous System
The part of the nervous system responsible for voluntary movements and sensory perception.
Sensory Receptors
Sensory Receptors
Nerve cell endings that detect environmental stimuli and generate action potentials.
Afferent Neurons
Afferent Neurons
Nerve cells that carry sensory information from receptors to the central nervous system.
Interneurons
Interneurons
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Sensory Homunculus
Sensory Homunculus
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Motor Neurons
Motor Neurons
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First Order Neurons
First Order Neurons
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Second Order Neurons
Second Order Neurons
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Third Order Neurons
Third Order Neurons
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Cerebral Cortex
Cerebral Cortex
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Primary Motor Cortex
Primary Motor Cortex
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Premotor Cortex
Premotor Cortex
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Somatosensory Cortex
Somatosensory Cortex
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Layers of Somatosensory Cortex
Layers of Somatosensory Cortex
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Somatosensory Area I
Somatosensory Area I
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Pacinian Corpuscles
Pacinian Corpuscles
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Ruffini’s Corpuscles
Ruffini’s Corpuscles
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Static Position Sense
Static Position Sense
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Kinesthesia
Kinesthesia
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Muscle Spindles
Muscle Spindles
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Golgi Tendon Organs
Golgi Tendon Organs
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Chemoreceptors
Chemoreceptors
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Receptor Potential
Receptor Potential
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Injection Sensation
Injection Sensation
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Classes of Mechanoreceptors
Classes of Mechanoreceptors
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Tactile Receptors
Tactile Receptors
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Free Nerve Endings
Free Nerve Endings
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Root Hair Plexus
Root Hair Plexus
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Merkel's Discs
Merkel's Discs
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Meissner's Corpuscles
Meissner's Corpuscles
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Proprioreceptors
Proprioreceptors
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Crude Touch Receptors
Crude Touch Receptors
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Sensory Transduction
Sensory Transduction
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Adaptation
Adaptation
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Tonic Receptors
Tonic Receptors
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Phasic Receptors
Phasic Receptors
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Two-Point Discrimination
Two-Point Discrimination
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Receptive Field Size
Receptive Field Size
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Lateral Inhibition
Lateral Inhibition
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Dorsal Column Function
Dorsal Column Function
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Vibration Sensation
Vibration Sensation
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Thalamus Role
Thalamus Role
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Study Notes
Somatic Sensory
- Somatic sensory system is responsible for receiving information from the body's surface and internal organs, including touch, temperature, pain and position.
- The system has various receptors, each sensitive to specific types of stimuli.
- Afferent neurons carry sensory information from receptors to the central nervous system (CNS).
- Interneurons in the CNS process the sensory input.
- Motor neurons carry signals from the CNS to effectors, such as muscles and glands, producing responses.
- Somatic sensory signals travel along specific pathways to reach the brain, the primary somatic sensory cortex interprets the signals and determines the location, intensity, type of stimulus.
- There are different types of sensory receptors, such as mechanoreceptors, thermoreceptors, and nociceptors, each with different functions, sensitivities, and locations in the body.
Learning Objectives
- Discuss the organization and features of the sensory nervous system.
- Describe the classification, characteristics, and functions of sensory receptors.
- Explain the properties of receptor potential.
- Examine how the brain perceives stimulus intensity and quality.
- Discuss the sensory homunculus.
- Analyze the sensory pathways and their functions.
Organization of the Somatic Nervous System
- Somatic receptors, such as nerve endings, generate action potentials (electrical signals) when stimulated.
- These signals travel through afferent neurons (sensory neurons) to the CNS.
- Interneurons in the CNS process the sensory information, interpret its meaning, and plan appropriate responses.
- Motor neurons (efferent neurons) carry the response signals from the CNS to skeletal muscles, causing muscle movement.
- This process is fundamental to voluntary movements.
Processing at the Circuit Level
- First-order neurons conduct impulses from receptors to the spinal cord or brainstem.
- Second-order neurons carry the signal to the thalamus.
- Third-order neurons transmit signals to the somatosensory cortex of the cerebrum, enabling conscious perception.
Cerebral Cortex
- The cerebral cortex has three main functional areas: motor areas, sensory areas, and association areas.
- Motor areas control voluntary movement.
- Sensory areas provide awareness of sensations.
- Association areas integrate information for purposeful actions.
- Each hemisphere is responsible for the sensory and motor functions of the opposite side of the body.
Primary Motor Cortex
- The primary motor cortex is located in the precentral gyrus of the frontal lobe.
- Pyramidal cells in this area control voluntary movements.
- The lateral corticospinal/pyramidal tract is an important descending pathway for motor signals.
Premotor Cortex
- Involves the coordination of several muscle groups for simultaneous or sequential movement.
- The premotor cortex sends activation signals to the primary motor cortex.
- It influences and acts as a memory bank for skilled motor activities.
- Damage here affects coordinated and patterned movements.
Somatosensory Cortex
- Sensory signals from various modalities terminate in the somatosensory cortex, situated behind the central fissure.
- The anterior half of the parietal lobe receives and interprets somatosensory signals.
- The posterior half of the parietal lobe processes signals for high-level interpretations, which are interpreted at a much higher level than the initial input.
Layers of the Somatosensory Cortex & their function
- The six layers receive sensory information and transmit the signal to different layers in the nervous system.
Sensory Cortex Organization
- The sensory cortex is organized into vertical columns representing different sensory modalities.
- Bilateral excision of the somatosensory area I will affect the person's ability to localize sensations.
Somatosensory Association Areas
- Brodmann's areas 5 and 7 analyze sensory information to provide a deeper understanding of sensory input.
- These areas receive information from the somatosensory cortex, brain stem nuclei, and other regions, for a holistic perception of touch.
General Senses
- General senses describe sensitivity to temperature, pain, touch, pressure, and proprioception.
- Sensation is the initial perception of the stimuli, while perception is the conscious recognition.
Classification of Somatic Senses
- Mechanoreceptors respond to mechanical stimuli: touch, pressure, vibrations, stretch, and itch.
- Thermoreceptors detect heat and cold.
- Nociceptors respond to potentially harmful stimuli (tissue damage).
Other Classifications of Somatic Senses
- Exteroreceptors respond to stimuli outside the body, including touch, pressure, pain.
- Proprioreceptors inform about the body's position, tendon, and muscle tension.
- Visceroreceptors provide information about the internal organs.
- Deep sensation originates from the body's deep tissues, such as muscles and bones.
Free Nerve Endings
- Free nerve endings are the simplest sensory receptors.
- They are branching tips of dendrites without specialized structures.
- They respond to several types of stimuli, enabling diverse sensations within the body.
Receptive Field
- The area monitored by a single receptor cell is called the receptive field.
- The larger the receptive field, the more difficult it is to locate a stimulus.
Nociceptors
- Nociceptors, or pain receptors, are sensitive to factors that damage tissue, including extremes of temperature, mechanical damage, and chemicals.
- They are present in various locations on the body, within the skin, joint capsules, periosteum and around blood vessels etc.
- Pain signals are carried via two types of sensory fibers: Type A and Type C fibers.
- Type A fibers transmit fast pain, while Type C fibers transmit slow pain.
Thermoreceptors
- Free nerve endings located in the dermis, skeletal muscles, liver, and hypothalamus, respond to change in temperature.
- They conduct information along pathways similar to those of painful sensations
3 Classes of Mechanoreceptors
- Tactile receptors respond to touch, pressure, and vibration.
- Baroreceptors detect pressure changes within the blood vessels, digestive system, and urinary tracts.
- Proprioceptors report the positions of joints and muscles.
- Fine touch and pressure receptors have narrow receptive fields, providing precise location, shape and texture awareness.
- Crude touch and pressure receptors have wider receptive fields, resulting in less accurate localization.
Tactile Receptors
- Tactile receptors range in complexity and include free nerve endings, specialized sensory complexes, and accessory structures.
- Touch, pressure, and vibratory sensations result from stimulation of tactile receptors.
- Pressure and vibration also result from deeper tissue deformation, whereas, touch sensation generally results from stimulation of receptors in the skin or subcutaneous tissue.
6 Types of Tactile Receptors
- Six types are free nerve endings, root hair plexuses, Merkel’s tactile discs, Meissner’s tactile corpuscles, Pacinian corpuscles, and Ruffini’s corpuscles.
- Each type of tactile receptor is specialized to detect different types of tactile information with specific sensitivities and adaptations.
Proprioceptive Senses
- Proprioception, or the sense of body position, includes static position sense and rate of movement sense (kinesthesia).
- Knowledge of position relies on awareness of joint angle and rate of change of the joints in all planes of movement.
- Multiple receptors, including deep receptors (corpuscles), and muscle spindles, provide position information.
3 Major Groups of Proprioceptors
- Muscle spindles monitor muscle length and trigger stretch reflexes.
- Golgi tendon organs sense tension in tendons, important for muscle contraction.
- Receptors in joint capsules provide information about pressure, tension and movement at the joints
Chemoreceptors
- Chemoreceptors detect chemical changes in the body, specifically monitoring pH, carbon dioxide, and oxygen levels in arterial blood.
- These are located in the carotid bodies and aortic bodies.
Characteristics of Receptor Potential
- Stimulus is any change that can be detected by the body.
- Sensory receptors detect these stimuli and convert them into graded potentials (receptor potentials).
- Afferent neurons transmit signals to the CNS by using action potentials, propagating throughout the nervous system, enabling effective information transfer.
- Sensory transduction converts the stimulus energy into a receptor potential, which triggers an action potential if it reaches a threshold level.
Conversion of Receptor Potential into Action Potential
- In specialized afferent endings, stimulus-sensitive channels are opened, causing net Na+ entry, leading to receptor potential.
- Adjacent region voltage-gated Na+ channels open due to local current flow, leading to action potential initiation in the sensory fiber.
- In separate receptor cells, the process is similar, with stimulus-sensitive channels permitting net Na+ entry.
- Neurotransmitter release leads to opening of receptor channels at afferent endings, resulting in action potential initiation.
Adaptation
- Adaptation is a reduction in sensitivity to a constant stimulus.
- Tonic receptors are continuously active and do not adapt; they provide ongoing information, such as proprioceptive information for maintaining posture.
- Phasic receptors rapidly adapt and respond only to changes in the stimulus, helping to filter out constant stimuli, such as touch from clothing.
Overall Characteristics of Signal Transmission and Analysis in the Dorsal Column
- The dorsal column transmits information, including highly localized touch, pressure, vibration, and proprioception, to the brain.
- Two-point discrimination is a measure of acuity; the smaller the receptive field, the greater the discrimination ability.
- Lateral inhibition sharpens the sensory signals, enhancing the contrast and accuracy of localization for each specific stimulus.
Three Major Somatic Sensory Pathways
- The three main pathways are posterior column pathways, anterolateral pathways, and spinocerebellar pathways.
- The posterior column pathway is responsible for highly localized sensations.
- The anterolateral pathway transmits less critical signals.
- The spinocerebellar pathways carry proprioceptive information related to the position of skeletal muscles, tendons, and joints, impacting the body's movement.
Posterior Column Pathway
- This pathway transmits highly localized sensations like fine touch, pressure, vibration, and proprioception from the body to the brain.
Posterior/Dorsal Column - Medial Lemniscal System
- This system handles touch sensations for localization, fine pressure sensations and vibratory sensations, including sensations from muscles and joints.
2) Anterolateral Pathway
- This pathway transmits crude touch, pressure, pain, temperature, tickle, and itch sensations.
- This system is less critical to localize and discriminate sensations.
2) Anterolateral Pathway - Characteristics of Transmission
- The anterolateral pathway has slower conduction than the dorsal column.
- Spatial localization is less precise.
- It can process rapid changes effectively and adapt quickly.
3) Spinocerebellar Pathway
- This pathway provides proprioceptive information about the position of skeletal muscles, tendons, and joints to the cerebellum.
Visceral Sensory Information
- Interoceptors monitor visceral tissues and organs, collecting information primarily from the thoracic and abdominopelvic cavities.
- This system includes nociceptors, thermoreceptors, tactile receptors, baroreceptors, and chemoreceptors for internal sensations.
Descending (Motor) Pathway
- Upper motor neurons in the CNS initiate voluntary movements.
- Lower motor neurons in the brainstem and spinal cord directly trigger muscle contractions.
- Damage or destruction to lower motor neurons affects voluntary and reflex control.
Corticospinal Pathway
- The corticospinal pathway (pyramidal system) enables voluntary control over skeletal muscles.
- Upper motor neurons in the motor cortex descend through the brain stem and spinal cord to synapse with lower motor neurons.
Motor Homunculus
- The motor homunculus depicts a map of the body's motor cortex, where specific areas control specific parts of the body.
- This map features precise localization of body parts to specific cortical regions.
Somatic Motor Commands (Summary)
- The somatic motor commands originate in the brain, brainstem, or thalamus, which involve various processing centers prior to sending signals.
- These commands influence voluntary movements but can also control subconscious activities for posture, movement, and muscle tonus.
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Description
Test your knowledge on the somatic sensory system, including the functions of various receptors and the roles of neurons and interneurons in response to stimuli. This quiz covers key concepts relevant to the understanding of somatic sensations and their processing in the nervous system.
