Somatosensory System Flashcards
What is the first step in mechanotransduction?
Learning Objective 1: Explain how a physical or chemical stimulus causes excitation of primary afferent fibers.
The first step is the deformation of the sensory receptor membrane, which opens ion channels and generates a receptor potential.
How does a receptor potential lead to action potential generation?
Learning Objective 1: Explain how a physical or chemical stimulus causes excitation of primary afferent fibers.
If the receptor potential exceeds the threshold, voltage-gated sodium channels open, initiating an action potential that propagates along the afferent fiber.
What types of stimuli can activate primary afferent fibers?
Learning Objective 1: Explain how a physical or chemical stimulus causes excitation of primary afferent fibers.
Physical stimuli like touch, pressure, vibration, and stretch, or chemical stimuli such as inflammatory mediators.
What are the key properties of primary afferent neurons?
Learning Objective 2: Describe the sensory receptive properties of primary afferent neurons.
Modality, threshold, adaptation, conduction velocity, and receptive field size.
Define the term “modality” in relation to afferent fibers.
Learning Objective 2: Describe the sensory receptive properties of primary afferent neurons.
Modality refers to the type of stimulus a receptor is sensitive to, such as touch, pain, or temperature.
How does adaptation affect the response of mechanoreceptors?
Learning Objective 2: Describe the sensory receptive properties of primary afferent neurons.
Adaptation refers to how quickly a receptor stops responding to a constant stimulus. Rapidly adapting receptors respond to changes, while slowly adapting receptors provide continuous information.
Name the main types of mechanoreceptors in the skin.
Learning Objective 3: Give examples of mechanoreceptors in the skin, their adequate stimuli, and functions.
Merkel discs, Meissner’s corpuscles, Pacinian corpuscles, and Ruffini endings.
What type of stimulus do Pacinian corpuscles respond to?
Learning Objective 3: Give examples of mechanoreceptors in the skin, their adequate stimuli, and functions.
Pacinian corpuscles detect vibration and deep pressure with rapid adaptation.
Which mechanoreceptor is responsible for detecting light touch and pressure?
Learning Objective 3: Give examples of mechanoreceptors in the skin, their adequate stimuli, and functions.
Merkel discs, which respond to sustained pressure and fine touch.
What is a dermatome?
Learning Objective 4: Describe the segmental organization of sensory input to the spinal cord and body surface dermatomes.
A dermatome is an area of skin innervated by a single spinal nerve.
How is sensory input organized in the spinal cord?
Learning Objective 4: Describe the segmental organization of sensory input to the spinal cord and body surface dermatomes.
Sensory information enters the spinal cord through dorsal roots and is organized segmentally, with each spinal level corresponding to a specific body region.
Which laminae of the spinal cord are associated with pain and temperature?
Learning Objective 5: Know the laminae of the grey matter that contain terminals of specific primary afferents.
Laminae I and II (the substantia gelatinosa) process nociceptive and thermal information.
Where do large, myelinated fibers terminate in the spinal cord?
Learning Objective 5: Know the laminae of the grey matter that contain terminals of specific primary afferents.
Large fibers (Aβ) terminate in laminae III-V, which process mechanosensory input.
Where does decussation occur in the dorsal column medial lemniscal (DCML) pathway?
Learning Objective 6: Describe the anatomy of the DCML and STT tracts and their clinical relevance.
The DCML pathway decussates at the medulla.
Where does decussation occur in the spinothalamic tract (STT)?
Learning Objective 6: Describe the anatomy of the DCML and STT tracts and their clinical relevance.
The STT decussates immediately at the spinal cord level where it enters.
What sensory modalities do the DCML and STT convey?
Learning Objective 6: Describe the anatomy of the DCML and STT tracts and their clinical relevance.
DCML transmits touch, vibration, and proprioception, while STT transmits pain and temperature.
What is lateral inhibition, and how does it enhance sensory information?
Learning Objective 7: Describe sensory information modification during ascent to the somatosensory cortex.
Lateral inhibition sharpens contrast between stimuli by inhibiting neighboring neurons, enhancing signal precision.
Where is the primary somatosensory cortex located?
Learning Objective 8: State the location and subdivisions of the somatosensory cortex.
It is located in the postcentral gyrus of the parietal lobe.
Where is the primary somatosensory cortex located?
Learning Objective 8: State the location and subdivisions of the somatosensory cortex.
It is located in the postcentral gyrus of the parietal lobe.
What is the somatotopic organization of the somatosensory cortex?
Learning Objective 9: Appreciate the cortical representation of the body surface in the ‘homunculus.’
The homunculus represents the body surface map, with larger areas devoted to regions with finer tactile discrimination (e.g., hands, face).
How does the parietal cortex contribute to somatosensory perception?
Learning Objective 10: Explain the integrative function of the parietal cortex in somatosensory perception.
It integrates multisensory information, contributing to spatial awareness and object recognition.
What are the effects of parietal cortex damage?
Learning Objective 10: Explain the integrative function of the parietal cortex in somatosensory perception.
Damage may lead to deficits such as neglect syndrome, inability to recognize objects by touch (astereognosis), and impaired spatial processing.
