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Questions and Answers
What is ataxia?
What is the name of the sensation that depends on intact touch and pressure sensation?
At what temperature range is the peak stimulation of cold fiber?
What type of receptor is responsible for pain sensation?
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What is the minimum distance required for two touch stimuli to be perceived as separate?
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Which part of the brain is responsible for temperature sensation?
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Which pathway is responsible for transmitting pain sensations?
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Which receptors are responsible for detecting vibration sensations?
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What is the function of the Cerebellum in relation to somatosensory sensations?
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Which of the following best describes the function of the Fasciculus Cuneatus?
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What is the name of the 'map' of the body in the cerebral cortex?
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Which type of fibers are responsible for transmitting touch and pressure sensations?
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Where are the cell bodies of the Primary Afferent Neurons located?
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What type of fibers are associated with sensations of temperature, pain, and light touch?
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Where do the 2nd Order Neurons receive information from?
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What is the function of the Ventral Roots of Spinal Cord Ganglia?
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What is the name of the pathway that carries signals from the Dorsal Horn to the Brainstem to the Thalamus and finally to the Somatosensory Areas?
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What is the name of the fibers that are organized in a way that the ones in the medial part of the dorsal column are called the Fasciculus Cuneatus?
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What type of pain is typically felt in the skin and is elicited by mechanical and thermal stimuli?
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What occurs when nerve endings are injured, leading to an increase in sensitivity of pain receptors?
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What condition is caused by demyelination of sensory neurons secondary to an untreated syphilis infection?
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What type of fibers transmit Physiologic Pain?
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What is characterized by a loss of ability for extreme hot and cold sensations and a loss of pain and temperature sensations in the back and arms?
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What is an example of a condition where pain is felt considerably away from the structure causing the pain?
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What is the function of enkephalins in the CNS?
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Which pathway is responsible for transmitting temperature sensations?
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What is the result of an injury to the Thalamic Nuclei?
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What is the term for the inability to recognize complex objects/forms by feeling them on the opposite side of the body?
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What is the result of a spinal cord transection?
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What is the term for the diminished tactile sensations?
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Study Notes
Ataxia
- Ataxia is a degenerative disease of the nervous system, characterized by symptoms similar to being drunk, such as slurred speech, stumbling, falling, and incoordination.
Types of Fibers
- Type Aβ: associated with mechanoreceptors, responsible for touch and pressure sensation
- Type Aδ: associated with thermoceptors, responsible for cold and pain sensation
- Type C: associated with free nerve endings, responsible for pain and temperature sensation
Somatosensory System
- The ability to identify objects by handling them without looking at them depends on intact touch and pressure sensation
- Thermoceptive sensation:
- Freezing cold: <15°C
- Cold: 15-20°C
- Cool: 20-30°C
- Indifferent (warm or cold): 30-38°C
- Warm: 38-43°C
- Hot: 43-47°C
- Burning hot: 47-59°C
- Thermoreceptors:
- Cold receptors: stimulated by cold temperatures
- Warm receptors: stimulated by warm temperatures
- Nociceptors:
- Pain receptors: located immediately under the skin
- Free nerve endings of Type Aδ and some Type C: stimulated by extreme degrees of temperature
- Vibratory sensation:
- Depends on the combination of cutaneous and separate neural pathways
- Pattern of stimulation and cortical components are synthesized
- Two-Point Discrimination:
- Ability to perceive two touch stimuli as two separate sensations at a minimum distance
- Minimal distance by which two touch stimuli must be separated to be perceived as separate is called the "Two-Point Threshold"
- Stereognosis:
- Ability to recognize objects by touch
Insular Cortex and Fasciculus
- The Insular Cortex is responsible for temperature sensation
- Fasciculus Cuneatus: receives signals from the upper extremities
- Fasciculus Gracilis: receives signals from the lower extremities
Somatosensory Areas
- Primary Somatosensory Area (Brodmann Area 3, 1, and 2): responsible for processing sensory information
- Accessory Somatosensory Area (Brodmann Area 5 and 7): responsible for processing sensory information
- The "map" of the body is called the Sensory Homunculus, with the largest areas representing the face, hands, and fingers
Dorsal Column or Lemniscal Pathway
- Fine touch and pressure sensation
- Vibratory sensation
- Position sensation
- Spinothalamic or Anterolateral Tract: responsible for pain and temperature sensation
Pain Sensation
- Epicritic pain: sharp, pricking pain, easily localized
- Protopathic pain: poorly localized, unpleasant, and associated with nausea and autonomic symptoms
- Hyperalgesia: increased sensitivity of pain receptors
- Allodynia: when normally innocuous stimuli cause pain
- Excruciating pain: difficult to treat, often radiates or referred to other areas
Sensory Pathways
- The signals travel from the receptors to the Somatosensory Areas 1 and 2 along the pathways
- 1st Order Neurons: primary afferent neurons that receive the transduced signal and send the information to the CNS
- 2nd Order Neurons: located in the Spinal Cord or Brainstem, receive information from one or more primary afferent neurons and transmit it to the Thalamus
- 3rd Order Neurons: located in the relay nuclei of the Thalamus, encoded sensory information ascends to the Cerebral Cortex
- Higher Order Neurons: located in the appropriate sensory area of the Cerebral Cortex, result in a conscious perception of the stimulus
Injuries and Abnormalities
- Ataxia: manifestation of Cerebellum dysfunction
- Brown-Sequard Syndrome: half of the Spinal Cord is transected, manifestations include ipsilateral paralysis, loss of proprioceptive/vibration sensation, and contralateral loss of pain/thermal sensations
- Syringomyelia: loss of ability for extreme hot and cold sensations, loss of pain and temperature sensations in the back and arms
- Tabes Dorsalis: caused by demyelination of sensory neurons secondary to an untreated syphilis infection, degenerating nerves are in the Dorsal Columns of the Spinal Cord
- Paresthesia: shooting/burning pains, pricking sensations
- Hypoesthesia: diminished tactile sensations
- Glossodynia: burning or tingling sensation of the lips, mouth, and tongue
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Description
Explore the journey of sensory signals from receptors to the Somatosensory Areas 1 and 2, including the role of 1st and 2nd Order Neurons. Learn about the primary afferent neurons, dorsal root, and spinal cord ganglia. Test your knowledge of the human sensory system!
