Somatic Afferent Pathway Lesions

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Questions and Answers

Which structure is responsible for transmitting sharp, acute, or prickling pain?

Thermal receptors

Fast pain fibers (correct)

Slow pain fibers

Mechanoreceptors

What is the function of the dorsal root ganglion?

To transmit thermal signals to the brain

To transmit pain signals to the brain (correct)

To transmit touch signals to the brain

To transmit pain signals from the sensory cortex

What is the term for the sense of touch?

General somatic afferents

Somatic sensation (correct)

Pain sensation

Thermal sensation

What is the purpose of using a needle or pinprick on the skin?

To elicit acute pain sensations Signup and view all the answers

Which structure is the final destination of pain signals from the periphery?

Sensory cortex Signup and view all the answers

What is the term for the sensation of warmth or coldness?

Thermal sensation Signup and view all the answers

What is the function of mechanoreceptors?

To detect touch Signup and view all the answers

What is the purpose of using unmarked glass bottles with warm or cold water?

To elicit thermal sensations Signup and view all the answers

What is the primary function of proprioception?

Detecting movement and position of body parts Signup and view all the answers

Which type of sensory innervation is found adjacent to the nuclear bag?

Annulospiral endings Signup and view all the answers

What is the primary function of the macula and crista ampullaris?

Detecting movement of fluid inside the cochlea Signup and view all the answers

What type of receptors are responsible for detecting specific chemicals in the taste buds?

Chemoreceptors Signup and view all the answers

What type of nerve fibers are responsible for transmitting warmth sensations?

Small unmyelinated nerve fibers Signup and view all the answers

What is the temperature range in which thermoreceptors are most sensitive?

Above 10°C and below 34°C Signup and view all the answers

Which type of receptors respond to extreme temperatures?

Thermoreceptors Signup and view all the answers

What type of endings are responsible for detecting cold temperatures?

Naked / free nerve endings of myelinated nerve fibers Signup and view all the answers

What type of nerve endings respond to different chemical stimuli and mediate the itch sensation?

Free nerve endings Signup and view all the answers

What is the function of type 1 glomus cells in the carotid and aortic bodies?

Respond to decreased PaO2 and increased PCO2 in the blood Signup and view all the answers

What is the primary function of photoreceptors?

Detecting electromagnetic radiation or light Signup and view all the answers

What is the effect of a wisp of cotton on the right or left eye?

Eye will close Signup and view all the answers

What is the term for the detection of muscle contractions and stretch?

General Somatic Afferents Signup and view all the answers

Which nerve carries the afferent signal in the direct corneal blink reflex pathway?

CN V1 (Ophthalmic) Signup and view all the answers

What is the function of nociceptors?

Respond to painful stimuli Signup and view all the answers

What is the effect of stimulating the motor nucleus of CN VII in the direct corneal blink reflex pathway?

Eye will close Signup and view all the answers

What type of receptor is responsible for the sensation of numbness in the face?

Free Nerve Ending Signup and view all the answers

Where is the spinal nucleus of CN V located?

R spinal nucleus of CN V Signup and view all the answers

What tract is responsible for transmitting pain and temperature sensations from the face?

Trigeminothalamic Tract Signup and view all the answers

What is the location of the VPM of Thalamus?

Just above the lip of the Sylvian fissure Signup and view all the answers

What is the diagnosis for V.J., a 60-year-old woman with numbness in her right face, arm, and leg?

Neuropathy Signup and view all the answers

What is the function of the dorsal horn?

Transmitting pain and temperature sensations Signup and view all the answers

What is the function of the ventral trigeminothalamic tract?

Transmitting pain and temperature sensations from the face Signup and view all the answers

What is the location of the lesion in V.J.'s case?

Left brainstem tegmentum Signup and view all the answers

What type of sensations are subserved by the anterior spinothalamic pathway?

Light or crude touch, itch, tickle, and sexual sensation Signup and view all the answers

Why is it that painful stimuli may activate both itch and pain sensory neurons, but only pain is perceived?

Because itch is inhibited by inhibitory interneurons in the spinal cord Signup and view all the answers

A lesion on which surface of the brain could lead to sensory deficits in the toes?

Medial cortical surface Signup and view all the answers

What type of receptors are responsible for proprioception?

Golgi tendon organs and neuromuscular spindles Signup and view all the answers

Is a direct corneal reflex thought to blink the opposite side of the stimulus?

No Signup and view all the answers

What is the function of the spinal nucleus of the trigeminal nerve?

To process sensory information from the face Signup and view all the answers

Which of the following is NOT a type of sensation mediated by the general somatic afferents?

Hunger Signup and view all the answers

What is the term for the sensory pathway that transmits information from the periphery to the brain?

General somatic afferents Signup and view all the answers

Which of the following structures is NOT involved in the processing of sensory information from the periphery?

Cerebellum Signup and view all the answers

What is the term for the phenomenon where itch is inhibited by inhibitory interneurons in the spinal cord?

Itch suppression Signup and view all the answers

Study Notes

Somatic Sensation Modalities and Receptors

Somatic sensation refers to the sense of touch and is composed of multiple modalities, each with its own specific stimulus and receptors.
Modalities of somatic sensory perception:
- Pain (transmitted by various fibers)
  - First pain: initial sharp, acute, or prickling pain, transmitted by "fast" fibers
  - Second pain: slow, dull/burning, aching, transmitted by "slow" fibers
- Thermal (sensation changes in temperature)
  - Warmth: increase in temperature
  - Cold: decrease in temperature
- Proprioception (sense of body part position and movement in space)
  - Unconscious: detecting muscle length and tendon force needed in coordinated movements
  - Conscious: body position

Anatomy of General Somatic Afferents

Detects position and movement of joints
Detects whether muscles are contracted or relaxed
Detecting muscle contractions and stretch
Provides information on static limb position (muscle length, rate of change of muscle length)
Types of sensory innervation:
- Annulospiral endings: found adjacent to nuclear bag (fast)
- Flower-Spray endings: found on the nuclear chain (slow)
Found in synovial joints

Receptors

Thermoreceptors: detect temperature changes (~2°C, especially above 10°C and below 34°C)
- Located at the dermis
- Warmth receptors: not yet identified, probably naked/free nerve endings
- Cold receptors: naked/free nerve endings of myelinated nerve fibers (Aδ fibers) branching into skin
Photoreceptors: detect electromagnetic radiation or light (e.g., rods and cones of the retina)
Chemoreceptors: detect specific chemicals
- Taste: taste buds (SVA)
- Olfaction: olfactory receptors (SVA) in olfactory epithelium
- Blood Gasses: carotid and aortic bodies that contain type 1 glomus cells
Itch receptors: free nerve endings on the epidermis that respond to different chemical stimuli

Nociceptors

Pain receptors that respond to different specific stimuli
Structure: free nerve endings
Categorized according to function and response to specific stimuli
Mediates either fast or slow pain
- Fast pain: mainly cutaneous, responds to high threshold stimuli
- Thermoreceptors: respond to extreme temperatures (>45°C or close to the ipsilateral eyelids)

Ascending Tracts and Pathways

Free nerve endings: contralateral ventral trigeminothalamic tract
Laterality: R location, Gasserian ganglion, R spinal nucleus of CN V, VPM of thalamus, L just above the lip of the Sylvian fissure (left side)

Case Study

V.J. is a 60 y.o. woman with numbness in her right face, arm, and leg
Neurologic examination revealed:
- ↓ pinprick, temperature, and light touch sensation over the right face, especially around the mouth
- Intact direct and consensual corneal reflex with cotton wisp on both corneas
- ↓ light touch, pinprick, temperature, and vibration sense on the right body, especially on the right hand and foot
- 2-point discrimination 15 mm on the tip of the right index finger vs. 4 mm on the tip of the left index finger (normal)
- No deficits in mental status, motor, and reflexes

Review Questions

1. [T/F] Lateral spinothalamic pathway subserves light or crude touch, itch, tickle, and sexual sensation: F
1. [T/F] Painful stimuli may activate both itch and pain sensory neurons, but only pain will be perceived because itch is inhibited by inhibitory interneurons in the spinal cord: T
1. A lesion on the medial cortical surface could lead to sensory deficits on which of the following structures: c. Toes
1. [T/F] Golgi tendon organs and neuromuscular spindles are receptors for proprioception: T
1. [T/F] A direct corneal reflex would blink the opposite side of the stimulus (contralateral): F

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Description

Identify the possible structures involved in the loss of pain sensation or pinprick sensation on the right toe. Test your knowledge of the anatomy of general somatic afferents and the pathway from receptors to the sensory cortex.