NEU_LEC_11
SOMATOSENSORY SYSTEM AND PAIN
1. Review of Somatosensory System
The somatosensory system processes sensory information, notably pain, crucial for survival.
3. Review of Touch
3.1 Receptor Cells and Touch Sensation
Receptor cells respond to various energy stimuli, converting them to electrical signals for the nervous system.
The sensation of touch is transmitted via the Dorsal Column Pathway from peripheral receptors to the primary somatosensory cortex.
3.2 Types of Receptor Cells in Skin
Free Nerve Endings: Epidermis (detects pain and temperature)
Merkel's Discs: Dermis (detects light touch and object feeling)
Meissner's Corpuscles: Found in the hypodermis (detects touch)
Pacinian Corpuscles: Detect vibration and pressure
Ruffini Corpuscles: stretch
4. Pacinian Corpuscle and Vibration Detection
4.1 Structure and Function
The Pacinian Corpuscle consists of a connective tissue capsule with fluid-filled lamellae.
Responsible for detecting vibrations over 200 Hz and transforming them into action potentials through the stretching of the nerve membrane.
4.2 Mechanism of Vibration Detection
Vibrations cause membrane stretching, opening Na+ channels, resulting in a graded receptor potential.
If the potential exceeds a threshold, an action potential is generated, traveling through sensory nerves to the spinal cord and brain.
5. Ascending Pathways for Touch Sensation
5.1 Dorsal Column Pathway
Sensory information ascends from the periphery through the spinal cord to the primary somatosensory cortex via the Dorsal Column Pathway.
Key brain areas involved: medulla, thalamus, and primary somatosensory cortex (S1).
5.2 Body Representation in the S1 Region
The primary somatosensory cortex organizes sensory information from various body parts, represented in a somatotopic manner (homunculus).
More sensitive areas (e.g., hands, lips) occupy larger cortex areas than less sensitive regions (e.g., trunk).
6. Pain Sensation
6.1 Definition and Importance
Pain is an unpleasant sensory and emotional experience linked to tissue damage.
Acts as a protective mechanism prompting responses to minimize bodily risk and communicate distress.
6.2 Pain Receptors (Nociceptors)
Nociceptors detect thermal, mechanical, and chemical stimuli associated with pain; located in both superficial and deep tissues.
Notable absence of pain receptors in the brain allows for painless surgical procedures.
They are located in the skin, cornea, joints, muscles, and internal organs.
No pain receptors are in the brain.
6.3 Types of Nerve Fibers
A Fibers: Myelinated, transmit pain signals rapidly.
C Fibers: Unmyelinated, transmit signals slowly, associated with persistent dull pain.
7. Types of Nociceptors
Vanilloid Receptor 1: Activated by high temperatures and recognizes pain from burning sensations.
They are located on C fibers.
TRPM3 Receptors: Detects higher temperatures and initial sharp pain.
They are located on A fibers.
8. Pathways and Transmission of Pain
8.1 Pain Perception Mechanism
Tissue injury leads to the release of neurochemicals (Substance P, serotonin, and histamine) that stimulate nociceptors and cause inflammation.
Pain information travels to the brain through the spinothalamic pathway, involving several neural structures.
8.2 Spinothalamic Pathway Explanation
The pathway crosses in the spinal cord and ascends to various brain regions including the thalamus and cingulate cortex, addressing pain processing in the body.
Specifically the pathway goes from the receptors, to crossing over in the spinal cord, to the medulla, to the pons, through the mid brain (periaqueductal gray), through the thalamus, into the primary cortex.
9. Types of Pain
Short-term Pain: Immediate withdrawal reflex to prevent tissue damage.
Chronic Pain: Persists for over three months, may affect daily life (e.g., arthritis).
Neuropathic Pain: Pain sensation post-injury healing (e.g., phantom limb pain).
9.1 Phantom Limb Pain
A phenomenon where individuals feel pain in a limb that is no longer present, often requires targeted interventions.
9.2 Congenital Insensitivity to Pain (CIP)
A rare condition causing individuals to not feel pain due to mutations of gene SCN9A leading to an absence of sodium channels on nociceptors so pain information is not transmitted to the brain; increases risk of severe injuries.
10. Pain Management Techniques
Analgesic Drugs: Morphine and other opiates reduce pain by mimicking endogenous opioids.
Morphine is a powerful analgesic drug.
It mimics the body's endogenous opioids to relieve pain.
It primarily binds to mu opioid receptors in the brain and spinal cord.
This binding inhibits pain transmission and can produce feelings of euphoria.
While effective for pain management, prolonged use can lead to:
Tolerance
Dependence
Potential for addiction.
Electrical Stimulation: Can alleviate pain symptoms.
Placebos: Can induce pain relief through psychological mechanisms.
Acupuncture: Alternative method potentially effective in pain reduction.
Endogenous Opioids
Definition: Natural pain-relieving substances produced by the body, crucial for pain modulation and pleasure.
Types
Endorphins: Pain relief and happiness, released during exercise and stress.
Enkephalins: Peptides that regulate pain and mood in the brain and spinal cord.
Dynorphins: Affect mood and are involved in stress and pain response.
Mechanism
Bind to mu, delta, and kappa opioid receptors, inhibiting pain transmission and inducing euphoria.
Triggers
Released by physical activity, stress, or emotional responses like laughter.
Clinical Significance
Understanding them aids in developing pain management treatments and alternatives to synthetic opioids.
10.1 Tolerance and Dependence on Analgesics
Prolonged use of analgesics can lead to tolerance (increased dosage needed for pain relief) and dependence, escalating the risk of addiction and overdose.
10.2 Naloxone as an Opioid Antagonist
Naloxone (Narcan) is an opioid antagonist used to reverse opioid overdose by preventing binding at mu receptors, crucial for emergency responses.
Endogenous opioids are natural pain-relieving substances produced by the body, essential for pain modulation and promoting feelings of pleasure. Key points include:
Types:
Endorphins: Linked to pain relief and happiness; released during exercise and stress.
Enkephalins: Short peptides in the brain and spinal cord that regulate pain and mood.
Dynorphins: Involved in stress and pain response, affecting mood.
Mechanism: They bind to mu, delta, and kappa opioid receptors in the nervous system, inhibiting pain transmission and inducing euphoria.
Triggers: Released by physical activity, stress, or emotional responses like laughter.
Clinical Significance: Understanding endogenous opioids aids in developing pain management treatments and alternatives to synthetic opioids, reducing addiction risk.
NEU_LEC_11
SOMATOSENSORY SYSTEM AND PAIN
1. Review of Somatosensory System
The somatosensory system processes sensory information, notably pain, crucial for survival.
3. Review of Touch
3.1 Receptor Cells and Touch Sensation
Receptor cells respond to various energy stimuli, converting them to electrical signals for the nervous system.
The sensation of touch is transmitted via the Dorsal Column Pathway from peripheral receptors to the primary somatosensory cortex.
3.2 Types of Receptor Cells in Skin
Free Nerve Endings: Epidermis (detects pain and temperature)
Merkel's Discs: Dermis (detects light touch and object feeling)
Meissner's Corpuscles: Found in the hypodermis (detects touch)
Pacinian Corpuscles: Detect vibration and pressure
Ruffini Corpuscles: stretch
4. Pacinian Corpuscle and Vibration Detection
4.1 Structure and Function
The Pacinian Corpuscle consists of a connective tissue capsule with fluid-filled lamellae.
Responsible for detecting vibrations over 200 Hz and transforming them into action potentials through the stretching of the nerve membrane.
4.2 Mechanism of Vibration Detection
Vibrations cause membrane stretching, opening Na+ channels, resulting in a graded receptor potential.
If the potential exceeds a threshold, an action potential is generated, traveling through sensory nerves to the spinal cord and brain.
5. Ascending Pathways for Touch Sensation
5.1 Dorsal Column Pathway
Sensory information ascends from the periphery through the spinal cord to the primary somatosensory cortex via the Dorsal Column Pathway.
Key brain areas involved: medulla, thalamus, and primary somatosensory cortex (S1).
5.2 Body Representation in the S1 Region
The primary somatosensory cortex organizes sensory information from various body parts, represented in a somatotopic manner (homunculus).
More sensitive areas (e.g., hands, lips) occupy larger cortex areas than less sensitive regions (e.g., trunk).
6. Pain Sensation
6.1 Definition and Importance
Pain is an unpleasant sensory and emotional experience linked to tissue damage.
Acts as a protective mechanism prompting responses to minimize bodily risk and communicate distress.
6.2 Pain Receptors (Nociceptors)
Nociceptors detect thermal, mechanical, and chemical stimuli associated with pain; located in both superficial and deep tissues.
Notable absence of pain receptors in the brain allows for painless surgical procedures.
They are located in the skin, cornea, joints, muscles, and internal organs.
No pain receptors are in the brain.
6.3 Types of Nerve Fibers
A Fibers: Myelinated, transmit pain signals rapidly.
C Fibers: Unmyelinated, transmit signals slowly, associated with persistent dull pain.
7. Types of Nociceptors
Vanilloid Receptor 1: Activated by high temperatures and recognizes pain from burning sensations.
They are located on C fibers.
TRPM3 Receptors: Detects higher temperatures and initial sharp pain.
They are located on A fibers.
8. Pathways and Transmission of Pain
8.1 Pain Perception Mechanism
Tissue injury leads to the release of neurochemicals (Substance P, serotonin, and histamine) that stimulate nociceptors and cause inflammation.
Pain information travels to the brain through the spinothalamic pathway, involving several neural structures.
8.2 Spinothalamic Pathway Explanation
The pathway crosses in the spinal cord and ascends to various brain regions including the thalamus and cingulate cortex, addressing pain processing in the body.
Specifically the pathway goes from the receptors, to crossing over in the spinal cord, to the medulla, to the pons, through the mid brain (periaqueductal gray), through the thalamus, into the primary cortex.
9. Types of Pain
Short-term Pain: Immediate withdrawal reflex to prevent tissue damage.
Chronic Pain: Persists for over three months, may affect daily life (e.g., arthritis).
Neuropathic Pain: Pain sensation post-injury healing (e.g., phantom limb pain).
9.1 Phantom Limb Pain
A phenomenon where individuals feel pain in a limb that is no longer present, often requires targeted interventions.
9.2 Congenital Insensitivity to Pain (CIP)
A rare condition causing individuals to not feel pain due to mutations of gene SCN9A leading to an absence of sodium channels on nociceptors so pain information is not transmitted to the brain; increases risk of severe injuries.
10. Pain Management Techniques
Analgesic Drugs: Morphine and other opiates reduce pain by mimicking endogenous opioids.
Morphine is a powerful analgesic drug.
It mimics the body's endogenous opioids to relieve pain.
It primarily binds to mu opioid receptors in the brain and spinal cord.
This binding inhibits pain transmission and can produce feelings of euphoria.
While effective for pain management, prolonged use can lead to:
Tolerance
Dependence
Potential for addiction.
Electrical Stimulation: Can alleviate pain symptoms.
Placebos: Can induce pain relief through psychological mechanisms.
Acupuncture: Alternative method potentially effective in pain reduction.
Endogenous Opioids
Definition: Natural pain-relieving substances produced by the body, crucial for pain modulation and pleasure.
Types
Endorphins: Pain relief and happiness, released during exercise and stress.
Enkephalins: Peptides that regulate pain and mood in the brain and spinal cord.
Dynorphins: Affect mood and are involved in stress and pain response.
Mechanism
Bind to mu, delta, and kappa opioid receptors, inhibiting pain transmission and inducing euphoria.
Triggers
Released by physical activity, stress, or emotional responses like laughter.
Clinical Significance
Understanding them aids in developing pain management treatments and alternatives to synthetic opioids.
10.1 Tolerance and Dependence on Analgesics
Prolonged use of analgesics can lead to tolerance (increased dosage needed for pain relief) and dependence, escalating the risk of addiction and overdose.
10.2 Naloxone as an Opioid Antagonist
Naloxone (Narcan) is an opioid antagonist used to reverse opioid overdose by preventing binding at mu receptors, crucial for emergency responses.
Endogenous opioids are natural pain-relieving substances produced by the body, essential for pain modulation and promoting feelings of pleasure. Key points include:
Types:
Endorphins: Linked to pain relief and happiness; released during exercise and stress.
Enkephalins: Short peptides in the brain and spinal cord that regulate pain and mood.
Dynorphins: Involved in stress and pain response, affecting mood.
Mechanism: They bind to mu, delta, and kappa opioid receptors in the nervous system, inhibiting pain transmission and inducing euphoria.
Triggers: Released by physical activity, stress, or emotional responses like laughter.
Clinical Significance: Understanding endogenous opioids aids in developing pain management treatments and alternatives to synthetic opioids, reducing addiction risk.
