2022-04-05 14:25:23

Prelude 3:46

Prelude 2:49

Announcements

  • Papers or final blog post due Next Tuesday, April 12

Today’s Topics

  • More on somatosensation
  • Pain
  • Action!

Somatosensation

From skin to brain

  • Cutaneous receptors
  • Dorsal root ganglion
  • Ventral posterior lateral thalamus
  • Primary somatosensory cortex (S-I)
    • Post-central gyrus of parietal lobe

Dermatomes

Dermatomes

Functional segregation

Functional segregation

  • Separate pathways for different information types
  • Dorsal column/medial leminiscal pathway
    • Touch, proprioception
  • Spinothalamic tract
    • Pain, temperature

Somatatopic maps

Non-uniform mapping of skin surface

Non-uniform mapping of skin surface

Columnar organization/functional segregation

Phantom Limbs

What/where

  • Perceiving Where
    • Somatotopic maps – where on skin
    • Kinesthesia – configuration of limbs
  • Perceiving What
    • Patterns of smoothness, roughness, shape, temperature

Somatosensation in other animals

Pain

The neuroscience of pain

  • Nociceptors (Latin nocere to harm or hurt) detect harmful or potentially harmful stimuli of varied types:
    • chemical
    • mechanical
    • thermal

Nociception

  • External
    • Skin, cornea (eye), mucosa
  • Internal
    • Muscles, joints, bladder, gut

Different types of nociceptors…

  • metabolism (acidic pH, hypoxia, …)
  • cell rupture (ATP and glutamate)
  • cutaneous parasite penetration (histamine)
  • mast cell (white blood cell) activation (serotonin, bradykinin, …)
  • immune and hormonal activity (cytokines and somatostatin)

Fast (\(A\delta\)) and slow (\(C\)) transmission to CNS

Projection to brain via anterolateral system

Key CNS nodes in network

  • Periaqueductal grey (PAG) in midbrain
  • Insular cortex (insula)
  • Hypothalamus
  • Amygdala

Key CNS nodes in network

  • Thalamus
    • Ventroposterior lateral nucleus
    • Ventroposterior medial nucleus
    • Ventromedial nucleus

Pain in the brain

Pain in the brain

“…we used machine-learning analyses to identify a pattern of fMRI activity across brain regions — a neurologic signature — that was associated with heat-induced pain. The pattern included the thalamus, the posterior and anterior insulae, the secondary somatosensory cortex, the anterior cingulate cortex, the periaqueductal gray matter, and other areas…”

(Wager et al., 2013)

Pain relief

  • Prostaglandins
    • hormone-like effects, but released in many places
    • trigger vasodilation and inflammation

Pain relief

  • Paracetymol (acetaminophen)
    • Mechanism not fully understood
    • inhibits synthesis of prostaglandins via cyclooxygenase (COX) enzyme
    • may modulate endocannabinoid system
  • Nonsteroidal anti-inflamatory drugs (NSAIDs): aspirin, ibuprofen
    • Also inhibit prostaglandins via COX

Pain relief

  • Opioids
    • Activate endogenous opioid systems
    • multiple receptor types (\(\delta\), \(\kappa\), \(\mu\),…)
    • peripheral sensory neurons, amygdala, hypothalamus, PAG, spinal cord, cortex, medulla, pons,…
    • brainstem opioid neurons provide descending inhibition of nociceptors

Pain relief

  • Capsaicin
    • Binds to TrpV1/VR1 thermo/nociceptors
    • Eventually causes decrease in TrpV1 response
    • Alters how peripheral neuron responds to mechanical stimulation
    • (Borbiro, Badheka, & Rohacs, 2015)

Pain relief

  • Why rubbing can help

Gate control theory (Melzack & Wall, 1965)

Gate control theory (Melzack & Wall, 1965)

Psychological & physical components of pain

Main points

  • Somatosensation
    • Exteroception via
      • Cutaneous receptors + proprioception
    • Interoception via
      • Widely distributed receptors
      • Specific and non-specific

Main points

  • Pain
    • Multiple receptor channels
    • Highly interconnected CNS network
    • Multiple targets for modulation

Action

The neuroscience of action

  • What types of actions are there?
  • How are they produced?
    • By the muscles
    • By the nervous system

Remember

  • Nervous system “output” includes
    • Movements
    • Autonomic responses
    • Endocrine responses

Types of actions

  • Reflexes
    • Simple, highly stereotyped, unlearned, rapid
  • vs. Planned or voluntary actions
    • Complex, flexible, acquired, slower
  • Discrete (reaching) vs. rhythmic (walking)
  • Ballistic (no feedback) vs. controlled (feedback)

Multiple, parallel controllers

Key “nodes” in network

  • Primary motor cortex (M1)
  • Non-primary motor cortex
  • Basal ganglia
  • Brain stem
  • Cerebellum
  • Spinal cord

Muscle classes

  • Axial
    • Trunk, neck, hips
  • Proximal
    • Shoulder/elbow, pelvis/knee
  • Distal
    • Hands/fingers, feet/toes

Muscles

Muscle types

  • Smooth
    • Arteries, hair follicles, uterus, intestines
    • Regulated by ANS (involuntary)
  • Striated (striped)
    • Skeletal
    • Voluntary control, mostly connected to tendons and bones
  • Cardiac

Muscle types

How skeletal muscles contract

  • Motoneuron (ventral horn of spinal cord)
  • Neuromuscular junction
    • Releases ACh

From spinal cord to muscle

Next time…

  • More on action

References

Borbiro, I., Badheka, D., & Rohacs, T. (2015). Activation of TRPV1 channels inhibits mechanosensitive piezo channel activity by depleting membrane phosphoinositides. Sci. Signal., 8(363), ra15. https://doi.org/10.1126/scisignal.2005667

Craig, A. D. (2002). How do you feel? Interoception: The sense of the physiological condition of the body. Nat. Rev. Neurosci., 3(8), 655–666. https://doi.org/10.1038/nrn894

Melzack, R., & Wall, P. D. (1965). Pain mechanisms: A new theory. Science, 150(3699), 971–979. https://doi.org/10.1126/science.150.3699.971

Papini, M. R., Fuchs, P. N., & Torres, C. (2015). Behavioral neuroscience of psychological pain. Neurosci. Biobehav. Rev., 48, 53–69. https://doi.org/10.1016/j.neubiorev.2014.11.012

Wager, T. D., Atlas, L. Y., Lindquist, M. A., Roy, M., Woo, C.-W., & Kross, E. (2013). An fMRI-based neurologic signature of physical pain. N. Engl. J. Med., 368(15), 1388–1397. https://doi.org/10.1056/NEJMoa1204471