exam 2 : Touch and Pain

Somatosenses

Interoception: one’s own body ● Exteroception: external world

Types:Somatosenses

Cutaneous Senses: surface of body ● Nociception: noxious stimuli ● Proprioception: body parts in space

Some Stimuli

Pressure, vibration • Heating, cooling • Tissue damage

Skin • Protection + Thermoregulation

Epidermis, dermis, and subcutaneous tissue

Detecting and Transducing Cutaneous Stimulation Adaptation • Slowly-adapting

(tonic receptors): stimulus is present

Detecting and Transducing Cutaneous StimulationRapidly-adapting (phasic receptors):

change in stimulus

Small receptive fields:

easy discrimination

Large receptive fields:

difficult discrimination

Skin movement activates

mechanoreceptors

Mechanoreceptors • Merkel’s disks:

edges and points

MechanoreceptorsMeissner’s corpuscles:

: light touch, edge contours

Mechanoreceptors • Ruffini corpuscles:

static force, skin stretch

MechanoreceptorsPacinian corpuscles:

highfrequency vibrations, deep pressure

Thermoreceptors • Free nerve endings • 15 to 45 degrees C

Transient receptor potential channels

TRPV1 Receptors: warmth

TRPM8 Receptors: coolness

Pain

Nociceptors

Free nerve endings • Aδ and C fibers

Aδ: sharp, highly-localized pain • C: dull, throbbing pain

Often polymodal

Allodynia:

Touch-related stimuli cause pain

Hyperalgesia:

Abnormally heightened perception of pain

Chronic pain:

Pain with no pain-producing stimuli

Congenital Insensitivity to Pain:

Inability to feel pain

The Somatosensory Pathways: Head/Fac

CN V (Trigeminal nerve)→ pons → ventral posterior medial nucleus → S1

he Somatosensory Pathways

Dorsal ganglia → medulla → ventral posterior lateral nucleus → S1

Body information:Somatosensory

dorsal column-medial lemniscus

SomatosensoryPain/temperature:

spinothalamic tract

spinothalamic tract→

Dorsal root ganglia → ventral posterior lateral nucleus → S1 and other brain areas (e.g., in limbic system)

Somatosensory Cortex

• S1 • Somatotopic organization

Why Do We Experience Pain?

Health and safety • Bottom-up influences • Top-down influences

S1:

: SensoryPain

PainACC:

Immediate emotional consequences

PainPFC:

Long-term emotional implications

Phantom limb:

: pain that appears to originate in an amputated limb

Pathway modulating pain

Limbic system structures → periaqueductal grey → medulla

Reducing Pain • Placebo analgesia

Efficacy related to perceived value

Things that can lead to analgesia without exogenous opioids

Pleasant things • Distraction (for acute pain)