Somatosensory and Pain Pathways

Where are first-order sensory neurons?

Peripheral receptors in the dorsal root ganglion that detect the first stimulus and

Where are second order sensory neurons?

Soma in the spinal cord or brain stem

Where are third order sensory neurons?

Thalamus

What is primary somatosensory area?

Awareness of location on the body w/ high sensitivity and large cortical representation

The dorsal lemniscus columns are for?

Touch, pressure, vibrations, and proprioception

Ventral spinothalamic tracts are for?

Touch

Lateral spinothalamic tracts are for?

Pain and temp and chemical

The spinal cord contains _____ tracts of axons?

Ascending

2nd order neurons will ____ and ascend to the ____?

Decussate

thalamus

A-delta fibers transmit what?

Immediate sharp pain from mechanical damage and exterminator heat and cold

C-fibers will transmit what?

Dull burning pain, slow chronic thermal gradients - detects all kinds of pain

Spinothalamic pathways will decussate where?

At the level they enter

How does mechanical deformation result in pain?

Stretches or damage will open ion channels resulting in graded potentials

How does application of chemicals result in pain?

Opens ion channels in chemoreceptors

How do changes in temp result in pain?

Alters permeability of membrane in thermoreceptors

Explain the process of transduction?

Mechanical stimulus deforms receptor region resulting in GP which leads to AP, energy is converted to frequency coded AP which results in Neurotransmitters

A very high environmental stimulus means the receptor is _____ resulting in?

Deformed resulting in GP increasing to threshold resulting in an AP

Most sensory neurons are ____?

Specific to their stimulus

Phasic stimulation is _____?

Adaptive meaning once the stimulus is applied the receptors are less responsive to it

Tonic stimulation is ____?

Non-adabpitve - once stimulation is applied response doesn't stop until removed

Of the two skin receptors Meissner corpus is ____ and Merkel cells are _____?

Rapid (Tactile perception)

Slow (light touch pressure)

Of the two deep/ SQ receptors Pacinian corpuscle is _____ and Ruffini is ____?

Very rapid (Muscles)

Slow (joint capsules)

Most specialized receptors are controlled by receptors?

AB

Alpha delta fibers will have ___ axons but ____ ending?

C fibers will have ____?

Myelinated axons

Non-myelinated

Not myelinated

Pain will not occur where?

Brain no nerve endings

Free nerve endings w/ what will sense temperature extremes and chemicals?

Transiet receptor potential channels

Warm receptors will do what?

Increase AP on C fibers

Cold receptors will do what?

Increase AP on Alpha-delta w/ non-mylenated endings

Pain is a ___ stimulus?

Tonic

Tissue damage will cause ___?

Hyperalgesia (increased sensitivity to pain)

What molecules will lead to dull pain?

Prostaglandins

Bradykinins

Substance P - Increase blood flow to region via mast cells

What two things will result in C fibers enhancing pain?

Central sensitization - Repeated stim of dorsal horn neurons

Peripheral sensitization - Glutamate receptors are recruited making C fibers more sensitive

Substance P will affect the thalamus for proception of pain as well as the ____ and ____?

Somatosensory cortex - location

Reticular formation - awareness of pain

The hypothalamus limbic system is responsible for?

Behavioral response to pain

What are pain modulating systems of the CNS?

Endogenous opioid mechanism that block substance P in the spinal cord in periaqueductal gray matter of the midbrain

____ is a substance that will inhibit the release of substance P to alleviate pain?

Enkephalin

Substance P interacts w/ _____ receptors

Enkephalin interacts w/ ____ receptors

NK-1 receptors

U-opioid receptors

Where are u receptors located?

Dorsal horn of spinal cord

What will block u-opiod receptors as a competitive antagonist?

Naloxone

What naturally occurring hormone will suppress substance P and chronic pain?

Serotonin and NE

An epidural can block pain w/out?

Interfering w/ motor or sensory functions

How do NSAIDS block pain?

Block COX-2 resulting in no prostaglandins

What is a endocannabinoids?

Modulate pain and increase physical activity

Lamina 1 projects into the ___?

Thalamus

Lamina 2 is responsible for?

Inhibiting and exciting interneurons and modulating pain perception

Lamina V is responsible for?

Receiving nociceptive signals from skin and viscera leading to referred pain