NURS113 Lecture Notes - Lecture 5: Spinal Nerve, Cerebral Cortex, Third Order
14 Jun 2018
School
Department
Course
Professor
UNIT 3 - PAIN AND PNS
Michelle TA Availability:
Tuesday - 1630 - 1730
Wednesday - 1630 - 1730
Thursday - 1530 - 1630
- Every second Thursday starting February 1
PNS Nerve Terminology
- Afferent or sensory neurons
- Carries information to the CNS
- Efferent or motor neurons
- Carries information to effector organs
- Action potentials
- The movement of electrical charge along axon membrane carries information
Types of neurons
- First order neurons
- Transmits sensory information (pain, temperature and light touch) from the periphery to
CNS (spinal cord)
- Second order neurons
- Communicate from spinal cord and travel directly to the thalamus
- Third order neurons
- From thalamus to the cerebral cortex
- Thalamus → relay station that takes info from the spinal cord and decides where
it should go
Pain
- Something is wrong; a warning system → warning sign to your body that something is wrong
- Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue
injury
- Primarily a protective mechanism
- Tells you that something is going wrong or something IS going to go wrong
- Common definition → whatever the person says it is
- Subjective
- Pain is whatever the experiencing person says it is
- If someone says they are having pain, I have to believe them → even though they don’t
look like it, you still have to believe them because it’s something only THEY
THEMSELVES understand and feel
- Nociceptor
- Receptor at end of a sensory neuron’s axon that responds to tissue damage/injury by
sending information to the spinal cord and brain
- In fingers or toes stuff → sensory axons that responds to injury
- Periphery
- Nociceptor specialized receptor that SENDS messages of pain
Nociception
- Mechanism
- How does the brain label it and how do you perceive it as a painful stimuli and what does your
brain tell you to do → nociception
- 4 stages
- Transduction
- Damaged cells release neurotransmitter and generates an AP
- Transmission
- Movement of AP along
neurons from the
nociceptor to the spinal
cord and brain
- Perception
- Which part of your brain is
a part of that and how does
it get labelled and
determined → is the pain
something that you can
live with, comfortable, or
the worst pain in the world
- Brain receives pain signals
and recognizes and
responds to pain
- Modulation
- Activation of descending pathways that exert inhibitory effects on pain
transmission
- Tries to reduce the painful stimulus coming to the spinal cord
Two types of neurons for transmission
- AP from afferent pathway to the CNS via spinal cord
- nociceptor s have 2 different types of axons
- C fiber
- Higher threshold for pain
- 90%
- Small
- Unmyelinated (so it’s a slow pain)
- Slow in onset and longer duration
- Burning, aching and throbbing sensation
- Persistent heat and temperature transmitted up C fibers
- Sunburns
- Chemical burns
- A-delta fiber
- Lower threshold for pain
- 10%
- Large
- Myelinated (travels very quickly)
- Fast pain; fast onset and shorter duration (do not last long)
- Sharp, stabbing and acute pain
- Thermal or mechanical
- So if you put your hand on a stove it’s a fast pain and you modulate by
immediately taking your hand off that stove
Transmission
- Neurons enter the spinal cord through the dorsal horn, synapse with the interneurons and cross to
the anterolateral tract
- Nociceptors terminate in the spinal cord
- Anterolateral tract divides into
- Neospinothalamic tract carries the a-delta fibers info TO the thalamus
- Paleospinothalamic tract carries the c fibers info to the RAS in the brain stem →
thalamus
- From thalamus to
- Limbic cortex (emotional response)
- Are you annoyed, gonna cry, going to laugh because of this pain?
- Primary somesthetic cortex (location, intensity)
- So like where is it and how bad is the pain so how does it feel (sharp, really
intense)
