Touch and Pain (The Somatosensory System) Flashcards
1
Q
What is the somatosensory system?
A
- Part of the nervous system.
- Responsible for processing sensory information e.g., touch, temp, and proprioception (awareness of movement).
1
Q
What are sensory receptors?
A
- Specialised structures that respond to stimulation e.g., light, chemical and thermal energy.
- Responsible for converting various forms of energy into electrical signals interpreted by the nervous system.
- Respond to stimulation.
2
Q
What happens in response to stimulation?
A
- Membrane potential of receptor cells changes
- **Receptor potentials are converted into action potentials in different actions. **
- Receptors can tell us about strength, location, and type/duration of stimulus.
3
Q
How is the sensory system organised?
A
1 - Association Sensory Cortex
2 - Secondary Sensory Cortex
3 - Primary Sensory Cortex
4 - Thalamus
5 - Receptors
*Complexity of analyses increases, neurons respond to stimuli of greater specificity and complexity.
4
Q
What is the Hypothalamus? Give an example of how it works.
A
-
Receives information and designates it to where it needs to go (sits at the top of the brain stem).
e.g. For a blue water bottle = photoreceptors in the eyes detect an object in front, but it is the visual cortex that puts information together to interpret and make sense of it is a blue water bottle.
5
Q
What are most sensory receptors in the somatosensory system known as?
A
= **Mechanoreceptors **
- Receptors that are sensitive to physical distortion e.g., bending or stretching.
- Respond to mechanical stimulation (touch, vibration, and pressure are detected by receptors.
6
Q
Dorsal horn function:
A
- Receives sensory input from the dorsal root and processes information before transmitting it to higher brain centres.
7
Q
Ventral horn function:
A
- Sends motor commands before transmitting them to glands, controlling voluntary and involuntary processes.
8
Q
Ventral root function:
A
- Transmits motor signals from the spinal cord to muscles, exiting from the ventral side and connecting to the ventral horn.
9
Q
Nerve Pathway Near Spinal Cord:
A
- Nerves split and attach to the dorsal and ventral cords as they approach the spinal cord.
10
Q
What are dermatomes?
A
- Area of skin that gets its sensation from a specific spinal nerve root.
- Sends signals for things like pressure, pain, and temp.
11
Q
What are Afferent nerves (sensory nerves)?
“A” for arriving…
A
- Carry signals from sensory receptors (like those in the skin or organs) towards the CNS.
- Transmit sensory information.
12
Q
What are efferent nerves (motor nerves)?
“E” for exiting…
A
- Carry signals away from CNS.
- Transmit motor commands from CNS to muscle, glands, and organs.
- Direct movements, actions, and physiological responses.
13
Q
What are primary afferent nerves (A - beta fibres)?
A
- First Nerve: Carries information from receptor to spinal cord.
- Function: Transports stimulation across sensory nerves toward the CNS via the dorsal horn.
- Touch vs. Pain: Information about touch reaches the brain faster than pain due to A beta fibers.
14
Q
What are the different types of Primary Afferent Nerves:
A
*differ due to the amount of myelination, and diameter:
More myelination = faster the conduction of the electrical impulse.
Wider the diameter = faster the conduction of the electrical impulse.
15
Q
Somatosensory - how does information reach the cortex?
A
- Stimulation on body: Detected by mechanoreceptors, which send information across primary afferent nerve (A-beta fibers) to the dorsal horn of the spinal cord.
- Ascent to medulla: The information ascends to the medulla as it enters the spinal cord.
- First afferent synapse: Occurs with a second neuron in the medulla.
- Crossover: The second neuron crosses over and ascends on the opposite side to reach the brain’s thalamus.
- Third neuron: Receives information and carries it to the primary somatosensory cortex.
- Cortex analysis: The cortex analyses and interprets the information.
16
Q
What are the 3 neurons involved in somatosensory?
A
- First order neuron = primary afferent nerve.
- Second-order neuron = first afferent neuron synapses with a second neuron in the Medulla.
- Third-order neuron = from the Thalamus to the Primary Somatosensory Cortex.
17
Q
What are primary afferent nerves?
A
- Information from the nociceptor that travels to the spinal cord via two types of axons:
18
Q
What are the 2 different primary afferent nerves?
A
A delta fibres (15-30 m/s) - short duration pricking pains.
**C fibres **(1-2m/s) - long lasting dull pain.
= difference in conduction speed can explain why pain sometimes feels like it has two different phases.
19
Q
What is the primary somatosensory cortex?
A
- First cortical structure within the somatosensory hierachy.
- Analyses sensory information.
- Lies on the postcentral gyrus, receving inputs from ventral posterior nucleus of thalamus.
20
Q
What did ‘Penfileld’ do?
A
- First used electical stimulation to map organisation of somatosensory cortex.
- Maps the body across brain area, with regions of the body not being uniformly represrted across brain region.
21
Q
Somatosensory cortex example…
e.g., The hands and lips….
A
- have large amount of surface area across somatosensory region, despire being smaller features.
- reflects importance for tactile perception, motor control, and communciation.
- Highlights brains ability to adapt to specific needs/demands of body parts.
22
Q
What is the assocation cortex?
A
- Helps us do complex things like talk, pay attention, control emotions, and move our bodies.
- Integrates different types of sensory information.
- Brain’s command centre for higher-level thinking/behaviour.
23
Q
What can damange to the association cortex result in?
A
- Neglect syndrome and asomatognosia (patients behave as if their body parts do not belong to them)
24
What is pain **(ISAP., 1994)**?
- Unpleasant snesory and emotional experience a**ssociated with actual/potetial tissue damage**.
25
What is congenital insensitivity to pain?
Individuals who cannot experience pain, even if in the most extreme conditions.
26
What can congenital insensitivity to pain lead to?
- No response to injury, and difficulty in differentiating between stimuli.
- Potential low life expectancy (due to the accumilation of injuries and health issues).
27
What are nocieptors/pain receptors?
- **Detect noxious/painful stimuli.**
- Free nerve endings located in most body tissues.
- Sensory receptors that respond to tissue damange e.g., extremes in temperatures.
28
How does descending pain control work?
- The periaqueductal gray (PAG) in the midbrain receives input from various brain regions, including the cortex and amygdala.
- **Has pain-suppressing effects and can block pain when electrically stimulated. **
- Frontal areas send signals to midbrain, which sends pain-relieving signals to spinal cord's dorsal horn, blocking pain signals to brian.
29
What happens when PAG is activated?
- Neurons travel down to the raphe nuclei in the medualla, sending pain-suppressing signals.
- **Meduallry neurons then go to the spinal cord's dorsal horn, reducing painful response. **
30
What is the pathway for touch and pain? What does it do?
**Anteriolateral pathway.**
- Nociceptors detect information and send it to the primary afferent nerves of pain.
31
How does information reach the cortex after primary afferent nerves of pain?
1. Nociceptors detect painful stimulus.
2. Information ascends the spinal cord via primary afferent nerve.
3. Enters spinal cord through dorsal horn.
4. As they enter, immediately synapse with second neuron at dorsal horn.
5. Second neuron crosses over and travels to Thalamus.
6. From Thalamus, the information is passed onto the Cortex through a third neuron.
32
How does information reach the cortex for pain?
- **Information synapses with second neuron at spinal cord,** which then crosses over the ascend to the Thalamus.
33
How does information reach the cortex for touch?
- Information synapses and crosses over at the Medulla.
- Touch information ascends ipsilaterally (same side) whereas pain information ascends contralaterally (opposite side) to the stimulus.
34
What is the pain pathway?
- Primary afferents carry pain signals from the body to the spinal cord.
- To the **ventral posterior thalamus.**
- Finally to the brain's somatosensory cortex - being known as the **anterolateral pathway** and is responsble for detecting and locating pain.
35
What happens in the pain pathway?
Here's the condensed information:
- **Pain signals**: Travel from the site of injury to the spinal cord via primary afferents.
- **Ascent**: Signals ascend opposite to the stimulus from the spinal cord.
- **Thalamus**: Reach the ventral posterior thalamus, a relay station in the brain.
- **Processing**: Finally, signals are sent to the somatosensory cortex, where the brain processes the pain sensation.
36
What is the difference between nociception vs pain?
Nocieption = injury or tissue damage which can lead to pain.
Pain = an unpleasant sensory and emotional experience assocaited with actual or potential pain.
= can experience pain without tissue damage/have tissue damage and not experience pain.
37
# Breecher., (1959)
What is an example study on central modulation (pain)?
- Depsite being severly wounded during action, American service personnel reported little to no pain from the injury.
- Concluded that the meaning behind the wounds inflicted mediated the painful responses.
38
What is peripheral pain modulation?
- Encompasses a variety of mechanims that regulate the transmission of pain signals at the level of the PNS.
- By modulating pain signals before they reach the CNS, peripheral pain modulation can effectively reduce pain perception and provide relief from discomfort.
39
# (Melzack and Wall., 1965)
What is the gate control theory?
| mechanism that enables peripheral pain modulation..
- Proposed there is a **hypothetical gate like mechanism located in the dorsal horn** of the spinal cord that influences pain.
- Both **touch and pain fibres enter spinal cord from dorsal horn.**
- The gate can also be influenced by central factors through desecnding pain pathway e.g., emotional/psychological state.
40
# Gate control theory
What happens when the gate opens?
- When the gate opens, there is an experience of pain.
- A Delta and C fibres = if these are active, this opens the gate, enabling pain signals to reach the brain.
41
# Gate control theory
What happens when the gate is closed?
- When the gate is closed, there is a suppression of pain.
- A beta fibres (larger touch fibres).
- If these are active, it shuts the hypothetical gate, inhibiting signals of pain to reach the brain.
42
What is the Substantia Gelitanosa?
- Specific region within the dorsal horn of the spinal cotd, processes touch to sensations.
- In the context of the somatosensory touch pathway, the substantia geltinosa serves as an important relay station for incoming sensory signals from the body to the CNS.
43
How does the Substantia Gelitanosa process pain?
1. Painful experience where nocicieptors detect it.
2. Information is sent along the a-delta, and c fibres.
3. Enter the spinal cord, and synapses to a second neuron.
4. This sends signals towards the brain.
44
What is the inhibitory interneuron?
- If it is active, it inhibits other structures.
- Touch is applied to the painful area, as the pain is experienced.
- Mechanoreceptor detect touch and sends signals across.
- a-beta fibres to the brain (synapses at the medulla).
45
What happens if you hurt yourself?
- Action potential is sent across a-delta, and c-fibre = inhibits the inhibitory interneuron.
- If inhibitory strucutre is active, it can no longer supress acitivity of second nueron which oepns the gate so pain reaches the cortex.
