BioPsy: Finals L2.5 - Somatosensation

Somatosensation

Refers to the senses of the body. Includes various types of senses.

Somatic Senses

• Position Sense

• Vibration Sense

• Touch

• Pain

• Temperature

Somatosensory Receptors

Are specialized sensory nerves that respond to various stimuli, including vision, hearing, taste, and smell, as well as general somatic senses which make up the somatosensory system, which is involved in the sense of touch, proprioception, pain, and temperature. [Taken from Google]

Mechanoreceptors

• Responds to physical forces.

• Responds to physical stimuli.

  • Position

  • Vibration

  • Touch

• Deep within our skin, they are concerned with body position.

• Helpful in detecting vibrations in our body.

Nociceptors

• Somatosensory Receptors that creates ‘pain’.

Thermoreceptors

Somatosensory Receptors responsive to temperature.

Skin

Specifically where the somatosensory receptors are located.

Large Diameter Axon and Thick Myelin Sheaths

The Somatosensory axons that are responsible for Position, Vibration, and some form of touch usually has:

1. ______________

2. ______________

Small Diameter Axon and Thin or No Myelin Sheaths (Unmyelinated Axons)

The Somatosensory axons that are responsible for Pain and Temperature, usually has:

1. ______________

2. ______________

The speed of action potential equal to Axons & Myelin Sheaths

1. The thicker the axons & myelin sheath, the faster the conduction of action potential.

2. The thinner they are, the slower the conduction of action potential.

Fine touch sense

Tends to travel to fast somatosensory neurons

Gross touch sense

Tends to travel in slow somatosensory neurons

Pain

• Begins with specialized receptor, a bare nerve ending. Because of the axons carrying pain information have little to no myelin sheaths, they conduct impulses relatively slowly.

• 2 - 20 m/s

Sharp Pain

• Conveyed by thicker axons.

• Released a neurotransmitter called glutamate and also releases certain typed of neuropeptides.

  • Substance P

  • CGRP

Calicitonin Gene Relatide Peptide (CGRP)

One of the transmitters released during sharp pains.

Duller Pain

• Conveyed by thinner axons.

• Released a neurotransmitter called glutamate.

Paths of the pain sensitive cells

Pain sensitive cells in our spinal cord that relay information to several sites in the brain.

• Ventral Posterior Nucleus

• Somatosensory Cortex

Spinal Path: Pain

Crosses immediately from the receptors on one side of the body to attract ascending contralateral side of the spinal cord.

Spinal Path: Touch

• Ipsilateral side of the spinal cord to the Medula

• Crosses the contralateral side.

Emotional Pain

Painful stimuli also opens a pathway to the:

Medula > Thalamus > Amygdala > Hippocampus > Prefrontal Cortex > Anterior Cingulate Cortex

These areas not react to the sensation, but rather the emotional aspect.

(e.g., Seeing someone you love experience pain, you experience a sympathetic pain)

Hypnosis

• Some people are suggestive to _______, this is because of a decrease of response cingulate cortex without much effect to our somatosensory cortex.

Cingulate Gyrus

People with damage to this part of the brain still feels pain, but does not distresses them.

Hurt feelings

Resembles physical pain is some regards. It shows up as activity in both the emotional areas, especially in the Cingulate Cortex and the sensory areas responsive to physical pain.

Tickle

• When you touch yourself, your brain compares the resulting stimulation to the expected stimulation and generates a weaker somatosensory response than you would experience from an unexpected touch.

• The sense of anticipation prepares the brain for the tickle.

Itch

Happens when:

1. Mild tissue damage is present (e.g., when your skin is healing from a cut). The body releases histamines and is not reduced by using Capsaicin.

2. Contact from certain plants (Cowhage) and is not reduced by taking antihistamines.

The receptors are slow to respond and when they do, the axons transmit impulses at an usually slow velocity of only ½ m/s or 3-4 seconds from foot to brain.

Histamines

It dilates blood vessels and produces an itching sensation. Can be reduced by using antihistamines

Cowhage

Tropical plants with barbed hair. Can be reduced by using Capsaicin.

Vigorous scratching

Inhibits itch due to mild pain as it relieves itch.