The Somatosensory System

The Basics: What does it do?

1. (sensations)

2.

3.

The Somatosensory System

1. Tells us what the body is up to and whats going on in the enviornment by providing bodily sensations such as Touch, Temperature, Pain, Position in Space, and Movement of the Joints

 2. Allows us to distinguish between what the world does to us and what we do to it

3. It has a closer relationship with movement than the other senses do

Humans have two types of skin:

1.

2.

1. Hairy Skin

2. Glabrous Skin (smooth sensitive skin)

-contains large numbers of sensory receptors

Three Main Types of Somatosensory Perception

1. ____________- Perception of fine touch and pressure

2. ___________- Perception of the location and movement of the body

3. _______________- Perception of pain and tempurature

Three Main Types of Somatosensory Perception

1. Hapsis (ability to identify objects by touch)

Perception of _______________

2. Proprioception

Perception of ______________

3. Nociception

Perception of ______________

Dorsal Root Ganglion Neuron

- The dendrite and axon...

- The tip of the dendrite....

-Relation to the each spinal cord segment

- Relation to spinal cord on the whole

Dorsal Root Ganglion Neuron

- The dendrite and axon are contifuous and carry sensory information from the skin to the central nervous system.

- The tip of the dendrite is responsive to sensory stimulation

-Each spinal cord segment has one dorsal-root ganglion on each side that contains many dorsal root ganglion neurons

- In the spinal cord, the axons of these neurons may synapse onto other neurons or continue up to the brain 

Dorsal-Root Ganglion Neurons

1. __________________

-Large, well-myelinated axons (fast)

2. ________________

-Small axons with little or no myelination (slow)

3. ________________

Loss of incoming sensory input usually due to the damage to sensory fibers; also loss of any afferent input to a structure

Dorsal-Root Ganglion Neurons

1. Proprioceptive and Haptic Neurons 

- Definition

2. Nociceptive Neurons (Pain)

- Definition

3. Deafferentation

 -Definition

Somatosensory Pathways to the Brain

Dorsal Spinothalamix Tract

-Carries...

-How does the synapse occur?

-Explain crossover...

-

Somatosensory Pathways to the Brain

____________________

-Carries haptic and proprioceptive information

-Axons from the Dorsal Root Ganglion Neurons enter the spinal cord and ascend ipsilaterally until they synapse in the dorsal column nuclei

-Axons from the dorsal column nuclei cross over to the opposite side of the brain and project up through the brainstem as part of a pathway called the medial lemniscus

Somatosensory Pathwaus to the Brain

Ventral Spinothalamic Tract

-Carries...

-crossover...

-How do they get to the brain?

Somatosensory Pathways to the Brain

_____________________

-Carries nociceptive (pain and temperature)

-Acons from the dorsal-root ganglion neurons enter the spinal cord and cross over right away and synapse onto seurons on the contralateral side

-Axons from contralateral spinal cord then ascend to the brain where they join with other axons froming the medial lemniscus, eventually synapsing with neurons located in the ventrolateral nucleus of the thalamus

-Neurons from the thalamus then project to the somatosensory cortex

Pain

Pain receptors/Nociceptors

-Where are they found

-Threshold Level...

-prostaglandins

- pain receptors stimulated by....

Pain

Pain receptors/___________

-found in skin tissues surrounding muscles, internal organs, and membranes around bones

-have high threshold for stimulation- must be "irritated" into firing

-_________ irritate receptors (pain medications try to stop these)

-pain receptors stimulated by cuts, heat, chemical irritants, lack of blood glow and many other noxious stimuli

Other pain pathways from spinal cord to brain

Chemical Effects in Pain

-Build up in responsiveness in the ___________ of spinal cord

Chemical Effects in Pain

 dorsal horns

opioid peptides or endorphins

-release by dorsal horns inhibits release of Substance P

-endorphin neurons and receptor sites exist in periaqueductal gray area as well

endorphins also found in limbic system- involved in emotion

Influences on Pain Perception

1.

2.

3.

4.

5.

6.

1. Learning (cultural and social)

2. Attentiveness

3. Anxiety

4. Suggestibility

5. Hypnosis provides pain relief without endorphins

6. Brain may generate pain in absence of external stimulations

Within each ear, there is a vestibular organ that contains

1.

2.

1. Three semicircular canals

2. Otolith organs (utricle and saccule)

Vestibular organs have two functions

1.

2.

1. Tell us the position of the body in relation to gravity

2. Signal changes in the direction and speed of movements of the head

Two main somatosensory areas in the cortex

1. Primary Somatosensory Cortex

Function? Location?

2. Secondary Somatosensory Cortex

-Location?

Two main somatosensory areas in the cortex

1. ______________________________

- Receives projections from the thalamus

-Located within the postcentral gyrus, right behind the central fissure

2. _______________

Located behund the primary somatosensory cortex

What do these do?

1. Primary somatosensory cortex

2. Secondary somatosensory cortex

1. receives sensory information from the body

2. receives sensory information from the primary cortex