The Somatosensory System Flashcards

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1
Q

What is somatosensation?

A

Somatosensation is sensory category that includes all sensation received from the skin and mucous membranes.

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2
Q

What are the three layers of skin?

A

Epidermis, dermis, and the subcutaneous layer

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3
Q

What is the epidermis?

A

The epidermis is the very top layer of skin which is a thin barrier to water and diseases.

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4
Q

What is the dermis?

A

Below the epidermis is a thicker layer (the dermis) which contains blood vessels, sweat glands, hair follicles, and other important glands and structures.

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5
Q

What is the subcutaneous layer?

A

the deepest layer of your skin. It’s made up mostly of fat cells and connective tissue. The majority of your body fat is stored here. The subcutaneous layer acts as a layer of insulation to protect your internal organs and muscles from shock and changes in temperature.

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6
Q

What do these neurons require?

A

They require many types of receptors to convert many types of sensory input.

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7
Q

What are encapsulated mechanoreceptors?

A

They are special sensory receptors that respond to touch, pressure, and vibration. They respond to mechanical stimuli.

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8
Q

What are the four major types of encapsulated mechanoreceptors?

A

Meissner’s corpuscles, Ruffini’s corpuscles, Pacinian corpuscles, and Merkel’s disks.

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9
Q

What do all four types of mechanoreceptors have?

A

They all have long thickly myelinated axons that help information get to the brain quickly. However, some temperature and pain information doesn’t have this as it is not as critical for survival.

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10
Q

What are pacinian corpuscles?

A

Located in the subcutaneous layer of the skin, they detect deep vibrations and pressure.

When the stimulus is applied, the corpuscle deforms and the fluid is smooshed. Once the stimulus is gone, the corpuscles fluid redistributes–reshaping it.

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11
Q

What are Meissner’s corpuscles?

A

Located in the dermis, these corpuscles are smaller than the pacinian and can be found in hairless places.

They convert low frequency vibrations or little flutters.

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12
Q

What are Ruffini’s corpuscles (endings)?

A

Located in the dermis, they can be found on both hairy and hairless skin and they detect skin stretch and tangential force.

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13
Q

What are Merkel’s disks?

A

Located in the dermis, they can be found on hairy and hairless skin and convert light touch. They perceive light touch, shape, and texture.

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14
Q

What is the difference between Pacinian and Meissner’s corpuscles vs. Ruffini’s endings and Merkel’s disks?

A

Pacinian and Meissner’s corpuscles both have a rapid adapting property while Ruffini’s endings and Merkel’s disks don’t adapt rapidly. They fire action potentials for the entire duration of the touch stimulus.

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15
Q

What are touch receptive fields?

A

Each mechanoreceptor responds to a touch stimulus in a specific area of the skin, a region called the receptive field of the receptor. When the receptive field is touched, the mechanoreceptor will be activated.

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16
Q

What is two-point discrimination?

A

This is a measure of how close two nearby objects that are both touching the skin can be to one another before your skin cannot tell that they are truly two distinct points.

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17
Q

What are dermatomes?

A

A dermatome is all the skin innervated by one level or segment of spinal cord.

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18
Q

What must all receptors do?

A

They all have to send their axons with info to the brain except for the ones in the face and neck which use cranial nerves.

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19
Q

How are the thirty spinal segments divided up?

A

There are thirty spinal segments which are divided into four major groups named based on that specific part of the vertebrae. There are eight cervical spine segments, twelve thoracic spine segments, five lumbar and five sacral.

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20
Q

Why are dermatomes useful?

A

They can help point out places where a certain condition is, diagnosing and assessing these conditions.

21
Q

What are temperature receptors called?

A

Thermoreceptors - they don’t have any specializations and are therefore free nerve endings.

22
Q

What are thermoreceptors?

A

These receptors react to temperature. They are divided into high and low thresholds.

Low-threshold receptors - react to 15 degrees C - 45 degrees C

High threshold receptors - react to below 15 degrees C and higher than 45 degrees C

The information has a slow transmission to the brain because it is not as critical.

23
Q

What are nociceptors?

A

Nociceptors are specialized nerve endings that detect and transmit pain signals. They are found throughout the body and are sensitive to stimuli like extreme temperatures, pressure, and chemicals released during tissue damage or inflammation. When activated, nociceptors send signals to the brain, helping us perceive and respond to pain.

24
Q

What is hyperalgesia?

A

Hyperalgesia is when the threshold is reduced for an inflamed area so that you’re more gentle towards that area and so it heals faster. The area becomes red, warm, and swollen.

25
Q

What is Congenital analgesia?

A

Congenital analgesia is a hereditary insensitivity to pain and is rare because is so dangerous to one’s health. This can be caused by defects in the free nerve endings.

26
Q

Why is pain so important?

A

Pain is important it is one of the most crucial signs for survival. Without it, a child doesn’t learn to avoid dangerous things like fire and sharp objects.

27
Q

Where are pain receptors located?

A

They are located in the epidermis and are free nerve endings.

28
Q

What do all three of the sensory neurons discussed have in common?

A

They all have nerve endings or dendrites in the skin and synapse on to the next neuron somewhere in the spinal cord or brainstem. This means those neurons are really long!

29
Q

What is the dorsal root ganglion ?

A

The nerve endings in the skin synapse onto the cell bodies. The cell bodies are in little bundles located in the dorsal root of each spinal segment called the dorsal root ganglion.

30
Q

What are afferents?

A

Afferent neurons are sensory neurons that carry nerve impulses from sensory stimuli towards the central nervous system and brain

31
Q

What are efferents?

A

Efferent neurons are motor neurons that carry neural impulses away from the central nervous system and towards muscles to cause movement.

32
Q

What is proprioception?

A

Proprioception is being aware of the movement and position of the body. This is calculated by the stretch and force of muscles, joints, and tendons using mechanoreceptors.

33
Q

What do all somatosensory pathways involve?

A

They all involve a chain of neurons starting in the peripheral neurons in the skin and ending in the cerebral cortex.

34
Q

What does each pathway do?

A

Each pathway crosses the center of the body once. The pathways bring info from the left side of the body to be processed by the right side of the brain and vice versa.

35
Q

Where does each pathway synapse in the brain?

A

The thalamus, and then this info is relayed to the cerebral cortex.

36
Q

Which two systems are used to bring information from the rest of the body to the brain?

A

The Dorsal Column Medial Lemniscal System and the Anterolateral Spinothalamic System

37
Q

What does the Dorsal Column Medial Lemniscal System do?

A

This system is used to bring information about touch and proprioception to the brain. The dorsal columns are white matter (myelinated axons) which take the information to the spinal cord.

38
Q

What is the medial lemniscus?

A

This is the pathway that winds its way through the brainstem to the thalamus.

39
Q

Where do sensory axons enter the spinal cord?

A

They enter the spinal cord at the dorsal root and join up with the band of white matter at the top part (dorsal part) of the spinal cord.

40
Q

How does information from the lower body travel?

A

This info travels in the middle of the bundle and synapses in the bottom of the brainstem in the gracile nucleus of the medulla.

41
Q

How does information from the upper body travel?

A

This info travels towards the side of the bundle and synapses in the cuneate nucleus in the medulla.

42
Q

Are there separate pathways for the upper and lower body information to travel?

A

They are kept separate throughout travelling through the spinal cord but after the first synapse onto the second neuron all the info is bundled up. The first neuron in this pathway is really long and either extends from your big toe of your finger all the way to the brainstem.

43
Q

What do some axons in the pathway do?

A

Some axons synapse immediately onto other neurons in the spinal cord to create repetitive movements (like walking). But most axons don’t synapse onto another neuron until the two dorsal column nuclei (gracile nucleus and cuneate nucleus).

44
Q

What happens after the neurons synapse in the two dorsal column nuclei?

A

These axons then cross onto the other side of the nervous system . These axons weave through the other half of the brainstem until they reach the thalamus. This is where they synapse onto the final neuron in the pathway in the VPL (ventral posterior lateral) nucleus in the thalamus.

45
Q

What does the third and final neuron in the pathway do?

A

This third neuron travels to the primary somatosensory cortex, where all somatosensation is processed.

46
Q

What does the anterolateral
spinothalamic system do?

A

Pain and temperature info travels through this system. Sensory axons enter the spinal cord through the dorsal root and immediately synapse in the grey matter (cell bodies) within the spinal cord onto the second neuron in the pathway.

47
Q

How does the pain and temp. info travel? (second neuron)

A

The second axon travels up to the brain in the side portions of the spinal cord toward the top.

48
Q

What similarities do both systems have?

A

The pathways bring info from the left side of the body to be processed by the right side of the brain and vice versa.

Despite the fact that the AS travels up the spinal cord through grey matter and the DCML travels through white matter, both of them are pretty much the same except for the info they carry.

49
Q

Where does the anterolateral
spinothalamic system synapse last?

A

After traveling all the way up, the third neuron synapses in the VPL nucleus of the thalamus (same as the DCML).