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Behavioral Neuroscience > Chapter 8- Sensory processing > Flashcards

Chapter 8- Sensory processing Flashcards

1
Q

Transduction

A

Conversion of stimulus energy into an electrical signal

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2
Q

With touch, how is the stimulus converted in an electrical signal?

A

Touch (change in pressure) affects receptors that create a receptor potential (open ion channels) and ions flow into the cell, creating what’s similar to an IPSP or an EPSP. Receptor potentials can create an action potential if they depolarize the cell enough.

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3
Q

Somatosensory system transduces (3)

A
  1. Pressure (mechanoception)
  2. Pain (nociception)
  3. Temperature (thermoreception)
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4
Q

Mechanosensation

A

Mechanical stimulation of the skin- when you feel pressure or vibration

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5
Q

Nociception

A

These receptors detect pain and temperature (hot or cold). Sometimes, this can indicate a harmful stimulus, but not always.

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6
Q

Layers of the skin (3)

A
  1. Epidermis
  2. Dermis
  3. Hypodermis
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7
Q

Epidermis

A

The outermost and thinnest layer of the skin. Nerve endings are located in the epidermis, and detect pain and temperature. The receptors are very sensitive to change- pain and temperature aren’t necessarily bad things, but they need to be close to the surface to detect damage

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8
Q

Receptor cell

A

Receptor cell= the cell that holds the receptor (which senses the world). Different receptor cells have their endings in different layers of the skin

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9
Q

Which receptors are found in the dermis? (3)

A
  1. Merkel’s disc
  2. Meissner’s corpuscle
  3. Hair follicle receptor
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10
Q

Merkel’s disc

A

Slow-adapting touch receptor found in the dermis. They are activated by fine touch, like if you touch a small bump (Braille), an edge, or a textured surface. Located in skin regions where we can discriminate fine details by touch (fingertips, tongue, and lips).

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11
Q

Meissner’s corpuscle

A

Fast adapting touch receptors located in the dermis. Activated by light touch or light pressure, like if something brushes against your hand. Located in skin regions where we can discriminate fine details by touch (fingertips, tongue, and lips).

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12
Q

Hair follicle receptor

A

Light touch- senses movement of hair since it’s wrapped around the hair follicle. Each hair has a hair follicle that extends down into the dermis, so these receptors are located in the dermis. Each hair follicle has a receptor ending wrapped around it to sense movement of hair

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13
Q

How does the receptivity of the sensory receptors in the dermis compare to those in the epidermis?

A

Receptors in the dermis aren’t as sensitive as the receptors in the epidermis because they aren’t detecting harmful things. However, they still need to be relatively close to the surface because they are detecting things with fine resolution

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14
Q

Dermis

A

The dermis contains a web of nerve fibers, as well as blood vessels, hair follicles, and connective tissue.

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15
Q

Hypodermis

A

The hypodermis is the inner layer and provides an anchor for muscles and helps shape the body.

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16
Q

Receptors found in the dermis (2)

A
  1. Pacinian corpuscle

2. Ruffini’s ending

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17
Q

Pacinian corpuscle

A

The onion-like outer portion of the Pacinian corpuscle shields the underlying nerve fiber from most stimulation- only strong pressure and vibration of an appropriate frequency will pass through the nerve fiber and stretch the nerve fiber to reach threshold. The skin gets this type of rapid vibration as it moves across an object’s surface, so Pacinian corpuscles are fast responding and fast adapting receptors.

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18
Q

Ruffini’s ending

A

Activated when the skin gets stretched- stretching out fingers, someone is pulling your arm, etc. Skin stretching is done by the muscles underneath the skin- the skin doesn’t necessarily stretch itself. That’s why these receptors are located in the hypodermis.

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19
Q

When would all touch receptors be stimulated at the same time?

A

With daily events, a combination of receptors are usually simulated, and the brain then combines this information. For example- if someone is pulling you, you can tell that they’re pulling you and that they also have cold hands. The same transduction pathway occurs for all cell types

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20
Q

Where are cell bodies for the Pacinian corpuscles located?

A

Cell bodies for Pacinian corpuscles are in the dorsal root ganglia of the spinal cord. Sometimes referred to as unipolar or bipolar cells

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21
Q

Transduction of Pacinian corpuscles (3 steps)

A
  1. Mechanical stimulus stretches the corpuscle membrane (the part that looks like an onion). Since it has multiple layers, there are many different ways that can contort and stretch. Normally closed ion channels (when they’re at rest) are physically stretched open
  2. Na+ channels open and corpuscle depolarizes
  3. If threshold potential reached- an action potential is generated
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22
Q

Which ion channels are found in Pacinian corpuscles?

A

Pressure sensitive sodium channels. The cell depolarizes as sodium enters.

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23
Q

What happens when a Pacinian corpuscle is exposed to a weak stimulus?

A

With a weak stimulus- light touch or gentle vibration in this case- it will open some sodium channels, but not enough sodium will flow in. No action potential will be generated

24
Q

Receptor potential

A

A receptor potential is most similar to a postsynaptic potential. Receptor potentials can have different sizes- the exact same concept as IPSP/EPSP. You’ll get an action potential if the receptor potential is large enough when you get to the axon hillock. Receptor potential caused by sensory detection

25
Q

How do we distinguish between stimuli? (3)

A
  1. Number of neurons activated- something that is higher pressure will activate more pacinian corpuscles
  2. Number of action potentials- a strong stimulus generates more action potentials
  3. Pattern of action potentials
26
Q

Sensory adaptation

A

Progressive loss of response to stimulus. As the stimulus continues, the cells no longer fire to respond as often and less action potentials will be generated. However, receptors still allow for detection of change. Beneficial for the brain to stop noticing things that aren’t harmful to you- lets your brain pay attention to more important things to help with survival

27
Q

Slow adapting receptors

A

These receptors continue to detect the stimulus without adaptation.

28
Q

Receptive field

A

An area where a stimulus will alter a single neuron or cell body’s activity- if you touch one area, which neuron will it activate? Receptive fields overlap, each cell body has its own size of receptive field. Some cells have much smaller receptive fields than others, for example, light touch and fine touch cells have very small receptive fields. Information is brought to the brain separately so the brain can tell where on the body the information is coming from.

29
Q

How is somatosensory information carried from the skin to the brain?

A

Touch receptors send their axons to the spinal cord, where they enter the dorsal horn and then travel to the brain along the spinal cord’s dorsal column of white matter (this is the dorsal column system). The axons go to the brainstem, where they synapse on neurons of the dorsal column nuclei in the medulla. Then, the axons cross the medulla to the opposite side of the brain and ascend to a group of nuclei of the thalamus. Outputs from the thalamus go to the primary somatosensory cortex (S1).

30
Q

Dorsal column system

A

Main pathway that carries information about touch to the brain. Fibers leave cutaneous receptors and enter the spinal cord through the dorsal roots. They then travel up the spinal cord to the medulla, where they synapse on the next neurons in the pathway. The fibers then cross to the other side of the brain and synapses in the thalamus. Then, goes to the somatosensory cortex. Information from the right side of the body is received in the left somatosensory cortex.

31
Q

Dermatomes

A

Topographic map of our bodies- the information comes into different areas of the spinal cord depending on where on the body it was generated. Information from the backs of the legs goes to the sacral area of the spinal cord, information from the front and sides of the legs, top of the feet, and lower back go to the lumbar area, and so on. Inputs from dermatomes are segregated at all levels

32
Q

Information from the arms, upper back, shoulders, neck, and back of the head goes to which area of the spinal cord?

A

Cervical

33
Q

Topographic maps

A

Different parts of the primary somatosensory cortex represent different parts of the body. Information is further preserved in the somatosensory cortex due to the homunculus concept (one to one area of the somatosensory cortex matched to a specific area of the body).

34
Q

How does the size of a body part correspond to the size of the area representing it in the somatosensory cortex?

A

Some smaller areas of the body are represented by smaller brain areas. However, the fingers and hands are very sensitive and take up more space in the somatosensory cortex. There are more receptors in the fingers and hands- you can easily tell if you’ve been touched in 2 different areas on the fingertips, even if the areas are close together. The same wouldn’t be true on the back, since there aren’t many receptors

35
Q

How do we know that receptive fields are plastic?

A

The size of receptive fields can change with activity. For example, The right hands of people who are right handed are slightly more sensitive and have a larger receptive field. A piano player has developed dexterity on both sides, resulting on mostly equal activity on both sides of the brain.

36
Q

Purpose of pain (3)

A
  1. Acute pain tells us when something is harming us and to avoid it
  2. Chronic pain can make us not feel good and rest so we don’t hurt ourselves more
  3. Pain can also be a social signal- kids who hurt themselves will cry and then adults will pay attention/help them. In animals, one animal indicating pain could make others in its herd not want to do the thing that caused pain
37
Q

When is pain generated? (3)

A

When mechanical pressure on the skin causes tissue damage. Examples:

  1. Bleeding, swelling, tissue damage
  2. High temperature, burns
  3. Chemical damage
38
Q

Pain is detected by

A

Pain receptors (nociceptors) located on free nerve endings. Nociception is a more general term including both ligand gated and temperature gated channels

39
Q

After cells are damaged, what activates pain?

A

With damage, the surrounding cells (general cells) will stretch or burst open and release compounds. Those signals can activate pain- includes prostaglandin, serotonin, potassium, and leukotrienes can be released- they will bind with different receptors on nerve free endings, so potassium can flow in and generate a receptor potential. Receptor potential can generate an action potential if large enough

40
Q

How do aspirin, ibuprofen, and acetaminophen work?

A

By preventing synthesis of prostaglandin

41
Q

Temperature gated receptors (3)

A
  1. TRPV1
  2. CMR1
  3. TRPM3
    These receptors are all found on different cells
42
Q

TRPM3

A

Receptor that only responds to very hot stimuli

43
Q

TRPV1 receptors

A

Receptors that detect warm heat. They can also be acted on by capsaicin, the active ingredient in spicy peppers and hot sauce, causing a burning sensation.

44
Q

CMMR1 receptors

A

Receptors that detect cold temperature, can be activated by menthol. Peppermint and some cough drops have menthol in it, which is why they feel cooling.

45
Q

Nerve fibers that convey temperature information (2)

A
  1. C fibers are unmyelinated

2. A delta fibers are myelinated

46
Q

C fibers

A

Unmyelinated nerve fibers that carry information from CRM1 and TRPV1 receptors- this information won’t cause a reflex and takes a while to reach the brain- there’s a delay in perceiving how hot something is

47
Q

A delta fibers

A

Myelinated nerve fibers. Associated with TRPM3 receptors, which detect very hot stimuli. This information travels quickly (to prevent damage from very hot stimulus), and causes a withdrawal reflex. However, some information also goes up to the brain.

48
Q

How does pain travel to the brain?

A

Sensations of pain and temperature are transmitted separately from touch, along the anterolateral/spinothalamic system. Free nerve endings in the skin send their axons to synapse on neurons in the dorsal horn of the spinal cord. Pain is also different from touch because the information crosses over in the spinal cord, before the brain stem. Spinal cord neurons send their axons across the midline to the opposite side and up the anterolateral column of the spinal cord to the thalamus. Pain information is brought to sites in the brainstem, which controls pain related behavior like vocalization. Pain is then distributed to thalamic and cortical areas, with the cingulate cortex especially activated by pain information.

49
Q

Pain withdrawal reflex

A

When you touch something hot, the information goes to pain receptors, dorsal side of spinal cord, synapses directly on a neuron on the spinal cord so it can go to the ventral horn. Motor response is immediately released- A delta fibers are responsible for this

50
Q

How does information from A delta fibers travel to the brain?

A

The pain pathway splits, with some information going to the brain but the rest going to the ventral spinal cord for a motor response- this is the information used for a withdrawal reflex. Information coming in the right hand goes to the right dorsal horn, immediately crosses to the left dorsal horn, then goes up to the brain (and stays on that side). The information going to the brain is the reason why you consciously perceive pain after the withdrawal reflex occurs.

51
Q

Where do axons from the spinothalamic tract synapse?

A

In the thalamus.

52
Q

The thalamus sends axons to (touch)

A

The somatosensory cortex (homunculus- goes to the appropriate part of the cortex for the body part). Different types of information will cross at different points and arrive at the somatosensory cortex at different times

53
Q

Neuropathic pain

A

Chronic pain is caused by something that appropriately caused pain (due to tissue damage), but pain continues after the injury has healed (stimulus has disappeared).

54
Q

What could be the cause of chronic/neuropathic pain?

A

Neuropathic/chronic pain may be due to inappropriate signaling of pain by neurons. Microglia/macrophages at the injury site release chemicals that cause inflammation to allow for healing. It’s possible that the cells stay there inappropriately and continue to release pain signals. It’s also possible that dorsal horn neurons can become hyperexcitable, leading to chronic pain

55
Q

Phantom limb pain

A

Occurs when someone who has had an amputation feels pain where the limb used to be. Could be due to inputs in the spinal cord- nerve endings still exist in the area

56
Q

How do people sometimes not feel pain even when they have a severe injury?

A

This is due to the descending pain modulation pathway, which uses serotonin. It’s called “descending” because the signal originates in the cortex and goes back down. Doesn’t usually happen in daily life, only in situations of extreme danger. Stops the pain from being overwhelming so people can respond to the situation

57
Q

Descending pain modulation pathway

A

Free nerve endings are still activating and sending pain signals. The brain sends inhibitory signals from the cortex down the spinal cord via the serotonin neurotransmitter system. This prevents the pain signal from being transferred from the free nerve ending to the dorsal horn (signal never enters the spinal cord). Can completely block the sense of pain or significantly reduce it

Behavioral Neuroscience (11 decks)

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