Introduction

Question 1

If you want to build a sensing machine, what would you need?

Answer 1

• Something that receives and translates information into the language of the machine → sensory receptors and axons that translate the energy of the stimulus into electrical signals.
• Something that transports information for processing → axons that transport the signal to the series of relay nuclei.
• Something that integrates and processes information → interneurons and local circuitry in nuclei that process the signal.

Question 2

What’s the difference between non-sensory and sensory neurons?

Answer 2

• Non-sensory neurons can generate an action potential through EPSP or IPSP
• Sensory neurons have a different morphology and respond differently. Here a change in light/dark causes a change in membrane potential which leads to the release of neurotransmitters.

Question 3

What are mechanical receptors?

• To what do they respond?
• What is their reaction?

Answer 3

• Receptors that respond to touch and proprioception, hearing and balance.
• The physical stretch or tension on the receptor deforms the membrane and opens the channels.

Question 4

What are chemical receptors?

Answer 4

Receptors that respond to pain, itch, small, taste. Here a chemical binds to the receptor.

Question 5

What are photoreceptors?

• To what do they respond?
• What is their reaction?

Answer 5

• Receptors that respond to vision via photoreceptors in the retina.
• It results in the change in conformation of a photosensitive protein.

Question 6

What are thermal receptors?

• To what do they respond?
• What is their reaction?

Answer 6

• Respond to temperature.
• Receptor activation results in the change of postsynaptic potential.

Question 7

This picture depicts the different mechanoreceptors that are located in the skin.

Explain how Meissner corpuscle mechanoreceptors respond to the sensing of a stimulus.

Answer 7

Meissner corpuscle → responds to light touch and are able to rapidly adapt to stimuli by firing high frequency action potentials, therefore these receptors are very sensitive. But they are less accurate in sensing stimuli.

Question 8

This picture depicts the different mechanoreceptors that are located in the skin.

Explain how Merkel cells respond to the sensing of a stimulus.

Answer 8

Merkel cells are the most accurate in sensing stimuli (shape, intensity of stimulus)

Question 9

This picture depicts the different mechanoreceptors that are located in the skin.

Explain how Ruffini corpuscle mechanoreceptors respond to the sensing of a stimulus.

Answer 9

Ruffini corpuscle receptors are less sensitive and mostly respond to sustained pressure, but show little adaptation.

Question 10

This picture depicts the different mechanoreceptors that are located in the skin.

Explain how Pacinian corpuscle mechanoreceptors respond to the sensing of a stimulus.

Answer 10

Pacinian corpuscle receptors react differently, but react very well to the stimulus (very small changes in stimuli, but not able to distinguish shape changes and fine details).

Question 11

What is proprioception?

Answer 11

It is the sense of self-movement and body position → the position of the muscles and joints of the body.

Question 12

Why is the location of receptors important?

Answer 12

In order to respond appropriately to a stimuli, it is Important to know the position or location of the stimuli.

Question 13

• What is a topographic map?
• What is retinotopy?

Answer 13

• A topographic map is the ordered projection of a sensory surface (e.g. retina or skin) or an effector system (e.g. musculature), to one or more structures of the central nervous system.
• Retinotopy is the mapping of the visual input from the retina to neurons, particularly those neurons within the visual stream.

Question 14

What determines the spatial resolution of a stimulus?

Answer 14

The size of the receptive field and the density of receptors

Question 15

Why is the intensity of the stimulus important?

Answer 15

Receptors have a certain sensory threshold (which is determined by the sensitivity of the receptors). The intensity of the stimulus determines whether an action potential is triggered.

Question 16

What happens when there’s a change in the intensity of the stimulus?

Answer 16

This results in a change in membrane potential, which also affects the chances of generating an action potential.

Question 17

What happens when a receptor potential is achieved, but this doesn’t result in an action potential?

Answer 17

Then information will be lost, because the threshold for action potential is not reached. Cells can react, but the brain cannot.

Question 18

There are different responses to a stimulus:

• Slowly adapting responses
• Rapidly adapting responses
• Adaptation

Describe these responses.

How does the stimulus change in time (how does it detect the change in stimulus)?

Answer 18

• Slowly adaptic responses → changes in stimulus are coded in frequency. Here they continue in responding to the stimulus.
• Rapidly adapting responses → only respond to changes in stimulus intensity and thus fire action potentials at the start (and end) of the stimulus.
• Adaptation → a constant stimulus fades from consciousness (habituation).

Sensory systems are able to detect contrasts and motion

Question 19

What are sensory systems able to detect?

Answer 19

Contrasts and motion

Question 20

What is parallel processing?

Answer 20

The ability of the brain to simultaneously process incoming stimuli of differing quality.

Question 21

What is convenient about parallel processing of stimuli?

Answer 21

It increases the speed of processing

Question 22

Is topographical representation maintained during parallel processing?

Answer 22

Yes, in the brain the orderly spatial relationship between the distribution of neural receptors in an area of the body and the related distribution of neurons representing the same functions in cortical sensory region of the brain is maintained during parallel processing.

Question 23

What occurs during parallel processing?

Answer 23

Decussation → the cross-over of sensory information to the opposite hemisphere.

Question 24

What else is important during parallel processing?

Answer 24

Feedback connections/descending projections, to modulate/process the information.

Question 25

Through what brain area does all sensory information pass?

Answer 25

Through the thalamus (thalamic filter)

Question 26

How is the thalamus divided and how does touch and visual sensory information pass through these different nuclei in the thalamus?

Answer 26

Different nuclei divided into anterior, lateral and medial thalamus.

• touch → VPM and VPL
• visual information → LGL and MGN

From these thalamic nuclei, the stimuli then project to the middle layers of the cortex.

Question 27

How is the cortex organized?

Answer 27

Cortex contains (functional) columns that are dedicated to processing of different sensory stimuli, also each column has 6 layers (where each layer has a different function)

Question 28

Explain this picture from a touch stimuli on the hand to processing in the brain.

Answer 28

A touch stimuli on the skin of the hand is directed into the brain as a signal and will at last arrive in the fourth cortical layer. Then the information will spread through the cortex to layers 2 and 3 that are important for connecting different cortical regions and to layers 5 and 6 that are important for sending signals to e.g. the basal ganglia and thalamus.

Question 29

Is the topographical representation also maintained in the sensory cortex? Name an example also

Answer 29

Yes, see picture (you can see that for different places on the same finger there’s functional organization in the cortex and that there’s also a difference between slowly and rapidly adapting neurons.

Question 30

This picture supports the latter question/answer about topographical representation in the cortex.

Answer 30

Ok

Question 31

Less than ¼ of the cortex contains projection areas- the rest is involved with language. reasoning, moral thought