Lecture 5 - Intro to Sensory Systems

Question 1

What are the four common features of sensory perception?

Answer 1

1. Sensory transduction, the process in which a receptor cell converts the energy in a stimulus into a change in the electrical potential across the membrane.
2. Range, sensory information is carried in a limited range of intensities, meaning the brain sees a filtered version of the world.
3. Organization, the sensory cortex is highly organized with specific regions for specific sensory areas (sensory cortex).
4. The organization and processing of the information is hierarchical.

Question 2

What are sensory receptors?

Answer 2

Specialized cells that convert sensory energy into neural activity.

Each of our senses [5 senses] have different variations of these receptors.

Each system has it’s own type of energy it wants to respond to.

All different receptors have different receptor fields.

Question 3

Receptor Density?

[body distribution]

Answer 3

Receptor density is essneital for determining the sensitivity of a sensory system.

They are not evenly distributed across the body.

Think of the homunculus.

The more receptors in a dense area, the more sensitive [ie. dogs & smell].

Question 4

Neural relays

[How many receptors are there? Do they interact? If so, where/how?]

Answer 4

Visual rceptors, auditory receptors, & somatosensory receptors.

All receptors connect to the cortex.

They allow for interaction to happen between sensory system, they all go through the Thalamus at some point and end up in the cerebral cortex.

Question 5

Variety of Eyes:

Between how many nm of the electromagnetic spectrum can we sense?

Answer 5

380-760 nm.

Our colour pallet is pretty limited, with the remaining trillion of nm escaping our view.

Question 6

What are the main structures of the eye?

Answer 6

• Cornea, the clear outer covering.
• Iris, which opens and closes to allow in more or less light. The hole in the iris is called the pupil.
• Lens, which focuses light and bends to accomodate near or far objects.
• Retina, which is where light energy initiates neural activity.

Question 7

What do glasses/contacts do to correct vision?

Answer 7

They fix your lack of lens ability to adjust to different distances and such.

Question 8

The kind of color vision available for different species is revealed through?

Answer 8

The relative sensititives, or absoprtion spectra, of the species’ photoreceptor types.

Some species have colour vision, other’s do not.

Question 9

Visual Sensation:

Photoreceptors?

Answer 9

Visual processing = photoreceptors [its their job].

There are two basic types, rods and cones.

Question 10

Photoreceptors:

Rods?

Answer 10

These are more numerous than cones & are used mainly for night vision.

They only have one pigment type, and are sensitive to low levels of light [dim].

Question 11

Photoreceptors:

Cones?

Answer 11

There are three types of pigment, which allow for a detailed version of our vision [without them, everything would just be blurry].

They are highly responsive to bright light, specialized for color and high visual acuity.

Found in the fovea only.

Question 12

Where are cones found?

Answer 12

In the fovea only.

Question 13

What are the three types of pigments found in cones?

Answer 13

• 419 nm = blue [short wavelength].
• 531 nm = green [middle wavelength].
• 559 nm = red [long wavelength].

Question 14

What is the rough ratio between the three colour of cones?

Answer 14

There is approximately an equal number of both red and green, but fewer blue cones.

Question 15

How is visual stimuli transduced?

Answer 15

Through photoreceptors.

Done through a light sensitive pigment.

Question 16

What is a clear example of the process of sensory transduction?

Answer 16

Pacinian corpuscle, a skin receptor.

Question 17

Tactile Sensation:

A stimulus to the corpuscle opens ____channels and produces a __.

Answer 17

Sodium; graded generator potential.

Question 18

How does auditory sensation work?

Answer 18

Hair cells respond [vibration] to mechanial distortrion of vibrating fluid in the ear.

As the hair cells move, tiny strings pull open a channel to allow an influx of sodium through them.

How much the hairs bend causes them to fire more or less, which is a response to different tones.

Question 19

Auditory Sensitivity:

We can detect signals that vibrate the eardrum by about __?

Answer 19

A picometre.

Question 20

How is our auditory system enhanced?

Answer 20

By an active process in cochlear hair cells that amplifies acoustic signals several hundred-fold, sharpens frequency selectivity and broadens the ear’s dynamic range.

Not a one-to-one ratio, we have a funnel.

Our ears gather a bunch of sounds and then filter it / funnel it, so we are focusing on one thing / not focusing on everything around us.

This is also why sounds can be painful [because it is not a one-to-one ratio].

Question 21

Perception is …?

Answer 21

Relative!

We all perceive things differently, simple as that.

Question 22

Sensory Adaption:

Arm tapping example?

Answer 22

If someone is holding our arm and someone taps it at the same time, we would feel both [both stimulus], sensory adaptation allows this.

Without this, if we peaked and then a second stimulus came in contact, there would be no way for us to tell / realize.

Question 23

What are the benefits of adapation?

Answer 23

Helps us ignore innocuous stimuli

Adaptation helps to avoid saturation of neuronal firing rates, allowing us to detect change in stimulus intensity over a larger range of intensities [Simpler terms: we have a capacity for all these things, if we were always at the peak, we would never be able to know more, but sensory adaptation allows for us to do so and come back down, allowing more input].

Question 24

Two types of of adapting receptors/cells?

Answer 24

Phasic & Tonic receptors.

Question 25

Differences between a phasic & tonic receptor?

Answer 25

• Phasic: these generally adapt fast, displaying adaption and decreasing frequency of action potentions.
• Tonic: these generally adapt slowly, showing slow or no decline in action potential frequency.

Question 26

An example of sensory adapation?

Answer 26

Adapting to the feeling of our clothes against our skin.

We are aware we have clothes on, but not actively aware of the feeling of them until we think about them.

Question 27

Sensory Modalities:

Range?

Answer 27

We have different sensory modalities that respond to different energies.

Question 28

What does sensory information need to be coded in? What is the problem with it?

Answer 28

Action Potentials.

Problem is that they are so predictible, always having the same size and duration. This means we cannot adjust to cover a large range of sensory information while remaining sensitive to subtle changes in intensity.

Question 29

How do we solve the issue that comes alongside the fact that sensory information needed to be coded in action potentials?

Answer 29

Range fractionation, which allows us to increase the range of our senses.

Question 30

What is the general rule of range fractionation?

Answer 30

The sensory systems use sensory receptor cells, each specializing in just one part of the overall range of intensities, to cover the whole range.

Question 31

Sensory information travels from the sensory surface to the ___?

Answer 31

Highest levels of the brain.

Question 32

Where do all the touch neurons come from?

Answer 32

Periphery

Question 33

What are the axons of dorsal root ganglion neurons known as?

Answer 33

Afferents.

In the PNS, afferents refer to the axons that relay sensory information into the CNS.

Question 34

What is considered the major input from all sensory information?

Answer 34

The thalamus.

Question 35

When Penfield mapped the relation between each site of stimulation, what did he discover?

Answer 35

The human primary somatosensory cortex [SI].

This was organized according to a map of the body surface [homunculus brain and man].

Question 36

Somatosensation?

(primary, secondary, tertiary)

Answer 36

• Touching on hand, shoot up nerve, to spinal cord, to thalamus, and tell u palm has been touched.
• Secondary area is going to tell you what the object is.
• Tertiary area, if someone is holding my hand, and then I hear their voice and recognize it, I can associate them.

Question 37

Primary sensory cortex?

Answer 37

Area that receives most of its input directly from the thalamic relay nuclei of that system.

Question 38

Secondary sensory cortex [non primary]?

Answer 38

A system that comprises the areas of sensory cortex that receive most of their unput from the primary sensory cortex of that system.

Question 39

Association cortex?

Answer 39

Any area of cortex that receives input from more than one sensory system. Most input come via areas of the secondary sensory cortex.