Midterm 2 Review

Question 1

Receptor Cells

Answer 1

-Detect Stimuli
-Transducers of the nervous system
-Specialized
neurons that detect physical
attributes about the world and
convert them into electrical signals
that the nervous system can process
— action potentials

Question 2

Stimulus

Answer 2

Physical event that triggers a sensory response

Question 3

Labeled Lines

Answer 3

The nerve fibers that
carry information about each sensory
modality are segregated from one
another, keeping information about
different sensory modalities separate
until they reach the brain

(Note: In the brain, information about
different sensory modalities
eventually gets combined
together…a concept called binding!)

There can even be labeled lines
within a particular sensory
modality, like for different types of
touch (light, stretch, pain, etc.)

Question 4

Thalamus

Answer 4

Information from most sensory
modalities pass through the thalamus
on the way to the cortex

Question 5

Sensation that does not pass through the thalamus on the way to the cortex

Answer 5

olfaction

Question 6

Sensation vs Perception

Answer 6

Sensation: The detection of
physical stimuli by receptor cells.

Perception: Conscious awareness of
the stimuli detected by our receptors

Perception is influenced by your expectations,
current state, and past experiences. Thus perception is a personal interpretation of the
sensations your body detects.

Question 7

Bistable perception

Answer 7

when a stimulus can be
perceived in two (or
more) different ways,
but not simultaneously

Question 8

Synesthesia

Answer 8

Stimulation of one
sensory pathway causes perception in another

Grapheme-Color Synesthesia:
letters or numbers are perceived as
inherently colored

Question 9

change in voltage in a receptor cell in
response to a physical stimulus

Answer 9

Generator Potential

Question 10

PIEZO

Answer 10

Some mechano sensory neurons have a special ion channel on their membrane called PIEZO.

PIEZO is normally closed. But when the membrane
of the cell is touched, PIEZO opens and lets ions flow in, depolarizing the sensory neuron.
Neurons expressing PIEZO are sensitive to touch

Question 11

TRPV1

Answer 11

Other sensory neurons in the skin have a special
ion channel on their membrane called TRPV1

TRPV1 is normally closed. But when the
membrane of the cell is heated up, TRPV1 opens
and lets ions flow in, depolarizing the sensory
neuron.
Neurons expressing TRPV1 are sensitive to heat

Question 12

the spring-like
connectors that connect stereocilia in hair cells, allowing ions to flow in when the cilia are deflected

Answer 12

tip-links

Question 13

Hair Cells

Answer 13

specialized neurons that are the
transducers of hearing

They don’t have axons or dendrites, but they DO detect
inputs (at the sterocilia) and they do release
neurotransmitter (at their bases)

When the stereocilia of hair cells are deflected, springloaded gates — called tip links — are open, allowing
ions to flow into and depolarize the hair cells

Question 14

Receptor Cells for the Eyes

Answer 14

Cones: (Color) Active at high light
levels and responsible for color
vision and have a high density
at the fovea, the central
portion of the retina at which
we have the highest visual
acuity. The photopic system
is for color vision

Rods: Active at low levels of
light, most responsible for our
peripheral vision. The
scotoptic system

Rods and cones rest at a relatively
depolarized membrane potential, and they
are constantly releasing glutamate.
When light hits a photoreceptor, it causes
the receptor cell to hyperpolarize and
therefore release less glutamate.
The amount of neurotransmitter release
onto the bipolar cell is proportional to the
membrane potential.
Rods and cones communicate with graded
potentials rather than action potentials

Question 15

When a photoreceptor detects light its membrane potential becomes

Answer 15

Hyper polarized

Question 15

Odorant Receptors

Answer 15

Gprotein coupled receptors, just like some of the neurotransmitter receptors in the brain

Different receptors in the nose are sensitive to different odorants. In actuality, odorants are ligands for olfactory receptors

The mammalian genome encodes ~1000 odorant receptors, but each receptor neuron has receptors for only one oderant

We have ~2,000,000 receptor cells, so ~2,000 receptor cells have the exact same receptor for detecting the same oderant.

The axons of all of the receptors that express a particular receptor converge at the same glomerulus in the olfactory bulb.

Question 15

Coding

Answer 15

Attributes of sensory stimuli are reflected
in the pattern of neurons that respond to a stimulus
and the pattern of action potentials produced by
neurons.

Question 16

Encode

Answer 16

The pattern or neurons that respond to a
stimulus, and the pattern of action potentials they
produce, encodes physical features of the world.
Note that receptor cells are the only cells that
actually respond to physical features of the world!
Other neurons only respond to action potentials
that they receive

Question 17

Receptive fields in somatosensation

Answer 17

Many neurons have a center-surround receptive field. The rate at which a neuron produces action potentials (its firing rate) is
increased at the center of the RF and is decreased as you move away. Move far enough away, and the neuron’s firing rate is unaffected by stimulation.

Question 17

Decode

Answer 17

The capacity for downstream neurons (or
human observers) to read out action potential
patterns and to understand what is happening in
an animal’s world

Question 18

Receptive fields in vision

Answer 18

Retinal ganglion cells have
center-surround receptive fields.
On-center/off-surround:
These neurons respond when
there is light at the center of the
receptive field and darkness in an
annulus around it.
RGCs are the output of the retina
and their axons terminate in the
visual thalamus.
Visual thalamus neurons also
have center-surround receptive
fields for points in space…there
is not elaboration of receptive
fields at that synapse.

Question 19

Receptive fields

Answer 19

Visual and somatosensory
receptive fields are usually
sorted by space

Auditory receptive fields are
usually sorted by frequency

In vision, hearing, and touch,
when you sort stimuli by these
features, a neuron’s receptive
field “makes sense” — it has a
bell-shaped curve

Question 20

IT Cortex

Answer 20

Neurons are responsive to specific shapes or objects

Question 21

Complex Receptive fields

Answer 21

The V1 neuron will respond when
all three of its presynaptic
neurons are simultaneously
activated (by a bar like this one)

Question 22

tip-links

Answer 22

the spring-like
connectors that connect stereocilia in hair cells, allowing ions to flow in when the cilia are deflected

Question 23

Generator Potential

Answer 23

The change in voltage in a receptor cell in response to a physical stimulus is called the generator potential

Threshold: Stimulus intensity that is just adequate to produce an action potential in a receptor cell.

Question 24

Movement

Answer 24

A movement is a single
relocation of a body part.
Some movements are
intentional. Others are
reflexive

Question 25

Reflex

Answer 25

A reflex is a simple,
unlearned, and stereotyped
response to a particular
stimulus.

Question 26

Act

Answer 26

An act is a complex
behavior made up of
multiple movements

Question 27

Motor Plan

Answer 27

A motor plan is a plan for a series of muscle contractions with a single goal in mind

Motor plans are often
optimized for the following
goals:
(1)Accuracy: to prevent or minimize errors
(2)Speed: to complete a task quickly and efficiently

The speed/accuracy tradeoff is the concept that improvement in one of these goals usually comes at some cost to the other goal.

Question 28

NMJ

Answer 28

The NMJ is the “final synapse” - it is the
last stop where the nervous system
(motor neurons) meets the muscles.
We call the NMJ a perfect synapse
because when a motor fires an action
potential it always causes an action
potential in the associated muscle fibers.
In contrast, within the brain, a presynaptic
action potential does not always cause a
postsynaptic action potential.
Even though the NMJ is perfect, that does
not mean that a plan in the motor cortex
will always be perfectly executed!

Question 29

6th sense — it allows us to
know where are bodies are in space

Answer 29

Propioception

Question 30

Proprioception

Answer 30

By knowing how much each muscle is stretched relative to its resting point, we can infer where are all of our limbs are. By knowing how much tension is on each muscle, we can figure out how strong of a command we need to send to our muscles to keep our joints in place or to move them.

Muscle spindles respond to stretch. Golgi tendon organs are sensitive to tension

Question 31

Pathways for controlling muscles

Answer 31

The brain sends signals to motor neurons in the spinal cord via the pyramidal system and the extrapyramidal system.

Question 32

Measuring the tuning curve of a
motor cortex neuron

Answer 32

First, nestle your recording electrode next to a single M1 neuron.
Next, have the monkey reach in one direction while recording the action potentials produced
by the neuron.
Then have the monkey move in other directions.
Count the # of APs produced in each direction.
Most neurons fire the most when the
monkey reaches in one direction and a bit less when the monkey reaches in nearby directions, which produces a tuning curve that is bell-shaped

Question 33

Population Coding

Answer 33

Population coding allows us to decode an actionfrom many motor cortex neurons
When a monkey makes a
movement in a direction, some
neurons are active.
When a monkey moves in a different direction, a partially overlapping population is active.
Although neuron “a” is weakly active during both movements, we can decode the movement
Monitoring many neurons simultaneously allows us to decode movement direction