Midterm 2 Review Flashcards
Receptor Cells
-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
Stimulus
Physical event that triggers a sensory response
Labeled Lines
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.)
Thalamus
Information from most sensory
modalities pass through the thalamus
on the way to the cortex
Sensation that does not pass through the thalamus on the way to the cortex
olfaction
Sensation vs Perception
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.
Bistable perception
when a stimulus can be
perceived in two (or
more) different ways,
but not simultaneously
Synesthesia
Stimulation of one
sensory pathway causes perception in another
Grapheme-Color Synesthesia:
letters or numbers are perceived as
inherently colored
change in voltage in a receptor cell in
response to a physical stimulus
Generator Potential
PIEZO
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
TRPV1
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
the spring-like
connectors that connect stereocilia in hair cells, allowing ions to flow in when the cilia are deflected
tip-links
Hair Cells
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
Receptor Cells for the Eyes
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
When a photoreceptor detects light its membrane potential becomes
Hyper polarized
Odorant Receptors
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.
Coding
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.
Encode
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
Receptive fields in somatosensation
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.
Decode
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
Receptive fields in vision
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.
Receptive fields
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
IT Cortex
Neurons are responsive to specific shapes or objects
Complex Receptive fields
The V1 neuron will respond when
all three of its presynaptic
neurons are simultaneously
activated (by a bar like this one)
tip-links
the spring-like
connectors that connect stereocilia in hair cells, allowing ions to flow in when the cilia are deflected
Generator Potential
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.
Movement
A movement is a single
relocation of a body part.
Some movements are
intentional. Others are
reflexive
Reflex
A reflex is a simple,
unlearned, and stereotyped
response to a particular
stimulus.
Act
An act is a complex
behavior made up of
multiple movements
Motor Plan
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.
NMJ
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!
6th sense — it allows us to
know where are bodies are in space
Propioception
Proprioception
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
Pathways for controlling muscles
The brain sends signals to motor neurons in the spinal cord via the pyramidal system and the extrapyramidal system.
Measuring the tuning curve of a
motor cortex neuron
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
Population Coding
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
