Behavioral Neuroscience Exam 2

transduction

translating sensory events into changes in a cells membrane potential. occurs in sensory receptors (not neurotransmitters)

sensory receptors

specialized cells that respond to a particular type of energy with a change in membrane potential (sensory transduction)

mechanical energy

energy that interests the CNS that involves touch, proprioception, pain, hearing, and balance

thermal energy

energy that interests the CNS that involves changes in skin temperature

chemical energy

energy that interests the CNS that involves smell and taste

light energy

energy that interests the CNS that involves vision

receptor or generator potentials

changes in receptor membrane potential during sensory transduction. it is a non-conducting local event (not an action potential, APs go long distances), it is graded, meaning proportional to size of stimulus (not all or nothing like AP)

transmission via primary sensory cells

neurons whose dendrites are specialized to transduce specific stimuli. It goes sensory event - receptor potential in dendrite - trigger APs - CNS

transmission via secondary sensory cells

typically not neurons, but synapses on neurons, specialized to transduce specific type of sensory information. It goes sensory event - receptor potential in secondary cell - release NT - trigger APs in sensory neurons - CNS

threshold

the stimulus has to be a particular minimum magnitude to elicit a response in a receptor cell

through labeled lines. information travels along different routes using same code. these are modality specific

How does information travel from sensory cells to the CNS?

spatial coding/place coding

different stimuli affect different neurons because they're located in different places

topographic organization

individual receptors detect stimuli at particular locations, and each location is ordered in a sensible, consistent way throughout the nervous system

temporal coding

more intense stimulus, more APs in a given neuron.

population coding

sensory receptors have threshold, more intense stimulus - more neurons firing.

receptive fields

the area whose stimulation changes the cells membrane potential. ex: area of skin that when touched excites a particular touch receptor.

All receptive fields vary in size. size is related to acuity, or ability to discriminate fine detail. size of receptive fields varies inversely with the density of innervation (how many receptor cells are within a particular area) The more receptive fields per unit area, smaller receptive fields. more density of innervation = smaller receptive field

Are all receptive fields the same size? What determines size?

density of innervation

how many receptor cells are within a particular area

electromagnetic radiation

waves are characterized by wavelength and amplitude. light can be absorbed, reflected, and refracted

sclera

outer surface (white stuff you see) on the eye

choroid

pigmented epithelium plus vasculature. lines inside of the eye. in some species it is highly reflective. it is reflective in all species, just some more than others. this is why you get red eye in pictures

vitreous and aqueous humors

fluids that fill each compartment of the eyeball

cornea

main light bender (refraction) of the eye

iris

controls the amount of light and depth of field in the eye

pupil

opening whose size is regulated by iris in the eye

lens and ciliary muscles

controls fine focus via accommodation (change in lens shape to focus near and far)

1. ciliary muscles contract - lense is rounder - focus on nearby objects

2. ciliary muscles relax - lanse is flatter - focus on far away objects

What are the different types of accommodation by the lens?

retina

part of the eye that is light sensitive, houses receptor cells plus neurons, site of transduction

1. ganglion cell layer

2. bipolar cell layer

3. photoreceptor layer

What are the three main layers of the retina?

photoreceptor layer

contains rods and cones

rods

respond to all visible wavelengths. about 100 million per eye. responsible for sceptic vision (low light) and between vision (same response, regardless of wavelength). 1000 times more sensitive than cones

cones

3 types, each tunes to particular wavelength. about 4 million per eye (less than rods). responsible for photopic vision (bright light) and color vision

Varies. more rods toward periphery, cones concentrated in center at the fovea

What is the distribution of rods and cones in the retina?

1. bipolar cell layer

2. ganglion cell layer

3. fiber layer

What are other layers of the retina?

bipolar cell layer

layer that has special neurons that dont produce APs (not really neurons)

ganglion cell layer

layer that has projection neurons, produce APs, about 1 million per eye

fiber layer

layer that has ganglion cell axons, exit at optic disc

retinal interneurons

horizontal cells - synapse on photoreceptors, bipolars. amacrine cells - synapse on bipolar, ganglions. local processing

Rhodopsin

What photopigment do rods have?

Outer segment of cone or rod

Where is the photopigment located?

One of 3 opsins

What photopigment do cones have?

The outer segments of rods and cones have photopigment, light hits the receptor cell, photopigment bleaches because light causes a chemical damage, this generates receptor potential, and causes chemical change releasing opsin

How does photopigment work?

In complete darkness, rods are depolarized. This is due to an influx of Na+ through G protein linked channels, Na+ channels are open. This results in the constant release of glutamate

Why are photoreceptors depolarized in the dark?

Light strikes the rod, rhodopsin bleaches. This releases opsin. Opsin activates transducin- a G protein. Transducin activates an enzyme that breaks down cGMP. Less cGMP - less Na+ influx - hyperpolarization - less glutamate release

Why are photoreceptors hyper polarized in the light?

Graded. Not all or none, more light means more hyperpolarization

Does light cause a graded or all or nothing potential?

When light turns on. Light hits photoreceptors, Na+ current stops. Because glutamate is inhibited by synapse, less inhibitory Glutamate is released onto bipolar cell. This means more excitatory glutamate is released onto ganglion cell.

When and how do ON bipolar cells respond?

When light does not hit photoreceptors, Na+ current starts. More excitatory glutamate is released onto bipolar cell. More excitatory glutamate is released onto ganglion cell.

When and how do OFF bipolar cells respond?

Photoreceptors synapse in bipolars (and horizontals), synapses are either excitatory or inhibitory. Change in activity of photoreceptors produced graded potentials in bipolars, altering release of NT. Change in bipolar NT release alters rate of APs in ganglion cells

Transmission of information across layers

Rods. Rhodopsin responds to a single photon

Are rods or cones more sensitive to light?

Weak stimulation of receptive field is more likely to alter firing of ganglion cell. Thus, good sensitivity: ability to detect weak stimuli. But, low acuity: poor ability to discriminate fine detail

There is much convergence of rods onto ganglion cells. What does this cause?

1. High cell density: fovea is all cones, small receptive fields

2. Dedicated lines: no convergence: 1 cone - 1 bipolar - 1 ganglion cell. So high acuity, but only useful with a lot of light

What are the two specializations of the central retina?

Modality: labeled lines

Intensity(brightness): temporal coding- brighter means faster production of APs. Not linear- best discrimination at lower intensities (can tell differences in brightness when there is less light)

Location: place coding (reinotopy). Each neuron carries info from tiny part of retina. Brain integrates across all retinal neurons to form picture

Visual coding

Center/surround receptive fields

Record activity of ganglion cells while stimulating areas of retina

Have steady, slow baseline activity. Will either increase or decrease activity when certain parts of the receptive field are stimulated more or less relative to other parts

In diffuse (no differences in brightness) light, certain ganglion cells:

Is circular, has a center and surround. Center: either excited (ON center) or inhibited (OFF center) by light. Surround: does opposite

Each cells receptive field:

Lateral inhibition

Excitation of one receptor cell produces excitation of directly synapsing bipolar, but inhibition of neighboring bipolar (indirectly)

Lateral inhibition. Horizontal cells account for lateral division, which explains center/surrounding receptive fields.

What is center-surround organization due to?

Excitation and inhibition cancel, so no change in baseline AP rate

What happens when light hits a whole receptive field?

The center is excited, part of inhibitory surrounded in dark, so less inhibition. This leads to a higher AP firing rate.

What happens when the center of a receptive field has all light, but part of surrounding is in dark?

The excitatory center is in the dark, but part of inhibitory is surrounded in light. This leads to a lower AP firing rate.

What happens when the center of a receptive field has all dark, but part of surrounding is light?

Excitation and inhibition cancel, so no change in baseline AP rate

What happens when the whole receptive field is in the dark?

Many ganglion cells that code for color have antagonistic receptive fields similar to ganglion cells that receive input from rods. The two colors are represented in each receptive field are complementary colors. This opponent color system explains why we cannot see a reddish green or a bluish yellow

Color vision involving ganglion cells and receptive fields:

80% parvocellular cells: little cells. Small receptive fields. Discrimination of fine detail, color sensitive

10% magnocellular cells: big cells. Large receptive fields, detect stimuli with low contrast. Not color sensitive.

10% nonM-nonP cells: medium cells. Different characteristics than P and M. Color sensitive

Ganglion cell classifications

The optic chiasm

Nasal information crosses, temporal information does not. Thus, left visual field goes to right side of brain and vice-versa

1. Suprachiasmatic nucleus: day/night cycle

2. Accessory optic system: reflexive eye movements

3. Pretectum: adjust pupil size to ambient light

4. Superior colliculus: orienting reflexes

5. Lateral geniculate nucleus (LGN): pathway light information takes to give us vision.

Each is extracting different information from the visual field

What five targets can retinal ganglion cells project to?

Thalamo-cortical pathway

Conscious experience of vision, pattern detection, retina - LGN (part of thalamus) - primary visual cortex (occipital lobe)

Lateral geniculate nucleus

Main target of retina in primates. 6 numbered layers and Koniocellular layers. Each layer gets input from only one eye. Topographic representation of retinal surface/ visual field. Not accurate, exaggerates central retina. part of the thalamus.

Axons from LGN make up the optic radiation. Synapse on neurons in primary visual cortex (aka V1, striate cortex)

LGN to cortex

When you stain it, it has a striated appearance

How did striate cortex get its name?

Layers 1-3: output to deep layers and Extrastriate cortex

Layer 4: input from LGN, binocular integration, projections to superficial layers

Layer 5: nonthalamic outputs

Layer 6: output to LGN

What is the structure of the primary visual cortex?

The primary visual cortex is the first place that cells are getting input from both eyes

What is the special thing about the primary visual cortex involving eyes?

Recorded activity of single cells in cats visual cortex. Identified two types of cells that they categorized based on the types of stimuli required to produce maximum responses.

Describe Hubel and Wiesel's experiment

because they get excited by bar or edge shapes. Have an elongated center - surrounded receptive fields. Simple cells are tuned to bar or edge shapes, a certain width, a certain orientation, and a certain location in the visual field

Why are simple cells called bar or edge detectors?

They proposed that the receptive field of a simple cell is the sum of several LGN neurons receptive field. This allows extraction of information not possible until this point.

What did Hubel and Wiesel propose about simple cells?

Complex cells have larger receptive fields that are also tuned to bar shapes, and a certain axis of orientation. BUT with complex cells, the precise position of stimulus in the receptive field is less crucial. Movement across the receptive field is a very effective stimulus for certain complex cells - this suggests those cells may be involved in the detection of motion

How are complex cells different than simple cells?

They proposed complex cells receive input from a group of simple cells with same axis of orientation but with slightly offset receptive fields

What did Hubel and Wiesel propose about complex cells?

Hubel said that perception of an evenly lit interior depends on the activation of cells having fields at the borders and on the absence of activation of cells whose fields are within the borders, since such activation would indicate that the interior is not evenly lit. So our perception of the interior as black, white, gray, or green has nothing to do with cells whose fields are in the interior. What happens at the borders is the only information you need to know.

What did Hubel say about simple and complex cells with contours of shapes?

primary visual cortex: columns

cells receiving input from same port of retina grouped together. cells with similar functions group together. simple and complex cells are organized and group together.

orientation specificity

each column has preferred stimulus orientation. Adjacent columns respond best to slightly different orientations.

binocular interactions

first interaction between information from both eyes

in V1

Where do binocular interactions first occur?

binocular - respond to input from either eye. BUT, they have a preferential response to one eye

Most neurons in the primary visual cortex are ____________

ocular dominance

preferential response to one eye by neurons

ocular dominance columns

cells with the same preference to one eye grouped together

blobs

appear to receive direct inputs from Konicellular layers of LGN. involved in analysis of color. cells are not orientation specific - probably not concerned about contour, just hue.

cortical modules

functional units that combine location (retinotopy), orientation columns (form), ocular dominance columns (binocular info), blobs(color). You get a module that can analyze all of the features of a stimulus from a particular area of the visual field from both eyes. Put about 1000 modules together and you get analysis of the whole visual field

visual association cortex

about 20+ cortisol areas outside of primary visual cortex. two different streams of information:

*dorsal stream - analysis of object location and motion

*ventral stream - object recognition

muscle

consists of hundreds of muscle fibers

a single motor neuron axon

Each fiber in a muscle is innervated by _________

No, muscles can only pull. this is why muscles need antagonistic pairs. Involves flexors (pull towards body) and extensors (pull away from body)

Can muscles push and pull?

"lower" motoneurons

ventral horn of spinal cord. axons exit via ventral root. innervate muscle fibers.

motor unit

a motor neuron (alpha) and all the muscle fibers it innervates.

Motor units vary in size.

leg: 1 motorneuron: 1000 + muscle fibers

finger: 1 motorneuron: 3 muscle fibers

small units = fine precise measurements

large units = lots of force

Sizes of motor units

neuromuscular junction

synapse between motoneuron axon and muscle fiber. Action potential in axon causes ACh to release. ACh binds to receptors on muscle fiber. This causes depolarization. Na+ channels open, which causes action potential in fiber. Action potential in the fiber causes sarcoplasmic reticulum to release Ca2+. The Ca2+ release causes muscle filaments to slide together

actin

thin part of filament

myosin

thick part of filament

A single action potential in a motoneuron produces a single twitch of a muscle fiber.

What does a single action potential cause in muscles?

A postsynaptic potential always causes the muscle fiber to fire (and twitch)

What does a postsynaptic potential cause?

extrafusal fibers (work)

type of muscle fiber that is innervated by alpha motoneurons (about 70% of all muscle fibers)

intrafusal fibers (spindles)

type of muscle fiber that is innervated by gamma motoneurons. monitor muscle length and maintain posture and coordinate movement