neurobio exam 2

proprioception

sense position/movement of body parts, part of somatic sensaton

interoception

sense of internal organ function, part of somatic sensation

mechanoreceptors

convert mechanical force to neural skin

Pacinian corpuscles

mechanoreceptors in the dermis, large and less sensitive, have swelling around axon terminals that protect center axon from indentation=fast adapting, slower, smaller response, response best at 300 Hz

Merkel’s disks

mechanoreceptors in epidermis

Meissner’s corpuscles

mechanoreceptors in dermis, small and more sensitive, response best at 50 Hz

receptive field

region of sensory surface when stimulated, changes membrane potential of a neuron

mechanosensitive ion channels

convert mechanical force to receptor potential of mechanoreceptors, could open due to force on membrane or extracellular structures OR force on cytoskeleton (pulling on cytoskeletal protein)

adaptation and receptive field size of different skin sensory receptors

rapid and small: meissner

rapid and large: pacinian

slow and small: merkel

slow and large: ruffini

Piezo 1 and Piezo 2

mechanosensitive non selective cation channels, important for touch sensation, trimer opens/closes to let Ca2+ and Na+ through when mechanical force exerted upon it

Cre/Lox 9 gene knockout

Cre is a recombinase that can cut DNA between 2 Lox P sites it recognizes—from bacteriophage; can be used in vivo, used to study gene function; study in mice by crossing homozygote mice to get ride of the gene

markel cells and piezo 2

markel cells require piezo 2 to transduce mechanical stimuli into electrical signals

primary afferent axons definition

axons bringing info from somatic sensory receptors to the spinal cord or brain stem

primary afferent axon types

A alphas: proprioceptors of skeletal muscle

A B: mechanoreceptors of skin

A (partial charge :( ): pain and temp

C: pain, temp. itch

(get thinner as go down)

A B

touch sensitive axons in spinal cord

spinal segments

cervical, thoracic, lumbar, sacral (going down)

dermatomes

area of skin innervated by the right and left dorsal roots of a single spinal segment

sensory map

one to one correspondence between spinal segments and dermatomes

somatotopy

the topographic organization of somatic sensory pathway in which neighboring receptors in skin feed info to neighboring cells in target brain structure—helps find where touch is happening

the homunculus

a sensory map for touch sensation: mapping of body surface onto primary somatosensory cortex; NOT proportional

nociceptors

pain receptor neurons; most are polymodal

3 types of nociceptors:

mechanical, thermal, and chemical

nociceptor activation

ion channels can be opened by

1. strong mechanical stimulation, extreme temps, O2 deprivation, or chemicals

2. substances released by damaged cells- proteases (bradykinin), ATP, K ion, OR histamine

capsaicin

temp sensation, activates cloning of TRPV1, which responds to both hot peppers and high temp

1st and 2nd pain are caused by ____ afferent fibers

different—A (partial charge) then C

transient receptor potential (TRP) channel family

cation channels that can be activated by various stimuli (chemicals, light, temp)

TRPV1: hot and capsaicin; enables hot sensing

TRPM8: cold and menthol; enables cold sensing

hyperalgesia

heightened sensitivity to pain

thermoreceptor TRP channels

hot and cold of varying sensitivities

2 major ascending pathways of somatic sensations

1. dorsal column: touch

2. spinothalamic pathway: pain and temps

-cross midline at diff places=brain senses feeling from opp side of body

visible light range

400-700 nm

structure of eye

eye collects light, focuses on retina, and forms image

retina

where we process light; laminar organization (seemingly inside out layers); light passes through ganglion cells and bipolar cells before reaching photoreceptors

fovea

thinnest part of retina

photoreceptors

convert light to neural signals, 2 kinds—cones and rods

cones

day time vision, color, less sensitive to light, 3 types

rods

night time vision, black and white, more sensitive to light, 1 type

central retina

the fovea, almost all cones, highest visual acuity

peripheral retina

higher ratio of rods, more sensitive to low light

rhodopsin

GPCR; light sensor in rods

retinal

vitamin A derivative that is light sensitive and serves as a cofactor for rhodopsin—changes configuration (cis to trans) when hit by light= activate rhodopsin through conformational change=cascade in photoreceptors for potential

rods in light

light activates GPCR; transducin (g protein) is stimulated); PDE activated; PDE reduces cGMP by hydrolyzing; Na+ channels close=cell repolarizes (cell is off); release of Glu is decreased = RODS HYPERPOLARIZED

rods in dark

cGMP is not hydrolyzed because PDE is not activated; Na+ ions move in= RODS DEPOLARIZED (dark current)

duplex retinal

2 complementary systems in the eyes—rods and cones

scotopic condition

night lighting; rods contribute to vision

photopic conditions

day lighting; cones contribute to vision

mesopic conditions

indoor lighting; both rods and cones contribute

phototransduction in cones

3 cones:

1. blue: short wavelength, blue cone opsin (S opsin)

2. green: medium wavelength, green cone opsin (M opsin)

3. red: long wavelength, red cone opsin (L opsin)

rod has ___ opsin: _____, and cones have ___

1; rhodopsin

3

central visual pathway

photoreceptors in eyes—other retinal neurons—LGN (lateral geniculate nucleus)—visual cortex

vertical pathway of retina cells

direct path; 1. gangion: excitatory 2. bipolar: excitatory or inhibitory 3. photoreceptors

indirect path of retina cells

modulates retinal processing in direct path by lateral connections: 1. amacrine: receive input from bipolar, project to bipolar, ganglion, and amacrine 2. horizontal: receive input from photoreceptors and provide inhibitory feedback signals

only retinal neurons that fire AP—all others produce graded changes in membrane potential

ganglion

flow of visual info flows which way in retina

indirect path—>vertical path

light flows which way in retina

vertical path—>indirect path

receptive field

area of retina where light changes a neuron’s firing rate

how is AP of ganglion cells used to relay visual info to brain

neural computation

on center/off surround retinal ganglion cell

neuron’s activity highest when light is on in center and off in surround

off center/on surround retinal ganglion cell

neuron’s activity is lowest when light is on in center and off in surround

why are 2 diff kinds of antagonistic RGCs important

contrast—seeing black vs white

see where edges are

to explain diff center surround receptive fields for RGCs

-ON center or OFF center— nature of synapse between center photoreceptor and bp cell in direct path

-for antagonistic center/surround receptive fields: lateral inhibition via horizontal cells in indirect path

the synapse between center photoreceptor and bp cell determines

if receptor field of bp cell is on or off center

excitatory and hyper

off center

inhibitory and de

on center

lateral inhibition

inhibitory neurons project laterally to inhibit each neuron’s neighbor; sharpens differences between neighboring neurons

parallel info processing

-enabled by diverse retinal cell types and precise connections

-simultaneous input from 2 eyes—input compared in cortex, determine depth/distance, info on light/dark, info on color

why do center and surround have opp rxns to light

horizontal cells create surround part and inhibit center

retinofugal path

visual path from eye to brain: retina; optic nerve; optic chiasm; optic tract; LGN; optic radiation; primary visual cortex (V1)

where do ganglion cell axons from the nasal retina cross? what does this cause?

optic chiasm; means temporal retina projects to ipsilateral (same) side and nasal retina projects to contralateral side (opposite) side

decussation

crossing of a fiber bundle from 1 side to another

retinotopy

topographic organization of visual pathway in which neighboring cells in retinal send info to neighboring cells in target brain structure—creates sensory map for visual pathway: provide spatial info of visual field

anterograde tracing

identify neural connections from the source (cell body) to point of termination (synapse)

retrograde tracing

identify neural connection from point of termination (synapse) to origin (cell body)

left and right eye projections are ___ when they reach LGN and primary visual cortex

segregated by eye and RGC type

LGN layers

-in all primates: all layers are monocular= each neuron only responds to light in 1 eye

**layer 1 is outermost, layer 6 is innermost

-layers 2,3,5: from ipsilateral eye

-layers 1,4,6: from contralateral eye

-layer size: 1 and 2: larger neurons, 3-6: smaller neurons

types of RGCs

1. M (magnocellular) type: 5%, larger receptive field; 1/2; transient response

2. P (parvocellular) type: 90%, smaller receptive field; 3-6; sustained response

3. nonM-nonP: 5%; koniocellular

striate cortex is the

primary visual cortex AKA area 17, receives and processes visual info

receptive fields of LGN neurons are ____ to ganglion cells that feed them

almost identical

striate cortex

also layered, 4—>2/3—>5/6, not really layers but alternating bands—ocular dominance columns

most LGN neurons project to layer ___ of striate cortex

4- M to layer IVCa and P to IVCB

a few LGN neurons project to layers ____ of striate cortex

2 and 3: koniocellular LGN axons make synapses primarily in layers II and III

physiology of layer IVC neurons in striate cortex

monocular, one receptive field from one eye

where are first binocular neurons found

layer III of striate cortex, then others in layers superficial to IVC are binocular

intra cortical connections in striate complex

some cortical neurons project locally to deeper or shallower layer, “radial” connections—est. columns of interacting neurons, others project sideways=horizontal connections

binocular receptive fields

orientation (neuron fires AP depending on orientation of light in visual field=analyze object shape) and direction selective (neuron fires AP depending on movement of bar of light=analyze object motion), input from both eyes

vertically adjacent cortical neurons tend to have similar _______ selectivity= ______

orientation; orientation-selective columns

simple cells

binocular, orientation selective, elongated on or off center flanked with 1 or 2 antagonistic surrounds

complex cells

binocular, orientation selective, on AND off responses with no distinct on and off regions

cytochrome oxidase blobs

-cytochrome: enzyme used for cell metabolism

-blobs: cytochrome oxidase-stained pillars in striate cortex, each 1 centered on an ocular dominance column in layer 4

-receive koniocellular inputs from LGN

blob receptive fields

monocular, no direction selectivity, likely orientation selectivity, specialized for analysis of object color

cortical module of striate complex

each module is capable of analyzing every aspect of portion of the visual field

sensory system of NS

stimuli—>transduction—>sensory neuron activity—>input

motor system of NS

CNS—>motor neuron—>muscle activity—> output

muscle contractions

-can be antagonist (against) or synergist (with) to each other

-muscles PULL dont push

lower MNs

-located in ventral horn

-2 types

1. alpha MN: directly trigger muscle contraction through force; synapse attached to normal muscle fibers

2. gamma MN: indirectly modulate force; synapse to modified muscle fibers (intrafusal fibers)

neuromuscular junctions

chemical synapses between MNs and muscle

muscle is made of

actin (thin filament) and myosin (thick filament)—>sarcomeres—>myofibril—> muscle fiber—> muscle

sliding filament model of muscle contraction

Ca2+ binds to troponin=myosin head binds to actin=myosin moves=filaments slide

**z lines further apart when muscle is relaxed

muscular excitation-contraction coupling

MNs excited=release ACh=large EPSP=muscle AP=Ca2+ release=Ca2+ bind to troponin=myosin binds to actin and slides, then EPSPs ends and resting potential returned to and Ca2+ is reuptaked by sarcoplasmic reticulum

motor unit

1 MN and all muscle fibers it innervates; elementary component of motor control, 3-1000 muscle fibers per motor unit; 3 types—fast fatigue, fast fatigue resistant, and slow

each MN can innervate ____ muscle fibers, but muscle fibers are each only innervated by ___ MN

many; 1