Neuro Block 2

stimulus detector

stimulus detector

level of sensory processing that converts environmental stimulus to neural signal

initial receiving center

level of sensory processing in CNS that receives input from stimulus detector

integration center

level of sensory processing where information is filtered/processed/integrated from groups of initial receiving centers

primary sensory cortex

level of sensory processing involving perception

stimulus detector units

specialized receptors depolarized directly by environmental stimuli

sensory transduction

conversion of stimulus energy into electrical energy

limbic system

region of brain where smell is integrated through

thalamus

region of brain where all senses except smell are integrated through

occipital lobe

location of primary visual cortex

temporal lobe

location of primary auditory cortex and taste + olfaction limbic cortex

parietal lobe

location of primary somatosensory cortex (touch)

association cortex

located near primary sensory areas, involved in perception, integrating sensory modalities

retina

part of CNS where vision stimulus detector units and initial receiving centers are located; where light energy is turned into neural activity

cochlea

part of inner ear where auditory stimulus detector units are located; energy from pressure waves is transduced into neural signals; hollow structure, filled with lymphatic fluid

medulla

initial receiving center for audition, somatosensation (in addition to spinal cord), gustation, and equilibrium

skin, muscle, joints

where somatosensory stimulus detector units are located

tongue, throat

where gustatory stimulus detector units are located

nose, throat

where olfactory stimulus detector units are located

olfactory bulbs

initial receiving centers for olfaction

vestibular organ

part of inner ear that contains stimulus detector units for equilibrium

somatosensory system

encodes and processes sensory information (touch, pressure, vibration, limb position, heat, cold, pain, itch, etc) from the skin, muscles, and viscera

proprioception

kinesthesia; position of limbs in space

pseudo-unipolar neuron

one single axon with two branches

peripheral branch

part of pseudo-unipolar neuron that extends from the periphery to the cell body

central branch

part of pseudo-unipolar neuron that extends from the cell body to the CNS

somatosensory receptive field

location on the body where a stimulus will affect the activity of a given somatosensory neuron

two point discrimination

the minimum interstimulus distance required to perceive two simultaneously applied stimuli as distinct (higher receptor density = greater discrimination)

dermatome

area of the skin innervated by a single spinal segment

slowly adapting receptors

afferent neurons whose firing rate decreases after stimulus onset, but the decrease is gradual and firing lasts as long as the stimulus is present; conveys static qualities of a stimulus, such as information about the size and shape of a stimulus

rapidly adapting receptors

afferent neurons whose firing rate decreases rapidly after stimulus onset and can stop entirely before the stimulus has ended; signals start of a stimulus, but not continued presence; conveys dynamic qualities of the stimulus such as information about ongoing stimulation (movement)

A-beta-fibers

touch fibers; light touch, pressure, vibration, >22 micrometers, highly myelinated fibers, fast conducting

type I A-delta-fibers

nociceptive fibers for gross touch, fast pain, high heat (>53C), capsaicin-insensitive, 12-22 micrometers, little myelination

type II A-delta-fibers

nociceptive fibers for gross touch, fast pain, low heat (>43C), capsaicin-sensitive, 12-22 micrometers, little myelination

C-fibers

nociceptive fibers for slow pain, low pH, heat, capsaicin-sensitive, <12 micrometers, unmyelinated

somatosensory pathway 1

mechanosensory; fine tactile (touch), pressure, vibration

somatosensory pathway 2

pain, temperature, itch

encapsulated nerve endings (corpuscles)

mechanoreceptors; tip of sensory axon embedded in specialized connective tissue; sense touch, including fine tactile, vibration, and pressure; proprioceptive; in non-hairy skin

Piezo2

channels that convert mechanical signals to electrical signals

Meissner's corpuscles

encapsulated nerve endings closest to skin surface; sense light touch, vibrations of textured objects against skin, and slippage between skin and object (grip)

Merkel cells

encapsulated nerve endings enriched in fingertips and lying in tips of primary epidermal ridges (fingerprints); sensory axons in close contact with a connective tissue capsule within the skin; highest spatial resolution (0.5mm); fine touch

Ruffini's corpuscles

encapsulated nerve endings that sense stretching of skin by deforming sensory axon when skin stretched; sensory axons run through bundles of collagen fibers deep in the skin

Pacinian corpuscles

encapsulated nerve endings with large sensory axons embedded in fluid-filled layers of special connective tissue cells located deep in the skin; sensitive with large receptive fields; respond mainly to high frequency vibration (grasping, picking up, putting down)

muscle spindles

intrafusal fibers stretch and activate (depolarize) afferent sensory neurons, which signal length of muscle and rate of stretch

stretch reflex

muscles contract in response to stretching; sensory afferents signal stretch to spinal cord, where they synapse directly onto motor neurons

Golgi tendon organs

consist of a capsule attached to a tendon on one end and a muscle on the other; single afferent neuron innervates when tension is applied, signaling muscle contraction

dorsal column pathway

carries afferent mechanosensory input (tactile, proprioception) from spine to brain; first synapse at secondary sensory neurons in medulla; decussation level at medulla

decussation

crossing over of neural fibers

somatopy

topical organization of the body's surface sensations within each division of the primary somatosensory cortex (post central gyrus)

cortical plasticity

functional remapping of brain based on experience, "use it or lose it"

pain

unpleasant sensory and emotional experience associated with actual or potential tissue damage (subjective component)

nociception

encoding and processing of noxious stimuli by the CNS and PNS (relative objective component)

analgesia

relief from pain

noxious stimuli

stimuli that are actually or potentially damaging to tissue, including mechanical, thermal, or chemical stimuli; lead to release of a variety of substances that act on nociceptors

free nerve endings

receptor ending of somatosensory neuron that senses noxious stimuli (pain, temperature, itch, etc); tip of sensory axon in cutaneous tissue without anything surrounding it

high-threshold mechanoreceptors

nociceptors that respond to intense mechanical stimulation

chemosensitive nociceptors

nociceptors that respond to chemicals released in response to tissue damage and inflammation and some noxious chemicals that come into contact with skin

thermal nociceptors

nociceptors that respond to extreme heat or cold

transient receptor potential (TRP) channels

ion channels that activate in response to mechanical, thermal, and chemical (in addition to GPCRs) stimuli; influx of calcium and/or sodium causes depolarization

phasic receptors

receptors that produce an initial burst of activity firing but reduce if stimulus maintained

tonic receptors

receptors that produce constant rate of firing for length of the stimulus; most nociceptors

first pain

sharp pain usually in a specific location; short duration; carried by lightly myelinated, small-diameter axons (A delta fibers)

second pain

diffuse pain (dull aching); longer-lasting; carried by unmyelinated, very small-diameter axons (C-fibers)

spinothalamic pathway

carries afferent pain and temperature input from spine to brain; first synapse at neurons in dorsal horn; decussation level where afferent nerve enters spinal cord

referred pain

pain experienced as coming from one location when it is actually coming from a different source; pain caused in an internal organ can be confused by neurons in the spinal cord for pain from a peripheral location on the skin

central sensitization

activity-dependent increase in excitability of neurons in the dorsal horn of the spinal cord following high levels of activity in peripheral afferents

hyperalgesia

a normally painful stimulus is now perceived as significantly more painful

allodynia

a normally innocuous stimulus is now perceived as painful

gate theory

input from large, myelinated touch afferents synapse onto spinal interneurons, which can in turn block input from small, unmyelinated pain afferents

supraspinal mechanism

periaqueductal gray matter can inhibit spinal pain input

massage

high pressure causes large myelinated touch and pressure receptors (A-beta-fibers) to activate spinal inhibitory neurons that "drown out" pain signals from nociceptors

acupuncture

needles move to create steady stream of non-pain impulses by stimulating specific points which affect A-beta-fibers

acute pain

protective; occurs in presence of stimulus or tissue repair following injury

chronic pain

deleterious; occurs without an obvious stimulus or injury; >3mo; migraines, arthritis, fibromyalgia, low back pain, diabetic neuropathy

Mu opioid receptor

targeted by opioids to reduce firing of action potential at primary and secondary afferent and decrease pain signal transmission

optogenics

using light to control a limited population of neurons

Arch

inhibits neurotransmission in the presence of yellow light; could be used to treat pain

photoreceptors

retinal cells that convert light energy into neural activity; rods and cones; graded membrane potential, release Glu, hyperpolarized by light, only one type

lateral geniculate nucleus

part of thalamus that is first synaptic relay in primary visual pathway

light

electromagnetic radiation

high energy waves

gamma and cool colors

low energy waves

radio waves and hot colors

optics

study of light rays and their interactions

reflection

bouncing of light rays off a surface

absorption

transfer of light energy to a particle or surface

refraction

bending of light rays from one medium to another

cornea

transparent outer layer that allows light into eye

sclera

white of eye, opaque; tough protective cover

iris

colored part of eye; involuntary (smooth) muscle forms a ring that contracts and relaxes to control the amount of light that enters the eye

pupil

circular opening in iris where light comes through

lens

bends light as it comes into eye to focus it onto retina

ciliary muscle

smooth muscle that contracts and relaxes to control lens shape

accommodation

contraction of ciliary muscles causes lens to change shape, which focuses an image on retina

myopia

nearsighted; focus is in front of retina; eyeballs too elongated and lens too curved

hyperopia

farsighted; focus is behind retina; eyeball too short and lens too flat

horizontal cells

retinal cells involved in lateral control and mediation of bipolar cells and ganglion cells

bipolar cells

retinal cells that form middle layer of neurons that process visual info; graded membrane potential, release Glu, ON or OFF center cells; perform sign conserving/inverting operation

amacrine cells

retinal cells involved in lateral control and mediation of bipolar cells and ganglion cells

ganglion cells

retinal cells that receive visual input from bipolar cells; axons form optic nerve; generate action potentials, ON or OFF center

fovea

center of retina specialized for high acuity vision; contains more cones

blind spot

location on retina where axons of retinal ganglion cells come together and form the optic nerve; blood vessels enter and exit eyes