Midterm 1 2E03 (regular flashcards)

What is the perception process that turns environmental stimuli into action?

1. Environmental stimulus (light hits apple) 2) Light reflected to eyes and transformed 3) Receptor processes (transduction) 4) Neural processing (signal transmission to brian) 5) Perception 6) Recognition 7) Action (behavioural response)

Neural processing

signals are transmitted to the brain and changed along the way

Transduction

The transformation of environmental energy into electrical energy by sensory receptors.

Sensation

sensory processes detect information from the physical world and transform them into biological signals

Perception

a single unified awareness of a stimulus that in turn arises from the sensation produced by our sensory systems; gives meaning/purpose to the detected sensation

Afferent

towards CNS

Efferent: away from CNS

What is the difference between sensation and perception?

Sensation is the process of detecting stimuli, while perception is the interpretation of those stimuli.

Ligand-gated ion channel

ligand molecule binds, opens channel pore

G-protein coupled receptor ion channel

GPCR activates G protein; leads to signal cascade

stretch/pressure gated ion channel

deformation of membrane causes conformational change

Action potential steps

Na+ rushes in. Adjacent membrane depolarizes to let in even more Na+ (Na+ influx) Neuron recovers by sending K+ out (K+ efflux). Hyperpolarization

law of dynamic polarization

action potentials are only transmitted in one direction

What is the absolute threshold?

The minimum stimulus level required to be registered by the brain as a sensory event.

Synaptic Transmission

1. AP arrives at terminal 2. Depolarization opens voltage gated Ca2+ channels 3. Ca2+ triggers vesicle fusion 4. Neurotrnasmitters diffuse along synaptic cleft, bind to receptors 5. response in post-synaptic cell.

excitatory neurotransmitter

brings membrane potential above threshold, causes firing

inhibitory neurotransmitter

brings membrane potential below threshold, inhibits firing

Bipolar neuron

one axon and one dendrite; sensory

Pseudo-unipolar neuron

peripheral axon and central axon; sensory

Multipolar axon

many dendrites, one axon; motor and interneuron

Peripheral vs central axon

peripheral axon gathers info while central axon extends to spinal cord

Coronal axis

front vs back

Sagittal axis

left vs right

transverse axis

above vs below

rostral vs caudal

rostral is toward nose and caudal is back of head

4 lobes of the brain

Frontal, parietal, temporal and occipital

Gyri

crests of cortical tissue

Sulci

grooves in cortical tissue

cerebral cortex

thin layer covering entire cerebrum; grey matter

White matter

consists of the long axons of neurons that transmit impulses to more distant regions of your brain

Thalamus

relay station for sensory and motor information, except smell

How many cranial nerves

12

Ganglia

local accumulations of neurons and glia in PNS

Spinal/peripheral nerves

31 pairs bundles of peripheral axons sheathed by glial cells

Signal Detection Theory

A theory that takes into account non-sensory factors that can affect signal detection.

Electroencephalography (EEG)

electrical activity via scalp electrodes, roughly locating response; how activity flows through the brain over time

Magnetoencephalography (MEG)

changes in tiny magnetic fields created by electrical flow

Magnetic resonance imaging (MRI)

magnet influences atom spin, energy detected as they return to normal. Provides structural info on soft, water rich tissues

Functional MRI (fMRI)

shows evidence of oxygen demand; blood oxygen level depended (BOLD). indirect measure, with time delay but good for subcortical

Positron emission tomography (PET)

tracer injected into bloodstream (2DG), camera detects emitted radiation from more metabolically active areas. Good for deep strucutres

Efficient coding models

sensory systems become tuned to predicatability in natural environments so they compress redundant info and highlight less predictable bits

Bayesian models

earlier observations should bias expectations for future events. If predictions don’t match inputs than adjust models for future

Who pioneered psychophysics?

Gustav Fechner

Absolute threshold

minimum stimulus required to be registered as a sensory event

Just noticeable difference (I)

how much does stimulus need to change to produce a detectable difference

perceptual equivalence point vs JND

50% vs 75%

Weber’s law equation

delta I = k*I

Weber-Fechner’s Law equation

Sensation (S) = k * log (I)

Power law for Sensation

S = a * I^b

What shape do most stimuli follow (e.g. power law)? what happens to b?

most are logarithmic (b<1) but pain is exponential (b>1)

What is d’ in SDT?

d’ is the measure of a relative sensitivity of different individuals

What is beta in SDT?

criterion, how nonsensory factors may influence judgments

Receiver Operation Characteristic plot

plots false alarms vs hits; for a fixed d’, changing criterion changes pattern of hits and false alarms

Kinesthesia

internal sensation arising form muscles, tendons, joints; informs us of positions and movements of limbs

Epidermis

Outermost layer, protective shield with several sublayers

Dermis

bulk of skin tissue, contains most receptors and nerve endings for touch

How do touch receptors differ? 4x

1. type of stimulation 2. transmission speed 3. rate of adaptation 4. size of receptive field

What type of neurons are touch receptors?

pseudounipolar

Are touch neurons myelinated?

Axons can be myelinated or not

What factors affect speed at which afferent fibres conduct, and how?

axon diameter and myelination; more myelin and larger diameter = faster

Function of A-alpha fibres?

proprioception

Function of A-beta fibres

type of fibers serving mechanoreceptors

Function of A-delta fibres

pain and temperature

Function of C fibres

pleasant touch, pain, temperature and itch

What are mechanoreceptors?

Sensory receptors that respond to mechanical stimulation such as pressure and vibration.

Pacinian corpuscle

fast changes, fine texture perception e.g. mosquito on skin

Ruffini capsule

lateral skin stretch e.g. control of finger position, slippage

Meissner corpuscle

things moving against skin, stable grasp e.g. cup slipping out of hand

Merkel cell

coarse texture, pattern and form perception, fine details; e.g. braille

SAI

Merkel cells

SA II

Ruffini capsule

FA I

Meissner corpuscle

FA II

Pacinian corpuscle

What type of fibres for thermoreceptors?

A-delta and C fibres, lack specialized endings

mechanoreceptor type i

small receptive field

mechanoreceptor type ii

large receptive field

transient receptor potential (TRP)

non-selective ion channel (Na+ and Ca2+); open when heat/cold

What type of fibres for nocireceptors? What’s different

A-delta for sharp intense pain

C-type for pressure, heat/cold, chemicals; longer term throbbing

Acid-sensing ion channels (ASIC)

pain due to pH change (acidity); low O₂

Ligand-gated ATP receptors (P2X)

binding of extracellular ATP

What kind of fibres for pleasant touch?

C-tactile (CT) fibres

What type of fibres for kinesthetic receptors?

A-delta fibres

Case of Ian Waterman

lost proprioception, could not move unless he could see his limbs

Dorsal root ganglion (DRG)

a collection of neuronal cell bodies of sensory neurons, where axons of various receptors converge into a single spinal nerve

Dorsal root ganglion vs dorsal horn

The cell bodies of sensory neurons are located in the dorsal root ganglion, whereas the axons continue into the spinal cord and typically synapse in the dorsal horn

What format is touch pathway encoded in?

Labelled lines

Dermatome

The innervation from a single DRG and its spinal nerve

How many dermatomes are there?

there are 30 in total - 8 cervical, 12 thoracic, 5 lumbar and 5 sacral

What fibres in DCML pathway?

A-alpha and A-beta fibres

What fibres in spinothalamic pathway?

A-delta and C fibres

How is the dorsal horn organized?

somatotopically

DCML pathway vs Spinothalamic (function)

DCML is responsible for precise sensory perception (fine touch, vibration, and proprioception), whereas spinothalamic handles crude touch and the perception of noxious stimuli like pain and temperature

DCML pathway vs Spinothalamic (pathway)

In the spinal cord, the DCML fibers travel in the dorsal columns (fasciculus gracilis and cuneatus) before synapsing in the medulla oblongata, whereas the spinothalamic fibers ascend in the anterolateral spinal cord. 

DCML pathway vs Spinothalamic (decussation)

DCML fibers decussate in the medulla oblongata, while spinothalamic fibers decussate at the level of the spinal cord where they enter. 

What is the difference threshold?

The smallest amount of change in a stimulus that can be detected.

Where is primary somatosensory cortex (S1) located?

postcentral gyrus, in the parietal lobe

Is S1 contralateral or ipsilateral?

Contralateral - each side receives info from the opposite side of the body

How many layers in the cerebreal cortex?

It has 6 layers, with different compositions, input/output relationships; somatosensory info at layer 4

How are detection and 2-point thresholds similar and different?

similar patterns generated by mechanoreceptor size and clarity but face has lowest detection threshold whereas finger has lowest 2-point threshold

What factors affect tactile sensitivity?

sex, age, genetics (autism)