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Brain Cell Types

• Neurons transmit electric and chemical signals throughout the body.
• Glia cells support neurons and regulate the chemical content of extracellular space.
• Astrocytes are a type of glia cell.
• Oligodendrocytes and Schwann cells insulate axons.
• More glia exist than neurons in the thalamus, midbrain, brainstem, and cerebral cortex.
• Ependymal cells line fluid-filled ventricles.
• Microglia clean up debris from degenerating neurons.
• Vasculature carries blood, capillaries, arteries, and veins.

Neurons

• Main components include the soma, axon hillock, dendrites (or neurites), and axon terminal.
• The soma contains the cell body, organelles, and nucleus.
• The rough ER and ribosomes in the soma are involved in protein synthesis.
• The smooth ER and Golgi apparatus in the soma handle protein sorting.
• The axon hillock is where action potential is generated.
• Dendrites receive information from other neurons post-synaptically.
• The axon terminal releases signals pre-synaptically at a synapse.

Membrane

• Ions are electrically charged atoms that are important for neural signaling and naturally flow to opposite charges.
• A cell membrane separates ions, which are not permeable to ions.

Ion Movement

• Ions flow from high to low concentration following the concentration gradient.
• Ion channels are selectively permeable to specific ions and span the cell membrane.
• At rest, there is more potassium (K+) inside the cell and more sodium (Na+) outside the cell.
• Higher potassium concentration exists inside cells, and higher sodium concentration exists outside the cell.

Electrical Theory

• Electric charge depends on the balance of protons and electrons in an atom.
• Ions are crucial for neural signaling and follow the opposite charge.
• Positive ions include sodium (Na+), potassium (K+), and calcium (Ca2+).
• Negative ions include chloride (Cl-).
• Electric potential is the energy required to move a positive ion to a positive source.
• Positive ions have more energy near their source but lose energy moving toward negative sources.
• Potential difference refers to the energy charge difference between two locations.
• Current is the movement of charged particles.

Membrane Potential

• Resting Membrane Potential - Neurons voltage across cell membrane.
• Averages -70mV
• Determined by uneven distribution of ions inside and outside the cell.
• The inside is more negatively charged, and the outside is more positively charged.
• RMP is maintained by Potassium Leak Channels.
• [K+] leaks, keeping the inside of the cell negative.

Cell Membrane Channels

• Two main channel types are the Voltage-Gated Ion Channels and the Ligand-Gated Ion Channels.
• Voltage-Gated Ion Channels open at a membrane potential threshold, usually around -45mV.
• Charge changes in the protein subunit cause these channels to open, allowing Na+ to flow into the cell.
• Ligand-Gated Ion Channels open when a ligand or neurotransmitter binds to it, causing shape change opens it.

Channel Outcomes

• Two outcomes when channels open are Depolarization and Hyperpolarization
• Depolarization occurs when the membrane potential becomes more positive.
• Hyperpolarization happens when the membrane potential becomes more negative.

Membrane Potential Threshold & Action Potentials

• Membrane Potential Threshold is typically around -45mV.
• Voltage generates an action potential, initiating action potential propagation.
• This threshold triggers voltage-gated ion channels to open.
• Action Potential is a temporary shift in neuron membrane potential caused by ions flowing in and out of the cell
• It’s an all-or-nothing event
• A spike generates/propagates along multiple axon points; starts at the axon hillock and leaves via axon terminal.
• Membrane potential goes from -70mV to 30mV back to -70mV at each spot.

Phases

• Triggering Event triggers (+), depolarizes cell body
• Positive ions flow into cell body which causes positive charge which triggers [Voltage-Gated lon channels] to open and Na+ enters cell
• Depolarization occurs and [Voltage-gated Sodium Channels] at axon hillock open
• Na+ flows which depolarizes axon at the location and that causes signal to send at the axon terminal
• Hyperpolarization returns cell back to the RMP (-70mV) by taking out (+) from cell and returns to (-)
• [Voltage-gated Sodium Channels] close, so Na+ stops
• More [K+ Channels] open and K+ flows out
• Sodium Potassium Pump Reestablishes [resting membrane potential] against concentration gradient

Neural/Brain Recordings

• Two things that can be recorded from single neurons
• Action Potentials
• Subthreshold Membrane Fluctuations
• Two forms of recordings:
• Intracellular Recordings record activity inside of each cell and Record AP + Subthreshold membrane potentials
• Advantage = High spatial resolution. - Can identify location signal
• Extracellular Recordings record activity near cell and of nearby cells and Record AP + LFPs
• LFP: Sums up the membrane fluctuations of nearby neurons
• Cell that you're closest to = largest AP amplitude
• Further you are from cell - smaller AP amplitude

Extracellular Recording Devices

• Extracellular Recordings records activity near cell and of nearby cells, records action potential + LFPs
• Cells you're closest to - Larger AP; further you are = Smaller AP
• 5 Types of Electrodes Used in Extracellular Recordings:
• Classical Electrode: records a few cells. Has a few microns of metal exposed at the tip.
• Matrix Electrode: many classical electrodes are attached and allows for recordings of subpopulations
• Laminar Probe: shows how [neural activity] differs as you go deeper in the brain
• Utah Array
• Neuropixels Probe records thousands of neurons and Each square of electrode records hundreds of neurons

Electrode Shape & Impedance

• 2 Important considerations for Electrodes:
• Size - Electrode size of [metal contact tip] is important
• Smaller exposed contact tip = smaller brain area sampled= locate stimulus better- Good spatial resolution and Smaller exposed metal contact= smaller brain area sampled. Better localized stimulus Good Spatial Resolution
• Electrode Impedance: How much electrode resists the flow of [electrical current]
• a. High Impedance - Easier to record AP - Small electrode
• b. Low Impedance - Larger electrode tip; Neurons closer to probe have greater action potential amplitude

Neural/Brain Recording Methods

• Neural = brain/cranial
• Neural Recording Methods allow us to measure brain activity
• 3 Neural Recording Methods:
• LFP - Electrical signals in the brain, represent the summed membrane fluctuations of [nearby cells] and High temporal resolution
• EEG
• fMRI

LFP Forms

• 2 forms of LFPs:
• LFP From Extracellular Depth Electrode: Measure the activity of up to 1000 nearby cells and signal comes from neurons close to electrode tip
• LFP From Electrocorticography (ECoG)- Records brain activity using electrodes on surface of the brain
• Typically for epilepsy patients to pinpoint where seizures are and the Signal is generated by the activity of superficial layers in in cerebral cortex

EEG, fMRI

• EEG- Records summed synchronizes activity of neurons that share [spatial orientation] -Primarily records primordial cells in the cortex.
• Advantages - [High] Temporal Resolution which records at it occur and [Poor] Spatial Resolution
• fMRI- Averages neural activity detects changes) in blood oxygen BOLD- -Indirect measure of neural activity by fluctuations in blood oxygen levels (BOLD) -Uses machine mag field to excite hydrogen atoms in body then measure the waves High Spatial Res
• High Spatial Resolution - Locates activity better [spatial orientation]
• Poor Temporal Resolution -Measurements taken every 2 seconds [temporal orientation.]

Neural Recording Methods

• Single unit recordings Records 1 cell and Highest Spatial Resolution
• LFP Records summed act subthreshold fluctuations and High Temporal Resolution
• EEG Records summed synch activity of million cells
• fMRI Measures BOLD and measure in of neuron indirectHigh/spatialRes

Interpretation

• Spike Rate- Neuron spiking is time intervals and Reflects intensity [ temporal orientation.]
• Helps reduce and variability provides stable activity.
• Each interval divided binary code to network.
• Training to know, to predict the category stimuli by response pattern

Recording Summed

Detailed info/ onrate is recorded during a invasive

• LFP subthreshold fluctuation
• invasive/ temporal resolution. Signal activity of
• EEG- the electrical with skull portal, classifier to decode brain. Decode of
• fMRI: blood imaging requires classifier to determine decode.

Neural Prosthesis

• Stable longtime record signals time, to provide, provide.

Brain Organization Terms

• Anterior = front
• Posterior = back
• Dorsal = top
• Ventral = bottom
• Lateral = side
• Medial = middle

Brain Anatomy

• 4 lobes
• Frontal lobe: Involved in decision making
• Temporal lobe: Processes auditory
• Occipital lobe: Processes visual
• Parietal lobe: Processes touch/ special

Brain Structures

Central sulcus -separates parietal frontal, allows to increased by area cortical

• Feedway pathway
• Higher level and info is Anterior along and pathway information post Anterior back Feed forward

Pathways

• Thalamic has a recive that data and sensory
• Thalamic focuses most sensory.
• Thalamic has senses their through using or feedway
• Thalamus information higher cortex a first to recive

Cortex Aeras

• Higher. Are connected feedway
• Top what, are objects
• bottom features each and contributes

Cortex Structue

• Neo six differences sized.
• Has pyramidal exitory. Or
• Layer receives of that cells. Vertically repeat. Info areas

Brain Network & Basal Ganglia

• Subtly movement
• Contribute to selection which help action.
• Circuits regulator voluntary
• Ganglia help by 3 main circuits
• STN = Excite that
• Thalamic movement from movement. By cortex .
• Path and to the cortex
• Cerebral except.

Brain Network Type

• Cerebeller cerebllar cortex
• Receive copies. From
• Motor to epi memory for memories.

Brain Network Features

• Regular-Node and neighbor Fashion
• Random-Info VeryFast short
• Connected brain for types

Brain Activity& Features

• Activity of and high degree each.
• tracer detect axon
• MRI diffusion
• If oscillating areas connected.

Brain Feature Connections

• DTI mapping different hubs via white
• DTI identifying regions through signal

Brain Area Altered

• Areas different regions vision
• Area Disorganized healthy most 44 region, region 37
• Aphasia: Is cellular which critical often taken protein build up
• Coma: area
• Have in Pplsleep

Receptive Maps

• Field
• Area size which respond
• Tells object size
• Big object and recognitions
• Big: recognize detects exists. Can big there Small localized.
• Inter stimuli 1 location can't location there

Neural Environment

• Neirons
• Small: to to sees combination neurons create, which
• Large location nearby

Sensory Field

• Sonatas stimulated touch, touch touch. Small touch is light. Light light there

Receptive Descrptive

• The sensory to from dimension . Location sensory of each.

Receptive Organization

• Each sensory various various identify. Objects, processing there. Visual contains left right. Each cover

Types of Topographic Maps

• Sound in cortex a various areas each
• Bodies a respond touch