Chapter 1 Brain Bee: Brain Basics

Chapter 1

Parietal lobe location

at top of brain, immediately behind frontal lobe.

What makes up the Forebrain

structures of limbic system and cerebral cortex

Midbrain location

beneath the thalamus.

What do regions of the midbrain do/what does midbrain include

Has distinct groups of neurons that coordinate eye movements like blinking/focusing, and trigger reflexes to sound (jump when startled by loud noise). Other regions inhibit unwanted body movements and help coordinate sensory input and motor output to manage fine motor control.

Hindbrain

plays role in glucose regulation and sleep and includes some regions that help control movement.

What makes up the hindbrain

pons, medulla, cerebellum

Cerebellum location

tucked under occipital lobe at very back of brain

Pons location

below cerebellum

Brainstem parts

made up of midbrain, pons, and medulla.

What expanded in vertebrates

Regions that could rapidly process visual and auditory information and trigger appropriate escape, feeding, or mating behaviors also expanded in vertebrates.

How does brain turn moving shapes into recognizable characters and scenery.

Process begins with photoreceptors. Once the wavelengths reach the optic nerve, they travel through optic tract to thalamus. There, neurons respond to shape color, or movement of objects and pass signals to primary visual cortex in occipital lobe.

Where do alpha waves originate

Alpha: In awake brain. Originate mainly in parietal and occipital lobes when brain is relaxed and eyes are closed.

Frequency of alpha waves

Frequency from 8-13 Hz.

Frequency of beta waves

14-30 Hz

What are beta waves made by

Typically made by frontal and parietal regions of brain when it processes sensory input or concentrates on a task.

Amplitude ranges of beta

5-10 uV

Amplitude ranges of theta

5-10 uV

Mechanism used to analyze process info

When signals come to a brain region, they engage in local neural circuits (interconnected neurons that turn entering signals into output patterns that can be sent to other parts of the brain).

local neural circuits

interconnected neurons that turn entering signals into output patterns that can be sent to other parts of the brain

Cerebral cortex packed with

neural circuits.

What happens to the signal each time it is fed forward

Each time the signal is fed forward, it is transformed somehow, building outputs that encode complex information.

What percent of neurons are excitatory

Most neurons (80% of them) are excitatory.

In many parts of cerebral cortex, most common type of excitatory neuron is

pyramidal cell

Where does excitatory neuron act

passes signals through a circuit and sends output to other brain parts

Neurons that are normally local and often loop responses back to earlier segments of a circuit are normally

inhibitory.

Interplay between signals in a circuit are important in

learning, tuning, and smoothing signals sent to body and other parts of brain.

How can neurons be organized in a circuit

in different input ways

What happens in feed-forward inhibitory circuit

inhibitory interneurons connect neighboring neural circuits so that excitatory signals in one column simultaneously send inhibitory signals to adjacent columns, reducing their activity.

What happens in feedback inhibition

neurons send signals to their downstream excitatory neighbors and to interneurons that reach back and inhibit preceding layers of the same circuit.

Recurrent neural networks

neurons inside interconnected circuits send feedback signals to one another.

Axon

extension from cell body that may branch before ending in axon terminals. Neuron's electrical signals travel down its axon.

What are the types of glial cells in CNS

astrocytes, microglia, ependymal cells, and oligodendrocytes

Astrocytes

form network in the brain that regulates ion concentrations around neurons, provides them with nutrients, and helps regulate formation of new connections between neurons.

Oligodendrocytes:

improve neuron function by wrapping axons in fatty sheath called myelin.

Ions that enter/leave the cell have what affect on the cell

they change the voltage difference across the membrane. Change in voltage influences the neuron's likelihood of generating an electrical signal.

What is membrane potential affected by

Membrane potential affected by signals arriving from other neurons in its circuit, which can make the membrane potential less negative (depolarized), or more negative (hyperpolarized) by opening ion channels in dendrites.

What makes an action potential

If sum of all signals at dendrite rises to match membrane's threshold voltage, a series of voltage-sensitive ion channels opens automatically triggering an electrical impulse called an action potential

What does action potential do

moves down the axon towards the next neuron in the circuit.

What happens when action potential arrives at axon terminal

voltage change triggers ion channels in the membrane to open. This lets calcium ions flow into cell. When calcium ions bind to packages of neurotransmitter molecules called synaptic vesicles, the vesicles fuse with the cell membrane at the axon terminal and empty their contents into synaptic cleft. Then, pieces of axon terminal membrane cycle back into soma as new vesicles, which are refilled with neurotransmitter molecules.

What do calcium ions bind to

bind to packages of neurotransmitter molecules called synaptic vesicles

What are types of substances that are neurotransmitters

Amino acids, gases, small organic chemicals, and short peptides.

Where can non-peptides be synthesized

in axon terminal

Examples of non-peptide neurotransmitters

dopamine and acetylcholine

How are peptide-based neurotransmitters built

Axon terminal doesn't have molecular machinery for building proteins, so peptide-based neurotransmitters are built in ribosome-rich space of cell body. Vesicles with neurotransmitter "cargos" bud off from wall of Golgi apparatus, then bind to proteins called kinesins that work their way down the axon along microtubules.

microtubules

filamentous parts of the cellular skeleton

After neurotransmitters are released from axon terminal, what do they do

they drift across synaptic cleft until they reach the outer surface of dendrite (region that looks thick or dense in highly magnified images). This region - postsynaptic density - has a high concentration of neurotransmitter receptors.

What do neurotransmitters do in postsynaptic neuron

Receptors are linked to ion channels so that when neurotransmitter molecules dock on their receptors, they open those channels, changing the voltage across postsynaptic membrane.

How do neurotransmitters change voltage across postsynaptic membrane

Receptors are linked to ion channels so that when neurotransmitter molecules dock on their receptors, they open those channels, changing the voltage across postsynaptic membrane.

What do ionotropic receptors do

Channel is normally closed, but when receptor protein changes shape when neurotransmitter attaches, tunnel in center of ion channel widens so that ions can move through.

Metabotropic receptors

receptor and ion channel are different proteins located at a distance from one another, but they are linked by a cascade of biochemical steps that are triggered when a neurotransmitter binds to the receptor. Result may be opening an ion channel some distance away or activating other intracellular molecules. Neurotransmitter molecules only bind to their receptors for short time. Once they detach, the ion channels return to their resting state and stop changing charge across membrane.

Excitatory neurons make what

make neurotransmitters that open ion channels that depolarize the dendrite's membrane.

Action of AMPA receptors

When activated, action of AMPA receptors are fast and brief

What does GABA bind to

Binds to ionotropic receptors and metabotropic receptors.

Ionotropic GABA receptors have what

have ion channels that let negatively charged chloride ions enter the cell.

Metabotropic GABA receptors do what

open ion channels that release potassium ions.

What happens with action of any GABA receptor

In both cases, ion movement pushes membrane potential downward and inhibits a neuron from firing.

Neurons have receptors for what

many molecules that can change how they function.

Molecules that neurons have receptors for:

hormones, neuromodulators, prostaglandins,

Example of neuromodulator

endocannabinoid

Neuromodulators

a messenger released from a neuron in the central nervous system, or in the periphery, that affects groups of neurons, or effector cells that have the appropriate receptors.

If receptor is on surface of cell, what do they do

If receptor is on surface of cell, bound molecule changes receptor's shape across the cell membrane and starts a chain of intracellular reactions. This signal transduction pathway ultimately modifies neuronal function, either by shifting the cell's ion balance or by changing the activity of specific enzymes.

Molecules that can diffuse through cell membrane

steroid hormones like estradiol or cortisol

In cell membranes, neurons have different combos of receptors that can do what

capable of detecting neuromodulator that influence neuronal behavior (ex: hormones like vasopressin, estradiol, or cortisol)

Hormones that can influence neuronal behavior examples

hormones like vasopressin, estradiol, or cortisol

Each cell type builds proteins from what

from a slightly different subset of genes in its genetic code.

Mechanics causing neurons to express some genes and not others

This is area of intense research. Many mechanisms depend on chemical changes to chromatin (complex of protein and DNA that compactly packages the long DNA molecule inside the nucleus).

Chemical changes that tighten chromatin complexes do what

shut down the genes on that DNA segment

Chemical changes that spread out chromatin complexes do what

activate the genes on that DNA segment

What is Tay-Sachs caused by

caused by mutations in a gene that codes for part of a fat-metabolizing enzyme called beta-hexosaminidase A.

Ex of neuron structure and function variants

Tay-Sachs

What is Tay-Sachs

fatal degenerative neurological condition - caused by mutations in a gene that codes for part of a fat-metabolizing enzyme called beta-hexosaminidase A. Bc variant enzyme is poor at breaking down specific fats, these build up in neurons and become toxic.

Parietal lobe function:

Integrate sensory signals from skin, process taste, and process some types of visual info.

What does limbic system include

Hippocampus, Amygdala, thalamus, hypothalamus

Basal Ganglia function

helps regulate complex body movements.

Pons function

Influence breathing and posture.

What appeared as the hindbrain

cerebellum

How did hindbrain develop over time

Cerebellum appeared as hindbrain and expanded regions that control escape movements and orient the body. Both functions are more important to fish than a sedentary lancelet buried in the sand.

What formed cerebral hemispheres

Over time, new types of neurons made forebrain balloon out, forming cerebral hemispheres.

Amplitude ranges of alpha

20-200 uV

Spinal tracts

chains of neurons that pass signals through brainstem and spinal cord. Signals either travel upward from sensory receptors in skin and muscle to thalamus and parts of cortex that interpret touch and pressure, or they travel down from brain parts that induce movement, passing from medulla and spinal cord before projecting to body's muscles.

Networks that loop hippocampus into sensory cortex pathways help

brain analyze whether environmental signals are familiar or part of new situation.

Related networks linking hippocampus to thalamus and hypothalamus allow

memory to influence conscious behavior and unconscious physiological responses.

Reflex loops

circuits eliciting action well before thoughts. Actions are controlled locally by info going in and out of spinal cord or subcortical regions of brain, and never reach the cortex.

How are neurons organized in cerebral cortex

into stacks of distinct layers that span thickness of cortex like shelves in bookcase.

What does each neuron form connections with

each neuron forms connections with cells in layers above and below

What do neurons in a column form

Neurons in a column form a single chain, and signals that enter the circuit travel down that chain from one neuron to the next.

What percent of neurons are inhibitory

20%

How many sets of branched dendrites in each pyramidal cell? Where is it

Each pyramidal cell has 2 sets of branched dendrites (one set at apex and another set of shorter dendrites at the base) that collect signals from neurons in every layer of the cortex.

Multi-branched axon does what

Multi-branched axon sends single electrical to multiple destinations

Neurons that pass signals forward through circuit and eventually send outputs to other parts of brain are normally

excitatory.

Where do inhibitory neurons act

normally local; often loop responses back to earlier segments of a circuit

What may seizure disorders like epilepsy be caused by

imbalance in activity of excitatory and inhibitory neurons.

Neuron organization affects

how a circuit manages information.

Examples of recurrent neural networks

feedback inhibition system and feed-forward inhibitory circuit

Functional unit of neural circuits and networks

neuron

Dendrites

branched projections that extend from cell body and collect incoming signals from other neurons.

What do neuron's electrical signals travel down

axon

Axon terminal

where the signal is passed across a synapse to other cells.

Glia

support cells that neurons are associated with.

Why is previous belief of glia outnumbering neurons questionable.

Recent studies say that in some regions of the brain of humans and other primates, ratio is closer to 1:1. However, ratio of glia: neuron differs greatly between regions.