Evolution and Embryonic Development - Neuroscience

Evolution

Lancelet

  • using our ancestor, the Lancelet (amphioxus) we were able to figure out how the brain revolutionized and developed

  • A simple tube known as the notocord started out as a small tube that eventually evolved into the midbrain, hindbrain, and forebrain. (this there proving that humans and the lancelet are common ancestors)

  • The reason why they grew is because they wanted to have more neuron processing power (and numbers) which means we get smarter and more evolved!

  • they also grew because they needed more tactics to escape predators, obtain auditory information, feeding, and mating

Neural networks

  • Neural tract: Bundle of nerve fibers (chain of neurons) that transport messages from one place or another (In the brain or spinal cord - like a messenger highway) - Groups of these Neural tracts are called a neural network (they can analyze and organize messages really fast)

  • A example of a neural network is the corpus callosum because it sends signals from the left and right hemispheres.

  • Dorsal stream: Information gets sent from the occipital lobe to the parietal lobe (Above) Example: You see a tissue box and you try to grab it but you can grasp it→visual deception → “Where/How?”

  • Ventral stream: information sent from the occipital lobe to the temporal lobe (under/below) - Example: helps you recognize and identify objects, you see a tissue box and you know its there but you dont know what it is.→ “What"?”

Medical technology - Neuroimaging

EEG

  • Also known as the Electroencephalogram

  • Used to test the amount of electrical activity in the brain → monitors electrical activity

  • Electrodes are placed on a scalp and measure waves given off by nuerons

  • It can measure brain timing, sleep cycles, and seizure activity

  • has good time resolution (how fast it can track changes and activity in the brain) → high resolution (eeg) means you can see it frame by frame (if you put it together it can flow like a video) while low resolution means you can only see snapshots

  • non-invasive → nothing enters the body (no needles/surgery/etc)

  • not so expensive

  • functional→Sees the function of the brain

  • poor spatial resolution→less detailed map of the brain so its hard to pinpoint anything

  • cant pinpoint anything exact

MRI

  • uses magnets and radio waves to take images of the brain

  • really good at taking images of the brain

  • Shows anatomy of the brain: shape, size, structure

  • structural → shows the structure of the brain

  • no risk of radiation

  • not invasive

  • can get images from every angle → Good spatial resolution

  • Pretty expensive

  • Bad for people with claustrophobia (fear of tight spaces)

  • people with metal implants (ex. Pacemakers) can not do a MRI

  • good for tumors and injuries (sometimes brain bleeds)

fMRI

  • non-invasive

  • Functional ( sees the function in the brain)

  • looks at blood flow and oxygen flow through the brain

  • looks at oxygenated blood

  • shows what brain areas are active during tests

  • good spatial resolution (quality)

  • no radiation

  • slower, expensive, sensitive to movement

PET scan

  • shows brain activity by the chemicals in the brain

  • invasive because RADIATION tracer is injected into a person

  • Functional test

  • Areas that gave more of the radiation tracer means more activity → shows what areas are more active

  • shows brain metabolism

  • shows neurotransmitter activity

  • expensive

  • poor time resolution

  • can detect diseases early

CAT/CT scan

  • A X-ray scan that creates cross sections of the brain

  • Structural

  • faster and used during emergencies

  • like am MRI but faster and use

  • uses radiation

  • less detailed then a mri

  • cheaper

MEG

  • Measures magnetic fields used by the brain

  • neurons create tiny magnetic signals and the MEG picks them up

  • good time resolution

  • painless and safe

  • larger and more expensive then a EEG

  • better spatial resolution

  • limited availability

Embryonic Development

  • A zygote is a fertilized egg which uses the process of mitosis and differentiation to grow

The early stages of economic development

  • Formation and induction: The nervous system begins to form → neural plate forms into the neural tube, induction sends signals to tell cells what to become (specialization)

  • Proliferation: Rapid mitosis, create cells rapidly (neurons and glial cells)

  • Migration: neurons move to their designated locations (aka brain organization), astrocytes guide to final destination, midbrain, hindbrain, and forebrain are formed→ drinking, drugs, radiation and alcohol can effect the migration which could cause disabilities and epilepsy

  • Synapse formation: form gaps, synapses join with other neural synapses, creates neural network, molecular cues tell the growth cones where to connect to, axons need to forma connection so GABA and Glutamate is released to dendrites to create proteins so they could come together and form a synapse, presynaptic (axon) and post synaptic(dendrite) specialize, immature neurons placed near cardiac tissue created acetylcholine while separated cells created norepinephrine

  • myelination: the neurons get myelinated

  • pairing back/pruning/Apoptosis: Neurons without enough tropic factors→(nerve growth factor) (unused or weak) get removed (die)

Formation and Induction

  • There are 3 layers: endoderm, mesoderm, and ectoderm (bacteria)

  • Neural induction allows cells to become specialized.

  • the neural tube forms from the ectoderm (skin) and goes into the mesoderm

  • From the notochord, which is in the mesoderm, sonic the hedgehog signaling molecules go up to tell the cells what to become

  • the order it goes in is: gila→motor→sensory→internuerons→any other cell (ex:Lung cell)

symmetrical vs asymmetrical

  • symmetrical means that when a cell is split, it forms two identical daughter cells

  • asymmetrical means that when a cell is split, it forms one daughter cells and a differentiated cell

Microcephaly

  • caused by asymmetrical division

  • small head

  • caused by protein defects

Macrocephaly

  • big head

  • protein defect

  • symmetrical division

pre synaptic vs postsynaptic

  • presynaptic: releases neurotransmitters by becoming specialized

  • postsynaptic: dendrites create proteins to anchor dendrites and axons together to create synapses

  • improper synapse formation causes autism

  • lost of synapses causes alzheimer’s

  • saltatory conduction is electrical signals leaping down a axon

  • MYELINNATED: White matter

  • UNMYLINATED: Grey matter