BIOPSYC CH 4

When in embryonic development do/does:

• Neurons develop: The CNS begins forming when the embryo is about 2 weeks old. The neural tube forms and eventually develops into the brain and spinal cord.

• Neurons multiply: New neurons/cells are produced, primarily early in life. Cells lining the ventricles divide, producing more neurons than will ultimately survive.

• Neurons migrate: Newly formed neurons move to their eventual locations. Some neurons don't reach their final destinations until adulthood.

• Neurons form synapses (“synaptogenesis”): Synapses form between neurons. This is described as the final stage of neural development, but synapses continue forming throughout life.

• Synaptic connections prune: When axons initially reach their targets, they connect with several cells. Some connections are strengthened while others are eliminated.

• Synapses reorganize: The brain can reorganize itself in response to experience. Gaining and losing dendritic spines represents the formation and loss of connections.

• Myelination occurs: Glial cells produce a fatty sheath around some axons. It begins in the spinal cord, then progresses to the hindbrain, midbrain, and forebrain. It continues gradually for decades.

What is a gene, and how does it relate to chromosomes?

• a unit of heredity that maintain their structural identify from one generation to another; 1 gene = enough DNA to code for 1 protein

• More accurately, genes are sections of DNA, and chromosomes are strands of DNA containing many genes.

DNA

• DNA = Deoxyribonucleic acid

  • Double-stranded molecule

  • Serves as the template for RNA

  • Contains genetic information.

RNA

• RNA = Ribonucleic acid

  • Single-stranded chemical

  • Codes for proteins.

Transcription

• DNA → RNA = transcription

  • A section of DNA is used as a template to make RNA.

• RNA → protein

Chromosomes

• Sex chromosome differentiation for female vs. male

  • Female = XX

  • Male = XY

• Mother always contributes an X

• Father contributes either X or Y

  • X from father → XX, Y from father → XY

Autosomal vs. sex-linked genes

• Autosomal genes

  • All genes except sex-linked genes

  • Located on the non-sex chromosomes.

• Sex-linked genes

  • Genes located on the sex chromosomes

  • Usually refers to X-linked genes

  • Example from the slides: red-green color deficiency.

Epigenetics

• changes in gene expression without changing the DNA sequence.

  • Genes don't directly produce behaviors.

  • Genes produce proteins that increase the probability that a behavior will develop under certain circumstances

Determinants of neuronal survival

• What is released by surrounding cells to promote neuron survival?

  • Neurotropins are chemicals that promote the survival and activity of neurons.

• What happens to axons that fail to find a target?

  • Axons that are not exposed to neurotropins after making connections undergo apoptosis – a preprogrammed mechanism of cell death

Neurotropins (e.g., nerve growth factor)

• NGF

  • NGF is a type of protein

  • Released by muscles

  • Promotes the survival and growth of axons.

Plasticity

• Plasticity = the brain's ability to reorganize itself in response to experience.

  • ex: practicing a skill can cause the brain to reorganize to support that skill.

  • ex: Focal hand dystonia (“musicians' cramp”)

    • Fingers become clumsy

    • May fatigue easily

    • Can make involuntary movements

    • Extensive brain reorganization causes touch responses for different fingers to overlap.

Phantom limb syndrome

• What is it and what is its cause at the neural level?

  • Phantom limb: The continuation of sensation from a body part that has been amputated.

    • A person may feel like the missing body part is still there, even though it physically isn't.

  • When a body part is amputated, the original axons degenerate. This leaves vacant synapses in the brain. Other axons sprout into those vacant synapses. The cortex reorganizes itself and becomes responsive to other parts of the body. Because the brain's sensory representation has changed, stimulation of another body part can sometimes produce a sensation that seems to come from the missing limb

Ischemic vs. hemorrhagic stroke (and the difference treatments for both)

• ischemic - Blood clot or obstruction blocks an artery, Neurons lose their oxygen and glucose supply, Most common type

• hemorrhagic - An artery ruptures, Neurons are flooded with excess blood, calcium, oxygen, and chemicals, Less frequent type

• both cause edema (accumulation of fluid on the brain)

• treatment differences - blood thinners for ischemic to remove and restore flow and hemorrhagic focuses on controlling the bleeding and reduce pressure

Axon/collateral sprouting vs. denervation supersensitivity

• axon: New branches form from undamaged axons and attach to vacant receptors/synapses. grows new connections

• denervation: After an incoming axon is destroyed, the postsynaptic neuron becomes more sensitive to the neurotransmitter. occurs at dendrites and can have consequences like chronic pain

Know stages and steps of processes of development of neurons

• proliferation - production of new cells/neurons in the brain primarily occurring early in life

  • Far more neurons are produced than will ultimately survive

• migration - the movement of the newly formed neurons and glia to their eventual locations (some don’t reach their destination until adulthood)

  • Occurs in a variety of directions throughout the brain

• differation - forming the axon and dendrites that gives the neurons its distinctive shape.

  • The axon grows first either during migration or once it has reached its target and is followed by the development of the dendrites

• myelination - The process by which glia produce the fatty sheath that covers the axons of some neurons

  • First occurs in the spinal cord and then in the hindbrain, midbrain and forebrain

  • Occurs gradually for decades

• synaptogensis - the formation of the synapses between neurons

  • Occurs throughout the life as neurons are constantly forming new connections and discarding old ones

  • Slows significantly later in the lifetime