Nervous System Structure

The Structure of the Nervous System

• The notion that we only use part of our brain is incorrect; we utilize all neurons actively to some extent.
• Long-term inactive neurons die because of lack of neurotrophic factors.
• The idea that neurons die progressively starting at age 25, leading to significant neuron loss at old age, is primarily incorrect
• Healthy, non-demented elderly individuals experience only limited neuron loss (max 5%).
• Neurogenesis, the production of new neurons, continues in at least three brain regions throughout life, albeit at a low rate, disproving the misconception that no new neurons are born after early brain development.
• Gray matter contains cell bodies, while white matter contains myelinated axons.
• The mammalian nervous system is composed of the central division, encompassing the brain and spinal cord, and the peripheral division, which includes the network of nerves throughout the body.
• The brain's surface features bumps (gyri) and grooves (sulci), which form as a result of the cerebral cortex's extensive surface area expansion during fetal development.
• A fissure is a natural separation in the brain.
• The cerebrum is the largest part of the brain.
  • Its left hemisphere controls the right side of the body.
• The cerebellum controls movement.
  • It controls the ipsilateral side of the body.
• The brain stem regulates vital functions.
• The cerebrum includes the frontal, parietal, occipital, and temporal lobes.
• The Sylvian fissure marks the boundary between the frontal and temporal lobes.
• Phrenology is relating skull size to specific behavioral traits.

Anatomical References

• Adaptations are represented in the species structure and brain function.
• Anterior/rostral points towards a rat's nose.
• Posterior/caudal points towards a rat's tail.
• Dorsal points up in rats.
• Ventral points down in rats.
• Humans have different anatomical references.
• Bilateral symmetry means the right side of the brain and spinal cord mirrors the left.
• Viewing the brain's internal structure typically requires sectioning it.
• Sagittal, horizontal, and coronal planes are the three standard anatomical planes for sectioning.
• The brain is hollow, containing fluid-filled caverns and canals within the ventricular system.
• The ventricular system includes the lateral ventricles, third ventricle, cerebral aqueduct, and fourth ventricle.
• Volume ventricles are about 150 ml.
• Cerebrospinal fluid (CSF) is produced by the choroid plexus at a rate of about 500 ml/day within the ventricles of the cerebral hemisphere.
• CSF flows from the cerebrum's paired ventricles through central cavities in the brain stem.
• CSF exits the ventricular system into the subarachnoid space, where it is absorbed by blood vessels at arachnoid villi
• Hydrocephalus occurs if CSF flow from the choroid plexus to the subarachnoid space is impaired.
• The skull of babies is still soft, the skull will expanse in response to fluid.
• In adults, the brain tissues compresses which leads to impairments.
• Treatment implies draining off the excessive fluid.
• CT scans generate slice images of the brain.
• MRI scans take horizontal and coronal views of the brain.
• PET scans show brain activity for different abnormalities, such as Alzheimer's.
• fMRI scans also show brain activity.

Learning and Memory

• Maximize the use of short-term and long-term memory.
  • Focus and take regular breaks.
• Facilitate the transition from STM to LTM with effective sleep.
• Optimize memory retrieval.
  • Provide a context, forming larger brain networks.
• Reduce unwanted forgetting.
  • Repeat study material reinforcing synapses.

Neurons and Glia

• Neurophilosophy combines Neuroscience with Philosophy; understanding brain cells equals understanding mental abilities.
• Neurons sense environmental changes, communicate them, and command body responses.
• Glia contribute to brain function by insulating, supporting, and nourishing neighboring neurons.
• If the brain was a chocolate chip cookie, the neurons were the chocolate chips, while the space filling cookie dough was the Glia.
• Freshly prepared brain tissue has a uniform cream appearance.
  • Staining is mandatory to see its individual cells.
• Nissl stain: basic dyes that stain nuclei/material surrounding neuron nuclei, distinguishing neurons from glia to study neural arrangement.
• Golgi stain: silver chromate solution makes a small percentage of neurons darkly colored entirely.
  • It shows that neurons have at least two distinguishable parts.
• Neurons consist of neurites (axons and dendrites) radiating from central region (cell body/soma) that contains cell nucleus.
• Golgi believed that neurites of different cells fuse together to form a continuous reticulum, or network.
• Cajal argued against Golgi by explaining that neurites don't fuse , proving the neuron doctrine: neurons communicate by contact , not continuity.
• Cell body gives rise to a single axon, that axon has consistent diameter throughout length, while branches extend at right angles and cover great distances.
• Dendrites usually do not extend longer than 2 mm, and they taper to fine point from cell body.
• Neuronal membrane separates the inside of the neuron.
  • Its protein composition depends on whether it is in the soma, dendrites, or axon.
• The cell body contains the same organelles found in all animal cells.
• The cytoskeleton gives the neuron its characteristic shape.
  • It is composed of the microtubules, microfilaments, and neurofilaments.
  • The cytoskeleton is not static.
• The axon initiates in the axon hillock.
• The axon lacks in ribosomes with no protein synthesis ; all proteins originate in the soma.
• Axons length ranges from less than a millimeter to over a meter long.
  • They often branch (axon collaterals) to reach parts of the nervous system.
• Axon collaterals communicating with same cell is called recurrent collaterals.
• Axon diameter varies affecting speed of electrical signal, the thicker axons make impulse travel faster.
• All axons include an axon hillock (beginning), an axon proper (middle), and axon terminal (end), the last point makes contact with other neurons to pass information creating the synapses connections.
• Terminal arbor are all branches created on their ends with a synapse, the connection point.
• Innervation creates a synaptic contact, and the cell provide Innervation.
• Synaptic vesicles inside the axon contain neurotransmitters.
• The synapse has two sides: presynaptic and postsynaptic.
  • The space in-between is called the synaptic cleft.
• The neurotransmitter synaptic transmission transfers information of another neurons.
• The axon is transferred in electrical impulses, terminal converts it to a neurotransmitter , this chemical is converted back in electrical one .
• All dendrites form a 'dendritic tree' .
• Dendritic branch are covered with thousands of synapses.
• Dendritic spines are specialized structure in dendrites, that are believed to isolate chemical reaction triggered by stimulation, spine structure is sensitive to stimulation features.
• Neurons are classified by the total number of neurites that extend from soma.
  • A neuron with one neurite is a unipolar.
  • A neuron with two neurites is a bipolar.
  • A neuron with three or more neurites are multipolar.
• Classification of neurons is unique to a part of the brain.
• Stellate cells are star shaped, while pyramidal cell are pyramid shape.
• Spiny neurons have dendrites with spines, aspinous neurons do not have spines on dendrites.
• Primary sensory neurons have neurites in sensory surfaces of the body.
• Neurons with axons that form synapses with muscles are called motor neurons.
• Interneurons form connections with just other neurons.
• Golgi type 1 or projections neurons long axons extending from one brain part.
• Golgi type 2 or local circuit neurons, short axons , not beyond cell body vicinity
• Motor neurons release acetylcholine at their synapses and are classified cholinergic.
• Astrocytes fill spaces between neurons, regulating chemical content, neurotransmitter activity, and extracellular concentration.
• Oligodendroglial and Schwann cells, form myelin sheath (layers of membrane) insulating axons, found only in CNS/PNS, interrupted by nodes of Ranvier where axonal membrane is exposed.
• Ependymal cells line fluid filled ventricles, orienting cell migration during brain development
• Microglia : like phagocytes: debris by degenerating neurons.

Intellectual Disability, Alzheimer's Disease, and Brain Organization

• Elaborate dendritic tree is due to the Complexity of synaptic connections which froms over time.
• Intellectual disability is the result of Disruption on the brain development : affects the synaptic conections.
• Low functioning childs have fewer spines.
• Alzheimer's disease: is based disruption of the neuronal cytoskeleton of the cerebral cortex.
• Neurofibrillary tangles in cerebral cortex are likely what causes of Alzheimer related symptoms.
  • The component is paired helical filaments and the protein Tau.
• In Alzheimers's the Tau is hyperphosphorylated and detaches from the microtubules in soma that causes withering axons, impeding information/ normal operation. Abnormal secretion of amyloid which leads to tangle formation then creates amorphus structures called amyloid plaques , this is first step.
• Alzheimer is the result of amyloid-b protein. Early Alzheimer are done by using a test: normal logic combination , normal people makes early , when alzeihmer happens they do' not work because no difference in remembering combination, both alnzeihmer/ normal people have no difference.
  • Alzheimer's starts after age 65, presenile form before 35. Social contacts /stressufl events play , people with Alzheimer's does not die because of Alzheimer but because of complications. Cholinergic system collapse first. Reversible phosphorylation of tau during Hibermation provides an unique open to study of physiological regulation of tau phosphorylation.
• Primitive brains - collection of neurons spread: more sensory input appears on sensory input.
• Bigger : bigger number of nerves: the human number is 40 billion neurons, and 100 billion cells. Larger brains are Energetically is expensive.
• The Mammals have between a brain , low -fat storage , correlate most strong in species with more body weight.
• Few mammals get to combine high storage with large brains, because they do not heavy energy - aquatic /primates as humans have.
• To evolve brain: increase energy intake , and reduce energy allocation.
• Two legs- walking savings energy , human can dealing with food because they are fat in comparison with other primates and evolution /bigger brains are related cognitive skills , neocortex is made sensory motor and associated that contains many of the cortex Neocortex with 6 layers ,less layers is old: now this shrinking body without size in the prefrontal coretex and cerebullum that involves .
• Planning complex complex behaviors, complex personality expression ,decsioins and social behavior. Bigger part involves white matter.