Cells and Structures of the Brain (Chapter 1)

Levels of Analysis in Behavioral Neuroscience:

Social level (social interaction) → organ level (brain, spinal cord, etc) → neural systems level (eyes + visual brain regions) → brain region level (visual cortex) → circuit level → cellular level → synaptic → molecular

Structure/History:

Neurons, glial cells, synapse
Structure known thanks to Ramon y Cajal (1852 - 1934) using a camera affixed to a microscope
==The Neuron Doctrine==::neurons are structurally, metabolically, and functionally independent; info is transmitted from neuron to neuron across a synapse

Parts of the Neuron:

==Dendrites==::branches
==Soma (cell body)==::contains info
==Nucleus==::inside the cell body
==Axon hillock:==:signals are computed (like doing math); if the signal is positive enough, the AH will send it along to fire
==Axon==::transmits info thru the conduction zone; can be coated in myelin sheaths (made by glial cells)
==Nodes of ranvier==::gaps b/w each myelin sheath
==Axon collateral==::branching of the axon towards the end, leads to the axon terminal/terminal endings/terminal end bulbs (the neurotransmitter is packaged in the terminal bulbs)
Classes of Neurons: * ==Motor neurons==::synapse on muscle and make them move * ==Sensory neurons==::receive info from enviro, like touch cells - external source and coding * ==Interneurons==::covers actions b/w motor and sensory

Shapes of Neurons:

==Multi-polar==::many dendrite branches
==Bipolar==::one dendritic branch
==Unipolar==::no clear dendritic branches connected to the cell body - these are mostly found in the spinal cord

Synapses:

Key terms: synaptic cleft, presynaptic neuron, postsynaptic neuron, neurotransmitters, receptors
==Synaptic Vesicle==::internal membranes, inside each are packaged NTs - the NTs dock and diffuse across the synaptic cleft to be received by the receptors to bind → the closer the space is/the more receptors there are, the less likely it is for the NTs to float away
==Neural Plasticity==::happens at the level of the synapse - mods made to catch more/less NTs in the synaptic cleft

Glial Cells:

==Oligodendrocytes==::specialized cells in the brain/spinal cord (CNS) that form myelin sheaths around axons (this is their only job) * The more insulation, the faster the neuron → myelin sheaths speed up travel of action potentials
==Schwann cells==::individual cells building myelin for motor neurons; each individual cell has its own nucleus; only in the PNS * MS attacks oligodendrocytes and kills portions of myelin sheathing in the CNS - causes neurons to slow down/not perform properly
==Astrocytes==::control blood flow using their end feet on capillaries; “huggies” around synapses; help for the outer layer of the BBB; thousand of processes from a single cell body
==Radial glial cells==::only during prenatal development, help cell migration
==Tumors==::almost always driven by glial cells (glioma), astrocytes in particular are the worst (astrocytoma)
==Microglial cells==::housekeepers, chomp up debris in brain that shouldn’t be there → if they chomp too much, there is inflammation and swelling (edema)

The Cranial Nerves:

Some are essential for facial movement; several explain the reasoning behind palsies * Human eye controlled by 4 separate cranial nerves * Vagus nerve is perhaps the most important

The Autonomic Nervous System (ANS):

==Sympathetic==::fight or flight, stress response
==Parasympathetic==::existence, “strive to be,” healthy state for the body (homeostasis)

Anatomical Locations of/in the Brain:

==Parietal lobe==::integrates motion w/vision, post central gyrus is responsible for feelings/perceptions of touch * Cortex has 6 distinct layers - can see w/stains under a microscope
==Occipital lobe==::vision
==Temporal lobe==::sound/audio, object memory, ability to recreate images w/missing info, organizes sensory info before it’s used for memory and coding
==Frontal lobe==::pre-central gyrus “motor cortex” - sends signals to muscles for voluntary movement * Supplemental and pre-motor cortex help plan movement (everything posterior to frontal pole = motion; everything anterior to frontal pole = PFC) * PFC - decision making, weigh consequences, consider future - last area of the brain to fully develop (not until mid/late-20s)
==Basal ganglia==::set of structures essential for movement * Caudate nucleus, putamen, globus pallidus, substantia nigra (home of lots of dopamine neurons - dies in Parkinson’s disease)
==Cingulate gyrus==::emotion regulation
==Hippocampus==::learning new things and being able to verbalize them
==Amygdala==::codes emotions as you’re acquiring new experiences * Things that are more emotional signals the hippocampus to work stronger to remember the experience/feeling
==Thalamus==::sensory relay center - sends out info from external world to appropriate cortical structure to deal w/it
==Hypothalamus==::master regulator - all hormones used by entire body
==Corpus callosum==::band of axons that connect the 2 spheres of the brain so they can talk to each other
==Reticular formation==::essential for arousal, regulates sleep signals
==Pons==::bridge b/w cerebellum and cerebrum, home of a lot of cranial nerves
==Medulla==::core region for survival, regulates breathing w/o conscious thought (if damaged via fracture or compression you will die)
==Pituitary gland==::interface b/w hypothalamus and body - allows hormones to go to bloodstream
==Cerebellum==::22% of human brain; responsible for balance/coordination, guides standard gait and precision movements
==Superior and inferior colliculi== * Superior - peripheral vision and reaction * Inferior - unconscious auditory processing and sound from weird angles
==Olfactory bulbs==::sense of smell

Cerebral Ventricles:

Inside and outside of brain bathed in fluid; ventricles hold the fluid
Continuous system carries down thru spinal cord - must flow freely across all domains
==Sub-arachnoid space==::fluid sitting here; thin fibers like a spider’s web to give it form, but also space for the fluid to flow
==Cerebral spinal fluid==::made of salts and sugars * Salts give it buoyancy so we don’t feel the weight of brain/fluid

Glymphatic System:

System to get rid of brain waste - transported through spinal fluid * Sent to other parts of the body to be discarded * Only works during slow wave sleep - about 4 hrs

Arterial Circulation of the Brain:

Brain’s energy comes from blood since it hold nutrients
2 major arteries - vertebral set of arteries along the spinal cord that merge in the basilar artery and the internal carotid arteries tucked deep inside the neck tissues * Come together to form the Circle of Willis (ACA, MCA, PCA)

Stroke:

2 types - ischemic stroke and cerebral hemorrhage * Hemorrhage::artery is hemorrhaging and basically exploded; causes intracranial pressure → loss of consciousness, headache, vomiting * ==Ischemic==::a blood vessel becomes occluded and the blood supply to part of the brain is partially/totally blocked
Blood flow to the brain is suddenly disrupted
Ischemic stroke is most common type of stroke (85-90%)
Cerebral cortex involvement * ==Aphasia==::inability to speak/understand language from involvement of Broca’s or Wernicke’s area * ==Apraxia==::altered voluntary movements * Disorganized thinking, confusion, hyper-sexual gestures (frontal lobe) * Altered vision (occipital lobe) * Memory deficits (temporal lobe) * Hemineglect (parietal lobe)
Cerebellum involvement * Trouble walking, altered movement coordination, dizziness
Prognosis * Disability affects 75% of stroke survivors enough to decrease their employability * Dysfunctions correspond to damaged areas in brain * Coma and death