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

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