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