Final Exam pre Midterms Flashcards
Split Brain Surgery
Done to alleviate epileptic seizures. Sever the corpus callous. The hemispheres can’t communicate directly with one another. Coordinated movement is still possible thanks to the brainstem and spinal cord.
Corpus callosum
The bundle of white matter tracts connecting the left and right hemispheres.
Cerebral Hemispheres
Consciously process sensory information and initiate purposeful movement.
Lateralized function of cerebral hemisphere
Left brain:
- Control of muscles on right half of the body
- Couple language comprehension, speech, writing
- Processing right half of visual field
Right brain:
- Control of muscles on left half of the body
- Limited language, small ‘dictionary’
- Processing left half of visual field
Vision and the Hemispheres
When focusing on a fixation point, vision is divided into a left and right visual field:
The left visual field is processed by the right half of each eye. The right visual field is processed by the left half of each eye.
Nasal half of visual information (half closer to the midline) crosses over at the optic chasm.
Left hemisphere of brain processes right visual field. Right hemisphere processes left visual field.
Gazzaniga’s Interpreter Theory
In experiments with split brain patients, researchers give a visual command to the nonverbal right brain. Then ask the patients to verbally explain why they had done that thing. The left brain would create a story to explain the behaviour. Gazzaniga theorized that this is how unified conscious experience arises. Our behaviour is out of our control (no free will). The left brain develops a meaningful narrative through which we can understand our experiences.
Atoms
Every element is a type of atom. Atoms can and to form molecules. If an atom or molecule has a charge, it is an ion.
CHNOPS
Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur
The CHNOPS elements form 5 main molecules
Water, sugar, fat (lipids), nucleic acids, amino acids.
RNA
Single stranded chain of nucleic acids. Fragile. Ribozymes: Subgroup of RNA that catalyze chemical reactions. Thought to give rise to first life on Earth.
DNA
Double stranded chain of nucleic acids. Stable. In eukaryotes, stored safely in the nucleus. Primary storage of genetic info today.
Cell membrane
Phospholipid bilayer. Hydrophilic (water loving) phosphate head. Hydrophobic (water hating) lipid tail. The structure makes diffusion across the membrane difficult - a good thing if you want an enclosed cell.
Prokaryotic Cells
Single cell organisms. Cell membrane filled with cytoplasm (salty, nutrient filled liquid inside a cell). DNA, RNA, and ribosomes floating around.
Eukaryotic Cells
Single- or multi-cell organisms. Contains organelles like mitochondria and nucleus. Can now store DNA and create energy.
Protein Synthesis
- A segment of DNA in the nucleus is unraveled and a complementary strand of RNA is created (mRNA) - Transcription.
- mRNA leaves the nucleus
- Ribosome latches onto mRNA, recruits tRNA to bring in complementary amino acids - Translation.
- Amino acids are added to a growing chain that eventually breaks off and folds into a protein.
What is a neuron
A specialized type of cell that is electrically excitable. Neurons send electrical and chemical signals that permit fast communication.
Reticular Theory (Golgi)
Believed that the brain was a physically connected network
Neuron Doctrine (Cajal)
Believed that the brain was composed of individual cells communicating.
Soma
Cell body. Location of the nucleus and other organelles.
Dendrites
Sites for receiving chemical or sensory input.
Axon
Electrical signals (action potentials) are sent down the axon. Only one axon, but that axon can branch many times.
Axon terminals
End of axon, where the action potential triggers the releases of neurotransmitter.
Phospholipid Bilayer
Cell membrane. Ions cannot move across it. Hydrophilic (water loving) phosphate head. Hydrophobic (water hating) lipid tail. Inside: Cytosol (salty like solution filled with potassium, chloride, and sodium).
What makes a cell specialized?
All cells within an organism have the same DNA. Not all cells read the same sections of DNA. A section of the DNA (the gene) codes for a certain protein (strings of amino acids). Other sections of DNA define what cells should read the gene and when. Neurons are filled with proteins that determine the cell’s role.
How do neurons communicate - Electrically
Relies on membrane potential (Vm = difference in charge between inside and outside of cell). Within a cell.
How do neurons communicate? - Chemically
Relies on neurotransmitter release from axon terminal onto other neurons. Between cells.
Ions
Molecules carrying electrical charge.
Cations (+): Na+, K+, Ca2+, Mg+
Anions (-): Cl-
Setting the Resting Membrane Potential
Inside: 0mV
The outside (extracellular space) will always be 0 mV; it is the baseline against which we compare the cell’s internal charge.
Sodium Potassium Pump
Sets the concentration gradient (difference in amount of an ion present in one area vs another); sends Na+ out of cell, K+ into cell. Sets resting membrane potential.
What determines where ions want to go?
Diffusion: Ions want to be spread out from other like ions. If many of the same ions are close together (e.g. all within the cell), there is a pressure to spread away.
Electrostatic force: Ions want to be spread out from similarly charged ions. Opposite charges attract, similar charges repulse.
Potassium Leak Channel
Allows K+ to move freely in / out of cell; K+ leaking out sets negative Vm (-70mV). Sets resting membrane potential.
What starts an action potential?
We now have a negatively charged cell - positive ions want to come in because of electrostatic pressure. Sodium ions also want to come in to move down the concentration gradient. Some depolarizing stimulus (e.g., neurotransmitters released from another cell, sensory stimulus), then receptor binding opens ion channels, allowing initial influx of Na+.
Voltage-Gated Sodium Channel
Opens when the cell is slightly depolarized (-40mV); ball and chain blocks pore, inactivates channel after opening. During action potential.
Voltage-Gated Potassium Chanel
Opens during the upswing of the action potential (0mV); responsible for the return to baseline Vm. During action potential.
Action Potential Stage 1 - Baseline
Vm: -70mV
What’s Happening: Na+/K+ pump changes ion concentrations; K+ leak channel brings K+ out.
Diffusion: Na+ wants in, K+ wants out.
Electrostatic Force: Na+ wants in
Action Potential Stage 2 - Stimulus
Vm: -40mV
What’s Happening: External input depolarizes cell; a few VG Na+ channels open.
Diffusion: Na+ wants in, K+ wants out.
Electrostatic Force: Na+ wants in
Stage 3 of Action Potential - Upswing
Vm: Increasing towards peak
What’s Happening: Tons of VG Na+ channels open: VG K+ channels begin to open
Diffusion: Na+ wants in, K+ wants out.
Electrostatic Force: Na+ wants in, K+ wants out
Stage 4 of Action Potential - Peak
Vm: +40mV
What’s Happening: VG Na+ channels are plugged by ball and chain; VG K+ channels still opening.
Diffusion: Na+ wants in, K+ wants out
Electrostatic Force: K+ wants out
Action Potential Stage 5 - Downswing
Vm: Decreasing towards hyper polarization
What’s Happening: VG K+ channels open
Diffusion: Na+ wants in, K+ wants out
Electrostatic Force: K+ wants out
Action Potential Stage 6 - Hyperpolarization
Vm: -80mV
What’s Happening: Some VG K+ channels are still open, K+ leaves, sends Vm. more negative than baseline.
Diffusion: Na+ wants in, K+ wants out.
Electrostatic Force: Na+ wants in
Action Potential Stage 7 - Return to Baseline
Vm: -70mV
What’s Happening: VG K+ channels close; Vm set by Na+/K+ pump and K+ leak channel.
Diffusion: Na+ wants in, K+ wants out
Electrostatic Force: Na+ wants in
Diffusion during action potential
The force of diffusion never changes because the relative concentrations never change
Why doesn’t the action potential travel backwards?
An action potential involves an influx of positive charge into the cell. The influx of positive ions pushes other positive ions away (down the concentration gradient). Previously active voltage-gated Na+ channels are in refractory period (ball is clogging the pore), influx of positive ions cannot reopen them.
Myelination
Wrapping an insulating layer of fat around segments of the axon. Propagating the action potential can be slow and axons can be long, myelination makes this more efficient.
Glia - Astrocytes
Janitors of the cell. Break down and clean up waste. Provides scaffolding for other cellular functions.
Glia - Microglia
Provide immune support. Regulate cell development and response to injury.
Glia - Oligodendrocytes
Create myelin, wrap it around nearby axons. Can provide sheath for 50 axons. Schwann cells - equivalent in peripheral nervous system.
Glia - Ependymal cells
Line the ventricles. Circulate cerebrospinal fluid.
Saltatory Conduction
Insulation means the ions inside myelinated axon segments are insensitive to charge differences outside. Positive charge quickly travels down axon and is repropagated at nodes of Ranvier.
Nodes of Ranvier
Unmyelinated segments of membrane at which the action potential is repropagated.
Voltage-Gated Calcium Channel
Ca2+ into the cell triggers neurotransmitter release. At axon terminal.
Two main types of receptor
- Ionotropic: Ion channels. Direct, fast effect on cell potential. Excitatory EPSP: Na+ permeable. Inhibitory IPSP: Cl- permeable.
- Metabotropic: G-protein coupled receptors. Can act indirectly on ion channels. Slower modification of cell excitability.
Excitatory Postsynaptic Potential (EPSP)
Na+ permeable. Does not always induce an action potential in the postsynaptic neuron.
Inhibitory Postsynaptic Potential (IPSP)
Cl- permeable. does not always prevent an action potential in the postsynaptic neuron.
How do neurotransmitters get removed? - Reuptake
Reuptake proteins transport neurotransmitter back across the membrane of the presynaptic cell. Neurotransmitter can then be repackaged into vesicle for another round of release.
How do neurotransmitters get removed? - Enzymatic Deactivation
Enymes (proteins dedicated to destruction) break down neurotransmitter in the synapse.
How do neurotransmitters get removed? - Diffusion
Released neurotransmitter moves down its concentration gradient, away from initial release site.
Metabotropic Receptors
Metabotropic receptors have lots of different effects on the cell - depends on the receptor and the signalling cascade its activation causes.
G protein coupled receptors
G proteins are proteins that use GTP as an energy source for chemical reactions. Logan binding to receptor drives a sequence of events by which the G protein can catalyze chemical reactions around the cell.
Steps of a G protein coupled receptor
- Neurotransmitter binds and the receptor changes shape, forcing the G protein to let go of GDP from a previous activation.
- A nearby GTP molecule can bind to the newly opened site on the G protein
- The G protein and its bound GTP will dissociate from the receptor and catalyze chemical reactions.
- The G protein will eventually convert GTP to GDP, at which point it will reassociate with the receptor.
Where do synapses form? - Dendritic
Neurotransmitter is released into dendrites (either smooth shaft or spines)
Where do synapses form? - Somatic
Neurotransmitter is released onto the cell body. These synapses exert great control over whether the cell fires, due to proximity to the axon hillock.
Where do synapses form? - Axoaxonic
Neurotransmitter is released onto axon terminal. Can suppress or amplify VG Ca2+ activation if neuron 2 has an action potential. Amount of Ca2+ entry determines how much NT is released.
The Life of a Neurotransmitter
- Synthesized from a precursor molecule (an amino acid) by enzymes in the axon terminal.
- Neurotransmitter is packaged into vesicles by transporter proteins.
- Vesicles are released into the synapse through fusion to the membrane (exocytosis)
- Some neurotransmitter binds to postsynaptic receptors, some binds to auto receptors to down regulate release.
- Neurotransmitter in the synapse is cleared away by reuptake proteins (return neurotransmitter to cell it was released from) and enzymes (degrade neurotransmitter)
Neurotransmitters
Made of modified amino acids. Synthesized locally in axon terminals. Secreted from small synaptic vesicles. Activates Ionotropic and metabotropic receptors. Yes reuptake.
Neuropeptides
Made of short strings of amino acids. Synthesized in soma, transported down the axons. Secreted from large dense core vesicles. Activates metabotropic receptors. No reuptake.
Lipid-Based Signalling Molecules
Made of Lipids (e.g., a chunk of cell membrane). Synthesized as needed (not very clear). Secreted from postsynaptic cell (does not require vesicles). Activates metabotropic receptors. No reuptake.
Drugs - Direct and Indirect
Exogenous chemicals that alter cell function at low doses.
Direct: affect activity by binding to postsynaptic receptor.
Indirect: affect activity by interacting with something other than the postsynaptic receptor.
Direct Drugs - Competitive
Affect activity by binding to postsynaptic receptor at the same site as endogenous neurotransmitter. Agonist: Full, Partial. Antagonist: Full.
Direct Drugs - Noncompetitive
Affect activity by binding to postsynaptic receptor at a different site than endogenous neurotransmitter. Agonist: Full, Partial, Positive Allosteric Modulator. Antagonist: Full, Negative Allosteric Modulator.
Partial Agonists
Can cause a net increase or decrease in postsynaptic activity. Depends on baseline activity at the synapse. If there is no receptor binding, the receptor activation is 0%. At a highly active synapse, neurotransmitter is frequently binding to receptors. Neurotransmitter binding causes maximal activation of receptor - at baseline, receptors are activated 100%. The drug has higher affinity, so binds to receptors instead of neurotransmitter, BUT it doesn’t activate them as strongly - receptors are activated 50%.
Positive Allosteric Modulators
A positive allosteric modulator amplifies the effect of neurotransmitter binding. Alcohol and benzodiazepines are both examples of positive allosteric modulators for GABA.
Negative Allosteric Modulators
A negative allosteric modulator decreases the effect of neurotransmitter binding.
Glutamate
Neurotransmitter. Excitatory effect, permits Na+ influx.
Repeat Administration effect on Tolerance
Drug effects are lessened due to the body down regulating natural processes that do the same thing. E.g., if dopamine levels are elevated because of regular cocaine use, the body will synthesize less dopamine to bring levels closer to normal.
Repeat Administration effect on Withdrawal
Cessation after regular use causes the inverse of symptoms. E.g., stimulant withdrawal causing fatigue, opiate withdrawal causing dysphoria.
Dopamine
Neurotransmitter. Reinforcement effect, volitional
GABA
Neurotransmitter. Inhibitory effect, permits Cl- influx.
Acetylcholine
Neurotransmitter. Attention effect, muscle contraction.
Serotonin
Neurotransmitter. Mood, sleep/wake states.
Norepinephrine
Neurotransmitter. Arousal effect, attention.
Peripheral Nervous System (PNS)
Rest of nervous system besides brain and spinal cord. Myelinated by Schwann cells. Uses the lymphatic system: blood leaks out of vessels through capillary gaps, becomes lymph. Lymph provides nutrients and cleans up waste. Recycled back into bloodstream.
Opioids
Neuropeptides. Analgesic, pleasure.
Endocannabinoids
Lipid-Based Signaling Molecule Neuromodulation, appetite, memory.
Central Nervous System (CNS)
The brain and spinal cord. Myelinated by oligodendrocytes. Does not use lymphatic system: no capillary gaps in blood vessels, protected by blood-brain barrier. CNS makes its own interstitial fluid (cerebrospinal fluid).
Division of the PNS - Somatic
Somatic: Sensing the external environment. Controls skeletal muscles. ‘Voluntary’.
Afferents: Sensory signal from eyes, ears, skin to CNS.
Efforts: Motor signals from CNS to skeletal muscles.
Neuraxis
Line along the length of the CNS (following the spinal cord and brain). The anatomical directions follow the neuraxis, which is why it gets wonky with humans and our bent heads.
Division of the PNS - Autonomic
Sending the internal environment. Controls smooth & cardiac muscle, glands. ‘Involuntary’.
Afferents: Sensory signal from internal organs to CNS.
Efferents: Motor signal from CNS to internal organs. Divided into sympathetic & parasympathetic.
Sympathetic: Fight or flight. Facilitates survival response. Prioritizes processes immediately necessary for survival.
Parasympathetic: Rest and Digest. Facilitates activities during relaxed state. Prioritizes increasing energy stores.
Choroid Plexus
Site of CSF production - tissue in all ventricles.
Lateral Ventricles
Two large ventricles’ mirrored across the sagittal plane.
Cerebral Ventricles
CSF (cerebrospinal fluid) is a nutrient filled solution the brain sits in. It is constantly circulated around the keep the brain healthy and refreshed.
Third ventricle
Between the thalamic nuclei; along the midline
Brain Development & Neoteny - 0-1 month
Neural tube forms - made of neural progenitor cells.
Fourth ventricle
Posterior to other ventricles, between pons and cerebellum.
Cerebral Aqueduct
Connects the third and fourth ventricle
Brain Development & Neoteny - 2-4/5 months
Asymmetrical division of NPCs: One NPC divides into one NPC and one neuron / glial cell. Neurogenesis = birth of new neurons.
Brain Development & Neoteny - 4/5+ months
Apoptosis: programmed cell death.
Brain Development & Neoteny- 1-2 months
Symmetrical division of neural progenitor cells: One NPC divides into two identical NPCs. Line the inside of the neural tube / ventricular zone.
The Midbrain - Tectum
Unconscious sensory processing.
Superior colliculi: Orient towards peripheral visual stimuli.
Inferior Colliculi: Orient towards peripheral auditory stimuli.
The Hindbrain - Medulla
Regulates autonomic, involuntary functions (e.g., coughing, sneezing). Processing internal sensation. Area postrema.
The Hindbrain - Medulla
Regulates autonomic, involuntary functions (e.g., coughing, sneezing). Processing internal sensation. Area postrema.
The Hindbrain - Pons
Relay between cerebrum and cerebellum. Medulla and pons contain many cranial nerve nuclei.
The Hindbrain - Pons
Relay between cerebrum and cerebellum. Medulla and pons contain many cranial nerve nuclei.
The Hindbrain - Cerebellum
Coordinate muscle movement and timing. Integrating sensory and motor information.
The Hindbrain - Reticular Formation
Regulates overall arousal state.
The Forebrain - Thalamus
Control of arousal and sleep/wake states. Similar function to pons: relay ascending sensory info to cortex, relay descending motor info to spinal cord.
The Midbrain - Tegmentum
Coordinating reflexive species-typical behaviours. E.g., pain, threat response.
The Forebrain - Hypothalamus
Control of autonomic nervous system. Control of the endocrine system - similar to medulla, but medulla signals with axonal projections, hypothalamus signals via hormones in bloodstream.
Limbic System
Hippocampus: Episodic memory formation.
Amygdala: Emotion recognition and processing.
Cingulate cortex: Connecting limbic structures
The Forebrain - Cerebral Cortex
Sheet of grey matter that folds into:
1. Sulci: small grooves, central sulcus: divides rostral and caudal brain.
2. Fissures: large grooves, longitudinal fissure: divides the two hemispheres, lateral fissure: divides frontal and temporal lobes.
3. Gyri: ridges between sulk / fissures
Four lobes of the cerebral hemisphere and their controls
- Frontal: Movement
- Parietal: Touch information
- Occipital: Visual information
- Temporal: Auditory information
Basal Ganglia
Involved in movement, motivation, and learning. Receives input from the forebrain and dopamine neurons in the midbrain. Damage results in movement problems.
Studying the Brain (structure, correlations, causality)
We can understand structure through imaging the brain, we can make correlations by recording neural activity during behaviour, we can understand causality by manipulating activity and observing what behaviour is produced.
CT - computerized tomography
Utilizes X-rays to image brain structure. Structural purpose. Cheap, fast, noninvasive. Poor spatial and temporal resolution.
fMRI - functional magnetic resonance imaging
Same as MRI, but utilizing the difference in magnetic fields around oxygenated vs non oxygenated blood to measure activity. Correlational purpose. Good temporal and spatial resolution, noninvasive. Expensive.
MRI - magnetic resonance imaging
Utilizes radio waves emitted from magnetically aligned water molecules. Different density of different substances create image. Structural purpose. High spatial resolution, noninvasive. Expensive.
Studying the Rodent Brain - Calcium Imaging
Ca2+ flows into the cell following an action potential. We can express a fluorescent molecule that is brighter when bound to calcium. The amount of fluorescence is a proxy for neuronal activity.
DTI - diffusion tensor imaging
Same as MRI, but changes in direction speed of radio wave emittance from water molecules resolves resolves axon tracts. Structural purpose. High spatial resolution for microstructure of axon tracts. Expensive.
PET - positron emission tomography
Radioactive molecule is injected, can record use of that molecule via energy emission. Correlational purpose. Can make any isotope radioactive - image whatever you want. Expensive, isotopes must be synthesized within hours of imaging.
Studying the Rodent Brain - Neuronal Tracing
Inject a molecule to stain pre- or post-synaptic connections.
Retrograde: Trace afferents (cells innervating cell of interest). Fluorogold.
Anterograde: Trace efferents (cells innervated by cell of interest). PHA-L