Nervous System and Physiological Responses

• Neurons are the origin of behavior.

Components of the Neuron

• Early philosophers compared the brain to a loom, a woven web of fine threads, during the 1880s.
• Santiago Ramon y Cajal, a physician, discovered how to stain neurons in the brain in the late 1880s.
• Staining neurons highlights entire cells and reveals they come in different shapes and sizes.
• The technique used to stain neurons is called a golgi stain.
• Neurons are composed of three basic parts.

Neuron Parts

• The cell body is the largest component that coordinates information-processing tasks and keeps the cell alive.
• Protein synthesis, energy production, and metabolism occur in the cell body.
• The cell body contains a nucleus that houses chromosomes containing DNA.
• A porous cell membrane encloses the cell body, allowing molecules to flow in and out.
• Dendrites are branches that receive information from other neurons and relay it to the cell body.
• The axon is a long, thin fiber that carries information to other neurons, muscles, or glands.
• Axons can be up to a meter in length, from the base of the spinal cord to the big toe.
• A myelin sheath covers the axon, which is an insulating layer of fatty material.
• Glial cells compose the myelin sheath and are support cells found in the nervous system.
• Glial cells serve roles crucial to the function of the nervous system.
• Some glial cells digest parts of dead neurons.
• Other glial cells provide physical and nutritional support for neurons.
• They help form the myelin that insulates axons of nearby neurons, allowing them to transmit information more quickly and efficiently.
• Demyelinating diseases, e.g., multiple sclerosis, cause the myelin sheath to deteriorate, slowing communication from one neuron to another.
• Demyelinating diseases can lead to loss of feeling in limbs, blindness, and difficulties with movement and cognition.
• Dendrites and axons don't actually touch.
• A small gap exists between the axon of one neuron and the dendrites or cell body of another called a synapse.
• A synapse is the junction or region between the axon of one neuron and the dendrites or cell body of another.
• Many of the billions of neurons in your brain have thousands of synaptic junctions each. Adult brains have trillions of synapses.
• Transmission of information across the synapse is fundamental to communication between neurons.
• Synapses allow us to think, feel, and behave.

Neurons Specialized by Function

• There are 3 major types of neurons, each performing distinct functions.
• Sensory neurons receive information from the outside world and convey it to the brain via the spinal cord.
• Sensory neurons Have specialized endings on their dendrites that receive signals for light, sound, touch, taste, and smell.
• The endings of sensory neurons in our eyes are sensitive to light.
• Motor neurons carry signals from the spinal cord to the muscles to produce movement.
• Motor neurons often have long axons that reach to muscles at our extremities.
• Interneurons connect sensory neurons, motor neurons, or other interneurons.
• Interneurons comprise most of the nervous system.
• Interneurons work together in small circuits to perform simple tasks, identifying where a sensory signal is coming from, and more complex tasks, such as recognizing a face.

Neurons Specialized by Location

• Purkinje cells are a type of interneuron that carries information from the cerebellum to the rest of the brain and spinal cord
• Purkinje cells Have dense, elaborate dendrites that look like bushes. Pyramidal cells are neurons with a pyramid (triangle) shaped cell body found in the cerebral cortex Have a single, long dendrite among many smaller dendrites Bipolar cells are a type of sensory neuron found in the retinas of the eye Have a single axon and a single dendrite.
• All different types of neurons exist to allow the brain to process different types of information.

10% Brain Usage Myth

• The statement, "we only use 10% of our brains" is false.
• Chabris and Simons (professors) broke down this statement and explained that it is false.
• The entire brain is put to use.
• Unused neurons atrophy.
• The myth arose from seeing areas “lighting up” in a brain scan, but the dark regions aren't dormant or unused.
• The 10% myth and other neuromyths were presented to 242 primary and secondary school teachers in the Netherlands and UK
• 47% of teachers believed the 10% myth.
• 76% believed that enriching children's learning environments would “strengthen" their brains - this is also false.
• 94% of teachers believed that students performed better when learning in their "preferred style", but this has little to do with how effectively they learn.
• Neuromyths have widespread appeal and spread rapidly in fields like business and self-help.

The Electrochemical Actions of Neurons: Information Processing

• Our thoughts, feelings, actions depend on neural communication.
• Neurons use chemical and electrical signals to communicate.
• First, an electric signal is conducted inside the neuron, from the dendrites to the cell body, then down to the axon.
• Second, a chemical signal is transmitted from one neuron to another, across the synapse.
• These stages are called the electrochemical action of neurons.

Electrical Signaling: Conducting Information Inside a Neuron

• A neuron's cell membrane has pores that act as channels to allow ions to flow in and out of the cell.
• Ions are molecules that carry a small positive (+) or negative (-) electric charge.
• The flow of ions across a neuron's cell membrane creates the conduction of electric current within the neuron.

The Resting Potential: The Origin of the Neuron's Electrical Properties

• When neurons are at “rest”, positively charged potassium ions (K+) and negatively charged protein ions (A-) are more abundant inside the neuron than outside in the fluid-filled space between neurons (the synapse).
• Positively charged sodium ions (Na+) are more abundant outside the neuron.
• The resulting effect is that the inside of a neuron has a small negative charge, relative to the outside.
• This imbalance between the inside and the outside is called the resting potential.
• Resting potential is the difference in charge between the inside and outside of a neuron's cell membrane, usually about -70 millivolts.
• One reason for the different concentrations of ions inside and outside the cell membrane is channels in the cell membrane that restrict the movement of ions going in and out of the cell.
• Like a dam, they can be opened, allowing ions to rush across the membrane in a fraction of a second.

The Action Potential: Sending Signals Across the Neuron

• Biologists working with giant squid axon noticed that stimulating the axon with an electric shock set off a much larger electrical impulse; a spike in voltage that travelled down the axon in a wave while maintaining its intensity.
• They used a squid because its axons are 100x larger than human axons.
• They inserted a thin wire into the squid axon so it touched the jellylike fluid inside and placed another wire just outside the axon in the watery fluid that surrounds it. and Found the electrical difference between charges, which equals the resting potential.
• The action potential is an electric signal conducted along the length of the neuron's axon to a synapse
• Action potentials are fundamental for everything we think, feel, and do. Only occur when the electric shock reached a certain level, or threshold.
• Above that threshold, more electric shock did not increase the strength of the action potential.
• The action potential is all or none.
• Below the threshold, the electric shock will fail to produce an action potential.
• Psychologists say a neuron “fires” because of the all-or-nothing nature of the action potential.

The Action Potential Moves Across the Neuron in a Domino Effect

• Action potential occurs due to changes in the axon's membrane channels.
• During resting potential, the membrane channels for sodium (Na+) ions are closed.
• However, when the electrical charge across the cell membrane reaches the threshold, sodium channels in the cell membrane open up like floodgates, and Na+ ions from outside rush in almost instantaneously.
• This inrush of positively charged ions surges electric charge from -70 mV to +40 mV in less than a millisecond.
• This triggers a domino effect all the way down the axon, increasing electric charge in neighboring areas, and causing all the Na+ channels to open up, letting more Na+ in and increasing the charge even more.
• This effect is called action potential.
• In many neurons, the myelin sheath around the axon increases conductivity of the action potential.
• Myelin sheaths prevent electric current from leaking out of the axon.
• It keeps the charge high along the axon, similar to insulation covering wires on a power cord.
• Myelin sheaths don't cover the entire axon, rather clumps around it with little break points between clumps (looks like sausage links).
• Break points are called the Nodes of Ranvier (named after Louis Ranvier, who discovered them).
• Current jumps quickly from node to node in a process called salatory conduction
• Action potential spreads onward, not backward
• Sodium channels in each region of the axon are temporarily inactivated after the action potential passes over them - just like dominos knocked over cannot be knocked over until they are set up again
• This inactive period is called a refractory period, which is the time following an action potential during which a new action potential cannot be initiated
• During this time the electrical/ chemical balance of the neuron is restored
• Na+ channels briefly close, and K+ channels open, allowing excessive potassium ions to escape the cell
• This returns the electrical charge inside the cell membrane to a negative state.
• To restore the chemical balance, special channels called ion pumps redistribute the ions
• It pushes all excessive Na+ back out of the cell and pulls necessary K+ back in.
• This rebalances concentrations and restores resting potential.
• After the sodium channels and ion pumps restore balance thedominoes are "set back up"and ready to be knocked over again when triggered.

Chemical Signaling: Transmission Between Neurons

• The synaptic space makes neurons not actually touch each other, so action potential needs another way to reach the end of the axon.
• Axons have hundreds / thousands of branches that reach out to other neurons and organs.
• Axons usually end in terminal buttons = knoblike structures that branch out from an axon.
• Terminal buttons are filled with tiny “bags” that contain neurotransmitters = chemicals that transmit information across the synapse to a receiving neuron's dendrites.
• Receiving dendrites contain receptors = parts of the cell membrane that receive the neurotransmitter and either initiate or prevent a new electric signal.
• Axon potential in the sending neuron - presynaptic neuron, travels down the length of the axon to terminal buttons.
• Here, it stimulates the release of neurotransmitters from vesicles (bags) to synapses.
• These quickly float across the synapse (fluid) and bind to receptor sites on the nearby dendrite of the receiving postsynaptic neuron
• The neurotransmitter activates nearby ion channels and increases or decreases voltage across the cell membrane.
• Postsynaptic neurons might activate nearby ion channels, raising or lowering the voltage across the cell membrane.
• Depending on timing or combination of neurotransmitters acting on the receiving neuron, the voltage might reach a threshold, triggering a whole new action potential.
• This is how neurotransmitter's chemical "messages" create an electrical signal, and neuronal communication can continue from neuron to neuron.
• Neurons form pathways characterized by different types of neurotransmitters.
• One kind of neurotransmitter might be prevalent in one part of the brain, whereas a different kind might be prevalent in another.
• Certain neurotransmitters will only bind to specific receptor sites on a dendrite as a lock and key system.
• Their molecular structures must fit each other.
• Neurotransmitters leave the synapse through 3 processes

How Signals Stop Sending

• Neurotransmitters leave the synapse through 3 processes.
• Reuptake occurs when neurotransmitters are absorbed by the terminal buttons in the presynaptic neuron's axon or absorbed by neighboring glial cells
• Enzyme deactivation occurs when specialized enzymes break down neurotransmitters.
• Diffusion occurs when neurotransmitters drift out of the synapse and are no longer able to reach receptors.

Types and Functions of Neurotransmitters

• Acetylcholine is a neurotransmitter involved in a number of functions, including voluntary motor control
• Acetylcholine is found in neurons of the brain and synapses where axons connect to muscles and body organs, like the heart
• Helps activate muscle movements
• Contributes to regulating attention, learning, sleeping, dreaming, and memory
• Alzheimer's is associated with the deterioration of Acetylcholine producing neurons.
• Dopamine regulates motor behavior, motivation, pleasure, and emotional arousal
• Dopamine plays a role in motivated behaviors, like pleasure-seeking and associated actions with rewards
• Dopamine plays an important role in drug addiction.
• High levels of dopamine can be linked to schizophrenia
• Low levels of dopamine can be linked to Parkinson's Disease.
• Glutamate is the major excitatory neurotransmitter in the brain and enhances the transmission of information between neurons
• GABA is the major inhibitory neurotransmitter in the brain and slows the transmission of information between neurons.
• Too little glutamate, or too little GABA can cause neurons to become overactive and induce seizures
• Norepinephrine is a neurotransmitter involved in states of vigilance, or heightened awareness of dangers in your environment.
• Serotonin is a neurotransmitter involved in the regulation of sleep and wakefulness, eating, and aggressive behavior.
• Norepinephrine and serotonin are related and both affect mood and arousal
• Low levels of either are implicated in mood disorders like depression
• Endorphins are neurotransmitters that act within the pain pathways and emotion centers of the brain
• They play a role in dulling pain and elevating moods
• "Runner's high" is caused by the release of endorphins in the brain.

Neurotransmitter Balance

• Each neurotransmitter affects thoughts, feelings, and behavior differently.
• A delicate ballance of all neurotransmitters is needed.
• Sometimes, imbalances occur naturally, leading to mood disorders.
• Other times, we seek things out that cause imbalances with drugs, alcohol, and smoking etc.
• For instance, LSD is similar to serotonin and binds easily with serotonin receptors in the brain, "tricking” receptor sites.

How Drugs Mimic Neurotransmitters

• Drugs can increase, interfere with, or mimic the function of neurotransmitters
• Agonists are drugs that increase the action of a neurotransmitter
• Antagonists are drugs that decrease the function of a neurotransmitter.
• Other drugs alter a step in the production or release of neurotransmitters.
• Some have a chemical structure similar to neurotransmitters that they can successfully "fool” the receiving neuron's receptors into binding successfully.
• L-dopa is a drug used to treat Parkinson's disease.
• Parkinson's is caused by the loss of neurons that make dopamine by modifying I-dopa already naturally present in the body
• Taking L-dopa increases the concentration in the brain Engaging surviving neurons to produce more dopamine, acting as an agonist
• Amphetamine is a popular street drug that stimulates the release of norepinephrine and dopamine
• It creates an excess of neurotransmitters that flood the synapse, activating their receptors over and over, and creating a pleasurable effect
• Amphetamine is an agonist.
• Propanolol is a "beta blocker" that obstructs norepinephrine receptor sites in the heart
• It causes heart rate to slow down and is helpful for conditions causing the heart to beat too fast.
• Propanolol acts as an antagonist.

The Organization of the Nervous System

The Nervous System is an interacting network of neurons that conveys electrochemical information throughout the body.

Divisions of the Nervous System

The divisions are:

• Central nervous system
• Peripheral nervous system

Nervous Systems

• The central nervous system is composed of the brain and the spinal cord
• It Receives sensory information from the outside world and Processes and coordinates this information
• The central nervous system Sends commands to the skeletal / muscular systems for action with the brain at the top and the spinal cord branching down
• Nerves that process sensory information and relay commands connect to the spinal cord.
• The peripheral nervous system connects the central nervous system to the body's organs and muscles
• The peripheral nervous system is composed of two major subdivisions: somatic and autonomic.
• The somatic nervous system is a set of nerves that conveys information between skeletal muscles and the central nervous system
• We use the somatic nervous system to consciously think, perceive, and coordinate our behavior, e.g., reaching for an object.
• The autonomic nervous system is a set of nerves that carries involuntary and automatic commands that control blood vessels, body organs, and glands
• It works on its own to regulate body systems outside of conscious control.
• The autonomic nervous system has two subdivisions: sympathetic and parasympathetic
• The sympathetic nervous system is a set of nerves that prepares the body for action in challenging / threatening situations
• The parasympathetic nervous system helps the body return to a normal resting state, reversing functions of the sympathetic nervous system
• Restores the body to a calm and composed state
• The parasympathetic nervous system constricts pupils and slows heart rate/respiration
• It also Diverts blood flow and decreases activity in sweat glands
• The sympathetic and parasympathetic nervous systems control sexual behavior in tandem
• The parasympathetic nervous system engorges blood vessels and causes erection
• The sympathetic nervous system is responsible for ejaculation
• These also cause same effects in females for arousal / orgasm

Components of the Central Nervous System

Spinal cord responsible for simple, but important tasks Spinal reflexes are simple pathways in the nervous system that rapidly generate muscle contractions, e.g., quickly pulling your hand away from a hot stove. Sensory neurons send inputs directly into spinal cord Through a few connections within the spinal cord, interneurons relay sensory inputs to motor neurons that connect to your arm muscles and force you to quickly retract your hand

• This completes reflex arc, a neural pathway that controls reflex actions that includes sensory neurons, interneurons, and motor neurons. Brain and spine are both responsible for tasks more complex than simple reflexes Peripheral nervous system sends messages from sensory neurons through the spinal cord to the brain. Brain sends commands for voluntary movement through the spinal cord to motor neurons, who's axons project out to skeletal muscles Damage to the spinal cord severs the connection from the brain to the sensory and motor neurons that are crucial to sensory perception and movement People with damage at specific places in the spinal cord lose motor function, sensation of touch, and pain below where the injury took place The higher up on your spinal cord you were injured, the more functions lost Christopher Reeves, the actor for Superman, damaged his spinal cord in a horseback riding accident, resulting in the loss of sensation and motor control everywhere below the neck.

Investigating the Brain: Studying the Damaged Brain

• Research in neuroscience aims to link the loss of specific perceptual, motor, emotional, cognitive functions to a specific area of the brain
• From loss of function can inform about what said brain areas usually perform.
• Damaged brains are not the same as atypical brains - there are natural variations in structure or function of brains that produce variations between individuals in how they function.

Brain Study History

• The history of neuroscience begins with Paul Broca (1824-1880)
• He described a patient who could no longer speak but could still understand language due to small damage in the left frontal lobe.
• This was some of the earliest evidence that speech production and speech comprehension are separate in the brain and that the left hemisphere is crucial to language abilities

The Emotional Functions of the Frontal Lobes:

• Phineas Gage was a railroad worker from Vermont impaled by a 13 pound iron tamping rod after accidentally exploding explosive powder was packing in a crevice.
• The rod entered through his lower left jaw and exited through the middle top of his head causing significant personality changes from the incident.
• He went from "mild-mannered, quiet, conscientious hard worker" to "irritable, irresponsible, indecisive, and profane”.
• His case was extremely valuable because it allowed researchers to investigate the hypothesis that the frontal lobe regulates emotion, planning, and decision making.

The Distinct Roles of the Left and Right Hemispheres

• The cerebral cortex is divided into two hemispheres.
• The hemispheres usually act as one integrated unit, though some disorders prevent this.
• For instance, people with epilepsy have frequent seizures that create a “firestorm” in the brain.
• To alleviate the severity of a firestorm doctors can sever the corpus callosum in a split-brain procedure, resulting in a seizure remaining isolated in one hemisphere of the brain.
• The procedure helps pain, but causes unusual behavior.
• Roger Sperry experimented with split-brain procedure patients.
• Sperry asked a person to look at a spot in the center of a screen and tried projecting stimulus to both the left and right visual fields separately.
• When stimulus was projected to the left visual field (left hemisphere controls speaking), they could verbalize what they were seeing
• However, they couldn't reach over with their left hand to pick it up because the right hemisphere controls the left hand
• These experiments prove the right hemisphere had no clue what was happening because the two sides could not communicate
• When split-brain patients saw a chimeric face (half one face, half another).
• Patients could only describe the left side because speech is controlled by the left hemisphere.
• These studies show that the left and right hemispheres perform different functions but work together in the presence of an intact corpus callosum.

Studying the Brain's Electrical Activity

• Scientists can study the link between brain structures by recording electrical activity of neurons.
• An electroencephalograph is a device used to record electrical activity in the brain.
• Electrodes are placed on the outside of the head
• An EEG can amplify electric signals so they can be detected, even if they are occurring deep in the brain.
• Using this technique, we can determine how much brain activity is happening during different experiences and states of consciousness.
• Brain shows different patterns of activity while awake and while asleep.
• EEGs cannot read minds but it can reveal abnormal activity patterns associated with brain injuries or disorders.
• Today, EEGs are used to understand brain processes involved with sleep, social interaction, and everyday activities.
• David Hubel and Torsten Weisel discovered another approach, inserted electrodes into occipital lobes of anesthetized cats and observed action potential patterns in individual neurons
• They Amplified signals through a loudspeaker and Flashed lights in front of animals eye
• The scientists discovered that neurons in the primary visual cortex are activated when a contrast between light and dark occurs in part of the visual field.
• Since then, many studies have shown that neurons in the primary visual cortex respond to particular features of visual stimuli, contrast, shape, and color for instance
• These neurons are called feature detectors because they respond to only certain aspects of a visual image.
• Other studies have shown a variety of features detected by sensory neurons.
• Some visual processing neurons are only specialized for detecting faces, which when damaged results in face blindness

Using Brain Imaging to Study Structure and to Watch the Brain in Action

• Studies can use a third way to look into the human brain which involves neuroimaging techniques
• Advanced technology is used to provide information about basic brain structure allowing researchers to spot abnormalities or changes in brain structure
• Functional brain imaging provides information about brain activity while people perform cognitive or motor tasks.

Structural Brain Imaging

• A CT scan rotates around a head and takes x-ray photographs of the brain at different angles
• Computers combine images to get full 360, detailed view of brain
• Scans can be used to locate lesions and tumors, which show up as darker in the scan because they are less dense than the cortex
• An MRI scan uses a magnetic field to line up nuclei of specific molecules in the brain tissue
• This Reveals brain structures with different molecular compositions and produces images of soft tissue at a higher resolution than CT scans do.
• It also Gives psychologists a clearer picture of the structure/ volume of the brain and Helps localize brain damage
• Diffusion Tensor Imaging, DTI, is used to visualize white matter pathways (connecting regions of the brain to each other)
• DTI Measures rate/ diffusion of water molecules, which reveal the pathways of white matter and Helps map connectivity in the human brain
• DTI is Crucial to the Human Connectome Project, which aims to provide complete map of neural pathways in the brain, available online

Functional Brain Imaging

• Functional Brain Imaging allows us to see the brain in action
• Positron Emission Tomography (PET) is used to determine what parts of the brain are being activated during cognitive tasks.
• This injects a harmless radioactive substance into the bloodstream, then scans the brain by radiation detectors Shows when more energy/ blood is flowing to a certain area.
• Functional Magnetic Resonance Imaging (fMRI) is most commonly used today, since it gives a picture of the level of activation in each brain area.
• The technique Detects difference between oxygenated hemoglobin and deoxygenated hemoglobin when exposed to magnetic pulses
• Hemoglobin is the molecule in our bloodstream that carries oxygen to tissues like the brain, so the brain knows where to provide it.
• More hemoglobin collects at more active areas of the brain
• fMRI and PET scans can indicate functions like activity in the auditory cortex of a person listening to music.

fMRI advantages over PET scans

• fMRI can localize changes across briefer periods
• Useful Analyzing process's that occur quickly (reading a word, face, etc.)
• You can also explore the relationship of brain regions with each other, using resting state functional connectivity.
• Participants can rest quietly while fMRI measurements are made. Functional connectivity measures which brain activities are highly correlated/ connected with each other.
• Transcranial Magnetic Stimulation can be used to mimic brain damage by delivering a magnetic pulse, passing through the skull to deactivate neurons in the cerebral cortex for a short period directed to specific brain regions

Transcranial Magnetic Stimulation

• Can be directed to specific brain regions
• Observe temporary changes in behavior and establish causal relationships Discoveries:
• Interfering with a particular region reduce the details people remember from past experiences, and imagine in future experiences.
• Early studies showed that students with high honors had larger brains than others at the age of 19, this was discovered by Sir Francis Galton.

Is a larger brain a smarter brain?

• It was discovered a century later that the earlier studies had discrepancies and failed to establish that such a relationship existed.
• Methods have become more accurate over time, so much old information is false
• More recent experiments with extremely large bodies of work have recently shown between a +.19 and +.27 correlation between brain volume and intelligence due to the diversity of the sample
• We can deduce that this is a genuine correlation not caused by age, socioeconomic status, etc, however, it's still nonetheless small, and we do not know if a larger brain volume causes a increase in intelligence or if people with higher intelligence use their brain in a way that produces more volume

Genetics

• The field begs the question, can a behavior be genetically determined?
• At minimum, the answer is no.
• Genes code for proteins
• Organisms are built from proteins
• This means behavior is not governed by single proteins
• This means there is not “schizophrenia gene” because you can have multiple genes related to disease, and still not develop said disease Most functions (and dysfunctions) require many many many proteins
• The distance between genes and behavior is very, very far

So is our behavior shaped by genetics?

• The answer tends to be yes.
• Our cells, especially your nervous system, are scaffold upon which you are built Differences in genes lead to differences in your nervous system, and this lead to differences in your potential
• Some people's gene combinations make them more predisposed to certain behaviors, lust, distraction, mental illnesses etc.. Tryon's experiment with “maze bright", smart, and "maze dull", dumb, rats, referred to rats that succeeded and failed at working throughout mazes.

Nature and nurture

• Which is more important? That's the wrong question. They are not pitted verse one another, you cannot have one without the other
• Misconceptions arise like "the heritability estimate for IQ is 0.5”
• It's important to understand that they Describe variance, not correlation This shows for a group, that 50% of variability in IQ can be related to differences in genes and Does not say anything about specific individuals
• Arms Are arms 0% genetic? Most people are born with arms, but why some of us are born with fewer is due to environmental factors
• Heritability is a measure of how well differences in people's genes account for differences in their traits. For arms, heritability is close to 0, since variance is environmental

Human Brain Facts

• Despite being only around 2-3% of your body weight, it consumes a lot of resources, needing Over 20% of your energy.
• It's also Slightly larger in men than in women and offers Huge individual variation. Composed of neurons, glia, stem cells and blood vessels <<100 billion neurons (hard to say, many estimates put it at 80-85 billion), more than half of which are cerebellum (small section at the back of your brain). Has a Consistency of soft tofu
• The shape is Convoluted in order to fit more of the cortex (cortical tissue) Most of brain's heavy lifting is done by the cerebral cortex.
• Cells are not replaced, meaning little to no neurogenesis occurs as an adult.
• Brain doesn't "eat itself" but waste proteins accumulate that would normally "clean out" during sleep.

Neuron or glia?

Neurons

• Have axons
• Release the very fast, directive mode of communication via axons and action potentials.

Glia

Referred to as support cells There Are at lest four glial cell types: Microglia, Macroglia, Ogliodendrocyte, Schwann Cell and Astrocytes Matter White matter is composed of Myelinated axons while the Grey Matter covers Cell bodies of neurons

Neuron Shapes

Neuron Shape comes in many types but similar designs Dendrite -> soma -> axon -> terminals 3 importnant shapes to remember: A. Pyramidal B. Stellate C. Purkinje Stellate, star shaped, found in areas under the cortex where single axons emerges. Purkinje cells comprise of rich dendritic branching, important for coordination, motor control etc All cell types converge on a cell body with axon as output, and axon heads to terminal Neurons come in two basic shapes: Projection type and Interneurons that are small and star shaped

Glial Cell Types

• Are half of your blood brain barrier
• Play a key role in providing for the needs of your neurons'
• Any oxygen, glucose, amino acids, all pas through astrocytes before reaching neurons.
• Not only playing a support role: Are a team player in the tripartite synapse that influences glia transmitters- pre-synaptic axon, post synaptic axon, and astrocytes interact (3).
• Glia shapes conditions at this synapse.
• Neuron do no operate in a void

Neuronal communication

Neuron is a Resting membrane potential (or membrane voltage) between -60 and -80 mV meaning, the voltage inside the neuron is 60-80 mV less than outside the neuron- is like potential energy at the top of said energy field. Outside the cell is always negative with respect to the inside cell. Neuronal communication is chemical

• Communicating in a neuron revolves around positives: sodium (Na+) and potassium (K+)
• As they move into or out of cell, they change the potential aka voltage at the membrane.
• Note: absence of positive indicates negative.

Chemical and electrical gradients

• Ions want to flow from high concentration to low concentration, thus wanting to move from a “swimming pool" to cells
• The amount in different areas is also affected, if they can’t move they will apply a force
• Neuron must have a Cell membrane with: Lipid bylayer that contains lipids, that is tightly packed, that contains hydrophobic and and hydrophilic
• Channels allow passive diffusion while in a membrane, and Pumps actively push ions against any gradient

Resting Membrane Potential

• Sodium/potassium pump is always working, and Sodium exits the cell, potassium enters the cell"
• Thus making Na+ channel is closed.
• The cell will always have More sodium outside and potassium inside but it cannot get out because it needs a push and Thus more volume in space and gradient

Explore the effects of propanolol on the heart and CNS functions. Learn about the somatic and parasympathetic nervous systems. Understand fight or flight responses, spinal reflexes, and neuron resting potential.