Chapter 3: Neuroscience and Behavior
Demyelinating diseases
(Example is multiple sclerosis); deterioration of myelin sheath and slowing of transmission of info from one neuron to another
What is the measure of a neuron's resting potential and when was it first measured?
-70 mV; 1930s
What tells the dendrites which of the neurotransmitters flooding into synapse to receive?
1. Neurons tend to form pathways in the brain characterized by specific types of neurotransmitters 2. Lock and key system (neurotransmitters and receptor sites) -> only some neurotransmitters bind to specific receptor sites on dendrite
How many chemicals play a role in transmitting info through your brain?
60
What is the cell body surrounded by?
A porous cell membrane that allows some molecules to flow into and out of the cell
Methamphetamine
Affects pathways for dopamine, serotonin and norepinehrine at neuron's synapses; difficult to interpret -> combination of agonist and antagonist effects alters functions of neurotransmitters that help us perceive and interpret visual images == strange hallucinations
What disease is associated with the deterioration of ACh-producing neurons?
Alzheimer's disease (memory impairments)
What two drugs prevent the reuptake of norepinephrine and dopamine as well as stimulate increased release?
Amphetamine and cocaine, two agonists
What is the imbalance following the refractory period reversed by?
An active chemical pump in cell membrane that moves Na+ outside axon and moves K+ inside axon
Action potential
An electric signal that is conducted along the length of a neuron's axon to a synapse
Myelin sheath
An insulating layer of fatty material, composed of glial cells
Propranalol
Antagonist; beta blocker -> blocks receptor site for norepinephrine in heart -> norepinephrine can't bind to these receptors so heart rate slows down (helpful for those people with disorders where the heart beats too fast or irregularly)
How many nerve cells are there in your brain?
Approximately 100 billion
Why do SSRIs help people suffering from clinical depression?
Because they have reduced levels of serotonin (elevates mood), the block of reuptake allows more of the neurotransmitter to remain in the synapse and produces greater activation of serotonin receptors
What are nodes of Ranvier?
Breakpoints in the myelin sheath; the myelin doesn't cover entire axon, but rather clumps around axon with break points
Axons
CARRIES information to other neurons, muscles, or glands (the long thing covered by myelin sheath connecting cell bodies to its dendrites)
Lighting a match can be compared to an action potential because both events:
Can be described as all-or-none events
Motor neurons
Carry signals from spinal cord to muscles to produce movement; often have long axons that stretch to muscles at extremities
Neurons
Cells in nervous system that communicate with one another to perform information-processing tasks
Threshold
Certain level ONLY at which action potential occurs
Neurons are not connected physically but communicate _____ with each other at the ________
Chemically; synpase
Endorphins
Chemicals that act within pain pathways and emotion centers of brain; dulls experience of pain and elevates moods
Neurotransmitters
Chemicals that transmit information across synapse to a receiving neuron's dendrites
What are the two ways neurons communicate info within and between themselves?
Conduction and transmission
Interneurons
Connect sensory neurons, motor neurons, or other interneurons
Nucleus
Contained within the cell body; houses chromosomes that contain your DNA
What are the two types of specialized extensions of the cell membrane that allow them to communicate?
Dendrites and axons
Resting potential
Difference in electric charge between the inside and outside of a neuron's cell membrane
How does the electric charge of the action potential move down the axon?
Domino effect -> when action potential generated at beginning, spreads short distance -> generates action potential at nearby location -> etc
________ is the neurotransmitter that regulates MOTOR BEHAVIOR, motivation, pleasure, and emotional arousal
Dopamine
How does L-dopa alleviate symptoms of Parkinson's disease?
Dopamine is created by modification of common molecule called L-dopa. Ingestion of L-dopa will elevate amount in brain and spur surviving neurons to produce more dopamine -- L-dopa acts as an agonist for dopamine
Where does dopamine play a role?
Drug addiction
Antagonists
Drugs that block function of neurotransmitter; blocks action of neurotransmitter (structurally similar to neurotransmitter that is able to bind with the receptor)
Agonists
Drugs that increase action of a neurotransmitter; activates neurotransmitter (structurally similar to neurotransmitter that is able to bind with the receptor)
Why does action potential reach a value above 0?
During resting potential, channels allowing K+ to flow out are open. When charge raised to threshold value, channels briefly shut down and channels that allow flow of positively charged sodium ions (Na+) are opened. As Na+ is more concentrated on the outside, it flows inside and increases positive charge inside axon relative to the outside.
Within a neuron, information is transmitted as a(n) ________ travels from the dendrites to the cell body and throughout the axon
Electrical signal
Synaptic transmission
Electrochemical action where action potential travels down length of one axon, through the synapse and then on to the next neuron; allows neurons to communicate
What chemical is runner's high attributed to?
Endorphins
What happens when amphetamine and cocaine prevent reuptake with the increased release that has been stimulated?
Flood in synapses of these neurotransmitters; increased activation of receptors
Pyramidal cells
Found in cerebral cortex; triangular cell body and single long dendrite among many other dendrities
What did Santiago Ramon y Cajal?
He learned about a new technique for staining neurons in the brain and realized they came in different shapes and sizes. Neurons are composed of three basic parts: the cell body, the dendrites, and the axon
What are high levels of dopamine linked to and what are low levels linked to?
High: Schizophrenia, amphetamine psychosis Low: Parkin's disease; tardive dyskensia
How do drugs affect the nervous system?
Increasing, interfering with, or mimicking the manufacture of neurotransmitters
What kind of neurons is most of the nervous system composed?
Interneurons
Serotonin
Involved in regulation of sleep and wakefulness, eating, and aggressive behavior, mood, impulsivity, aggression, appetite
Norepinephrine
Involved in states of vigilance; heightened awareness of dangers in environment; food intake (stimulates intake of carbohydrates)
What causes the conduction of an electric signal within the neuron?
Ions that flow across the neuron's cell membrane
What does the myelin sheath do?
It facilitates the conduction of the action potential
Synapse
Junction or region between the axon of one neuron and the dendrites or cell body of another
Terminal buttons
Knoblike structures that branch out from an axon
Cell body (Soma)
Largest component of the neuron that coordinates the information-processing tasks (protein synthesis, energy production, and metabolism) and keeps the cell alive
What is Parkinson's disease caused by?
Loss of neurons that use the neurotransmitter dopamine
Glutamate
Major excitatory neurotransmitter in brain; enhances transmission of info between neurons
What happens when action potential reaches its maximum?
Membrane channels return to original start and K+ flows until axon returns to resting potential; refractory period
_______ acts both as an agonist and as an antagonist to alter neurotransmitters that affect perception and interpretation of visual images
Methamphetamine
The neurotransmitter dopamine is involved in
Motivation and pleasure
What is Parkinson's disease?
Movement disorder characterized by tremors and difficulty initiating movement
Conduction
Movement of electric signal within neurons, from dendrites to cell body, then throughout the axon
Transmission
Movement of electric signals from one neuron to another over synapse
The _________ is made up of glial cells and helps to insulate the axon
Myelin sheath
Do increases in electric shock above threshold increase the strength of the action potential?
NO. The action potential is all or none.
Where is acetylcholine found?
Neurons of brain and in synapses where axons connect to muscles and body organs
Acetylcholine (ACh)
Neurotransmitter involved in voluntary motor control among other things like regulation of attention, learning, sleeping, dreaming, and memory
Dopamine
Neurotransmitter regulating motor behavior, motivation, pleasure, and emotional arousal
What happens to neurotransmitters left in synapse after chemical message is relayed?
Neurotransmitters leave synapse through three processes: 1. Reuptake: neurotransmitters reabsorbed by terminal buttons of presynaptic neuron's axon 2. Destroyed by enzymes in enzyme deactivation (specific enzymes break down specific neurotransmitters) 3. Neurotransmitters can bind to receptor sites called autoreceptors on presynaptic neurons (detect how much neurotransmitter has been released into synapse and tell neuron to stop releasing neurotransmitter when excess is present)
What are the two neurotransmitters that influence mood and arousal?
Norepinephrine and serotonin
Having low levels of which two chemicals can cause mood disorders?
Norepinephrine and serotonin; mood, impulsivity, aggression, appetite
Beta blocker
Obstructs receptor site for norepinephrine in the heart; helps people with increased or irregular heartbeat as well as to those with stage fright
Where is Na+ more concentrated in during resting potential? Action potential?
On the outside during resting; inside during action
Receptors
Parts of cell membrane (of receiving neuron) that receive neurotransmitters and either initiate or prevent a new electric signal
Amphetamine
Popular drug that stimulates release of norepinephrine and dopamine
How does a neuron communicate with another neuron?
Presynaptic neuron has K+ and Na+ flowing across it -> action potential travels down length of axon to terminal buttons -> stimulates release of neurotransmitters from vesicles into synapse -> float across and bind to receptor sites on nearby dendrite of receiving neuron (postsynaptic neuron)
GABA (Gamma-aminobutyric acid)
Primary inhibitory neurotransmitter in brain; stops firing of neurons
Dendrites
RECEIVE information from other neurons and relay it to the cell body
Sensory neurons
Receive information from the external world and convey information to the brain via the spinal cord; specialized endings on dendrites that receive signals for light, sound, etc
A battery that is not connected to anything is a good analogy for the _______ of a neuron
Resting potential
The process that occurs when the presynaptic terminal buttons reabsorb a neurotransmitter is referred to as
Reuptake
What do too much glutamate and too little GABA cause?
Seizures
SSRIs
Selective serotonin reuptake inhibitors; block reuptake of neurotransmitter serotonin
What are the three major types of neurons?
Sensory neurons, motor neurons, interneurons
A person suffering from depression may be suffering from low levels of norepinephrine and _________, because both of these are involved in mood and arousal
Serotonin
What is LSD structurally very similar to?
Serotonin; binds with serotonin receptors in brain and produces similar effects on thoughts, feelings, and behaviors
Ions
Small electrically charged molecules
What do glial cells do?
Some digest parts of dead neurons; others provide physical and nutritional support for neurons, others form myelin
Glial cells
Support cells found in the nervous system (10-50x number of neurons)
Neurotransmitters are chemicals that transmit info across the _______ to dendrites on the receiving neuron
Synapse
The knob-like structures that branch out from an axon and release neurotransmitters are referred to as ___________
Terminal buttons
What does the resting potential arise from? Describe the ion state at resting potential.
The difference in concentrations of ions; resting state is high concentration of positively charged ion potassium (K+) and negatively charged protein ions (A-) INSIDE neuron's cell; OUTSIDE there are lots of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-) -> K+ concentrations is controlled by channels in cell membrane; resting state they flow freely while Na+ and other ions' channels are closed -> K+ move out of neuron through open channels; resting potential is potential energy
Postsynaptic neuron
The receiving neuron
Presynaptic neuron
The sending neuron; the neuron through which K+ and Na+ are currently flowing across through
If the dendrites of a neuron were compared to a telephone receiver, then the soma could be compared to:
The switchboard
What did Cajal observe about the dendrites and axons?
They don't actually touch each other -> Small gap between axon of one neuron and dendrites of another (synapse)
What were scientists surprised by when observing the squid's neurons (HINT: has to do with charge?)
They measured the action potential at charge of +40 mV, which is well above zero NOT simply loss of -70 mV resting potential because this would only have brought charge back to zero
What effect do noepinephrine and dopamine have on the body?
They play a critical role in mood control; increases in either result in euphoria, wakefulness, and a burst of energy. Noepinephrine increases heart rate so an overdose can cause the heart to contract so rapidly that heartbeats do not last long enough to pump blood effectively
Refractory period
Time following an action potential during which a new action potential cannot be initiated; an imbalance of ions (lots of extra Na+ ions inside and a lot of extra K+ ions outside the axon)
What is a terminal button filled with?
Tiny vesicles containing neurotransmitters
Purkinje cell
Type of interneuron that carries info from cerebellum to rest of brain and spinal cord; dense, elaborate dendrites resembling bushes
Bipolar cells
Type of sensory neuron found in retinas of eyes; single axon and single dendrites
Prozac
Used to treat depression; neurotransmitter agonist -> blocks reuptake of serotonin == part of selective serotonin reuptake inhibitors (SSRIs)
Saltatory conduction
When electric current passes down length of myelinated axon, charge jumps from node to node rather than having to traverse entire axon
