Unit 4: Biological Bases Of Bahviour (Chapter 3) Flashcards
Sensory neurons
Carry messages from the sensory organs (e.g., eyes, tongue, skin) to the spinal cord and the brain.
Neuron
Cell of the nervous system specialized for sending and receiving neural messages. There are approx. 100 billion neurons in the brain making 100 trillion connections.
Motor neurons
Carry messages from the brain and spinal cord to muscles and glands.
Interneurons
Within the the brain and spinal cord collect, integrate, & retrieve messages from various sources.
Dendrites
Receive chemical messages from other neurons. Search to increase the surface area of the cell to recieve messages.
Cell body/soma
Collects neural impulses, contains the nucleus, sustains cell functions.
Axon
Transports electrical impulses to other neurons via the terminal branches.
Axon terminals/terminal branches
Convert electrical signals into chemical messages for other neurons.
Myelin sheath
Fatty layer that insulates the axons & speeds up transmission of electrical signals. Helps speed up the propagation of the action potential by ensuring the electrical messages meet less resistance.
“Underdevelopped prefrontal cortex” = Neurons not all myelated yet! Slower messages sent at 0.5-2 m/s.
Glia
Nervous system cells that perform variety of critical support functions. Make up the myelin sheath around neurons to insulate, support and nourish neurons and modulate neuronal function.
Glial cell functions
- Provide structural support & scaffolding for neurons (“guide them”).
- Clean up debris.
- Form blood-brain barrier (prevent blood toxins to enter the brain tissue).
- Facilitating neurons between neurons and pruning unneeded (excess/weak) connections.
- Nutrient supply.
- Insulation (myelin sheath).
Action potential
Electrical impulses fired off by neurons to “talk” to one another. Generated at the junction between the axon and the cell body. Causes the depolarization (rapid change in voltage) of said area and the opening of sodium channels. Travel down the length of the axon to its terminal, where they signal release of chemical messages to neighbouring cells.
Cell membrane
Thin fatty “skin” enclosing the neuron:
- Separates the intracellular fluid inside the neuron and extracellular fluid
outside the neuron.
- Intracellular and extracellular fluids contain various electrically charged particles (ions). Ex: sodium (Na+), chloride (Cl-), potassium (K+), calcium (Ca2+).
- Cell membrane is selectively permeable, allowing for passage of certain ions and not others.
Resting potential
Electrical charge across the membrane (~70 millivolts). In this state:
- More negatively charged particles inside the cell than outside.
- Neuron cannot fire action potential.
Ion channels
“Gate-type structures” in the cell membrane at the end of the axon, adjeacent to the soma. Open when the neuron is sufficiently stimulated by other neurons, and allow positively charged Na+ ions to enter. Electrical charge then begins to reverse.
I.e. the channels that allow chemical ions to enter and exit the neuronal membrane to generate the voltage for resting and action potentials.
Depolarization
The reversal of the electrical charge (more +) across the membrane of the neuron. The first phase of the action potential.
Less of a difference in the charges of the extracellular and intracellular liquids.
Voltage threshold
Critical level to which a neuron’s membrane potential must be depolarized to initiate action potential (~55 mV). Once threshold is passed, voltage-gated ion channels open allowing positively charged sodium (Na+) ions to flood in. The interior of the cell is now more + charged than the outside. All or nothing response. There is no such thing as a strong/weak action potential.
Repolarization
The portion of the action potential where the during which the cell returns to its resting potential. As depolarization occurs, channels that were letting sodium (Na+) pass through close, but potassium (K+) channels remain open and those ions flow out of the cell.
Refractory period
Temporary dip below resting potential. During this period it is very hard to get the neuron to fire again. This period also ensure that action potential is propagated forward.
Synaptic cleft
Gap separating neurons. To traverse synapse, electrical signal has to be converted to a chemical one. To do do, presynaptic neurons send neurotranmitters.
Neurotransmitters
Chemical messengers released upon arrival of the action potential. Sent by presynaptic neurons to convert the electrical signal to a chemical one, and allow it to traverse synapse. Cross the synaptic cleft to bind to receptors on the postsynaptic neuron.
Receptor
Channel in membrane of a neuron that binds neurotransmitters in a “lock-and-key” manner.
Tidying up the synapse : Diffusion
Neurotransmitters drift out of synapse.
ESSENTIAL TO TIDY UP THE SYNAPSE TO TERMINATE THE CHEMICAL MESSAGE.
Tidying up the synapse : Degradation
Neurotransmitters are broken down in the synapse.
ESSENTIAL TO TIDY UP THE SYNAPSE TO TERMINATE THE CHEMICAL MESSAGE.
Tidying up the synapse : Reuptake
Neurotransmitters are reabsorbed into the presynaptic terminal branches.
ESSENTIAL TO TIDY UP THE SYNAPSE TO TERMINATE THE CHEMICAL MESSAGE.
Excitation
Receiving neuron slightly depolarized. Moves it closer towards voltage threshold and increases likelihood of initiation of action potential.
Inhibition
Receiving neuron slightly hyperpolarized. Moves it further from threshold & reduces likelihood of action potential.
Ex: Coordination between muscle contraction (excitatory inputs) and muscle relaxation (inhibitory inputs) required for coordination.
Ex 2: Tetanus lockjaw (bacteria destroys inhibitory inputs).
Neurotransmitter (amino acid): GABA (Gamma-aminobutyric acid)
Most common inhibitory neurotransmitter; downregulation of stress, anxiety, fear.
- Many sedative drugs act by targeting GABA receptors.
- Alcohol also promotes activity at GABA receptors.
Neurotransmitter (amino acid): Glutamate
Binds to exitatory receptors; helps form long-term memories.
Amino acids
The brain’s most abundant class of neurotransmitters, including glutamate (important for neuronal exitation), and gamma-aminobutyric acid (GABA, important for neuronal inhibition and the regulation of muscle tone).
Neurotransmitter: Acetylcholine
- Can trigger both excitatory and inhibitory signals.
- Commonly found in neuromuscular junction (drugs that interfere with ACh, like curare, used as a bioweapon, result in paralysis and death).
- Plays key role in autonomic nervous system, which carries commands from brain to glands & organs, regulates cardiac activitiy.
- Brain circuits involved in learning and memory (low levels associated with dementia of Alzheimer’s disease).
Monoamines
A neurochemical class that inlcudes norepinephrine, dopamine and seratonin (important for fight-or-flight and reward responses).
Neurotransmitter (monoamine): Norepinephrine/noradrenaline
Important for “fight or flight response”; contributes to arousal & vigilance.
- In excess, can contribute to high blood pressure, anxiety.
Neurotransmitter (monoamine): Serotonin
Contributes to regulation of sleep, appetite, mood, and aggression.
- Thought to play in depression, although precise mechanism still debated.
Neurotransmitter (monoamine): Dopamine
Involved in movement, planning, and aspects of reward.
- Most addictive drugs (ex: meth) stimulate increased activity in dopaminergic circuits.
- Excess levels associated with schizophrenia, low levels with Parkinson’s disease.
Neurotransmitters (neuropeptides): Endorphins
- “Endogenous morphine”.
- Promote feelings of pleasure and
reduce pain. - The OPRM1 gene codes for the opioid receptor where endorphins bind.
Ex: Rat mom + affection study (high vs low LG).
Psychoactive drugs
Chemical substances that alter a person’s thoughts, feelings, or behaviors by influencing the activity of neurotransmitters in the nervous system.
- Includes prescription medications like anti-depressants and drugs like cocaine, heroin, LSD, etc.
- Other commonplace examples: caffeine, nicotine and alcohol.
Agonist
Enhances action of a neurotransmitter by increasing release, blocking its reuptake, or mimicking neurotransmitter & activating its postsynaptic receptor.
Ex: Heroin.
Antagonist
Inhibits actions of a neurotransmitter by blocking release, destroying neurotransmitter in synapse, or mimicking neurotransmitter & binding to a postsynaptic receptor to block neurotransmitter.
Ex: Naloxone = opioid receptor antagonist used upon overdose.
Opioid addiction model
- Opioid drugs (e.g., heroin) hijack & eventually overpower reward function of endogenous opioids.
- Repeated use causes changes to receptor structure (decreased # or sensitivity).
- Tolerance to drug, loss of sensitivity for naturally occuring rewards. Taking larger doses of the drug for the same effect.
- Locus of control for drug-seeking behaviour shifts from positive reinforcement (taking drug to feel good) to negative reinforcement (taking drug to alleviate negative feelings/withdrawal).
Nervous system
Complex network of nerves (bundles of neurons) that controls & regulates all bodily functions. Subdivisions include:
- Central nervous system (brain, spinal cord). Sensory and motor nerves that travel throughout the body.
- Peripheral nervous system (nerves connecting brain to the rest of your body).
Peripheral nervous system subdivisions
Somatic nervous system:
- Carries commands for voluntary movement from CNS to muscles.
- Brings sensory input to CNS; allows you to feel external sensations.
Autonomic nervous system:
- Carries involuntary commands to organs, blood vessels, & glands.
- Operates outside your conscious control.
- Allows you to feel internal sensations.
- Further subdivided into sympathetic and parasympathetic branches.
Sympathetic nervous system
Prepares body for situations requiring
expenditure of energy (fight-or-flight
response). Acts on blood vessels, organs and glands.
- Pupil dilation, increased breathing, heart rate, & blood flow to muscles.
- Redirects energy from non-essential
processes (e.g., digestion).
“Has sympathy for you.”
Parasympathetic nervous system
Controls blood vessels, glands & organs during calm periods; returns body to resting state (rest-and-digest).
- Nutrient storage, repair, growth.
Endocrine system
Network of glands (hormone-secreting organs) that work together with CNS and PNS.
Hormone
Blood-borne chemical messengers that enable the brain to regulate the body’s activities.
- Slower than CNS neurotransmitters
- Travel over greater distances
- Involved in regulating arousal, metabolism, growth, & sex.
Adrenal glands
Located on top of kidneys.
- SNS activates adrenal glands during
stressful/threatening events → release of adrenaline and cortisol.
- Boost energy, increased heart rate, blood pressure, blood sugar levels.
- Cortisol has slower onset but longer lasting efects (not the first rush of stress!).
Pituitary gland
The ‘master endocrine gland’ located at the base of the brain.
- Directs other glands
- Regulates hunger, sexual arousal,
growth, sleep (via pineal gland), navigation of social world.
Oxytocin
Hormone released into bloodstream by
pituitary gland.
- Involved in parturition (stimulates uterine contractions during birth).
- Artificial forms of oxytocin used to
induce labour.
- Promotes lactation.
- Thought to play role in social bonding.
Ex: A tale of two voles study = Prairie voles (high density of oxytocin receptors in reward related areas of the brain, pair bonds after mating) VS montane voles (low density of oxytocin recpetors in said regions, no pair bonds, more solitare).
Ex: Humans and economic trust game.
