Chapter 3: Neuroscience and Behavior 3.1-3.3 Flashcards
Neurons
Cells in the nervous system that communicate with each other to perform information processing tasks
Cell body
Aka the soma is the largest component of the neuron that coordinates the information-processing tasks like protein synthesis, cell production, and metabolism, and keeps the cell alive; enclosed by a porous cell membrane that allows some molecules to flow into and out of the cell
Nucleus
Contained in the cell body and houses chromosomes that contain your DNA
What are the two types of specialized extensions of the cell membrane?
Dendrites and axons
Dendrites
Greek for “tree,” receive information from other neurons and relay it to the cell body
Axon
Carries information to other neurons, muscles, or glands; can be very long
What covers the axon (in many neurons)?
Myelin sheath, an insulating layer of fatty material composed of glial cells (Greek for “glue”)
Glial cells
Support cells found in the nervous system that serve different functions like digesting parts of dead neurons, providing physical and nutritional support for neurons, and forming myelin that insulates the axon and allows it to carry information more efficiently
Demyelinating diseases
E.g. multiple sclerosis, cause the myelin sheath to deteriorate, slowing the communication from one neuron to another which lead to problems like loss of feeling in limbs, partial blindness, difficulties in coordinated movement and cognition
Synapse
Junction or region between the axon of one neuron and the dendrites or cell body of another
What are the three major types of neurons?
Sensory, motor, and interneurons
Sensory neurons
Receive information from the external world and convey this information to the brain via spinal cord; have specialized endings on their dendrites that receive signals for light, sound, touch, taste, and smell
Motor neurons
Carry signals from the spinal cord to the muscles to produce movement, often have long axons that reach to muscles at our extremeties
Interneurons
Connect sensory neurons, motor neurons, or other interneurons; work together in small circuits to perform tasks like identifying the location of a sensory signal and recognizing a familiar face
Purkinje cells
Type of interneuron that carries information from the cerebellum to the rest of the brain and the spinal cord; have dense elaborate dendrites that resemble bushes
Pyramidal cells
Found in the cerebral cortex, have a triangular cell body and a single, long dendrite among many smaller dendrites
Bipolar cells
Type of sensory neuron found in the retinas of the eye, have a single axon and a single dendrite
What are the two stages of electrochemical action in neurons?
Conduction and transmission
Conduction
Movement of an electric signal within neurons, from the dendrites to the cell body, then throughout the axon
Transmission
Movement of a signal from one neuron to another as a result of chemical signalling across the synapse
Resting potential
The difference in electric charge due to varying concentrations of ions between the inside and outside of a neuron’s cell membrane
When is a neuron in resting state?
Inside the neuron’s cell membrane, there is a high concentration of positively charged potassium ions (K+) and larger negatively charged protein ions (A-) compared to outside it. Outside the neuron’s cell membrane, there is a high concentration of positively charged sodium ions (Na+) and negatively charged chloride (Cl-). A- ions are larger and carry a stronger charge than the others so the inside of the cell membrane is negatively charged at -70 millivolts relative to the outside during resting potential.
Action potential
Electric signal that is conducted along the length of a neuron’s axon to a synapse
Explain “the action potential is all or none”
Electric stimulation or shock below the threshold fails to produce an action potential while electric stimulation at or above the threshold always produces the action potential at the same magnitude (value is above zero at +40 millivolts)
How does the total charge inside the axon change from negative to positive?
During resting potential, voltage-gated channels for Na+ ions are closed. When the voltage across the cell body membrane reaches the threshold, sodium-specific channels on the nearby axons open up and Na+ ions rush out into the cell instantaneously, changing the total charge in the axon from negative to positive in less than a millisecond.
What two events restore the negative charge of the resting potential?
(1) Na+ channels are inactivated or in a refractory period for several milliseconds, stopping the flow of Na+ ions (2) Channels specific to K+ ions open, allowing K+ ions inside the cells to exit, then the channels close
Refractory period
The time following an action potential during which a new action potential cannot be initiated; limits the number of times a neuron can fire and keeps the action potential from travelling back to the cell body
Explain the domino effect of action potential across the neuron
When the first voltage channels open, Na+ ions spread and increase the electrical charge down the inside of the axon. When the voltage around adjacent voltage channels reaches the threshold, those open and let in more Na+ ions that spread further. The influx of Na+ ions triggers the nearby channels to open (each reaching +40) and the process repeats down the entire axon.
What is the effect of the myelin sheath on the action potential?
Conduction of the action potential is greatly increased by the presence of a myelin sheath around the axon; prevents electric current from leaking out of it
What is the structure of the myelin sheath?
Doesn’t cover the entire axon; has break points called nodes of Ranvier between clumps
Saltatory conduction
Electric current jumps quickly from node to node where it slows down, which then helps speed the flow of information down the axon
Terminal buttons
Knoblike structures at the end of an axon which are each filled with tiny vesicles or bags that contain neurotransmitters
Neurotransmitters
Chemicals that transmit information across the synapse to a receiving neuron’s dendrites
Receptors
Found in the dendrites of the receiving neuron; parts of the cell membrane that receive neurotransmitters and either initiate or prevent a new electric signal
What are presynaptic and postsynaptic neurons?
The sending neuron is presynaptic and the receiving neuron is the postsynaptic neuron
Synaptic transmission
The sending of neurotransmitters from the presynaptic neuron down the axon to the terminal buttons where they are released from vesicles into the synapse, then received by binding to receptor sites on the nearby dendrite of the postsynaptic neuron
What tells dendrites which of the neurotransmitters flooding into the synapse to receive?
(1) Neurons tend to form pathways in the brain that are characterized by specific neurotransmitters (2) Like a lock-and-key system, only some neurotransmitters bind to specific receptor sites on a dendrite
What three processes make neurotransmitters leave the synapse?
Reuptake, Enzyme deactivation, Diffusion
Reuptake
Neurotransmitters are absorbed by the terminal buttons of the presynaptic neuron’s axon or by neighbouring glial cells
Enzyme deactivation
Specific enzymes break down specific neurotransmitters
Diffusion
Neurotransmitters drift out of the synapse and can no longer reach receptors
How do autoreceptors stop the release of more neurotransmitters?
Neurotransmitters can bind to receptor sites on the presynaptic neuron. These autoreceptors can detect how much of a neurotransmitter has been released and stop the release of more.
What are some of the most common neurotransmitters in the nervous system?
Acetylcholine (ACh), Dopamine, Glutamate, GABA (gamma-aminobutyric acid), Norepinephrine and Serotonin, Endorphine
Acetylcholine (ACh)
Involved in voluntary motor control, regulation of attention, learning, sleeping, dreaming, and memory; associated with Alzheimer’s disease where there is deterioration of ACh-producing neurons
Dopamine
Regulates motor behaviour and emotional arousal, plays roles in basic motivated behaviors like seeking pleasures (e.g. drug addiction) or actions with rewards; high levels are linked to schizophrenia while low levels are linked to Parkinson’s disease
Glutamate
Major excitatory neurotransmitter, meaning it enhances the transmission of information between neurons
GABA (gamma-aminobutyric acid)
Primary inhibitory neurotransmitter in the brain, meaning it prevents the firing of neurons
What can cause seizures?
Too much glutamate or too little GABA make neurons overactive, causing seizures
Norepinephrine and Serotonin
Influence mood and arousal; low levels of each are linked to mood disorders
Norepinephrine
Involved in states of vigilance or a heightened awareness of dangers in the environment
Serotonin
Involved in the regulation of sleep and wakefulness, eating, and agressive behavior
Endorphine
Chemical that acts within the pain pathways and emotion centers of the brain; dulls the experience of pain and elevates moods; causes the “runner’s high”
Agonists
Drugs that increase the action of a neurotransmitter
Antagonists
Drugs that diminish the function of a neurotransmitter
Examples of agonist drugs
Clondine bind to autoreceptors and block their inhibitory effect, Levodopa or L-dopa increase the production of neurotransmitters (converted to dopamine which medicates Parkinson’s), Amphetamines increase the release of neurotransmitters, Prozac blocks the reuptake of neurotransmitters, Nicotine binds to postsynaptic receptor sites and activates them
Examples of antagonist drugs
Caffeine activates autoreceptors so they inhibit release of neurotransmitters, AMPT block production of neurotransmitters, Botullinium toxin block the release of neurotransmitters, Naloxone bind to receptor sites and block neurotransmitters
Selective serotonin reuptake inhibitors (SSRIs)
Drugs that block the reuptake of neurotransmitter serotonin to treat clinical depression e.g. Prozac
Beta blockers
Obstruct receptor sites in the heart for norepinephrine, a neurotransmitter that increases one’s heartbeat e.g. propranalol
Nerves
Bundles of axons and the glial cells that support them
Nervous system
An interacting network of neurons that conveys electrochemical information throughout the body
What are the two major divisions of the nervous system?
Central nervous system (CNS) and the peripheral nervous system (PNS)
Central nervous system
Composed of the brain and spinal chord; receives sensory information from the external world, processes and coordinates this, and sends commands to the skeletal and muscular systems for action
Brain and spinal chord
Brain contains structures that support the most complex perceptual, motor, emotional, and cognitive functions of the nervous system; Spinal chord are nerves that process sensory information and relay commands to the body connected to it
Peripheral nervous system
Connects the central nervous system to the body’s organs and muscles
What are the two major subdivisions of the peripheral nervous system?
Autonomic and somatic
Somatic nervous system
Set of nerves that conveys information between voluntary muscles and the central nervous system
Autonomic nervous system
Set of nerves that carries involuntary and automatic commands that control blood vessels, body organs, and glands
What are the two major subdivisions of the ANS?
Sympathetic and parasympathetic nervous systems
Sympathetic nervous system
Set of nerves that prepares the body for action in challenging or threatening situations
What happens when your sympathetic nervous system kicks into action?
Dilates pupils, increases heart rate and respiration to pump more oxygen into muscles, diverts blood flow to brain and muscles, activates sweat glands to cool your body, inhibits salivation and bowel movements to conserve energy, suppresses body’s immune responses and responses to pain and injury
Parasympathetic nervous system
Helps the body return to a normal resting state and reverses the effects of the sympathetic nervous system e.g. constricts pupils and diverts blood flow to digestive system
Spinal reflexes
Simple pathways in the nervous system that rapidly generate muscle contraction
Reflex arc
Neural pathway that controls relflex actions
