Neurons and the Nervous System Flashcards
What’s a neuron?
Cells in the nervous system that communicate with one another through electrochemical signals to perform information-processing tasks.
What are neurons composed of?
The cell body (soma), dendrites and axons
What’s the purpose of the cell body?
To coordinate the information processing tasks and keep the cell alive
What’s the purpose of the dendrite?
To receive information from other neurons and relay it to the cell body
What’s the purpose of the axon?
To transmit information to other neurons, muscles or glands
What’s the myelin sheath?
An insulating layer of fatty material that covers the axon that allows signals to be transmitted more effectively
What are glial cells?
Support cells found in the nervous system that make up the myelin sheath. Glial cells can digest dead neurons, provide physical and nutritional support for neurons or form more myelin.
Why are demyelinating diseases (e.g. multiple sclerosis) so debilitating?
When the myelin sheath degenerates, transmission is slowed.
What are the different types of neurons (by function)?
- Sensory
- Motor
- Interneuron
What is the purpose of the sensory neuron?
Receive information from the external world through specialized endings on their dendrites and convey this information to the brain via the spinal cord
What is the purpose of the motor neuron?
Carry signals from the spinal cord to the muscles to produce movement
What is the purpose of the interneuron?
Connect sensory neurons, motor neurons or other interneurons
Where are mirror neurons found in many animals?
Frontal and parietal lobes
When are mirror neurons activated?
When an animal performs a behaviour (e.g. grasping) or when it observes another animal performing a behavior
When is the mirror neuron response the strongest?
When observing actions that were embedded in a context (e.g., grasping a cup to take a drink), as you can recognize the other person’s intentions
Why are mirror neurons important?
Facilitates smooth social interaction and suggests inborn neural basis for empathy
What are the different neurons by location?
- Purkinje
- Pyramidal
- Bipolar
What are purkinje cells?
Type of interneuron that carries information from the cerebellum to the rest of the brain and spinal cord
What are pyramidal cells?
Found in the cerebral cortex have a triangular cell body and a single long dendrite among many smaller dendrites
What are bipolar cells?
Type of sensory neuron found in the retinas of the eye and have a single axon and a single dendrite
2 stages of neural communication
- Conduction of electric signals within neuron
- Transmission of chemical signals between neurons
What’s resting potential?
The difference in electrical charge between the inside and outside of a neuron’s cell membrane
How does resting potential arise?
From the difference in the concentrations of ions inside and outside the neuron’s cell membrane
In a resting state, what is the ion concentration?
High concentration of positively charged sodium ions and negatively charged chloride ions outside the neuron’s cell membrane, negatively charged protein ions inside
What is ion concentration controlled by?
Channels in the axon membrane that allow molecules to flow in and out of the neuron
Which channels are open and which ones are closed during resting potential?
Potassium ions are open, sodium ions are closed
What is action potential?
An electrical signal that is conducted along the length of a neuron’s axon to the synapse
Why is an action potential an all or nothing phenomenon?
When the action potential occurs it always occurs with exactly the same characteristics and the same magnitude. Electric stimulation must also be above the threshold or the action potential won’t happen at all.
What happens when the threshold is reached?
Potassium channels briefly shut down, sodium channels open, allowing a flow of sodium ions into the axon. This pushes the action potential to its max value of +40mV.
What happens when the action potential reaches its maximum?
The membrane channels return to their original state.
What’s the refractory period?
The time following an action potential during which a new action potential cannot be initiated
What reverses the imbalance of ions following an action potential?
An active chemical “pump” in the cell membrane moves sodium outside the axon and moves potassium inside the axon
Once the action potential is generated how does it move down the axon?
The action potential is generated at the beginning of the axon and travels a short distance, then generates one at another location and it spreads. This ensures the action potential doesn’t dissipate over the distance it travels.
How does the myelin facilitate the transmission of the action potential? What is this process called?
There are breaks in the myelin called the Nodes of Ranvier. The action potential “jumps” from node to node. This process is called saltatory conduction.
What do axons end in?
Terminal buttons – knoblike structures that branch out from an axon and is filled with vesicles
What do the vesicles in terminal buttons contain?
neurotransmitters
What are neurotransmitters?
Chemicals that transmit information across the synapse to a receiving neuron’s dendrites
How do dendrites receive neurotransmitters?
They contain receptors - parts of the cell membrane that receive neurotransmitters and either initiate or prevent a new electrical signal
What is the purpose of synaptic transmission?
Allows neurons to communicate and results in thoughts, emotions and behaviour
How do neurotransmitters leave the synapse?
Autoreceptors, reuptake and enzyme deactivation
Autoreceptors
Detect how much of a neurotransmitter has been released into a synapse and signal the neuron to stop releasing neurotransmitters when an excess is present.
Reuptake
Neurotransmitters are reabsorbed by the terminal buttons of the presynaptic neuron’s axon
Enzyme deactivation
Neurotransmitters are destroyed by enzymes in the synapse
Acetylcholine
Involved in a number of functions including voluntary motor control, attention, learning and memory. Deterioration of Ach producing neurons can lead to Alzheimer’s.
Dopamine
Regulates motor behavior, motivation, pleasure, and emotional arousal
Glutamate
Major excitatory neurotransmitter involved in information transmission throughout the brain
GABA
Major inhibitory neurotransmitter in the brain
Norepinephrine
Influences mood and arousal
Serotonin
Involved in the regulation of sleep and wakefulness, eating, and aggressive behavior
What is dopamine implicated in?
Addiction, schizo, Parkinson’s
Endorphins
Chemicals that act within the pain pathways and emotion centers of the brain
What drugs increase the action of a neurotransmitter?
Agonists
What drugs block the function of a neurotransmitter?
Antagonists
How do some agonists and antagonists work?
They have a structure similar to the neurotransmitter and can bind to that neurotransmitter’s receptor
What is L-Dopa?
Agonist used to treat Parkinson’s that causes neurons to produce more dopamine. Effectiveness fades over time and it can disrupt the body’s reward system.
What does meth do to the body?
Affects pathways for dopamine, serotonin and norepinephrine. Alters function of neurotransmitters that help us perceive and interpret visual images.
How do amphetamine and cocaine work?
Stimulates release + prevents reuptake of norepinephrine and dopamine. This excess results in euphoria, wakefulness and burst of energy.
How does a postsynaptic membrane adapt to chronically high dopamine levels and what’s the effect of this?
It produces new receptors, which results in depression and cravings.
What’s the nervous system?
An interacting network of neurons that conveys electrochemical information throughout the body
What are the two divisions of the nervous system?
Central and peripheral
What is the central nervous system?
Composed of brain and spinal cord
What is the peripheral nervous system?
Connects the central nervous system to the body’s organs and muscles. Divided into somatic and autonomic.
What is the somatic nervous system?
A set of nerves that conveys information into and out of the central nervous system
What is the autonomic nervous system?
The autonomic nervous system is a set of nerves that carries involuntary and automatic commands that control blood vessels, body organs and glands. Works outside of conscious control.
What are the subdivisions of the autonomic nervous system?
Sympathetic and parasympathetic
What is the sympathetic nervous system?
A set of nerves that prepares the body for action in threatening situations. Dilates pupils, accelerates heartbeat, inhibits digestive activity, stimulates release of certain hormones.
What is the parasympathetic nervous system?
Helps the body return to a normal resting state
What are spinal reflexes?
Simple pathways in the nervous system that rapidly generate muscle contractions
How does the PNS communicate with the CNS?
Through nerves that conduct sensory information into the brain, carry commands out of the brain
How does the brain send commands for voluntary movement?
Through the spinal cord to motor neurons. Damage to the spinal cord severs this connection. Damage to higher parts usually results in greater impairment.
