Neurons Week 5 Flashcards
Santiago Ramón y Cajal. Ramón y Cajal (1911) discovery
concluded that discrete individual neurons are the structural and functional units of the nervous system.
Camillo Golgi.
Golgi stained tissue
- characteristic of a Golgi stain is that it only stains approximately 1–2% of neurons permitting the observer to distinguish one cell from another.
Resting Membrane Potential
what occurs in a neuron at rest, when it is theoretically not receiving or sending signals.
number of neurons in human brain
100 billion neurons
3 components of neurons
dendrites,
the soma,
the axon
Define dendrites
Part of a neuron that extends away from the cell body and is the main input to the neuron.
Define soma
Cell body of a neuron that contains the nucleus and genetic information, and directs protein synthesis.
Define nucleus
Collection of nerve cells found in the brain which typically serve a specific function.
Define axon
main output of the neuron.
Part of the neuron that extends off the soma, splitting several times to connect with other neurons
Define synapse
Junction between the presynaptic terminal button of one neuron and the dendrite, axon, or soma of another postsynaptic neuron.
What is the terminal button?
The part of the end of the axon that form synapses with postsynaptic dendrite, axon, or soma.
What are spines?
Protrusions on the dendrite of a neuron that form synapses with terminal buttons of the presynaptic axon.
what is synaptic gap?
Also known as the synaptic cleft; the small space between the presynaptic terminal button and the postsynaptic dendritic spine, axon, or soma.
5 nanometers
What are synaptic vesicles
Groups of neurotransmitters packaged together and located within the terminal button.
What are neurotransmietters
Chemical substance released by the presynaptic terminal button that acts on the postsynaptic cell.
Not all neurons are equal,
what are three main categories of neurons:
- Unipolar - ideal for relaying information forward, so they have one neurite (axon) and no dendrites.
- Bipolar - involved in sensory perception, have one axon and one dendrite which help acquire and pass sensory information to various centers in the brain.
- multipolar - communicate sensory and motor information in the brain. one axon and many dendrites which allows them to communicate with other neurons.
glia cell - oligodendroglia
forms the myelin sheaths
GLIA DO NOT PARTICIPATE IN COMMUNICATION BETWEEN CELLS
glia cells, such as microglia and astrocytes
digest debris of dead neurons, carry nutritional support from blood vessels to the neurons, and help to regulate the ionic composition of the extracellular fluid.
GLIA DO NOT PARTICIPATE IN COMMUNICATION BETWEEN CELLS
two stages of electrochemical action in neurons.
- electrical conduction of dendritic input to the initiation of an action potential within a neuron.
- chemical transmission across the synaptic gap between the presynaptic neuron and the postsynaptic neuron of the synapse.
Cations
Positively charged ions
anions
negatively charged ions
composition of intracellular and extracellular fluid (4)
sodium (Na+)
potassium (K+)
chloride (Cl–)
anions (A–)
Define cell membrane
A bi-lipid layer of molecules that separates the cell from the surrounding extracellular fluid.
What are ion channels
Proteins that span the cell membrane, forming channels that specific ions can flow through between the intracellular and extracellular space.
What is diffusion?
The force on molecules to move from areas of high concentration to areas of low concentration.
What is electrostatic pressure?
The force on two ions with similar charge to repel each other; the force of two ions with opposite charge to attract to one another.
equilibrium potential
voltage at which no ions flow
resting membrane potential
The voltage inside the cell relative to the voltage outside the cell while the cell is a rest (approximately -70 mV).
Anions (A-):
Anions are highly concentrated inside the cell and contribute to the negative charge of the resting membrane potential. Diffusion and electrostatic pressure are not forces that determine A– concentration because A– is impermeable to the cell membrane. There are no ion channels that allow for A– to move between the intracellular and extracellular fluid.
Potassium (K+):
The cell membrane is very permeable to potassium at rest, but potassium remains in high concentrations inside the cell. Diffusion pushes K+ outside the cell because it is in high concentration inside the cell. However, electrostatic pressure pushes K+ inside the cell because the positive charge of K+ is attracted to the negative charge inside the cell. In combination, these forces oppose one another with respect to K+.
Chloride (Cl-):
The cell membrane is also very permeable to chloride at rest, but chloride remains in high concentration outside the cell. Diffusion pushes Cl– inside the cell because it is in high concentration outside the cell. However, electrostatic pressure pushes Cl– outside the cell because the negative charge of Cl– is attracted to the positive charge outside the cell. Similar to K+, these forces oppose one another with respect to Cl–.
Sodium (Na+):
The cell membrane is not very permeable to sodium at rest. Diffusion pushes Na+ inside the cell because it is in high concentration outside the cell. Electrostatic pressure also pushes Na+ inside the cell because the positive charge of Na+ is attracted to the negative charge inside the cell. Both of these forces push Na+ inside the cell; however, Na+ cannot permeate the cell membrane and remains in high concentration outside the cell. The small amounts of Na+ inside the cell are removed by a sodium-potassium pump, which uses the neuron’s energy (adenosine triphosphate, ATP) to pump 3 Na+ ions out of the cell in exchange for bringing 2 K+ ions inside the cell.
Sodium potassium pump
An ion channel that uses the neuron’s energy (adenosine triphosphate, ATP) to pump three Na+ ions outside the cell in exchange for bringing two K+ ions inside the cell.
Hodgkin and Huxley action potential
A transient all-or-nothing electrical current that is conducted down the axon when the membrane potential reaches the threshold of excitation. -70 mV
threshold of excitation
Specific membrane potential that the neuron must reach to initiate an action potential. around -50 mV.
types of fluctuations in the neuron’s membrane potentials (2)
- excitatory postsynaptic potentials
- inhibitory postsynaptic potentials
excitatory postsynaptic potentials
A depolarizing postsynaptic current that causes the membrane potential to become more positive and move towards the threshold of excitation.
inhibitory postsynaptic potentials
A hyperpolarizing postsynaptic current that causes the membrane potential to become more negative and move away from the threshold of excitation.
What are ionic recpetors
Ion channel that opens to allow ions to permeate the cell membrane under specific conditions, such as the presence of a neurotransmitter or a specific membrane potential.
What part of the neuron carries the action potential and is the main source of output?
axon
What insulating substance allows for an electrical signal to travel much faster down an axon?
myelin sheath
What type of neuron receives environmental stimuli and helps people perceive?
sensory neuron
Communication within a neuron is electrical, and between neurons is ______.
chemical
The electrostatic charge within a neuron must reach the ______before the neuron will fire.
threshold of excitation
What current causes depolarization, increasing the likelihood that the neuron will fire?
excitatory postsynaptic potential
Differentiate the functional roles between the two main cell classes in the brain, neurons and glia.
Describe how the forces of diffusion and electrostatic pressure work collectively to facilitate electrochemical communication.
Define resting membrane potential, excitatory postsynaptic potentials, inhibitory postsynaptic potentials, and action potentials.
Explain features of axonal and synaptic communication in neurons.
Define hormones
An organic chemical messenger released from endocrine cells that travels through the blood to interact with target cells at some distance to cause a biological response.
what is the endocrine glands
A ductless gland from which hormones are released into the blood system in response to specific biological signals.
neurotransmitters
Chemical substance released by the presynaptic terminal button that acts on the postsynaptic cell.
testosterone
The primary androgen secreted by the testes of most vertebrate animals, including men.
progestin
A class of C21 steroid hormones named for their progestational (pregnancy-supporting) effects. Progesterone is a common progestin.