The Neuron Flashcards
Structure of neurons and chemistry at rest
What is another name for the cell body?
The soma
What is the name of where the cell body joins the axon?
Initial segment/ Axon Hillock
What are collaterals of the neuron?
Branches from axon; more collaterals are present closer to end of the neuron = more influence
What are processes?
Long extensions
What is the myelin sheath?
Layers of modified plasma membrane, comprised of Glial cells
What cells are the myelin sheath comprised of in the PNS?
Schwann cells
What cells are the myelin sheath comprised of in the CNS?
Oligodendrocytes
What direction do afferent neurons run in?
Towards CNS; are sensory neurones
What part of the afferent neurons is in the CNS?
Central process (axon) enters CNS
What parts of the afferent neurons are in the PNS?
Cell body and peripheral process (dendron) are in PNS
What direction do efferent neurons run in?
Away from CNS; are motor neurons
What parts of the efferent neurons are in the CNS?
Cell body and its dendrites are located in the CNS
What part of the efferent neurons is in the PNS?
Axon is in the PNS, extended peripherally
Where are interneurons located?
Within the CNS
What are interneurons?
Relay neurons; signal changers/integrators; process information
What does the number of interneurons indicate about the complexity of the required action?
More interneurons in a pathway indicates increased complexity of action
What is the ratio of afferent: efferent: interneurons?
1 afferent: 10 efferent: 200,000 interneurons
What are the four main glial cells?
Oliodendrocytes, ependymal, microglia, astrocytes
What are oliodendrocytes?
Make up the myelin on axins
What are ependymal cells?
Line fluid-filled cavities; regulate production and flow of CSF
What are microglia?
Macrophage-like cells which perform immune function for nervous system
What are astrocytes?
Regulate extracellular fluid composition, especially at the end of the neuron, by removing K+ and NTs around the synapse; Form blood-brain barriers at capillary walls to protect neuron; Metabolically sustain neurons by providing glucose and removing ammonia; Guide neurons as they migrate to destination, and stimulate neuronal growth in embryos
What is polarity?
Intracellular charge
What is value?
The potential difference
What is electrical potential?
The attraction of opposite charges if not separated by a barrier
What is the resting membrane potential?
Voltage difference between inside and outside of cells; -70mV
How is an electrostatic gradient created?
Intracellular is polarised due to having lower +ve charge
How is a concentration gradient created?
Ionic imbalance between inside and outside of cell
What does the membrane potential depend on?
Depends on concentration gradients and membrane permeabilities of Na+ and K+
What is the overall effect of concentration and electrostatic gradients on Na+ and K+?
Na+: both pull in
K+: concentration gradient pushes out, electrostatic pulls in
How is the K+ equilibrium potential reached?
K+ diffuse down concentration gradient out of cell when K+ channels open; P.d. is created as excessive positive charge is present in extracellular fluid due to Na+ and K+; K+ flux influenced, and less positive charge inside cells pulls K+ back in, creating electric potential; when fluxes due to concentration and electrical gradients become equal, membrane potential is same as the K+ equilibrium potential for that ion; no net movement of K+
What does the NERNST equation describe?
Magnitude and direction of equilibrium potential is different for different ions and depends on concentration gradients
What is the NERNST equation?
Eion = 61/Z log ([out]/[in])
What is the order of membrane permeability to the significant ions?
Cl- > K+ > Na+»_space; proteins-
What is the largest contribution to the membrane potential?
Generated largely from K+ movement out of cell down concentration gradient, making inside more negative than positive (but is not equal to K+ equilibrium potential, although much closer than to Na+ equilibrium potential)
How does Na+ neutralise the effect of some K+ moving out?
A small number of Na+ channels are channels are open in resting state, allowing Na+ into cells
What is the function of the Na+/K+ ATPase pumps?
Maintain concentration gradients, by moving 3Na+ out and 2K+ in; create small electrogenic effect by a small negative potential (electrogenic pumps); contribute directly to membrane potential; balance ion leakage through open channels down concentration gradients
