The Neuron

Question 1

What is another name for the cell body?

Answer 1

The soma

Question 2

What is the name of where the cell body joins the axon?

Answer 2

Initial segment/ Axon Hillock

Question 3

What are collaterals of the neuron?

Answer 3

Branches from axon; more collaterals are present closer to end of the neuron = more influence

Question 4

What are processes?

Answer 4

Long extensions

Question 5

What is the myelin sheath?

Answer 5

Layers of modified plasma membrane, comprised of Glial cells

Question 6

What cells are the myelin sheath comprised of in the PNS?

Answer 6

Schwann cells

Question 7

What cells are the myelin sheath comprised of in the CNS?

Answer 7

Oligodendrocytes

Question 8

What direction do afferent neurons run in?

Answer 8

Towards CNS; are sensory neurones

Question 9

What part of the afferent neurons is in the CNS?

Answer 9

Central process (axon) enters CNS

Question 10

What parts of the afferent neurons are in the PNS?

Answer 10

Cell body and peripheral process (dendron) are in PNS

Question 11

What direction do efferent neurons run in?

Answer 11

Away from CNS; are motor neurons

Question 12

What parts of the efferent neurons are in the CNS?

Answer 12

Cell body and its dendrites are located in the CNS

Question 13

What part of the efferent neurons is in the PNS?

Answer 13

Axon is in the PNS, extended peripherally

Question 14

Where are interneurons located?

Answer 14

Within the CNS

Question 15

What are interneurons?

Answer 15

Relay neurons; signal changers/integrators; process information

Question 16

What does the number of interneurons indicate about the complexity of the required action?

Answer 16

More interneurons in a pathway indicates increased complexity of action

Question 17

What is the ratio of afferent: efferent: interneurons?

Answer 17

1 afferent: 10 efferent: 200,000 interneurons

Question 18

What are the four main glial cells?

Answer 18

Oliodendrocytes, ependymal, microglia, astrocytes

Question 19

What are oliodendrocytes?

Answer 19

Make up the myelin on axins

Question 20

What are ependymal cells?

Answer 20

Line fluid-filled cavities; regulate production and flow of CSF

Question 21

What are microglia?

Answer 21

Macrophage-like cells which perform immune function for nervous system

Question 22

What are astrocytes?

Answer 22

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

Question 23

What is polarity?

Answer 23

Intracellular charge

Question 24

What is value?

Answer 24

The potential difference

Question 25

What is electrical potential?

Answer 25

The attraction of opposite charges if not separated by a barrier

Question 26

What is the resting membrane potential?

Answer 26

Voltage difference between inside and outside of cells; -70mV

Question 27

How is an electrostatic gradient created?

Answer 27

Intracellular is polarised due to having lower +ve charge

Question 28

How is a concentration gradient created?

Answer 28

Ionic imbalance between inside and outside of cell

Question 29

What does the membrane potential depend on?

Answer 29

Depends on concentration gradients and membrane permeabilities of Na+ and K+

Question 30

What is the overall effect of concentration and electrostatic gradients on Na+ and K+?

Answer 30

Na+: both pull in

K+: concentration gradient pushes out, electrostatic pulls in

Question 31

How is the K+ equilibrium potential reached?

Answer 31

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+

Question 32

What does the NERNST equation describe?

Answer 32

Magnitude and direction of equilibrium potential is different for different ions and depends on concentration gradients

Question 33

What is the NERNST equation?

Answer 33

Eion = 61/Z log ([out]/[in])

Question 34

What is the order of membrane permeability to the significant ions?

Answer 34

Cl- > K+ > Na+&raquo_space; proteins-

Question 35

What is the largest contribution to the membrane potential?

Answer 35

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)

Question 36

How does Na+ neutralise the effect of some K+ moving out?

Answer 36

A small number of Na+ channels are channels are open in resting state, allowing Na+ into cells

Question 37

What is the function of the Na+/K+ ATPase pumps?

Answer 37

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