How Nerves Work

Question 1

what are the 3 subdivisions of the nervous system?

Answer 1

Somatic nervous system
Autonomic nervous system
Enteric nervous system

Question 2

What are the 6 different regions of spinal nerves

Answer 2

Cranial
cervical
thoracic
lumbar
sacral
coccygeal

Question 3

what is a ganglion?

Answer 3

collection of nerve cell bodies

Question 4

what types of information do afferent and efferent neurones convey?

Answer 4

afferent - sensory

efferent - motor

Question 5

what types of information do the dorsal and ventral roots correspond to ?

Answer 5

dorsal - afferent

ventral - efferent

Question 6

what is the function of the dendrites?

Answer 6

receive information from other neurons

Question 7

what are the 3 parts of the axon and their functions?

Answer 7

initial segment (axon hillock) - triggers action potential
Axon - sends action potential
Axon terminals (presynaptic) - release transmitter

Question 8

what separates interneurones from afferent and efferent neurones?

Answer 8

interneurones are found only within the central nervous system

Question 9

what are glia?

Answer 9

specialised cells in the CNS, they compose 90 percent of cells in the CNS

Question 10

name 3 types of glia and their function

Answer 10

astrocytes - surround blood vessels and produce the blood brain barrier
oligodendrocyes - form myelin sheaths in the CNS

Question 11

what is the resting membrane potential?

Answer 11

the resting electrical charge across a cell membrane (usually around -70mV)

Question 12

what is the equilibrium potential?

Answer 12

when the electrical gradient pulling potassium into the cell equals the concentration gradient drawing potassium out of the cell

Question 13

what is the effect of a raised ECF concentration of potassium?

Answer 13

depolarises the cell (reduces resting membrane)

Question 14

how does the blood brain barrier resist changes in extracellular potassium?

Answer 14

astrocytes and tight junctions between capillaries in the brain keep the potassium confined to the capillaries; hence no change in ECF potassium.

Question 15

why is the RMP closer to -70mV as opposed to the -90mV resting potential of potassium?

Answer 15

other leaky channels such as sodium and chlorine
electrogenic nature of the sodium potassium pump
large, negatively charged intracellular molecules.

Question 16

what is the purpose of a graded potential?

Answer 16

to “decide” whether or not to fire an action potential

Question 17

give 4 examples of graded potentials

Answer 17

generator potentials
postsynaptic potentials
endplate potentials
pacemaker potentials

Question 18

why are graded potentials only useful over short distances?

Answer 18

they are decremental so they cannot travel over long distances without the signal dissipating

Question 19

what signals the intensity of a stimulus in a graded potential?

Answer 19

amplitude.

Question 20

are graded potentials depolarising or hyperpolarising?

Answer 20

Can be either; depolarising would be an EPSP, hyperpolarising would be an IPSP.

Question 21

how would a hyperpolarising postsynaptic potential hyperpolarise a cell?

Answer 21

open Cl- channels (fast IPSP) or open more K+ channels (slow IPSP)

Question 22

how would a depolarising postsynaptic potential depolarise a cell?

Answer 22

open channels that are permeable to both Na+ and K+; more sodium enters the cell than potassium escapes (fast EPSP). closes channels that allow K+ out of the cell (slow EPSP)

Question 23

are postsynaptic potentials produced by ligand or voltage gated channels?

Answer 23

ligand gated

Question 24

are action potentials produced by ligand or voltage gated channels?

Answer 24

voltage gated

Question 25

graded potentials can summate; true or false?

Answer 25

true

Question 26

what is the difference between temporal and spatial summation?

Answer 26

temporal summation is when the same stimulus is applied more than once, spatial summation is when 2 different stimuli are applied.

Question 27

what is the purpose of synaptic integration?

Answer 27

the process of summating all the synaptic inputs to determine whether the initial segment reaches threshold and an action potential is fired.

Question 28

Chemically, what causes the massive depolarisation that leads to an action potential being fired?

Answer 28

massive influx of sodium into the cell.

Question 29

what is the refractory period?

Answer 29

length of time after firing the action potential where the cell is unable to be excited.

Question 30

what signals stimulus intensity in action potentials?

Answer 30

frequency.

Question 31

how do action potentials self propagate?

Answer 31

the massive depolarisation caused by the influx of sodium causes the next set of sodium channels to also become depolarised and open; more sodium flows into the cell and the action potential self propagates.

Question 32

why can an action potential only self propagate in one direction?

Answer 32

because the sodium channel "behind" the one that is open is in its refractory period, which means it is unable to open and so the wave of depolarisation can only spread "down" the cell.

Question 33

what is the effect of myelination of a nerve cell?

Answer 33

increases the distance an action potential can travel without dissipating. sodium channels are only present at the gaps (nodes of ranvier) between the myelin sheaths.

Question 34

what is the clinical importance of de-myelination?

Answer 34

action potentials cannot travel far enough down the axon to make the next node depolarise to threshold and hence, conduction fails - multiple sclerosis, guillain barre syndrome.

Question 35

how would a compound action potential be viewed on a graph?

Answer 35

fastest conducting APs are registered first (obviously), then the slower ones.

Question 36

what triggers contraction in muscles?

Answer 36

Action potential in the sarcolemma

Question 37

what are the steps that lead to contraction in muscle with regard to the neuromuscular junction?

Answer 37

AP travels down motor neurone opens voltage gated calcium channels in the presynaptic terminal causes release of ACh across synapse. Ach binds to nicotinic receptors opens ligand gated Na/K channels evokes an end plate potential which always depolarises adjacent membrane to threshold Depolarisation opens more voltage gated Na+ channels - new AP ACh is removed by acetylcholinesterase.

Question 38

What differences are there between synapses in the NMJ and the CNS?

Answer 38

much wider range of transmitters in CNS Range of postsynaptic potentials. Synaptic integration CNS synapses can have different anatomical arrangements (axo somatic, axo dendritic and axo axonal) Convergence and divergence in synaptic connectivity. feedback inhibition monosynaptic and polysynaptic pathways