8: Nervous System Structure

Question 1

membrane potential

Answer 1

uneven distribution of charges = potential difference
resting = -70mV
outside cell has high concentrations of Na+
inside cell high concentrations of K+

Question 2

passive movement

Answer 2

concentration gradient maintained by moving K+ out cell and Na+ in cell
K+ moves out faster as can diffuse easier
net loss of positive ions as chemical gradient stronger than electrical
sodium-potassium pump is active process that exchanges 3 Na+ for 2 K+
= overall balance

Question 3

changes in membrane potential

Answer 3

stimulus can open channels changing potential
sodium changes charge towards 0mV
potassium changes charge away from 0mV
-80mV = hyperpolarisation

Question 4

graded potentials

Answer 4

only affect limited portion of membrane, response to environmental stimuli
step 1: exposure to chemical, sodium channels open, sodium enters cell, membrane potential rises = depolarisation
step 2: sodium travelling through channels produces local current, depolarises nearby membrane, change in potential proportional to stimulus
step 3: stimulus removed, potential returns to normal = repolarisation

Question 5

action potentials

Answer 5

electrical signal that effects entire membrane
begin near axon hillock, travel along axon
generated by opening and closing of gated sodium/potassium
all-or-none = every stimulus that brings membrane to threshold will generate identical action potential

Question 6

propagation

Answer 6

movement of action potential through axon

Question 7

continuous propagation

Answer 7

in unmyelinated axon
first section of membrane depolarised to +30mV
second section depolarises, develops action potential
first section enters refractory period - cycle
1 direction , 1m/s

Question 8

saltatory propagation

Answer 8

in myelinated axons
depolarisation only occur at nodes
action potential jumps from node to node
18-40m/s

Question 9

synapses

Answer 9

used for communication between neurons and other cells
synaptic cleft = space between two membranes
synaptic terminal = mitochondria, synaptic vesicles, endoplasmic reticulum

Question 10

chemical synapses

Answer 10

release of chemicals called neurotransmitters
most common type

Question 11

neurotransmitters

Answer 11

chemical compounds released by neuron
excitatory = cause depolarisation of post synaptic membranes = promote action potential
inhibitory = cause hyperpolarisation of postsynaptic membranes = suppress action potential

Question 12

cholinergic synapses

Answer 12

neurotransmitter acetylcholine (ACh) is released
ACh binds to Ach receptors and depolarises postsynaptic membrane
ACh removed by AChE

Question 13

norepinephrine (NE)

Answer 13

excitatory effect
important in brain and portions of ANS
released by adrenergic synapses

Question 14

dopamine

Answer 14

CNS neurotransmitter released in brain
excitatory or inhibitory effect
inhibition for precise control of movemnts
dopaminergic synapses

Question 15

serotonin

Answer 15

found in CNS
serotonergic synapses