chapter 15 control and co-ordination

Question 1

dendrites

Answer 1

carry impulse towards cell body

Question 2

axon

Answer 2

carries impulse from cell body

Question 3

what are impulses

Answer 3

brief changes to the distribution of electrical charges across the membrane

Question 4

roles of sensory receptor cells

Answer 4

1. detects stimuli
2. acts as transducer which converts stimulus energy
   into electrical energy , produces a receptor potential
   that is strong enough to pass an impulse along the
   sensory neurone

Question 5

taste chemoreceptor cells

Answer 5

1. Na+ ions diffuse into cells via microvilli and increases
   the positive charge in the cell.
2. membrane is depolarised and an receptor potential
   is produced
3. volted-gated Ca+ channel opens and Ca+ ions
   enters cells
4. trigger the movement of vesicles containing
   neurotransmitters and neurotransmitters are released
5. neurotransmitters stimulates an action potential in
   the sensory neurone and the impulse is send to the
   taste centre in the brain

Question 6

resting potential

Answer 6

1. Na+/K+ pump, 3 Na+ ions out and 2 K+ ions in. An
   electrochemical gradient is set up, K+ will diffuse out
   as Na+ diffuses in via channel proteins
2. more K+ channels open than Na+ channels and the
   membrane is more permeable to K+ than Na+. More
   K+ leaves than Na+ enters, leaking of K+ is
   responsible for resting potential

Question 7

depolarisation

Answer 7

1. voltage-gated K+ channels remains closed
2. voltage-gated Na+ channels opens, Na+ ions enters cell and membrane becomes less negative generating an action potential
3. the size of the action potential is at +30mV, the higher the intensity of the stimulus the higher the frequency of the action potentials

Question 8

repolarisation

Answer 8

1. voltage-gated Na+ channel closes

2. voltage-gated K+ channel opens and K+ ions moves out of the cell

Question 9

refractory period

Answer 9

1. voltage-gated Na+ channels remains closed
2. voltage-gated K+ channels closes but there is a
   delay hence excess K+ ions are leaked out
3. when in refractory period, no action potential can be
   generated hence ensure one-way transmission of
   action potential

Question 10

saltatory conduction

Answer 10

.faster transmission
.action potential only at nodes of Ranvier
.local circuit lengthens
.action potential ‘jumps’ from nodes to nodes

Question 11

cholinergic synapse

Answer 11

1. action potential reaches the presynaptic membrane
2. voltage-gated Ca2+ channel is open, membrane
   becomes more permeable to Ca2+ and Ca2+ enters
   the presynaptic membrane
3. vesicles containing ACh moves towards the
   presynaptic membrane and fuses with the membrane.
   ACh is released into the synaptic cleft
4. ACh diffuses across the synaptic cleft
5. ACh binds with the receptor porteins on the
   postsynaptic membrane
   6.receptor proteins changes shape and Na+ channel
   opens. Na+ enters the postsynaptic neurone causing it
   to be depolarised, an action potential is generated
   7.ACh is broken down by acetylcholinesterase in the
   synaptic cleft into acetate and choline and ACh is
   recycled to be used in the process of ATP
   8.depolarisation stops at the postsynaptic membrane
   so there is no continuous production of action
   potential which may lead to paralysis

Question 12

muscle contraction

Answer 12

1. cholinergic synapse (whole process)
2. Ca2+ in sarcoplasm binds to troponin, troponin changes shape and moves away from tropomyosin. Exposes the myosin-binding site on actin and the myosin head will attach to the actin forming a cross bridge

Question 13

sliding filament model

Answer 13

1. myosin head with ADP and pi forms a cross bridge with actin and pi is released
2. myosin head tilts and pulls on actin, power strokes moves the actin towards the M line and the sarcomere shortens. ADP is released.
3. ATP binds to the myosin head and ATPase hydrolyses ATP to ADP and pi. myosin head lets go of actin and returns to original position.