neural communication 5.1.3

Question 1

general structure of a neurone

Answer 1

dendrites= send impulses to the cell body
axon= sends impulses away from the cell body
cell body= releases neurotransmitters contains the nucleus
myelin sheath= insulation. Made by Schwan cells
node of Ranvier=gape between the myelin sheath

Question 2

transducers

Answer 2

-a cell that converts one form of energy into another. e.g. sensory receptors to an electrical impulses

Question 3

4 types of sensory receptors

Answer 3

• mechanoreceptors= pressure +movement e.g. Pacinian corpuscles
  -chemoreceptors= chemicals e.g. smell and taste
  -thermoreceptor=heat
  -photoreceptors=light can be found in the retina

Question 4

Pacinian corpuscles

Answer 4

-when pressure is appllied the membrane surrounding the neurone streches causing gaps between phospholipids,
-this opens sodium channels
-sod ium rushes in along electrochmical gradient generating an action potential

Question 5

resting potential

Answer 5

• sodium-potassium pump moves 3 sodium ions out and 2 potassium ions in by active transport
  -sodium ion channels closed and potassium ion channels are open allowing facilitated diffusion
  -therfore membrane is more permeable to potassium ions
• therefore the membrane is polarised.( more positive outside than inside)
  -resting potential= -70

Question 6

depolarisation

Answer 6

• stimulus causes sodium ion channels to open so sodium ions diffuse into the cell. (membrane is more permeable to sodium)
  -when the potential difference reaches -55v, positive feedback occurs so more sodium ion channels open and more sodium ions diffuse into the cell.
  -depolarisation occurs (inside more positive than outside). reaches+40v

Question 7

repolarisation

Answer 7

• sodium ion channels close and potassium channels open. potassium diffuses out of the cell bringing the potential difference back to more positive than inside.
  -there is a potential difference overshoot. making the cell hyperpolarised
  -original potential difference is returns and resting potential is maintained by the sodium-potassium pump
• reactionary period= recovery period. after action potential neurones cant be excited straight away

Question 8

cholinergic synapse in neurotransmission

Answer 8

• action potential in pre-synaptic neurone causes depolarisation of the membrane therefore opening voltage-gated calcium ion channels to open
  -calcium ions move down the electrochemical gradient causing acetylcholine vesicles to fuse with the membrane releasing ACTH by diffusion
  -ACTH binds to complementary receptors on the post-synaptic neurone causing sodium channels to open
• sodium ions diffuse into the post synaptic neurone, down the electrochemical gradient causing depolarisation triggering a new action potential
  -ACTH left in the cleft is hydrolysed by acetylcholinesterase into aecetic acid + choline. sodium ion channels close
  -mitochondria in the pre-synaptic neurone undergo respiration producing ATP which binds to acetate and choline reforming ATCH

Question 9

synaptic divergences and convergence

Answer 9

• divergence=one neurone connects to many information can be dispersed to different parts of the body
  -convergence= many neurones connect to one neurone. information can be amplified

Question 10

types of summation

Answer 10

• spatial summation=many different neurones collective trigger a new action potential by combining neurotransmitters being released to generate a new action potential
• allows convergence =one post-synaptic cell receives impulses from a number of different presynaptic cells
  -divergence= impulse from on presynaptic cell is spread over multiple postsynaptic cells
• alos filkters out bavkground of low level stimuli
  -temporal=one neurone releases neurotransmitters repeatedly over a short period of time to add up enough to exceed a threshold
  -filters out background of low level stimuli

Question 11

why can impulses only be transmitted one way

Answer 11

• receptors for neurotransmitters are only on the postsynaptic neurone

Question 12

myelinated neurone vs unmyelinated neurone

Answer 12

• in myelinated neurones action potential jumps from one node to the next (saltatory conduction) .it is fast and travel long distances
  -in non myelinated neurones. Action potential need to be generated along the whole axon

Question 13

importance of frequency of stimuli

Answer 13

-If there is a stronger stimuli, the magnitude of the action potential does not get larger
-however= there will be a higher frequency of nerve impulses

Question 14

all-or-nothing principle

Answer 14

-action potential is only generated if the stimulus reaches the threshold value of -55mv.
-action potential is the same magnitude regardless of the strength of the stimulus

Question 15

inhibitory and excitatory synapses.

Answer 15

inhibitory=less likely to initiate a action potential
exicitory=more likely too

Question 16

Sensory neurone

Answer 16

• Dendron present and links to the cell body;
  -Cell body in the middle of the neurone; and not in the CNS; -dendrites don’t connect to the cell body;
  -axon is shorter than the motor neurone;
  -Neurone connects to the sensory receptor;

Question 17

Motor neurone

Answer 17

-No dendrons;
-Cell body is at the end of the neurone; and in the CNS; dendrites are directly connected to the cell body;
- axon is longer than the sensory neurone;

Question 18

Relay neurone

Answer 18

-short axon
-dendrites present
-found in the CNS

Question 19

Saltatory conduction

Answer 19

-Membrane is only depolorised at the nodes of ranvier;
-creates a longer localised circuit; -increases the rate of impulse transmission;

Question 20

Why does the synapse allow transmission in one direction

Answer 20

• Vesicles containing neurotransmitter are only found in the presynaptic knob;
• Receptors on the sodium voltage gated channels can only be found on the postsynaptic membrane;
• Calcium channel can only be found on the presynaptic membrane;

Question 21

Outline the role of the synapse

Answer 21

-Allows neurones to communicate/cell signaling;
- Ensure transmission in one direction;
- Allows convergence/impulses from more than one neurone to be passed to a single neurone;
- Allows divergence/impulses from a single neurone to be passed to more than one neurone;
-Filters out ‘background’ of low level stimuli;
- Prevent fatigue/overstimulation;
-Allows many low level stimuli to be amplified;