Nervous System

Question 1

what are neurones

Answer 1

specialised nerve cells for transmitting electrical impulses throughout the body

Question 2

role of sensory neurones

Answer 2

carry impulses from sensory receptors to CNS

Question 3

role of relay neurones

Answer 3

carry impulses within CNS, between other neurones

Question 4

role of motor neurones

Answer 4

carries impulses from CNS to effectors

Question 5

what is the role of the myelin sheath

Answer 5

surrounds and insulates part of the axon to prevent passage of ions into/out of the axon

Question 6

what is the role of the schwann cell

Answer 6

remove debris via phagocytosis
aid regeneration
their membranes form the myelin sheath

Question 7

what are sensory receptors

Answer 7

specialised cells that detect stimuli from the environment

Question 8

name types of receptors

Answer 8

photoreceptors
chemoreceptors
mechanoreceptors
thermoreceptors

Question 9

stages of receptor cell function

Answer 9

resting potential - cell surface membrane has volage across it due to difference in ion conc
stimulus detected - cell surf membrane becomes more permeable - ions can flow in & out
generator potential - altering of membrane voltage creates a generator potential
if generator potential reaches threshold - triggers action potential

Question 10

what are pacinian corpuscles

Answer 10

mechanoreceptors in the skin that detect pressure & vibrations

Question 11

describe a pacinian corpuscle

Answer 11

contain the ending of a sensory neurone, wrapped in layers of lamellae (connective tissue) with viscous gel between each layer

Question 12

describe what happens when the pacinian corpuscle is stimulated

Answer 12

lamella deform, pressing on sensory ending
this stretches the neurones membrane, causing it to change shape
this opens stretch mediated sodium channels in membrane, increasing membranes permeability to sodium ions
sodium ions diffuse into neurone, depolarising it and creating generator potential
if signal reaches threshold, action potential is triggered

Question 13

how is resting potential achieved

Answer 13

sodium potassium pumps - active transporters that move 3NA+ out of neurone for every 2K+ they move in
K+ channels - allow diffusion of K+ out, down its conc gradient
Na+ channels - closed, preventing movement of NA+ into neurone

Question 14

how is an action potential generated

Answer 14

1. resting potential - membrane is polarised at -70mV
2. stimulus - voltage gated sodium channels open so more sodium flows in, making inside less negative
3. depolarisation - threshold potential of around -55mV is reached, more sodium channels open, causing influx of sodium
4. repolarisation - at around +3-mV sodium channels close, potassium channels open so potassium flows out
5. hyperpolarisation - excess of potassium leaves, potential drops below -70mV resting level
6. refractory period - various ion pumps & channels work together to restore membrane back to resting potential

Question 15

What is the role of the refractory period

Answer 15

Ensures action potentials don’t overlap
Limits frequency that impulses are transmitted
Guarantees impulses travel in only 1 direction

Question 16

What is the refractory period

Answer 16

Recovery phase where neurone cannot generate another action potential

Question 17

How can’t the membrane generate another action potential during the refractory period

Answer 17

Sodium ion channel remain closed during repolarisation

Question 18

How do action potentials travel along the neurone

Answer 18

1. Sodium ion channels open = depolarisation
   This allows positive ions to spread sideways
2. Adjacent voltage gates sodium ion channels open in response
3. This leads to depolarisation of nearby membrane areas
4. This continues down the neurone as an advancing wave is formed
5. Areas of membrane that have just experienced depolarisation are in the refractory period (sodium io channels are closed)
6. This ensures wave moves in one direction, preventing backward flow of nerve impulse

Question 19

What are the 3 factors affecting speed of transmission of an action potential

Answer 19

Myelination
Axon diameter
Temperature

Question 20

How does myeliantion affect speed of transmission of action potential

Answer 20

Enables saltatory conduction
So action potentials jump between nodes of ranvier

Question 21

How does axon diameter affect speed of transmission of action potential

Answer 21

Larger axon diameter means less resistance to ion flow = wave of depolarisation travels faster along axon

Question 22

How does temperature affect speed of transmission of action potential

Answer 22

Higher temps accelerate the diffusion of ions = faster depolarisation & faster impulse transmission
However temps above 40 degrees can case proteins in membrane to denature

Question 23

What is a synapse

Answer 23

A junction where info is transferred from one neurone to another or an effector cell

Question 24

What key roles do synapses play in neural communication

Answer 24

1. Transmit info through release of NTs
2. Summation (temporal and spatial)

Question 25

Describe the key structures of a synapse

Answer 25

Presynaptic neurone - releases NTs into synapse Synaptic knob - section at end of presynaptic neurone that contains organelles needed for NT production Synaptic vesicles - sacs within synaptic knob that stores NTs until released Synaptic cleft - gap between presynaptic and postsynaptic neurones membranes Postsynaptic neurone - neurone receives NTs and can generate new action potentials NT receptors - specific molecules on postsynaptic membrane that bind with NTs

Question 26

What effect does an excitatory NT have on the postsynaptic membrane

Answer 26

Depolarisation

Question 27

Give an example of an excitatory NT

Answer 27

Acetylcholine in the CNS

Question 28

Do excitatory NTs generate an action potential

Answer 28

Yes - if threshold is reached

Question 29

What effect do inhibitory NTs have on the postsynaptic neurone

Answer 29

Hyperpolarisation

Question 30

Give an example of an inhibitory NT

Answer 30

Acetylcholine at cardiac synapses

Question 31

Do inhibitory NTs generate an action potential

Answer 31

No - they prevent action potentials

Question 32

What are the 2 types of summation

Answer 32

Spatial Temporal

Question 33

What is spatial summation

Answer 33

Multiple presynaptic neurones converge on a singe post synaptic neurone or effector cell The combined input of NTs can trigger post synaptic firing

Question 34

What is temporal summation

Answer 34

Repeated firing by a presynaptic neurone which leads to continuous NT release Increased amount of NT makes it more likely to trigger postsynaptic firing

Question 35

Describe the key steps in synaptic transmission

Answer 35

1. Action potential arrives at presynaptic knob 2. Causing voltage gates calcium ion channels to open so calcium ions flow into pre synaptic knob 3. This causes synaptic vesicles to fuse with presynaptic membrane 4. Vesicles release NTs into the synaptic cleft via exocytosis, NTs rapidly diffusing across synaptic cleft 5. NTs bind to receptor proteins on postsynaptic membrane, causing receptors to change shape 6. This opens sodium ion channels in postsynaptic membrane, leading to depolarisation 7. If this depolarisation reaches threshold level, action potential is triggered in postsynaptic neurone

Question 36

What are cholinergic synapses

Answer 36

Synapses which uses acetylcholine as their NT

Question 37

What happens after ACh binds to receptors and triggers a response

Answer 37

1. ACh is broken down by acetylcholinesterase into choline and acetate 2. These breakdown products are then reabsorbed into presynaptic knob via active transport 3. And recycled to synthesise more ACh 4. ACh is transported into synaptic vesicles ready for another action potentials

Question 38

Why is it important that NTs like ACh are removed from the synaptic cleft

Answer 38

To prevent stimulus from being maintained (continuous stimulation) So allows another stimulus to affect the synapse And NT recycling