Communication By Neurones

Question 1

What is the central nervous system composed of?

Answer 1

-brain
-spinal cord

Question 2

What are the 2 systems the peripheral nervous system makes up?

Answer 2

-somatic nervous system = voluntary e.g skeletal movements
-autonomic nervous system = involuntary e.g control of heart rate

Question 3

What is an action potential?

Answer 3

Signals transmitted as changes in electrical potential along neurones

Question 4

What stimuli are detected by your ears, tongue, nose, and retina?

Answer 4

-ears= sounds
-tongue= chemicals (taste)
-nose= chemicals (smell)
-retina= light changes

Question 5

What does a sensory neurone do?

Answer 5

-transmit nerve impulses from receptors to the central nervous system (brain and spinal cord)

Question 6

What is the structure of a sensory neurone?

Answer 6

-short dendrites
-one long dendron to carry nerve impulses from receptor cells to the cell body
-one short axon that carries impulses away from cell body to the CNS

Question 7

What do motor neurones do?

Answer 7

-transmit nerve impulses from the CNS to effectors

Question 8

What is the structure of a motor neurone?

Answer 8

-have many short dendrites that carry nerve impulses from CNS to the cell body
-one long axon that carries nerve impulses from the cell body to effector cells

Question 9

What do relay neurones do?

Answer 9

-transmit nerve impulses between sensory neurones and motor neurones

Question 10

What is the structure of a relay neurone?

Answer 10

-have many short dendrites that carry nerve impulses from sensory neurones to cell body
-one axon that carries nerve impulses from the cell body to motor neurones

Question 11

What do all neurones have in their cell bodies and in their structure?

Answer 11

-a nucleus
-cytoplasm
-all other organelles that you’d usually find in a cell
-schwann cells
-nodes of ranvier
-myelin sheath (protects and provides insulation, remove cell debris by phagocytosis)

Question 12

Explain the role of sensory receptors

Answer 12

-different stimuli have different forms of energy e.g light and chemical
-but your nervous system only sends information in the form of nerve impulses (electrical impulses)
-sensory receptors convert the energy of a stimulus into electrical energy, acting as transducers (something that converts one form of energy into another)

Question 13

What are pacinian corpuscles and how do they work?

Answer 13

-they’re mechanoreceptors, detecting mechanical stimuli e.g pressure and vibrations, found in your skin
-they contain the end of a sensory neurone, called a sensory nerve ending, which is wrapped in lots of layers of connective tissue lamellae
-when a pacinian corpuscle is stimulated e.g by a tap on the arm, the lamellae are deformed and press on the sensory nerve ending. This causes deformation of stretch-mediated sodium channels in the sensory neurone’s cell membrane. The sodium ion channels open and sodium diffuses into the cell, creating a generator potential. If the generator potential reaches the threshold, it triggers an action potential

Question 14

Describe the conditions of a neurones cell membrane when it is polarised at rest

Answer 14

-in its resting state the outside of the membrane is positively charged compared to the inside, because there are more positive ions outside the cell than inside
-this makes the membrane polarised, as there is a difference in charge
-the membranes resting potential is about -70mV
-the resting potential is created and maintained by sodium-potassium pumps and potassium ion channels in the membrane

Question 15

Explain the role of the sodium-potassium pump

Answer 15

-moves 3 sodium ions out of the neurone, but membrane isn’t permeable to sodium ions so they can’t diffuse back in
-this creates a sodium ion electrochemical gradient because there are more positive sodium ions outside the cell than inside
-it also moves 2 potassium ions into the neurone, but the membrane is permeable to potassium ions so they diffuse back out through potassium channels
-this makes the outside positively charged compared to the inside

Question 16

Explain the role of a stimulus in creating an action potential/ depolarisation of the membrane

Answer 16

-a stimulus excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down gradient, making the inside of the neurone less negative
-depolarisation occurs if the potential difference reaches the threshold, and the voltage gated sodium ion channels open, so more sodium ions diffuse into the neurone. This is positive feedback

Question 17

Explain the stage of hyperploarisation

Answer 17

-at a potential difference of around +30mV the sodium ion channels close and voltage gated potassium ion channels open.
-the membrane is more permeable to potassium so potassium ions diffuse out of the neurone down gradient
-the potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone, causing potential difference to become more negative than the resting potential (-80mV)

Question 18

Explain the stage of repolarisation

Answer 18

-most voltage gated potassium ion channels close
-sodium potassium pump removes 3 sodium ions and brings in 2 potassium ions
-this restores the resting potential of -70mV

Question 19

Explain what the absolute refractory period is

Answer 19

-after an action potential, the neurone cell membrane can’t be excited again straight away, because the ion channels are recovering and they can’t be made to open
-sodium ion channels are closed during repolarisation
-potassium ion channels closed during hyperpolarisation

Question 20

Explain how a wave of depolarisation is created through the neurone

Answer 20

-when an action potential happens, some of the sodium ions that enter the neurone diffuse sideways, causing sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part
-this causes a wave of depolarisation along the neurone
-the wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an action potential

Question 21

Explain what the all or nothing response is

Answer 21

-once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is. If the threshold isn’t reached, an action potential won’t fire.

Question 22

What effect does a bigger stimulus have on an action potential?

Answer 22

-it causes action potentials to fire more frequently, as opposed to increasing in size
-so if the brain receives a high frequency of action potentials, it interprets this as a big stimulus and responds accordingly

Question 23

Explain how myelin sheath affects the propagation of action potentials
Include what saltatory conduction is

Answer 23

-myelin sheath is an electrical insulator
-it is made up of schwann cells
-between the Schwann cells are small spaces called nodes of ranvier, and sodium ion channels are concentrated here
-in a myelinated neurone, depolarisation only happens at the nodes of ranvier
-neurones cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node, which is very fast= SALTATORY CONDUCTION
-in a non myelinated neurone the impulse travels as a wave along the whole length of the axon membrane, which is a bit slower

Question 24

Explain which 2 other factors affect the propagation of action potentials

Answer 24

1) diameter of the axon = the greater the diameter, the faster the impulse speed, as reduces leakage of ions making it easier to maintain the potential

2) temperature = higher temperatures increase kinetic energy and rate of diffusion/ too high temperatures denatures the proteins in the cell membranes and affects fluidity of bilayer, stopping propagation

Question 25

Explain what the relative refractory period is

Answer 25

-as long as the stimulus exceeds the normal threshold value, a new action potential will be generated
-the degree to which it needs to exceed the threshold value decreases over the time period

Question 26

What is a synapse and what’s its function?

Answer 26

-the junction between 2 neurones, or a neurone and an effector cell
-the synaptic cleft is the tiny gap between the cells at a synapse
-it allows information to be transmitted between neurones using neurotransmitters because an action potential can’t cross the synaptic cleft
-it ensures the nerve impulses are unidirectional

Question 27

What is the presynaptic neurone and the post synaptic neurone?

Answer 27

-presynaptic neurone = the neurone before the synapse, that contains vesicles filled with neurotransmitters
-postsynaptic neurone = the neurone after the synapse, with receptors on its membrane for the neurotransmitters to bind to

Question 28

Name some examples of neurotransmitters

Answer 28

-adrenaline
-dopamine
-serotonin
-ACETLYCHOLINE (must know) shortened to ACh

Question 29

What are synapses called that have acetylcholine as their transmitter?

Answer 29

Cholinergic synapses

Question 30

What are synapses called that have adrenaline as their transmitter?

Answer 30

-adrenergic synapses

Question 31

Explain the process of how neurotransmitters transmit nerve impulses between neurones

Answer 31

1) an action potential arrives at the synaptic knob of the presynaptic neurone
2) this stimulates voltage gated calcium ion channels in presynaptic neurone to open
3) calcium ions diffuse into the synaptic knob
4) the influx of calcium ions into the synaptic knob cause the synaptic vesicles to move to the presynaptic membrane. They then fuse with the presynaptic membrane
5) the vesicles release the neurotransmitter into the synaptic cleft by exocytosis
6) the neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane
7) this causes sodium ion channels in the postsynaptic neurone to open. The influx of sodium ions into the postsynaptic membrane causes depolarisation. An action potential on the postsynaptic membrane is generated if the threshold is reached
8) the neurotransmitter is removed from the synaptic cleft so the response doesn’t keep happening

Question 32

Explain the events that occur at a chollnergic synapse (synapse for acetylcholine neurotransmitter)

Answer 32

1) action potential arrives
2) calcium ions enter the cytoplasm, and acetylcholine is released through exocytosis of synaptic vesicle
3) ACh binds to sodium channel receptors on postsynaptic membrane, producing a graded depolarisation
4) depolarisation ends as ACh is broken down into acetate and choline by acetylcholinestrase enzyme (AChE)
5) the synaptic knob reabsorbs choline from the synaptic cleft and uses it to synthesise new molecules of acetylcholine

Question 33

Explain the difference between an excitatory and inhibitory synapse

Answer 33

-excitatory = neurotransmitters depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached
-inhibitory = when neurotransmitters bind to receptors on the postsynaptic membrane, they hyperpolarise the membrane, preventing an action potential from being fired

Question 34

What is a synaptic divergence?

Answer 34

When one neurone connects to many neurones information can be dispersed to different parts of the body

Question 35

What is synaptic convergence?

Answer 35

When many neurones connect to one neurone information can be amplified (made stronger)

Question 36

What is spatial summation?

Answer 36

-when neurones converge, the small amount of neurotransmitter released from each neurone can be enough altogether to reach the threshold in the postsynaptic neurone and trigger and action potential
-this allows signals from multiple stimuli to be coordinated into a single response

Question 37

What is temporal summation?

Answer 37

-where 2 or more nerve impulses arrive in quick succession from the same presynaptic neurone. This makes an action potential more likely because more neurotransmitter is released into the synaptic cleft