Wjec Biology // By4 // 4.7 // Nervous System

Front 1

Nervous System
1. Examples of Receptors
2. What makes up the CNS?
3. Examples of Effectors
4. How do sensory receptors act as tranducers?

Back 1

1. Eyes, Skin, Ears
2. Brain, Spinal Cord - process info and initiate a response
3. Muscles or glands
4. Detect one form of energy and convert it to electrical. Electrical impulses.

Front 2

Reflex Arc
1. What is a reflex arc and their function?
2. What is the pathway of a reflex arc?
3. What is the nerve pathway of the reflex arc?

Back 2

1. Rapid, involuntary response resulting from a stimulus. Their action is involuntary and protective in function.
2. Stimulus - Receptor - Co-Ordinator - Effector - Response
3. Sensory - Relay - Motor

Front 3

Neurones
1. What are the types of neurones?
2. What does a neurone cell consist of?
3. What is the function of the ribosomes?
4. What are dendrites?

Back 3

1. Sensory, Relay, Motor
2. Nucleus, Granular Cytoplasm, Ribosomes/Nissl Granules
3. Form nissl granules which form neurotransmitters
4. Thin extensions that carry an impulse

Front 4

Neurones Continued
1. What does the axon end form?
2. What is the structure of an axon?
3. What is the function of Myelin Sheath?
4. What is the function of the Nodes of Ranvier?
5. Effect of these adaptations?

Back 4

1. Synapses
2. Has Myelinated sheaths/schwann cells and nodes of ranvier
3. Electrical insulator, preventing electrical stimulation
4. This is where impulse is transmitter, saltatory conduction.

Front 5

Nerve Impulse
1. Resting Potential

Back 5

-40mV - inside is more negative than outside - membrane is polarised.
- Na+ and K+ ions transported across membrane via A.T
- Involves Na-K pumps, which maintain the conc and uneven distribution of NA+ and K+ across the membrane.
- Na+ are passed out faster, and K+ can diffuse back out faster than Na+ ions can diffuse back in. Net result is outside is more positive than inside.
- Making inside negative

Front 6

1. Action Potential
2. What is the use of the refractory period?

Back 6

1. Potential inside is -70mV and positive becomes +40mV.
Membrane is now polarised, and lasts for three milliseconds.
- Membrane increases permeability to Na+
- Influx of Na+ depolarising the membrane
- K+ diffuse out and repolarise the membrane
- Over shot of K+ leads to the refractory period
- K+/Na+ pumps restore the ionic balance

- Ensures impulse to go in one direction and limit frequency

Front 7

Nerve Impulse
1. How action potential travels along axon
2. What is the all or nothing law?
3. What effects intensity of the impulse?

Back 7

1. Action potential causes small electric current across the membrane, depolarising a small portion. This then initiates the depolarising of the next portion (usually node of ranvier)
Sodium pump is active all the time, restoring the resting potential, once restore another impulse can be transmitted. Outflux of K+ cause neurone to be polarised behind impulse
2. If stimulus is below threshold intensity no action potential is initiated. If it exceeds it, action potential is initiated.
3. Frequency of the action potential changes as intensity increases.
So strong stimulus = greater frequency of A.P

Front 8

Nerve Impulse
1. One factor determining speed of conduction (Myelination)
2. Second factor determining speed of conduction
(Axon Diameter)

Back 8

1. Myelination - speeds up by insulating axon. Depolarisation can and A.P cannot occur in myelinated parts. This causes impulse jumps from node to node. This is called Saltatory Conduction
2. Diameter of the axon - greater diameter of axon, greater velocity of transmission.

Front 9

Synapses
1. What is the size of the gap between dendrites and branches of axon?
2. Structure of a synapse
3. What is the process of synaptic transmission called?
4. Example of neurotransmitters?

Back 9

1. 20um
2. Axon > Synpatic Knob > Synaptic Vesicle > Presynaptic Membrane > Synaptic Cleft > Protein Channels > Receptor Molecule > Post Synaptic Membrane
3. --?
4. Noradrenaline or Acetylcholine

Front 10

Synaptic Transmission
1. Describe

Back 10

1. Arrival of impulse in synaptic know alters its permeability, causing an influx of Ca+ to enter.
This causes synaptic vesicle to fuse with presynaptic membrane
This releases a neurotransmitter into the synaptic cleft
Neurotransmitter then diffuses across the synaptic cleft
Attaches to receptor site on postsynaptic membrane, depolarising it and initiating an impulse in the next neurone
Postsynaptic membrane contains specific protein receptors which transmitter molecules combine. Opening up the membrane allowing for Na+ to diffuse into posy synpatic neurone, depolarising it initiating A.P
Neurotransmitter is quickly destroyed by enzymes limiting the effect.
ATP is required to reform transmitter molecules and store them in vesicles

Front 11

Function of Synapses
1. What are the function of synapses?

Back 11

Transmit info between neurones
Pass impulse in one direction only
Acts as junctions
Filter out low level stimuli
Protection from over stimulation

Front 12

Effect of Drugs
1. What are excitatory drugs?
2. What are inhibitory drugs?

Back 12

Excitory drugs stimulate the nervous system by creating more A.P in the post synaptic membranes
Inhibitory drugs inhibit nervous system by creating fewer A.P in post synaptic membrane. Acting on the neuromuscular juncyion.

Front 13

Photoperiodism
1. What are the two forms of Phytochrome?
2. Why does Pfr accumulate in the day?
3. What is the hormone that dictates flowering?

Back 13

1. Phytochrome 660 (Pr) red light >>>>> Phytochrome 720 (Pfr) far-red light
Pfr to Pr is a slow conversion
2. Plants measure length of darkness by amount of phytochrome. Pfr in the daylight is the main form.
3. Florigen

Front 14

1. Day neutral plants
2. Long-day plants
3. Short-day plants

Back 14

1. Not affected by day length
2. Flowering is induced by exposure to dark periods shorter than critical length. Will only flower on high levels of Pfr. If photoperiod is interrupted by darkness, flowering still occurs.
3. Flowering is induced by exposure to dark periods longer than critical length. Will only flower if Pfr is low enough. If dark period is interrupted flowering is prevented