1. Nervous System

2. Development of Control Systems
Response to stimuli (MRSGREN) essential for survival
Single celled organisms versus multi-cellular organisms
Differentiation/specialisation
Need coordination
Nervous versus endocrine
Both work together
e.g. rabbit running from fox – what systems involved?

3. Sense organs detect change (receptors)
Effectors respond
Distance between two
Complex organisms have many sensors and effectors
CNS – every sensor and effector has at least 1 link
Locomotion led to brain in anterior
Spinal cord links brain to rest of body

4. Nervous System 3 functions:
1. Collect information about external environment
2. Process and integrate this information (often in relation to previous experience)
3. Act upon information by coordinating the organisms activities.

8. Neurones

10. Types of neurone sensory neurone relay neurone (interneurone)
motor neurone

11. Structure Cell body with nucleus
Dendrites transmit impulses to cell body
Impulses leave via axon
Myelin sheath composed of Schwann cells
Neurons packed and wrapped to form nerves
May contain sensory, effector or mixture

12. Nerve Structure

14. Multiple Sclerosis Schwann cells make up myelin sheath
70% lipid, 30% protein
Provides insulation and allows rapid conduction of electrical signals
Gradual degradation of myelin sheath
Demyelinated axons (plaques)
Cannot conduct impulses

16. Effects of MS
Affects optic nerve, cerebellum, cervical spinal cord, ventricles in brain
Symptoms – weakness of limbs, pins and needles, numbness, blurred vision and eye pain.
Relapse and remission cycle
No cure
More women (3:2)
Temperate climate

17. Resting Potential Neurons have an electrical potential
(voltage) across the cell membrane, i.e. membrane is POLARISED.
The inside of the cell is more negative
than the outside
This is called the Resting Membrane Potential = 70mV

18. Resting Potential

19. What causes this?

20. What causes this?
Concentrations of K+ and COO- ions are high inside the neuron
Concentrations of Na+ and Cl- are high outside the neuron
Membrane is more permeable to K+ than Na+
Concentration of K+ inside 20x greater so K+ ions rapidly diffuse out until equilibrium reached
This results in the inside being more negative than outside

21. Cont’d
Difference in concentration of ions maintained by active transport against concentration gradient
Sodium/potassium CATION pumps transport Na+ out and K+ in
Requires ATP

22. Cation Pumps

23. Action Potential
Explanation of Action Potential

24. Action Potential
Stimulation can reverse the charge on a neuron (-70 to +40mV)
Membrane DEPOLARISED
If stimulus exceeds certain value (THRESHOLD) an action potential results
Rapid reversal of the resting membrane
potential that travels down the axon

25. Cont’d
Above the threshold value size of action potential remains the same
ALL or NOTHING RESPONSE
Size of action potential remains constant as it passes along neurone

26. Action Potential

27. Ion Movement Action potential result of sudden influx of Na+ ions
Due to increased permeability of membrane
Cation pump maintains high levels of Na+
Influx of Na+ depolarises membrane
Positive feedback
K+ moves in opposite direction
Continues until membrane repolarised
VOLTAGE GATED CHANNELS

30. Action potential animation
Action potential propagation animation

31. Refractory Period
After an action potential, outward movement of K+ quickly restores resting potential
But for 1ms after action potential influx of Na+ is prevented
Called REFRACTORY PERIOD
A new AP cannot be generated during this time

32. Importance of Refractory Period
Action potential can only be propagated in the region which is not refractory
Impulse moves in forward direction
By the end of the refractory period the action potential has passed further down the nerve so a second action potential is separated from 1st by 1ms
Limits frequency of impulses along nerve

33. Refractory Cont’d Has two parts: ABSOLUTE refractory period – 1ms
No new impulse can be propagated
RELATIVE refractory period – 5ms
New impulses only propagated if stimulus is more intense than normal threshold

34. Transmission of Impulse
Action potential moves rapidly along neurone
0.5 m/s to 100 m/s
2 factors affect speed
Diameter of axon
Myelin sheath

35. Saltatory Conduction Myelin sheath not continuous
Nodes of RANVIER every 1mm
Action potential can only form in unmyelinated areas so jump from node to node

37. Nervous Impulse Animation