Biology 30 NERVOUS SYSTEM 1. Nervous System Overview 2. The Neuron 3. Reflex Arc

1. Biology 30NERVOUS SYSTEM 1.    Nervous System Overview 2.    The Neuron 3.    Reflex Arc 4.    The Action Potential 5.    The Synapse / Neurotransmitters 6.    Nervous System Diseases 7.    Drugs 8.    PNS 9.    CNS 10. The Brain

2. General Functions • Reception 2. Conduction 3. Interpretation and Organization 4.  Transmission The nervous systems main function is to maintain homeostasis: a maintenance of the internal environment i.e. pH, body temp, glucose levels, BP, water levels, etc

3. Nervous System Organization

4. The Neuron- The functional unit of the nervous system, it conducts nerve impulses • There are 3 kinds of neurons: • 1) sensory neurons (afferent)- take impulses from the body receptors to the CNS • 2) motor neurons (efferent)-take impulse away from the CNS and to the muscles and glands • 3) interneurons- are actually in the CNS (in the brain and spinal cord) • ***Neuroglia (glial cells)- supportive cells that aid the interneurons of the brain. Nourish neurons, removes waste from neurons, and protect neurons.

6. The Neuron has 3 basic Basic parts: 1) cell body- nucleus and cytoplasm • 2) Dendrites-finger-like projections of cytoplasm of cell body. They receive information • 3) Axon-extension of cytoplasm. Transmit impulse away from the body

8. Some neurons contain the following additional parts: MyelinSheath-a white fatty covering that insulates the axon. Schwann cells produce the myelin sheath • Schwann cells- a special kind of glial cell that produces a myelin sheath that wraps around the axons as insulation • On top of protection, the myelin sheath allows for faster conduction of impulses and greater power of regeneration • The myelin sheath is NOT continuous but rather forms intermitted gaps called the Nodes of Ranvier. Impulses will now ‘jump’ from Node to Node rather then slowly moving through the entire length of the axon. (faster impulses)

10. All nerves of the PNS, as well as all motor and sensory neurons are myelinated, only some of the nerves in the CNS are myelinated • Non- Myelinated neurons in the brain= grey matter • Myelinated nerves in the brain are called white matter

11. Neuron structure

13. Nerves • Individual neurons are organized into tissues called nerves.

14. Repairing Damaged Nerves • Nerves in the PNS are surrounded by a thin membrane called the neurilemma which helps to regenerate damaged axons • Nerves in CNS lack neurilemmas and cannot be repaired • Area of research: stem cells, brain band-aid

15. Reflex Arc • automatic, quick, involuntary responses to internal or external stimuli. • does not immediately involve the brain. • allows quicker reaction times to a potentially harmful stimulus

16. Stretch Reflex • Stretch Reflex

17. 5 Components of a Reflex Arc: 1. Sensory receptor -sensessomething 2. Sensory neuron -sends signal to the CNS 3. Interneuron- registers signal 4. Motor neuron -sends response back 5. Effector-caries out the action

18. Action Potential • A nerve impulse is an action potential • An action potential is an electrochemical event with a rapid change in polarity (relative electrical potential) down a nerve cell that results in the conduction of a nerve impulse.

19. Steps of a Nerve Impulse (Action Potential1. Resting Potential • Polarization: voltage difference of -70mV across a nerve cell membrane • caused by the sodium potassium pump (gate): more sodium is pumped out than potassium is pumped in, resulting in a negative charge inside the axon of the neuron

20. also potassium moves out by diffusion more easily than sodium moves in • Result: excess positive charge outside the membrane and negative charge inside the membrane

21. 2. Stimulation / Depolarization • A threshold stimulus must be applied (a change in pH, pressure, or an electrical stimulus) This causes the sodium potassium pump to cause Na+ gates to open and tons of Na+ rush into the cell, and small amounts of K+ to move out • membrane becomes depolarized (+ 40 mV)

22. 3. Re-polarization • After the wave of impulse has move through Na+ gates close to stop inflow • change in electrical potential causes K+ channels to open and K+ ions rush out of the cell

23. Restores the polarized state but now is hyperpolarized – more positively charged on the outside than the resting state (over-shoot) (also the ion concentrations are reversed from the resting state )

24. 4. Refractory period • resting potential (-70mv) mustbe restored before the neuron can fire again • Na+ are pumped out and K+ are pumped back into the cell using ATP energy. • The

25. The Action Potential

26. The Action Potential in Action Neuron Action Potential Propagation

27. Saltatory Action • the speed of the nerve impulse is increased by jumping from node of Ranvier to node of Ranvier (gated channels are found only at the nodes) Propagation of the Action Potential

28. Threshold level – minimum depolarization that must be reached (usually around +30mV) before sufficient Na+ gates open to continue the action potential All or None Response – if the threshold level is not reached, the action potential will not occur at all. If the threshold is reached or exceeded a full action potential will result. The wave of depolarization is self propagating, meaning that it will continue without any aid until its passed on to the next neuron

29. How do we differentiate intensity? Ex hot vs warm?

30. Intensity is determined by: 1. the number of neurons that fire simultaneously 2. the frequency at which the neurons fire 3. the threshold level of different neurons (lower threshold neurons are more likely to fire, and are found in more “sensitive” areas)

31. The Synapse and Neurotransmitters • Neurons are NOT physically attached to each other, but are separated by a gap (synaptic cleft), the electrical impulse cannot just simply cross the gap to the next dendrite, something is needed • Neurotransmitters are stored in synaptic vesicles of the axon and are released to carry the information across this synaptic gap

32. The Synapse Terminal Axon

33. Structures in the Synapse • Pre-synaptic membrane – membrane found at the synaptic ending of the neuron sending information • Post-synaptic membrane- membrane found at the dendrite of the neuron receiving information • Synaptic cleft – space between the pre and post synaptic membranes.

34. Neurotransmitters continue the impulse across the synaptic cleft Crossing the impulse across the gap is a chemical reaction • 1) The end of pre-synaptic axon contains vesicles that have specialized neurotransmitters (NTs), as the impulse gets to the end of the axon the NTs are released in to the gap • 2) The NTs diffuse across the gap and attached to specialized receptors found on the post synaptic dendrite. • 3) The wave of depolarization continues on the through the next neuron

35. excitatory neurotransmitters – cause the opening of Na+ channels to cause depolarization Neurotransmitters

36. 2. inhibitory neurotransmitters –block Na+ channels and open K+ channels ions which causes hyper-polarization -inhibits action potentials

37. Summation – at any given time there are many neurons acting and releasing NTs into the synaptic cleft, the net effect of excitatory and inhibitory neurotransmitters is called summation • ONLYif there is adequate excitation to reach the threshold, the neuron will fire.

38. -may require more than one neuron to release neurotransmitters

39. A response may involve both excitatory and inhibitory neurotransmitters • Ex) Throwing a ball: Triceps contracts and bicep relaxes

40. Integration – the degree of sensation felt or the degree of response created by the brain depends on the number of neurons that fire

41. There are 9 universally recognized neurotransmitters: aspartate, glycine, GABA, glutamate, dopamine, nor-epinephrine, epinephrine, seratonin, and acetylcholine.

42. Some of the more common neurotransmitters (and their enzymes) include:

43. Removing Neurotransmitters To be effective, the NTs must NOT linger around in the gap, other wise successive impulses will occur. NTs are removed from the gap by: 1. Degradation by enzymes in the synaptic cleft 2. Re-uptake by the pre-synaptic membrane 3. Diffusion out of the synaptic cleft 4. Inability to bind due to competitive inhibitors

44. The Effects of Drugs • Drug – anything that is not food that alters the normal bio-chemistry of the body in some way.

45. Stimulant – mimics neurotransmitter, decreases rate of breakdown of neurotransmitter or increases release of neurotransmitter • Depressant – blocks receptor site, decreases production of neurotransmitter, or increases the breakdown of neurotransmitter

46. Alcohol: - depressant -seems to enhance GABA -leads to lack of coordinated response, and loss of normal social inhibitions. -may also weaken the effect of glutamine, an excitatory neurotransmitter, leading to sluggishness and lack of co-ordination. Close to Home Animation: Alcohol

47. Marijuana: - a depressant and hallucinogen -acts on the canniboid receptors of the brain that affect concentration, perception and movement. -may have an impact on the activity of seratonin, GABA and norepinephrine in the brain • not physically addicting, however this is a gateway drug and may be psychologically addicting

48. Cocaine: -a stimulant -blocks the re-uptake of dopamine, causing an adrenaline like effect from the dopamine -as dopamine levels increase in the synapse, the body produces less, thus making cocaine very physically addicting Close to Home Animation: Cocaine

49. Crystal meth: -a stimulant -passes directly through neuron membranes and causes excessive release of dopamine -leads to feelings of euphoria, psychosis, delusions and extreme aggressiveness.

50. Ecstasy: - a stimulant and hallucinogen -affects neurons in the brain by causing an over-production of serotonin. -creates shorter feelings of pleasure, however use can result in brain damage, and cardiac arrest.