1. Topic 6.5Nerves, Hormones and Homeostasis IB Biology

2. Nervous System Central Nervous System (CNS): brain and spinal cord relays messages, processes and analyzes information Peripheral Nervous System (PNS) peripheral nerves: cranial and spinal (outside CNS) connects sense organs to CNS connects CNS to muscles and glands

3. Peripheral Nervous System Sensory division (from receptors to CNS) Motor division (from CNS to effectors) Somatic: voluntary Autonomic: involuntary Sympathetic: “fight or flight” Dilates pupil/relaxes lens Inhibits digestion Increases heart rate Dilates bronchioles Stimulate liver: glycogen -> glucose Relaxes bladder Parasympathetic: opposite - conserves energy (“rest and digest”)

4. Neurons Specialized cells that carry electrical impulses node of Ranvier Motor Neuron

5. Neurons under a microscope

7. Myelin: insulating material

8. Demyelination = myelin is destroyed e.g. multiple sclerosis

9. Spinal cord

10. Types of Neurons Sensory Neuron Sensory Neurons: transmit electrical impulses from sensory receptors to the CNS Relay Neurons (Interneurons): move impulses inside the CNS Motor Neurons: take impulses from CNS to effectors (glands/muscles) Motor Neuron

11. Reflex

12. How the impulse is transmitted Impulse begins when a neuron is stimulated by another neuron or by the environment Electrical impulse moves in one direction: Dendrites -> Cell Body -> Axon Synapse: gap between 2 neurons Neurotransmitters send the signal to the following neuron No myelin = 5-25m/s With myelin = 10-120m/s

13. How the impulse is transmitted Neuron not transmitting an impulse: membrane has an electrical potential (voltage) called resting potential Caused by the imbalance of K + and Na + across the membrane (Na + /K + pumps) = polarization Electric difference (voltage): -70mV

14. When there is a stimulus... Na+ gates open = Na + enter the cell Electrical potential of the cell changes depolarization (normal charge is reversed) = +30mV Action potential is recorded Na + channels close K + channels open repolarization occurs (charges back to normal) K + channels stay open longer hyperpolarization = -85mV (refractory period = prevents one impulse to catch up with another) Stimulus = self-propagating http://outreach.mcb.harvard.edu/animations/actionpotential.swf

17. The Synapse Synapse = gap between neurons Action potential cannot cross gap: neurotransmitters carry the impulse Neurotransmitters: stored at the end on axons (glutamate, GABA, acetylcholine, norepinephrine, dopamine, serotonin, nitric oxide, etc) Voltage Ca+2 gated ions open -> calcium flows inside neuron Calcium help vesicles fuse with membrane -> neurotransmitters are released These bind with neuroreceptors Voltage gated ions are activated = depolarization Impulse is passed on to post-synaptic neuron Neurotransmitters = broken by enzymes and reabsorbed by pre-synaptic neuron

20. Negative Feedback 2

22. Control of Body Temperature Hypothalamus controls body temperature, preventing cooling/overheating Skin arterioles: vasoconstriction (prevents heat loss) ; vasodilation (more blood near surface – heat is transferred out) Shivering Hairs with erector muscle Sweat glands

23. Control of Blood Glucose Pancreas is an endocrine gland It releases insulin ( cells) and glucagon ( cells) Receptors present on liver cells Negative feedback occurs

24. Diabetes mellitus Glucose builds up in blood = cells lose water (a lot of urine is produced) Glucose appears in urine Type I: juvenile - no insulin is produced because  cells are destroyed (autoimmune) Type II: adult - reduced sensitivity to insulin / less receptors