Topic 6.5 Nerves, Hormones and Homeostasis

6.5.1 CNS, PNS and neurones CNS = brain and spinal cord PNS = all nerves outside the CNS – 2 categories of peripheral nerves: Spinal nerves - 31 pairs emerge from spinal cord Cranial nerves – 12 pairs emerge from the brain stem Neuron(e) = nerve cells which conduct electrical impulses – Sensory neuron = bring info to the CNS Sensory receptors found in our sense organs – Motor neurons = carry response info from CNS to muscles or glands

6.5.2 Draw and label a motor neuron Cell body contains: – nucleus – rER and sER – golgi apparatus – ribosomes – lysosomes – mitochondria (also found in the axon) action potential

6.5.3 Conduction of nerve impulses from receptors to effectors sensory neurons - send message from receptors to CNS PICK UP STIMULUS motor neurons – receive message from CNS to effectors (muscles or glands) RESPOND relay neurons – found in spinal cord connect sensory and motor neurons reflex arc – allows for quick reaction….brain not involved

6.5.4 Resting and Action Potentials resting potential – measured in millivolts, mV – when not sending an impulse – is polarized – active transport of Na + and K + in two different directions (Na + goes out of axon, K + goes into cytoplasm) – requires protein channels and ATP * 3 Na + out and 2 K + in * many – ions inside axon * net positive charge outside the axon * net negative charge inside axon

6.5.4 (cont.) action potential – resting potential sets up [ ] gradients – Na + diffuses into the axon and K + diffuses out – occurs in a small area of the axon which initiates the next area and so on down the axon – called depolarization repolarization = active transport to pump the two ions to their resting potential refractory period = time it takes for 1 neuron to send an action potential and then repolarize

6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron average resting potential = -70 mV (outside is + compared to inside) average action potential = when value reaches +40 mV the Na + pores shut and K + pores open K + pores shut when -70 mV is restored threshold potential = -40 to -50 mV is the depolarization necessary to generate an impulse

6.5.6 Explain the principles of synaptic transmissions neurotransmitters are chemicals which transmit the impulse across the synapse (ex. acetylcholine, serotonin and dopamine)

6.5.6 (cont.) mechanisms of synaptic transmission: – Calcium ions (Ca 2+ ) diffuse into terminal buttons on end of axon – vesicles with neurotransmitters fuse with membrane of presynaptic neuron – neurotransmitters diffuse across synaptic gap and bind with receptor of post synaptic neuron – this opens sodium ion channels and initiates an action potential – neurotransmitters are degraded by enzymes – ion channels close

6.5.7 Endocrine system consists of glands that secrete hormones Endocrine glands are ductless Exocrine glands have ducts ex. sweat glands Secrete hormones into bloodstream Only cells with special receptors will react to the presence of the hormone = target cells Endocrine and nervous systems work together to maintain homeostasis

6.5.8 Homeostasis involves maintaining the internal environment within certain limits includes: blood pH, CO 2 [ ], blood glucose [ ], body T° and water balance Each has a set point value (normal) – ex. body T° = 98.6°F or 37°C, blood pH = 7.4 There are inevitable fluctuations of these “normal” values Negative feedback mechanisms keep values within a limited range O 2 and CO 2 levels are monitored by chemoreceptors in walls of certain blood vessels

6.5.9 Homeostasis involves monitoring and correcting by negative feedback mechanisms

Explain control of body T° include: transfer of heat in blood, roles of hypothalamus, sweat glands, skin arterioles and shivering Thermoregulation = controlling body T° Thermoreceptors in skin and hypothalamus gland monitors changes Too hot: – Vasodilation = blood vessels in skin become wider to increase blood flow and increase heat loss to environment – Sweating = evaporation of fluid from skin requires energy which is taken from body (panting does the same) – Decreased metabolism = reduces heat produced by many rxs

(cont.) Too cold: – Vasoconstriction = blood vessels of skin contract to reduce heat loss – Shivering = muscular contractions produce heat – Increased metabolism Hypothalamus: – Receives info from thermoreceptors in skin and activates cooling or heating mechanisms

Explain control of blood glucose levels include: roles of glucagon, insulin and α and β cells in pancreas Pancreas is both endocrine (islets of Langerhans produce hormones to control blood glucose levels) and exocrine gland (produce digestive enzymes) found below stomach When we eat blood glucose levels increase – glucose used for cellular respiration (make ATP) – levels must be maintained by negative feedback Islets of Langerhans cells have chemoreceptors which are sensitive to glucose levels

(cont.) If blood glucose, α cells in the islets secrete glucagon Glucagon = hormone travels to liver where liver cells (hepatocytes) will convert glycogen to glucose If blood glucose, β cells in the islets secrete insulin Insulin = hormone travels to all parts of body and causes muscle cells and hepatocytes to convert glucose to glycogen or converted to fat in adipose tissue

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Distinguish between type I and type II diabetes Diabetes (diabetus mellitus) is a disease characterized by hyperglycemia (high blood sugar) Type I is caused when β cells of pancreas do not produce enough insulin Type II is caused by body cell receptors that do not respond properly to insulin

Type I Diabetes Autoimmune disease = bodies immune system attacks and destroys β cells so little or no insulin is produced < 10% of diabetics are type I Causes: body produces antibodies against insulin and/or β cells in islets of Langerhans Treatment: – regular injections of insulin (protein digested in stomach so can’t be taken orally) – Pancreas transplant or β cell transplantation

Type II Diabetes Body no longer responds properly to insulin Known as insulin resistance Most common form of diabetes 90% Causes: – Genetic history – Obesity – Lack of exercise – Advanced age – Ethnicity (Aboriginal Australians, Native Americans and Maoris) Treatment: – Reduced carbohydrate intake and increased exercise – Weight loss – Medication to lower glucose levels and increase production of insulin