Topic 6.5Nerves, 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)

actionpotential

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 restoredthreshold 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 (Ca2+) 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, CO2 [ ], 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

• O2 and CO2 levels are monitored by chemoreceptors in walls of certain blood vessels

6.5.9 Homeostasis involves monitoring and correcting by negative feedback mechanisms

6.5.10 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 changesToo 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

6.5.10 (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

6.5.11 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

6.5.11 (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

6.5.11 (cont.)

6.5.12 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