Human Physiology IIEssential Questions• How are messages transported through the body? • How do feedback mechanisms play a role in maintaining homeostasis? • To what extent should we ‘mess’ with chemical transmitters in our body?

Topics • 6.5 Nerves, hormones, homeostasis• 6.6 Reproduction• E4 Neurotransmitters and synapses• HL E5 The human brain, 11.4 Reproduction

Major assessments• Learning log• Fetal pig dissection lab• Unit test

Upcoming Dates 2015

• Biology IA: February 23 – 27th

• IB Mock: March 11 – 15• IB Exam: April 30th – May 22nd

6.5 Nerves, hormones, homeostasis

Nervous System• Central Nervous System = brain + spinal cord• Peripheral Nervous System = nerves which

communicate motor and sensory signals between CNS and rest of body

5.4, 5.5 Nerve impulse• Nerve impulses conducted along a

neuron; Result of change in concentration of sodium and potassium ions across membrane of neuron

• Resting potential = electrical potential across a cell membrane when not propagating an impulse

• Action potential = reversal then restoration of electrical potential between inside and outside of neuron as impulse passes along it

1. Arrival of Action Potential causes Na+ channels to open and Na+ to rush in => internal potential reversed (more positive inside than outside) DEPOLARIZATION

2. K+ channels open and K+ flows out=> internal charge is negative again REPOLARIZATION

6.5 Nerves, hormones, homeostasisE4 Neurotransmitters and synapses

How is information transmitted between neurons?

• Dendritic end to terminal end: synaptic gap• Electrical impulse converted to chemical

neurotransmitter

E4.2 Decision making

• A neuron receives many excitatory and inhibitory stimuli

• If the sum of the signals is inhibitory, then no AP propagated

• If the sums of the signals is excitatory, then AP is propagated

6.5 Nerves, hormones, homeostasisE4 Neurotransmitters and synapses

E4.1 – 4.3 Excitatory/inhibitory NT• Excitatory NT: excite the post synaptic neuron via

depolarization • Na+ channels open, Na+ rushes in membrane

potential depolarizes AP activated • Dopamine, Acetylcholine• Cholinergic synapse

E4.1 – 4.3 Excitatory/inhibitory NT• Inhibitory NT: inhibit the post synaptic

neuron via hyperpolarization • K+ channels open, K+ rushes out OR Cl-

channels open, Cl- rushes in hyperpolarization no AP

• Adrenergic synapse

E4.1 – 4.3 GABA

• Opens Cl- channels in the post synaptic membrane, Cl- rushes in, hyperpolarizing post synaptic neuron and not firing AP

• GABA has calming or ‘depressive’ effect

• Alcohol mimics GABA

E4.3 Drugs Can change synaptic transmission

– Block a receptor of a neurotransmitter

– Block release of a neurotransmitter from the presynaptic membrane

– Enhance release of a neurotransmitter

– Enhance neurotransmission by mimicking a neurotransmitter

– Block removal of a neurotransmitter

Research topics

• Drugs– Excitatory drugs: Nicotine, cocaine, amphetamine– Inhibitory drugs: Benzodiazepine, alcohol,

tetrahydrocannabinol (THC)• Research

– Biochemical action at the synapse – Effect on mood– Dangers of addiction

• Mini presentation

7. Homeostasis• Homeostasis = maintaining the internal

environment of the body between limits

• Maintain internal environment between limits– Blood pH, carbon dioxide

concentration, blood glucose concentration, body temperature, water balance

• Endocrine system consists of glands that release hormones that are transported in blood

8. Negative Feedback Mechanism• set-point: a constant value to which

a variable is constrained

• receptors: sensors respond to stimuli

• control center: receives information from sensors, compares the value to a set-point and direct actions to return the variable to its set-point

• effectors: a mechanism for taking action to return a variable to its set-point

• responses: the resulting action produced by an effector

10. Thermoregulation

• Set point: core body temperature: 37C

• Sensors: blood and body temperatures above and below 38C

• Control center: Hypothalamus thermostat sensitivity to blood temperature + connection to pituitary gland

10. Thermoregulation: EffectorsResponse to overheating Response to chilling

Vasodilation (skin arterioles become wider) Increase heat loss

Vasoconstriction (skin arterioles become narrower) decreasesheat loss

Skeletal muscles remain relaxed decrease heat generation

Skeletal muscles cause rapid contractions (shivering) increase heat generation

Sweating Increase heat loss No sweating decrease heat loss

9. Control of glucose• Set point: Blood glucose

= 90 mg/100 ml• Sensors: Glucose

detectors in pancreas islet beta/alpha cells

• Control center: Pancreas islet beta/alpha cells

9. Thermoregulation: EffectorsResponse to high blood glucose

Response to low blood glucose

• Beta cells release insulin

• Insulin stimulates liver and muscle cells to absorb glucose and convert to glycogen --> decrease in blood sugar

• Alpha cells produceglucagon

• Glucagon stimulates liver cells to break down glycogen and release glucose into blood increase in blood sugar