Nerves, hormones & homeostasis

6.5.1 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurones that can carry rapid electrical impulses

6.5.3 State that nerve impulses are conducted from receptors to the CNS by sensory neurones, within the CNS by relay neurones, and from the CNS to effectors by motor neurones.

The CNS Brain & spinal cord Receive sensory information from receptors Interpret & process that sensory information Initiate a response

Types of neurones Sensory neurones – bring information to the brain & spinal cord Relay neurones – the CNS Motor neurones – carry response information to muscles Sensory & motor neurones = PNS

Categories of peripheral nerves Spinal nerves – 31 pairs (left & right) emerge directly from the spinal cord. Mixed nerves – some sensory/some motor Cranial nerves – 12 pairs emerge from the brain stem

6.5.2 Draw & label the structure of a motor neurone.

6.5.4 Define resting potential and action potential (depolarization and repolarization)

Resting Potential Neuron is ready to receive a stimulus The neuron is polarized Maintained by active transport Sodium (Na+) transported out of the neuron to intercellular fluid Potassium (K+) transported in the neuron to the cytoplasm Negatively charged organic ions permanently located in the cytoplasm

Action Potential = nerve impulse Action potential has a voltage Voltage is measured in millivolts Axons carry messages away from the cell body Some axons have myelin sheath around them Myelin sheath increases the rate of the rate of the action potential

6.5.5 Explain how a nerve impulse passes along a non- myelinated neurone.

Action Potential Movement of ions is not along the neuron Ions diffuse from outside the axon to the inside (Na+) & Ions diffuse from inside the axon to the outside (K+) The diffusion is the action potential Called depolarization

Return to the Resting Potential Neurons may send dozens of action potentials in a short time Can’t send an action potential until the ions reset themselves Must use active transport REPOLARIZATION Time it takes to to send an action potential and then repolarize is called REFRACTORY PERIOD

6.5.6 Explain the principles of synaptic transmission.

How Neurons communicate with each other. Sensory pathway is unidirectional 1 st neuron = presynaptic neuron 2 nd neuron = postsynaptic neuron SYNAPSE – area between the 2 neurons Terminal Buttons – swollen membranous areas at the end of the axons

Mechanism of synaptic transmission 1.Calcium ions (Ca 2+ ) diffuse into the terminal buttons 2.Vesicles containing neurotransmitters fuse with the plasma membrane & release neurotransmitter 3.Neurotransmitters diffuses across the synapse 4.Neurotransmitter binds with a receptor protein 5.Binding results in an ion channel opening & sodium ions diffusing in

Mechanism of synaptic transmission cont. This initiates the action potential to begin moving down the postsynaptic neuron Neurotransmitter is degraded by specific enzymes and is released from the receptor protein The ion channel closes to sodium ions Neurotransmitter fragments diffuse back across the synaptic gap to be reassembled in the terminal buttons of the presynaptic neuron

/synaptic.swf Let’s do this tutorial

6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood

Endocrine System A stimulus is received & processed Hormones are secreted into the blood, ductless They are carried to the target tissue

6.5.8 State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentrations, body temperature and water balance.

Homeostasis Body typically stays within certain limits (normal limits) Each variable has an expected value or set point Physiological changes to bring a value back to the set point are called negative feedback mechanisms

Endocrine System The action of the hormone changes conditions of the tissue This change is monitored through feedback Most hormonal changes are negative feedback

6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms

Too Hot? Get Cooler!!! How do you do this? Stimulus Receptor Control center Effector

Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalmus, sweat glands, skin arterioles and shivering

Explain the control of blood glucose concentration, including the roles of glucagon, insulin and and cells in the pancreatic islets

Blood glucose levels Blood glucose level is the concentration of glucose dissolved in blood plasma Glucose needed for cell respiration Eat carbohydrates Digested to glucose Glucose absorbed into bloodstream Blood glucose must be maintained close to the set point

Blood glucose cont. Glucose routed to the liver via hepatic portal vein Glucose concentration varies in vein Only major blood vessel in which blood glucose concentration fluctuates greatly Other blood vessels receive blood after liver hepatocytes action 2 hormones Insulin glucagon antagonistic

What if glucose levels go above the set point? Beta cells produce insulin Insulin is secreted & absorbed by blood Insulin’s effect on body cells Opens protein channels in cell membranes Channels allow glucose to diffuse into the cell by facilitated diffusion If blood high in glucose enters the liver, insulin stimulates the hepatocytes to take in glucose and convert it to glycogen Glycogen stored as granules in the cytoplasm of the hepatocytes & muscles

What is the glucose level goes too low? When? You haven’t eaten for several hours or exercise vigorously for a long time Body needs the glycogen stored in liver & muscles Alpha cells of the pancreas begin to produce 7 secrete glucagon. Glucagon circulates in the bloodstream & stimulates hydrolysis of the granules of stored glycogen Hydrolysis produces glucose

Distinguish between type I and type II diabetes.

Diabetes Characterized by hyperglycaemia (high blood sugar) Type I = Beta cells don’t produce enough insulin Type II = body cell receptors don’t respond to insulin Therefore, people have plenty of glucose but can’t use it

How to Control the two types? Type I – insulin injections Type II – controlled by diet

Uncontrolled diabetes Damage to the retina- blindness Kidney failure Nerve damage Increased risk of cardiovascular disease Poor wound healing Possible gangrene

Type I Diabetes Autoimmune disease Immune system attacks & destroys beta cells Less than 10% of diabetics Most often children or young people 90% of diabetics Genetic history, obesity, lack of exercise, advanced age