6.5 Nerves, hormones and homeostasis

Click4Biology

Textbook Chapter 6

Practice Quiz

6.5.1 

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

No other structural or functional divisions of the nervous system are required.

6.5.3 

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

The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

The CNS consistes of the brain and the spinal cord.

The PNS consists of the sensory and motor neurons that extend from the CNS to the rest of the body.

The neuron is the specialized cell of the nervous system. It has an elongated structure for carrying signals through the body. I think of them like wires in electronic devices. 

Sensory neurons bring signals to the CNS from the body.

Motor neurons carry signals from the CNS to the body.

Interneurons or relay neurons are part of the CNS and make connections between the sensory and motor neurons.

• For example, a signal begins in a specialized receptor cell - like the cells of the eyes, ears, or skin - and travels through sensory neurons to the CNS. The CNS processes the information and sends a signal through motor neurons to cause some response - like focusing the eyes or moving an arm.

The PNS is divided into the somatic nervous system and the autonomic nervous system.

The somatic nervous system consists of neurons that can be consciously controlled - like the skeletal muscles.

The autonomic nervous system consists of neurons that are unconsciously controlled - like heart and stomach muscles. (Think "automatic" for "autonomic")

The signals of the nervous system are called impulses, and the impulse is an electrical change that moves through the neuron cell. At the end of each neuron the electrical impulse causes a chemical called a neurotransmitter to be released. The neurotransmitter signals the next neuron to send an impulse.

A nerve is a bundle of neurons.

http://activity.ntsec.gov.tw/lifeworld/english/content/brain_cc8.html

6.5.2 

Draw and label a diagram of the structure of a motor neuron.

Include dendrites, cell body with nucleus, axon, myelin sheath, nodes of Ranvier and motor end plates.

Impulse moving through three neurons with a close-up of the synapse:

http://www.health.bcu.ac.uk/physiology/pharmacology01.htm 

http://www.enchantedlearning.com/subjects/anatomy/brain/Neuron.shtml

6.5.4 

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

Impulse Animation (youtube)

Summary Video with music from Daft Punk! (ignore the extra information)

Resting potential: the neuron maintains a relatively positive charge on the outside of the plasma membrane, and a relatively negative charge on the inside of the membrane. This requires the active tranpsort of ions (Na⁺ and K⁺), so maintaining the resting potential actually requires energy (ATP to pump the ions).

http://waynesword.palomar.edu/chemid2.htm

Action potential (the impulse): the movement of a change in the membrane's charge: the outside becomes negative and the inside becomes positive. The reversal of the charge happens extremely quickly and moves along the neuron. The change in charge is caused by the movement ions. The membrane goes back to normal (resting potential) after the action potential passes.

http://waynesword.palomar.edu/chemid2.htm

Depolarization: the beginning of the action potential - the movement of Na⁺ ions from outside to inside causing a change in the charge.

Repolarization: the end of the action potential - the movement of K⁺ ions from inside to outside causing the charge to return to normal (resting potential).

6.5.5 

Explain how a nerve impulse passes along a non-myelinated neuron.

Include the movement of Na⁺ and K⁺ ions to create a resting potential and an action potential.

Proteins in the plasma membrane control the resting and action potential of the neuron.

Resting Potential

Protein pumps use ATP to move Na⁺ outside the cell and K⁺ inside the cell to maintain the resting potential (positive outside/negative inside - even though both ions are positive, there is a relative difference in electrical charge across the membrane: it may be better to say more positive outside, less positive inside). 

Channel proteins allow the facilitated diffusion of ions, Na⁺ or K⁺, but they are "gated" or closed during resting potential - otherwise the pump would never be able to maintain the charge difference.

Action Potential

When the neuron is stimulated, the gated Na⁺channel proteins open, and the Na⁺ diffuses into the cell, changing the charge. (depolarization)

This causes adjacent Na⁺channel proteins to open, and the change in charge moves along the neuron.

Behind the action potential, the K⁺channel proteins open, and the K⁺ions diffuse outside.

This returns the membrane potential to the resting state. (repolarization)

http://soe.ucdavis.edu/ss0708/eghbalis/Notes/U12Notes.html

In the above diagram, the action potential moves from left to right.

Note that in the following simulation the action potential goes from right to left.

Keep watching it.

You'll notice the high concentration of Na⁺ outside during the resting potential.

You'll see the Na⁺ move inside during the action potential (depolarization).

You'll see the K⁺ move outside during the repolarization, called the "falling" phase

The graph at the bottom shows the change from negative to positive within the axon as the action potential moves

http://www.interactive-biology.com/99/the-isoelectric-point-and-how-it-leads-to-an-action-potential/

6.5.6 

Explain the principles of synaptic transmission.

Include the release, diffusion and binding of the neurotransmitter, initiation of an action potential in the post-synaptic membrane, and subsequent removal of the neurotransmitter.

Synaptic Transmission

The electrical impulse that moves through a neuron cannot move across the synapse betweeen two neurons.

In the synapse - the space between the neurons - the signal is a chemical called a neurotransmitter.

There are many kinds of neurotransmitters.

Neurotransmitters stimulate receptor proteins on the next neuron.

The receptor proteins begin a new action potential in the next neuron.

A neuron produces neurotranmitters and stores them in vesicles in the axon terminals.

When an impulse reaches a terminal, it causes Ca²⁺ ions to diffuse into the cell.

The Ca²⁺ ions cause exocytosis - the vesicles join with the plasma membrane and release the neurotransmitters into the synapse.

The neurotranmitters diffuse across the synapse to the next neuron.

When the neurotransmitters bind with the receptor proteins on the next cell, the proteins open their gates to allow Na⁺ to move inside.

This is the beginning of a new action potential in the next cell.

The neurotransitters are released from the receptor proteins, and the neurotranmitters are broken down by enzymes from the receptor proteins.

The receptor proteins on the postsynaptic neuron (the next cell) close the Na⁺ gates.

The neurotransmitter pieces are absorbed by the first neuron and are re-formed to be used again.

Because of the impulses and the neurotransmitters, the nervous system uses electrical and chemical signals.

Neurons brings information from inside the body and from the outside world to the brain. Inside the brain, billions of neurons make complex connections to process the information - this includes understanding sight, hearing, touch, smell, taste, and other internal sensations like hunger, thirst, and temperature. Right now you are seeing symbols called letters arranged in patterns called words. The words are arranged in larger structures called sentences within even larger contexts that the brain understands (science topic in English language). And you understand all this relatively easily. Your eyes transmit the images of the letters to the brain which perceives them as meaningful words and sentences, and the brain understands the information with prior knowledge. Your brain may or may not remember the new information. If it does, it can recall the same information later; it can even apply this information to related contexts. This process is not only the realm of education - the work of students and teachers - but also part of every aspect of everybody's life - social relations, careers, spirituality, etc.

Your brain understands the world around it. Your brain reacts to the outside world. Your brain has complex thoughts and feelings. Your brain even tries to understand itself. 

All of this - even what you are thinking right now - is simply the action of neurons.

6.5.7 

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

The Endocrine System

Like the nervous system, the endocrine system is a communication and control system of the human body.

The endocrine ssytems consists of organs called glands.

The glands are very different from one another in their structure and function and are located in different areas of the body.

Glands produce chemicals called hormones. Hormones are chemical signals that stimulate specific cells in the body.

Glands release hormones into the bloodstream where they travel thoughout the body stimulating specific cells.

http://3.bp.blogspot.com/-X5NpzrbtJPQ/TV96bCm8VPI/AAAAAAAAAPw/IxV9CnDA2bg/s1600/EndocrineSystemChart.png

6.5.8 

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

(The internal environment consists of blood and tissue fluid.)

Homeostasis is the maintenance of the internal conditions of the body. 

The internal conditions of the body must stay within certain limits for the body to function properly.

• For example, the human body needs to stay at approximately the same temperature all the time. If the body gets too hot or too cold, the body reacts to return the temperature to normal.

Maintaining homeostasis is essential for staying alive. If the internal conditions of the body move too far from homeostasis for too long, serious damage and death can result.

Stimulus: anything that causes a response. (plural: stimuli)

Response: a reaction to a stimulus.

A stimulus can be almost anything - change in temperature, something the eyes see, a sound. A response to a stimulus  usually maintains homeostasis or survival.

Internal conditions of the human body:

• temperature
• blood pH
• carbon dioxide concentration
• blood glucose concentration
• water balance

6.5.9 

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

Negative feedback loops are stimulus and response mechanisms for maintaining homeostasis. 

Receptors detect changes in internal conditions that are outside the limits of homeostasis, and they send a signal to the brain or endocrine system.

The brain or gland sends a signal to an effector or target organ to cause a response.

The response corrects the internal condition to within the range of homeostasis.

6.5.10 

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

Thermoregulation (example of a negative feedback loop)

http://www.jirvine.co.uk/Biology_GCSE/B1A/b1al3.htm

The diagram above shows the response "shivering" for the stimulus "cold" and "sweating" for "hot."

The hypothalamus is the part of the brain that controls body temperature.

http://www.mrothery.co.uk/module4/webnotes/Mod4Notes2ndhalf.htm

6.5.11 

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

Regulation of blood glucose concentration

http://www.jirvine.co.uk/Biology_GCSE/B1A/b1al3.htm

Blood glucose concentration is controlled by the gland called the pancreas that secretes the hormones glucagon and insulin. 

Glucagon is secreted by alpha (α) cells of the pancreas.

Glucagon causes the liver to break down glycogen into glucose and release it into the blood.

Insulin is secreted by beta (β) cells of the pancreas. 

Insulin causes the liver to absorb glucose from the blood and convert it into glycogen.

http://www.endocrineweb.com/conditions/diabetes/normal-regulation-blood-glucose

The graph shows how blood glucose concentration is regulated to maintain homeostasis.

http://www.mrothery.co.uk/module4/webnotes/Mod4Notes2ndhalf.htm

6.5.12 

Distinguish between type I and type II diabetes.

Aim 8: Diabetes is having an increasing effect on human societies around the world, including personal suffering due to ill health from the diabetes directly but also from side-effects such as kidney failure. There are economic consequences relating to the health-care costs of treating diabetics.

TOK: The causes of the variation in rates of type II diabetes in different human populations could be analysed. Rates can be particularly high when individuals consume a diet very different to the traditional one of their ancestors, for example, when having migrated to a new country. There are genetic differences in our capacity to cope with high levels of refined sugar and fat in the diet. Humans also vary considerably in how prone they are to become obese.

Diabetes mellitus: a disease caused by a problem with the homeostasis of blood glucose concentration. 

Type I Diabetes: (also known as insulin-dependent, early-onset, or juvenile diabetes) a deficiency of insulin occurs because the immune system destroys the beta (β)cells of the pancreas, so glucose is not absorbed from the bloo and remains high. The disease is treated by injections of insulin (usually produced by genetically engineered bacteria!)

Type II Diabetes: (also known as noninsulin-dependent or late-onset diabetes) liver cells do not have functioning receptors for insulin, so they do not absorb glucose from the blood. Treatment with injections of insulin is not effective, but the blood glucose concentration can be regulated by controlling the diet - eating complex carbohydrates and fiber that release glucose slowly, and avoiding saturated fats and simple sugars (monosaccharides).

Both types of diabetes cause a high level of blood glucose concentration.

This causes water loss from cells due to osmosis.

Cells metabolize proteins and fats because they don't have glucose.

The breakdown of protein for energy can result in organ damage.

Long-term damage can effect the eyes, kidneys, and cardiovascular system.