AP Biology Notes Outline Enduring Understanding 3.E

L. Carnes

Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to life processes.

Enduring Understanding 3.E:

Transmission of information results in changes within and between biological systems.

Learning Objectives: Essential Knowledge 3.E.1: Individuals can act on information and communicate it to others.

– (3.40) The student is able to analyze data that indicate how organisms exchange information in response to internal changes and external cues, and which can change behavior.

– (3.41) The student is able to create a representation that describes how organisms exchange information in response to internal changes and external cues, and which can result in changes in behavior.

– (3.42) The student is able to describe how organisms exchange information in response to internal changes or environmental cues. Essential Knowledge 3.E.2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses.

– (3.43) The student is able to construct an explanation, based on scientific theories and models, about how nervous systems detect external and internal signals, transmit and integrate information, and produce responses.

– (3.44) The student is able to describe how nervous systems detect external and internal signals. – (3.45) The student is able to describe how nervous systems transmit information. – (3.46) The student is able to describe how the vertebrate brain integrates information to produce a response. – (3.47) The student is able to create a visual representation of complex nervous systems to describe/explain how these systems detect external and internal

signals, transmit and integrate information, and produce responses. – (3.48) The student is able to create a visual representation to describe how nervous systems detect external and internal signals. – (3.49) The student is able to create a visual representation to describe how nervous systems transmit information. – (3.50) The student is able to create a visual representation to describe how the vertebrate brain integrates information to produce a response.

Bozeman Instruction Videos: http://www.bozemanscience.com/ap-biology/ 3.E.1 - #040: Information Exchange 3.E.2 - #041: The Nervous System

Required Readings: 3.E.1 – Ch. 11 & Ch. 45 (pp. 992-993 / Figure 45.21) 3.E.2 – Ch. 48 3.E.2 – Ch. 49 (pp. 1064-1078) 3.E.2 – Ch. 50 (pp. 1109)

Practicing Biology Homework Questions: Questions #40-51

Essential Knowledge 3.E.1: Individuals can act on information and communicate it to others.

Evolution operates on genetic information that is passed to subsequent generations. However, transmission of non-heritable information also determines critical roles that influence behavior within and between cells, organisms and populations. These responses are dependent upon or influenced by underlying genetic information, and decoding in many cases is complex and affected by external conditions. For example, biological rhythms, mating behaviors, flowering, animal communications and social structures are dependent on and elicited by external signals and may encompass a range of responses and behaviors. Populations of organisms exist in communities. Individual behavior influences population behavior, and both are the products of information recognition, processing and transmission. Communication among individuals within a population may increase the long-term success of the population. Cooperative behavior within a population provides benefits to the population and to the individuals within the population. Examples of benefits include protection from predators, acquisition of prey and resources, sexual reproduction, recognition of offspring and genetic relatedness, and transmission of learned responses.

Organisms exchange information with each other in response to internal changes and external cues, which can change behavior. Transmission of non-heritable information can determine critical roles that influence behavior within and between cells, organisms, and populations. These responses are dependent upon or influenced by underlying genetic information, and decoding in many cases is complex and affected by external conditions. Illustrative Examples Include:

• Fight or flight response • Predator warnings • Plant-plant interactions due to herbivory

Figure 45.21: Stress and the Adrenal Gland http://learn.genetics.utah.edu/content/cells/cellcom/ Stressful stimuli cause the hypothalamus to activate the adrenal medulla via nerve impulses and the adrenal cortex via hormonal signals. The adrenal medulla mediates short-term stress response by secreting epinephrine and norepinephrine (see diagram for affects). The adrenal cortex controls prolonged responses by secreting corticosteroids (see diagram for affects). Plant-Plant Interactions due to Herbivory The volatile molecules a plant releases in response to herbivore damage can function as an “early warning system” for nearby plants of the same species. For example, lima bean plants infested with spider mites release a cocktail of volatile chemicals that signal “news” of the attack to neighboring, non-infested plants. In response to these chemicals, non-infested lima bean leaves express different genes. As a result of the activation of specific genes by these released volatile chemicals, noninfested neighbors become less susceptible to spider mites and more attractive to another species that preys on spider mites. Communication occurs through various mechanisms. Living systems have a variety of signal behaviors or cues that produce changes in the behavior of other organisms and can result in differential reproductive success. Illustrative examples include:

• Herbivory responses; territorial marking in animals; coloration in flowers, etc. Animals use visual, audible, tactile, electrical and chemical signals to indicate dominance, find food, establish territory and ensure reproductive success. Illustrative examples include:

• Territorial marking; predator warning; coloration; swarming behavior in insects, bee dances, bird songs, etc. Responses to information and communication of information are vital to natural selection and evolution. Natural selection favors innate and learned behaviors that increase survival and reproductive success. Illustrative examples include:

• Migration patterns; courtship behaviors; foraging behaviors; avoidance behaviors; etc. Cooperative behavior tends to increase the fitness of the individual and the survival of the population. Illustrative examples include:

• Pack behavior; schooling behavior; predator warning; swarming behavior.

Essential Knowledge 3.E.2: Animals have nervous systems that detect internal and external signals, transmit and integrate information, and produce responses.

Organ systems have evolved that sense and process external information to facilitate and enhance survival, growth and reproduction in multicellular organisms. These include sensory systems that monitor and detect physical and chemical signals from the environment and other individuals in the population and that influence on animal’s well-being. The nervous system interacts with sensory and internal body systems to coordinate responses and behaviors, ranging from movement to metabolism to respiration. Loss of function and coordination within the nervous system often results in severe consequences, including changes in behavior, loss of body functions, and even death. Knowledge and understanding of the structures and functions of the nervous system are needed to understand this coordination. The features of an animal’s nervous system are evolutionarily conserved, with the basic cellular structure of neurons the same across species. The physiological and cellular processes for signal formation and propagation involve specialized membrane proteins, signaling molecules and ATP. Neurological signals can operate and coordinate responses across significant distances within an organism. The brain serves as a master neurological center for processing information and directing responses, and different regions of the brain serve different functions. Structures and associated functions for animal brains are products of evolution, and increasing complexity follows evolutionary lines. The Central and Peripheral Nervous System In vertebrates the CNS is composed of the brain and spinal cord (the brain provides integrative power that allows for complex behavior in animals; the spinal cord conveys information to and from the brain and generates basic patterns of locomotion.) The peripheral nervous system (PNS) is composed of nerves and ganglia and functions to transmit information to and from the CNS and plays a large role in regulating an animal’s movement and internal environment. Figure 48.3 Summary of Information Processing http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html Nervous systems process information in three stages: sensory input, integration, and motor output

• Sensors detect external stimuli and internal conditions and transmit information along sensory neurons

• Sensory information is sent to the brain or ganglia, where interneurons integrate the information

• Motor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity

The neuron is the basic structure of the nervous system that reflects function. The structure of the neuron allows for the detection, generation, transmission and integration of signal transmission.

• A typical neuron has a cell body (contains nucleus and organelles), dendrites (cell extensions that receive incoming messages from other cells), and axons (transmit messages to other cells). Many axons have a myelin sheath that acts as an electrical insulator.

• Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron.

• Neurons use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance).

A CLOSER LOOK: Form Fits Function in the Neuron Most of a neuron’s organelles are in the cell body – nerve cells have well-developed rough ER and golgi bodies (make lots of proteins)

• Most neurons have dendrites, highly branched extensions that receive signals from other neurons – increased surface area for reception.

• The axon is typically a much longer extension that transmits signals to other cells at synapses. • A synapse is a junction between an axon and another cell. The synaptic terminal of one axon passes information across the

synapse in the form of chemical messengers called neurotransmitters. • Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell)

Several factors affect the speed at which action potentials are conducted: 1. Axon Diameter: wider axons conduct action potentials more rapidly than narrow ones because resistance to electrical current is

inversely proportional to the cross-sectional area of a conductor. Think of a wide hose and a narrow hose – through which one will water travel faster? Through the wide hose because there is less resistance.

2. Myelin Sheath: axons have narrow diameters but can still conduct action potentials at a high speed because of the layer of electrical insulation that surrounds the axon. These layers are poor conductors surrounding the axon, so the electrical signal is not lost to the external environment during transmission. The purpose of myelin sheath is to speed up conduction by insulating the nerve in intervals. This intermittent insulation causes action potential to jump from one node of Ranvier to the next.

3. Nodes of Ranvier: voltage-gated sodium channels are restricted to gaps in the myelin sheath – the extracellular fluid is in contact with the axon membrane only at these nodes. Action potential jumps from one node of Ranvier to the next. This jumping of action potential speeds up conduction in the axon.

Action potentials propagate impulses along neurons. Membranes of neurons are polarized by the establishment of electrical potentials across the membranes. In response to a stimulus, Na

+ and K

+ gated channels sequentially open and cause the membrane to become locally depolarized. Na

+/K

+ pumps, powered by

ATP, work to maintain membrane potential. Membrane & Resting Potential Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential.

• Messages are transmitted as changes in membrane potential • The resting potential is the membrane potential of a neuron not sending

signals. • Ion pumps and ion channels maintain the resting potential of a neuron.

Figure 48.6 The Basis of the Membrane Potential In a mammalian neuron at resting potential, the concentration of K

+ is greater inside the cell, while the concentration of Na

+ is

greater outside the cell : • Sodium-potassium pumps use the energy of ATP to maintain these K

+ and Na

+ gradients across the plasma membrane.

These concentration gradients represent chemical potential energy. • The opening of ion channels in the plasma membrane converts chemical potential to electrical potential. • A neuron at resting potential contains many open K

+ channels and fewer open Na

+ channels; K

+ diffuses out of the cell.

Anions trapped inside the cell contribute to the negative charge within the neuron. • In a resting neuron, the currents of K

+ and Na

+ are equal and opposite, and the resting potential across the membrane

remains steady.

Understanding Action Potentials Action potentials are the signals conducted by axons – they propagate impulses along neurons. Neurons contain gated ion channels that open or close in response to stimuli:

• In response to a stimulus, Na+ and K

+ gated channels sequentially open and cause the membrane to become locally

depolarized. • Membrane potential changes in response to opening or closing of these channels. • Na

+ /K

+ pumps, powered by ATP, work to maintain membrane potential.

• An action potential can be broken down into a series of stages • (See Figure 48.10 The role of voltage-gated ion channels in the generation of an action potential) • http://bcs.whfreeman.com/thelifewire/content/chp44/4402s.swf

(1) RESTING STATE - The activation gates on the Na+ and K+ channels are closed, and the membrane’s resting potential is maintained. (2) DEPOLARIZATION - A stimulus opens the activation gates on some Na+ channels. Na+ influx through those channels depolarizes the membrane. If the depolarization reaches the threshold, it triggers an action potential. (3) RISING PHASE OF ACTION POTENTIAL - Depolarization opens the activation gates on most Na+ channels, while the K+ channels’ activation gates remain closed. Na+ influx makes the inside of the membrane positive with respect to the outside. (4) FALLING PHASE OF ACTION POTENTIAL - The inactivation gates on most Na+ channels close, blocking Na+ influx. The activation gates on most K+ channels open, permitting K+ efflux which again makes the inside of the cell negative. (5) UNDERSHOOT - Both gates of the Na+ channels are closed, but the activation gates on some K+ channels are still open. As these gates close on most K+ channels, and the inactivation gates open on Na+ channels, the membrane returns to its resting state. During the refractory period after an action potential, a second action potential cannot be initiated. The refractory period is a result of a temporary inactivation of the Na

+ channels.

Figure 48.11 Conduction of an action potential http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html An action potential can travel long distances by regenerating itself along the axon - action potentials travel in only one direction: toward the synaptic terminals.

1) An action potential is generated as Na+ flows inward across the membrane at one location.

2) The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K+ flows outward.

3) The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon.

Transmission of information between neurons occurs across synapses. The vast majority of synapses are chemical synapses. In most animals, transmission across synapses involves chemical messengers called neurotransmitters, which are stored in the synaptic terminal. Illustrative examples of neurotransmitters include:

• Acetylcholine • Epinephrine • Norepinephrine • Dopamine • Serotonin • Transmission of information along neurons and synapses results in a response that can be stimulatory or inhibitory. • Example: Dopamine & Serotonin: released at many sites in the brain and affect sleep, mood, attention, and learning. • Example: Epinephrine and norepinephrine can act as neurotransmitters and hormones – generally secreted in response to

stress. • WATCH THESE ANIMATIONS – be able to describe SPECIFIC examples of neurotransmitters and their effect on cells:

– http://sites.sinauer.com/neuroscience5e/animations06.01.html – http://sites.sinauer.com/neuroscience5e/animations06.02.html – http://sites.sinauer.com/neuroscience5e/animations06.03.html – http://sites.sinauer.com/neuroscience5e/animations06.04.html – http://sites.sinauer.com/neuroscience5e/animations06.05.html

Figure 48.15 A chemical Synapse http://bcs.whfreeman.com/thelifewire/content/chp44/4402003.html

1) When an action potential depolarizes the plasma membrane of the synaptic terminal, it 2) opens volted-gated Ca2+ channels in the membrane triggering an influx of Ca2+ 3) The elevated Ca concentration in the terminal causes synaptic vesicles to fuse with the presynaptic membrane 4) The vesicles release neurotransmitter into the synaptic cleft 5) The neurotransmitter binds to the ion-channels in the postsynaptic membrane, opening the channels and allowing the flow

of both Na and K 6) When the neurotransmitter releases from the receptors, the channels close and synaptic transmission ends. 7) After release, the neurotransmitter may diffuse out of the synaptic cleft, may be taken up by surrounding cells, or may be

degraded by enzymes

Different regions of the vertebrate brain have different functions. http://www.youtube.com/watch?v=oGjaP_bO37I Each side of the cerebral cortex is divided into four lobes, and each lobe has specialized functions.

Forebrain (cerebrum): functions in information processing / divided into right and left hemispheres. Right and left sides control the opposite side of the body. Midbrain (brainstem): functions in homeostasis, coordination of movement, and conduction of information to and from higher brain centers. Hindbrain (cerebellum): coordinates movement and balance (i.e. hand-eye coordination).