Animal Homeostasis

• Homeostasis maintains internal conditions for proper organism functioning.

Maintaining Homeostasis

• A dynamic process involving changing external/internal conditions.
• The ideal range for an internal condition changes.

Animal Homeostasis

• Animals can move and get energy from food.
• Animals have determinate growth and specialized sensory organs.
• They possess a brain which acts as a central control center.
• Body systems collaborate to maintain homeostasis.

Homeostatic Systems

• Nervous system integrates information regarding all conditions.
• Sensory system collects and transmits information to the nervous system.
• Endocrine system coordinates responses with the nervous system via hormones.

Animal Homeostatic Systems: Components

• Integrating centers receive and interpret messages from various conditions sensors.
• Sensors are cells or organs which detect internal and external conditions.
• Each sensor monitors specific conditions.
• Sensors send signals to the integrating center constantly, or when conditions change.
• One condition is monitored by multiple different sensors.
• Effectors' function depends on the condition monitored by the homeostatic system.
• Set points are optimum levels for monitored conditions; acceptable ranges vary.
• Integrating centers are parts of the brain.
• Sensors are located throughout the body.
• Effectors include muscle cells.
• Negative feedback counteracts changes, while positive feedback amplifies changes which do not occur indefinitely.
• Regulate detectable conditions
• Work as networks, not on/off switches, and involve multiple components.

Nervous System

• The sensory division collects internal/external environment data.
• Motor division distributes data to effectors for proper responses.

The CNS

• Processes, integrates, and coordinates sensory data, motor commands, intelligence, emotion, learning, and memory.

Neurons

• Are nervous system cells that transmit signals
• There are three functional categories: sensory, interneurons, and motor neurons.
• Sensory neurons collect and transmit information about conditions.
• Interneurons integrate the information and send directions.
• Motor neurons carry directions to effectors.
• Dendrites receive signals.
• Cell body receives and integrates sent signals.
• Axons transmit signals.
• The axon hillock is a meeting point between the cell body and axon (signals start here).
• Synaptic terminals are axon branch ends, that transmit signals to the next cell.
• Glial cells (glia) support neurons, and do not transmit signals.
• Schwann cells insulate PNS neurons.

Nerve Signals

• Nerve signals are transmitted along neurons as electrical signals by moving charges/ions.
• Selectively permeable membranes w/proteins tightly control molecule movement.
• Membrane proteins are specific, and neuron membranes possess a number of membrane proteins.
• Channels let molecules move from high to low concentrations.
• Chemically gated channels open/close with molecule interaction.
• Voltage-gated channels respond to charge changes inside and outside the neuron.
• Sodium-potassium pumps use energy for directed Na+ and K+ movement.
• They pump out three Na+ ions for two K+ ions and always function.
• Sodium-potassium pumps establish more Na+ outside, and more K+ inside the neuron, resulting in a positively charged environment.
• Membrane potential is the charge difference across neuron membranes.
• Resting potential occurs when not sending signals (gated Na+/K+ channels are closed and sodium-potassium pumps function).
• Stimuli alter neuron membrane potential, specific effects depend on the stimulus.
• Membrane potential reversal results in the inside becoming more positively charged.
• Action potential=signal generated when membrane potential reversal reaches threshold.

Additional Info

• Dendrites are extensions receiving signals.
• Axons transmit signals from the hillock, while synaptic terminals transmit the signal to new cells.
• Glial cells support neurons and do not transmit signals.
• There are two kinds of ions that are important for nervous system signals K+ and Na+.
• Sodium-potassium pumps use energy and function continuously.
• Allow sodium out and potassium into neurons
• Channels allow molecules to move from higher to lower concentrations.
• Sodium-potassium pumps use energy to move Na+ and K+ in specific directions.

Action Potentials

• Generated when membrane potential reversal reaches threshold, involving coordinated voltage-gated Na+/K+ channel openings.
• Sodium-potassium pumps continuously function.
• Threshold membrane potential change causes voltage-gated Na+ channels to open- inside gets more positive.
• Action potentials are local events occuring in a specific place which don't vary in size.

Action Potentials: Stimuli Strength

• It is communicated by action-potential frequency; transmitted in one direction from the axon hillock towards the synaptic terminal.
• Signal transmission along axons is like a stadium wave.
• Action potentials are transmitted in one direction; prevented by myelin sheaths.
• Signals travel faster along myelinated axons.

Reminders

• Sodium ions diffuse in all directions inside an axon

Signal Transmission: Synapses

• Signals pass at synapses where synaptic terminals contact receiving cells.
• Sending neurons form synapses with receiving cells.

Types of Synapses

• Electrical synapses (rare) transmit action potential signals via ion flow directly and rapidly, without modification.
• Chemical synapses use neurotransmitters that cross a gap, which slows transmission, but allows modifying signals.

Chemical Synapses

• Neurotransmitters are chemical messages that deliver signals; different neurons produce different types, stored in synaptic terminal vesicles.
• Neurotransmitters interact with receptor proteins on receiving cell membranes.
• Once the Action potential reaches the synaptic terminal, stored neurotransmitters release to the synaptic cleft.
• Effects of neurotransmitters depend on their type.
• The ability of a receiving neuron either increases or decreases the ability to generate action potentials.
• Same neurotransmitter has different effects based on different chemical synapses/receptors.
• Neurotransmitters are removed from Synaptic cleft
• Opening Na+ channels makes membrane potential closer to threshold (inside more positive.
• This makes action potentials more likely Opening K+ channels make membrane potential further from threshold (outside even more positive).
• This makes action potentials less likely. The importance of Rapid removal is so can send different signal is possible.

Signal Integration

• Individual neurons receive and integrate multiple signals.
• Signals cause local membrane potential changes depending on the sum of excitatory and inhibitory signals.
• Action potentials are only generated if signals reverse membrane potential to threshold (or more).
• Electrical synapses transmit signals directly, chemical synapses transmit signals through the nervous system.
• Both synapses types allow for signal transmission

Drugs Affect Signal Transmissions

• By controlling the amount of neurotransmitters released.
• This can also involve increasing or inhibiting removal of neurotransmitters from a Synapse.
• Interact with neurotransmitter receptor by Blocking interaction of neurotransmitter will decrease the response.
• By Mimicking effects of neurotransmitter (increase response)
• Caffeine blocks the interaction of adenosine.

Sensory System

Sensory Receptor Cells

• Detect and convert stimuli into signals.
• Sensory neurons act as receptor cells, including modified epithelial (skin) cells.
• They detect chemicals, sound, balance, temperature, touch, and light.
• A change in membrane potential alters the stimulus, depending on strength.
• All messages are transmitted to the CNS as action potentials.

Sensory Receptor Cells (Modified Epithelial Cells)

• Change the membrane potential, which alters neurotransmitter release.
• The neurotransmitter's effects determine action-potential signals.

Action Potential Signals

• Are interpreted by the CNS via stimulus strength and location.
• Strength indicated by frequency, type/location is determined by the link.
• Different sensory receptor cells communicate to different CNS interneurons.

Perception

• Is a conscious awareness of stimuli through interpretation and integration by the CNS.
• Many stimuli are subconsciously processed, with variable levels of perception.
• Sensory adaptation decreases response to continuous stimulus.
• Sensory receptor cells stop responding and ignore stimuli using CNS to focus on changes.
• CNS "filters out" signals.
• Perception of the world depends on what sensory cells detect, and how signals are wired.

Sensory System

• Encompasses vision, taste, smell, balance, and hearing

Synesthesia

• A condition where one sense is perceived as an additional one

Vision

• Detecting Light

• Photoreceptors are sensory receptor cells to detect and convert light stimuli into nervous system signals.

• Visible light detects ranges of light wavelengths.

• Rods are photoreceptors that are very sensitive (detect low light levels), but do not interpret the colors.

• Cones are less sensitive to light but detect different wavelengths. Signals are interpreted and integrated from three types of cones by interneurons in the brain which helps us perceive a range of colors.

• The membrane disks possess light-detecting molecules and release neurotransmitters which synapse.

• Retinal is a pigment molecule that absorbs light and is made from Vitamin A.

• Opsin protein determines what wavelength of light absorbs.

• Rods = one type of opsin protein.

• Cones = each type has a different kind of opsin protein.

• Retinal shape changes the membrane potential, which decreases the amount of neurotransmitter released.

• Absorbing light causes retinal pigment to change its shape.

• Reduction in the amount of inhibitory neurotransmitter allows action potential signals to be transmitted to the brain.

• Why must straight forms of retinal must be replaced, because they cannot absorb light.

• This is why it can take time for your eyes to adjust in a dark room because your rods are absorbing light.

• Photoreceptor signals take an indirect route to brain interneurons via bipolar and ganglion cells.

• Ganglion cells send action-potential signals to interneurons after receiving neurotransmitter signals.

• Photoreceptors absorb light which decreases inhibitory neurotransmitter release.

• The excitatory neurotransmitter reverses ganglion cell membrane potential which sends signals to the brain.

• Signals are transmitted through multiple cells allows partial light integration and processing.

• Signals from rods amplifies low light ( images are fuzzier)

• Signals from cones are sharper and sensitive to light

Rods and Cones

• Rods: very sensitive (able to detect low levels of light), signals are not interpreted as different colors.
• Cones: less sensitive to light but three kinds that detect different wavelengths/colors, signals are interpreted and integrated.
• The way rods and cones are similar is they both have membrane disks with light-detecting neurons.
• One way rods and cones are different is cones are much less sensitive to light than rods.
• Opsin protein determines absorption, causing membrane potential changes and reduced neurotransmitter release.
• Colorblindness hinders distinction, and can occur due to some visual components.
• Current hypothesis: color blindness is due to the inability of cone proper function.

Taste and smell: chemoreceptors

• Sensory receptor cells that detect chemicals, that interact with cell membranes.
• Each type interacts and alters membrane potential turning it into action potential signals.
• Stimuli detected by the brain triggers a change of membrane potential.
• Action potential signals only send to the brain if stimuli causes a threshold change.

Taste

• Taste receptor cells are organized in taste buds with multiple cells housed in papillae.
• Taste receptor cell signals are interpreted as five basic tastes.

Five Basic Taste Categories

• Sweet
• Bitter
• Salty
• Umami
• Sour
• Integration allows wide flavor range

Receptor Proteins

• Approximately 30 different receptor proteins have been identified.
• Multiple different sweet receptor proteins and umami receptor proteins identified.
• One receptor cell only has one type of receptor protein that interacts with a particular taste of chemicals.
• Taste buds are composed of multiple taste receptor cells that detect different tastes.

Hypothesis

• Individual papillae can respond to multiple tastes because papillae have receptor cells associated with different tastes.

Hormones

• Are chemical messages important for long distance communication, produced and released in response to stimuli.
• Hormones travel through the bloodstream, but only target cells respond.
• Receptors and hormones are specific for cell response.
• A cell can respond to different hormones depending on the signal.
• Receptors for hormones have same effects on different cells.

Intro to Endocrine System

• Hormones have effects on different responses, processes, and the target cells that can have a similar or an opposite effect.
• The Endocrine system releases hormones.
• Pineal gland
• Hypothalamus
• Pituitary gland
• Thyroid
• Parathyroid
• Adrenal gland
• Pancreas

Type of Hormones cell

• Endocrine
• Neurosecretory cells sends nervous and endocrine system signals.
• Hormones travel via the bloodstream and reach all cells where they are released into synaptic clefts to act as communication links.
• Interaction must be specific, allows communication to cells that are not neurons where types can have different effects.
• Key point: Regulatory mechanisms that involve multiple signals are important when the response does not directly counteract the stimulus

Endocrine System: Hypothalamus and Pituitary Gland

• The Hypothalamus integrates & transmits both signals in the nervous and endocrine systems, transmits hormone signals involving the pituitary gland.
• The Pituitary gland releases hormones to other tissues.
• This includes hormone signals to other cells/organs.
• And is composed of two parts that are physically and functionally, which include the posterior and anterior pituitary glands.
• Posterior pituitary (extension of hypothalamus) releases Hormones in response to nervous system signals.
• Oxytocin involves in childbirth, lactation, reproductive
• ADH triggers changes that help maintain water balance -Anterior pituitary produces Endocrine cells (produce hormones).
• Releasing hormones which promote the release of specific anterior pituitary hormone
• Key point: Hormones communicate to endocrine organ cells and other body cells Which Includes the: Releasing hormone from hypothalamus
• Communication of anterior pituitary hormones to other endocrine organs is important for coordinating release of other hormone signals
• Inhibiting hormone prevents TRH when interacting with anterior pituitary receptor. Inability of anterior pituitary cells to respond to TRH = no TSH released. TSH required to stimulate thyroid hormone release from thyroid. Increased TRH in blood is inhibited by the thyroid.

Thyroid Hormone Regulation

• Release is inhibited by thyroid hormone by thyroid levels by anterior pituitary. Elevated levels of thyroid are still higher than higher than normal due to TRH. Blood glucose
• Main energy source for brain cells
• "Fast" energy source
• Glucose obtained in absence of oxygen.
• Insulin produced in released beta cells
• Glucagon produced in released by alpha cells.
• Antagonistic hormes cause responses in target cells result in effects.

• Insulin causes the target cells to take in and store glucose from the bloodstream, with Beta cells lowering the glucose. Alpha cells detect low blood. Target cells produce glucose and release stored glucose. Alpha cells detect higher food glucose
• The pancreas acts as sensors and integrating in centers in regulation of blood glucose levels
• Alpha and beta cells act as sensors
• Endocrine system example: stress response (blood glucose levels). -Levels determines overall change in blood glucose is not a "all or nothing" situation.

Endocrine System Example

• Diabetes: inability to regulate blood glucose levels due to lack of proper insulin signaling

• Stress response: a wide array of changes that occur in response to stressors. Short-term : prepares body for immediate action, short lived Long-term helps maintain hormone triggers the changes in response to stress, long-lasting

• Adrenal glands: neurosecretory cells, endocrine cells. Response: prepares body for immediate action. The Main hormone = epinephrine .Increases heart rate and opens airways.

• Long-term: cortisol promotes availability, while shunting energy.The primary is cortisol

• Liver cells release glucose where Muscle cells switch to use fat instead of glucose, while the immune system cells reduce activity.

• Release via negative feedback loop. Levels show ACTH is required for stress.

Animal Homeostasis Systems

• Glucagon, epinephrine, and cortisol all cause responses in target cells which increases glucose levels.
• Components are: Nervous system, sensory system and endocrine system .
• These are playing a primary role in collecting info transmitting the body is coordinating activities.
• Key Note*: Neurosecretory cells allow communication between nervous system Nervous system and endorse system similarities, long distance communication .
• key difference* -Signals cannot reach systems -Transmitted more quickly.

Endocrine and Nervous system relation

• Endocrine system- Signals can reach all cells, transmit is slower uses hormone.

What is evolution

• Biological evolution : change in the distribution of heritable phenotypes .
• Microevolution changes the distribution of heritable phenotypes Population is group of the process of evolution Heritable in The is specific DNA sequence
• Mutations: random in DNA sequence of springs.
• Natural differences in selection the population that include sexual selection and heritable changes These lead to mechanisms to changes within the change in population.