bio unit 2 topic 1

What is homeostasis and how does it work?

Homeostasis is the maintenance of a stable internal environment through a stimulus-response model where a change in internal/external conditions is detected by a receptor then info is processed by a control center with an effector producing a response. Negative feedback counteracts the original change and returns the body to its set point of optimal factors.

What are sensory receptors, examples, and how are they classified?

Sensory receptors are specialised cells that detect stimuli and convert them into electrical signals. Chemoreceptors: chemicals, themorereceptors: temp changes, mechanoreceptors: pressure/touch/vibration/stretch, photoreceptors: light, nociceptors: tissue damage/pain

What are effectors?

Effectors are organs or tissues that produce the corrective response to restore homeostasis after receiving signals from the nervous or endocrine system.

Muscles respond to neural stimuli by contracting/relaxing and produce movement/physiological changes.

Glands respond by producing and secreting substances such as hormones, enzymes or sweat.

How do you interpret a feedback control diagram?

A feedback control diagram shows how the body detects and responds to changes in internal condition to maintain homeostasis.

1. stimulus - change in internal or external environment

2. receptor - detects the change and sends info to the control centre

3. control centre - recieves info, compares it to the set point and determines the appropriate response

4. effector carries out the response

5. response - counteracts the original change and helps restore normal conditions

What are the 2 communication pathways for a feedback system?

Nervous System: Information travels as electrical impulses through neurons

Endocrine System: Information travels as hormones through the bloodstream over a longer long-term process.

What is metabolism?

Metabolism is the sum of all chemical reactions occuring in a living organism that are necessary to sustain life.

What are catabolic reactions?

Catabolic reactions are metabolic reactions that break down large molecules into smaller molecules. They usually release energy which can be stored in ATP.

What are anabolic reactions?

Anabolic reactions are metabolic reactions that build larger, more complex molecules from smaller molecules. They require an input of energy, usually from ATP

What is the difference between catabolic and anabolic reactions?

• Catabolic = breakdown of molecules and release of energy

• Anabolic = synthesis of molecules and requirement for energy

How are enzymes related to metabolism?

Enzymes are biological catalysts that control the rate of metabolic reactions by lowering the activation energy required for reactions to occur.

What are optimum conditions for an enzyme?

Optimum conditions are the temperature, pH and other environmental conditions at which an enzyme works most efficiently, meaning its reaction rate is at its highest.

What are tolerance limits for enzymes?

Tolerance limits are the range of conditions an enzyme can function in before its activity is reduced too much or the enzyme becomes denatured.

Why do changes in metabolic activity affect the optimum conditions for enzyme activity?

Changes in metabolic activity can alter internal conditions such as temperature, pH, and substance concentration. If these conditions move outside the enzyme’s tolerance limits, enzyme activity decreases, so the enzyme no longer works at its optimum rate.

What happens to enzymes if conditions move outside their tolerance limits?

Enzymes become less effective because their active site changes shape. If the change is severe, the enzyme may become denatured, which reduces or stops its catalytic activity.

What is negative feedback?

Negative feedback is a homeostatic mechanism that detects a change from the set point and activates a response that opposes that change, returning conditions toward normal.

How does negative feedback help maintain enzyme activity?

Negative feedback maintains internal conditions such as temperature and pH within the enzyme’s optimum range, so metabolic reactions can continue efficiently.

How do metabolism, enzymes and negative feedback connect?

Metabolism depends on enzyme-controlled reactions. If internal conditions change, enzyme activity may decrease. Negative feedback restores conditions toward the set point, keeping them within the enzyme’s tolerance limits so metabolism can continue normally.

What is a nerve cell (neuron)?

A nerve cell is a specialised cell that receives, processes and transmits nerve impulses as part of the nervous system.

What is the function of dendrites?

Dendrites are branched extensions of the neuron that receive signals from other neurons or sensory receptors and carry them toward the cell body.

What is the function of the soma or cell body?

The soma, also called the cell body, contains the nucleus and organelles. It controls the cell’s activities and integrates incoming signals.

What is the function of the soma or cell body?

The soma, also called the cell body, contains the nucleus and organelles. It controls the cell’s activities and integrates incoming signals

What is the function of the axon?

he axon is a long projection that carries the nerve impulse away from the cell body to other neurons, muscles or glands.

What is the function of the myelin sheath?

he myelin sheath is a fatty insulating layer around the axon that increases the speed of impulse transmission by reducing signal loss.

What are nodes of Ranvier?

Nodes of Ranvier are the gaps between sections of myelin along the axon. They allow the nerve impulse to jump from node to node, which speeds up transmission.

What is the function of the axon terminal?

The axon terminal is the end of the axon that forms a synapse with another neuron, muscle cell or gland cell. It releases neurotransmitters.

What is a synapse?

A synapse is the junction between two neurons or between a neuron and an effector cell, where communication occurs chemically through neurotransmitters.

What is a synapse?

A synapse is the junction between two neurons or between a neuron and an effector cell, where communication occurs chemically through neurotransmitters.

What is the order of structures in a neuron?

Dendrites → Soma / cell body → Axon → Myelin sheath and nodes of Ranvier along the axon → Axon terminal → Synapse

What is the function of a sensory neuron?

Sensory neurons carry nerve impulses from sensory receptors to the central nervous system.

What is the function of an interneuron?

Interneurons connect neurons within the central nervous system. They process and relay signals between sensory neurons and motor neurons.

What is the function of a motor neuron?

Motor neurons carry nerve impulses from the central nervous system to effectors, such as muscles or glands.

How do sensory neurons, interneurons and motor neurons differ?

• Sensory neurons carry impulses to the CNS from receptors

• Interneurons carry impulses within the CNS

• Motor neurons carry impulses from the CNS to effectors

What is a nerve impulse?

A nerve impulse is an electrical signal that travels along a neuron as an action potential.

What is an action potential?

An action potential is a rapid change in membrane potential that travels along the axon and carries the nerve impulse.

How does a nerve impulse travel along the axon?

The action potential moves along the axon as a wave of electrical change. In myelinated axons, the impulse travels faster because it jumps between nodes of Ranvier.

Why does myelin increase the speed of a nerve impulse?

Myelin insulates the axon, so the action potential does not need to travel along every part of the membrane. Instead, it jumps between nodes of Ranvier, which speeds up conduction.

How is a nerve impulse passed across a synapse?

The impulse is passed chemically across the synapse using neurotransmitters.

What is the presynaptic neuron?

The presynaptic neuron is the sending neuron. It releases neurotransmitters from vesicles at the axon terminal

What is the postsynaptic neuron?

The postsynaptic neuron is the receiving neuron. It has receptors that bind to neurotransmitters.

What is the synaptic cleft?

The synaptic cleft is the small gap between the presynaptic and postsynaptic neurons that neurotransmitters must cross.

What are vesicles in synaptic transmission?

Vesicles are small membrane-bound sacs in the axon terminal that store neurotransmitters and release them into the synaptic cleft.

What are neurotransmitters?

Neurotransmitters are chemical messengers released from the presynaptic neuron that carry the signal across the synapse.

What do receptors do in synaptic transmission?

Receptors on the postsynaptic membrane bind to specific neurotransmitters, which triggers a response in the postsynaptic neuron.

What is signal transduction in synaptic transmission?

Signal transduction is the process where neurotransmitter binding to receptors causes a change inside the postsynaptic cell, leading to a new electrical signal or cellular response.

What is the sequence of synaptic transmission?

• An action potential reaches the presynaptic axon terminal

• Vesicles release neurotransmitters

• Neurotransmitters diffuse across the synaptic cleft

• They bind to receptors on the postsynaptic neuron

• This triggers signal transduction

• A new impulse is started in the postsynaptic neuron

What is the difference between impulse transmission along a neuron and across a synapse?

Along the neuron, the impulse is transmitted electrically as an action potential. Across the synapse, the signal is transmitted chemically using neurotransmitters.

What is a nerve impulse?

A nerve impulse is a signal transmitted through the nervous system. It involves two processes:

1. Transmission of an action potential along a neuron

2. Synaptic transmission between neurons

What is resting potential?

Resting potential is the stable electrical charge difference across a neuron’s membrane when it is not transmitting an impulse. It is usually about -70 mV, with the inside of the neuron more negative than the outside.

Why is resting potential important for nerve impulses?

Resting potential creates the electrochemical conditions needed for an action potential to be generated when a strong enough stimulus is received.

How is resting potential maintained?

Resting potential is maintained by the sodium-potassium pump, which uses energy to actively transport 3 sodium ions (Na⁺) out of the cell and 2 potassium ions (K⁺) into the cell.

How do potassium leak channels help maintain resting potential?

Potassium ions can leak out of the neuron through potassium channels, which makes the inside of the neuron more negative and helps maintain resting potential.

What is an action potential?

An action potential is a rapid electrical signal that travels along the axon of a neuron.

What is the threshold in nerve impulse transmission?

Threshold is the critical membrane potential that must be reached for an action potential to begin. It is approximately -55 mV.

What is depolarisation?

Depolarisation is the process where the neuron's membrane becomes less negative because sodium ions (Na⁺) enter the neuron through voltage-gated sodium channels.

What happens when voltage-gated sodium channels open?

Sodium ions (Na⁺) rush into the neuron, causing depolarisation and triggering the action potential.

What happens when voltage-gated potassium channels open?

Potassium ions (K⁺) leave the neuron, causing the membrane to become more negative again. This is called repolarisation.

What is repolarisation?

Repolarisation is the return of the membrane potential back toward the resting potential after depolarisation, mainly due to potassium ions leaving the neuron.

How does an action potential travel along the axon?

The action potential travels as a wave of depolarisation and repolarisation along the axon, allowing the nerve impulse to move from one end of the neuron to the other.

What is the role of the myelin sheath in nerve impulse transmission?

The myelin sheath insulates the axon and increases the speed of transmission by preventing the impulse from spreading out along the axon membrane.

What are nodes of Ranvier and why are they important?

Nodes of Ranvier are gaps in the myelin sheath. They allow the impulse to jump from node to node, which greatly increases the speed of transmission.

What is saltatory conduction?

Saltatory conduction is the process where the action potential jumps from one node of Ranvier to the next along a myelinated axon.

What happens when an action potential reaches the axon terminal?

It triggers the release of neurotransmitters from the presynaptic neuron into the synapse.

What happens when the action potential reaches the axon terminal?

It opens voltage-gated calcium channels, allowing calcium ions (Ca²⁺) to enter the axon terminal.

Why are calcium ions important in synaptic transmission?

Calcium ions trigger synaptic vesicles to move to the presynaptic membrane and fuse with it, allowing neurotransmitters to be released.

What are synaptic vesicles?

Synaptic vesicles are small membrane-bound sacs in the axon terminal that store neurotransmitters.

What is the effect of an excitatory neurotransmitter?

An excitatory neurotransmitter causes depolarisation of the postsynaptic membrane, making it more likely that a new action potential will form.

What is the effect of an inhibitory neurotransmitter?

An inhibitory neurotransmitter causes hyperpolarisation, making the postsynaptic neuron less likely to generate an action potential.

What is signal transduction in synaptic transmission?

Signal transduction is the process where a chemical signal is converted back into an electrical signal in the postsynaptic neuron.

What happens after neurotransmitters bind to receptors?

The postsynaptic neuron either:

• becomes depolarised and generates a new action potential, or

• becomes hyperpolarised and is less likely to fire

Why does synaptic transmission occur in one direction?

Neurotransmitters are released only from the presynaptic neuron and receptors are on the postsynaptic neuron, so the signal moves in one direction.

How is synaptic transmission ended?

Neurotransmitters are either broken down by enzymes or taken back up into the presynaptic neuron by reuptake channels, which stops the signal and prepares the synapse for the next impulse.

What is the endocrine system?

The endocrine system is a body system made up of glands that secrete hormones into the bloodstream to regulate physiological processes and maintain homeostasis.

What is the main role of the endocrine system?

Its main role is to regulate body functions such as blood glucose levels, metabolism and body temperature using hormonal control.

What is negative feedback?

Negative feedback is a self-regulating mechanism where a change in a variable triggers a response that opposes the original change and returns conditions toward a set point.

How does negative feedback help maintain homeostasis?

Negative feedback keeps internal conditions stable by detecting deviations from normal and activating responses that restore the variable to its normal range.

Why does the endocrine system rely on negative feedback?

It uses negative feedback to prevent hormone levels or body conditions from moving too far away from their optimal range, helping maintain homeostasis.

What is the stimulus-response model in the endocrine system?

It is the sequence where a stimulus is detected by receptors, a hormone is released by an endocrine gland, and a response occurs in target cells to restore balance.

What begins the endocrine stimulus-response model?

A stimulus, such as a change in blood glucose level or body temperature, begins the response.

What do receptors do in the endocrine system?

Receptors detect changes in the internal environment and send information so the body can respond appropriately.

What acts as the control centre in endocrine regulation?

An endocrine gland acts as the control centre by detecting the change and releasing the appropriate hormone.

What are hormones?

Hormones are chemical messengers secreted by endocrine glands into the bloodstream or lymphatic system to regulate target cells.

How do hormones reach their target cells?

Hormones travel through the circulatory system or lymphatic system until they reach cells with the correct receptors.

What are target cells?

Target cells are cells that have specific receptors for a particular hormone, so they can respond to it.

Why do hormones only affect certain cells?

Only cells with the specific receptor for that hormone can bind to it and respond.

Where are hormone receptors found?

Hormone receptors may be found on the cell surface or inside the cell, depending on the hormone.

What happens when a hormone binds to its receptor?

The binding triggers a cellular response that may change gene expression, enzyme activity or membrane permeability.

What kinds of changes can hormones cause in cells?

Hormones can activate or inhibit processes such as gene expression, enzyme activity, or the movement of substances across membranes.

What does insulin do?

Insulin lowers blood glucose by promoting glucose uptake by body cells, especially muscle and liver cells.

What does glucagon do?

Glucagon raises blood glucose by stimulating the liver to release stored glucose into the bloodstream.

What happens when blood glucose rises after a meal?

The pancreas detects the rise in blood glucose and releases insulin, which causes cells to take up glucose and lowers blood sugar back to normal.

What happens when blood glucose levels fall?

The pancreas releases glucagon, which stimulates the liver to break down stored glycogen and release glucose, raising blood sugar back to normal.

How is blood glucose control an example of negative feedback?

When blood glucose rises or falls, the body releases hormones that reverse the change and restore glucose levels to the normal range.

What affects a cell’s sensitivity to a hormone?

A cell’s sensitivity depends on the number of receptors it has for that hormone.

What is upregulation?

Upregulation is when a cell increases receptor numbers, making it more sensitive to a hormone.

What is downregulation?

Downregulation is when a cell decreases receptor numbers, making it less sensitive to a hormone.

Why do cells downregulate receptors?

Cells may reduce receptor numbers when hormone levels are high to prevent overstimulation.

Why do cells upregulate receptors?

Cells may increase receptor numbers when hormone levels are low to improve their response to the hormone.

Why is regulation of receptor numbers important?

It allows cells to adjust their sensitivity so hormonal signals stay effective and physiological processes can be controlled precisely.

How does insulin affect its target cells?

Insulin binds to receptors on muscle and liver cells, triggering glucose uptake and metabolism, which lowers blood glucose.

How does adrenaline affect its target cells?

Adrenaline binds to receptors on heart cells, increasing heart rate and the strength of contraction.