BIOL 1030 / Topic 7: Control Systems

Control system

Control system

System regulating internal functions.

There are two divisions of control systems in animals. What are these types? What do they have in common?

Endocrine and nervous.

What does the endocrine system use and what is it used for?

Control system using chemical signals, which are slow to go on and off, used for homeostasis and metamorphosis, among others.

What does the nervous system use and what is it used for?

Control system using electrical signals, which are fast to go on and off, used for sensation and coordination of motion.

What is a chemical signal? Usually, what part of a word gives away that it corresponds to a chemical signal?

Also called a hormone, this is a molecule carrying a message for cells, kicking off responses.

“-crine” means chemical signal.

What are the five types of chemical signals involved in both control systems, endocrine and nervous?

Autocrine, paracrine, endocrine, neuroendocrine, and synaptic.

Autocrine signals

Signals diffused locally to trigger a response in the cells that secrete them.

Paracrine signals

Signals diffused locally to trigger a response in neighbouring cells.

Endocrine signals

Signals diffused into bloodstream or hemolymph and trigger responses in target cells anywhere in the body.

Neuroendocrine signals

Signals from neurons diffused into bloodstream and trigger responses in target cells anywhere in the body.

Synaptic signals

Signals diffused across synapses and trigger responses in cells of target tissues.

What are the types of hormones primarily based on their structure?

Polypeptide, amino, and steroid hormones.

Polypeptide hormones

Water-soluble proteins that can travel anywhere, typically reaching receptors in membranes.

Amino hormones

Amino acid derivatives that can be water or lipid-soluble, typically reaching receptors in membranes or nuclei or cytoplasm.

Steroid hormones

Cholesterol derivatives that are lipid-soluble, typically reaching receptors on membranes in nuclei or cytoplasm.

What is the typical pathway of hormones?

1. Hormones are transported in blood through bulk flow. They’re essentially carried by a moving fluid.

2. Hormones travel to targets where the signal is detected.

3. A receptor detects the signal, whether or not the receptor is on the membrane or in the cytoplasm.

4. Signal transduction pathway is activated, relaying info to the nucleus.

5. Gene expression, increasing or decreasing in response.

There are three types of endocrine system pathways discussed in the lecture. What are these pathways?

Simple endocrine pathway, neuroendocrine pathway, and hormone cascade.

Simple endocrine pathway

Endocrine system pathway wherein there is one hormone and one target.

Neuroendocrine pathway

Endocrine system pathway wherein the source of the hormone is a neuron, involved with the hypothalamus and pituitary gland.

Where is the hypothalamus found, and what does it do?

Part of the brains of vertebrates, receives information from nerves throughout the body, including the brain, and, in response, initiates endocrine signalling appropriate to environmental conditions.

Where is the pituitary gland found, and what does it do?

A major endocrine system organ near the hypothalamus, synthesizing, storing, and secreting hormones.

The hypothalamus is considered the link between the _____ ______ ______ and _______ via the _____. Fill in the blanks.

The hypothalamus is considered the link between the central nervous system and endocrine system via the pituitary gland.

What are the two types of loops in the endocrine system?

Positive feedback loop and negative feedback loop.

Positive feedback

A loop in which the response increases the initial stimulus.

Negative feedback

A loop in which the response reduces the initial stimulus.

Hormone cascade

Endocrine system pathway with series of tropic hormones.

There are two types of hormones based on their targets and their goal. What are these two types of hormones?

Tropic and non-tropic.

Tropic hormones

Hormones acting on another endocrine gland to activate release of other hormones.

Non-tropic hormones

Hormones acting directly on target tissues or cells.

Insulin

Hormone regulating blood glucose levels via glycogen synthesis.

Glycogen

Stored form of glucose, made of many connected glucose molecules.

Glucagon

Hormone raising blood glucose levels via glycogen breakdown.

How does homeostasis work with high glucose in blood?

1. Stimulus: High blood glucose. Detected by pancreatic beta cells.

2. Response: Pancreatic beta cells secrete insulin.

3. Target of insulin: Liver, muscles, etc.

4. Response: Decrease blood glucose via glycogen synthesis.

How does homeostasis work with low glucose in blood?

1. Stimulus: Low blood glucose. Detected by pancreatic alpha cells.

2. Response: Secretion of glucagon.

3. Target of glucagon: Liver.

4. Response: Increase blood glucose via glycogen breakdown.

What is the specific pathway for the hormonal control of moulting in insects?

PTTH

1. Prothoracicotropic hormone (PTTH) secreted by brain.

2. Prothoracic gland is targeted.

3. Release of ecdysteroid from prothoracic gland is the response.

ECDYSTEROID

1. Ecdysteroid is secreted by prothoracic gland.

2. Epidermis is targeted.

3. Induction of moulting is the response

What is the specific pathway for the hormonal control of metamorphosis in insects?

1. Juvenile hormone is secreted by corpora allata organ.

2. Entire body is targeted.

3. Maintenance of larval stage is the response.

If juvenile hormone is ___, metamorphosis occurs. If it is ____, metamorphosis is maintained.

If juvenile hormone is low, metamorphosis occurs. If it is high, metamorphosis does not occur.

What are excitable cells, and what are the two excitable cells, unique to animals?

Neurons and muscle fibres. Excitable cells are cells that can rest and activate.

What are examples of stimuli that can activate excitable cells?

Tissue damage, noxious chemicals, and neurotransmitters.

Membrane potential

Measure of charge gradient across plasma membrane.

What are the two states of membrane potential? Define them.

Resting membrane potential and action potential.

Resting membrane potential (V_R)

Membrane potential as a result of the combined effect of ion channels and pumps; usually (-)ive.

Action potential

Membrane potential as a result of the combined effects of more membrane channels and pumps.

Neuron

Excitable cell carrying electrical signals, constituting the nervous system.

There are two divisions of the nervous system. What are they, and what makes them up?

• Central nervous system, which includes the brain and the spinal chord.

• Peripheral nervous system, which includes everything else.

What are the three types of neurons? How do they differ?

• Sensory neurons, relaying signals from PNS to CNS.

• Interneurons, contained and relaying signals within CNS.

• Motor neurons, relaying signals from CNS to PNS.

Explain how the resting membrane potential of neurons work.

1. Na⁺ and K⁺ pumps continually pump Na⁺ out and K⁺ in via active transport in a ratio of 3:2, respectively.

2. Non-gated Na⁺ channels leak Na⁺ back in and non-gated K⁺ channels leak K⁺ back out via passive transport. Stable ion gradients are established, wherein [Na⁺] is high outside, and [K⁺] is high inside.

3. We get a membrane potential ∆V of -70mV because of this leak equilibrium.

To get to the excited state, to achieve action potential, what needs to happen?

1. Resting state. The gated Na⁺ and K⁺ ions are closed.

2. Slow depolarization. Ligand-gated Na⁺ channels open in response to chemical signal, and Na⁺ influx is small. If small depolarizations add up and reaches threshold, the cell becomes excited, and action potential is generated.

3. Rapid depolarization. The sum of small depolarizations also open voltage-gated Na⁺ channels. Na⁺ influx amount is large.

4. Rapid repolarization. Most Na⁺ channels become inactivated, and Na⁺ influx stops. Most voltage-gated K⁺ channels open, and K⁺ efflux is large.

5. Short hyperpolarization. K⁺ efflux continues to a small extent, causing short hyperpolarization.

6. Return to resting state by closing all gated channels.

Stimulus causes neuronal depolarization, which is dependent on the stimulus strength. What are the three types of stimuli based on this?

1. Subthreshold stimuli.

2. Threshold stimuli, which produces action potential.

3. Suprathreshold stimuli, which also produces action potential.

Synapse

A junction between two nerve cells, consisting of a small gap that impulses pass across by diffusion of a neurotransmitter.

Neurotransmitter (NT)

A chemical signal that transmits signals across a synapse from one neuron to another.

How many NTs are made by one neuron?

One neuron can only synthesize one type of NT.

How does cell-cell communication via synapse occur?

1. Action potential depolarizes presynaptic cell’s membrane.

2. Depolarization opens voltage-gated channels, triggering influx of Ca²⁺ ions.

3. The Ca²⁺ concentration increase causes synaptic vesicles to fuse with presynaptic membrane, releasing NTs into synaptic cleft.

4. NT binds to ligand-gated ion channels in post-synaptic membrane.

What can either happen once the NT binds to ligand-gated ion channels? What happens after the crossing of the synapse?

Excitatory postsynaptic potential and inhibitory postsynaptic potential.

Explain how excitatory postsynaptic potential works.

If the NT released by the presynaptic cell is excitatory, the response at the postsynaptic cell is the opening of ligand-gated Na⁺ channels when bound to the NT. Na⁺ influx, causing depolarization.

Explain how inhibitory postsynaptic potential works.

If the NT released by the presynaptic cell is inhibitory, the response is the opening of ligand-gated Cl^- channels when bound to NT. Cl^- inflow, causing hyperpolarization.

How many PSP is enough to elicit a response? Why does this happen?

Multiple. Many. Target cells are innervated by multiple neurons, with some having excitatory NTs and some having inhibitory NTs.

Summation is the adding up of all signals from multiple neurons to a post-synaptic cell. What are the two types of summation, and how do they differ?

• Temporal summation is when one signal reaches and is repeated over time.

• Spatial summation is when multiple, simultaneous signals reach from different neurons.

What are the three stages of information processing by a nervous system? Define each.

1. Sensory input, the gathering of information or data, by way of neurons and synapses.

2. Integration, the processing of information in brain.

3. Motor output, the conducting of electrical signals from brain and spinal cord to muscles and organs.

Nerve net

Diffuse organization of neurons, common in Radiata and Echinodermata when they’re adults, with the latter taking pentaradial symmetry.

Nerves

Bundled organization of neurons, common in animals that are bilaterally symmetric when they’re adults.

How does the organization of the Radiata nervous system relate to its activity?

Their interconnected nerve cells in their nerve net is perfect for contraction and expansion of gastrovascular cavity.

How does the organization of the nervous system in echinoderms relate to its activity?

Within each arm, the radial nerve is linked to a nerve net from which it receives input and to which it sends signals controlling muscle contraction.

How does the organization of the nervous system in Bilateria (except echinoderms) relate to its activity?

The activities of these animals are somewhat more complex, and the best way to put it is that these animals benefit from their nervous system, which is cephalized.