Nervous and Endocrine Systems Quiz

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Questions and Answers

What is the primary role of H^+^ ions in the acid growth hypothesis?

To break cross links in cell walls (correct)

To dissolve calcium pectate glue

To stimulate calcium uptake

To encourage water movement through xylem

Which hormone is primarily involved in influencing root and shoot elongation?

Cytokinin

Auxin (correct)

Gibberellin

Ethylene

How do gibberellins primarily function in plant growth?

Regulating photosynthesis rates

Promoting stem internode elongation and seed germination (correct)

Inhibiting leaf senescence

Stimulating nutrient absorption in roots

What consequence does the entry of Ca^2+^ into hinge cells have?

It results in water entering by osmosis, expanding the cells Signup and view all the answers

Which adaptation helps the plant avoid energy waste during closure when stimulated by debris?

Gaps between stiff hairs allow insects to escape Signup and view all the answers

What is the primary form of transmission used by the nervous system?

Electrical impulses Signup and view all the answers

Which of the following characteristics is true for the endocrine system?

Chemical messengers travel through blood Signup and view all the answers

What type of neurone transmits impulses from sensory receptors to the central nervous system (CNS)?

Sensory neurone Signup and view all the answers

Which neurone type is found entirely within the central nervous system (CNS)?

Intermediate neurone Signup and view all the answers

What characterizes the duration of effects produced by the nervous system?

Temporary Signup and view all the answers

What does a reflex arc primarily allow for?

Immediate responses without brain involvement Signup and view all the answers

Which of the following elements requires a large amount of energy during its transmission?

Nervous system impulses Signup and view all the answers

Where are receptors for the endocrine system typically located?

On cell surface membranes or within cells Signup and view all the answers

What is the primary function of myelin in nerve cells?

To enhance the speed of nerve impulse conduction Signup and view all the answers

What are the regions called that are uncovered between Schwann cells?

Nodes of Ranvier Signup and view all the answers

How does myelination affect the leakage of ions in nerve cells?

It prevents ion leakage, increasing conduction speed Signup and view all the answers

What is the typical resting potential of an axon?

-70 mV Signup and view all the answers

Which statement best describes saltatory conduction?

It speeds up nerve impulses by allowing them to jump between nodes Signup and view all the answers

What occurs during the depolarization phase of a nerve impulse?

Sodium ions enter the neuron, causing a change in membrane potential Signup and view all the answers

What role do sodium-potassium pumps play in resting potential?

They regulate the concentrations of Na+ and K+ across the membrane Signup and view all the answers

What is the effect of having a thinner axon on the transmission of nerve impulses?

It causes greater resistance, thus slower transmission Signup and view all the answers

What does hyperpolarization indicate about the cell potential?

It becomes more negative than resting potential. Signup and view all the answers

How does the brain interpret the strength of a stimulus?

By the frequency of action potentials. Signup and view all the answers

What role do receptor cells play in sensory perception?

They convert energy from one form to electrical impulse. Signup and view all the answers

What happens when the receptor potential reaches the threshold?

It generates action potential in the sensory neurone. Signup and view all the answers

What is the peak value of an action potential?

+30mV. Signup and view all the answers

What effect does the refractory period have on action potential frequency?

It determines the maximum frequency at which impulses can be transmitted. Signup and view all the answers

Where are chemoreceptors primarily located on the tongue?

Inside the taste buds. Signup and view all the answers

What initiates the release of neurotransmitters from receptor cells?

Opening of voltage-gated Ca^2+^ channels. Signup and view all the answers

What role does the sarcoplasmic reticulum (SR) play in muscle contraction?

It transports Ca^2+ ions into the cisternae. Signup and view all the answers

Which protein is responsible for covering the myosin binding sites on actin when the muscle is relaxed?

Tropomyosin Signup and view all the answers

During muscle contraction, what happens to the I band?

It decreases in length. Signup and view all the answers

What initiates the process of muscle contraction at the cellular level?

Depolarization of the sarcolemma. Signup and view all the answers

What is the main function of ATP during muscle contraction?

To hydrolyze and release energy for myosin heads. Signup and view all the answers

What type of energy source is creatine phosphate in muscle tissue?

An immediate energy source Signup and view all the answers

What occurs at the M line during muscle contraction?

Where myosin filaments are anchored. Signup and view all the answers

How does the Venus flytrap initiate the closing of its trap?

By generating a potential from deflected hairs. Signup and view all the answers

What is the role of troponin in muscle contraction?

To bind calcium ions and initiate changes in tropomyosin. Signup and view all the answers

Which statement about the sliding filament theory is correct?

Actin and myosin filaments do not change in length during contraction. Signup and view all the answers

Study Notes

Nervous System and Endocrine System

The nervous system uses electrical impulses which are instantaneous.
The endocrine system uses chemical messengers (hormones), which travel slowly through the blood.
The nervous system has a short-term effect, while the endocrine system has a long-lasting effect.
The nervous system has a localised effect, while the endocrine system has a widespread effect.
Both the nervous system and endocrine system involve cell signalling, signal molecule binding to a receptor, and chemicals.

Neurones

Sensory neurones transmit impulses from receptors to the central nervous system.
Intermediate neurones transmit impulses from sensory to motor neurones.
Motor neurones transmit impulses from the central nervous system to effectors.

Reflex Arc

A reflex arc is a pathway that transmits impulses from a receptor to an effector, without involving the conscious regions of the brain.
This pathway includes a sensory neurone, relay neurone (sometimes) and a motor neurone.
The effector acts before the brain processes the impulse, causing a fast, automatic response, which is useful in response to danger.

Myelin Sheath

Myelin is made by Schwann cells wrapping around the axon.
The uncovered regions between Schwann cells are called the Nodes of Ranvier.
About a third of axons on motor and sensory neurones are surrounded by myelin sheaths.

Speed of Conduction

Myelination increases the speed of conduction because it stops depolarisation from occurring and prevents the leakage of ions.
It also causes saltatory conduction, where action potentials jump from one node to the next, which is 50x faster than unmyelinated axons.
The diameter of an axon also affects the speed of transmission; thinner axons have a greater resistance, which slows down transmission.

Transmission of Nerve Impulses

Nerve impulses are transmitted along the axon as waves of depolarisation, causing changes in the potential difference across the membrane (action potential).

Resting Potential

Resting axons have a slightly negative electrical potential inside, producing a potential difference of about -70mV inside compared to the outside.
This is achieved by the plasma membrane being impermeable to Na+ and K+, and by sodium-potassium pumps actively pumping 3 Na+ out and 2 K+ in, increasing the concentration of K+ inside and Na+ outside.
There are more K+ channels than Na+ channels so K+ diffuses out of the cell faster than Na+ diffuses in.

Action Potential

Action potentials have a constant peak value of +30mV.
The brain interprets the position and nature of stimulus from the location of the neurone sending the signal.
The brain interprets the strength of a stimulus by the frequency of action potentials.
Stronger stimuli result in a higher frequency of action potentials.
Stronger stimuli also cause more neurones to be stimulated, so the number of neurones carrying action potentials can also indicate the strength of the stimulus.

Receptors

A receptor cell converts energy from one form into an electrical impulse, initiating an action potential.
Receptor cells are often found in sense organs and are specialised to detect a specific type of stimulus
Some receptors are the ends of sensory neurones, so there is no synapse between the receptor cell and the sensory neurone.

Taste

The tongue has papillae that contain taste buds, which contain chemoreceptors that detect chemicals.
For example, when sodium chloride is detected, Na+ ions diffuse through highly selective channels and cause depolarisation of the membrane, resulting in a receptor potential.
If sufficient stimulation is produced, voltage-gated Ca2+ channels open and Ca2+ enters the cell, causing exocytosis of neurotransmitter vesicles.
The neurotransmitters cause an action potential in the sensory neurone, which travels to the cortex of the brain.

Muscles

A muscle is made up of bundles of muscle fibres called fascicles.
Each muscle fibre is made of regular arrangements of myofibrils that produce the striated appearance of muscle fibres.

Structure of a Muscle Fibre

The sarcolemma splits into many infoldings called T-tubules.
The sarcoplasm contains many mitochondria that generate ATP for muscle contraction.
The sarcoplasmic reticulum contains protein pumps that transport Ca2+ into the cisternae of the SR.

Structure of Myofibrils

Myofibrils are made up of contractile units called sarcomeres (between two Z discs) that are made of thin and thick protein filaments.
Myosin, a fibrous protein with a globular head, makes up the thick filament.
Actin, a globular protein, forms a thin filament, where two chains of actin overlap.
Tropomyosin is a fibrous protein that is twisted around the actin chain.
Troponin is a protein attached to the actin chain at regular intervals.
The Z line is where actin filaments are attached to.
The M line is where the myosin filaments are attached to.
The A band is the darker part in the centre of the sarcomere where actin and myosin overlap.
The H band is the grey area within the A band where only myosin is present.
The I band is the white area next to the Z line, where only actin is present.

How Muscles Contract

Muscle movement is caused by contraction, which pulls the Z discs closer together by a sliding process.
The energy for this process comes from ATP in the myosin heads (an ATPase).

Process of Muscle Contraction

The sarcolemma is depolarised by an incoming action potential, which spreads along the membrane and down the T-tubule.
Ca2+ ions are released from the sarcoplasmic reticulum (using ATP) and bind to troponin, causing it to change shape.
This causes tropomyosin to move, exposing myosin binding sites on the actin filament.
Myosin heads bind to these sites to form cross-bridges.
Myosin heads tilt, pulling the actin filaments towards the centre of the sarcomere (M line).
The heads hydrolyse ATP, providing energy for the heads to let go of actin and return to their original position.
This continues as long as binding sites are open and ATP is in excess.
The process can be reversed by muscle relaxation (no cross-bridges) and contraction of the antagonist muscle, which pulls the filaments further away and lengthens the sarcomere.

Providing Energy for Muscle Contraction

ATP is provided for muscle contraction by respiration and lactic fermentation, with creatine phosphate providing an immediate source of energy that regenerates ATP in the absence of respiration.

Electrical Communication in Plants

Venus flytraps are carnivorous plants that obtain nitrogen by digesting small animals.
They have nectar glands that attract insects, and trigger hairs on their lobes that respond when deflected.
If two hairs (or one hair touched twice) are stimulated within 20-35s, action potentials travel across the lobe to close it.

Mechanism for Closing the Flytrap

The deflection of sensory hairs opens Ca2+ channels in the cells at the base of the hairs, causing Ca2+ to enter and generate a receptor potential.
H+ ions are pumped into the cell walls, breaking cross-links.
Calcium pectate in the middle lamella dissolves.
Ca2+ enters the hinge cells, causing water to enter by osmosis, so these cells expand.
The lobes of the leaves flip rapidly from convex to concave.
Further deflection of the hairs causes Ca2+ to enter gland cells, causing exocytosis of vesicles containing digestive enzymes.

Adaptions for Energy Efficiency

Stimulation of a single hair doesn't trigger closure, which prevents a waste of energy on stimuli like rain and debris.
Gaps between the hairs allow small insects to crawl out, so the plant doesn't waste energy digesting a small meal.

Chemical Communication in Plants

Plant growth regulators include auxins (influence root and shoot elongation) and gibberellins (influence seed germination and stem internode elongation).

Auxins

Plants make several auxin chemicals, the main one being IAA (indole-3-acetic acid).
Auxins are synthesised in growing tips, or meristems.
Auxins bind to protein receptors, stimulating ATPase to pump H+ into cell walls, reducing the pH.

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Description

Test your knowledge on the functions of the nervous and endocrine systems, including their differences and cell signaling processes. Explore the roles of neurones and the concept of reflex arcs in this quiz designed for biology students.