Nervous System, Muscle Contraction, and Plant Coordination Lecture Notes

Flashcards covering the physiology of neurons, synaptic transmission, muscle contraction mechanisms, and plant coordination responses as detailed in the lecture transcript.

What are the three basic components shared by most types of neurons?

Dendrites, Axon, and Cell body (Soma).

What is the function of Nissl granules in the neuron cell body?

They are groups of rough endoplasmic reticulum and ribosomes associated with the synthesis of proteins, including neurotransmitters.

Which type of neuroglia cell forms the myelin sheath in the nervous system?

Schwann cell.

What is saltatory conduction?

The process where an action potential jumps from node to node (nodes of Ranvier) along a myelinated axon, allowing the impulse to travel much more quickly.

Compare the impulse conduction speed of myelinated versus unmyelinated axons.

Impulses travel up to $200\,m/s$ along myelinated axons compared to $2\,m/s$ in unmyelinated axons.

How does the myelin sheath reduce energy expenditure for the neuron?

It reduces the quantity of sodium and potassium ions that need to be pumped to restore resting potential.

What are the three types of neurons required for the stimulus-response pathway?

Sensory neurons, Relay neurons (interneurons), and Motor neurons.

What is the typical resting potential of a neuron?

Approximately $-70\,mV$, where the inside is more negative relative to the outside.

What active process maintains the electrochemical gradient of the resting potential?

The sodium-potassium pump ($Na^+/K^+$ pump).

What occurs during depolarization in an action potential?

In response to a stimulus, voltage-gated $Na^+$ channels open and sodium enters the neuron by diffusion, making the membrane potential positive.

What causes hyperpolarization during the repolarization phase?

Slow $K^+$ gates remain open longer than needed to restore the resting state, causing an excessive efflux of potassium ions.

What are the two ways organisms determine the size of a stimulus according to the 'all or nothing' response?

1. Frequency coding (number of impulses in a given time). 2. Having different neurons with different threshold values.

Describe the sequence of events when an action potential reaches the axon terminal at a synapse.

Voltage-gated calcium channels open, $Ca^{2+}$ diffuses into the cell, promoting the fusion of neurotransmitter-containing vesicles with the membrane for release by exocytosis.

What is the specific neurotransmitter used at neuromuscular junctions to trigger muscle contraction?

Acetylcholine (ACh).

What enzyme stops the end plate potential (EPP) by degrading acetylcholine?

Acetylcholinesterase (AChE).

What are the repeating contractile units within a myofibril called?

Sarcomeres.

What are the two different myofilaments that make up myofibrils?

Thin filament (actin) and thick filament (myosin).

What is the function of the sarcoplasmic reticulum in muscle fibers?

It is a specialized endoplasmic reticulum that stores calcium ions ($Ca^{2+}$).

Explain the role of $Ca^{2+}$ in actin and myosin cross-bridge formation.

Calcium ions bind to troponin, reconfiguring the troponin-tropomyosin complex to expose binding sites for myosin heads on the actin filament.

What occurs during the 'power stroke' of muscle contraction?

The myosin head tilts and pulls the actin filament towards the centre of the myosin filament (H zone), causing the release of ADP.

How is the myosin head moved back to its original position after the cross-bridge is broken?

ATPase hydrolyses ATP into ADP + Pi to release the energy required for the movement.

What is a transducer in the context of sensory organs?

A receptor cell that converts the energy of stimuli (light, heat, sound) into electrical impulses in neurons.

What is the mechanism of salty taste perception in chemoreceptors?

Sodium ions from food diffuse through selective channel proteins in the microvilli, leading to depolarization (receptor potential).

What specific conditions trigger the closing of a Venus Fly Trap?

When two trigger hairs are touched, or one hair is touched twice within $35\,seconds$.

According to the acid growth hypothesis, how does auxin facilitate cell elongation?

Auxin causes ATPases to pump protons ($H^+$) into the cell wall; the resulting acidity activates expansins to loosen the cell wall, allowing the cell to expand via turgor pressure.

What is the primary natural auxin and from which amino acid is it synthesized?

Indole-3-acetic acid (IAA), synthesized from tryptophan.

How does gibberellin stimulate the germination of barley seeds?

Gibberellin causes the breakdown of DELLA proteins in the aleurone layer, inducing the transcription of genes for $\alpha$-amylase, which then hydrolyses starch in the endosperm into maltose.