Introduction to the Nervous System

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Questions and Answers

What are the main components of the central nervous system (CNS)?

Autonomic system and sensory neurons

Peripheral nerves and motor neurons

Dorsal root ganglia and skeletal muscles

Brain and spinal cord (correct)

Which subsystem of the peripheral nervous system (PNS) carries action potentials to skeletal muscles?

Somatic efferent neurons (correct)

Visceral afferent neurons

Sympathetic ganglia

Diencephalon

What role do glial cells play in the regeneration of neurons in the central nervous system?

Support vascular supply

Promote neuron growth

Inhibit regeneration (correct)

Facilitate synapse formation

Which of the following correctly identifies the subdivisions of the peripheral nervous system?

Sensory and motor subsystems Signup and view all the answers

What is the primary function of afferent neurons within the peripheral nervous system?

Carry stimuli from receptors Signup and view all the answers

Which structures are part of the brainstem?

Medulla, pons, and midbrain Signup and view all the answers

What features inhibit the regeneration of CNS axons following damage?

Local environment's inhibitory features Signup and view all the answers

How are the regions of the nervous system organized?

In a hierarchy of functional organization Signup and view all the answers

What is the main role of the nucleus in a neuron?

Blueprint for protein assembly Signup and view all the answers

During which phase of an action potential does the inside of the neuron become positively charged?

Depolarization Signup and view all the answers

Which structure in the neuron is responsible for processing and sorting secretory and membrane components?

Golgi apparatus Signup and view all the answers

What triggers the opening of voltage-gated Na+ channels during an action potential?

Threshold potential around -55 mV Signup and view all the answers

What happens during the process of repolarization in a neuron?

Na+ channels close while K+ channels open Signup and view all the answers

What effect does hyperpolarization have on a neuron?

Temporarily increases the negative charge beyond resting potential Signup and view all the answers

What role do free ribosomes play in a neuron?

Assemble cytosolic proteins Signup and view all the answers

How does the electrotonic current affect a neuron's action potential?

Depolarizes adjacent membrane segments to threshold Signup and view all the answers

What effect does acetylcholinesterase have on acetylcholine in the neuromuscular junction?

It breaks down acetylcholine into acetate and choline molecules. Signup and view all the answers

Which statement correctly describes the role of the nicotinic receptors at the neuromuscular junction?

They facilitate the diffusion of Na+ ions into the muscle cell. Signup and view all the answers

What is the consequence of inhibiting acetylcholinesterase in the neuromuscular junction?

Prolonged availability of acetylcholine at the synapse. Signup and view all the answers

Which type of muscle comprises approximately 40% of the body's total muscle mass?

Skeletal muscle Signup and view all the answers

How is skeletal muscle primarily activated?

Via neural activation from a motor nerve. Signup and view all the answers

Which structure in skeletal muscle fibers plays a crucial role in energy production?

Mitochondria Signup and view all the answers

What occurs during the generation of an action potential at the neuromuscular junction?

Voltage-gated Na+ channels open due to end-plate potential. Signup and view all the answers

What differentiates neuromuscular junction transmission from neuron-to-neuron synaptic transmission?

The exclusive use of acetylcholine at neuromuscular junctions. Signup and view all the answers

What is the role of titin in the sarcomere?

Maintains the side-by-side relationship of actin and myosin Signup and view all the answers

Which component of the sarcomere interacts directly with calcium ions to initiate muscle contraction?

Troponin Signup and view all the answers

What is the primary function of T tubules in muscle fibers?

Facilitate the spread of action potentials into the fiber Signup and view all the answers

What are the results of the binding of acetylcholine to nicotinic receptors at the neuromuscular junction?

Depolarization leading to an end-plate potential Signup and view all the answers

How do myosin heads contribute to the shortening of the sarcomere?

By flexing and relaxing to pull actin filaments together Signup and view all the answers

What happens to calcium ions during muscle relaxation?

They are pumped out of the cytoplasm and sequestered in the sarcoplasmic reticulum Signup and view all the answers

What is the function of myosin in the contraction of muscle fibers?

It facilitates cross-bridge cycling necessary for contraction Signup and view all the answers

What occurs during the excitation-contraction coupling process?

The sarcoplasmic reticulum releases calcium ions into the cytoplasm Signup and view all the answers

What triggers the contraction of muscle fibers during the action potential?

Release of stored Ca2+ ions from the sarcoplasmic reticulum Signup and view all the answers

What is the role of dihydropyridine (DHP) receptors in muscle contraction?

Link action potential and Ca2+ release from the sarcoplasmic reticulum Signup and view all the answers

Which step in the myosin cycle involves the release of ADP and inorganic phosphate?

Step C: Cross-bridging flex of the myosin head Signup and view all the answers

What happens after rigor mortis sets in due to lack of ATP?

Myosin heads remain flexed and attached to actin fibers Signup and view all the answers

Which characteristic is NOT associated with fast-twitch muscle fibers?

Rich blood supply Signup and view all the answers

What primarily causes the muscle relaxation after contraction?

Reabsorption of Ca2+ ions into the sarcoplasmic reticulum Signup and view all the answers

Which of the following events occurs first in the myosin cycle?

Hydrolysis of ATP Signup and view all the answers

What kind of muscle fibers are characterized by a high myoglobin content and slower contraction speeds?

Slow-twitch fibers Signup and view all the answers

Study Notes

Nervous System Introduction

The nervous system coordinates behavior and transmits signals.
It is composed of the central nervous system (CNS) and peripheral nervous system (PNS).
The CNS includes the brain and spinal cord, while the PNS consists of sensory and motor neurons.
The PNS is further divided into sensory and motor subsystems.
Sensory subsystems involve afferent neurons transmitting stimuli.
Motor subsystems consist of somatic and visceral efferent neurons.
Somatic efferent neurons carry action potential commands to skeletal muscles.
Visceral efferent neurons control smooth muscle and glands.

CNS Division

Six major regions: spinal cord, medulla, pons, midbrain, diencephalon, and telencephalon.
Cerebellum located dorsal to pons and medulla is sometimes considered a seventh major region.
Brainstem: medulla, pons, midbrain.
Forebrain: diencephalon and telencephalon.

Neuron Signaling Functions

Receptors receive neurochemical signals from presynaptic terminals of other neurons.
These signals are transduced into small voltage changes and integrated into an action potential on the axon.
The action potential travels rapidly to distant presynaptic terminals, triggering the release of chemical neurotransmitters onto another neuron or muscle cell.

Neurons and Electrical Potential

Neurons and muscle cells have an electrical potential measured across their cell membrane.
The magnitude and sign of this potential can change due to synaptic signaling or environmental energy transduction.
When the membrane potential reaches a threshold, an action potential occurs, moving rapidly along the neuronal axon.

Action Potential

Resting State: The neuron is at rest with a negative charge inside and a positive charge outside.
Threshold: A stimulus causes the neuron to reach a threshold potential, usually around -55 mV.
Depolarization: Voltage-gated sodium (Na+) channels open, allowing Na+ ions to rush into the cell, making the inside more positive.
Peak: The inside of the neuron becomes positively charged, reaching about +30 mV.
Repolarization: Sodium channels close and voltage-gated potassium (K+) channels open, allowing K+ ions to flow out, restoring the negative charge inside.
Hyperpolarization: The neuron temporarily becomes more negative than its resting state due to the continued outflow of K+ ions.
Restoration: The sodium-potassium pump restores the original ion balance, returning the neuron to its resting state.

Neuromuscular Junction

Acetylcholine binds to nicotinic receptors on the muscle cell membrane, opening the channel and allowing Na+ ions to diffuse into the muscle cell.
This leads to depolarization of the postsynaptic muscle cell membrane.
The neuromuscular junction produces an end-plate potential, opening voltage-gated Na+ channels to generate an action potential.
Acetylcholinesterase, anchored to the synaptic cleft, breaks down acetylcholine into acetate and choline molecules.
Inhibition of acetylcholinesterase can prolong acetylcholine at the synapse, leading to physiological consequences.

The Physiology of Muscle

There are three types of muscle: skeletal, cardiac, and smooth muscle.
Skeletal muscle, comprising 40% of the body, is crucial for understanding its function and control by the nervous system.
Smooth muscle and cardiac muscle make up almost 10% of the body.
Skeletal muscle consists of a central, fleshy, contractile muscle belly and two tendons.

Skeletal Muscle Structures

Each muscle belly consists of muscle fibers spanning from the origin to its insertion point.
These fibers contain multiple nuclei, mitochondria, and intracellular organelles.
The outer limiting is called the sarcolemma, and each fiber is innervated by one motor neuron.
Myofibrils are smaller subunits arranged parallel along the fiber's length and consist of repeating sarcomeres, the basic contractile units of the muscle fiber.
The sarcomere contains a Z disk at each end and numerous actin filaments.

Actin and Myosin

Actin filaments consist of two intertwined helical strands of actin and tropomyosin protein, wound together.
Troponin, a complex globular protein, binds tropomyosin and actin and has affinity for calcium ions.
Myosin protein polymers are suspended between and parallel to the actin filaments.
A myosin molecule is composed of a tail made of intertwined helices and two globular heads that bind to ATP and actin.
Titin, a spring-like protein in the sarcomere, attaches to myosin and Z disks, maintains the side-by-side relationship of actin and myosin, elasticity, and resting length of the sarcomere.

Sarcoplasmic Reticulum in Muscle

An intracellular storage organelle beneath the plasma membrane.
Forms a network around myofibrils, sequestering Ca2+ ions in relaxed muscle.
Similar to smooth endoplasmic reticulum in other cells.

Transverse Tubules (T tubules)

Periodic invaginations of the sarcolemma.
Perpendicular to the long axis of the muscle fiber.
Snake between myofibrils, forming junctions with the sarcoplasmic reticulum network.
Fills with extracellular fluid, allowing depolarization of action potential to the muscle fiber's interior.

Excitation-Contraction Coupling

Muscle cells and neurons have resting membrane potentials.
Muscle cell membrane can be depolarized via synaptic transmission at the neuromuscular junction.
Acetylcholine from the motor neuron activates nicotinic acetylcholine receptors in the muscle cell's motor end-plate region.
Action potential from the neuromuscular junction spreads along the muscle fiber and interior, reaching the sarcoplasmic reticulum and innermost muscle fiber regions.
Rise in cytoplasmic Ca2+ at the neuron terminal initiates transmitter release.
Dihydropyridine (DHP) receptors or ryanodine receptors link action potential and Ca2+ release.

Actin Myosin Interaction

When Ca2+ ions are available, the sarcomere shifts from relaxed to contracted state.
Actin filaments pull myosin filaments parallel, shortening the sarcomere.
In muscle, the interaction of myosin, ATP, and actin produces contraction and force.

Skeletal Muscle Classification: Fast Vs. Slow Fibers

Fast-twitch fibers: Skeletal muscle fibers with rapid contraction speeds, thicker, extensive sarcoplasmic reticulum, and less extensive blood and mitochondrial supplies.
Also known as white muscle.
Slow-twitch fibers: Skeletal muscle fibers with slower contraction speeds, thinner, rich blood and mitochondrial supply, and large myoglobin content.

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Description

This quiz introduces the basic structure and functions of the nervous system, covering both the central (CNS) and peripheral (PNS) divisions. It explains the roles of different neuronal types and regions of the CNS, including the brain and spinal cord. Test your understanding of these fundamental concepts.