Neurobiology and Muscle Physiology Quiz

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Questions and Answers

What is the primary function of the cell body in a neuron?

Forming the myelin sheath

Acting as the metabolic center (correct)

Storing synaptic transmitters

Transmitting electrical signals

Which part of the neuron is responsible for transmitting signals away from the cell body?

Axon (correct)

Myelin sheath

Dendrites

Terminal buttons

What distinguishes multipolar neurons from other types?

They have multiple dendrites and one axon (correct)

They contain no axon

They have many processes including axons

Only one process leads away from the soma

In which locations can bipolar neurons be found?

In the nasal cavity and retina Signup and view all the answers

What is a characteristic feature of unipolar neurons?

They communicate through their dendrites Signup and view all the answers

What role does the myelin sheath play in neuronal function?

It protects the axon and insulates electrical signals Signup and view all the answers

Which statement is true about anaxonic neurons?

They have multiple dendrites but no axon Signup and view all the answers

What structures arise from the axon of a neuron?

Terminal buttons Signup and view all the answers

Which protein complex binds to calcium ions during muscle contraction?

Troponin C Signup and view all the answers

What role do the light chains of myosin play in muscle contraction?

They serve a regulatory function at the hinge region. Signup and view all the answers

What happens to the sarcomere when a skeletal muscle fiber contracts?

The thin filaments slide past the thick filaments. Signup and view all the answers

Which protein helps to align the thick filament with the thin filament?

Titin Signup and view all the answers

What is the primary function of the myosin heavy chains?

To generate force during muscle contraction. Signup and view all the answers

Which protein spans the length of the thick filaments and contributes to stability?

Nebulin Signup and view all the answers

What is the role of tropomyosin in the context of muscle contraction?

To prevent actin from binding to myosin. Signup and view all the answers

Which component is essential for muscle contraction to occur as initiated by a motor neuron?

Calcium ions released from the sarcomere. Signup and view all the answers

What occurs during the power stroke in muscle contraction?

The head of myosin tilts to drag actin filament. Signup and view all the answers

What is the primary function of transverse tubules (T-tubules) in muscle cells?

To maintain calcium stores through depolarization. Signup and view all the answers

Which structure is formed by one T-tubule and two terminal cisternae?

Triad Signup and view all the answers

What do longitudinal tubules (L-tubules) collectively form in muscle cells?

Sarcoplasmic reticulum Signup and view all the answers

After a power stroke, what happens to the myosin head?

It breaks away from the active site and returns to a perpendicular position. Signup and view all the answers

What is the primary role of the sarcotubular system in muscle cells?

Transmission of impulse throughout the muscle. Signup and view all the answers

What happens after calcium ions are released into the sarcoplasm?

Calcium ions bind with TnC to elicit muscle contraction. Signup and view all the answers

What type of receptor is located on the T-tubule membranes?

Calcium channel DHPR Signup and view all the answers

What happens to the actin filament during the contraction process according to the walk along theory?

Actin is pulled towards the center of myosin. Signup and view all the answers

What is the primary role of the Ca2+ pump in the sarcoplasmic reticulum?

To sequester calcium ions away from the myofibrils. Signup and view all the answers

Which characteristic distinguishes multi-unit smooth muscle from unitary smooth muscle?

Multi-unit smooth muscle fibers can contract independently. Signup and view all the answers

What substances cover the outer surface of multi-unit smooth muscle fibers?

A thin layer of basement membrane-like substance. Signup and view all the answers

Which type of smooth muscle is characterized by fibers that contract as a single unit?

Unitary smooth muscle. Signup and view all the answers

In which locations would you typically find multi-unit smooth muscle?

In the ciliary muscles of the eye. Signup and view all the answers

What protein found in the sarcoplasmic reticulum enhances calcium ion storage?

Calsequestrin. Signup and view all the answers

What is a feature of unitary smooth muscle?

It has fibers that are aggregated into sheets. Signup and view all the answers

What is the primary reason for muscle paralysis in Myasthenia Gravis?

Inadequate transmission of signals at the neuromuscular junction Signup and view all the answers

Which factor contributes to muscle fatigue during prolonged exercise?

Decreased muscle blood flow and oxygen supply Signup and view all the answers

What initiates rigor mortis post-mortem?

Depletion of ATP in muscle cells Signup and view all the answers

How can the symptoms of Myasthenia Gravis be temporarily improved?

Administering anticholinesterase drugs Signup and view all the answers

What causes the rapid onset of muscle fatigue when blood flow is interrupted?

Loss of oxygen and nutrient supply Signup and view all the answers

What is a key structural difference between smooth muscle and striated muscle?

Smooth muscle's actin filaments do not have troponin complex. Signup and view all the answers

How does smooth muscle contraction initiate?

When calcium binds to calmodulin, activating myosin kinase. Signup and view all the answers

What role does myosin phosphatase play in smooth muscle contraction?

It stops contraction by removing phosphate from the regulatory chain. Signup and view all the answers

Which of the following best describes muscle hypertrophy?

It occurs due to an increase in actin and myosin filaments in muscle fibers. Signup and view all the answers

What connects actin filaments to dense bodies in smooth muscle?

Intercellular proteins and bridges. Signup and view all the answers

What happens when a smooth muscle's action potential occurs?

Calcium binds to calmodulin and activates myosin kinase. Signup and view all the answers

Which characteristic is NOT typical of multi-unit smooth muscle?

Smooth muscle fibers contract as a single unit. Signup and view all the answers

Which option best describes calmodulin's function in smooth muscle contraction?

It activates enzymes involved in muscle contraction. Signup and view all the answers

Study Notes

Nerve and Muscle Physiology

The functional unit of the central nervous system (CNS) is the neuron.
Neurons transmit electrical signals to each other.
There are approximately 14 billion neurons in the CNS, with 75% located in the cerebral cortex.
A neuron typically has a cell body (soma), dendrites, and an axon.
The cell body contains the nucleus and is the metabolic center of the neuron.
Dendrites extend outwards from the soma and branch extensively.
Axons are long, fibrous structures originating from a thickened area called the axon hillock.
Terminal buttons arise from the axon and store synaptic transmitters.
Myelin sheath forms from Schwann cells and surrounds the axon.

Types of Neurons

Multipolar neurons: Have many poles. One pole gives rise to the axon, and others give rise to dendrites. Found in the brain and spinal cord.
Bipolar neurons: Have one axon and one dendrite. Examples include olfactory cells in the nasal cavity, some retinal neurons, and sensory neurons in the inner ear.
Unipolar neurons: Have only a single process leading away from the soma. Represent neurons that carry sensory signals to the spinal cord.
Anaxonic neurons: Have multiple dendrites but no axon. Found in the brain and retina.

Organization of Nerve Fibers

The cell bodies of neurons are often grouped into nuclei or laminae within the grey matter of the CNS, or in ganglia of the peripheral nervous system.
Nerve fibers run within the white matter of the CNS or along peripheral nerves.
Groups of nerve fibers in the same direction are typically bundled to form tracts, peduncles, or brachia (pathways).

Nerve Fiber Types

Peripheral nerves are composed of many axons bundled together within a fibrous envelope.
A (Alpha, Beta, Gamma, Delta) nerve fibers are myelinated, and carry sensory and motor information. Diameter ranges from 5-20 μm.
B nerve fibers are myelinated, carrying primarily preganglionic autonomic signals. Diameter of <3 μm.
C nerve fibers are unmyelinated; they carry primarily postganglionic autonomic signals and other sensory information. Diameter < 1.2 μm.

Excitation and Conduction

Nerves respond to various stimuli (electrical or chemical).
Stimulation in a nerve can produce a local potential and action potential.
Nerve response is dependent on conduction of ions across the cell membrane.
Neurons have a resting membrane potential of approximately -70 mV,. this is due to a separation of charges across the membrane.

Skeletal Muscle

A skeletal muscle is an organ composed of various tissues: skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue.
Each skeletal muscle has three layers of connective tissue: epimysium, perimysium, and endomysium.
Epimysium surrounds the entire muscle and allows it to move independently, maintaining its structural integrity.
Perimysium surrounds bundles of muscle fibers (fascicles).
Endomysium surrounds each individual muscle fiber (cell) and plays a role in transferring force from the muscle fiber to the tendon.
Skeletal muscle cells are called myofibers and are cylindrical and elongated.
Myofibers are composed of numerous nuclei for the production of the proteins necessary for cell function.

Molecular Structure of Muscle

Sarcomere is the basic functional unit of the myofibril.
Sarcomeres are composed of contractile, regulatory, and structural proteins.
The shortening of sarcomeres is responsible for muscle contraction.
Thin filaments (actin) and thick filaments (myosin) are the main components within the sarcomere.
The arrangement of these filaments creates the striated appearance of skeletal muscle.
Thick filaments contain myosin, anchored to the M line.
Thin filaments are anchored to the Z discs and extends towards the center of the sarcomere.

Sliding Filament Model of Contraction

Muscle contraction involves the sliding of thin filaments past thick filaments.
The sliding utilizes ATP, generating force during the power stroke.
When stimulated, myosin heads bind to the actin, dragging the actin filament along and shortening the sarcomere.
The cross-bridges then detach along the myosin cycle.
Repetition of this process results in continuous muscle contraction.
Relaxation occurs when Ca2+ levels decrease, and myosin heads detach from actin.

Neuromuscular Transmission

The neuromuscular junction (NMJ) is the site where a motor neuron interacts with a muscle fiber.
The terminal buttons of the motor neuron innervate the junctional folds of the motor end plate.
The space between the nerve and the motor end plate is called the synaptic cleft.
Neurotransmitter acetylcholine (ACh) is crucial in transmitting signals from the nerve to the muscle.

Sequence of Events during Transmission

Nerve impulses arriving at the terminal buttons increase the permeability to calcium (Ca²+).
Ca²+ triggers the release of acetylcholine (ACh) containing vesicles into the synaptic cleft.
Acetylcholine diffuses to muscle receptors and activates them, leading to depolarization.
The muscle action potential is generated and initiates muscle contraction.
Acetylcholinesterase breaks down ACh, ending the signal.

Smooth Muscle

Smooth muscle is found in various organs and differs from skeletal muscle concerning its fiber organization and signaling.
Multi-unit smooth muscle fibers are discrete, operate independently, and are typically innervated by a single nerve fiber.
The outer surface of the fiber is insulated by basement membrane-like substance.
Example is ciliary muscles of the eye, the iris, and piloerector muscles.
Unitary smooth muscle fibers are aggregated in sheets, have cell membranes that are attached, and joined by many gap junctions.
The fiber contracts as a single unit(syncytial). The type of smooth muscle found in viscera.
Example includes muscles of the gut, bile ducts, ureters, uterus, and many blood vessels.
Smooth muscle contraction is regulated by calcium and ATP in a different mechanism compared to skeletal muscle contraction.
Actin filaments, connected by dense bodies, enabling force transmission among adjacent cells.

Muscle Hypertrophy

Hypertrophy is an increase in the total mass of a muscle.
Occurs due to increased actin and myosin filaments in muscle fibers.
Prolonged, strong contractions with loading are primary factors contributing to hypertrophy, causing significant development in 6-10 weeks.
There is a significant rate of synthesis of muscle proteins during development of hypertrophy.

Muscle Atrophy

Atrophy is a decrease in the total mass of muscle tissue.
The rate of decay of contractile proteins exceeds the rate of replacement during inactivity (unuse).
Continued shortening of a muscle can lead to reduced sarcomeres.
Loss of nerve supply is a substantial cause of muscle atrophy.
Degeneration changes appear in muscle fibers, and the associated nerve supply can recover in 3 months, while total recovery may take 1-2 years.
Atrophy is often followed by replacement of muscle fibers by fibrous and fatty tissue.
Resultant fibers in the later stages do not have contractile properties, and the replacement connective tissue continues shortening for months

Hyperplasia of Muscle Fibers

Hyperplasia is the moderate increase in the number of muscle fibers which occurs due to strenuous activity and force generation.
The mechanism is the linear splitting of predominantly enlarged fibers.

Myasthenia Gravis

Myasthenia Gravis is a form of neuromuscular disease that results in the inability of neuromuscular junctions to transmit sufficient signals from nerve fibers to muscle fibers resulting in muscle paralysis.
It is an autoimmune disease where the body's immune system attacks and negatively affects the body's own Acetylcholine-activated channel proteins.
End plate potentials become too weak to stimulate muscles, leading to significant weakness.

Muscle Fatigue

Muscle fatigue is the gradual decline in a muscle's ability to contract.
Prolonged contractions and the depletion of glycogen are primary factors.
Decreased ability of nerve signals to travel to the muscles can also contribute to fatigue.
Reduced blood flow and loss of oxygen and nutrients supply also contribute to muscle fatigue.

Rigor Mortis

Rigor Mortis is a post-death muscle tightening phenomenon that is usually caused by the depletion of ATP which is a necessary co-factor for muscle relaxation processes.
The muscles remain in a constricted state until protein degradation processes occur.
Degradation occurs due to the enzymes released by decaying cells called lysosomes. This process usually takes about 15-25 hours post-mortem.

Excitation-Contraction Coupling

It refers to the sequence of events that converts an electrical stimulus to a mechanical contraction in the muscle fibers.
Implicates the Sarcoplasmic reticulum and Transverse Tubules in transmitting and converting an electrical stimulus to a mechanical contractile action in the muscle tissues.

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Description

Test your knowledge on the structure and functions of neurons as well as muscle contraction mechanisms. This quiz covers key concepts related to different types of neurons and critical proteins involved in muscle function. Perfect for students studying neurobiology or muscle physiology.