Muscular System Organization

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Questions and Answers

Describe the organization of muscle tissue from cell to whole muscle to groups of muscles.

Muscle tissue is organized hierarchically: Muscle cells (fibers) contain myofibrils. Muscle fibers are bundled into fascicles. Fascicles are grouped together to form a whole muscle. Groups of muscles with similar functions work together.

What are the major functions of muscle tissue?

The major functions include producing movement, maintaining posture and body position, stabilizing joints, and generating heat.

Define the group actions of skeletal muscles: agonist, antagonist, synergist, and fixator.

Agonist: The primary mover muscle responsible for a specific movement. Antagonist: The muscle that opposes or reverses the action of the agonist. Synergist: A muscle that assists the agonist by adding extra force or reducing unwanted movements. Fixator: A synergist that immobilizes a bone or a muscle's origin.

What are the three components of a lever system in the context of muscles and bones?

The three components are: 1. Fulcrum (the joint), 2. Effort (muscle contraction force), 3. Load (the weight or resistance being moved). Signup and view all the answers

Describe the main components of a skeletal muscle fiber.

A skeletal muscle fiber (cell) is multinucleated and contains sarcolemma (plasma membrane), sarcoplasm (cytoplasm), myofibrils (contractile elements composed of sarcomeres), sarcoplasmic reticulum (stores calcium), and T-tubules (extensions of the sarcolemma). Signup and view all the answers

Explain the sliding filament theory, the contraction cycle, and the excitation-contraction coupling mechanism.

Sliding Filament Theory: Muscle contraction occurs when thin (actin) filaments slide past thick (myosin) filaments, shortening the sarcomere. Contraction Cycle: Myosin heads bind to actin (cross-bridge formation), pivot (power stroke), detach, and re-energize, repeating as long as calcium and ATP are present. Excitation-Contraction Coupling: An action potential travels down the sarcolemma and T-tubules, triggering calcium release from the sarcoplasmic reticulum. Calcium binds to troponin, moving tropomyosin and exposing actin binding sites for myosin. Signup and view all the answers

Describe the neuromuscular junction (NMJ), including its three main components and its importance.

The NMJ is the synapse between a motor neuron and a skeletal muscle fiber. Its components are: 1. Axon terminal of the motor neuron (contains synaptic vesicles with acetylcholine/ACh), 2. Synaptic cleft (space between neuron and muscle fiber), 3. Motor end plate (specialized region of the sarcolemma with ACh receptors). It is crucial for transmitting the nerve signal to initiate muscle contraction. Signup and view all the answers

Describe the sequence of events at the neuromuscular junction that leads to an action potential in the muscle fiber.

<ol> <li>Action potential arrives at the axon terminal. 2. Voltage-gated calcium channels open, and calcium enters the axon terminal. 3. Calcium entry causes synaptic vesicles to release acetylcholine (ACh) via exocytosis into the synaptic cleft. 4. ACh diffuses across the cleft and binds to ACh receptors on the motor end plate. 5. Binding opens ligand-gated cation channels, allowing sodium ions to enter the muscle fiber and potassium ions to exit, causing depolarization (End Plate Potential). 6. If depolarization reaches threshold, voltage-gated sodium channels open, initiating an action potential that propagates along the sarcolemma.</li> </ol> Signup and view all the answers

Compare and contrast Type I (slow-twitch) and Type II (fast-twitch) muscle fibers in terms of structure and function.

Type I (Slow-twitch): Smaller diameter, rich blood supply, many mitochondria, high myoglobin (red), aerobic metabolism, slow contraction speed, high fatigue resistance. Function: Endurance activities (e.g., posture, long-distance running). Type II (Fast-twitch): Larger diameter, poorer blood supply, fewer mitochondria, low myoglobin (white), anaerobic metabolism, fast contraction speed, low fatigue resistance (subtypes IIa and IIx exist). Function: Power activities (e.g., sprinting, weightlifting). Signup and view all the answers

What is the smallest form of muscle contraction called?

A muscle twitch. Signup and view all the answers

Explain the length-tension relationship in muscles. Why do muscles have an 'optimal functional length', and what happens if they contract when over-stretched or over-compressed?

The length-tension relationship describes how the force a muscle can generate depends on its length (degree of overlap between actin and myosin filaments) at the time of stimulation. Optimal functional length allows for the maximum number of cross-bridges to form, producing maximal tension. If over-stretched, filament overlap decreases, reducing cross-bridge formation and tension. If over-compressed (too short), filaments interfere with each other, and Z-discs impede further shortening, reducing tension. Signup and view all the answers

What is a motor unit, and what is motor unit recruitment?

A motor unit consists of a single motor neuron and all the muscle fibers it innervates. Motor unit recruitment is the process of increasing the number of active motor units to produce stronger muscle contractions. Signup and view all the answers

Describe the three types of muscle contractions: Isometric, Isotonic concentric, and Isotonic eccentric. What are the differences in their force outputs?

Isometric: Muscle develops tension but does not change length (load equals or exceeds tension). Isotonic concentric: Muscle shortens while maintaining tension (tension exceeds load). Isotonic eccentric: Muscle lengthens while maintaining tension (load exceeds tension). Generally, eccentric contractions can generate the most force, followed by isometric, and then concentric. Signup and view all the answers

What causes muscle fatigue?

Muscle fatigue is the physiological inability to contract effectively. Causes are complex and multifactorial but can include ionic imbalances (K+, Ca2+, Pi accumulation), depletion of energy reserves (ATP, glycogen, creatine phosphate), decreased neurotransmitter release at NMJ, and accumulation of metabolic byproducts (though lactic acid's role is debated). Signup and view all the answers

What are the effects of muscle fatigue?

Effects include reduced force production, slower contraction and relaxation times, decreased coordination, and potentially muscle soreness. Signup and view all the answers

How do muscles help maintain body homeostasis?

Muscles contribute to homeostasis primarily by generating heat (thermogenesis) through contraction (e.g., shivering), which helps maintain body temperature. They also aid in returning venous blood to the heart and protecting internal organs. Signup and view all the answers

Compare and contrast skeletal, smooth, and cardiac muscles regarding filament arrangement, role of calcium, and contraction strength/control.

Skeletal: Striated (regular sarcomere arrangement), voluntary control, Ca2+ from sarcoplasmic reticulum binds to troponin, rapid contraction, tires easily. Smooth: Non-striated (no sarcomeres), involuntary control, Ca2+ primarily from extracellular fluid binds to calmodulin, slow sustained contractions, fatigue resistant. Cardiac: Striated, involuntary control, Ca2+ from SR and extracellular fluid binds to troponin, rhythmic contractions, fatigue resistant. Signup and view all the answers

How many pairs of cranial nerves are there?

There are 12 pairs of cranial nerves. Signup and view all the answers

What are the overall functions of the nervous system?

The nervous system has three main functions: 1. Sensory input (gathering information from sensory receptors), 2. Integration (interpreting sensory input and making decisions), 3. Motor output (activating effector organs like muscles and glands). Signup and view all the answers

What are the five components of a reflex arc?

<ol> <li>Sensory receptor (detects stimulus), 2. Afferent pathway (sensory neuron conducts impulse to CNS), 3. Control center (integration center in CNS, often spinal cord), 4. Efferent pathway (motor neuron conducts impulse from CNS to effector), 5. Effector organ (muscle or gland that responds).</li> </ol> Signup and view all the answers

Compare and contrast the Autonomic and Somatic divisions of the nervous system.

Somatic Nervous System (SNS): Controls voluntary movements of skeletal muscles. Consists of single motor neurons from CNS to effector. Autonomic Nervous System (ANS): Controls involuntary actions of smooth muscle, cardiac muscle, and glands. Uses a two-neuron chain (preganglionic and postganglionic) to reach effector. Subdivided into sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) branches. Signup and view all the answers

What are the main differences between the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)?

CNS: Consists of the brain and spinal cord; acts as the integration and command center. PNS: Consists of nerves (cranial and spinal) and ganglia outside the CNS; carries messages to and from the CNS. Signup and view all the answers

What is the function of a neuron, and what are its three main structural components?

The function of a neuron is to transmit electrical and chemical signals (nerve impulses). Its three main structural components are: 1. Dendrites (receive signals), 2. Cell body (soma; contains nucleus and organelles), 3. Axon (transmits signals away from the cell body). Signup and view all the answers

Describe the role of the dendrites, cell body (soma), and axon in transmitting a neural signal.

Dendrites receive incoming signals (usually chemical neurotransmitters) from other neurons and transmit them as graded potentials towards the cell body. The cell body integrates these signals. If the threshold is reached at the axon hillock, the axon generates and propagates an action potential (nerve impulse) away from the cell body towards the axon terminal. Signup and view all the answers

How are neurons classified structurally, and what are the four main structural types?

Neurons are classified structurally based on the number of processes extending from the cell body. The four main types are: 1. Multipolar (most common; one axon, multiple dendrites), 2. Bipolar (one axon, one dendrite; rare, found in special sense organs), 3. Unipolar (Pseudounipolar) (single short process divides into peripheral and central processes; mainly sensory neurons), 4. Anaxonic (no distinguishable axon; found in CNS). Signup and view all the answers

Name the four types of CNS glial cells and the two types of PNS glial cells.

CNS Glial Cells: Astrocytes, Microglia, Ependymal cells, Oligodendrocytes. PNS Glial Cells: Schwann cells (Neurolemmocytes), Satellite cells. Signup and view all the answers

Describe how the anatomy of each type of CNS glial cell supports its specific function.

Astrocytes: Star-shaped with many processes; support/brace neurons, form blood-brain barrier, regulate chemical environment. Microglia: Small, thorny processes; phagocytize debris and pathogens. Ependymal cells: Ciliated, line ventricles; circulate cerebrospinal fluid (CSF). Oligodendrocytes: Branched cells; wrap processes around CNS axons to form myelin sheaths. Signup and view all the answers

What is membrane permeability, and which types of molecules pass easily versus not easily through the neuron membrane?

Membrane permeability refers to the ease with which substances can cross the cell membrane. Small, nonpolar molecules (like O2, CO2, lipids) pass easily through the lipid bilayer. Ions and large polar molecules (like glucose, amino acids) cannot pass easily and require transport proteins (channels or carriers). Signup and view all the answers

How do ion channels affect the permeability of neurons?

Ion channels are proteins embedded in the neuron membrane that create pores allowing specific ions (like Na+, K+, Cl-, Ca2+) to pass through. By opening or closing, these channels change the membrane's permeability to specific ions, which underlies changes in membrane potential. Signup and view all the answers

Ions require special channel proteins to enter and exit cells.

True (A) Signup and view all the answers

Describe the relative concentrations of Na+, K+, Cl-, and large anions inside and outside a typical resting neuron.

Outside the cell: Higher concentration of Na+ and Cl-. Inside the cell: Higher concentration of K+ and large negatively charged molecules (proteins, anions). Signup and view all the answers

Explain how concentration gradients and electrical potentials create an electrochemical gradient across the neuron membrane.

A concentration gradient is the difference in ion concentration across the membrane. An electrical potential (voltage) is the difference in electrical charge across the membrane. The electrochemical gradient combines these two forces; it represents the net driving force acting on an ion, determining the direction and magnitude of its movement across the membrane if channels are open. Signup and view all the answers

What are the two main types of protein channels for ions in neurons?

The two main types are: 1. Leak (non-gated) channels, which are always open, and 2. Gated channels, which open or close in response to specific signals (voltage changes, ligand binding, mechanical stimulation). Signup and view all the answers

How are leak and gated ion channels essential for the development of an action potential?

Leak channels (especially K+ leak channels) establish the resting membrane potential. Gated channels (voltage-gated Na+ and K+ channels) are essential for generating the action potential. Depolarization to threshold opens voltage-gated Na+ channels (rapid depolarization), followed by the opening of voltage-gated K+ channels and inactivation of Na+ channels (repolarization). Signup and view all the answers

Describe the sequence of events that must occur for an action potential to be generated.

<ol> <li>Resting state: All gated Na+ and K+ channels are closed. 2. Depolarization: A stimulus causes depolarization to threshold level. 3. Rising phase: Voltage-gated Na+ channels open rapidly, causing Na+ influx and rapid depolarization. 4. Falling phase: Voltage-gated Na+ channels inactivate, and voltage-gated K+ channels open, causing K+ efflux and repolarization. 5. Undershoot (Hyperpolarization): Some K+ channels remain open, causing membrane potential to dip below resting level briefly. 6. Return to resting state: Na+/K+ pump restores ion gradients.</li> </ol> Signup and view all the answers

What is the role of the sodium-potassium pump in maintaining the resting membrane potential and enabling action potentials?

The sodium-potassium pump (Na+/K+ ATPase) actively transports 3 Na+ ions out of the cell for every 2 K+ ions it pumps in. This maintains the concentration gradients for Na+ and K+ across the membrane, which are essential for establishing the resting membrane potential and providing the driving force for ion movements during an action potential. It counteracts the passive leakage of ions. Signup and view all the answers

What factors influence the conduction speed of an action potential?

Two main factors influence conduction speed: 1. Axon diameter (larger diameter = faster conduction due to less resistance to current flow), 2. Degree of myelination (myelinated axons conduct much faster via saltatory conduction than unmyelinated axons via continuous conduction). Signup and view all the answers

Explain the difference between continuous and saltatory conduction.

Continuous conduction occurs in unmyelinated axons; the action potential propagates sequentially along the entire length of the membrane. Saltatory conduction occurs in myelinated axons; the action potential 'jumps' from one node of Ranvier (gap in myelin) to the next. This is much faster and more energy-efficient. Signup and view all the answers

How does an action potential arriving at the axon terminal stimulate the release of neurotransmitters from vesicles?

<ol> <li>Action potential arrives at the axon terminal. 2. Depolarization opens voltage-gated Ca2+ channels. 3. Ca2+ ions flow into the axon terminal. 4. Increased intracellular Ca2+ triggers the fusion of synaptic vesicles (containing neurotransmitters) with the presynaptic membrane. 5. Neurotransmitters are released into the synaptic cleft via exocytosis.</li> </ol> Signup and view all the answers

Distinguish between pre-synaptic and post-synaptic cells.

The pre-synaptic cell (usually a neuron) is the cell that transmits the signal by releasing neurotransmitters. The post-synaptic cell (neuron, muscle cell, or gland cell) is the cell that receives the signal by binding the neurotransmitters to its receptors. Signup and view all the answers

What are EPSP and IPSP?

EPSP (Excitatory Postsynaptic Potential) is a temporary, localized depolarization of the postsynaptic membrane, making the neuron more likely to fire an action potential (e.g., caused by Na+ influx). IPSP (Inhibitory Postsynaptic Potential) is a temporary, localized hyperpolarization or stabilization of the postsynaptic membranepotential, making the neuron less likely to fire an action potential (e.g., caused by K+ efflux or Cl- influx). Signup and view all the answers

Movement of ions such as sodium, potassium, chloride, or calcium across the neuron membrane can affect its membrane voltage.

True (A) Signup and view all the answers

Explain temporal and spatial summation of synaptic potentials.

Temporal summation: Occurs when a single presynaptic neuron fires repeatedly in rapid succession, causing sequential EPSPs or IPSPs to add up at the postsynaptic membrane. Spatial summation: Occurs when multiple different presynaptic neurons fire simultaneously, their individual EPSPs and/or IPSPs adding together at the postsynaptic membrane. Signup and view all the answers

What is neural integration?

Neural integration is the process by which individual neurons process (summate) the incoming signals (EPSPs and IPSPs) they receive from other neurons to determine whether or not to fire an action potential. It involves weighing the excitatory and inhibitory inputs. Signup and view all the answers

What are the two main functional types of neurotransmitter receptors?

The two main types are Ionotropic receptors and Metabotropic receptors. Signup and view all the answers

Describe ionotropic receptors.

Ionotropic receptors are ligand-gated ion channels. When a neurotransmitter binds to them, the channel opens directly, allowing specific ions to pass through and causing a rapid, short-lived postsynaptic potential (EPSP or IPSP). Signup and view all the answers

The effect of a neurotransmitter (excitatory or inhibitory) depends solely on the neurotransmitter molecule itself, not the receptor it binds to.

False (B) Signup and view all the answers

Describe the development of the Central Nervous System (CNS) from a neural tube.

The CNS develops from the ectoderm, which forms a neural plate that folds inward to create a neural groove and then fuses to form the neural tube. The anterior portion of the neural tube expands and differentiates into the primary brain vesicles (forebrain, midbrain, hindbrain), which further develop into the major brain regions. The posterior portion develops into the spinal cord. Signup and view all the answers

What are the five secondary developmental regions (vesicles) of the brain, and which major brain areas arise from each?

<ol> <li>Telencephalon (from forebrain) -> Cerebrum (cerebral hemispheres). 2. Diencephalon (from forebrain) -> Thalamus, Hypothalamus, Epithalamus. 3. Mesencephalon (from midbrain) -> Midbrain (part of brainstem). 4. Metencephalon (from hindbrain) -> Pons (part of brainstem), Cerebellum. 5. Myelencephalon (from hindbrain) -> Medulla oblongata (part of brainstem).</li> </ol> Signup and view all the answers

Describe the primary functions associated with the major developmental regions of the brain (cerebrum, diencephalon, brainstem, cerebellum).

Cerebrum: Higher mental functions (thought, memory, consciousness, voluntary movement). Diencephalon: Sensory relay (thalamus), homeostasis control (hypothalamus), endocrine regulation (epithalamus/pineal). Brainstem (Midbrain, Pons, Medulla): Basic life support (breathing, heart rate), relay station, cranial nerve origins. Cerebellum: Coordination, balance, motor learning. Signup and view all the answers

How is the brain oriented relative to the bones of the skull?

The brain sits within the cranial cavity. The cerebrum's lobes are named after the overlying skull bones: Frontal lobe under the frontal bone, Parietal lobes under the parietal bones, Temporal lobes under the temporal bones, and Occipital lobe under the occipital bone. The cerebellum lies inferior to the occipital and temporal lobes, within the posterior cranial fossa. Signup and view all the answers

Name the five lobes of the cerebral cortex.

The five lobes are the Frontal lobe, Parietal lobe, Temporal lobe, Occipital lobe, and the Insula (located deep to the lateral sulcus). Signup and view all the answers

How are motor and sensory functions generally distributed in the cerebrum?

Motor functions are primarily controlled by the Frontal lobe, especially the precentral gyrus (primary motor cortex). General sensory functions (touch, temperature, pain) are primarily processed in the Parietal lobe, specifically the postcentral gyrus (primary somatosensory cortex). Visual processing is in the Occipital lobe, auditory processing in the Temporal lobe, and gustatory (taste) in the Insula. Signup and view all the answers

What is cerebral hemispheric lateralization?

Cerebral hemispheric lateralization refers to the specialization of function in one cerebral hemisphere compared to the other. While both hemispheres work together, certain tasks are predominantly controlled by one side (e.g., language often localized to the left hemisphere, spatial skills often to the right). Signup and view all the answers

Describe the location and general functions of the limbic system.

The limbic system is a group of structures located medially in the cerebral hemispheres and diencephalon (including parts of the thalamus, hypothalamus, amygdala, hippocampus, cingulate gyrus). Its functions are primarily related to emotion, motivation, learning, and memory. Signup and view all the answers

Which parts of the brain are primarily involved in the storage of long-term memory?

The hippocampus plays a crucial role in consolidating short-term memories into long-term explicit memories. Long-term memories themselves are stored widely throughout the cerebral cortex in areas relevant to the type of memory (e.g., visual memories in visual cortex). The amygdala is involved in emotional memories, and the cerebellum in procedural (motor skill) memories. Signup and view all the answers

What are some proposed mechanisms of memory consolidation?

Memory consolidation involves strengthening synaptic connections. Proposed mechanisms include Long-Term Potentiation (LTP), changes in gene expression leading to synthesis of new proteins, formation of new dendritic spines or synapses, and reorganization of neural circuits. Sleep also plays a critical role in consolidating memories. Signup and view all the answers

What is Long-term potentiation (LTP) and how is it related to memory?

Long-term potentiation (LTP) is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It involves strengthening synapses, making postsynaptic neurons more easily activated by presynaptic input. LTP is considered a key cellular mechanism underlying learning and memory formation, particularly in the hippocampus. Signup and view all the answers

Flashcards

Muscle Tissue Organization

Cells to groups of muscles.

Skeletal Muscle Group Actions

Agonist, Antagonist, Synergist, and Fixator.