Overview of Autonomic Nervous System and Muscle Physiology

What is the location of preganglionic cell bodies in the autonomic nervous system?

In the CNS (central nervous system), with axons synapsing on postganglionic neurons in autonomic ganglia outside the CNS.

What neurotransmitter is released by preganglionic neurons in the autonomic nervous system?

Acetylcholine (ACh).

Where are postganglionic cell bodies located in the autonomic nervous system?

In the ganglia, with axons traveling to visceral effector organs.

What neurotransmitters can postganglionic neurons release?

Acetylcholine, norepinephrine, or neuropeptides.

What are the two types of ganglia in the sympathetic nervous system?

Paravertebral ganglia (sympathetic chain/trunk) and prevertebral ganglia (near abdominal aorta).

What type of ganglia is associated with the parasympathetic nervous system?

Cranial ganglia (in the head) and intramural ganglia (embedded in or near the walls of visceral target organs).

What types of receptors are found on postganglionic neurons in the autonomic nervous system?

Nicotinic ACh receptors.

What are adrenergic receptors and where are they found?

Alpha and beta receptors that respond to norepinephrine and epinephrine, primarily in the sympathetic nervous system.

What are muscarinic ACh receptors and their significance?

ACh receptors (M1-M5) found in the parasympathetic nervous system, especially M1 in the heart and M3 in smooth muscle and glands.

What is the origin of preganglionic neurons in the sympathetic nervous system?

They originate in the thoracolumbar spinal cord.

What is the primary function of the sympathetic nervous system?

To mobilize the body for activity and respond to stressful situations (fight or flight).

What neurotransmitter is primarily used in the effector organs of the sympathetic nervous system?

Norepinephrine (NE).

What is the origin of preganglionic neurons in the parasympathetic nervous system?

They originate in the brainstem and sacral spinal cord.

What is the primary function of the parasympathetic nervous system?

Restorative and energy-conserving functions (rest and digest).

What is Horner's Syndrome and its classic presentation?

A condition characterized by unilateral partial ptosis, miosis, and anhidrosis due to disruption of sympathetic nervous system supply.

What causes Autonomic Dysreflexia?

Spinal cord injury at or above T6, leading to exaggerated sympathetic responses and significant increases in blood pressure.

What are the signs of Autonomic Dysreflexia?

Increased blood pressure (at least 25 mmHg above baseline), bradycardia, and vasodilation above the level of injury.

What is the role of the medullary vasomotor center in Autonomic Dysreflexia?

It cannot provide normal corrective parasympathetic responses below the level of the spinal injury, leading to systemic hypertension.

What distinguishes the cellular structure of skeletal muscle from smooth and cardiac muscle?

Skeletal muscle has striated fibers, is multinucleated, and is under voluntary control, while smooth muscle is non-striated, involuntary, and cardiac muscle is striated and involuntary with intercalated discs.

What is the contractile apparatus in skeletal muscle?

It consists of myofibrils made up of sarcomeres, which contain actin and myosin filaments.

How does the contractile apparatus in smooth muscle differ from that in skeletal muscle?

Smooth muscle has a less organized structure with dense bodies instead of sarcomeres and is controlled involuntarily.

What is the unique feature of cardiac muscle cells?

They are striated, involuntary, and connected by intercalated discs which facilitate synchronized contraction.

What are skeletal cells characterized by?

A mixture of fiber types, a single motor unit (one motor neuron and all muscle fibers), with fibers located within the same muscle but not always adjacent.

What is the function of transverse tubules in skeletal muscle cells?

They increase surface area to spread out action potentials and are continuous with the extracellular fluid.

What do dihydropyridine receptors do in skeletal muscle cells?

They signal the inside of the cell that there is an incoming signal.

What do lateral sacs in skeletal muscle cells contain?

Calcium stores.

What is the role of the sarcoplasmic reticulum in muscle contraction?

It stores and releases Ca2+ and contains the Ca2+ release channel (ryanodine receptor).

What are the components of thick filaments in muscle cells?

Heavy chains, light chains, and heads with actin-binding sites for cross-bridge formation.

What are the components of thin filaments in muscle cells?

Actin, tropomyosin (which blocks myosin-binding sites at rest), and troponin (which binds Ca2+ to allow actin-myosin interaction).

What defines a sarcomere in muscle cells?

The basic contractile unit delineated by Z disks.

What are the characteristics of smooth muscle cells?

Spindle-shaped, small (30-200 um), with a single central nucleus and gap junctions.

What is the contraction speed and energy efficiency of smooth muscle?

Slow contraction speed and very efficient.

What neurotransmitters are involved in smooth muscle contraction?

Acetylcholine (ACh) and norepinephrine (NE).

What are the characteristics of cardiac muscle cells?

Striated, involuntary, branched cells with intercalated discs.

What is the contractile apparatus in cardiac muscle?

It includes troponin and tropomyosin, with Ca2+ coming from the sarcoplasmic reticulum and extracellular fluid.

How does cardiac muscle generate action potentials?

It is self-excitable (autorhythmic) and responsive to autonomic input.

What is the mechanism of excitation-contraction coupling in cardiac muscle?

It uses Ca²⁺-induced Ca²⁺ release (CICR) and has gap junctions for synchronized contraction.

What is the role of neurotransmitters in the neuromuscular junction (NMJ)?

ACh is released from the motor neuron, binds to nicotinic receptors, and triggers muscle contraction.

What is the process of generating an end plate potential (EPP) in skeletal muscle?

ACh binds to nicotinic receptors, allowing Na+ influx and K+ efflux, resulting in localized depolarization.

What happens when the EPP reaches threshold in skeletal muscle?

Voltage-gated Na+ channels open, causing rapid Na+ influx and generating an action potential.

What is the all-or-none response in skeletal muscle?

Muscle fibers either contract fully or not at all; graded force depends on recruitment.

How do smooth muscle contractions differ from skeletal muscle contractions?

Smooth muscle contractions are slow, sustained, and can be activated by stretch, hormones, or autonomic input.

What is the relationship between fiber length and shortening velocity in muscle tension development?

Shorter fibers can develop tension more quickly, while longer fibers may have a slower shortening velocity.

What is the optimal length (Lo) in the Length-Tension Relationship?

The muscle length where maximum active tension is produced due to optimal overlap between actin and myosin filaments.

What happens to muscle tension when it is too short?

Excessive overlap occurs, causing actin filaments to interfere with each other, which reduces tension.

What occurs when a muscle is too long in terms of tension?

There is little to no overlap between filaments, leading to fewer cross-bridges forming and reduced tension.

What is the mechanical response of a muscle fiber to a single action potential?

A twitch.

When is the velocity of muscle shortening maximal?

When afterload is zero.

How does the velocity of muscle shortening change as afterload increases?

It decreases.

What is the velocity of shortening at maximum afterload?

Zero.

What factors control the shortening velocity of a whole muscle?

The load on the muscle, the types of motor units in the muscle, and the number of motor units recruited to work against the load.

What is the effect of a single stimulus on muscle contraction?

It results in a brief contraction followed by full relaxation (twitch).

What occurs during low frequency stimulation of muscle fibers?

Gradually increasing contractions with each stimulus as the muscle warms up.

What happens at moderate frequency stimulation?

The next stimulus arrives before full relaxation, leading to increased force.

What is the result of high frequency stimulation on muscle fibers?

Partial dissipation of elastic tension between subsequent stimuli (unfused).

What occurs during very high frequency stimulation?

There is no time for dissipation of elastic tension between rapidly recurring stimuli (fused).

How does stimulus strength affect muscle contraction?

A stronger stimulus recruits more motor units, resulting in a stronger contraction.

What are Slow-Oxidative Fibers (type I) characterized by?

They are recruited first, have a smaller diameter, are used for endurance activities, rely on aerobic respiration, and have high fatigue resistance.

What are Fast-Glycolytic Fibers (type IIb) used for?

They are used for quick bursts of strong activation, such as jumping or sprinting, rely on anaerobic glycolysis, and have low fatigue resistance.

What characterizes Fast-oxidative/glycolytic Fibers (type IIa)?

They are used for moderate-intensity activities, utilize both aerobic and anaerobic processes, and have moderate fatigue resistance.

What are monocytes and their role in the immune system?

Monocytes are white blood cells that differentiate into macrophages and dendritic cells, crucial for phagocytosis, antigen presentation, and cytokine production.

What functions do macrophages serve in the immune system?

Macrophages perform phagocytosis, produce inflammatory cytokines, and present antigens to T cells, linking innate and adaptive immunity.

What are lymphocytes and their subtypes?

Lymphocytes are white blood cells central to the adaptive immune system, including B cells (produce antibodies), T cells (helper and cytotoxic), and Natural Killer Cells (destroy virus-infected cells and tumors).

What is the role of neutrophils in the immune response?

Neutrophils are the most abundant white blood cells, acting as first responders to infection, performing phagocytosis, and producing reactive oxygen species.

What is the function of eosinophils?

Eosinophils combat multicellular parasites, release toxic proteins, and are involved in allergic reactions and asthma pathogenesis.

What do basophils do in the immune system?

Basophils release histamine and other mediators during allergic reactions and help defend against parasites.

What is the role of mast cells?

Mast cells release histamine and other mediators upon activation, found in tissues exposed to the external environment.

What role do immunoglobulins play in the immune system?

They are proteins produced by B cells and plasma cells that function as antibodies.

What are the five main classes of immunoglobulins?

IgG, IgA, IgM, IgE, and IgD.

What are inflammatory mediators and how are they classified?

They are substances released during immune responses, classified as pre-formed (like histamines) or newly synthesized (like kinins).

What is the function of histamine in the immune response?

Histamine causes vasodilation and increases capillary permeability to allow white blood cells and proteins access to infected tissues.

What are cytokines and their role in the immune system?

Cytokines are small proteins that act as signaling molecules to mediate and regulate immunity, inflammation, and hematopoiesis.

What are some examples of cytokines?

Interleukins, interferons, and tumor necrosis factors.

What is the cellular immune response?

It involves CD8 T cells that directly kill virus-infected and cancer cells, while CD4 T cells activate macrophages and B cells.

What is the humoral immune response?

It involves B cells synthesizing antibodies against antigens, with helper T cells promoting B cell differentiation into plasma cells.

What is the function of the innate immune system?

It provides immediate defense against infection without prior exposure to the pathogen.

What is the primary function of bone marrow in the immune system?

It is the source of all immune cells and is involved in hematopoiesis.

What is the role of the thymus in the immune system?

It produces and differentiates T lymphocytes, crucial for T cell maturation.

What do lymph nodes do in the immune system?

They filter lymph fluid, trap pathogens, and promote adaptive immunity.

What is the function of the spleen?

It filters blood, removes damaged cells, and responds to blood-borne pathogens.

What is gut-associated lymphoid tissue (GALT) and its function?

It includes tonsils, Peyer patches, and the appendix, facilitating immune responses to ingested antigens.

What characterizes Type I hypersensitivity reactions?

They are IgE-mediated reactions that occur within 1 hour, causing symptoms like hives and anaphylaxis.

What are the symptoms of Type II hypersensitivity reactions?

They include cytotoxic reactions such as immune hemolytic anemia, occurring within hours to days.

What is the mechanism of action of cytotoxic T cells?

They directly kill virus-infected cells and cancer cells.

How do antibodies function in the humoral immune response?

They neutralize pathogens, enhance phagocytosis, and activate the complement system.

What are the components of the innate immune system?

Physical barriers, phagocytic cells, natural killer cells, and various plasma proteins.

What is the significance of memory cytotoxic T cells?

They provide recall responses for faster immune reactions upon re-exposure to the same pathogen.

What is the primary role of the spleen in relation to blood?

It acts as a reservoir for white blood cells and platelets while filtering blood.

What is the importance of the gut's lymphoid tissue?

It protects the body from intestinal pathogens and supports the production of immunoglobulins.

What symptoms are associated with hemolytic anemia and thrombocytopenia?

Goodpasture syndrome.

What characterizes Type III hypersensitivity reactions?

Immune complex-mediated reactions that occur within 1-3 weeks, caused by deposition of immune complexes in tissues, leading to conditions like SLE and serum sickness.

What are the symptoms of Type IV hypersensitivity reactions?

Contact dermatitis, tuberculin reaction, and chronic transplant rejection.

What is allergic rhinitis and what causes it?

An abnormal immune response to harmless environmental allergens, leading to tissue damage in the respiratory tract.

What are common allergens that trigger allergic rhinitis?

Pollen, perennial inhalants, and some occupational antigens.

What are the symptoms of allergic rhinitis?

Sneezing, pruritus, mucus hypersecretion, nasal stuffiness, and airway hyperresponsiveness.

What diagnostic tools are used for allergic rhinitis?

Skin testing and in vitro testing.

What complications can arise from allergic rhinitis?

Otitis media and sinusitis.

What are the treatment options for allergic rhinitis?

Avoidance of allergens, antihistamines for early phase, and corticosteroids for late phase.

What is the composition of intracellular fluid (ICF)?

Makes up ⅔ of total body water, low Na+ (14 mEq/L), and high K+ (120 mEq/L) concentration.

What is the composition of extracellular fluid (ECF)?

Makes up ⅓ of total body water, high Na+ (140 mEq/L), and low K+ (3.5-5.5 mEq/L) concentration.