Chapter 9: Muscular Tissue

Muscle Tissue Types

Muscle tissue is classified into three main types, each with distinct structure and function:

• Skeletal Muscle: Voluntary, striated muscle attached to bones; responsible for movement.

• Cardiac Muscle: Involuntary, striated muscle found only in the heart; responsible for pumping blood.

• Smooth Muscle: Involuntary, non-striated muscle found in walls of hollow organs; controls movements like peristalsis.

Example: Skeletal muscles contract to move limbs, while smooth muscle contracts to move food through the digestive tract.

Skeletal Muscle Functions

• Movement: Muscles pull on bones to produce movement.

• Posture: Maintain body position and stabilize joints.

• Heat Production: Muscle contractions generate heat, helping regulate body temperature.

• Protection: Muscles protect internal organs.

Motor Units and Muscle Types

A motor unit consists of a motor neuron and all the muscle fibers it innervates. The size and number of motor units affect muscle control and strength.

• Small motor units: Fine control (e.g., eye muscles).

• Large motor units: Gross movements (e.g., thigh muscles).

Isometric and Isotonic Contractions

• Isometric Contraction: Muscle tension increases, but length does not change (e.g., holding a weight steady).

• Isotonic Contraction: Muscle changes length while tension remains constant (e.g., lifting or lowering a weight).

Muscle Energy Sources (Aerobic vs Anaerobic)

• Aerobic Respiration: Uses oxygen to produce ATP; efficient, produces more ATP per glucose.

• Anaerobic Respiration: Does not require oxygen; produces less ATP and generates lactate.

Equation:

Example: Sprinting relies more on anaerobic metabolism, while marathon running uses aerobic metabolism.

Muscle Energy Use During Activity

• Muscles use stored ATP, then creatine phosphate, then switch to glycolysis and aerobic metabolism as activity continues.

Stored Sources of Energy for Muscles

• ATP: Immediate energy source.

• Creatine Phosphate: Rapidly regenerates ATP.

• Glycogen: Stored in muscle; broken down to glucose for ATP production.

Lactate in the Body

• Lactate is produced during anaerobic metabolism; can be converted back to pyruvate or used by the liver.

Muscle Recovery / Oxygen Debt

• After intense activity, muscles require extra oxygen to restore ATP, remove lactate, and replenish energy stores. This is called oxygen debt.

Muscle Fiber Types

• Slow-twitch (Type I): Endurance, aerobic, fatigue-resistant.

• Fast-twitch (Type II): Powerful, anaerobic, fatigue quickly.

Rigor Mortis

• Post-mortem muscle stiffness due to lack of ATP, preventing detachment of myosin from actin.

Skeletal Muscle Construction (Arrangement)

• Muscle fibers are organized into fascicles, surrounded by connective tissue layers (epimysium, perimysium, endomysium).

Locations of Calcium Storage in Muscle

• Calcium is stored in the sarcoplasmic reticulum of muscle cells.

The Sarcomere and Various Bands

• Sarcomere: Functional unit of muscle contraction.

• Bands: A band (thick filaments), I band (thin filaments), H zone (center of A band), Z line (sarcomere boundary).

Contractile and Regulatory Proteins

• Contractile: Actin (thin), myosin (thick).

• Regulatory: Troponin, tropomyosin (control contraction).

Thick and Thin Filaments

• Thick filaments: Composed of myosin.

• Thin filaments: Composed of actin, troponin, and tropomyosin.

Properties of Skeletal Muscle

• Excitability, contractility, extensibility, elasticity.

Excitation–Contraction Coupling

• Process linking muscle stimulation (action potential) to contraction via calcium release.

The Neuromuscular Junction

• Synapse between motor neuron and muscle fiber; acetylcholine triggers muscle action potential.

Chapter 11: Nervous Tissue

Nerves and Regeneration

• PNS nerves can regenerate if cell body is intact; CNS nerves have limited regeneration due to inhibitory environment.

Action Potential Frequency vs. Local Graded Potentials

• Action potentials: All-or-none, frequency encodes stimulus strength.

• Graded potentials: Vary in amplitude, decay with distance.

Factors Affecting Membrane Depolarization

• Ion channel type, neurotransmitter presence, membrane permeability, and ion concentration gradients.

Action Potential Generation

• Occurs when membrane depolarizes to threshold, opening voltage-gated Na+ channels.

• Equation:

Postsynaptic Potentials

• Excitatory (EPSP) or inhibitory (IPSP) changes in postsynaptic membrane potential.

Presynaptic and Postsynaptic Cells

• Presynaptic: Sends signal (neurotransmitter).

• Postsynaptic: Receives signal.

CNS and PNS Glial Cells

• CNS: Astrocytes, oligodendrocytes, microglia, ependymal cells.

• PNS: Schwann cells, satellite cells.

Relative and Absolute Refractory Periods

• Absolute: No new action potential possible.

• Relative: Action potential possible with stronger stimulus.

Factors Affecting Ion Channels

• Voltage, ligand binding, mechanical forces, phosphorylation.

The Depolarization Sequence

• Na+ influx causes depolarization; K+ efflux causes repolarization.

Chapter 12: Spinal Cord, Nerves, Reflexes

Reflex Speeds Between Reflex Types

• Monosynaptic reflex: Faster, single synapse (e.g., patellar reflex).

• Polysynaptic reflex: Slower, multiple synapses (e.g., withdrawal reflex).

Withdrawal Reflex

• Protective reflex causing rapid removal from harmful stimulus.

Crossed Extensor Reflex

• Compensates for withdrawal reflex by activating opposite limb muscles.

Cervical Plexus Nerve Roots and Innervations

• Formed by C1–C5; innervates neck, diaphragm (phrenic nerve).

Brachial Plexus Nerve Roots and Innervations

• Formed by C5–T1; innervates shoulder, arm, hand.

Parts of the Spinal Cord

• Gray matter: Cell bodies.

• White matter: Myelinated axons.

• Central canal: CSF flow.

Spinal Enlargement Functions

• Cervical and lumbar enlargements supply nerves to limbs.

Spinal Nerves

• 31 pairs; mixed sensory and motor fibers.

Nerve Connective Tissues

• Endoneurium: Surrounds individual axons.

• Perineurium: Surrounds fascicles.

• Epineurium: Surrounds entire nerve.

Cranial Nerves and Their Functions

• 12 pairs; sensory, motor, or mixed functions (e.g., optic nerve for vision).

Receptor Types

• Mechanoreceptors, thermoreceptors, nociceptors, photoreceptors, chemoreceptors.

Parkinson’s Causes

• Degeneration of dopamine-producing neurons in the substantia nigra.

CNS Brainstem Functions

• Controls vital functions: heart rate, breathing, consciousness.

CNS Cerebrum Functions

• Higher functions: reasoning, memory, voluntary movement.

Precentral and Postcentral Gyrus Functions

• Precentral gyrus: Primary motor cortex; initiates voluntary movement.

• Postcentral gyrus: Primary somatosensory cortex; processes sensory input.

Short-Answer Study Topics

Muscle Stimulation & Calcium Use

• Stimulation begins at the motor endplate, acetylcholine triggers action potential, depolarization spreads, sarcoplasmic reticulum releases calcium, calcium binds to troponin, allowing contraction.

• Calcium is essential for exposing binding sites on actin, enabling myosin to attach and contract muscle.

Muscle Tension & Contraction Types

• Four levels: latent period, contraction phase, relaxation phase, refractory period; tension changes over time.

• Isometric vs. isotonic: Isometric maintains length, isotonic changes length.

Myelin & Conduction Speed

• CNS: Oligodendrocytes; PNS: Schwann cells.

• CNS cells myelinate multiple axons; PNS cells myelinate one axon.

• Myelin increases conduction speed via saltatory conduction.

• Speed order: large myelinated > small myelinated > unmyelinated.

Graded Potentials vs. Action Potentials

• Graded: variable, local, decremental; Action: all-or-none, propagated.

• Graded potentials can summate (temporal/spatial) to reach threshold and trigger action potential at axon hillock.

Reflex Arc & Reflex Speed

• Five components: receptor, sensory neuron, integration center, motor neuron, effector.

• Monosynaptic faster than polysynaptic due to fewer synapses.

Functional Roles of Spinal Rami

• Dorsal ramus: innervates back muscles and skin.

• Ventral ramus: innervates limbs and anterior trunk.

• Ventral ramus forms plexuses for complex innervation.

• Rami communicantes connect spinal nerve to sympathetic division, carrying autonomic fibers.

Additional info: Academic context and explanations have been expanded for clarity and completeness, including definitions, examples, and tables for comparison.