BIO 141 Unit 3 Study Guide: Muscle Tissue and Nervous System

Chapter 10 – Muscle Tissue

Overview of Muscle Tissue

Muscle tissue is specialized for contraction and is essential for movement, posture, and various bodily functions. There are three main types of muscle tissue, each with distinct characteristics and functions.

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

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

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs (e.g., intestines, blood vessels).

Properties and Structure of Muscle Tissue

• Excitability: Ability to respond to stimuli.

• Contractility: Ability to shorten forcefully.

• Extensibility: Ability to be stretched.

• Elasticity: Ability to return to original length after stretching.

• Conductivity: Ability to conduct electrical signals.

Microscopic Anatomy of Skeletal Muscle

• Sarcolemma: Plasma membrane of a muscle fiber.

• Sarcoplasm: Cytoplasm of a muscle fiber.

• Sarcoplasmic Reticulum: Specialized endoplasmic reticulum that stores calcium ions.

• T Tubules (Transverse Tubules): Invaginations of the sarcolemma that help transmit action potentials.

• Myofibrils: Bundles of contractile filaments within muscle fibers.

• Myofilaments: Protein filaments (actin and myosin) responsible for contraction.

Functions of Muscle Fiber Structures

• Sarcolemma: Conducts action potentials.

• Sarcoplasm: Contains organelles and energy sources.

• Sarcoplasmic Reticulum: Releases and reabsorbs calcium ions.

• T Tubules: Distribute action potentials deep into the muscle fiber.

• Myofibrils: Perform contraction via sliding filament mechanism.

Myofilament Arrangement and Sarcomere Structure

• Thick Filaments: Composed mainly of myosin.

• Thin Filaments: Composed mainly of actin, along with troponin and tropomyosin.

• Sarcomere: The functional contractile unit of muscle, defined from Z line to Z line.

Band/Line	Description
A band	Dark region; contains thick filaments
I band	Light region; contains thin filaments only
H zone	Center of A band; thick filaments only
M line	Middle of sarcomere; holds thick filaments together
Z disc	Boundary of sarcomere; anchors thin filaments

Sliding Filament Theory

Muscle contraction occurs as thin filaments slide past thick filaments, shortening the sarcomere without changing the length of the filaments themselves.

• Myosin heads bind to actin, forming cross-bridges.

• ATP hydrolysis provides energy for the power stroke.

• Calcium ions bind to troponin, shifting tropomyosin and exposing binding sites on actin.

Events of Muscle Contraction

• Calcium binds to troponin.

• Tropomyosin shifts, exposing actin binding sites.

• Myosin heads bind to actin (cross-bridge formation).

• Power stroke occurs as myosin pulls actin filament.

• ATP binds to myosin, causing detachment from actin.

• ATP hydrolysis re-cocks the myosin head.

Neuromuscular Junction and Excitation-Contraction Coupling

• Motor Neuron: Releases acetylcholine (ACh) at the neuromuscular junction.

• ACh: Binds to receptors on the sarcolemma, initiating an action potential.

• Action Potential: Travels along sarcolemma and T tubules, triggering calcium release from the sarcoplasmic reticulum.

Muscle Relaxation

• ACh is broken down by acetylcholinesterase.

• Calcium is pumped back into the sarcoplasmic reticulum.

• Tropomyosin covers actin binding sites, ending contraction.

Muscle Metabolism and ATP Production

• Aerobic Respiration: Long-term ATP supply, requires oxygen.

• Anaerobic Glycolysis: Short-term ATP supply, produces lactic acid.

• Creatine Phosphate: Immediate ATP supply for short bursts.

Muscle Fatigue and Oxygen Debt

• Muscle Fatigue: Inability to contract due to ATP depletion, ion imbalances, or lactic acid buildup.

• Excess Post-exercise Oxygen Consumption (EPOC): Increased oxygen intake after exercise to restore metabolic conditions.

Smooth Muscle and Cardiac Muscle

• Smooth Muscle: Involuntary, found in walls of hollow organs, contracts via sliding filament mechanism but lacks sarcomeres.

• Cardiac Muscle: Involuntary, found only in the heart, cells connected by intercalated discs, contracts rhythmically.

Chapter 11 – Nervous System: Nervous Tissue

General Functions of the Nervous System

The nervous system is responsible for sensory input, integration, and motor output, allowing the body to respond to internal and external stimuli.

• Sensory Function: Detects changes inside and outside the body.

• Integrative Function: Processes and interprets sensory input.

• Motor Function: Initiates responses by activating muscles or glands.

Structural and Functional Divisions

• Central Nervous System (CNS): Brain and spinal cord; integration and control center.

• Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines between CNS and body.

• Somatic Nervous System: Voluntary control of skeletal muscles.

• Autonomic Nervous System: Involuntary control of smooth muscle, cardiac muscle, and glands.

Histology of Nervous Tissue

• Neuron: Functional unit of the nervous system; conducts impulses.

• Neuroglia: Support, protect, and nourish neurons.

Neuron Structure	Function
Cell body	Contains nucleus and organelles
Dendrites	Receive signals from other neurons
Axon	Transmits impulses away from cell body
Axon hillock	Initiates action potentials
Myelin sheath	Insulates axon, speeds conduction
Node of Ranvier	Gaps in myelin; facilitate saltatory conduction
Synaptic vesicles	Store neurotransmitters

Classification of Neurons

• Structural: Multipolar, bipolar, unipolar.

• Functional: Sensory (afferent), motor (efferent), interneurons (association).

Neuroglia Types and Functions

• Astrocytes: Support neurons, maintain blood-brain barrier.

• Oligodendrocytes: Form myelin in CNS.

• Schwann Cells: Form myelin in PNS.

• Microglia: Phagocytic cells, remove debris.

• Ependymal Cells: Line ventricles, produce cerebrospinal fluid.

Resting Membrane Potential and Action Potentials

• Resting Membrane Potential: The voltage difference across the membrane of a resting neuron, typically about -70 mV.

• Action Potential: Rapid change in membrane potential that travels along the axon.

Phases of Action Potential:

• Depolarization

• Repolarization

• Hyperpolarization

Key Ions: Na+, K+, Ca2+, Cl-

Synaptic Transmission

• Chemical Synapse: Neurotransmitter released from presynaptic neuron binds to receptors on postsynaptic cell.

• Electrical Synapse: Direct passage of ions via gap junctions.

Neurotransmitters and Receptors

• Acetylcholine (ACh): Excitatory at neuromuscular junctions.

• Enzyme: Acetylcholinesterase breaks down ACh.

• Other Neurotransmitters: Dopamine, serotonin, GABA, glutamate.

Myelination and Conduction

• Myelin Sheath: Increases speed of impulse conduction.

• Saltatory Conduction: Action potential jumps from node to node.

• Continuous Conduction: Occurs in unmyelinated fibers.

Integration and Neural Circuits

• Converging Circuits: Multiple inputs, one output.

• Diverging Circuits: One input, multiple outputs.

• Neuronal Pool: Functional groups of interconnected neurons.

Additional info: These study notes are based on the learning objectives for BIO 141 Unit 3, covering muscle tissue and nervous system structure and function. For detailed diagrams and further examples, refer to your course textbook or lecture materials.