Muscle and Nervous System Study Guide: Anatomy & Physiology

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Muscle Tissue and Physiology

Types of Muscle Tissue

Muscle tissue is classified into three main types, each with distinct structural and functional characteristics.

Skeletal Muscle: Voluntary, striated muscle attached to bones; responsible for body 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 movement of substances within these organs.

Example: Skeletal muscles move limbs, cardiac muscle contracts the heart, and smooth muscle regulates blood vessel diameter.

Characteristics and Functions of Muscle Tissue

Excitability: Ability to respond to stimuli.
Contractility: Ability to shorten forcibly.
Extensibility: Ability to be stretched.
Elasticity: Ability to return to original length after stretching.

Muscle Coverings and Attachments

Fascia: Connective tissue surrounding muscles.
Aponeuroses: Broad, flat tendons connecting muscles to bones or other muscles.
Tendons: Cord-like structures attaching muscle to bone.

Connective Tissue Sheaths

Epimysium: Surrounds entire muscle.
Perimysium: Surrounds bundles of muscle fibers (fascicles).
Endomysium: Surrounds individual muscle fibers.

Anatomy of a Muscle Fiber

Muscle fibers (cells) contain specialized structures for contraction.

Sarcolemma: Plasma membrane of muscle fiber.
Sarcoplasm: Cytoplasm of muscle fiber.
Myofibrils: Contractile elements composed of actin and myosin.

Neuromuscular Junction and Muscle Stimulation

The neuromuscular junction is where a motor neuron stimulates a muscle fiber.

Motor Neuron: Releases neurotransmitter (acetylcholine) at the synaptic cleft.
Action Potential: Electrical signal triggers muscle contraction.

Sliding Filament Theory

Describes how muscles contract at the molecular level.

Actin and myosin filaments slide past each other, shortening the muscle fiber.
ATP is required for myosin heads to detach and reattach to actin.

Equation:

Energy for Muscle Contraction

ATP: Primary energy source.
Creatine Phosphate: Rapidly regenerates ATP.
Cellular Respiration: Produces ATP in mitochondria using oxygen.

Muscle Fatigue and Soreness

Muscle Fatigue: Decline in ability to generate force, often due to lack of ATP or accumulation of lactic acid.
Muscle Soreness: Caused by microtears and inflammation after intense activity.

Motor Unit

Motor Unit: A single motor neuron and all the muscle fibers it innervates.

Isotonic and Isometric Contractions

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

Muscle Twitch, Tetany, and Refractory Period

Muscle Twitch: Single, brief contraction.
Tetany: Sustained contraction due to rapid stimulation.
Refractory Period: Time during which a muscle cannot respond to another stimulus.

Muscle System Clinical Terms

Term	Description
Fibrillation	Rapid, irregular muscle contractions
Muscular Dystrophy	Genetic disorder causing muscle weakness
Myalgia	Muscle pain
Myasthenia Gravis	Autoimmune disease causing muscle fatigue
Myoma	Muscle tumor

Nervous System and Nervous Tissue

Functions and Divisions of the Nervous System

Central Nervous System (CNS): Brain and spinal cord; processes information.
Peripheral Nervous System (PNS): Nerves outside CNS; transmits signals.

Neuroglial Cells

Astrocytes: Support neurons, maintain environment.
Oligodendrocytes: Form myelin in CNS.
Schwann Cells: Form myelin in PNS.

Neuron Anatomy and Function

Cell Body: Contains nucleus.
Dendrites: Receive signals.
Axon: Transmits signals.
Myelin: Insulates axon, speeds transmission.

Types of Neurons

Unipolar: One process.
Bipolar: Two processes.
Multipolar: Many processes.

Action Potential and Membrane Potential

Depolarization: Na+ enters cell, membrane potential becomes positive.
Repolarization: K+ exits cell, membrane potential returns to negative.
Hyperpolarization: Membrane potential becomes more negative than resting.

Equation:

Synapses

Electrical Synapse: Direct flow of ions between cells.
Chemical Synapse: Neurotransmitter release and binding.

Neurotransmitters

Excitatory: Promote action potentials (e.g., glutamate).
Inhibitory: Prevent action potentials (e.g., GABA).
Neuropeptides: Modulate pain and mood (e.g., enkephalins, endorphins).

Central Nervous System (CNS)

Regions and Organization

White Matter: Myelinated axons.
Gray Matter: Neuron cell bodies.

Brain Anatomy

Cerebrum: Higher functions, motor and sensory areas.
Diencephalon: Thalamus, hypothalamus, epithalamus; relay and control centers.
Brain Stem: Midbrain, pons, medulla oblongata; controls vital functions.
Cerebellum: Coordinates movement; arbor vitae is a key feature.

Ventricles and Meninges

Ventricles: Cavities containing cerebrospinal fluid (CSF).
Meninges: Protective membranes (dura mater, arachnoid mater, pia mater).
CSF: Produced by choroid plexus, circulates in ventricles and subarachnoid space.

Homeostatic Imbalances

Brain: Stroke, epilepsy, multiple sclerosis.
Spinal Cord: Paralysis, spinal shock.

Spinal Cord Anatomy and Pathways

Gray Matter: Central region, contains neuron cell bodies.
White Matter: Surrounds gray matter, contains myelinated axons.
Ascending Pathways: Sensory signals to brain.
Descending Pathways: Motor signals from brain.

Types of Neurons in Pathways

First-order Neuron: Sensory neuron.
Second-order Neuron: Interneuron in spinal cord or brainstem.
Third-order Neuron: Neuron in thalamus projecting to cortex.

Motor Neurons and Pathways

Upper Motor Neurons: Originate in brain, control lower motor neurons.
Lower Motor Neurons: Originate in spinal cord, innervate muscles.

Homeostatic Imbalances Affecting the CNS

Examples: Multiple sclerosis, Parkinson's disease, spinal cord injury.

Additional info: Some explanations and examples were expanded for clarity and completeness.