Anatomy & Physiology Study Guide: Muscle and Nervous System (Chapters 9–12)

Chapter 9 – Skeletal Muscle Tissue and Contraction

Properties and Structure of Muscle Tissue

Muscle tissue is specialized for contraction and movement, exhibiting unique physiological properties that distinguish it from other tissue types.

• Excitability: Ability to respond to stimuli by generating electrical signals.

• Contractility: Ability to shorten forcibly when stimulated.

• Extensibility: Ability to be stretched or extended.

• Elasticity: Ability to recoil to resting length after stretching.

• Smallest functional unit: The sarcomere is the basic contractile unit of muscle fiber.

• Connective tissue layers: Endomysium (surrounds individual muscle fibers), perimysium (surrounds fascicles), and epimysium (surrounds the entire muscle).

Muscle Contraction Mechanism

• Neurotransmitter: Acetylcholine is released at the neuromuscular junction to initiate muscle contraction.

• Calcium ions: Released from the sarcoplasmic reticulum, calcium binds to troponin, enabling actin-myosin interaction.

• Sliding filament theory: Describes how actin and myosin filaments slide past each other to produce contraction.

• Muscle tone: Continuous, partial contraction of muscles, important for posture.

• Recruitment: Increasing the number of active motor units increases muscle force.

• Hypertrophy: Increase in muscle fiber size due to exercise.

• Atrophy: Decrease in muscle fiber size due to disuse.

• Fatigue: Inability of muscle to maintain force of contraction after prolonged activity.

• Fast fibers: Contract quickly, fatigue rapidly.

• Slow fibers: Contract slowly, resist fatigue.

Example: During weightlifting, recruitment of additional motor units allows for increased force production.

Chapter 10 – Gross Anatomy of Muscles

Muscle Organization and Attachments

Muscles are named and organized based on their location, shape, and function. Understanding their attachments and actions is essential for identifying their roles in movement.

• Origin: The fixed attachment, usually proximal.

• Insertion: The movable attachment, usually distal.

• Agonist (prime mover): Muscle primarily responsible for movement.

• Antagonist: Muscle that opposes the action of the agonist.

• Synergist: Muscle that assists the agonist.

• Fixator: Muscle that stabilizes the origin of the agonist.

Major Muscle Groups and Actions

• Muscles of mastication: Insert into the mandible; masseter is the strongest muscle by weight.

• Facial expression: Muscles innervated by the facial nerve (e.g., orbicularis oculi, orbicularis oris, buccinator).

• Neck muscles: Sternocleidomastoid rotates and flexes the head.

• Abdominal muscles: Include external oblique, internal oblique, transversus abdominis, and rectus abdominis; support abdominal organs and aid in trunk movement.

• Thoracic muscles: Diaphragm is the primary muscle of respiration.

• Back muscles: Trapezius and latissimus dorsi are major superficial muscles.

• Upper limb muscles: Biceps brachii (flexes elbow), triceps brachii (extends elbow).

• Lower limb muscles: Quadriceps femoris (extends knee), hamstrings (flex knee), gastrocnemius (plantar flexes foot).

Example: The quadriceps femoris group is responsible for extending the knee during walking and running.

Chapter 11 – Nervous System Fundamentals

Organization and Function of the Nervous System

The nervous system is responsible for integrating sensory input and coordinating motor output. It is divided into the central nervous system (CNS) and peripheral nervous system (PNS).

• CNS: Consists of the brain and spinal cord.

• PNS: Consists of nerves and ganglia outside the CNS.

• Functional pathway: Sensory receptor → sensory neuron → integration center → motor neuron → effector.

• Neurons: Specialized cells for transmitting electrical impulses.

• Neuroglia: Support and protect neurons.

• Action potential: Electrical signal propagated along neurons; involves sodium and potassium ion movement.

• Reflex arc: Simple neural pathway mediating a reflex action.

• Spinal nerves: Emerge from the spinal cord; each spinal nerve is associated with a specific vertebral level.

Example: The patellar reflex (knee-jerk) is a classic example of a monosynaptic reflex arc.

Chapter 12 – Nervous Tissue and Surface Anatomy

Neurotransmitters and Synaptic Transmission

Neurotransmitters are chemicals that transmit signals across synapses between neurons or from neurons to muscles.

• Common neurotransmitters: Acetylcholine, dopamine, norepinephrine, serotonin, glutamate, and GABA.

• Acetylcholine: Specifically initiates skeletal muscle contraction.

Surface Anatomy and Clinical Landmarks

• Surface anatomy: Involves identifying anatomical structures by palpation (touching/feeling).

• Median cubital vein: Common site for venipuncture (drawing blood).

• Dorsalis pedis artery: Palpated on the top of the foot to assess peripheral circulation.

Example: The median cubital vein is often used for blood draws due to its accessibility and size.

Summary Table: Key Muscle and Nervous System Features

Feature	Muscle System	Nervous System
Basic Unit	Sarcomere	Neuron
Main Function	Contraction for movement	Signal transmission and integration
Key Chemical	Acetylcholine (at neuromuscular junction)	Various neurotransmitters (e.g., dopamine, GABA)
Clinical Landmark	Quadriceps femoris (palpation, strength)	Median cubital vein (venipuncture), dorsalis pedis artery (pulse)

Additional info:

• Action potentials in neurons are generated by the movement of sodium and potassium ions across the cell membrane, described by the Nernst equation.

• Muscle contraction is explained by the sliding filament theory, which involves the interaction of actin and myosin filaments.

• Surface anatomy is essential for clinical procedures such as injections, blood draws, and assessment of circulation.