Muscular, Nervous and Skeletal Systems (Video) - Vocabulary Flashcards
Muscular System - overview: Skeletal muscle is a type of muscle tissue that helps bones move around joints, allowing you to create movement.
Important Muscles for this Class
Chest (Pectoralis Major and Minor)
Used for pushing actions (like bench press, push-ups)
Main exercises: Bench press, push-ups, chest fly
Back (Latissimus Dorsi, Trapezius, Rhomboids, Erector Spinae)
Important for pulling, good posture, and keeping your spine stable
Main exercises: Pull-ups, rows, deadlifts
Shoulders (Deltoids – front, side, back)
Strong shoulders help with pushing, pulling, and lifting things overhead
Main exercises: Overhead press, lateral raises, face pulls
Arms (Biceps Brachii, Triceps Brachii)
Help with pulling (biceps) and pushing (triceps) movements
Main exercises: Bicep curls, tricep dips, skull crushers
Core (Rectus Abdominis, Obliques, Transverse Abdominis)
Makes your spine stable and helps transfer power between your upper and lower body
Main exercises: Planks, anti-rotation holds, hanging leg raises
Glutes (Gluteus Maximus, Medius, Minimus)
Powerful muscles for extending your hip, stabilizing, and helping with sports
Main exercises: Hip thrusts, squats, lunges
Quadriceps (Rectus Femoris, Vastus Lateralis, Vastus Medialis, Vastus Intermedius)
Main muscles that straighten your knee for actions like squats, lunges, and running
Main exercises: Squats, lunges, leg presses
Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus)
Help balance your quads, important for hip extension and keeping your knee stable
Main exercises: Romanian deadlifts, leg curls, hip hinges
Calves (Gastrocnemius, Soleus)
Important for walking, running, and jumping
Main exercises: Calf raises, sled pushes
How Skeletal Muscle is Organized
Epimysium: a layer around the whole muscle
Perimysium: a layer around each bundle (fascicle) of muscle fibers
Endomysium: a layer around each individual muscle fiber
These layers together help transfer the muscle's pulling force to the bone through a tendon.
Tiny Parts of a Muscle (from whole muscle to fiber)
Whole muscle
Tendon
Muscle belly
Fascicle (bundle of fibers)
Muscle fiber (individual cell)
This fiber is surrounded by the Endomysium and contains:
Myofibrils (tiny rods inside the fiber)
Myofilaments: actin (thin) and myosin (thick) (the parts that actually contract)
Connective tissue layers:
Epimysium (around the whole muscle)
Perimysium (around fascicles)
Endomysium (around individual fibers)
Muscle fiber components:
Sarcolemma: the outer skin of the fiber; controls what goes in/out and carries electrical signals (action potentials)
Nuclei: contain genetic information; help muscles adapt to exercise
Sarcoplasm: the gel-like fluid inside; holds energy (ATP, PCr), sugar (glycogen), and fat
Mitochondria: create energy (ATP) using oxygen
Sarcoplasmic Reticulum (SR): stores and releases calcium
Transverse Tubules (T-tubules): tubes that carry electrical signals deep into the muscle fiber
Myofibrils and Sarcomeres
Myofibril: a bundle of tiny threads (myofilaments) that run along the length of the muscle fiber.
Sarcomere: the basic unit of muscle contraction; found between two Z-lines; contains the actin and myosin that shorten the muscle.
Sections of the Sarcomere:
I-band: only thin (actin) filaments
A-band: the full length of the thick (myosin) filaments (includes where actin and myosin overlap)
H-zone: a lighter area in the middle of the A-band (only myosin)
M-line: the center of the sarcomere
Z-line: the borders of the sarcomere
Myofilaments Explained
Myosin (thick filament): has a head that grabs onto actin and pulls during muscle shortening (this is called a cross-bridge).
Actin (thin filament): made of round proteins; has spots where myosin can attach.
Tropomyosin: a rod that covers the myosin-binding spots on actin when the muscle is at rest.
Troponin: attached to tropomyosin; when calcium binds to it, tropomyosin moves to uncover the binding spots.
How Muscles Contract (Sliding Filament Theory) (ON THE EXAM)
8-Step Summary:
An electrical signal (action potential) travels down a nerve to the muscle and releases a chemical called acetylcholine (ACh) at the connection point.
ACh crosses a small gap and sticks to receptors on the muscle fiber.
This starts an electrical signal along the muscle surface (sarcolemma); it then goes down the T-tubules, causing calcium (Ca^{2+}) to be released from the SR.
Ca^{2+} binds to troponin.
This binding moves tropomyosin, exposing the myosin-binding spots on actin.
Once the spots are open, myosin heads attach to actin, forming cross-bridges. ADP and Pi are released, causing the myosin head to pull (this is the power stroke).
After pulling, myosin is in a low-energy state. A new ATP molecule binds, making myosin let go of actin. An enzyme (ATPase) then breaks down ATP to re-energize (detach) the myosin head.
This process keeps going as long as the muscle gets signals from its nerve.
Key idea: Actin and myosin themselves don't change length; instead, the Z-lines are pulled closer to the center, making the sarcomere (and thus the muscle) shorter.
To visualize: The A-band stays the same length, but the I-band gets shorter during contraction.
Types of Muscle Contraction
Concentric: muscle shortens as it creates force (e.g., lifting a weight up).
Eccentric: muscle lengthens while creating force (e.g., lowering a weight slowly).
Isometric (static): muscle creates force but doesn't change length (e.g., holding a weight still).
All three types are important and used in typical strength exercises.
Muscle Fiber Types (ON EXAM)
Type I: Slow-Oxidative (Slow Twitch) (Fatigue resistant)
Gets energy (ATP) mainly with oxygen; has many mitochondria; good at using oxygen; lots of blood supply; rich in myoglobin; very resistant to getting tired.
Type II: Fast Twitch
Gets energy mainly without oxygen (glycolytic); high ATPase activity; larger in size.
Subtypes:
Type IIa (oxidative-glycolytic): better at using oxygen than IIx; somewhat resistant to fatigue.
Type IIx (fast glycolytic): gets tired very quickly because of rapid waste buildup; fastest at contracting. (hyperthrophy)
Muscle Fiber Types and Use During Activities (summary)
Type I: used for everyday activities like walking, yard work; long-lasting endurance; low force/power needs.
Type II (IIa/IIx): used for activities needing high force/power like sprinting, Olympic lifting, throwing; short, powerful actions; varying ability to use oxygen.
Some activities use both types depending on how hard and how long you do them.
Nervous System (overview)
Organization:
Central Nervous System (CNS): Brain and spinal cord.
Peripheral Nervous System (PNS): Nerves outside the brain and spinal cord (cranial and spinal nerves).
Autonomic Nervous System (ANS): Controls automatic body functions like heart muscle, smooth muscle, and glands.
Parasympathetic Division: "Rest and digest" actions.
Sympathetic Division: "Active and alert" actions.
Somatic Nervous System: Controls voluntary movements of skeletal muscles.
Neurons (Nerve Cells)
Neurons: cells that send electrical signals; parts include the end of the axon, synaptic knob, cell body, dendrites, myelin sheath (insulation), and Node of Ranvier (gaps in insulation).
Motor neurons: send signals from the spinal cord to muscles.
Sensory neurons: carry signals from your body (periphery) to the spinal cord.
Supporting cells/structures also exist (e.g., Nissl bodies, Nucleus).
Sensory and Motor Control in Muscles
Muscle Spindle: a sensor inside the muscle that detects changes in muscle length, especially quick stretches.
Helps prevent overstretching.
Golgi Tendon Organ: a sensor at the muscle-tendon connection that senses too much tension (force); it helps prevent injury by making the muscle relax if the force is too high.
Sensory Neurons (structure)
Muscle spindle contains special muscle fibers (intrafusal fibers) inside a protective covering; the regular muscle fibers are called extrafusal fibers.
Signals from the spindle go to the CNS; gamma motor neurons can adjust how sensitive the spindle is.
Golgi tendon organ gives feedback about the tension in the tendon.
Motor Unit and How Force is Increased
Motor Unit: a single motor neuron and all the muscle fibers it controls; all fibers in one motor unit are the same type (e.g., all Type I).
How easily they get activated:
Type I motor units: activated easily; used for low-force actions.
Type II motor units: need higher force to be activated; recruited for stronger actions (IIx needs more than IIa).
Ways to increase muscle force:
Motor Unit Recruitment: activate more motor units to get more force.
Rate Coding: make already active motor units fire signals more quickly.
Smaller muscles tend to use rate coding more; larger muscles use recruitment more.
Size Principle
Motor units are called into action in a specific order based on intensity: slow-twitch (smaller, weaker) are recruited first; fast-twitch (bigger, stronger) are added as the intensity of the activity goes up.
Skeletal System
Functions: allows movement (muscles pull on bones); stores minerals (calcium, phosphorus); makes blood cells; protects organs and the spinal cord.
Divisions:
Axial Skeleton: bones of the head, spine, sternum, and ribs.
Appendicular Skeleton: bones of your arms and legs.
Example bones (some): sternum, kneecap, collarbone, shoulder blade, upper arm bone, ribs, spinal column, hip crest, pelvis, forearm bones (radius, ulna), wrist bones, hand bones, foot bones, thigh bone, shin bone, calf bone.
Bone Health and Changes Over Time
Bone is living tissue; it's constantly being rebuilt (remodeling) where old bone is removed (by osteoclasts) and new bone is formed (by osteoblasts).
Osteoporosis: when bone rebuilding gets messed up, leading to less bone density and a higher risk of broken bones.
Common broken bone spots: hip, spine, wrist.
Peak bone mass: the strongest bones you'll have, usually reached around age 20; influenced by your genes and lifestyle; menopause and getting enough calcium/vitamin D are important.
Practical tip: stay physically active to build strong bones, especially important for women.
Why Exercise Helps Bones
Wolff's Law: states that bone grows stronger where it gets stressed.
Exercises that put weight on your bones (like running, lifting weights) make your bones denser.
Especially, exercises where you resist lengthening (eccentric loading) seem great for bone growth.
More mechanical stress is good for both muscles and bones.
Tendons and Ligaments
Tendons: connect muscles to bones; mostly strong collagen fibers; built to handle the pulling force from muscles.
Ligaments: connect bones to other bones; also mostly collagen but contain some elastin (a stretchy protein).
The stretchy nature of ligaments helps keep joints stable while allowing them to move.