Lab Project: Build a Limb (Neuron Part) For this portion of my lab project I will be constructing a sensory neuron, interneuron, and motor neuron, as well as demonstrating a nerve impulse. I will show an axon in a resting potential and action potential state, and be revealing the sliding filament model found in muscle fibers. My goal of this presentation is to show the multiple steps associated with muscle contractions. Some of the various products I will be using to construct the neurons, demonstrate the sodium/potassium gates, and explain the sliding filament model are pictured below.
Transcript
Lab Project: Build a Limb (Neuron Part)For this portion of my lab project I will be constructing a sensory neuron, interneuron, and motor neuron, as well as demonstrating a nerve impulse. I will show an axon in a resting potential and action potential state, and be revealing the sliding filament model
found in muscle fibers. My goal of this presentation is to show the multiple steps associated with muscle contractions. Some of the various products I will be using to
construct the neurons, demonstrate the sodium/potassium gates, and explain the sliding filament model are pictured below.
A Little Background on MusclesSkeleton muscles support the body, make bones move, helps maintain body temperature, assist cardiovascular veins and lymphatic vessels, protects internal organs, and they stabilize joints. The muscles are compiled of bundles of fiber called fascicles and are covered in connective tissue called fascia which becomes the tendon beyond the muscle. The part of the muscle connected to bone that is stationary is known as origin; the part of the muscle connected to bone that moves is known as insertion.
Pic from Human Biology Pg 229-34
How does a Muscle Fiber Contract?
Contraction of muscle fibers (muscle cells) is from motor neuron stimulation. Every motor neurons branch (axon branches) lies
close to muscle fibers sarcolemma (plasma membrane). This is known as a neuromuscular junction. The end of the motor neurons branch is known as an axon terminal and contain
acetylcholine (neurotransmitter) which are released via synaptic vesicle when the axon terminal receives a nerve impulse. The
Ach binds to sarcolemma receptors which trigger the sarcolemma to send impulses down the T tubules (branches off
sarcolemma that cause Ca²+ to release) to the sarcoplasmic reticulum. Sarcomere contraction follows after the release of
calcium from the sarcoplasmic reticulum.
Sensory Receptors
Myelin Sheath made from Schwann Cells
Sensory Neuron
Cell Body
Interneuron with purple Dendrites
Axon
Axon Terminals
Myelin Sheath
Nodes of Ranvier
Motor Neuron with orange Dendrites
Axon
The nervous system has 3 important functions: to receive sensory input,
perform integration, and generate motor output.
Neurons - cells responsible for transmission of nerve impulses. Consist of a body containing the nucleus and organelles, dendrites which are short extensions that receive signals, and an axon which conducts impulses. The 3 types of neurons are sensory neurons (transports impulses to CNS), interneurons (receive messages and convey to motor neurons), and motor neurons (transports impulses from CNS to muscle). Sensory neurons detect changes in their environment from sensory receptors.Long axons are covered by myelin sheath’s which is a protective insulating phospholipid layer composed of Myelin (80% lipid fat / 20% protein). The gaps along axons where there is no myelin wrapped around it is called nodes of Ranvier, named after Louis-Antoine Ranvier who discovered it around 1878. A neuroglia known as Schwann cells (contain myelin in membrane) are responsible for the protection of long axons in the PNS, whereas oligodendrocytes protect the long axon’s in the CNS. Myelin gives a white appearance.
Picture & Verbiage from Human Biology Page 249
Different Types of Neurons:
A. Sensory neuron has a long axon covered by a myelin sheath that takes nerve impulses all the way from dendrites to the CNS.
B. In the CNS, some interneurons, such as this one, have a short axon that is not covered by a myelin sheath.
C. A motor neuron has a long axon covered by a myelin sheath that takes nerve impulses from the CNS to an effector.
Nerve impulses send messages throughout the whole nervous system. An axon is either resting or active; thus, they are either in the resting potential or the active potential state. A voltmeter can record which state the nerve is in by measuring the negativity of the inside of
a neuron compared to its outside.Resting Potential
• No impulse conducting within axon
• Inside more negative than outside
• About -60 to -70 millivolts
• Dissimilarity in ion dispersal on either side of membrane
• Dissimilar dispersal is due to sodium-potassium pump which maintains appropriate concentrations of sodium and potassium intracellular and extracellular
• Threshold is reached around 15 millivolts above resting membrane potential
• Repolarization occurs as potassium leaves axon
Pictures from Human Biology Pg 250
SEE MY DEMONSTRATION OF AN ACTION POTENTIAL!
1. This picture shows an axon in resting potential; having a difference in sodium and potassium ions between the
outside and inside of the axon. Since the axon is not conducting an impulse, the inside has a negative charge.
Outside Axon
Inside Axon
Axonal
Membrane
2. This picture shows an axon in action potential. The sodium gates have opened (red licorice) and sodium (green licorice bits) is moving in to the axon. The charge inside the axon is now changing from negative to positive (depolarization).
Inside Axon
Outside Axon
3. This picture shows the action potential ending. The sodium gates closed and the potassium gates have opened. Potassium is flowing out of the axon causing the negative charge in the axon to return (repolarization).
Inside Axon
Outside Axon
Nerve Impulse
Propagation of an Action PotentialAction potentials can be transmitted along the nodes by way of saltatory
conduction, where each action potential generates another by jumping. To ensure that nerve impulses (active
potentials) always travel down an axon to the end, the axon undergoes a
refractory period where the sodium gates cannot open.
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Pic from Human Biology Pg 251
Skeletal Muscle up CloseSarcolemma: Plasma Membrane
Sarcoplasm: Cytoplasm; contains organelles, glycogen (energy) and myoglobin (stores oxygen).
Sarcoplasmic Reticulum: Endoplasmic Reticulum
T Tubule: Tubes that dip into muscle fibers sarcoplasm to contact reticulum with impulses (for Ca²+ release).
Myofibrils: Contractile parts of fibers, encased by reticulum.
In each myofibril are sarcomeres between two lines (z lines) and contain two protein
myofilaments: thick filament (myosin) and thin filament (actin). The I band contains only actin, the H zone contains only myosin, the A band
contains both overlapping.
Pictures from Human Biology Pg 233
SEE MY MUSCLE FIBER MODEL ON THE NEXT SLIDE!
Skeletal Muscle Fiber
Skeletal Muscle Fiber
Sarcoplasmic reticulum (responsible for calcium
release): paper towel cardboard
Myofibrils: yellow and
orange licorice
Sarcolemma: white grip shelf liner
Nucleus: red Life Savers
T tubule: blue licorice
One Myofibril
Pic from Human Biology Pg 229
Muscle Contractions Start with Sarcomeres
SEE THE NEXT SLIDE TO VIEW MY SARCOMERE MODEL!
Z Line
Actin Myosin
Cross-bridge
Sarcomere has shortened due to myofibril contracting
Myosin
OneMyofibril
The thick filaments are constructed from molecules of a protein called myosin. Each sarcomeres has globular heads extending out the ends but not in the
middle. These extensions are known as cross-bridge. The thin filaments are
constructed from intertwining strands of the protein called actin. Once broken down by myosin, ATP supplies the
necessary energy for contraction. The cross-bridges on myosin pull actin towards the center. This process is
When the sarcoplasmic reticulum releases Ca²+ it binds with troponin, a protein found along the actin filament. Once the binding occurs between the Ca²+ and troponin, the protein threads called
tropomyosin shift on the actin filament exposing the myosin binding sites. This process now allows myosin and actin to bind.
Actin Filament Tropomyosin
Troponin Ca²+Myosin Binding Sites
Pic from Human Biology Pg 235
Once the myosin binding sites are exposed ATP is hydrolyzed to the myosin head. The ATP is then split into ADP and P (phosphate) allowing the myosin heads to attach to the actin’s binding sites
forming the cross-bridges. Once the ADP and P are released, the cross-bridges bend and pull the actin filaments inwards. This is known as the power stroke. The cross-bridges are broken when the
myosin head binds to ATP molecules again.
In this part of my lab experiment I have explained what a muscle is composed of and the steps involved with how a muscle contracts. I have broken down a neuron and explained the function of its axon, the function of sodium and potassium in an action potential, and the propagation of an action potential along the axon. I have demonstrated a muscle cell, its components, and how the components contribute to the process of muscle contraction. This was a fun and informational part of the lab project, and I believe it will help give a better understanding of moveable limb
