Neural Control Of Walking

By: Dana SoluriPeriod 8

CNS & PNS

• The Central Nervous System is composed of the brain and spinal cord.

• The Peripheral Nervous System is made up of the parts of the nervous system that extend past the spinal cord.

• The reflex arc begins with a signals sent from sensory neurons to your spinal cord. These signals are then passed on to a motor neuron. After this process, the muscles are stimulated. In reference to walking, the signals are sent to make sure the muscles contract.

Depolarization

• This is the decrease in the absolute value of a cell’s membrane potential. Depolarization starts when the sodium channels open. There are positive charged sodium ions that enter the axon. There is another positive charged ion in the axon when this happens. Also, there are negative charged ions outside the axon. This causes the inside to become more positive and the concentration of sodium grows greater as well.

• Depolarization is how an action potential moves along the neurons. An action potential is initiated when the membrane is depolarized completely.

• Following this is repolarization. This is when the sodium channels close and the potassium channels open allowing potassium to move free through the axon.

• While walking, the cell’s membrane potential gets more positive as well. By going through this process, there is a change in the polarization and it becomes more positive.

Motor Unit

• A single motor neuron and all the corresponding muscle fibers it innervates. When a motor unit is activated, all of its fibers contract.

• A variety of motor behaviors can be accomplished. For example,when the fibers contract in the muscle, it enables you to begin walking.

Neuromuscular Junction and Neurotransmitters

• When an impulse goes to the NMJ, ach is released from terminal axons into the synaptic cleft and combines with a transmitter-receptor complex. Neurotransmitters are chemicals that relay signals between a neuron and another cell. After the impulse combines with the transmitter-receptor complex there is a change in the electrical properties releases a endplate potential that spreads from the motor endplate to the extrajunctional sarcolemma which causes a action potential to travel the length of the fiber. After this process ends the muscle is ready for contraction.

• When you are walking, signals are sent between your cells from neurons to make sure that you make the correct movements with the right muscles.

Fast Twitch; Slow Twitch Fibers

• Fast twitch (Type I) use anaerobic metabolism to create fuel, they are much better at generating short bursts of strength of speed. These fibers fatigue quicker due to the large amounts of energy being used.

• Slow twitch (Type II) more efficient at using oxygen to generate more fuel for continuous, extended muscle contractions over a long time.

• When walking you are using more slow twitch fibers because they do contract as fast and you can walk for a long time A: Fast twitch fibers

B: Slow twitch fibers

C: Protein p27

A.The fast twitch fibers alternate with the slow twitch fibers

B. This shows straining of slow twitch fibers.

C. Protein is strongly expressed in plasma membrane and nuclei.

Muscle Spindles• Sensory receptors within the belly of a muscle, which

primarily detect changes in the length of a muscle. The changes in length found by the spindles play an important role in regulating muscle contraction, making sure there is not too much stretching.

• While walking, the muscles contract and they become shorter. The receptors process to the brain that you are walking and the muscles contract.

Golgi Tendon Organs• A proprioceptive sensory organ that is located at the intersection of

skeletal muscle fibers into the tendons of skeletal muscle. The golgi tendon organs send information to the central nervous system about force. If there is not much activity regarding the golgi tendon organs, more force can be exerted.

• When walking, you walk on different types of surfaces. Your nervous system realizes these changes. The golgi tendon organs measure the amount of force the muscle is exerting so you are using the right amount.

• When they release too much force, a neural message is sent to the spinal cord where they synapse with interneurons.

Neuromuscular Fatigue

• The decline in muscular tension capacity with repeated stimulation. There is a breakdown of Ach (Acetylcholine) a neurotransmitter which means there is no more muscle contraction.

• Hydrogen ions (free radicals) block the Ach receptors which means the signals are not sent very well to the muscle fibers. When there are less muscle contractions, you begin to get fatigued due to less force.

• When there is no more muscle contraction, this means you are getting very tired and need to stop.

Motor Unit Plasticity• Changes are made in neurons in your brain, central nervous

system and peripheral nervous system neurons.

• These changes that occur in the neurons are so that you can better cope with the environment. There are more neural connections being made.

• When you are walking, the structures in your brain and nerves change when you begin walking.

• Your brain and peripheral nerves reacts to the changes when you walk.

Neurons

Nerves

Plasticity is when there are many connections being made to other neurons.