Movement and Reflexes

Summary

In this video, Dr. Mike explains the process of motor movement and reflexes, starting with how the brain initiates movement through the motor cortex. He highlights the role of upper and lower motor neurons in sending signals to muscles, allowing voluntary movement. Reflexes, like the patellar reflex, are also discussed, showing how muscles contract to prevent damage when overstretched. The video emphasizes the importance of the upper motor neuron in controlling movement and inhibiting lower motor neurons. Dr. Mike also introduces the concept of lesions affecting these neurons, which will be explored in a future video.

Takeaways

• 😀 Motor movement starts in the brain, specifically in the motor cortex, which has a map of the body.
• 😀 Each body part has a designated area in the motor cortex, which sends signals to the muscles to initiate movement.
• 😀 The motor cortex sends a signal through the upper motor neuron to the brain stem and then to the spinal cord.
• 😀 The signal from the motor cortex travels down to the spinal cord and crosses to the opposite side before reaching the muscles.
• 😀 A two-neuron chain is involved in motor movement, with the upper motor neuron initiating movement and the lower motor neuron causing muscle contraction.
• 😀 Sensation, on the other hand, involves a three-neuron chain going toward the brain, unlike motor movement which uses a two-neuron chain moving away from the brain.
• 😀 Reflexes involve a rapid, involuntary response that bypasses the brain, occurring locally in the spinal cord.
• 😀 An example of a reflex is the patellar reflex, where hitting below the knee causes the quadricep muscle to contract reflexively.
• 😀 Reflexes help protect muscles from overstretching and potential injury by causing them to contract when stretched too far.
• 😀 The upper motor neuron not only initiates movement but also modulates it by inhibiting the lower motor neuron, which is crucial for coordinated muscle control.

Q & A

What is the role of the motor cortex in movement?

The motor cortex is responsible for initiating movement. It contains a map of the body, with specific areas dedicated to different body parts like the arms and legs. When we want to move a body part, a signal is sent from the motor cortex to start the movement.

How does the brain send a signal to move a body part?

The brain sends a signal from the motor cortex through a neuron, which travels down the brain stem, crosses to the opposite side, and moves down the spinal cord. This signal then synapses with a second neuron in the spinal cord, which eventually tells the muscle to contract.

What is the difference between motor movement and sensation in terms of neuron chains?

Motor movement involves a two-neuron chain, consisting of an upper motor neuron from the brain and a lower motor neuron in the spinal cord. Sensation, on the other hand, involves a three-neuron chain, where the signal travels toward the brain.

What is a reflex, and how does it differ from voluntary movement?

A reflex is an automatic response to stimuli that bypasses the brain and occurs directly in the spinal cord. For example, tapping the patella tendon triggers a reflex that makes the muscle contract. This is different from voluntary movement, which involves conscious brain control.

What happens when the quadricep is stretched too much?

When the quadricep is stretched too much, it triggers a reflex to contract in order to prevent injury. The muscle automatically reacts to avoid overstretching and damage.

How does the patella tendon tap demonstrate a reflex?

Tapping the patella tendon stretches the quadricep muscle, which activates sensory receptors. The sensory information is sent to the spinal cord, where it directly activates the lower motor neuron to make the muscle contract, bypassing the brain.

What is the role of the lower motor neuron in muscle contraction?

The lower motor neuron plays a critical role in muscle contraction. It is responsible for transmitting the signal from the spinal cord to the muscle, causing it to contract when activated.

Why is the upper motor neuron important for movement control?

The upper motor neuron is essential for initiating movement, but it also plays a crucial role in modulating that movement. It helps regulate and inhibit the lower motor neuron to ensure coordinated and controlled muscle contractions.

What could happen if the upper motor neuron is damaged?

Damage to the upper motor neuron can lead to impaired movement control and difficulty inhibiting the lower motor neuron, resulting in issues such as muscle spasticity or uncontrolled movements.

How do the upper and lower motor neurons work together?

The upper motor neuron initiates the movement and regulates the lower motor neuron, which directly stimulates the muscle to contract. The two work together to ensure smooth and controlled movement.