Lecture 5

Question 1

What is one important brain area that is responsible for voluntary movement, and what does it do?

Answer 1

One important brain area that is responsible for voluntary movement is the motor cortex, which exerts powerful control over the spinal cord, in part through direct control of its alpha motor neurons.

Question 2

Substania Nigra

Answer 2

• The substania nigra is an area of pigmented cells in the midbrain which is responsible for producing the neurotransmitter dopamine.
• This section of the brain plays an important role in the control of movement, and it also appears to interact in the process of addiction, as well.
• If you view a brain in cross-section, the substantia nigra is located in the midbrain, right at the tip of the brainstem.

Question 3

Flexor Reflex

Answer 3

A muscle that when contracted acts to bend a joint or limb in the body.

Question 4

Crossed Extensor Reflex

Answer 4

• Withdrawal reflex.
• When the reflex occurs the flexors in the withdrawing limb contract and the extensors relax, while in the other limb, the opposite occurs.
• An example of this is when a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body.
• The crossed extensor reflex is contralateral, meaning the reflex occurs on the opposite side of the body from the stimulus.

Question 5

Neuromuscular Junction

Answer 5

• A chemical synapse formed by the contact between the presynaptic terminal of a motor neuron and the postsynaptic membrane of a muscle fiber.
• Muscles will contract or relax when they receive signals from the nervous system. The neuromuscular junction is the site of the signal exchange.
• The steps of this process in vertebrates occur as follows:
  1. The action potential reaches the axon terminal.
  2. Voltage-dependent calcium gates open, allowing calcium to enter the axon terminal.
  3. Neurotransmitter vesicles fuse with the presynaptic membrane and acetylcholine (ACh) is released into the synaptic cleft via exocytosis.
  4. ACh binds to postsynaptic receptors on the sarcolemma.
  5. This binding causes ion channels to open and allows sodium ions to flow across the membrane into the muscle cell.
  6. The flow of sodium ions across the membrane into the muscle cell generates an action potential which travels to the myofibril and results in muscle contraction.