Question

Muscles are controlled by the nervous system. Muscles also send information back to the nervous system.

i. Describe one piece of information that muscles send back to the nervous system and a specialized receptor cell that detects and conveys that information. (1 point)

Many songbirds are sexually dimorphic: only male songbirds sing. The brains of male and female songbirds are different, too: the motor cortex of males is twice as big as the motor cortex in females. However, if you inject a female songbird with testosterone when she is young she will learn to sing and her motor cortex will be bigger, but not if you wait to inject her with testosterone until she is an adult. This process is called masculinization.

ii. What stage of development do you think is particularly important for the masculinization of the female songbird’s motor cortex and why? (2 point)

Each songbird can produce 100 unique notes, which are simple movements akin to a monkey pointing its finger to a point in space. A bird creates a song by picking 5 of these 100 notes and singing them one after the other. Imagine that you’re a scientist recording from all 1000 neurons in a songbird’s motor cortex.

iii. How many unique notes do you think a single neuron in the motor cortex would typically be active during? (1 point)

You want to decode what note a bird is singing by observing the activity of 1000 motor cortex neurons. During the first phase, you are allowed to observe the activity of all 1000 neurons as the bird sings each of its 100 notes a few times. In the second phase, the bird is placed in a sound proof room and he will sing 1 note.

iv. Why is the first phase important? (2 point)

v. How will you use what you learned during the first phase to know what note the bird is singing in the second phase? (1 point)

Answer 1

i) Much of the brain and nervous system is devoted to the processing of sensory input, in order to construct detailed representations of the external environment..Neurons are the basic functional units of the nervous system, and they generate electrical signals called action potentials, which allow them to quickly transmit information over long distances.Three types of neurons; sensory neurons, Motor neurons and interneurons.Motor neurons have a long axon and short dendrites and transmit messages from the central nervous system to the muscles (or to glands).

Through vision, audition, somatosensation, and the other senses, we perceive the world and our relationship to it. The relation between sensory input and the motor output are simple and inact. Example; If we touch a hot object,we immediately pull our hand.Usually, our conscious actions require not only sensory input but a host of other cognitive processes that allow us to choose the most appropriate motor output for the given circumstances. In each case, the final output is a set of commands to certain muscles in the body to exert force against some other object or forces (e.g., gravity). This entire process falls under the subject of motor control.

• The peripheral nervous system (PNS), which consists of the neurons and parts of neurons found outside of the CNS, includes sensory neurons and motor neurons. Sensory neurons bring signals into the CNS, and motor neurons carry signals out of the CNS.

• The cell bodies of some PNS neurons, such as the motor neurons that control skeletal muscle (the type of muscle found in your arm or leg), are located in the CNS. These motor neurons have long extensions (axons) that run from the CNS all the way to the muscles they connect with (innervate). Motor neurons get information from other neurons and convey commands to your muscles, organs and glands.

  Two main components of the PNS:

• sensory (afferent) pathways that provide input from the body into the CNS.
• motor (efferent) pathways that carry signals to muscles and glands (effectors)
• Neuron-to-neuron connections are made onto the dendrites and cell bodies of other neurons. These connections, known as synapses, are the sites at which information is carried from the first neuron, the presynaptic neuron, to the target neuron (the postsynaptic neuron). The synaptic connections between neurons and skeletal muscle cells are generally called neuromuscular junctions, and the connections between neurons and smooth muscle cells or glands are known as neuroeffector junctions.

• Somatic senses inform the nervous system about the external environment, but the response to that is through voluntary muscle movement.

• There are stretch receptors present in the muscle body are calles Muscle spindles,that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be processed by the brain as proprioception. The responses of muscle spindles to changes in length also play an important role in regulating the contraction of muscles, for example, by activating motor neurons via the stretch reflex to resist muscle stretch.