Overarching Function

The nervous system transmit signals across the body in order to respond to stimuli and maintain homeostasis. Signals are transmitted through the manipulation of ions. Action potential, or nerve impulses, create a negative flow of ions to transmit signals from one place to another.

Action Potential

At resting potential, the cell is relatively more negative than the outer space of the cell. During depolarization, sodium ion channels open. With sodium ions moving into the cell, the charge outside the cell becomes more negative, which then triggers a series of sodium ion channels to open up. The voltage in the cell now exceeds the outward current. Therefore, repolarization occurs, where potassium ion channels open up. Potassium ion transfers out of the cell, which makes the inner cell more negatively charged. Then the cell goes back to resting potential, where energy is used to for sodium-potassium pumps to regulate the ions in and out of the cell.

Basic structures and functions

Macroscopic structures

The brain and the spinal cord make up the central nervous system (CNS). The CNS coordinates all the body’s activities, whether voluntary or not. They relays messages, processes information, and analyzes responses. The CNS produces a response based on a stimulus.

1. Brain

   The brain is sometimes referred to as the “control center” of the body. The brain helps maintain homeostasis and is the organ “deciding” the activities. The cerebrum is the largest part of the brain and is divided into two halves called hemispheres. It carries out learning, memory, language, speech, voluntary body movements, and sensory perception. The smaller part of the brain is called the cerebellum. The cerebellum controls balance, posture, and coordination. The brain stem then connects with the spinal cord, a structure described below.

   

2. Spinal Cord

   The spinal cord is protected by the vertebra and connects the brain with the peripheral nervous system. Reflexes are processed in the spinal cord before even reaching the brain, such as the knee-jerk reflex (when someone hits your knee and you kick).

Microscopic structures

1. Neuron

   The neuron is the fundamental cell of the nervous system. This cell is responsible to passing on signals throughout the body. Its main structures include a cell body, which contains the nucleus, an axon, which is the “tail” of the neurons, and dendrites, which are like smaller axons. The dendrites are responsible for receiving messages, whereas the axon is responsible to sending off messages. In each section of the axon, the action potential is passed on. In the axon terminal (located at the end of the axon), there are synaptic vesicles, which contain neurotransmitters, as described below.

1. Neurotransmitter

   A neurotransmitter is a chemical that diffuses across a synapse and binds to ion channel proteins on a neighboring neuron. Action potential triggers the calcium gate to open, which releases neurotransmitter from synaptic vesicles. Neurotransmitters then bind to receptors and allow chemical messages to be passed on to different neurons, further triggers target cells to take action.

Connection to other systems

The nervous system connects with all the other systems in the body, as it produces a response to a stimulus. It is how your body makes decisions and how you sense. For example, the sensory receptors in the integumentary system perceive senses and transmit the signal through our nerves, further make us feel. Motor neurons are responsible for carrying signals from the central nervous system, towards muscles, and contract.

Differences between a frog and human

Frog and human nervous system are essentially, except for one difference. The spinal cord of a frog is shorter than a human’s. That is expected since humans are “longer” than frogs.