The Nervous System

The system governing sensation and neural communications.

Resting potential
The CNS to the rest of the body
Sympathetic and parasympathetic
Controlling voluntary movements
Cortical reorganization and experience-dependent plasticity

Overview of the Nervous System

The nervous system is a complex network of cells that carry signals or messages to and from the brain and spinal cord to different parts of the body. It is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).


The CNS consists of the brain and spinal cord, while the PNS includes all the nerves that connect the CNS to the rest of the body. The PNS can be further divided into the autonomic nervous system (ANS) and the somatic nervous system (SNS).

The autonomic nervous system (ANS) regulates involuntary functions such as heart rate, digestion, and breathing, while the somatic nervous system (SNS) controls voluntary movements and sensory information from the body.The nervous system is composed of two main types of cells: neurons, which transmit information, and glial cells, which support and protect neurons.



Neurons are the basic units of the nervous system, responsible for transmitting information throughout the body. They have a unique structure, consisting of a cell body, axons, and dendrites.

Axons carry signals away from the cell body, while dendrites receive signals from other neurons. Neurons can be classified based on their structure (multipolar, bipolar, pseudounipolar, unipolar) and function (efferent, afferent). Efferent neurons transmit information from the CNS to the body, while afferent neurons relay information from the body to the CNS.

The complex interplay between these different types of neurons allows for the efficient transmission of information and coordination of bodily functions. For example, when you touch something hot. The afferent neurons detect the heat and send a signal to the spinal cord, while the efferent neurons transmit a signal from the spinal cord to the muscles to move our hand hand.


Neuroglia, or glial cells, play a vital role in supporting and protecting neurons. They are responsible for maintaining the structural integrity of the nervous system and providing essential nutrients to neurons.


There are several types of glial cells, including oligodendrocytes, Schwann cells, astrocytes, satellite glial cells, microglia, and ependymal cells. Oligodendrocytes and Schwann cells produce myelin, a fatty substance that insulates axons and speeds up signal transmission. Astrocytes help maintain the blood-brain barrier and regulate the chemical environment around neurons.

The blood-brain barrier is a protective barrier between the blood vessels and the brain tissue, formed by a type of neuroglia called astrocytes. These astrocytes wrap themselves around the blood vessels in the brain, creating a barrier that prevents potentially harmful substances from entering the brain tissue.

Microglia act as the immune cells of the nervous system, while ependymal cells produce cerebrospinal fluid.

Action Potentials

Action potentials are the means by which neurons transmit information within the nervous system. An action potential is a rapid change in the electrical charge across a neuron’s membrane, allowing for the propagation of signals along the axon. This process involves several stages, including resting potential, depolarization, overshoot, and repolarization.


During resting potential, the neuron is not transmitting any signals, and its membrane is polarized, meaning there is an electrical charge difference between the inside and outside of the cell.. Depolarization occurs when the membrane potential becomes less negative, allowing for the initiation of an action potential.

Overshoot is the peak of the action potential, where the membrane potential becomes positive. Finally, repolarization restores the membrane potential to its resting state. An example of action potentials in the body is the transmission of sensory information from the skin to the brain, allowing us to perceive touch.

Synaptic Transmission

Synaptic transmission is the process by which neurons communicate with one another through specialized structures called synapses. At the synapse, neurotransmitters are synthesized and released by the presynaptic neuron, which then bind to receptors on the postsynaptic neuron, influencing its activity.


Neurotransmitter synthesis involves a complex biochemical process that requires specific enzymes and precursors. The precursors are molecules that are converted into neurotransmitters through a series of enzymatic reactions. Different types of neurons use different neurotransmitters, each with specific effects on the target cell.

Disruptions in the normal process of synaptic transmission can have significant effects on the functioning of the nervous system. For example, imbalances in neurotransmitter levels are implicated in various neurological and psychiatric disorders, such as depression and Parkinson’s disease.

Central Nervous System

The central nervous system (CNS) is composed of the brain and spinal cord, playing a critical role in controlling various bodily functions. it combines information from the entire body and coordinates activity across the whole organism.


The brain is divided into three main parts: the cerebrum, responsible for higher cognitive functions; the cerebellum, involved in motor coordination; and the brainstem, which regulates vital functions such as breathing and heart rate.

The spinal cord serves as a conduit for information between the brain and the rest of the body. The CNS is protected by the meninges (three protective layers of membranes that surround the brain and spinal cord and cushioned by cerebrospinal fluid. Damage to the CNS can have severe consequences, as seen in conditions like traumatic brain injury and multiple sclerosis.

Peripheral Nervous System

The peripheral nervous system (PNS) encompasses the nerves that connect the CNS to the rest of the body, controlling autonomic functions, motor movements, digestion, and relaying sensory information.


The PNS is divided into the sensory (afferent) division, which transmits information to the CNS, and the motor (efferent) division, which carries signals from the CNS to the body. The PNS also includes the somatic nervous system (SNS) and the autonomic nervous system (ANS).

Your peripheral nervous system is how your brain gets information about the outside world. Damage to the PNS can result in various disorders, such as peripheral neuropathy, Type II Diabetes and Guillain-Barré syndrome, which can cause muscle weakness, numbness, and pain.

Autonomic Nervous System

The autonomic nervous system (ANS) is a crucial component of the PNS, responsible for regulating involuntary bodily functions, such as heart rate, digestion, and respiration. The ANS is divided into two subsystems: the sympathetic (fight or flight) system, and the parasympathetic (rest and digest) system.


The sympathetic nervous system prepares the body for “fight or flight” responses by increasing heart rate and blood pressure, dilating the pupils, and redirecting blood flow away from the digestive system and towards the skeletal muscles. It is activated in response to stress, danger, or physical activity, and it helps to mobilize the body’s energy resources for immediate action.

The parasympathetic nervous system, on the other hand, helps the body to “rest and digest” by slowing down heart rate and respiration, constricting the pupils, and increasing digestive activity. It is activated during periods of relaxation, rest, and sleep, and it helps to conserve the body’s energy and restore its resources.
Disorders of the ANS can lead to various symptoms, such as orthostatic hypotension, fainting, and gastrointestinal problems.

Somatic Nervous System

The somatic nervous system (SNS) is another component of the PNS, responsible for controlling voluntary movements through the use of motor and sensory neurons. Motor neurons transmit signals from the CNS to the muscles, while sensory neurons relay information from the body to the CNS.


The somatic nervous system controls conscious and intentional movements of skeletal muscles, such as those involved in walking, running, or reaching for an object. It also plays a role in the sensation of touch, pain, temperature, and position sense.Disorders of the SNS can result in a range of symptoms, such as muscle weakness, tremors, and loss of sensation, as seen in conditions like amyotrophic lateral sclerosis (ALS) and Charcot-Marie-Tooth disease.


Neuroplasticity is the ability of the nervous system to adapt to changes in the environment, allowing for learning, memory, and recovery from injury. This process involves cortical reorganization, where the brain’s functional areas can shift in response to new experiences or damage, and experience-dependent plasticity, which refers to the strengthening or weakening of neural connections based on use.


An example of neuroplasticity is the improvement of motor skills through practice, such as learning to play a musical instrument. For example, in the case of playing a guitar, the motor cortex, which controls movement, undergoes changes as we practice the finger movements required to play the chords. Initially, playing a chord might require a lot of focus and effort, but with practice, the movements become more automatic, and the brain adapts to the new demands placed on it.

As we practice, our brains create new neural connections and strengthen existing ones, resulting in more efficient and coordinated movements. Neuroplasticity is essential for maintaining cognitive function and has therapeutic implications, such as in cognitive-behavioral therapy (CBT), which aims to rewire maladaptive thought patterns and behaviors.

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