Nervous System Basics Pt. 1
What is a Neuron Structure?
A neuron structure is a structure found in the nervous system that consists of a cell body, axons, dendrites, myelin sheath, nodes of ranvier, axon terminal, and synapse. They are also connected to other neurons or other parts of the nervous system, such as receptors. Neuron structures also can be unipolar, bipolar, multipolar, or pseudounipolar, depending on where they are needed in the system. Neuron structures are also classified by the number of processes that extend from their cell bodies. For example, the multipolar neurons, which have more then two processes extending, are the most common type of neuron structure.
The Structure of the Nervous System:
The nervous system is divided into two main structural parts: the central & peripheral nervous system. Located in the center of the body, and the main integration portion of the nervous system, the central nervous system houses the brain and spinal cord. Within the brain, are the cerebrum and brainstem. The cerebrum is located on the top portion and largest portion of the brain, housing the left and right cerebral hemispheres. The brain stem, which connects the cerebrum to the spinal cord, houses the midbrain pons medulla, and cerebellum. The peripheral nervous system, which extends nerves to the rest of the body, consists of nerves and the ganglia. The nerves carry the axons of neurons, and the ganglia are lumps connected to nerves, which also contains some neurons. The ganglia consists of afferent and efferent neurons. Afferent neurons carry information into the CNS, while efferent neurons carry information away into the PNS. Both the afferent and efferent neurons come together at the spinal nerve root to create the mixed nerve. In addition, there are 12 pairs of cranial nerves, and 31 pairs of spinal nerves.
Overview of the Neuron's Function:
The neuron’s primary function is to process and transmit information. The biological magnification of this process includes potentials (action, graded, resting, membrane). In a neuron cell body, without any input, there is a stable electrical charge (negative inside, positive outside). Once a stimulus has been provided for the neuron to function, excitatory and inhibitory inputs enter through the dendrites of an axon. Entering the cell body, they then enter in through the trigger zone of the axon (the location at which the axon branches away from the cell body). At the trigger zone, these graded potentials (summation of all excitatory and inhibitory inputs) change into membrane potentials. Once the membrane potential crosses the threshold potential, an action potential is formed, and is shot through the length of the axon. With the assistance of the myelin sheath and the diameter of the axon, the potential is able to cross the synapse into the target cell. Through the axon terminal, a neurotransmitter is released to bind onto the receptor of the target cell, in which the information is processed.
Neuron Structure Overview:
The neuron has various parts that make it up. This includes: neurites (dendrites and axons), the soma (cell body), the axon hillock (the point at which the axon leaves the dendrite), the axon terminal (the point at which an axon meets and stops at another neuron’s endpoint), the myelin sheaths (schwann cells essential for insulation), the nodes of ranvier (gaps that charges the impulse when traveled), and the synapse (the point at which an axon terminal comes close to touching the target cell). The axon stretches out for 1 meter or more, and is dependent on the transportation of substances, and transmission of impulses. There are various structural types of neurons, which differ in both the CNS and PNS. In the CNS, neurons start off as neural stem cells. This type turns into most cell types of the CNS. These neural stem cells differentiate into neuroblasts, and these types can only become neurons. After, these neuroblasts migrate to locations that their cell bodies will have after development. A structure called a growth cone guides the cell to its target, based on its environment. It is different for the PNS however. Cell structures in the PNS are either: unipolar, bipolar, multipolar, or pseudounipolar neurons. These are named after their number of processes that extend outwards, which guide the neurons giving them direction.
Anatomy of a Neuron
A neuron’s job is to transmit signals across its length. The neuron has various parts that make it up. This includes: neurites (dendrites and axons), the soma (cell body), the axon hillock (the point at which the axon leaves the dendrite), the axon terminal (the point at which an axon meets and stops at another neuron’s endpoint), the myelin sheaths (schwann cells essential for insulation), the nodes of ranvier (gaps that charges the impulse when traveled), and the synapse (the point at which an axon terminal comes close to touching the target cell). The schwann cells make up the myelin sheaths.
Introduction to Neural Cell Types
Neural cells are described as cells of the nervous system. These cells are responsible for cognition, consciousness, emotional interactions, social interactions, sensory perceptions, movement, and regulation of other bodily functions, such as breathing. There are two categories for neural cells: glia and neurons. Glia refers to the word “glue” because they were once thought to glue neurons together. Neuron comes from the term “nerve”. In addition, the Central Nervous System (CNS) consists of the brain, spine, and spinal cord. On the other hand, the Peripheral Nervous System consists of nerves and neurons. Neurons are found in both the CNS and PNS. In the CNS, neurons process and transmit information, while the glia supports the neurons in that function. Neurons and glia from the CNS originate from neural stem cells, while neurons and glia in the PNS, originate from neural crest cells. A neuron consists of a cell body (soma), processes that extend out of it, and terminal structures that end those processes.
Credit: Khan Academy Nervous System Intro. All entries are written by Jadon-Sean Sobejana
