Nervous System Structure and Function

The nervous system consists of a network of cells, with fibrous extensions, that carry information along specific pathways from one part of the body to another.1 The fundamental unit of the nervous system is the neuron, or nerve cell. The nerve cell is made up of a central body known as the soma, or nerve cell body, and it contains the nucleus. It has several long extensions called nerve fibers. There are two kinds of nerve fibers: axons, which carry information away from the cell body, and dendrites, which carry information toward the cell body. Most neurons have one axon and several dendrites. Neurons consist of a nerve cell body, which contains the nucleus, and several fibrous extensions. The fibers that carry impulses to the nerve cell body are dendrites. The fiber that carries the impulse away from the cell body is the axon. Sensory neurons have a long dendrite that carries information from the sense organ to the cell body. Motor neurons have a long axon that carries information from the cell body to a muscle or gland. Most neurons other than sensory neurons have many dendrites but only one axon.1


The nervous system has a high-level of control and integration of body systems. It response to external influences. The sympathetic nervous system prepares the body for activity and is known to be responsible for the fight or flight response.1 The sympathetic nervous system increases the heart rate as well as the blood pressure. This results in more blood flow to muscles and less to the digestive system. The pupils also dilate and the glycogen store are broken down to release glucose into the blood. The parasympathetic nervous system prepares body to rest.1 It is antagonistic to the sympathetic nervous system as it does the opposite of the system. This system decreases the heart rate as well as the blood pressure. It causes less blood to the muscles and more to the digestive system. The pupils also constrict. It also synthesizes glycogen for storage from glucose.


The feedback loop refers to the the positive feedback, negative feedback or reflex arc that occurs in the body. Positive feedback usually reinforces the initial event. An example would be where uterine contraction results in the release of oxytocin, which causes more uterine contraction. Another example is where blood clotting platelets activated at wound site attract more platelet activation and clumping. Negative feedback, on the other hand, counteracts the initial event. An example of this is when a drop in blood pressure causes ADH release, which increases it.1 Conversely, an increase in blood pressure causes a drop in ADH. The reflex arc occurs in response a painful stimulus. It is a type of negative feedback. An example would be the knee jerk reflex. By tapping the knee tendon, it causes sudden stretching of the muscle. This leads to contraction of the muscle that creates the knee jerk, an example of negative feedback. The spinal cord provides the synapse (or synapses if it’s polysynaptic) for the reflex arc. The reflex arc bypasses the brain as a result. The brain is still conscious of what is happening even though the reflex arc does not go to the brain. The brain is stillcapable of overriding spinal reflexes.


  • Neuron-structure
  • sympathetic-vs-parasympathetic
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