By serving as the body's control and communication center, the nervous system directs every body system as well as governs all movement, sensation, thought, and emotion. Essentially, the system gathers, interprets, and responds to environmental stimuli. It senses internal and external changes, analyzes and stores the sensory information, makes decisions about it, and responds to it. The nervous system allows communication among different parts of the body and the external environment outside the body. Anatomically, the nervous system consists of the central nervous system and the peripheral nervous system (2009). Functionally, the nervous system is divided into sensory divisions that convey impulses from the periphery to central nervous system and the motor division which works vice versa.
The central nervous system, or "CNS", includes the brain and the spinal cord of the body. The motor division of the peripheral nervous system, or "PNS", can be divided into two systems - the somatic nervous system and the autonomic nervous system. The somatic nervous system controls the voluntary movements of the skeletal muscles. The autonomic nervous system, on the other hand, controls activities in the body that are involuntary or automatic such as actions concerning the heart, the glands, and the digestive organs (2007). Also, with the endocrine system, the nervous system helps maintain homeostasis - homeostasis being the ability for the body to seek and maintain a condition of equilibrium. The nervous and endocrine systems regulate certain aspects of the body's internal environment. For instance, the nervous system regulates heart rate, and the endocrine system produces epinephrine. "Epinephrine is the fight or flight hormone in your body. It causes your heart rate to increase, your pupils to dilate, and the transport of more oxygen to go to your brain and muscles" (World of Anatomy and Physiology, 2007).
Moving on, nervous tissue consists of densely packed, intertwined nervous system cells. Nervous system cells fall into two categories - neurons (neural cells) and neuroglia (supporting cells). To be precise, "Neuroglia includes many types of cells that generally support, insulate, and protect the delicate neurons" (Marieb, 2007). These supporting cells include astrocytes, microglia, oligodendrocytes, ependymal cells, Schwann cells, and satellite cells. Astrocytes attach to neurons and capillaries. These cells help supply nutrients to neurons and control ions present around it. Microglia protects the CNS against microorganism and engulf dead neural tissue. Oligodendrocytes are small, branching cells with a cytoplasmic extension that is wrapped tightly around nerve fibers to form a myelin sheath. A myeline sheath being a phospholipid segmented covering that wraps around nerve fibers. Ependymal cells are cells that line the CNS cavities of the brain and spinal cord. Schwann cells also form a myelin sheath around nerve fibers found in the PNS. Finally, the satellite cells that are found in the PNS help maintain the chemical balance of neurons and act as protective cells (2007). Furthermore, neurons are highly specialized cells that conduct nerve impulses. Most of the neuronal bodies are found in the central nervous system. These cells have cytoplasmic processes called axons and dendrites which extend outwards from the cell body. Axons carry impulses away from the cell body while dendrites receive impulses from other cells and carry them towards the cell body.
Furthermore, electrical or chemical impulses move from one neuron to another across the synapse or junction between neurons. Most synapses exist between the axon and dendrite of a neuron. Synapses allow nerve impulses to travel in only one direction as well. An electrical synapse lets impulses move rapidly from one neuron to the next. Tissues such as cardiac and smooth muscle, contain many electrical synapses. A chemical synapse releases and receives neurotransmitters, chemicals that modify or trigger impulse transmission across the synapse. The neurotransmitter crosses the gap which receive the impulse. This results in neurotrasmission, which is basically the conduction of impulses throughout the nervous system. It occurs through the actions of neurons, which detect and transmit stimuli (2009). This electrical transmission occurs within the nerve fiber. Chemical transmission on the other hand occurs between two neurons or between a neuron and a muscle. Neurotransmitters are essential for neurotransmisson in the CNS. Other substances are also involved such as neuropeptides. Neuropeptides are molecules composed of short chains of amino acids that usually appear in the axon terminals of synapse.
The control centers for most of the nervous system functions are located in the brain. The cerebrum, cerebellum, diencephalon, and brain stem control specialized groups of function. The brain basically modulates the spinal cord which primarily acts as the reflex response center. Most simple reflexes result from neurotransmission through the reflex arc which is three neuron chain composed of sensory. connecting, and motor neurons. The major reflex center in the CNS, the spinal cord mediates most reflexes. Reflexes are automatic actions, such as a knee jerk in response to a tap to the patella. There are three common types of somatic reflexes (2009). The stretch reflex involves two neurons and one synapse, the flexor reflex involves sensory, motor, and connecting neurons and more than one synapse, and the crossed-extensor reflex which involves the flexor and contralateral reflex arc. The first of the three neuron chains is the sensory neuron which carries the impulse into the spinal cord through the dorsal root. The second is connecting neuron which relays the impulse into a motor neuron. Finally, the motor neuron sends out a motor impulse by the axon in the ventral root of the spinal cord.
The central nervous system, or "CNS", includes the brain and the spinal cord of the body. The motor division of the peripheral nervous system, or "PNS", can be divided into two systems - the somatic nervous system and the autonomic nervous system. The somatic nervous system controls the voluntary movements of the skeletal muscles. The autonomic nervous system, on the other hand, controls activities in the body that are involuntary or automatic such as actions concerning the heart, the glands, and the digestive organs (2007). Also, with the endocrine system, the nervous system helps maintain homeostasis - homeostasis being the ability for the body to seek and maintain a condition of equilibrium. The nervous and endocrine systems regulate certain aspects of the body's internal environment. For instance, the nervous system regulates heart rate, and the endocrine system produces epinephrine. "Epinephrine is the fight or flight hormone in your body. It causes your heart rate to increase, your pupils to dilate, and the transport of more oxygen to go to your brain and muscles" (World of Anatomy and Physiology, 2007).
Moving on, nervous tissue consists of densely packed, intertwined nervous system cells. Nervous system cells fall into two categories - neurons (neural cells) and neuroglia (supporting cells). To be precise, "Neuroglia includes many types of cells that generally support, insulate, and protect the delicate neurons" (Marieb, 2007). These supporting cells include astrocytes, microglia, oligodendrocytes, ependymal cells, Schwann cells, and satellite cells. Astrocytes attach to neurons and capillaries. These cells help supply nutrients to neurons and control ions present around it. Microglia protects the CNS against microorganism and engulf dead neural tissue. Oligodendrocytes are small, branching cells with a cytoplasmic extension that is wrapped tightly around nerve fibers to form a myelin sheath. A myeline sheath being a phospholipid segmented covering that wraps around nerve fibers. Ependymal cells are cells that line the CNS cavities of the brain and spinal cord. Schwann cells also form a myelin sheath around nerve fibers found in the PNS. Finally, the satellite cells that are found in the PNS help maintain the chemical balance of neurons and act as protective cells (2007). Furthermore, neurons are highly specialized cells that conduct nerve impulses. Most of the neuronal bodies are found in the central nervous system. These cells have cytoplasmic processes called axons and dendrites which extend outwards from the cell body. Axons carry impulses away from the cell body while dendrites receive impulses from other cells and carry them towards the cell body.
Furthermore, electrical or chemical impulses move from one neuron to another across the synapse or junction between neurons. Most synapses exist between the axon and dendrite of a neuron. Synapses allow nerve impulses to travel in only one direction as well. An electrical synapse lets impulses move rapidly from one neuron to the next. Tissues such as cardiac and smooth muscle, contain many electrical synapses. A chemical synapse releases and receives neurotransmitters, chemicals that modify or trigger impulse transmission across the synapse. The neurotransmitter crosses the gap which receive the impulse. This results in neurotrasmission, which is basically the conduction of impulses throughout the nervous system. It occurs through the actions of neurons, which detect and transmit stimuli (2009). This electrical transmission occurs within the nerve fiber. Chemical transmission on the other hand occurs between two neurons or between a neuron and a muscle. Neurotransmitters are essential for neurotransmisson in the CNS. Other substances are also involved such as neuropeptides. Neuropeptides are molecules composed of short chains of amino acids that usually appear in the axon terminals of synapse.
The control centers for most of the nervous system functions are located in the brain. The cerebrum, cerebellum, diencephalon, and brain stem control specialized groups of function. The brain basically modulates the spinal cord which primarily acts as the reflex response center. Most simple reflexes result from neurotransmission through the reflex arc which is three neuron chain composed of sensory. connecting, and motor neurons. The major reflex center in the CNS, the spinal cord mediates most reflexes. Reflexes are automatic actions, such as a knee jerk in response to a tap to the patella. There are three common types of somatic reflexes (2009). The stretch reflex involves two neurons and one synapse, the flexor reflex involves sensory, motor, and connecting neurons and more than one synapse, and the crossed-extensor reflex which involves the flexor and contralateral reflex arc. The first of the three neuron chains is the sensory neuron which carries the impulse into the spinal cord through the dorsal root. The second is connecting neuron which relays the impulse into a motor neuron. Finally, the motor neuron sends out a motor impulse by the axon in the ventral root of the spinal cord.
A picture of the central nervous system, or commonly known as the brain which is responsible for a humans . (Body by Design, 2010)
A picture of a neuron with incoming synapses, where the neuron is yellow and the synapses is red. (The Gale Encyclopedia of Science, 2010)
Neurons relay messages by accepting inputs at the dendrite and cell body, passing waves of electrochemical activity down the axon, and releasing chemical neurotransmitters from the axon to the next neuron at the synapse. (Biology, 2010)