Nervous System Parts and Function
- 2. NERVOUS SYSTEM Nervous system is the chief controlling and coordinating system of the body. It controls and regulates all activities of the body, whether voluntary or involuntary, and adjusts the individual (organism) to the given surroundings.
- 3. The basic working unit of the nervous system is a cell called a neuron. The human brain contains about 100 billion neurons. A neuron consists of a cell body containing the nucleus, and special extensions called axons (pronounced AK-sonz) and dendrites (pronounced DEN-drahytz). Nerves are cylindrical bundles of fibers that start at the brain and central cord and branch out to every other part of the body.
- 4. WHAT ARE THE PARTS OF THE NERVOUS SYSTEM? The nervous system consists of two main parts: Central nervous system Peripheral nervous system
- 5. CENTRAL NERVOUS SYSTEM The central nervous system is made up of the brain and spinal cord. The brain sends messages through the spinal cord and nerves of the peripheral nervous system to control the movement of the muscles and the function of internal organs.
- 6. BRAIN The brain is the center of our thoughts, the interpreter of our external environment, and the origin of control over body movement. Like a central computer, it interprets information from our eyes (sight), ears (sound), nose (smell), tongue (taste), and skin (touch), as well as from internal organs such as the stomach.
- 7. PARTS OF THE BRAIN The cerebrum is the largest part of the brain and is composed of right and left hemispheres. It performs higher functions like interpreting touch, vision and hearing, as well as speech, reasoning, emotions, learning, and fine control of movement. The cerebellum is located under the cerebrum. Its function is to coordinate muscle movements, maintain posture, and balance. The brainstem acts as a relay center connecting the cerebrum and cerebellum to the spinal cord. It performs many automatic functions.
- 8. SPINAL CORD The spinal cord is the highway for communication between the body and the brain. When the spinal cord is injured, the exchange of information between the brain and other parts of the body is disrupted.
- 9. PERIPHERAL NERVOUS SYSTEM The peripheral nervous system is made up of sensory neurons, ganglia (clusters of neurons) and nerves that connect to one another and to the central nervous system.
- 10. The peripheral nervous system is divided into the somatic and the autonomic nervous system. SOMATIC NERVOUS SYSTEM The somatic nervous system is under voluntary control, and transmits signals from the brain to end organs such as muscles. The sensory nervous system is part of the somatic nervous system and transmits signals from senses such as taste and touch (including fine touch and gross touch) to the spinal cord and brain. The autonomic nervous system is a 'self-regulating' system which influences the function of organs outside of voluntary control, such as the heart rate, or the functions of the digestive system.
- 11. AUTONOMIC NERVOUS SYSTEM The autonomic nervous system controls involuntary responses to regulate physiological functions. The brain and spinal cord from the central nervous system are connected with organs that have smooth muscle, such as the heart, bladder, and other cardiac, exocrine, and endocrine related organs, by ganglion neurons. The most notable physiological effects from autonomic activity are pupil constriction and dilation, and salivation of saliva. The autonomic nervous system is always activated, but is either in the sympathetic or parasympathetic state.
- 12. SYMPATHETIC NERVOUS SYSTEM The sympathetic system is activated during a “fight or flight” situation in which great mental stress or physical danger is encountered. Neurotransmitters such as nor epinephrine, and epinephrine are released, which increases heart rate and blood flow in certain areas like muscle, while simultaneously decreasing activities of non-critical functions for survival, like digestion. The systems are independent to each other, which allows activation of certain parts of the body, while others remain rested. PARASYMPATHETIC NERVOUS SYSTEM Primarily using the neurotransmitter acetylcholine (ACh) as a mediator, the parasympathetic system allows the body to function in a “rest and digest” state. Consequently, when the parasympathetic system dominates the body, there are increases in salivation and activities in digestion, while heart rate and other sympathetic response decrease. Unlike the sympathetic system, humans have some voluntary controls in the parasympathetic system. The most prominent examples of this control are urination and defecation.
- 13. PARASYMPATHETI C Body at rest SYMPATHETIC Emergency situations Eyes Constricts pupils Dilates pupils Heart Beat more slowly Beats faster and stronger Lungs Constricts airways Relaxes airways, which lets you breathe more deeply Digestion Stimulates digestion Inhibits digestion Muscles Reduces blood flow to skeletal muscles Increases blood flow to skeletal muscles