Tasting, smelling, seeing, hearing, thinking, dreaming, breathing, heart beating, moving, running, sleeping, laughing, singing, remembering, feeling pain or pleasure, painting, writing...you couldn't do any of these things without your nervous system!
The neuron is the functional unit of the nervous system 1
http://www.fulton.edzone.net/winkler/chapter08/chapter08.html 1 Higashida. “Ciencias de la Salud” Mc. Graw Hill, 2001
Three basic functions are performed by nervous systems:
Receive sensory input from internal and external environments . Sensory input can be in many forms, including pressure, taste, sound, light, blood pH, or hormone levels, that are converted to a signal and sent to the brain or spinal cord.
Integrate the input . In the sensory centers of the brain or in the spinal cord, the barrage of input is integrated and a response is generated.
Respond to stimuli . The response, a motor output, is a signal transmitted to organs than can convert the signal into some form of action, such as movement, changes in heart rate, release of hormones, etc.
Estructure of a Neuron Cell Body Dendrites Axon from other neurons Axon Myelin Dendrites from other neurons Audesirk Audesirk Byers Sixth Ed. Biology Life on earth, Instructions Resource CD-ROM, 2002 Prentice Hall Synaptic Terminals
The junction between a nerve cell and another cell is called a synapse . Messages travel within the neuron as an electrical action potential. The space between two cells is known as the synaptic cleft . To cross the synaptic cleft requires the actions of neurotransmitters which are stored in small synaptic vessicles clustered at the tip of the axon.
The plasma membrane of neurons, has an unequal distribution of ions and electrical charges between the two sides of the membrane. The outside of the membrane has a positive charge , inside has a negative charge . This charge difference is a resting potential and is measured in millivolts.
Passage of ions across the cell membrane passes the electrical charge along the cell. The voltage potential is -65mV (millivolts) of a cell at rest. Sodium ions are more concentrated outside the membrane, while potassium ions are more concentrated inside the membrane. This imbalance is maintained by the active transport of ions to reset the membrane known as the sodium potassium pump .
RESTING POTENTIAL ( Extracellular fluid ) (Negatively charge d neuron cytoplasm) ( Neuronal Membrane ) Org - Na + Org - Org - Org - Org - K + K + K + K + K + Cl - Cl - Cl - Cl - Na + Na + Na + Potassium Chanel Sodium chanel (c losed ) Audesirk Audesirk Byers Sixth Ed. Biology Life on earth, Instructions Resource CD-ROM, 2002 Prentice Hall
BEGINING OF ACTION POTENTIAL Org - K + K + K + Cl - Na + Na + K + Na + Na + Na + ( Extracellular fluid) ( Positive charge ) ( Negative charge ) Audesirk Audesirk Byers Sixth Ed. Biology Life on earth, Instructions Resource CD-ROM, 2002 Prentice Hall Org - Na + Org - Org - K + K + Cl - Na + K + K + K + K + Na + Na + Cl -
BEGINING OF ACTION POTENTIAL Audesirk Audesirk Byers Sixth Ed. Biology Life on earth, Instructions Resource CD-ROM, 2002 Prentice Hall
PROPAGATION OF ACTION POTENTIAL Audesirk Audesirk Byers Sixth Ed. Biology Life on earth, Instructions Resource CD-ROM, 2002 Prentice Hall
The somatic nervous system is connected to skeletal muscle, voluntary movement and skin sensation. The sensory-somatic system consists of
12 pairs of cranial nerves and
31 pairs of spinal nerves
The autonomic nervous system (ANS) which regulates individual organ function and homeostasis, and for the most part is not subject to voluntary control. It is also known as the visceral or automatic system . The autonomic nervous system has two subdivisions, the
the sympathetic system enables the body to be prepared for fear, flight or fight. Sympathetic responses include an increase in heart rate, blood pressure and cardiac output, a diversion of blood flow from the skin and splanchnic vessels to those supplying skeletal muscle, increased pupil size, bronchiolar dilation, contraction of sphincters and metabolic changes such as the mobilization of fat and glycogen.
In physiological terms, the parasympathetic system is concerned with conservation and restoration of energy, as it causes a reduction in heart rate and blood pressure, and facilitates digestion and absorption of nutrients, and consequently the excretion of waste products.