The Nervous System

I. The Nervous System A. The Nervous system controls & coordinates functions throughout the body and responds to internal & external stimuli. Choreographing a dance, Writing a song, Practicing lines in a play….have one thing in common.

II. Neurons A. Messages that are carried by the nervous system are called impulses and travel along neurons. B. Neurons can either be a sensory, motor or interneurons; but all have the same structures including: 1. Cell Body – contains nucleus, most of cytoplasm & most metabolic activity takes place here. 2. Dendrites – branched extensions, receive signals 3. Axon – carries impulses across neuron to another (covered by myelin) Sensory – detect external stimuli and send info to brain

III. Nerve Impulse A. An impulse begins when a neuron is stimulated by another neuron or by the environment. B. The flow of an impulse is similar to an electrical current through a wire as charged ions move along ion pumps across the neuron membrane changing the energy potential.

IV. The Synapse A. The synapse is where one neuron transmits the impulse to another neuron. (synaptic terminal) Ex. Motor neuron pass impulse to muscle cell B. The synaptic cleft is the space between neurons where neurotransmitters (chemicals used by neurons) to transmit an impulse.

V. Ion Pumps & Membrane Potential A. All neurons have a membrane potential. A difference between the inside of the cell (negative) and extracellular fluid (positive). 1. Polarized state resting potential (-70mV) B. Sodium-Potassium pump maintains the polarization by pumping ions that leak across the membrane 1. In order for the nerve to fire a stimulus it must be strong enough to overcome the resting potential (threshold)

V. Ion Pumps & Membrane Potential C. Neurons have gated-ion channels that open/close in response to a stimulus. 1. Only allowing one kind of ion to flow through D. If a stimulus triggers a sodium-ion gated channel to open sodium flows into the cytoplasm resulting in a decrease in polarization, becoming somewhat depolarized (making it easier for the nerve to fire). The opposite occurs if potassium-ion channel is stimulated and membrane is hyperpolarized.

V. Ion Pumps & Membrane Potential E. An action potential, impulse, can only be generated in an axon of a neuron. 1. When this occurs and the axon is stimulated the sodium channels open and sodium ions flood in the cell, potassium channels open and flood potassium out as a response causing a wave of depolarization reversing the action potential which only lasts a short time. F. The sodium-potassium pump restores the membrane to the original polarized condition (repolarization) or refractory period

VI. Division of the Nervous System A. The human nervous system can be divided into 2 parts: 1. Central nervous system – relays messages, processes & analyzes information 2. Peripheral nervous system – transmits impulses from sense organs to central nervous system & vice-versa

VII. Central Nervous System A. Central nervous system includes the brain & spinal cord. 1. These are surrounded by meninges & cerebrospinal fluid to not only act as a shock absorber but also allows exchange of nutrients and waste products

VII. Central Nervous System B. The Brain (consists of over 100 bill neurons): 1. Cerebrum – largest most prominent region of brain a. Responsible for voluntary activities, site for intelligence/learning & judgment b. Divided into regions called lobes based off the skull bones that surround the lobe (frontal, temporal, parietal, & occipital)

2. Cerebellum – second largest region of brain, located at the back of the skull. a. coordinates & balances actions of the muscles 3. Brain stem – located below cerebellum connecting brain to spinal cord consists of the pons & medulla oblongata a. control blood pressure, heart rate, breathing & swallowing

4. Thalamus – found between brain stem & cerebrum, a. receives messages from sensory receptors & relays message to cerebrum 5. Hypothalamus – control/analyze hunger, thirst, fatigue, anger & body temp. works with endocrine as well. 6. Spinal Cord – communication between brain & rest of body (31 pairs of nerve branches). Processes reflexes directly.

IIX. Peripheral Nervous System A. Peripheral nervous system consist of all the nerves, ganglia & associated cells that are not part of the brain & spinal cord. B. The peripheral is divided further into 2 systems: 1. Somatic nervous system 2. Autonomic nervous system

1. Somatic nervous system – regulates activities that are under conscious control a. allow quick reflex movement due to reflex arcs; inborn, automatic & protective. Only goes to spinal cord

2. Autonomic nervous system – regulates activities that are automatic, or involuntary movement a. Divided into 2 parts farther that oppose one another actions sympathetic & parasympathetic Ex. Sympathetic speed up heart rate during a run while the parasympathetic will decrease the heart rate when you finish