I. FUNCTIONS

A. monitors changes internally & externally

B. integration: interpretes the input and makes decisions

C. responds to input by activating effectors (muscles & glands)

II. ORGANIZATION

A. Central Nervous System (CNS)
     1. consists of two parts
          a. brain
          b. spinal cord
     2. responsible for integration; impulses are sent to the CNS, which decides what to do and sends instructions to the
               effectors

B. Peripheral Nervous System (PNS)
     1. consists of two types of nerves
          a. cranial - extend directly from the brain
          b. spinal - extend from the spinal cord to the rest of the body
     2. can be divided into two areas: PNS -> CNS nerves, and CNS -> PNS nerves
          a. sensory (afferent) division - carries impulses from the receptors to the CNS
               i. somatic - stimuli comes from the skin, skeletal muscles, etc.
               ii. visceral - stimuli comes from the internal organs
          b. motor (efferent) division - carries impulses from the CNS to effectors
               i. somatic - voluntary control of skeletal muscles
               ii. autonomic - involuntary control of cardiac & smooth muscles, glands
                   1. sympathetic division - activates the "fight or flight" response
                   2. parasympathetic division - returns the body to normal conditions

III. HISTOLOGY OF NERVOUS TISSUE

A. supporting cells - located around the neurons
     1. neuroglia (glial cells) - supporting cells in the CNS
          a. astrocytes - star-shaped and abundant; they connect the capillaries & the nerves
          b. microglia - oval with thorny processes; help eliminate infections & dead tissue
          c. ependymal cells - lining of the cerebrospinal cavities; cilia move the fluid around
          d. oligodendrocytes - form myeline sheaths to insulate nerves
     2. supporting cells in the PNS
          a. satellite cells - control the chemical environment
          b. Schwann cells - form myelin sheaths around axons

B. neurons (nerve cells)
     1. live a long time (your entire lifetime, if they stay healthy)
     2. they cannot reproduce (they're amitotic); once they're gone, they're gone
     3. high metabolic rate; so they use a lot of glucose & oxygen
     4. there are several features of a neuron
          a. cell body - contains the nucleus
          b. dendrites - short extensions from the cell body
          c. axon - long extension from the cell body; covered with a myelin sheath created by Schwann cells; in-between
               each Schwann cell is a node of Ranvier
     5. neurons can be classified by their structure
          a. multipolar - have 3+ processes; the most common type; some have no axon
          b. bipolar - have 2 processes; rare in adults, though found in the eye & nose
          c. unipolar - have 1 process
     6. neurons can be classified by their function
          a. sensory (afferent) neurons - pick up stimuli
          b. motor (efferent) neurons - carry responses to effectors (muscles & glands)
          c. associative neurons (interneurons) - take the impulse from the sensory neurons, decides what to do about it,
               and sends the response to the motor neurons

IV. NEUROPHYSIOLOGY

A. basic principles of electricity
     1. the difference in two voltages is called the potential
     2. in the body, electrical charges are provided by ions

B. resting membrane potential
     1. a resting neuron has an internal potential of about -70mV
     2. the potential is due to the difference in the sodium and potassium ion concentrations inside & outside of the cell

C. membrane potentials that act as signals
     1. a graded potential is a small, brief potential change that acts as a short-distance signal
     2. an action potential, or nerve impulse, is a large, brief depolarization signal
          a. it is an all-or-none phenomenon; strong stimuli can lead to more signals but with the same amplitude
          b. depolarization is when the inner membrane becomes less negative (more positive)
          c. the movement of the nerve impulse is the depolarization area moving down the nerve
          d. a nerve threshold must be reached before the action potential is generated
          e. there is a refractory period, which is a resting time when the impulse cannot be propagated
     3. nerves can be classified as A, B, or C; the classification is based on 3 things
          a. diameter of the nerve fiber
          b. degree of myelination of the nerve fiber
          c. speed of conduction

D. synapse - the junction between two neurons
     1. electrical synapses - allow ions to flow directly from one neuron to another
     2. chemical synapses - when an impulse reaches the end of an axon, calcium ions cause neurotransmitter to be
               released; the neurotransmitter diffuses across the synaptic cleft to the next neuron and initiate the impulse

E. neurotransmitters - chemicals that jump across synapses to carry nerve impulses
     1. can be classified by chemical structure
          a. acetylcholine - released at neuromusclular junctions to stimulate muscles
          b. biogenic amines - example: norepinephrine, a "feeling good" neurotransmitter
          c. amino acids
          d. peptides - example: endorphin, which acts as a natural pain killer
     2. can be classified by function
          a. they can be inhibitory or excitatory (or both)
               i. inhibitory - stop movement of an impulse
               ii. excitatory - increase movement of an impulse
          b. they can be direct or indirect
               i. direct - cause channel opening
               ii. indirect - act through second messangers