1. NOTES - UNIT 5 part 1: Nervous System Organization

2.  The nervous system has three overlapping functions:
1) SENSORY: gather information from sensory receptors; detect changes in the external or internal environment
2) INTEGRATION: information from sensory receptors is interpreted and associated with appropriate responses (sensation, memory, perceptions, decisions)
3) MOTOR OUTPUT: conduction of signals from the integration center to effector cells (muscle cells or gland cells)

3. The Nervous System is divided into:

4. *CENTRAL NERVOUS SYSTEM (CNS) brain and spinal cord
integration center 

5. *PERIPHERAL NERVOUS SYSTEM (PNS) nerves communicate motor and sensory
signals to and from CNS
and rest of body
made up of NERVES
(ropelike bundles
of neurons)

8. Nervous Tissue-Two Main Classes of Cells:
1) NEURONS (nerve cells):
functional unit of the nervous system
Specialized for nerve impulse (action potential) conduction
Provide most of the unique functions of the nervous system: sensing, thinking, remembering, controlling muscle activity, regulating glandular secretions
 transmit signals from one location to another
 made up of: DENDRITES, CELL BODY, AXON, & SYNAPTIC END BULBS OF AXON TERMINAL

10. DENDRITES (“little trees”): receiving/input parts of a neuron
CELL BODY: nucleus surrounded by cytoplasm and typical organelles (rough ER, mitochondria, lysosomes, golgi)

11. AXON: conducts nerve impulses toward another neuron, muscle fiber, or gland cell
Axons end by dividing into many fine processes called axon terminals
Axon terminals swell into synaptic end bulbs which contain synaptic vesicles storing neurotransmitters

13. many axons are enclosed by an insulating layer called the MYELIN SHEATH
Many-layered covering composed of lipid and protein
Increases the speed of nerve impulse conduction
Schwann cells in the PNS and Oligodendrocytes in the CNS produce myelin sheaths by wrapping themselves around and around axons
Axons with a myelin sheath: myelinated and
axons without: unmyelinated

14. Myelin producing cell; is this CNS or PNS?
Unmyelinated neuron

15. Gaps in the myelin sheath: Nodes of Ranvier

16. 3 Types of Neurons or Nerve Cells:
sensory neurons: detect many different types of stimuli & carry information to the brain
Interneurons: integrates/processes sensory information; axons extend for only a short distance & contact nearby neurons in the brain or spinal cord
motor neurons: carry information from the brain toward the spinal cord or out of the brain and spinal cord to muscles and glands

18. 2) NEUROGLIAL CELLS (SUPPORTING CELLS)
10 to 50 times more numerous than neurons
provide structure; protect, insulate, nourish, & assist neurons
Even though glia do not generate or conduct nerve impulses, they are actively involved in nervous tissue

19. 2) NEUROGLIAL CELLS-(SUPPORTING CELLS) continued
In contrast to neurons, some neuroglial cells can multiply & divide in the mature nervous system
Example of neuroglial cells: SCHWANN CELLS and OLIGODENDROCYTES
Example of neuroglial cell : ASTROCYTES: form connections between neurons; protect neurons from harmful substances; responsible for blood-brain barrier

20. Astrocyte
Nerve cells

22. Functions of the Blood Brain Barrier:
Protects the brain from "foreign substances" in the blood that may injure the brain.
Protects the brain from hormones and neurotransmitters in the rest of the body.
Maintains a constant environment for the brain.