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: CENTRAL NERVOUS SYSTEM (CNS)
brain and spinal cord
integration center/processing

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

5. 1 neuron (nerve cell)

6. Nervous Tissue-Two Main Types of Cells:
1) NEURONS (nerve cells):
functional unit of the nervous system
Specialized for nerve impulse (action potential) conduction
Transmit signals from one location to another
Provide most of the unique functions of the nervous system: sensing, thinking, remembering, controlling muscle activity, regulating glandular secretions
CNS neurons: no mitosis/repair
PNS neurons: some ability to repair themselves

7. The arrow shows the direction of the action potential message passing down one cell and then moving to the 2nd cell.

8. 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

9. Neuron Structure:
DENDRITES, CELL BODY, AXON, AXON TERMINAL, & SYNAPTIC END BULBS
DENDRITES (“little trees”): receiving/input parts of a neuron
CELL BODY: nucleus surrounded by cytoplasm and typical organelles (rough ER, mitochondria, lysosomes, golgi)
nucleus

10. AXON: conducts nerve impulses away from cell body & 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
Axon terminal

11. synaptic knobs from more than 1 neuron synapsing with the dendrites of 1 neuron

12. 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

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

14. Gaps in the myelin sheath where the axon is exposed: Nodes of Ranvier

15. SYNAPSE: chemical junction between a neuron and another cell; found between:
motor neuron & muscle cell
2 neurons
sensory receptor & sensory neuron
neuron & gland cell

16. Motor Neuron and Muscle Cell
Real vesicles!!

17. electrical signal  chemical signal  electrical signal
CHEMICAL SYNAPSES are separated by a synaptic cleft & a series of events converts:
electrical signal  chemical signal  electrical signal
Intercellular chemical signal: NEUROTRANSMITTERS

18. Synaptic Transmission Review…
An action potential (the electrical signal) reaches the end of the axon/synaptic end bulb
The action potential cannot cross the synaptic cleft
Causes neurotransmitters to be released from vesicles in the synaptic end bulb
The neurotransmitter reaches receptors in the cell of the postsynaptic membrane and causes a new impulse to be initiated

19. What Does the Neurotransmitter Message Say?
Some will cause an action potential
in the next cell (excitatory)
Some will inhibit an action potential
in the next cell (inhibitory)
About 50 different neurotransmitters have been identified

20. Examples of neurotransmitters:
Functions in:
Acetylcholine (ACh)
Neuromuscular junction; stimulates muscle contraction
epinephrine/ norepinephrine
attention & mental focus, cognition
*epin. & norep. also function as hormones in “fight or flight” response
dopamine/ serotonin
dop. & ser. both affect sleep, mood, attention, learning; *LSD & mescaline bind to serotonin receptors*
endorphins
Decrease perception of pain by CNS (inhibitory); *heroin & morphine mimic endorphins*
histamine
Release in hypothalamus promotes alertness

21. 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

22. 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 (PNS) and OLIGODENDROCYTES (CNS)
Example of neuroglial cell : ASTROCYTES: form connections between neurons; protect neurons from harmful substances; responsible for blood-brain barrier

23. Astrocyte
Nerve cells

24. Functions of the Blood Brain Barrier:
Maintain a constant external environment for brain cells.
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.