The Nervous System

1. The Nervous System • The master controlling and communicating system of the body • Method of communication? Electrical impulses

2. The Three Overlapping Functions • It uses millions of sensory receptors to monitor changes called stimuli inside and outside the body. • It processes and interprets this gathered information called sensory input and makes decisions on what should be done. This process is called integration. • It effects a response by activating muscles or glands via motor output.

3. Figure 7.1 page 223

4. Organization of the Nervous System • Structural Classification • Central Nervous System (CNS) – brain and spinalcord. They interpret incoming sensory information and issue commands in response • Peripheral Nervous System (PNS) – mainly nerves that extend from the CNS and act as communication lines. • Spinal nerves carry impulse to and from the spine • Cranial nerves carry impulse to and from the brain

5. Functional Classification (PNS only) • Sensory or afferent division – nerve fibers that carry impulses to the CNS from sensoryreceptors • Somatic sensory fibers come from the skin, skeletal muscles and joints • Visceral sensory fibers or visceral afferents come from the visceral (internal) organs

6. Functional Classification (PNS only) • Motor or efferent division – go from CNS to effector organs (muscles and glands) • Somatic nervous system – the voluntary nervous system. Allows us to consciously control skeletal muscles • Autonomic nervous system – the involuntary nervous system. Regulates events that need to be automatic and has two complimentary parts called Sympathetic and Parasympathetic

7. Flow Chart from Page 224

8. Cells of the Nervous System

9. Neurons • Also known as nerve cells • Highly specialized to transmit messages from one part of the body to another • The neuron has several important parts.

10. CellBody • Metabolic center of the neuron. • Contains the normal organelles except centrioles. • The neuron’s shape is the result of the rough ER (called Nissel substance) and the intermediate filaments (called neurofibrils)

11. Armlike Processes or fibers • Dendrites – many processes that carry information to the cell body • Axon – the one process that carries information away from the body. The axon arises from the conelike region called the axonhillock. It may have an occasional collateral branch (a split of the axon), but all axons branch profusely at their ends.

12. The Axon Terminals (Ends) • The end of the axon can branch hundreds or thousands of times. Each branch is known as an axonterminal • These contain hundreds of tiny vesicles that contain neurotransmitters. • When a signal reaches the end of the axon, the neurotransmitters are released across the synapticcleft or synapse (a space between the axon and the next cell)

13. Myelin • A whitish, fatty material that covers nerve fibers • It helps insulate and increase the transmission rate of nerve impulses

14. Types of Supporting Cells Known as neuroglia (“nerve glue”) or glia or glial cells

15. Astrocytes • Abundant star-shaped cells (make up almost 50% of neutral tissue) • Their numerous projections have swollen ends that cling to neurons. They then brace and anchor the neurons next to blood capillaries. • They form a living barrier between the capillaries and the neurons that keeps out harmful materials from the blood. • They also pick up extra ions and released neurotransmitters

16. Microglia • Spiderlike phagocytes that dispose of debris, including bacteria and dead brain cells

17. Ependymal Cells • Line the cavities of the brain and spinal cord. • Their beating of their cilia helps to circulate the cerebrospinal fluid. • This fluid fills the cavity and cushions the CNS

18. Oligodendrocytes • Cells that create a myelin sheath around axons inside the CNS • It has several cell extensions that wrap themselves around many different neurons.

19. Schwann cells • Cells that create a myelin sheath around axons outside the CNS • They roll around the nerve cell like a SwissCakeRoll • Most of its cytoplasm is squished to the outmost part of the cell. This is called the neurilemma • The spaces in between the Schwann cells are called the nodes of Ranvier

20. Picture Time • From Page 225 and 227 • Now on the SMART Board

21. Interesting fact • Most brain tumors are the result of glial cells forming the tumor. This is because neurons have lost their ability to divide. This is also why nerve damage can be so catastrophic for a person.

22. Cluster Terms • Nuclei – well protected clusters of cell bodies in the CNS • Ganglia – small collections of cell bodies found outside the CNS • Tracts – bundles of nerve fibers running through the CNS • Nerves – bundles of nerve fibers running in the PNS • White matter – dense collection of myelinated fibers • Gray matter – contains mostly unmyelinated fibers

23. Classification of Neurons • Functional classification • Sensory or afferent – carry messages from sensory receptors to the CNS. Have dendrite endings associated with specialized receptors • Motor or efferent – carry message to muscles or glands • Association – connect the motor and sensory neurons in neutral pathways

24. Classification of Neurons • Structural • Multipolar neuron – most common type. It has several processes branching from the neuron • Bipolar – only has two processes, axon and a dendrite. • Unipolar – have a single process emerging from the cell body. But this process doesn’t go too far before it splits into a peripheral (distal, dendrite) and central (proximal, axon) branch

25. Draw types from 231 • And physiology of the nerve assignment