Nervous System

1. Nervous System

2. Master controlling and communicating system of the body. • Electrical impulses are rapid, specific and cause almost immediate response.

3. Three overlapping functions: • Uses millions of sensory receptors to monitor changes occurring both inside and outside the body. (changes are stimuli/ gathered info is sensory input) • Processes/interprets sensory input and make decisions about what should be done (integration) • Effects a response by activating muscles or glands (motor output)

4. Divided in terms of structures (structural classification) or • In terms of activities (functional classification)

5. Structural Classifiction • Two subdivisions – central nervous systems (CNS) and peripheral nervous systems (PNS). • CNS – brain and spinal cord in dorsal body cavity • integrating and command centers of the nervous system. • Interpret incoming sensory information • Issues instructions based on past experience and current conditions.

6. PNS – part of the nervous system outside the CNS that serve as communication lines. • Nerves that extend from the brain and spinal cord • Spinal nerves carry impulses to and from the spinal cord. • Cranial nerves carry impulses to and from the brain

7. CNS

8. PNS

9. Functional classification • Two principle divisions – sensory (afferent) division and motor (efferent) divisions

10. Sensory • Keeps the CNS constantly informed of events going on both inside and outside the body • Nerve fibers convey impulses to the CNS from sensory receptors located in various parts of the body. • Somatic sensory – delivers impulses from the skin, skeletal muscles, and joints. • Visceral sensory – transmits impulses from visceral organs.

11. Motor • Carries impulses from the CNS to effector organs, muslces, and glands. • Impulses activate muscles/glands to cause their motor response. • Has two subdivisions • Somatic nervous system – voluntarily control our skeletal muscles. • Autonomic nervous system – regulates involuntary events ( smooth/cardiac muscles, glands) (two systems, sympathetic and parasympathetic)

12. Draw picture of CNS and PNS and explain both. • Then copy chart of nervous system onto back of paper and explain all parts.

13. Nervous tissue is made up of two principle types of cells • Supporting cells • neurons

14. Supporting Cells • Collectively called neuroglia • Includes many types of cells for support, insulation, and protection • Not able to transmit nerve impulses • Never lose their ability to divide

15. astrocytes • Star-shaped, abundant, nearly ½ the neural tissue • Cling to neurons • Braces/anchors neurons to nutrient supply lines (blood capillaries) • Forms a living barrier between capillaries and nuerons • Protect the neurons from harmful substances • Help control the chemical environment in the brain (picks up excess ions and recaptures released neurotransmitters)

17. Microglia • Spiderlike • Phagocytic on dead brain cells, bacteria, etc. • Ependymal cells • Line the cavities of the brain and spinal cord • Beating cilia helps to circulate the cerebrospinal fluid

19. Oligodendrocytes • Wrap flat extensions tightly aroudn the nerve fibers • Produces fatty insulating coverings called myelin sheaths • Two major varieties in the PNS – Schwann cells and satellite cells • Schwann cells form myelin sheaths around nerve fibers that extend from the CNSSatellite cells act as protective/ cushioning cells

21. Doodle Definitions • Draw a picture and write a sentence for each of the members of the neuroglia family: astrocyte, ependymal, microglia, oligodendrocyte, schwann cell, and satellite cell. • The picture should be anything that can help you remember what each thing does or looks like. For example microglia could be a spider.

22. Neurons • Highly specialized to transmit messages (nerve impuleses) from one part of the body to another. • Many common features • Neurons never actually tough other neurons • Cell body that contains the nucleus and is the metabolic center of the cell. ( if it is damaged the cell dies and is not replaced)

23. 1+ slender processes (fibers) extending from cell body ( vary in length from microscopic to four feet long – lumbar region of the spine to the big toe) • Processes that conduct electrical currents toward the cell body are dendrites (depending on type, a neuron may have hundreds of dendrites) • Processes that generate nerve impulses and conduct them away from the cell body are axons (only one axon) (some have a collateral branch along its length) (all branch to form hundreds to thousands of axonal terminals)

24. Tiny vesicles store neurotransmitters within each axonal terminal. • Axonal terminal is seperated from the next neuron by a tiny gap (synaptic cleft) • When impulses reach the axonal terminals they stimulate the release of neurotransmitters.

25. Most long nerve fibers are covered with a whitish, fatty material (myelin) • Protects and insulates the fibers • Increases the transmission rate of nerve impulses • Formed by many individual cells (oligodendrocytes or Schwann) • Gaps or indentations at regular intervals (nodes of Ranvier)

26. Bundles of nerve fibers (neuron processes) running through the CNS are tracts, in the PNS they are called nerves. • White matter are myelinated processes and gray matter is unmyelinated.

28. Classification • Functional classification • Groups neurons according to the direction the nerve impulse is traveling relative to the CNS. • Sensory (afferent neurons) • Carry impulses from sensory receptors (internal organs or the skin) to the CNS area • Dendrite endings associated with specialized receptors that are activated by specific changes

29. Skin ( cutaneous sense organs) • Pain receptors (bare dendrite endings) are the least specialized. • Most numerous (warning us of some type of body damage is occurring) • Muscles and tendons (proprioceptors) • Detect the stretch/tension in skeletal muscles, tendons and joints. • Information sent to the brain for proper adjustments to balance and posture.

30. Motor (efferent) neurons • Carry impulses from the CNS to the viscera and/or muscles and glands • Cell bodies always located in the CNS • Interneurons (association neurons) • Connect the motor and sensory neurons in a neural pathways. • Cell bodies are always located in the CNS

31. Structural classification • Based on number of processes extending from the cell body. • Several processes – multipolar neuron • All motor and association neurons • Most common structural type • Two processes (axon and a dendrite) – bipolar neurons. • Rare in adults – only in the eye and ear where they act as sensory receptor cells

32. Single process emerging from cell body – unipolar neurons. • Very short and divides almost immediatley into proximal (central) and distal (peripheral) fibers • Only the small branches at the end of the peripheral process are dendrites. • Remainder of peripheral processes and the central process function as axons. (in this case, the axon conducts impulses both toward and away from the cell body)

33. Class work and Homework • Class work: Draw, label and explain a neuron and its interaction with another neuron. • Home work: • Compare • 1: sensory, motor and interneurons • 2: uni, bi and multipolar neurons

34. Functional Anatomy of the Spinal Cord • Cylindrical, 17 inches long, continuation of brain stem from foramen magnum to L1 or L2. • Two-way conduction pathway to and from the brain. • A major reflex center. • Cushioned and protected by meninges • Meningal coverings do not end at L2 • Extend well beyond the end of the spinal cord

35. Functional Anatomy of the Brain • 4 major regions – cerebral hemispheres, diencephalon, brain stem, cerebellum

37. Cerebral hemispheres • Most superior part of the brain • Obscure most of the brain stem • Elevated ridges of tissue called gyriseperated by shallow grooves called sulci • Deeper grooves called fissures which separate large regions • Other fissures divide each cerebral hemisphere into a number of lobes (named for cranial bones over them)

39. Diencephalon • Interbrain • Sits anterior to the brain stem • Enclosed by the cerebral hemispheres • Major structures are thalamus, hypothalamus, epithalamus, • Hypothalamus • Plays a role in the regulation of body temperature, water balance, and metabolism. • Center for many drives and emotions (thirst, appetite, sex, pain, and pleasure centers) • Epithalamus • Forms cerebrospinal fluid

41. Brain stem • Control vital activities (breathing and blood pressure) • Midbrain, pons and medulla oblongata • Midbrain – reflex centers involved with vision and hearing. • Pons – control breathing • Medulla oblongata – regulate vital visceral activities (control heart rate, blood pressure, breathing, swallowing, vomiting, etc.)

42. Cerebellum • Precise timing for skeletal muscle activity • Controls balance so movements are smooth and coordinated.

43. Activity • Draw, label and explain the parts of the brain we have covered: 4 major regions – cerebral hemispheres, diencephalon (hypothalamus, epithalamus), brain stem (midbrain, pons, and medulla oblongata), cerebellum

44. Protection of the Central Nervous System • Nervous tissue is very soft and delicate • Irreplaceable neurons can be injured by slightest pressure • Protected by bone, membranes, cushion, blood-brain barrier

45. Bone- skull and vertebral column • Meninges – connective tissue membranes • Outermost layer – durra mater • Double-layered membrane surrounding the brain • One layer attached to the inner surface of the skull • Other layer forms the outermost covering of the brain (becomes spinal cord durra mater) • Middle layer – web-like arachnoid mater • Filled with cerebrospinal fluid • Inner most layer – pia mater • Clings tightly/follows folds of the surface of the brain and spinal cord

47. Cerebrospinal fluid – watery cushion • Similar to plasma • Continually formed from blood by the choroid plexus (clusters of capillaries hanging from the “roof” in each of the brain’s ventricles) • Protects the fragile nervous tissue from blows/trauma • continually moving (thru sc, subarachnoid, cerebral hemispheres, diencephalon, midbrain, pons, medulla) • Forms and drains at a constant rate to maintain normal pressure and volume (solutes include glucose, proteins, NaCl)

48. Blood Brain barrier • Neurons kept separated from blood-borne substances • Barrier made of least permeable capillaries in the body • Only water, glucose, and essential amino acids (water-soluble substances) pass easily • Nonessential amino acids and potassium ions are prevented and actively soluble molecules diffuse easily (why blood-borne alcohol, nicotine, and anesthetics affect the brain)

50. Autonomic nervous system • Also called the involuntary nervous system • Motor subdivisions of the PNS • Controls body activities automatically • Regulate cardiac muscle smooth muscles and glands • Two divisions – the sympathetic and parasympathetic • Both serve the same organs but cause essentially opposite effects • Counterbalancing each others activities to keep body systems running smoothly