Nervous System

1. Nervous System Objectives: Identify structures of the nervous system. Explain differences in the function of the peripheral nervous system and the central nervous system.

2. D. Nervous Tissue • Nervous tissue is: • found in the brain, spinal cord, and nerves. • made up of: • Neurons: nerve cells (bundles of axons) • Neuroglial cells: helper cells • “glia” = glue • Support and bind components of nervous tissue to each other and to blood vessels • Function similarly to connective tissue in other organ systems

3. Parts of a Neuron

4. Nervous System • Organs of this system are divided into 2 groups: • Central Nervous System (CNS) • Brain • Spinal cord • Peripheral Nervous System (PNS) • Composed of the nerves (peripheral nerves) that connect the CNS to other body parts • Functions of the nervous system: • Sensory • Integrative • Motor

5. 1. Sensory Function • Sensory receptors at the ends of peripheral neurons: • Gather info by detecting changes inside and outside the body. • Inside: temperature and oxygen concentration • Outside: light and sound intensities • Convert info into nerve impulses (electrochemical changes) which are transmitted along peripheral nerves to the CNS

6. 2. Integrative Function • Nerve impulses are integrated (brought together) in the CNS. • Allows us to make conscious or subconscious decisions.

7. 3. Motor Function • Peripheral nerves carry impulses from the CNS to effectors (responsive structures). • Effectors are NOT part of the nervous system, but include muscles and glands.

8. Motor Function • Motor functions can be divided into 2 groups: • Somatic nervous system • Consciously controlled (voluntary) • Controls skeletal muscle • Autonomic nervous system: • Involuntary • Includes heart, smooth muscle, and various glands

9. Nervous System Function Recap • Detects changes inside and outside the body, • Makes decisions based on the information received, and • Stimulates muscles or glands to respond. • What is the purpose of this process?????

10. Neuroglial Cells • Functions: • Fill spaces • Provide structural frameworks • Produce myelin • Carry on phagocytosis • Vary from CNS to PNS • Table: Type of Cell, Location, Function, Other specific info

11. CNS Neuroglial Cells • Greatly outnumber neurons in the CNS (think worker ants vs. Queen ant) • Microglial cells • Scattered throughout CNS • Support neurons and phagocytize bacterial cells and cellular debris • Oligodendrocytes • Occur in rows along nerve fibers • Provide layers of myelin around axons within brain and spinal cord

12. CNS Neuroglial Cells, continued…. • Astrocytes • Found between neurons and blood vessels • Provide structural support, help regulate nutrients and ions in tissues • Form scar tissue to fill spaces after CNS injuries • Ependymal cells • Form epithelial-like membrane in parts of the brain (choroid plexuses) • Form inner linings that enclose ventricles in the brain and central canal in the spinal cord

13. CNS Neuroglial Cells

14. PNS Neuroglial cells • Schwann cells: form myelin sheath around axons

15. Neurons • Vary in size and structure, but have common features: • Cell Body • Dendrites • Axon • Mature neurons do not divide, but neural stem cells can divide and form neurons or neuroglial cells.

16. 1. Cell Body • Contains normal cellular structures (golgi apparatus, mitochondria, cytoplasm, cell membrane, etc.) • Neurofibrils – fine threads that extend into the axon • Nissl bodies (chromatophilic substances) • Membranous sacs in the cytoplasm • Similar to rough ER • Ribosomes on Nissl bodies synthesize ______

17. 2. Dendrites • Usually short and highly branched (dendr = ?) • The main receptive surfaces for receiving communication from axons of other neurons

18. 3. Axons • Arise from a slight elevation of the cell body, called the axonal hillock. • Conduct nerve impulses away from the cell body • Contains many mitochondria, microtubules, and neurofibrils • Originates as a single structure, but may have branches, especially at the end to interact with receptive surfaces of other cells

19. PNS Axons • Enclosed in myelin sheaths composed of many Schwann cells • Myelin is a lipoprotein. • Neurilemma sheath surrounds the myelin sheath • Nodes ofRanvier – narrow gaps in the myelin sheath between the Schwann cells

20. Classification of Neurons • Classification based on Structural differences: • Bipolar neurons • Unipolar neurons • Multipolar neurons • Classification based on Functional differences: • Sensory neurons (afferent neurons) • Interneurons (association or internuncial neurons) • Motor neurons (efferent neurons)

21. Structural Differences • Sketch the neurons below. Notes on the next 3 slides:

22. Structural Differences, cont….. • Bipolar: • 2 processes • Axon • Dendrite • Found in specialized parts of the eyes, nose, and ears

23. Structural Differences, cont….. • Unipolar: • 1 process divides into 2 branches, which function as a single axon • 1 branch (peripheral process) associated with dendrites • Other branch (central process) enters brain or spinal cord

24. Structural Differences, cont….. • Multipolar: • Many processes arising from cell body: • 1 axon • Many dendrites • Most neurons whose cell bodies lie in the brain or spinal cord are multipolar. • Direction of impulse is ALWAYS from dendrites to axon.

25. Functional Differences • Sensory (afferent) neurons • From peripheral body parts to the brain or spinal cord • Have specialized receptor ends at the tips of their dendrites OR • Dendrites closely associated with receptor cells in the skin or sensory organs. • Most are unipolar, but some are bipolar.

26. Functional Differences, cont….. • Interneurons (association or internuncial neurons) • Lie entirely in the brain or spinal cord • Multipolar and link other neurons • Transmit impulses from one part of the brain or spinal cord to another • Motor (efferent) neurons • Multipolar • Carry nerve impulses from brain or spinal cord to effectors • Stimulate muscles or glands

27. Copy Diagram on Whiteboard • Identify the direction of nerve impulse. • How can you tell the direction? • Label all dendrites, cell bodies, and axons. • Label each nerve as either sensory neuron, interneuron, or motor neuron. • Color code the CNS and PNS portions of the pathway.

28. Reflex Arcs • Nerve impulse pathways that are responsible for involuntary actions • Look like the pathway you drew and labeled: • Receptor to • Sensory neuron to • (optional step) Interneurons in the CNS (a reflex center) to • Motor neurons to • Effector

29. Reflexes • Automatic subconscious responses to changes within or outside the body: • Maintain homoestasis: blood pressure, heart rate, respirations, digestion, temperature • Automatic actions: swallowing, coughing, sneezing, vomiting

30. 2 Examples of Types of Reflexes (?) • Knee-jerk reflex (patellar tendon reflex) • Employs only 2 neurons: sensory neuron communicating directly with a motor neuron • Withdrawal reflex: • A response to painful stimuli • Sensory neuron takes impulse to interneurons in the spinal cord reflex center, where it is transmitted to motor neurons. • Other interneurons carry impulses to the brain for processing of the experience and pain.

31. Knee-jerk Reflex (Fig. 9.16)

32. Withdrawal Reflex (Fig. 9.17)

33. CNS Structures • Meninges • Spinal cord • Brain

34. Meninges • Membranes between the bone and soft tissues of the nervous system • Function: ? • 3 layers: Orange analogy • Dura mater • Arachnoid mater • Pia mater • Meningitis (?)

36. Dura Mater • Outermost layer • Contains many blood vessels and nerves • Attaches to the inside of the cranial cavity and forms the internal periosteum (???) of the surrounding skull bones • Forms partitions between lobes of the brain • Continues into vertebral canal • Terminates as a blind sac below the end of the spinal cord

37. Arachnoid Mater • Thin, weblike membrane located between dura and pia maters • Lacks blood vessels • Spreads over brain and spinal cord, but does not dip into grooves and depressions on their surfaces

38. Pia Mater • Cerebrospinal fluid (CSF) – clear, watery fluid that fills space between arachnoid and pia maters • Pia mater – very thin and contains many nerves and blood vessels that nourish cells of the brain and spinal cord • Hugs surfaces and follows all irregular contours of brain and spinal cord • Subdural hematoma (?)

40. Review • List and describe the 3 layers of the meninges.

41. Spinal Cord • Slender nerve column that passes downward from the brain into the vertebral canal • Starts at the foramen magnum and ends between first and second lumbar vertebrae

42. Structure of Spinal Cord • 31 segments that each give rise to a pair of spinal nerves

43. Functions of the Spinal Cord • What do you think would be the functions of the spinal cord? • Conducting nerve impulses • Serving as a center for spinal reflexes • Nerve tracts (major nerve pathways) of the spinal cord are made up of axons that provide 2-way communication between brain and body parts: • Ascending tracts - sensory information to brain • Descending tracts – motor impulses from brain

44. Brain • About 100 billion multipolar neurons • 3 major portions: • Cerebrum • Largest part • Contains nerve centers associated with sensory and motor functions • Provides higher mental functions, including memory and reasoning • Cerebellum - includes centers that coordinate voluntary movements • Brain stem – • Connects parts of the nervous system (???) • Regulates some visceral (???) activities

45. Cerebrum • Cerebral hemispheres: 2 large, mirror-image halves • Corpus callosum: deep bridge of nerve fibers that connect the cerebral hemispheres • Surface of the cerebrum has: • Ridges: convolutions • Grooves: • Shallow grooves: sulci (sulcus, singular)– separates lobes • Deep Grooves: fissures • Longitudinal fissure – separates cerebral hemispheres • Transverse fissure-separates cerebrum and cerebellum

46. Locations and Boundaries of the Lobes of the Cerebral Hemisphere Use textbook, pp.227-228 to complete the table below.

47. Functional Regions of the Cerebrum Complete graphic organizer. Color-code and label diagram of association areas of the brain to correspond to your graphic organizer.

48. Hemisphere Dominance • Right-Left Brain Test • The dominant hemisphere controls the ability to use and understand language. • Which hemisphere do you think is dominant in most of the population? • Broca’s area (???) in the dominant hemisphere controls the muscles used in speaking.

49. Hemisphere Functions

50. Corpus Callosum (???) and Hemisphere Dominance • What is it? Nerve fibers connecting the 2 cerebral hemispheres • Functions: • Allows the dominant hemisphere to control the motor cortex of the non-dominant hemisphere. • Transfers info received by the non-dominant hemisphere to the dominant hemisphere for use in decision-making.