Presentation is loading. Please wait.

Presentation is loading. Please wait.

Copyright © 2010 Pearson Education, Inc. Chapter 11 Fundamentals of the Nervous System and Nervous Tissue Anatomy and Physiology I(2) Mr. Scott.

Similar presentations


Presentation on theme: "Copyright © 2010 Pearson Education, Inc. Chapter 11 Fundamentals of the Nervous System and Nervous Tissue Anatomy and Physiology I(2) Mr. Scott."— Presentation transcript:

1 Copyright © 2010 Pearson Education, Inc. Chapter 11 Fundamentals of the Nervous System and Nervous Tissue Anatomy and Physiology I(2) Mr. Scott

2 Copyright © 2010 Pearson Education, Inc. Functions of the Nervous System 1.Sensory input Information gathered by sensory receptors about internal and external changes 2.Integration Interpretation of sensory input 3.Motor output Activation of effector organs (muscles and glands) produces a response

3 Copyright © 2010 Pearson Education, Inc. Functions of the Nervous System

4 Copyright © 2010 Pearson Education, Inc. Divisions of the Nervous System Central nervous system (CNS) Brain and spinal cord Integration and command center Peripheral nervous system (PNS) Paired spinal and cranial nerves carry messages to and from the CNS

5 Copyright © 2010 Pearson Education, Inc. Peripheral Nervous System (PNS) Two functional divisions 1.Sensory (afferent) division Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints Visceral afferent fibers—convey impulses from visceral organs 2.Motor (efferent) division Transmits impulses from the CNS to effector organs

6 Copyright © 2010 Pearson Education, Inc. Motor Division of PNS 1.Somatic (voluntary) nervous system Conscious control of skeletal muscles 2.Autonomic (involuntary) nervous system (ANS) Visceral motor nerve fibers Regulates smooth muscle, cardiac muscle, and glands Two functional subdivisions Sympathetic Parasympathetic

7 Copyright © 2010 Pearson Education, Inc. Histology of Nervous Tissue Two principal cell types 1.Neurons—excitable cells that transmit electrical signals

8 Copyright © 2010 Pearson Education, Inc. Histology of Nervous Tissue 2.Neuroglia (glial cells)—supporting cells: Astrocytes (CNS) Microglia (CNS) Ependymal cells (CNS) Oligodendrocytes (CNS) Satellite cells (PNS) Schwann cells (PNS)

9 Copyright © 2010 Pearson Education, Inc. Astrocytes Most abundant, versatile, and highly branched glial cells Cling to neurons, synaptic endings, and capillaries Support and brace neurons Capillary Neuron Astrocyte

10 Copyright © 2010 Pearson Education, Inc. Microglia Small, ovoid cells with thorny processes Migrate toward injured neurons Phagocytize microorganisms and neuronal debris

11 Copyright © 2010 Pearson Education, Inc. Ependymal Cells Range in shape from squamous to columnar May be ciliated Line the central cavities of the brain and spinal column Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities

12 Copyright © 2010 Pearson Education, Inc. Figure 11.3c Brain or spinal cord tissue Ependymal cells Fluid-filled cavity (c) Ependymal cells line cerebrospinal fluid-filled cavities.

13 Copyright © 2010 Pearson Education, Inc. Oligodendrocytes Branched cells Processes wrap CNS nerve fibers, forming insulating myelin sheaths

14 Copyright © 2010 Pearson Education, Inc. Satellite Cells and Schwann Cells Satellite cells Surround neuron cell bodies in the PNS Schwann cells (neurolemmocytes) Surround peripheral nerve fibers and form myelin sheaths Vital to regeneration of damaged peripheral nerve fibers

15 Copyright © 2010 Pearson Education, Inc. Neurons (Nerve Cells) Special characteristics: Long-lived (  100 years or more) Amitotic—with few exceptions High metabolic rate—depends on continuous supply of oxygen and glucose Plasma membrane functions in: Electrical signaling Cell-to-cell interactions during development

16 Copyright © 2010 Pearson Education, Inc. Cell Body (Perikaryon or Soma) Spherical nucleus with nucleolus Well-developed Golgi apparatus Rough ER called Nissl bodies (chromatophilic substance)

17 Copyright © 2010 Pearson Education, Inc. Cell Body (Perikaryon or Soma) Network of neurofibrils (neurofilaments) Axon hillock—cone-shaped area from which axon arises Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS

18 Copyright © 2010 Pearson Education, Inc. Dendrites Short, tapering, and diffusely branched Receptive (input) region of a neuron Convey electrical signals toward the cell body as graded potentials

19 Copyright © 2010 Pearson Education, Inc. The Axon One axon per cell arising from the axon hillock Long axons (nerve fibers) Occasional branches (axon collaterals) Numerous terminal branches (telodendria) Knoblike axon terminals (synaptic knobs or boutons) Secretory region of neuron Release neurotransmitters to excite or inhibit other cells Telodendria Axon terminals

20 Copyright © 2010 Pearson Education, Inc. Axons: Function Conducting region of a neuron Generates and transmits nerve impulses (action potentials) away from the cell body Molecules and organelles are moved along axons by motor molecules in two directions: Anterograde—toward axonal terminal Examples: mitochondria, membrane components, enzymes Retrograde—toward the cell body Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins

21 Copyright © 2010 Pearson Education, Inc. Figure 11.4b Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Nucleus Nissl bodies Axon (impulse generating and conducting region) Axon hillock Neurilemma Terminal branches Node of Ranvier Impulse direction Schwann cell (one inter- node) Axon terminals (secretory region) (b)

22 Copyright © 2010 Pearson Education, Inc. Myelin Sheath Segmented sheath around most long or large- diameter axons It functions to: Protect and electrically insulate the axon Increase speed of nerve impulse transmission

23 Copyright © 2010 Pearson Education, Inc. Figure 11.5a (a) Myelination of a nerve fiber (axon) Schwann cell cytoplasm Axon Neurilemma Myelin sheath Schwann cell nucleus Schwann cell plasma membrane A Schwann cell envelopes an axon. The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath.

24 Copyright © 2010 Pearson Education, Inc. Unmyelinated Axons Thin nerve fibers are unmyelinated One Schwann cell may incompletely enclose 15 or more unmyelinated axons

25 Copyright © 2010 Pearson Education, Inc. Myelin Sheaths in the CNS Formed by processes of oligodendrocytes, not the whole cells Nodes of Ranvier are present No neurilemma Thinnest fibers are unmyelinated

26 Copyright © 2010 Pearson Education, Inc. White Matter and Gray Matter White matter Dense collections of myelinated fibers Gray matter Mostly neuron cell bodies and unmyelinated fibers

27 Copyright © 2010 Pearson Education, Inc. Functional Classification of Neurons Three types: 1.Sensory (afferent) Transmit impulses from sensory receptors toward the CNS 2.Motor (efferent) Carry impulses from the CNS to effectors 3.Interneurons (association neurons) Shuttle signals through CNS pathways; most are entirely within the CNS

28 Copyright © 2010 Pearson Education, Inc. Resting Membrane Potential Differences in ionic makeup Inside the neuron has lower concentration of Na + and Cl – than outside Inside has higher concentration of K + and negatively charged proteins (A – ) than outside

29 Copyright © 2010 Pearson Education, Inc. Resting Membrane Potential Negative interior of the cell is due to much greater diffusion of K + out of the cell than Na + diffusion into the cell Sodium-potassium pump stabilizes the resting membrane potential by maintaining the concentration gradients for Na + and K +

30 Copyright © 2010 Pearson Education, Inc. Membrane Potentials That Act as Signals Membrane potential changes when: Ion concentrations on two sides change Permeability of membrane to ions changes Changes in membrane potential are signals used to receive, integrate and send information

31 Copyright © 2010 Pearson Education, Inc. Changes in Membrane Potential Depolarization A reduction in membrane potential (toward zero) Inside of the membrane becomes less negative than the resting potential Increases the probability of producing a nerve impulse Hyperpolarization An increase in membrane potential (away from zero) Inside of the membrane becomes more negative than the resting potential Reduces the probability of producing a nerve impulse

32 Copyright © 2010 Pearson Education, Inc. Membrane Potentials That Act as Signals Two types of signals Graded potentials Incoming short-distance signals Action potentials Long-distance signals of axons

33 Copyright © 2010 Pearson Education, Inc. Graded Potentials Occur when a stimulus causes gated ion channels to open E.g., receptor potentials, generator potentials, postsynaptic potentials Magnitude varies directly (graded) with stimulus strength Decrease in magnitude with distance as ions flow and diffuse through leakage channels Short-distance signals

34 Copyright © 2010 Pearson Education, Inc. Action Potential (AP) Brief reversal of membrane potential with a total amplitude of ~100 mV Occurs in muscle cells and axons of neurons Does NOT decrease in magnitude over distance Principal means of long-distance neural communication

35 Copyright © 2010 Pearson Education, Inc. Graded Potentials vs. Action Potentials Graded Potential Chemically gated ion channels Stimulus is related to the strength Die out with increasing distance Due to leakage of the charge Short distance travel Action Potential Voltage gated ion channels Stimulus is consistent Do not decrease with distance Long distance travel Graded Potentials can cause Action Potentials

36 Copyright © 2010 Pearson Education, Inc. Action potential Resting state Depolarization Repolarization Hyperpolarization The big picture Time (ms) Threshold Membrane potential (mV) Figure (1 of 5)

37 Copyright © 2010 Pearson Education, Inc. Threshold At threshold: Membrane is depolarized by 15 to 20 mV Na + permeability increases Na influx exceeds K + efflux The positive feedback cycle begins Subthreshold stimulus— weak local depolarization that does not reach threshold Threshold stimulus—strong enough to push the membrane potential toward and beyond threshold AP is an all-or-none phenomenon—action potentials either happen completely, or not at all

38 Copyright © 2010 Pearson Education, Inc. Coding for Stimulus Intensity Action potentials do not vary and are independent of stimulus intensity How does the CNS tell the difference between a weak stimulus and a strong one? Strong stimuli can generate action potentials more often than weaker stimuli CNS determines stimulus intensity by the frequency of impulses Action potentials Stimulus

39 Copyright © 2010 Pearson Education, Inc. Conduction Velocity Conduction velocities of neurons vary widely Effect of axon diameter Larger diameter fibers = less resistance to local current flow = faster impulse conduction Effect of myelination Continuous conduction in unmyelinated axons is slower than saltatory (jumping) conduction in myelinated axons

40 Copyright © 2010 Pearson Education, Inc. Conduction Velocity Effects of myelination Myelin sheaths insulate and prevent leakage of charge Saltatory conduction in myelinated axons is about 30 times faster Voltage-gated Na + channels are located at the nodes APs appear to jump rapidly from node to node

41 Copyright © 2010 Pearson Education, Inc. Nerve Fiber Classification Group A fibers Large diameter, myelinated somatic sensory and motor fibers Group B fibers Intermediate diameter, lightly myelinated ANS fibers Group C fibers Smallest diameter, unmyelinated ANS fibers

42 Copyright © 2010 Pearson Education, Inc. The Synapse A junction that mediates information transfer from one neuron: To another neuron, or To an effector cell Presynaptic neuron—conducts impulses toward the synapse Postsynaptic neuron—transmits impulses away from the synapse

43 Copyright © 2010 Pearson Education, Inc. Types of Synapses Axodendritic Between the axon of one neuron and the dendrite of another Axosomatic Between the axon of one neuron and the soma of another

44 Copyright © 2010 Pearson Education, Inc. Electrical Synapses Less common than chemical synapses Neurons are electrically coupled (joined by gap junctions) Communication is very rapid, and may be unidirectional or bidirectional Are important in: Embryonic nervous tissue Some brain regions

45 Copyright © 2010 Pearson Education, Inc. Chemical Synapses Specialized for the release and reception of neurotransmitters Typically composed of two parts Axon terminal of the presynaptic neuron Receptor region on the postsynaptic neuron

46 Copyright © 2010 Pearson Education, Inc. Synaptic Cleft Fluid-filled space separating the presynaptic and postsynaptic neurons Prevents nerve impulses from directly passing from one neuron to the next

47 Copyright © 2010 Pearson Education, Inc. Synaptic Cleft Transmission across the synaptic cleft: Is a chemical event (as opposed to an electrical one) Involves release, diffusion, and binding of neurotransmitters Ensures unidirectional communication between neurons

48 Copyright © 2010 Pearson Education, Inc. Termination of Neurotransmitter Effects Within a few milliseconds, the neurotransmitter effect is terminated Degradation by enzymes Reuptake by astrocytes or axon terminal Diffusion away from the synaptic cleft

49 Copyright © 2010 Pearson Education, Inc. Synaptic Delay Neurotransmitter must be released, diffuse across the synapse, and bind to receptors Synaptic delay—time needed to do this (0.3– 5.0 ms) Synaptic delay is the rate-limiting step of neural transmission

50 Copyright © 2010 Pearson Education, Inc. Postsynaptic Potentials Graded potentials Strength determined by: Amount of neurotransmitter released Time the neurotransmitter is in the area Types of postsynaptic potentials 1.EPSP—excitatory postsynaptic potentials 2.IPSP—inhibitory postsynaptic potentials

51 Copyright © 2010 Pearson Education, Inc. Excitatory Synapses and EPSPs Neurotransmitter binds to and opens chemically gated channels that allow simultaneous flow of Na + and K + in opposite directions Short distance signaling Moves the polarity towards AP

52 Copyright © 2010 Pearson Education, Inc. Inhibitory Synapses and IPSPs Neurotransmitter binds to and opens channels for K + or Cl – Causes a hyperpolarization (the inner surface of membrane becomes more negative) Reduces the postsynaptic neuron’s ability to produce an AP

53 Copyright © 2010 Pearson Education, Inc. Neurotransmitters Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies 50 or more neurotransmitters have been identified Classified by chemical structure and by function

54 Copyright © 2010 Pearson Education, Inc. Chemical Classes of Neurotransmitters Acetylcholine (Ach) Released at neuromuscular junctions and some ANS neurons Synthesized by enzyme choline acetyltransferase Degraded by the enzyme acetylcholinesterase (AChE)

55 Copyright © 2010 Pearson Education, Inc. Chemical Classes of Neurotransmitters Biogenic amines include: Catecholamines Dopamine, norepinephrine (NE), and epinephrine Indolamines Serotonin (sleep) and histamine (wakeful, appetite, inflammation) Broadly distributed in the brain Play roles in emotional behaviors and the biological clock

56 Copyright © 2010 Pearson Education, Inc. Functional Classification of Neurotransmitters Neurotransmitter effects may be excitatory (depolarizing) and/or inhibitory (hyperpolarizing) Determined by the receptor type of the postsynaptic neuron GABA and glycine are usually inhibitory Glutamate is usually excitatory Acetylcholine Excitatory at neuromuscular junctions in skeletal muscle Inhibitory in cardiac muscle


Download ppt "Copyright © 2010 Pearson Education, Inc. Chapter 11 Fundamentals of the Nervous System and Nervous Tissue Anatomy and Physiology I(2) Mr. Scott."

Similar presentations


Ads by Google