Chapter 14 Nervous Tissue Neuron single cell Nerve

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Chapter 14 Nervous Tissue

Chapter 14 Nervous Tissue

 • Neuron = single cell • Nerve = bundle of cells targeting same

• Neuron = single cell • Nerve = bundle of cells targeting same muscle, organ, gland, etc. 2

Fig. 14. 1 Nervous System Organization • Structural organization • Central nervous system •

Fig. 14. 1 Nervous System Organization • Structural organization • Central nervous system • Peripheral nervous system • cranial nerves extend from brain • spinal nerves extend from spinal cord • ganglia are clusters of neuron cell bodies outside CNS Brain Spinal cord Central nervous system (CNS) Cranial nerves Peripheral Spinal nerves nervous Ganglia system (PNS)

Nervous System Organization • Functional organization • Sensory nervous system • receives sensory information

Nervous System Organization • Functional organization • Sensory nervous system • receives sensory information and sends to brain • afferent • Motor nervous system • transmits motor impulses from CNS to muscles or glands • efferent • SAME DAVE Fig. 14. 1 Brain Spinal cord Central nervous system (CNS) Cranial nerves Peripheral Spinal nerves nervous Ganglia system (PNS)

Fig. 14. 1 Nervous System Organization • Sensory nervous system divisions • Somatic sensory

Fig. 14. 1 Nervous System Organization • Sensory nervous system divisions • Somatic sensory receives info from skin, joints, skeletal muscles, eyes, ears, nose • Visceral sensory receives info from organs, glands, etc. • Changes in neuron’s environment are called stimuli

Fig. 14. 1 Nervous System Organization • Motor nervous system divisions • somatic motor

Fig. 14. 1 Nervous System Organization • Motor nervous system divisions • somatic motor division • under voluntary (conscious and unconscious) control • controls skeletal muscles • autonomic motor division • the involuntary nervous system • controls cardiac and smooth muscles, and glands

Fig. 14. 2 Functional Organization of the Nervous System Nervous system Sensory nervous system

Fig. 14. 2 Functional Organization of the Nervous System Nervous system Sensory nervous system Contains receptors Transmits information from receptors to the CNS Somatic sensory Receives sensory information from skin, fascia, joints, skeletal muscles, special senses Motor nervous system Transmits information from CNS to the rest of the body Sends motor information to effectors Visceral sensory Somatic motor Autonomic motor Receives sensory information from viscera “Voluntary” nervous system: innervates skeletal muscle “Involuntary” nervous system: innervates cardiac muscle, smooth muscle, glands

Dendritic spines Direction of nerve impulse ("input") Dendrites Cell body Axon hillock Axon Neurolemmocyte/

Dendritic spines Direction of nerve impulse ("input") Dendrites Cell body Axon hillock Axon Neurolemmocyte/ Schwann cell Axon terminals Nucleus • Axon collateral = side branch of neuron • Neurolemmocyte = Schwann cell = cell that wraps around and supports axon Direction of nerve impulse ("output") Axon collateral Neurofibril node Myelin sheath Synaptic knobs Input Output

Fig. 14. 3 Dendrites Nucleus Cell body Axon hillock Axon LM 100 x

Fig. 14. 3 Dendrites Nucleus Cell body Axon hillock Axon LM 100 x

Fig. 14. 4 Types of neurons • Unipolar have one process connecting axon to

Fig. 14. 4 Types of neurons • Unipolar have one process connecting axon to cell body • most sensory neurons in PNS Dendrites Cell body Short single process Peripheral process Central process Axon (a) Unipolar neuron

Fig. 14. 4 Types of neurons • Bipolar have two processes from cell body

Fig. 14. 4 Types of neurons • Bipolar have two processes from cell body • Present in olfactory epithelium of nose and retina of eye Cell body Dendrite Axon (b) Bipolar neuron

Fig. 14. 4 Types of neurons • Multipolar have many dendrites and one axon

Fig. 14. 4 Types of neurons • Multipolar have many dendrites and one axon • most common in human body • motor neurons that innervate muscles and glands Dendrites Cell body Axon (c) Multipolar neurons Input Output

Fig. 14. 5 • Interneurons integrate response to sensory input • communication between sensory

Fig. 14. 5 • Interneurons integrate response to sensory input • communication between sensory and motor neurons • lie entirely within CNS • multipolar structures Cell body Afferent of sensory (input) transmission neuron Posterior root ganglion Spinal cord Dendrites Sensory neuron Skin receptors Skeletal muscle Axon Interneuron Efferent (output) transmission Motor neuron

Glial cells • • AKA neuroglia occur within CNS and PNS smaller than neurons;

Glial cells • • AKA neuroglia occur within CNS and PNS smaller than neurons; capable of mitosis assist neurons with functions; protect and nourish neurons • 4 types – distinguished by size, intracellular organization, presence of specific cytoplasmic processes 14

Fig. 14. 6 Neuron Microglial cell Astrocyte Oligodendrocyte Myelinated axon Myelin sheath (cut) Capillary

Fig. 14. 6 Neuron Microglial cell Astrocyte Oligodendrocyte Myelinated axon Myelin sheath (cut) Capillary Ependymal cells Ventricle of brain

Fig. 14. 7 Astrocytes • Most abundant glial cells in CNS Perivascular feet Astrocyte

Fig. 14. 7 Astrocytes • Most abundant glial cells in CNS Perivascular feet Astrocyte • >90% of nervous tissue in some areas of brain • Lots of projection from surface • Touch capillary walls and neurons Neuron Capillary (a) Astrocyte

Fig. 14. 7 Astrocytes • Functions Neuron Perivascular feet • Help form blood-brain barrier

Fig. 14. 7 Astrocytes • Functions Neuron Perivascular feet • Help form blood-brain barrier (prevent unwanted materials from entering brain) • Regulate chemical composition of fluid within the brain • Help regulate synaptic transmission • Strengthen and organize (a) Astrocyte nervous tissue in CNS • Replace damaged neurons • Assist with neuronal development Astrocyte Capillary

Fig. 14. 7 Ependymal cells • in CNS • Line spinal cord and brain

Fig. 14. 7 Ependymal cells • in CNS • Line spinal cord and brain vesicles • Secrete cerebrospinal fluid • One side covered by cilia to create current to move fluid Central canal of Cilia spinal cord Ependymal cells Spinal cord (b) Ependymal cells

Fig. 14. 7 Microglial cells • In CNS Microglial cell • Fewest in CNS

Fig. 14. 7 Microglial cells • In CNS Microglial cell • Fewest in CNS • Small with slender branches • Travel through CNS • Replicate in response to infection • Remove debris (c) Microglial cell Neuron

Fig. 14. 7 Oligodendrocytes Oligodendrocyte • Have many processes extending from plasma membrane •

Fig. 14. 7 Oligodendrocytes Oligodendrocyte • Have many processes extending from plasma membrane • Wrap plasma membrane around neighboring axons = myelin • Provides insulation, increases speed of signals in neurons Axons (d) Oligodendrocyte Myelin sheath

Fig. 14. 7 PNS Glial Cells Posterior root ganglion Satellite cells • Surround cell

Fig. 14. 7 PNS Glial Cells Posterior root ganglion Satellite cells • Surround cell body of neurons in ganglia • Provide protection, support, nutrition Axon Cell body of Posterior root sensory neuron • Separate cell bodies from each other inside ganglia

Fig. 14. 7 PNS Glial Cells Neurolemmocytes/ Schwann cells Neurofibril nodes Axon • Similar

Fig. 14. 7 PNS Glial Cells Neurolemmocytes/ Schwann cells Neurofibril nodes Axon • Similar to oligodendrocytes of CNS • Each wraps itself around ONE axon • one axon myelinated by many Schwann cells Neurolemmocyte Myelin sheath • Provide insulation, speed signals carried by neuron

Page 422 An MRI shows a glioma (arrow). © Simon Fraser/Science Source

Page 422 An MRI shows a glioma (arrow). © Simon Fraser/Science Source

Fig. 14. 8 1. Neurolemmocyte starts to wrap around a portion of an axon.

Fig. 14. 8 1. Neurolemmocyte starts to wrap around a portion of an axon. Formation of Myelin Sheath Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display. Axon Neurolemmocyte Direction of wrapping

Fig. 14. 8 1. Neurolemmocyte starts to wrap around a portion of an axon.

Fig. 14. 8 1. Neurolemmocyte starts to wrap around a portion of an axon. Axon Neurolemmocyte 2. Neurolemmocyte cytoplasm and plasma membrane begin to form consecutive layers around axon. Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display. Direction of wrapping

Fig. 14. 8 1. Neurolemmocyte starts to wrap around a portion of an axon.

Fig. 14. 8 1. Neurolemmocyte starts to wrap around a portion of an axon. Axon Neurolemmocyte 2. Neurolemmocyte cytoplasm and plasma membrane begin to form consecutive layers around axon. 3. The overlapping inner layers of the neurolemmocyte plasma membrane form the myelin sheath. Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display. Direction of wrapping Cytoplasm of the neurolemmocyte Myelin sheath

1. Neurolemmocyte starts to wrap around a portion of an axon. 2. Neurolemmocyte cytoplasm

1. Neurolemmocyte starts to wrap around a portion of an axon. 2. Neurolemmocyte cytoplasm and plasma membrane begin to form consecutive layers around axon. 3. The overlapping inner layers of the neurolemmocyte plasma membrane form the myelin sheath. 4. Eventually, the neurolemmocyte cytoplasm and nucleus are pushed to the periphery of the cell as the myelin sheath is formed. Copyright © Mc. Graw-Hill Education. Permission required for reproduction or display. Axon Neurolemmocyte Direction of wrapping Cytoplasm of the neurolemmocyte Myelin sheath Neurolemmocyte nucleus

Oligodendrocytes Fig. 14. 9 Neurofibril node Axons Myelin sheath (a) CNS Neurolemmocytes (forming myelin

Oligodendrocytes Fig. 14. 9 Neurofibril node Axons Myelin sheath (a) CNS Neurolemmocytes (forming myelin sheath) Neuron cell body Neurofibril node Axon (b) PNS

Fig. 14. 10 Unmyelinated axons Neurolemmocyte 1 Neurolemmocyte starts to envelop multiple axons. 2

Fig. 14. 10 Unmyelinated axons Neurolemmocyte 1 Neurolemmocyte starts to envelop multiple axons. 2 The unmyelinated axons are enveloped by the neurolemmocyte, but there are no myelin sheath wraps around each axon. Unmyelinated axon Neurolemmocyte Axons Neurolemmocyte nucleus

Fig. 14. 10 Unmyelinated axons Myelin sheath Myelinated axon TEM 60, 000 x

Fig. 14. 10 Unmyelinated axons Myelin sheath Myelinated axon TEM 60, 000 x

Myelin and Signal Conduction • With myelin, signal in neuron appears to “jump” from

Myelin and Signal Conduction • With myelin, signal in neuron appears to “jump” from one node to another – called “saltatory conduction” • Signals travel faster along neuron Neurofibril nodes

Fig. 14. 11 Neuron regeneration 1 Trauma severs axon. Endoneurium Neurilemma Skeletal muscle fibers

Fig. 14. 11 Neuron regeneration 1 Trauma severs axon. Endoneurium Neurilemma Skeletal muscle fibers 2 The proximal portion of each severed axon seals off and swells. The distal portion of axon and myelin sheath disintegrate; the neurolemma survives. Endoneurium Sealed, swollen end of axon

Fig. 14. 11 Neuron regeneration Endoneurium Neurilemma 1 Trauma severs axon. Skeletal muscle fibers

Fig. 14. 11 Neuron regeneration Endoneurium Neurilemma 1 Trauma severs axon. Skeletal muscle fibers 2 The proximal portion of each severed axon seals off and swells. The distal portion of axon and myelin sheath disintegrate; the neurilemma survives. 3 Endoneurium Sealed, swollen end of axon Neurilemma and endoneurium form a regeneration tube.

Fig. 14. 11 Neuron regeneration Endoneurium Neurilemma 1 Trauma severs axon. Skeletal muscle fibers

Fig. 14. 11 Neuron regeneration Endoneurium Neurilemma 1 Trauma severs axon. Skeletal muscle fibers 2 The proximal portion of each severed axon seals off and swells. The distal portion of axon and myelin sheath disintegrate; the neurilemma survives. 3 Endoneurium Sealed, swollen end of axon Neurilemma and endoneurium form a regeneration tube. 4 Axon regenerates and remyelination occurs.

Fig. 14. 11 Neuron regeneration 1 Endoneurium Neurilemma Trauma severs axon. Skeletal muscle fibers

Fig. 14. 11 Neuron regeneration 1 Endoneurium Neurilemma Trauma severs axon. Skeletal muscle fibers 2 The proximal portion of each severed axon seals off and swells. The distal portion of axon and myelin sheath disintegrate; the neurilemma survives. 3 Neurilemma and endoneurium form a regeneration tube. 4 5 Endoneurium Sealed, swollen end of axon Axon regenerates and remyelination occurs. Innervation to effector is restored.

Page 427 Actor Christopher Reeve was a pioneer in challenging previous conceptions about neuron

Page 427 Actor Christopher Reeve was a pioneer in challenging previous conceptions about neuron regeneration. © Kenneth Lambert/AP Photo

Rob Smets Bullfighter, Professional Bull Riding Broke his neck 3 times, suffered same break

Rob Smets Bullfighter, Professional Bull Riding Broke his neck 3 times, suffered same break as Christopher Reeve. Sustained only limited mobility in his neck 37

Fig. 14. 12 Axon Myelin sheath Endoneurium Fascicle Perineurium Epineurium Blood vessels

Fig. 14. 12 Axon Myelin sheath Endoneurium Fascicle Perineurium Epineurium Blood vessels

Fig. 14. 12 Perineurium Fascicle Myelin sheath Axon Nucleus Endoneurium Neurofibril node Axon LM

Fig. 14. 12 Perineurium Fascicle Myelin sheath Axon Nucleus Endoneurium Neurofibril node Axon LM 550 x Myelin sheath Blood vessels SEM 450 x

Fig. 14 Electrical synapse Smooth muscle cells Presynaptic cell Gap junction Local current ++

Fig. 14 Electrical synapse Smooth muscle cells Presynaptic cell Gap junction Local current ++ + + Positively charged ions Plasma membrane (a) Electrical synapse Postsynaptic cell ++ ++ ++ Connexons Inner surface of plasma membrane

Fig. 14 Nerve impulse Axon Synaptic vesicles containing acetylcholine (ACh) Calcium (Ca 2+) ions

Fig. 14 Nerve impulse Axon Synaptic vesicles containing acetylcholine (ACh) Calcium (Ca 2+) ions Voltage-regulated calcium (Ca 2+) channel Synaptic cleft Acetylcholine binds to receptor protein, causing ion gates to open Presynaptic neuron Acetylcholine Sodium (Na+) ions Postsynaptic neuron Postsynaptic membrane Receptor protein

Fig. 14. 15 Input Output Input Input Output (a) Converging circuit Outputs (b) Diverging

Fig. 14. 15 Input Output Input Input Output (a) Converging circuit Outputs (b) Diverging circuit Output (c) Reverberating (d) Parallel-after-discharge circuit

Page 431 (a) Individuals with neurodegenerative diseases must overcome physical challenges to carry on

Page 431 (a) Individuals with neurodegenerative diseases must overcome physical challenges to carry on the activities of daily life. (a) Amyotrophic lateral sclerosis (scientist and writer Stephen Hawking). (b) Multiple sclerosis. (b)