Nervous System Honors Biology Powerpoint #3 Unit 8 – Chapter 35 pg The Senses Activities

Function of Nervous System:  Coordinates the body’s response to changes in its internal and external environments.

Overview of the Nervous System  Nervous system carries out task in 3 basic steps: 1.Sense organs receive information about changes in the body and the external environment, and transmit coded messages to the spinal cord and the brain 2.Brain and spinal cord process this information, relate it to past experiences, and determine what response is appropriate to the circumstances 3.Brain and spinal cord issue commands to muscles and gland cells to carry out such a response 12-3

2 subdivisions of the Nervous System: 1.Central Nervous System (CNS)  Brain & Spinal chord 2.Peripheral Nervous system (PNS)  All the nervous system except the brain and spinal cord; made of nerves and ganglia

Fig 9.2 7

Neurons Pyramidal neurons forming a network in the brain

Neuron: main functional units

Nerve- bundle of neurons Individual nerve fibers (neurons)

Neuron

Neurons  Neurons = cells that transmit the electrical impulses throughout the body  3 types of neurons: 1.Sensory: carry impulse from sense organ to spinal chord and brain 2.Interneurons: connect sensory and motor and carry impulses in between (found in spinal chord and brain) 3.Motor: carry impulse from brain and spinal chord to muscles and glands

3 types of Neurons

Neurons: Structure Cell Body (Soma): Cell’s “life support” center, contains organelles (mitochondria, golgi, lysosomes) Dendrites - Receives signal from sensory cell or neighboring neuron and conducts “signal” toward the cell body -- [input zone]

Myelin Sheath  Myelin sheath—an insulating layer around a nerve fiber (neuron)  Formed by oligodendrocytes in CNS and Schwann cells in PNS  Schwann cells form Neurilemma: thick, outermost coil of myelin sheath, contains nucleus and most of its cytoplasm (helps regenerate nerve if damaged)  No Neurilemma in CNS, can’t regenerate

12-20 Myelination in CNS Figure 12.7b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (b) Oligodendrocyte Nerve fiber Myelin

12-21 Myelination in PNS Figure 12.7a Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Axon (a) Myelin sheath Schwann cell Nucleus Basal lamina Neurilemma Endoneurium

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Fig

 Axon - [conducting zone]  conducts signal away from axon hillock of cell body to another neuron or effector cell  Axon Ending- a cluster of branches (100’s to 1000’s) that relays signal to next neuron / effector cell

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Fig

Synapse

 Narrow gaps in the myelin sheath between Schwann cells are called nodes of Ranvier.  Allows signal to “jumps” from node of Ranvier to node of Ranvier, increasing speed of impulse (with myelin sheath (225 mph / without 11 mph)

Schwann Cell Myelin sheathMyelinated axonNodes of Ranvier Nucleus of Schwann cell

Schwann cell Myelinated axonMyelin sheath Nucleus of Schwann cell Cytoplasm of Schwann cell SCHWANNCELLSCHWANNCELL

Multiple Sclerosis (MS) Immune System attacks Myelin in brain and spinal chord, as well as fibers themselves (autoimmune disorder)

Multiple Sclerosis (MS) Loss of motor functions

Classification of Neurons

 Structural classification 1.Multipolar neurons: many dendrites and 1 axon arising from cell bodies, commonly found in the CNS. 2.Bipolar neurons have a single axon and a single dendrite extending from opposite sides of the cell body, found only in eyes, nose, and ears 3.Unipolar neurons are found in ganglia outside the CNS and have one axon that divides; the peripheral process has dendrites near a peripheral body part and a central process that runs into the CNS. 36

Soma Dendrites Axon Multipolar Neuron

12-38 Supportive Cells (Neuroglia)  A bout 1 trillion (10 12 ) neurons in the nervous system  outnumber the neurons by as much as 50 : 1  Neuroglia or glial cells  Support and protect the neurons  Bind neurons together and form framework for nervous tissue  In fetus, guide migrating neurons to their destination  If mature neuron is not in synaptic contact with another neuron it is covered by glial cells  Prevents neurons from touching each other  Gives precision to conduction pathways

12-39 Neuroglial Cells of CNS Figure 12.6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ependymal cell Cerebrospinal fluid Neurons Astrocyte Perivascular feet Microglia Oligodendrocyte Capillary Myelinated axon Myelin (cut)

12-40 Types of Neuroglia  Four types occur only in CNS 1.Oligodendrocytes  Form myelin sheaths in CNS  Each armlike process wraps around a nerve fiber forming an insulating layer that speeds up signal conduction

Types of Neuroglia 2. Ependymal cells  Line internal cavities of the brain  Made of Cuboidal epithelium with cilia on apical surface  Secretes cerebrospinal fluid (CSF)  Clear liquid that bathes the CNS

12-42 Types of Neuroglia 3.Microglia  Small, wandering macrophages formed white blood cell called monocytes  Thought to perform a complete checkup on the brain tissue several times a day  Wander in search of cellular debris to phagocytize

Types of Neuroglia 4.Astrocytes  Most abundant glial cell in CNS  Cover entire brain surface and most nonsynaptic regions of the neurons in the gray matter of the CNS  Diverse functions  Form a supportive framework  Have extensions that contact blood capillaries that stimulate them to form a tight seal called the blood–brain barrier  Convert blood glucose to lactate and supply this to the neurons for nourishment  Nerve growth factors secreted by astrocytes promote neuron growth and synapse formation

12-45 Types of Neuroglia  Two types occur only in PNS  Schwann cells  Envelope nerve fibers in PNS  Produce a myelin sheath similar to the ones produced by oligodendrocytes in CNS  Assist in the regeneration of damaged fibers  Satellite cells  Surround the neurosomas in ganglia of the PNS  Provide electrical insulation around the soma  Regulate the chemical environment of the neurons