Chapter 12: Nervous System PDF

The Nervous System: An Introduction 1  The Nervous System: Intro By the end of this lecture you will... n Describe the structural and functional divisions of the nervous system n Describe the structural components of the neuron. n Describe the events of the actio...

The Nervous System: An Introduction 1  The Nervous System: Intro By the end of this lecture you will... n Describe the structural and functional divisions of the nervous system n Describe the structural components of the neuron. n Describe the events of the action potential, or nerve impulse n Describe the structure of a synapse. n List the six types of neuroglia in nervous tissue. n Define and describe a nerve n Describe the process of nerve regeneration in the peripheral nervous system. 2  Words/Concepts you will learn… n Neuron (and its n Terminate anatomy) n Synapse n Ganglion vs. nucleus n Electrochemical n Nerve vs. tract Communication n Effector cells n Depolarization/repolarization/ hyperpolarization n Action Potentials (all or none) 3 3 Main Functional Divisions 4 Basic Anatomical Divisions Central nervous system (CNS): integrating and command center Peripheral nervous system (PNS) Consists of nerves extending from brain and spinal cord Peripheral nerves link all regions of the body to the CNS Transmit sensory and motor information Ganglia: clusters of neuronal cell bodies 5 Further divided into... Somatic: Skin, skeletal muscles, bones Visceral: GI tract, lungs, heart, bladder, etc. 6 Figure 12.3 Schematic of levels of organization in the nervous system. Central nervous system (CNS) Peripheral nervous system (PNS) Brain and spinal cord Cranial nerves and spinal nerves Integrative and control centers Communication lines between the CNS and the rest of the body Sensory (afferent) division Motor (efferent) division Somatic and visceral sensory Motor nerve fibers nerve fibers Conducts impulses from the CNS Conducts impulses from to effectors (muscles and glands) receptors to the CNS Somatic nervous Autonomic nervous Somatic sensory fiber Skin system system (ANS) Somatic motor Visceral motor (voluntary) (involuntary) Conducts impulses Conducts impulses from the CNS to from the CNS to skeletal muscles cardiac muscles, smooth muscles, Visceral sensory fiber and glands Stomach Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Paraysmpathetic Mobilizes body systems division during activity Conserves energy Promotes house- keeping functions during rest Sympathetic motor fiber of ANS Heart Structure Function Sensory (afferent) Bladder division of PNS Parasympathetic motor fiber of ANS Motor (efferent) division of PNS  Concept Check! n What are the THREE functional divisions of the nervous system? n What are the TWO anatomical divisions of the nervous system? What are their parts? n Describe a nerve that carries pain information from your intestines to your spinal cord in two words. n Describe a nerve that carries motor commands to move your skeletal muscle in two words. 8  Dendrites Cell body The Typical Neuron The cell of the nervous system! Nucleus Axon Nucleolus Impulse direction Nissl bodies Node of Ranvier Axon Axon hillock Schwann terminals (a) Neurilemma cell Terminal branches Copyright © 2011 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. Properties of Neurons n Excitability - respond to stimuli n Conductivity - use electrical signals n Secretion - release of a chemical Electrochemical response to stimuli! 10  Parts of the neuron n Cell body (soma) ¡ Contains usual organelles plus other structures ¡ Most cell bodies in the CNS (Clustered into nuclei) ¡ Cell bodies in the PNS are clustered into ganglia n Dendrites ¡ Branch from the cell body ¡ Receptive sites for receiving signals from other neurons ¡ Transmit electrical signals toward the cell body  Parts of the neuron n Axons Nerve impulse (a.k.a. action potential) is generated at axon’s initial segment. ¡ Conducts the impulse away from the cell body ¡ Branches at end of axon - End in knobs called terminal boutons (axon terminals) ¡ Neurotransmitter released at the axon terminals  The Impulse: The Action Potential At rest – There is more Na+ outside than K+ inside. (3:2 ratio) The A.P. is a LOCAL change in voltage from the movement of ions (Na+ in, K+ out) 13 The Action Potential Peak Depolarization Repolarization Depolarization to threshold Hyperpolarization 14  Concept Check! n Draw a typical neuron and label its parts. What direction is information received from other neurons and what direction does the impulse travel within the neuron? n Draw and label the graph (time vs. mV) of the action potential. 15 Neural Communication: The Synapse 16 Neural Communication: The Synapse 17 Neural Communication: The Synapse: Variations 18 Review...Functional Divisions 19  Functional Classes of Neurons n Sensory (afferent, PNS) - almost always end in CNS n Interneurons - always in CNS, Integrative - process, store, retrieve, make decisions. 90% of all neurons. n Motor (efferent, PNS) - end (terminate) on effector cells - cells that can do a job - skeletal muscle, smooth muscle, cardiac muscle, or glands. 20 Functional Classification of Neurons - Illustration 21 22 Somatic vs. Visceral? Sensory vs. Motor? 23  (Neuro)glia: Supportive Cells Glia (or glial cells, neuroglia) are not neurons!! They are support or “housekeeping” cells n Astrocytes n Oligodendrocytes n Microglia n Ependymal cells n Schwann cells n Satellite cells 24  Glia: In CNS n Astrocytes (most abundant): § Nourish and support neurons § Form blood-brain barrier § Ion concentration § Neuron growth and connections n Oligodendrocytes: form myelin sheaths 25  Glia: In CNS n Ependymal cells - line CSF cavity; form and circulate CSF n Microglia (least abundant): engulf invading microorganisms and dead neurons 26  Glia: In PNS n Schwann cells: form myelin sheaths n Satellite cells: surround cell bodies in ganglia; support and nourish 27  Myelination (CNS and PNS) Myelin: lipoprotein Increases speed of nerve impulse conduction What happens in multiple sclerosis?? 28 Unmyelinated cells still have support 29  Nerves - collection of axons in the PNS Structural hierarchy of the nerve 30  Nerve damage and regeneration If... PNS 1. Axon becomes fragmented at injury Cell body intact site. No scar formation 2. Macrophages invade and destroy axon distal to injury site. 31  Nerve damage and regeneration 3. Schwann cells at injury site 4. Axon regeneration; form regeneration tube; axon new sheath forms. 32 filaments grow through tube.  Concept Check! n What are the 6 types of glial cells in nervous tissue? Which ones are found in the CNS, and which ones are in the PNS? n What are the four steps in regeneration of a nerve? How likely will that repair happen in the brain? 33