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CHP 9: NERVOUS TISSUE CHP 11: AUTONOMIC NERVOUS SYSTEM CHP 12: SOMATIC SENSES AND SPECIAL SENSES

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Chp 9: Nervous tissue chp 11: autonomic nervous system chp 12: somatic senses and special senses. Pages: Chp 9; 229-245 Chp 11; 277-288 . Chp 12; 289-319 . Chapter 9: Nervous Tissue Learning Objectives. - PowerPoint PPT Presentation

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Page 1: Pages: Chp  9;   229-245               Chp  11;  277-288 .               Chp  12;  289-319

CHP 9: NERVOUS TISSUE

CHP 11: AUTONOMIC NERVOUS SYSTEM

CHP 12: SOMATIC SENSES AND SPECIAL SENSES

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Chapter 9: Nervous TissueLearning Objectives

Describe the organization of the nervous system. Explain the three basic functions of the nervous

system. Contrast the histological characteristics and the

functions of neuroglia and neurons. Distinguish between gray matter and white

matter. Describe how a nerve impulse is generated and

conducted. Explain the events of synaptic transmission and

the type of neurotransmitters used.

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Structures of the Nervous System

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Organization of the Nervous System

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SUBDIVISIONS OF PNSSomatic Nervous System (SNS) Sensory neurons conveys information from somatic receptors

in head, body wall, and limbs, and from receptors for special senses of vision, hearing, taste, and smell to CNS

Motor neurons conduct impulses from CNS to skeletal muscles only; can be consciously controlled, voluntary actions

Autonomic nervous system (ANS) Sensory neurons convey information from autonomic sensory

receptors, located in visceral organs (stomach, lungs) to CNS Motor neurons conduct nerve impulses from CNS to smooth

muscles, cardiac muscles and glands; cannot be consciously controlled, involuntary actions

Two divisions of ANS are sympathetic division and parasympathetic division; these divisions usually perform opposite functions

“Fight-or-flight” responses emergency actions (sympathetic) “Rest-and-digest” activities GI tract activities

(parasympathetic)

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Enteric Nervous System (ENS)

nnGet a copy of checkpoint questions 1-3, complete them and hand them in…

b

Get a copy of checkpoint questions 1-3, complete them and hand them in…

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Functions of the Nervous System

Sensory functions _ (AFFECTORS) Sensory receptors_ detect stimuli inside and outside the body. - Sensory or afferent neurons carry information from cranial to spinal nerves into brain and spinal cord or visa versa

Integrative functions _(LIKE A CONTROL CENTER)

Process sensory information by analyzing and storing some of it and by making decisions for appropriate responses - Interneurons; have short axons that connect with neurons in brain, spinal cord, and ganglion; are majority neurons in the body

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Functions…continued Motor functions _(EFFECTORS) Respond the integrative decisions - Motor of efferent neurons carry information from brain toward spinal cord or out of brain to spinal cord into cranial or spinal nerves

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HISTOLOGY OF NERVOUS TISSUE Two types of cells

Neurons unique functions of the nervous system; sensing,

thinking, remembering, controlling muscle activity, and regulating glandular secretions

Neuroglia support, nourish, and protect neurons and maintain

homeostasis in the intestinal fluid that baths neurons

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Neurons

Three parts: Cell Body

nucleus surrounded by cytoplasm; includes RER, lysosomes, mitochondria, Golgi

synthesizes cellular molecules needed for a neuron’s operation Processes or extensions:

Dendrites (“little trees”) multiple per single axon combined with cell body receiving and input parts of a neuron

short, tapering, and highly branched, tree-branch array emerging from cell body

Axons_ conducts nerve impulses toward another neuron, muscle fiber, or

gland cell long, thin, cylindrical projection that joins cell body at a cone-shaped

elevation

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nn

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Classification of Neurons

STRUCTURAL CLASSIFICATION Multipolar neurons: have several dendrites and

one axon; most in brain and spinal cord Bipolar neurons: have one main dendrite and one

axon; retina of the eye, inner ear, olfactory area of brain

Unipolar neurons: dendrites and one axon fused together forming a continuous process that emerges from cell body; begin in embryo as bipolar neurons; most function as sensory receptors for touch, pressure, pain, or thermal stimuli. Cell bodies of most of this type located in ganglia of spinal and cranial nerves.

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Classification of Neurons

FUNCTIONAL CLASSIFICATION Sensory or afferent neurons: once sensory receptor activated,

these form an action potential in their axon that is conveyed into the CNS through spinal and cranial nerves contain sensory receptors at their distal ends or are located just

after sensory receptors that are separate cells; most unipolar in structure

Motor or efferent neurons: convey action potential away from CNS to effectors (muscles and glands) in PNS through cranial and spinal nerves Most are multipolar in structure

Interneurons or association neurons: integrate incoming sensory information from sensory neurons and then elicit a motor response by activating appropriate motor neurons Located within CNS between sensory and motor neurons; most

multipolar in structure

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Neuroglia

Smaller than neurons 5-50 times more numerous

”glue” that holds nervous tissue together do not generate or conduct nerve impulses can multiply and divide in mature nervous system in case of injury or disease multiply to fill in

spaces formerly occupied by neurons Gliomas: brain tumors derived from glia

called gliomas; very malignant and grow rapidly

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Myelination Myelin sheath, many-layered covering composed of lipids

and protein, surround the axons of most of our neurons. Two Functions:

(1) insulates the axon (2) increases the speed of nerve impulse conductionThe amount of myelin increases from birth to maturity

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Collections of Nervous Tissue

Clusters of Neuronal Cell Bodies Ganglion: cluster of neuronal cell bodies

located in PNS Nucleus: cluster of neuronal cell bodies in CNSBundles of Axons Nerve: bundle of axons located in PNS; cranial

nerves connect brain to periphery and spinal nerves connect spinal cord to periphery

Tract: bundle of axons located in CNS; tracts interconnect neurons in spinal cord and brain

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Gray and White Matter White matter: myelinated and unmyelinated axons of many

neurons which is white in color; also has blood vessels Gray matter: neuronal cell bodies, dendrites, unmyelinated

axons, axon terminals, and neuroglia white is grayish pink in color; also has blood vessels

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ACTION POTENTIALS AKA nerve impulses Two features of plasma membrane needed for action potentials in

muscle fibers and in neurons existence of resting membrane potential presence of specific types of ion channels

Membrane potential difference in the amount of electrical charge inside and outside plasma membrane.

membrane that has potential is polarized Resting membrane potential voltage difference between the

inside and outside of a plasma membrane when not responding to a stimulus, in muscle fibers and neurons voltage created by flow of ions

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Ion Channels Two types of ion channels:

Leakage channels allow small but steady stream of ions to leak across the membrane

Gated channels open and close on command

Voltage-gated channels are used to generate and conduct action potentials; open in response to a change in membrane potential

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Resting Membrane Potential

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Generation of Action Potential Action potential (AP) or impulse generates rapidly occurring

events that decrease and increase the membrane potential and eventually restore it to its resting state

Ability of muscle fibers and neurons to convert stimuli into action potential is called electrical excitability.

Stimulus in cell’s environment changes resting membrane potential; if stimulus causes cell to depolarize to a critical level; called a threshold (about -55mV) then an action potential arises

Two main phases: Depolarizing phase- rapidly occurring events that decrease

and eventually reverse polarization of membrane, makes inside more positive than outside; Na+ ions move into cell

Repolarizing phase- membrane polarization is restored to resting state; Na+ ions move back out cell restoring charge to original state

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All-or-None Principle

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Stimulus

Depolarizing phase Repolarizing

phase Reversal of polarization

Threshold

6After-hyperpolarizing phase

7.Resting membrane potential

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Conduction of Nerve Impulses Also called propagation

Way cells communicate information from one part of body to another

Nerve impulses travel from where they arise, usually axon hillock, along axon to axon terminal

Positive feedback process

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Continuous & Saltatory Conduction

Continuous conduction Step-by-step process; impulses travel a short

distance in 10 milliseconds Occurs in unmyelinated axons (muscle fibers)

Have smallest diameter Saltatory conduction

Impulses leap from one node of Ranvier to the next

Occurs in myelinated axons Have largest diameter

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Synaptic Transmission How synapses neurons communicate with other

neurons or with effectors through a series of events neuron sending the signal is called the presynaptic

neuron neuron receiving the signal called the postsynaptic

neuron A synaptic cleft separates the presynaptic and

postsynaptic neuronsNeurotransmittersDifferent neurotransmitters are found in synaptic vesicles. These different neurotransmitters have different effects.

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Postsynaptic: Deactivating Neurotransmitters Essential neurotransmitters are removed in order to

restore normal synaptic function Three ways:

Diffuse away from synaptic cleft (out of reach of receptors)

Destroyed by enzymes Actively transported back into neuron (reuptake)