Biology II - Chapter 9: The Nervous System (Part I)

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What does the nervous system include?

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1

What does the nervous system include?

brain, spinal cord, nerves

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What are the functions of the nervous system?

overall function - coordinate the body’s systems by receiving and sending information, maintaining homeostasis

<p>overall function - coordinate the body’s systems by receiving and sending information, maintaining homeostasis</p>
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Sensory Input

  • gathering information from receptors in the body

  • to monitor changes occurring inside and outside the body

  • changes = stimuli

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Integration

to process and interpret sensory input and decide if action is needed and where the action will occur

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Motor Output

  • a response to integrated stimuli

  • the response activates muscles or glands to maintain homeostasis

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What are the two divisions of the nervous system?

Central Nervous System (CNS), Peripheral Nervous System (PNS)

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Central Nervous System (CNS)

brain and spinal cord

<p>brain and spinal cord</p>
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Peripheral Nervous System (PNS)

  • nerves throughout the body

    • 31 pairs of spinal nerves

    • 12 pairs of cranial nerves

<ul><li><p>nerves throughout the body</p><ul><li><p>31 pairs of spinal nerves</p></li><li><p>12 pairs of cranial nerves</p></li></ul></li></ul>
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What are the functional classification of the peripheral nervous system?

sensory (afferent) division, motor (efferent) division

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Sensory (Afferent) Division

nerve fibers that carry information to the central nervous system

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Motor (Efferent) Division

nerve fibers that carry impulses away from the central nervous system, two subdivisions (somatic nervous system, autonomic nervous system)

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Somatic Nervous System

voluntary; ex. skeletal muscles

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Autonomic Nervous System

involuntary; ex. smooth and cardiac muscles, glands

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What are the nervous tissues (support cells)?

support cells in the CNS are grouped together as “neuroglia"; functions: to support, insulate, and protect neurons

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What are the types of support cells?

  • microglia

  • oligodendrocytes

  • astrocytes

  • ependymal cells

  • schwann cells'

  • satellite cells

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Microglia Cells

immune function; spider-like phagocytes that digest debris and kill bacteria

<p>immune function; spider-like phagocytes that digest debris and kill bacteria</p>
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Oligodendrocytes

make myelin sheath that provides insulation around the axons in the central nervous system

<p>make myelin sheath that provides insulation around the axons in the central nervous system</p>
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Astrocytes

abundant; star-shaped cells; brace neurons; connect blood vessels to neurons; form barrier between capillaries and neurons; control the chemical environment of the brain

<p>abundant; star-shaped cells; brace neurons; connect blood vessels to neurons; form barrier between capillaries and neurons; control the chemical environment of the brain</p>
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Ependymal Cells

forms membranes around tissue; lines cavities of the brain and spinal cord; circulates cerebrospinal fluid

<p>forms membranes around tissue; lines cavities of the brain and spinal cord; circulates cerebrospinal fluid</p>
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Schwann Cells

form the insulating myelin sheath around the neurons in the PNS (same function as oligodendrocytes, which are found only in the CNS)

<p>form the insulating myelin sheath around the neurons in the PNS (same function as oligodendrocytes, which are found only in the CNS)</p>
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Myelin Sheaths

insulate axons; schwann cells supply the myelin for peripheral neurons; oligodendrocytes myelinated the axons of the central nervous system

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What are the gaps in the sheath are called?

nodes of ranvier

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Satellite Cells

protect neuron cell bodies

<p>protect neuron cell bodies</p>
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Neurons

masses of nerve cells that transmit information (functional unit of the system); major regions are cell body and processes (dendrites and axons)

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Cell Body

contains the nucleus and other cell organelles

<p>contains the nucleus and other cell organelles</p>
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Dendrites

shorter, more numerous, receive information, conducts information toward the cell body

<p>shorter, more numerous, receive information, conducts information toward the cell body</p>
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Axons

single long fibers, conducts information away from the cell body

<p>single long fibers, conducts information away from the cell body</p>
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Where do axons ends?

in axonal terminals

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What do axonal terminals contain?

vesicles with neurotransmitters (different neurotransmitters for different muscles)

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What are axonal terminals separated from?

separated from the next neuron by a gap or a synapse

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Chromatophilic Substance (Rough ER)

transport system

<p>transport system</p>
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Myelin

insulation surrounding axons (white, fatty material)

<p>insulation surrounding axons (white, fatty material)</p>
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Nodes of Ranvier

gaps in the insulation

<p>gaps in the insulation</p>
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Neurofibrils

fibers within the axon

<p>fibers within the axon</p>
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Sensory (Afferent) Neurons

carry impulses from the sensory receptors to the CNS

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What are the sensory receptors?

cutaneous sense organs; proprioceptors; other sensory organs (eyes, ears, nose, mouth)

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Cutaneous Sense Organs

naked nerve endings (temperature and pain); Meissner’s Corpuscle (light touch); Pacinian Corpuscle (deep touch)

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Proprioceptors

detect stretch or tension in tendons, ligaments, or muscles

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Motor (Efferent) Neurons

carry impulses from the CNS to viscera, muscles, or glands

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Interneurons (Association Neurons)

found in neuro pathways in the CNS; connect sensory and motor neurons

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Myelinated

white matter

<p>white matter</p>
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Unmyelinated

grey matter

<p>grey matter</p>
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What are the functional parts of a neuron?

sensory, motor, interneurons

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What are the structural parts of the neuron?

bipolar, unipolar, multipolar

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FUN FACTS!!! :)

  • longevity - can live and function for lifetime

  • do not divide - fetal neurons lose their ability to under go mitosis; neural stem cells are an exception

  • high metabolic rate - require abundant oxygen and glucose

  • the nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be cause and sometimes involve the whole body

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What are some cell membrane potentials?

resting potential, threshold potential, action potential

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Nerve Impulse

weak electric current, like a wave

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How does Voltage-gated Na+ Channels work?

  1. neuron membrane maintains resting potential

  2. threshold stimulus is received

  3. sodium channels open

  4. sodium ions diffuse inward, depolarizing the membrane

  5. potassium channels open

  6. potassium ions diffuse outward, repolarizing the membrane

  7. the resulting action potential causes a local bioelectric current that stimulates the membrane

  8. wave of action potentials travel the length of the axon as a nerve impulse

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Depolarization

is the loss of the difference in charge between the inside and outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior

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Repolarization

  • is when potassium ions rush out of the neuron after sodium ions rush in

  • the sodium-potassium pump, using ATP, restores the original configuration

  • potassium ions diffuse out of the cell as the membrane permeability changes again restoring the negative charge on the inside of the membrane and the positive charge on the outside surface

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Nerve Impulse

speed is proportional to the size of the axon (a greater diameter = faster impulse); myelinated axons conduct impulses faster than unmyelinated ones

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What is the synapse?

is the junction between two communicating neurons; a nerve pathway is the path from which nerve impulses travels from neuron to neuron

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What is the synapse’s nerve pathway follow (in order)?

dendrite, cell body, along axon, synapse, dendrite

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54

What happens when electrical impulses are not able to cross the synapse to another nerve?

a neurotransmitter is released from a nerve’s axon terminal; he dendrite of the next neuron has receptors that are stimulated by the neurotransmitter; an action potential is started in the dendrite

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How are transmission of a signal at the synapses completed?

a neurotransmitter is released at the gap to signal the next neuron; receptors on the dendrite receive this chemical message

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Anatomy of the Synapse

  • A: Neuron (axon)

  • B: Neuron (dendrite)

  1. mitochondria

  2. vesicles

  3. receptor

  4. synapse

  5. receptor

  6. calcium channel

  7. release neurotransmitter

  8. re-uptake

<ul><li><p>A: Neuron (axon)</p></li><li><p>B: Neuron (dendrite)</p></li></ul><ol><li><p>mitochondria</p></li><li><p>vesicles</p></li><li><p>receptor</p></li><li><p>synapse</p></li><li><p>receptor</p></li><li><p>calcium channel</p></li><li><p>release neurotransmitter</p></li><li><p>re-uptake</p></li></ol>
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What are the types of neurotransmitter?

excitatory, inhibitory

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Excitatory

increase membrane permeability, increases chance for threshold to be achieved

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Inhibitory

decrease membrane permeability, decrease chance for threshold to be achieved

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What are several examples of neurotransmitters?

  • acetylcholine

  • dopamine

  • serotonin

  • endorphins

  • gaba (common)

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Acetylcholine

stimulates muscles contraction

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Dopamine

mood, makes happiness or some other emotion

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Serotonin

sleepiness; mood

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Endorphins

pain reduction; mood

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GABA (gamma-aminobutyric acid)

reduces the activity of the neurons to which it binds (inhibitory); most common type of receptor; 40% of all synapses work with GABA; GABA has a tranquilising effect; low levels of GABA associated with anxiety and phobia

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Agonist

molecule that has the same effect on the postsynaptic neuron as the neurotransmitter itself does

<p>molecule that has the same effect on the postsynaptic neuron as the neurotransmitter itself does</p>
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Antagonist

molecule that blocks the effect that the neurotransmitter normally has on the postsynaptic neuron

<p>molecule that blocks the effect that the neurotransmitter normally has on the postsynaptic neuron</p>
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Neuronal Pool

groups of neurons that make hundred of synaptic connections and work together to perform a common function; these “pools” help us remember sequential tasks (ex. tying a shoe, riding a bike)

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Reflex

rapid, predictable, and involuntary response to a stimulus; occurs over pathways called reflex arcs

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Reflex Arc

direct route from a receptor, to a sensory neuron, to a interneuron, to a motor neuron, to an effector

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What are the types of reflexes and regulations?

  • somatic reflexes

  • patellar, or knee-jerk, reflex

  • autonomic reflexes

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Somatic Reflexes

activation of skeletal muscles (ex. when you move your hand away from a hot stove)

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Patellar Reflex

is an example of a two-neuron reflex arc

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Autonomic Reflexes

smooth muscle regulation; heart and blood pressure regulation; regulation of glands; digestive system regulation

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Central Nervous System (CNS)

CNS develops from the embryonic neural tube

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What does the neural tube become?

the brain and spinal cord

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What does the opening of the neural tube become?

the ventricles

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What are the four chambers within the brain?

  • cerebral hemispheres (cerebrum)

  • diencephalon

  • brain stem

  • cerebellum

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What is the brain filled with?

cerebrospinal fluid

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Cerebrum

inky large part of the brain (cerebral cortex); includes more than half of the brain’s mass; higher mental function, solving problems

<p>inky large part of the brain (cerebral cortex); includes more than half of the brain’s mass; higher mental function, solving problems</p>
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What parts of the neuron are afferent?

dendrites, axon, axon terminal, cell body

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What parts of the neuron are efferent?

motor neuron,

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What are the two types of neurotransmitters, and what are they? Why does the body need it?

Excitatory and inhibitory; excitatory: increase membrane permeability, increases chance for threshold to be achieved; inhibitory: decrease membrane permeability, decrease chance for threshold to be achieved; why the body needs it: both are necessary for you to not be overstimulated (by too much excitatory) or have dulled senses (by too much inhibitory), Mr Ronnie says you need to have them, instead of not having any at all, because if you had none you “wouldn’t be able to feel anything.”

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