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Nervous SystemComponents: Brain, spinal cord, nerves, sense
organs, and associated structures.Functions:
Works with endocrine system to coordinate body activities.
Integrates and processes information from sense organs. Sends signals (instructions) to muscles and glands. Responds to internal stimuli.
Homeostatic Role: Regulates most organ activities along with endocrine
system.
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Human Nervous System
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Functions of Nervous Tissue
1. Sensory Input: Conduction of signals from sensory organs (eyes, ears, nose, skin, etc.) to information processing centers (brain and spinal cord).
2. Integration: Interpretation of sensory signals and development of a response. Occurs in brain and spinal cord.
3. Motor Output: Conduction of signals from brain or spinal cord to effector organs (muscles or glands). Controls the activity of muscles and glands, and allows the animal to respond to its environment.
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Nervous System Allows Us to Respond to Our Environment
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Cells of Nervous Tissue
1. Neuron: Nerve cell. Structural and functional unit of nervous tissue. Carry signals from one part of the body to
another.
2. Supporting cells: Nourish, protect, and insulate neurons.There are roughly 50 supporting cells for every
neuron.In humans, Schwann cells wrap around the axons
of neurons, forming a myelin sheath that is essential for transmission of nerve impulses.
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Neuron Structure Cell body : Contains nucleus and most
organelles.
Dendrites: Extensions that convey signals towards the cell body.Short, numerous, and highly branched
Axon: Extension that transmits signals away from the cell body to another neuron or effector cell.Usually a long single fiber.
Axon is covered by a myelin sheath made up of many Schwann cells that are separated by small spaces (Nodes of Ranvier).
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Structure of the Neuron
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Neuron StructureMyelin sheath and nodes of Ranvier greatly speed
up nerve impulses, which jump down axon from node to node.
Speed of signal
Myelinated axon 100 meters/second
Unmyelinated axon 5 meters/second
Multiple sclerosis: A disease in which a person’s
immune system destroys the myelin sheaths on
their neurons.
• Loss of muscle control
• Impaired brain function
• Death
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Neurons and Synapses
Types of Neurons
Sensory Motor Interneurons
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SpinalCord
BrainSensoryNeuron
Sensory Neurons
INPUT From sensory organs to the brain and spinal cord.
Drawing shows a somatosensory neuron
Vision, hearing, taste and smell nerves are cranial, not spinal
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SpinalCord
BrainSensoryNeuron
MotorNeuron
Motor Neurons
OUTPUT From the brain and spinal cord To the muscles and glands.
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SpinalCord
BrainSensoryNeuron
MotorNeuron
Interneurons
Interneurons carry information between other neurons only found in the brain and spinal cord.
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Structures of a neuron
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The cell body
Round, centrally located structure
Contains DNA Controls protein
manufacturing Directs metabolism No role in neural signaling
Contains the cell’s Nucleus
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Dendrites
Information collectors
Receive inputs from neighboring neurons
Inputs may number in thousands
If enough inputs the cell’s AXON may generate an output
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Dendritic Growth
Mature neurons generally can’t divide
But new dendrites can grow
Provides room for more connections to other neurons
New connections are basis for learning
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Axon
The cell’s output structure
One axon per cell, 2 distinct parts tubelike structure
branches at end that connect to dendrites of other cells
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Myelin sheath
White fatty casing on axon
Acts as an electrical insulator
Not present on all cells
When present increases the speed of neural signals down the axon.
Myelin Sheath
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How neurons communicate
Neurons communicate by means of an electrical signal called the Action Potential
Action Potentials are based on movements of ions between the outside and inside of the cell
When an Action Potential occurs a molecular message is sent to neighboring neurons
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Neuron to Neuron
Axons branch out and end near dendrites of neighboring cells
Axon terminals are the tips of the axon’s branches
A gap separates the axon terminals from dendrites
Gap is the Synapse CellBody
Dendrite
Axon
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Synapse
axon terminals contain small storage sacs called synaptic vesicles
vesicles contain neurotransmitter molecules
SendingNeuron
SynapseAxonTerminal
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Neurotransmitter Release
Action Potential causes vesicle to open
Neurotransmitter released into synapse
Locks onto receptor molecule in postsynaptic membrane
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Locks and Keys
Neurotransmitter molecules have specific shapes
positive ions (Na+ ) depolarize the neuron negative ions (Cl-) hyperpolarize
When NT binds to receptor, ions enter
Receptor molecules have binding sites
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Some Drugs work on receptors
Some drugs are shaped like neurotransmitters
Antagonists : fit the receptor but poorly and block the NT e.g. beta blockers
Agonists : fit receptor well and act like the NT e.g. nicotine.
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Summary
3 types of neurons The cell membrane Ion movements Action potentials Synapse Neurotransmitters Receptors and ions Agonists and
antagonists
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In this experiment you are required to say the color of the word, not what the word says. For example, for the word, RED, you should say "Blue."
GreenGreen
RedRed
BlueBlue