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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