The Nervous System & Neurons Chapter 7 Click pic

Overview of the Nervous System STRUCTURES: brain, spinal cord, & peripheral nerves FUNCTION: Recognizes and coordinates the body’s response to changes in its internal and external environments

Overview of the Nervous System The ultimate control of all the organ systems is done by the nervous system.

A. Neurons NeuronsNeurons are nerve cells that carry electrical impulses through the body Impulse = message Neurons are classified according to the direction an impulse travels. Click here

3 Types of Neurons Sensory –1. Sensory: carry impulses from sense organs to the brain Motor –2. Motor: carry impulses from the brain to muscles & glands Interneurons –3. Interneurons: connect sensory and motor neurons and process impulses

InterneuronSensory NeuronMotor Neuron

Reflex Arc Sensory Neuron Interneuron Motor Neuron

Structure of a Neuron Axon terminals Myelin sheath Cell body Nodes Axon Dendrites Nucleus

Dendrites –1. Dendrites: receive impulses

Cell body –2. Cell body: contains nucleus & cytoplasm, largest part of cell

Axon –3. Axon: transmit impulses away from cell body

Myelin Sheath –4. Myelin Sheath: covering that insulates the axon, sending the impulse faster and gives axon a whitish appearance –Neurons with axons that have myelin make up “white matter” in the brain, while neurons without myelin are called “gray matter”

Nodes –5. Nodes: gaps in the myelin sheath where membrane is exposed –Impulses jump from one node to the next

Axon terminals –6. Axon terminals: transmits impulse (message) to next cell

II. Transmission of an Impulse A nerve impulse is an electrical message. At rest, no impulse is being sent. The neuron must be stimulated (receive input) to send a impulse.

A. Resting Neuron STEP 1: At rest, the neuron is not transmitting an impulse –inside of cell has a net negative charge – –outside of cell has a net positive charge + Membrane PotentialThe cell membrane has Membrane Potential, the potential to carry an electrical current because there is a difference in charge sodium (Na + )potassium (K + ) –The ions sodium (Na + ) and potassium (K + ) cause the potential

(K + ) Click pic

Sodium-potassium pumps in the nerve cell membrane pumps sodium (Na + ) ions out of the cell and potassium (K + ) ions into the cell by means of active transport. As a result, the inside of the cell contains more K + ions and fewer Na + ions than the outside.

B. Stimulated Neuron stimulated by another neuron or the environment STEP 2: An impulse begins when a neuron is stimulated by another neuron or the environment –The stimulated impulse must reach threshold –The stimulated impulse must reach threshold, the minimum impulse strength needed to create a new impulse (all or none)

STEP 3: At the leading edge of the impulse, gates in the sodium channels open allowing positively charged sodium (Na+) ions to flow into the cell membane.

This reversal of charges is called is called the nerve impulse or an ACTION POTENTIAL (AP)

As the action potential passes, gates in the potassium channels open, allowing potassium (K+) ions to flow OUT of the cell –This restores the negative potential inside the axon.

STEP 4: The AP jumps from node to node along the axon

STEP 5: The AP continues along the axon in one direction to the axon terminals At Rest Action Potential

Action Potential Click here

C. Synapse Synapse:Synapse: the space where the axon terminal of one neuron can transfer an impulse to another neuron (or cell) –The small space between cells is the synaptic cleft –Axon terminals contain vesicles filled with neurotransmitter

Neurotransmitters (NTs)Neurotransmitters (NTs) are chemical signals of neurons that transmit an impulse across the synapse to another cell –NTs fit like a lock and key with receptors

Steps of Transmission STEP 6: Action Potential reaches axon terminal STEP 7: Neurotransmitter is released from vesicles into synaptic cleft STEP 8: Neurotransmitter binds to receptors on next neuron. STEP 9: Channels open, which creates a new action potential in next neuron hill.com/sites/ /st udent_view0/chapter45/ani mations.html#

Re-uptake of NTs Re-uptake: After the NT has done its job, it is taken back into the axon terminal so it can be used again or broken down.

Types & Effects of Neurotransmitters ► There are dozens of different NTs, but a few do most of the work. ► Each NT fits with its own specific receptor. ► It won’t cause a response without the right receptor dopamine Acetylcholine Serotonin GABA Endorphins

NTs can be excitatory or inhibitory –Excitatory NTs cause impulses in the next neurons –Inhibitory NTs stop an impulse from being sent in the next neuron Click here: Chemistry of Addition VideoChemistry of Addition Video

Major NTs 1) GABA (Gamma- aminobutyric acid) – Inhibitory –Effects: Relaxation, calming, anti-anxiety, and sleep –Depressant drugs like heroin, marijuana, and alcohol intensify effects of GABA

2) Glutamate – Excitatory –Effects: Stimulates learning and memory formation –Some drugs can interfere with glutamate, causing short-term memories not to be formed

3) Dopamine – Excitatory –Effects: Pleasure, Euphoria, Reward-centers, addiction, positive reinforcement, movement and posture –Most addictive drugs (cocaine, PCP, heroin, opiates, marijuana, and amphetamines) work by flooding the synapse with dopamine

4) Serotonin – Excitatory –Effects: Sleep, mood, appetite, pain, body temperature –Low serotonin linked to depression, suicide, impulsive behavior, and aggression –Alcohol, stimulants, marijuana and hallucinogens alter serotonin levels

5) Endorphins – Excitatory & Inhibitory –Effects: alertness, blocks pain, happy (runner’s high), sexual arousal –Often released after physical activity 6) Norepinephrine – Excitatory –Effects: alertness, energy, stress, sexual arousal

7) Acetylcholine – Excitatory –Effects: alertness, memory, muscle contraction, appetite, sexual arousal Click here: Crash Course-The Chemical MindCrash Course-The Chemical Mind

Effects of Drugs Many prescription and illegal drugs can alter the brain’s chemistry. –Many drugs are agonists (enhancers) of certain NTs that cause many of the pleasurable sensations of drugs and lead to addiction. –Addiction: chemical dependency on a substance as a result of it altering the brain’s chemistry after repeated use.

Ways Drugs interfere with Neurotransmission –1) Increase number of impulses –2) Release NT from vesicles with or without an impulse –3) Block reuptake or block receptors –4) Produce more or less NT –5) Prevent vesicles from releasing NT Click pic