NERVOUS SYSTEM

The message must get through…

Functions

Control and coordinate functions of the body

Respond to internal and external stimuli

Nerve Cells

Neurons = the cells of the nervous system that transmit impulses

Cell Part Functions

Dendrites - carry impulses toward the cell body from sense organs or other neurons

Axon Parts

Axon - carries impulse away from the cell body

Myelin - speeds up impulsesNodes - impulse jump from node to

nodeAxon terminals - secrete

neurotransmitters

3 Types of Neurons

1. Sensory: carry impulses from sense organs to spinal cord and brain

2. Motor: carry impulses from brain and spinal cord to muscles and glands

3. Interneurons: connect sensory and motor neurons and carry impulses between them

•Sensory neuronsSensory neurons - carry impulses to the - carry impulses to the interneurons of the braininterneurons of the brain•Interneurons of the brainInterneurons of the brain - interpret impulses - interpret impulses•Motor neuronsMotor neurons - carry impulses to the muscles - carry impulses to the muscles

Types of Neurons

Based on: Mader, S., Inquiry Into Life, McGraw-Hill

What is a nerve?

Nerve = a bundle of neuronsSynapse = small gap between 2

neurons or between neuron and muscle cell

Neurotransmitter = chemical used by a neuron to transmit an impulse across a synapse

Crossing a Synapse

1. Impulse arrives at axon terminal (A)2. Sacs release neurotransmitters into

the synapse between cells (C )3. Neurotransmitters (D) diffuse across

the gap and attach to receptor molecules (B) on the next cell’s dendrite (E)

4. Adjacent cell is stimulated to transmit an impulse

Synapses

Neurotransmitter being released into synapse and attaching to receptors on dendriteBased on Harvard Medical School

Family Health Guide

50 Known Neurotransmitters

• Examples include:

– Acetylcholine

– Dopamine

– Serotonin

Central Nervous System (CNS)

• Includes the brain and spinal cord

Brain Parts

a. Meninges: 3 layers of connective tissue that covers and protects the brain

b. Cerebrospinal fluid: fills space between the meninges layers

- acts as shock absorber

- involved in exchange of nutrients and waste

c. Cerebrum: largest part

- voluntary activities of the body

- intelligence

- learning

- judgment

d. Cerebellum: back of skull

- muscle coordination and balance

e. Brain stem: pons and medulla oblongata

- blood pressure

- heart rate

- breathing

- swallowing

f. Thalamus & hypothalamus: between brain stem and cerebrum

- receive messages from sense organs

- hunger and thirst

- fatigue and body temperature

- anger

Peripheral Nervous System (PNS)

• Nerves that branch off the brain and spinal cord

• Sensory division: sends nerve impulses from sense organs to brain

• Motor division: sends nerve impulses from brain to muscles or gland

Reflex

• Reflex = automatic response of the nervous system to a stimulus

• Examples:– blinking– coughing– jumping when startled– pulling away from a hot stove

Characteristics of Reflexes

• You are born with these reflexes

• Reflexes are protective

• Happen without you thinking about it because message only has to be sent to the spinal cord for the response to occur

Pathway

• receptor -->

• sensory neuron -->

• spinal cord -->

• motor neuron -->

• muscle (effector) which contracts

• message is also sent up to the brain

Drugs & The Nervous System

• Stimulants: caffeine, nicotine, cocaine, amphetamines– increase heart rate, blood pressure, and

breathing rate– increase release of neurotransmitters– makes you feel like you have energy

Depressants

• Depressants:– slows down heart rate, breathing rate– lowers blood pressure– relaxes muscles and relieves tension– enhance effects of neurotransmitters that

help nerve cells prevent nervous impulse transmission

– can be fatal if used in combination with alcohol

Alcohol

• Acts as depressant– slows down CNS and reflexes– decreases coordination and judgment– addictive– can cause blackouts and liver damage– if used during pregnancy can cause Fetal Alcohol

Syndrome in the baby which results in malformed face, delayed growth, poor motor development, learning problems

Cocaine

• Causes a sudden release of the neurotransmitter dopamine

• Gives intense feeling of pleasure and satisfaction

• addictive

Opiates

• Mimic natural chemicals in the brain (endorphins) that help relieve pain

• addictive

Marijuana

• THC is active ingredient

• Gives feeling of euphoria, disorientation

• Can cause memory loss, lack of concentration, reduced levels of testosterone

• Smoke is bad for lungs

Synapses

Neurotransmitter being released into synapse and attaching to receptors on dendriteBased on Harvard Medical School

Family Health Guide

Human behavior is controlled by natural Human behavior is controlled by natural chemical reward systems in the bodychemical reward systems in the body

For example, we like to eat fatty foods For example, we like to eat fatty foods because it make us feel goodbecause it make us feel good

It is the release of dopamine that is the It is the release of dopamine that is the chemical reward system responsible for the chemical reward system responsible for the good feelinggood feeling

Dopamine “reinforces behaviors essential to Dopamine “reinforces behaviors essential to our survival.”our survival.”

Importance of DopamineImportance of Dopamine

After neurotransmitter stimulates the After neurotransmitter stimulates the postsynaptic membrane, it is removed postsynaptic membrane, it is removed by an enzyme or transported out of by an enzyme or transported out of synapsesynapse

For example, acetylcholine is removed For example, acetylcholine is removed from synapses by an enzyme called from synapses by an enzyme called acetylcholinesteraseacetylcholinesterase

Synapses must be cleaned upSynapses must be cleaned up

1.1. After being released into the synapse (the gap After being released into the synapse (the gap between nerve endings and receiver cells), between nerve endings and receiver cells), dopamine binds to receptors on the next neurondopamine binds to receptors on the next neuron

2.2. The dopamine is either quickly reabsorbed or The dopamine is either quickly reabsorbed or broken down by the enzyme monoamine oxidase broken down by the enzyme monoamine oxidase (MAO)(MAO)

Dopamine’s Normal Action

Based on Time, May 5, 1997

Cocaine blocks the normal absorption of dopamine. As a result, dopamine accumulates in the synapse, where is stimulates the receiver cell.

Amphetamines stimulate excess release of dopamine, overwhelming the processes of reuptake and enzyme breakdown.

Nicotine stimulates the release of dopamine, while another substance in cigarette smoke blocks the action of MAO.

How Drug Affect Dopamine LevelsBased on Time, May 5, 1997

Physiology of AddictionPhysiology of Addiction• Drug enhances amount of dopamine in the Drug enhances amount of dopamine in the

synapsessynapses• Increased dopamine results in increased feelings Increased dopamine results in increased feelings

of pleasureof pleasure• Nervous system responds by reducing the Nervous system responds by reducing the

number of dopamine receptor sitesnumber of dopamine receptor sites• Addict must take more drug to produce the same Addict must take more drug to produce the same

“high”“high”• ““So while addicts begin by taking drugs to feel So while addicts begin by taking drugs to feel

high, they end up taking them in order not to feel high, they end up taking them in order not to feel low.”low.”