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 impulses Nodes - impulse jump from node to node Axon 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 neurons - carry impulses to theSensory neurons - carry impulses to the interneurons of the brain interneurons of the brain Interneurons of the brain - interpret impulsesInterneurons of the brain - interpret impulses Motor neurons - carry impulses to the musclesMotor neurons - 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 neurons Synapse = 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 dendrite Based 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: –b–blinking –c–coughing –j–jumping when startled –p–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 dendrite Based on Harvard Medical School Family Health Guide

Human behavior is controlled by natural chemical reward systems in the body For example, we like to eat fatty foods because it make us feel good It is the release of dopamine that is the chemical reward system responsible for the good feeling Dopamine “reinforces behaviors essential to our survival.” Importance of Dopamine

After neurotransmitter stimulates the postsynaptic membrane, it is removed by an enzyme or transported out of synapse For example, acetylcholine is removed from synapses by an enzyme called acetylcholinesterase Synapses must be cleaned up

1.After being released into the synapse (the gap between nerve endings and receiver cells), dopamine binds to receptors on the next neuron 2.The dopamine is either quickly reabsorbed or broken down by the enzyme monoamine oxidase (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 Levels Based on Time, May 5, 1997

Physiology of Addiction Drug enhances amount of dopamine in the synapsesDrug enhances amount of dopamine in the synapses Increased dopamine results in increased feelings of pleasureIncreased dopamine results in increased feelings of pleasure Nervous system responds by reducing the number of dopamine receptor sitesNervous system responds by reducing the number of dopamine receptor sites Addict must take more drug to produce the same “high”Addict must take more drug to produce the same “high” “So while addicts begin by taking drugs to feel high, they end up taking them in order not to feel low.”“So while addicts begin by taking drugs to feel high, they end up taking them in order not to feel low.”