The Nervous system

How does it work?

Communication

• Nearly all multicellular organisms have communication systems.

• Specialized cells carry messages from one cell to another so that communication among all body parts is smooth and efficient.

Communicate to maintain homeostasis• There are two systems used for

communication in your body:• The nervous system controls and

coordinates functions throughout the body and responds to internal and external stimuli with the use of nerves

• The endocrine system performs a similar function with the use of hormones

4

Nervous Response

• Stimulus: any change that results in a change in the organism.• temperature, light, pressure, sound,

smell, etc.• Response: any action resulting from a

stimulus.• contraction of muscle cells• secretion by a gland• stimulation of another nerve fiber.

Neurons

• Messages carried by the nervous system are electrical signals = impulses

• Nerve cells that transmit impulses = neurons• Sensory neurons: carry impulses from sense

organs to the spinal cord and brain• Motor neurons: carry impulses from the brain

and spinal cord to muscles and glands• Interneurons: connect sensory and motor

neurons and carry impulses between them

Parts of a Neuron

• Cell body = largest part containing nucleus and cytoplasm (most metabolic activity occur here)

• Dendrites = short, branched extensions spreading out from the cell body and they carry impulses from the environment or other neurons towards the cell body

• Axon = long fibers that carry impulses away from the cell body and ends at the axon terminal

Axon terminals

Myelin sheath

Nodes

Cell body

Axon

Nucleus

Dendrites

Section 35-2

A Neuron

Nerves

• Neurons bundle together to form nerves• Some nerves may be only a few neurons, and

others may be hundreds or thousands• The myelin sheath may insulate axons by

surrounding it• There may be some gaps in the myelin sheath

called nodes• Impulses jump from one node to the next,

increasing the speed impulses travel

Resting Nerve

• Nerve impulses are electrical• The electric potential is created as the

result of a sodium - potassium pump • It uses ATP to pump sodium ions (Na+)

out and potassium ions (K+) in = active transport

• This results in a negative charge inside the cell membrane and positive charge outside = resting potential

Nerve Impulse

• An impulse begins when a neuron is stimulated by another neuron or by the environment.

• An impulse causes positively charged sodium ions to flow in temporarily reversing the charge of the cell membrane = action potential

• As the impulse passes, positively charged potassium ions flow out and the charges restore to the normal resting potential

At the leading edge of the impulse, the sodium gates open. The membrane becomes more permeable to Na+ ions and an action potential occurs.

As the action potential passes, potassium gates open, allowing K+ ions to flow out.

The action potential continues to move along the axon in the direction of the nerve impulse.

At rest.

Action Potential

Action Potential

Section 35-2

Figure 35-7 An Impulse

Action Potential

Synapse

• At the end of the neuron, the impulse reaches an axon terminal where the impulse may be passed along to another neuron or another cell

• The location where a neuron can transfer an impulse to another cell = synapse

• The synapse is a small gap that separates the axon terminal from the dendrites of the next neuron or another cell

• The terminals contain tiny sacs or vesicles filled with neurotransmitters = chemicals used by a neuron to transmit an impulse across a synapse

• The neurotransmitters stimulate the next neuron• The impulse will continue with the stimulation exceeds the

cell’s threshold

Vesicle

Axon

Axon terminal

Synaptic cleft

Neurotransmitter

Receptor

Dendrite of adjacent neuron

Direction of Impulse

Section 35-2

Figure 35-8 The Synapse

Reaction activity

• Reaction time = the amount of time required for an impulse travel from your sensory neurons to your motor neurons

The Nervous System

• Neurons work together forming the nervous system

• There are two major divisions of the nervous system:• Central nervous system (CNS)• Peripheral nervous system (PNS)

Parts of the Nervous system

• Central nervous system (CNS):• Brain • Spinal Cord

• Peripheral nervous system (PNS):• Sensory division• Motor division

• Somatic nervous system• Autonomic nervous system

Central Nervous System

• The CNS is the control center of the body:• Relays messages• Processes information• Analyzes information

Brain and Spinal cord

• Both are • protected by bone• wrapped in 3 layers of connective

tissue = meninges• layers may have a space between

them filled with cerebrospinal fluid which protects (shock absorber) and exchanges nutrients and waste

Brain

• About 100 billion neurons, mainly interneurons

• Major parts of the brain:• Cerebrum • Cerebellum• Brain stem• Thalamus• Hypothalamus

Pons

Pituitary gland

Hypothalamus

Cerebrum

Medulla oblongata Spinal cord

Cerebellum

Pineal gland

Thalamus

Section 35-3

Figure 35-9 The Brain

Spinal Cord

• Links communication between the brain and the rest of the body

• 31 pairs of spinal nerves branch out from the spinal cord connecting brain to body

• Reflexes = quick, automatic responses to stimuli are processed directly in the spinal cord

Spinal nerve

Central canalGray matter

White matter

Meninges

Section 35-3

Figure 35-11 The Spinal Cord

Peripheral Nervous System• Consists of nerves and associated cells that

are not part of the brain or spinal cord• Receives information from the environment

and relays commands from the CNS to organs and glands

• Divided into two parts:• Sensory division: transmits impulses from sense

organs to the CNS• Motor division: transmits impulses from the CNS

to the muscles or glands

PNS animation (Pain receptor) : http://pennhealth.com/encyclopedia/em_DisplayAnimation.aspx?gcid=000054&ptid=17

Somatic System

• Part of motor division that regulates activities that are under conscious control (movement of skeletal muscles)

• Some reflexes too

What is a Reflex?

• A reflex is an involuntary behavior. Reflexes are usually coordinated in the spinal cord not the brain.• They are present from birth• They are automatic• They are meant to protect the body

• Examples:• blinking (keeps your eyes hydrated)• pulling your hand away when you touch something

hot.• changing pupil size as you move from dark to light.

Receptors & Effectors

• Receptor: a specialized nervous tissue that is sensitive to a specific stimulus.• nerve cells in skin• eyes• ears• taste buds

• Effectors: the part/s of the body that respond • muscles or glands

Reflex Arc

• The pathway that an impulse travels:• 1. from the sensory receptor • 2. up the sensory neuron • 3. over the synapse • 4. to the spinal cord (interneuron) • 5. over another synapse • 6. back down the motor neuron • 7. to the effector

Reflex arc animations: 1. http://www.sumanasinc.com/webcontent/animations/content/reflexarcs.html2. http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0016-swf_reflex_arc.swf

Autonomic System

• Part of the motor division that regulates activities that are automatic or involuntary (heart beat and smooth muscle in digestive system and blood vessels)

• Two parts that have opposite effects on the organs they control:• Sympathetic (“gas pedal”)• Parasympathetic (“brake”)

Concept Map

which consists of

is divided into

that make up

which is divided into

Section 35-3

The Nervous System

Sensory nerves

Motor nerves

Autonomic nervous system

Somatic nervous system

Central nervous system

Peripheral nervous system

Sympathetic nervous system

Parasympathetic nervous system

Sensory Receptors

• Neurons that react directly to stimuli from the environment and send impulses to other neuron and CNS• Light• Sound• Motion• Chemicals• Pressure• Changes in temperature

Sense organs

• Sensory receptors are concentrated in the sense organs:• Eyes• Ears• Nose• Mouth• Skin

Types of Sensory receptors• Sensory receptors within each organ

enable it to respond to particular stimuli. The five general categories of sensory receptors are:• Pain receptors• Thermoreceptors• Mechanoreceptors• Chemoreceptors• Photoreceptors

The 5 Senses

• See• Hear• Smell • Taste• Touch

See (Vision)

• Photoreceptors = sense light

Hearing and Balance• Sound = vibration in air

detected by mechanoreceptors

• Balance = As head moves, fluid shifts and hair cells bend and send impulses to the CNS to determine body motion and position

Smell• Smell = ability to detect chemicals

detected by chemoreceptors in nasal passageway and send impulses to CNS through sensory nerves

Taste• How food tastes is strongly

influenced by smell• Taste = ability to sense

chemicals by chemoreceptors in taste buds mostly on tongue (sweet, sour, salty and bitter – sensitivity is different on different parts of tongue)

Touch

• Skin = largest sense organ containing pain receptors, thermoreceptors, and mechanoreceptors

Senses activity

• Different parts of skin have different sensitivity because there’s a different numbers of receptors at different locations

Problems

• Drugs = substance that changes the structure or function of the body

• Drugs can interfere with the action of neurotransmitters at the synapse, which can disrupt the functioning of the nervous system

Stimulants

• Increase the actions regulated by the nervous system by increasing the release of neurotransmitters at synapses (increase heart rate, blood pressure, and breathing rate)• Amphetamines• Cocaine• Nicotine• Caffeine

Depressants

• Decrease the actions regulated by the nervous system (lowering heart rate, breathing rate, blood pressure, relaxing muscles, and relieving tension)• Alcohol• Tranquilizers

Alcohol

• One of the most dangerous and abused depressant drug that slows down functioning rate of CNS

• Fetal alcohol syndrome (FAS) = a group of birth defects caused by the effects of alcohol on the fetus (heart defects, malformed faces, delayed growth, and poor motor development

• Alcoholism = disease of people who have become addicted to alcohol

• Causes damage to liver where alcohol is broken down

Addictions

• Some drugs that act on neurons of the pleasure centers of the brain can produce an addiction = an uncontrollable craving for more of the drug or dependence on a drug• Cocaine – causes sudden release of the

neurotransmitter dopamine• Opiates – mimic natural endorphins to overcome pain• Marijuana – produces temporary feeling of euphoria

and disorientation

• Drug abuse = using any drug in a way that most doctors couldn’t approve

Section 35-5

Commonly Abused Drugs

Used to increase alertness, relieve fatigue

Used to relieve anxiety, irritability, tension

Used to relieve pain

Stimulants

Depressants

Opiates

Amphetamines

BarbituratesTranquilizers

MorphineCodeine

Increase heart and respiratory rates; elevate blood pressure; dilate pupils; decrease appetite

Slow down the actions of the central nervous system; small amounts cause calmness and relaxation; larger amounts cause slurred speech and impaired judgement

Act as a depressant; cause drowsiness, restlessness, nausea

Drug Type Medical Use Examples Effects on the body