Neurons & the Nervous System

Chapter 2: The Brain and Behavior

Central v. Peripheral• Central contains brain & spinal cord

– In a computer, this is your central processing unit (CPU)

• Peripheral – sensory & motor neurons that transmit messages between brain and muscles & glands– In a computer, this includes your

keyboard, mouse, CD-ROM, printer, etc.

Spinal cord is about 43 cm long in women and 45 cm long in men;

¾ inches thick

Autonomic v. Somatic• Somatic – voluntary - controls

purposeful body movements, movements for balance & posture– Consciously perceived sensations

• Autonomic – involuntary – automatic activities such as heartbeat, respiration, digestion, dilation of pupils, etc.– Some can be under conscious control

(i.e. respiration)– Smooth & cardiac muscle, some glands

Sympathetic v. Parasympathetic

• Sympathetic = “Fight-or-flight” response– Uses energy reserves to cope with stress

or emergency– Adrenaline!

• Parasympathetic = “Rest and digest”– Conserves & builds up stored energy

reserves The Sympathetic & Parasympathetic systems work

together to maintain homeostasis.

http://www.youtube.com/watch?v=Y5nj3ZfeYDQ

Today’s Goal Today’s Goal You will be able You will be able to….to….

• Identify the parts of a neuron and their functions in creating & sending neural messages.

• http://www.youtube.com/watch?v=sX87g3AHIbc

• http://www.youtube.com/watch?v=5uQZfaURU_Y&feature=related

• http://www.youtube.com/watch?v=Y5nj3ZfeYDQ

• http://www.youtube.com/watch?v=NqVeH26i7Kg&feature=related

Parts of the Neuron• Neurons: nerve cells• Dendrites: branch-like end of neuron which

receives messages• Cell body (soma): contains nucleus • Axon: long tail-like end of neuron which

transmits (sends) messages

There are 100 billion neurons in the human brain

There are 300 billion neurons in the octopus brain

• Myelin: fatty substance that speeds up transmission of impulse

• Terminal buttons: bulb-shaped structure at end of axon

The longest axon of a neuron belongs to what

animal?Giraffe – 15 feet! (from toe to neck)

Dendrites

Cell body (soma)Axon

Myelin sheath

Terminal buttons

There are more neurons in the brain than stars in the

Milky Way

Neuron Activity• You will need:

– 1 black pipe-cleaner– 2 white pipe-cleaners– 1 blue or orange pipe-cleaner– 2 white beads

Neuron Activity• Which part of the neuron do the white

pipe-cleaners represent?• Which part of the neuron does the blue

pipe-cleaner represent?• Which part of the neuron does the black

pipe-cleaner represent?• Which part of the neuron do the white

beads represent?

Types of Neurons• Afferent (sensory) neurons:

send messages from sensory receptors to the spinal cord & brain

• Efferent (motor) neurons: relay messages from brain & spinal cord to muscles & glands

• Interneurons: transmits neural stimulus between sensory & motor neurons

Today’s Goal Today’s Goal You will be You will be able to….able to….

• Describe how a neural impulse is generated and how neurons communicate in the brain and throughout the body.

• http://www.youtube.com/watch?v=90cj4NX87Yk&feature=related • http://www.youtube.com/watch?v=DF04XPBj5uc

The Synapse• Synapse (synaptic cleft): gap between

dendrites of one neuron and axon of another

• Receptor sites: parts of dendrite which receive neurotransmitters

• Neurotransmitters: chemical substances involved in sending neural impulsesAverage neuron makes about 1,000 synapses and receives 10,000 synapses

Axon of sending neuron

Terminal button

Synaptic cleft

Receptor sites

Dendrite of receiving neuron

Neural Impulse: electrochemical firing of a nerve cell

• Resting potential: electric potential when neuron not firing (-70 millivolts)

• Depolarization: neuron reduces resting potential by becoming positively charged

• Action Potential: neuron fires when it reaches +30-40 millivolts

• Repolarization: internal charge becomes more negative

• Refractory period: phase after firing an impulse, neuron will not fire

• All-or-none principle: neuron will fire or not fire, no in-between

Velocity of neural impulse is 250 mph

Resting potential

Today’s Goal Today’s Goal You will be You will be able to…able to…

• Discuss how the major neurotransmitters affect the body and one’s behavior

Learning Target: Describe neural communication and discuss the impact of neurotransmitters.

Review• Which nervous system is most active during

stress or a “fight-or-flight” situation?Sympathetic NS

In the graph…• When is the neuron

insensitive to incoming messages?

• When is the neuron depolarizing?

• When is the neuron at its resting potential?

• When is the neuron at its action potential?• When is the neuron repolarizing?

A

B

C

D

E

Substances that Affect Neurotransmitters

• Agonist: similar to the NT, mimics its effects

• Antagonist: inhibits the release of NT by sending neuron, or blocks receptor site for NT on receiving neuron

Neurotransmitters• Excitatory NT: increases the

likelihood that postsynaptic neuron will fire

• Inhibitory NT: decreases likelihood that postsynaptic neuron will fire

Neurotransmitters• Acetylcholine (ACh)

Function: Muscle contractions, learning, memory

EXCITATORY (sometimes inhibitory)Malfunctions: Alzheimer’s Disease

• Dopamine (DA)Function: Voluntary movement,

sensations of pleasure & rewardMalfunctions: Too little Parkinson’s,

Too much --> Schizophrenia

• Agonists cocaine & amphetamines• Antagonists Ritalin, alcohol

Neurotransmitters

• SerotoninFunction: Mood, appetite, sleep,

impulsivity, concentration

Malfunctions: Depression, Eating Disorders

• Agonists LSD, Prozac

Neurotransmitters

• NorepinephrineFunction: Alertness, arousal,

mood, heart rate/appetiteInhibitory & excitatoryMalfunctions: Depression

• Agonists Cocaine, amphetamines

Neurotransmitters

• GABA (most prevalent inhibitory NT)Function: Anxiety, sleep, seizuresMalfunctions: Anxiety disorders, tremors, insomnia

• Glutamate (main excitatory NT)Function: Memory & learningMalfunctions: Migraines, seizures, addictions

• EndorphinsFunction: Pain controlMalfunctions: None

Neurotransmitter Song • Choose a popular camp song or

rhyme• Change the lyrics to describe a

neurotransmitter or several neurotransmitters