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Chapter 2

The Brain or  Bio‐Psychology

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Glial Cells

Surround neurons and hold them in place

Make Myelin (covering for neurons)

Manufacture nutrient chemicals neurons need

Absorb toxins and waste materials

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Fig. 2-1, p. 28

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• When you pull your finger away from a hot candle flame, it is NEURONS sending signals from the finger to the brain and back to the muscles that are responsible.

• NEURONS sending information from your eye to your brain, and within your brain are responsible for you being able to see and read this.

• When a neuron sends this “information”, what is really happening?

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Information flows WITHIN and BETWEEN neurons.Let’s first focus on what happens “within” a neuron.

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Neuron at Rest• Resting Potential

– negative 70 mvolts: a state of polarization• Inside of cell is more negatively charged compared to outside

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– Neurons are surrounded by salty liquid with Na+, K+, Cl‐, and some other ions.

– Cell membrane is selectively permeable with “gates”.

– These gates arevoltage dependent.

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Fig. 2-3, p. 30

How does a neuron maintain this state of polarization?I.E. how does it keep the inside more negative than the 

outside?

• Sodium – PotassiumPump

• 3 NA+ pumpedout for every2 K+ pumped in.

• Net effect: Positives are pumped out.

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• Facts– Na+/K+ pump maintains ‐70 mvolt charge 

• Pumps Na+ out and K+ in.• Pumps 3 sodiums out for every 2 potassiums in

– Effect:  • Na+ wants in (concentration & electrical gradient)• K+ wants out (concentration gradient) a little more than it wants in (electrical gradient)

• Net effect is more “+ ions” are pumped out which leads to the outside being more positive (and inside more negative).

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The Action Potential• Time 1: Hyperpolarization (inside more negative)

• Time 3: Depolarization (inside less negative)

• Time 6: Action Potential

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The Action Potential: How do we get to a positive

charge inside?

• When the voltage level crosses a threshold, Na+ gates open and Na+ rushes in – Changes voltage inside to +30 mvolts.

• Follows the all‐or‐nothing law– All action potential amplitudes are the 

same

– Information is carried by frequency of firing

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• How to return to resting potential?

– K+ gates open and K+ moves out.

• Propagation of the action potential– Occurs when the rush of Na+ inside the cell pushes the + ions down the cell creating (propagating) a new action potential

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Nerve Conduction: The Action Potential

• What starts the action potential?– Dendrites are stimulated by other neurons

causing the voltage level to change and either • Depolarize or create action potentials (or

increase the likelihood of them) or• Hyperpolarize and make action potentials

LESS likely.

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Nerve Conduction: The Myelin Sheath & Nodes of Ranvier (Rahn-vee-ay)

Insulation layer covers axons in the brain and spinal cord.

Allows for high-speed conduction 10 times faster than if not insulated, up to 200 mph.

Multiple sclerosis occurs when immune system attacks the sheath

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The Synapse

• Synapse = the gap between neurons

• Sherrington (1906) & Loewi (1920) credited with discovery that the synapse was a “chemical thing”.

• When an action potential reaches the end of the neuron, causes chemicals (neurotransmitters) to be released into the gap between neurons.

• Over 100 neurotransmitters (NTs) are known.

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• Diffusion to postsynaptic is quick (milliseconds?).

• NTs fit into receptors on the postsynaptic cell like a lock/key.

• NTs can excite or inhibit postsynaptic cell.

• After NTs “do their thing” they back out and are either

– Recycled

– Degraded

– Diffuse away

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Excitatory and Inhibitory signals. Temporal vs. spatial summation

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Drugs and the Synapse

• Drugs work by doing one or more of the following to neurotransmitters:1. Increasing the synthesis.

2. Causing vesicles to leak.

3. Increasing release.

4. Decreasing reuptake.

5. Blocking the breakdown into inactive chemical.

6. Directly stimulating or blocking postsynaptic receptors.

Major Neurotransmitters

Acetylcholine (ACh)– Involved in memory and

muscle activity

• Dopamine – An excitatory transmitter

• Too much = psychotic symptoms

• Too little = Parkinson’s Disease

Serotonin– Enhances mood,

eating, sleep, and sexual behavior

• Endorphins– Reduce pain and

increase feeling of well-being

• Norephephrine

• GABA

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The Nervous System

Three types of neurons:

– Sensory: Carry input messages from the sense organs to the spinal cord and brain

– Motor: Transmit impulses from the brain and spinal cord to the muscles and organs

– Interneurons: Perform connective or associative functions in the nervous system

– See also temporal or spatial summation

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Fig. 2-6, p. 31

Sensory Neuron

Fig. 2-5, p. 30

Motor Neuron

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What do we call it when the signal doesn’t have to go to the brain in order for you to react to the heat?

R _ _ _ _ _ A _ _

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Organization of The Nervous System

Central Nervous System– Brain and Spinal Cord

Peripheral Nervous System Everything that isn’t in the CNS

– Connects the CNS with the muscles, glands, and sensory receptors

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The Peripheral Nervous System

Subdivided into:– Somatic nervous system: Consists of sensory

neurons and neurons that control voluntary or skeletal muscles.

– Autonomic nervous system: Controls glands and smooth muscles in bodily organs

• Sympathetic nervous system: arouses the body

• Parasympathetic nervous system: slows down body processes

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Glands make up the Endocrine SystemThese glands secrete Hormones that travel through the blood stream

Testicles secret testosterone

Ovaries secret estrogen

Adrenal glands secrete cortisol

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Studying the Brain

Destruction or surgical removal of neurons

Stimulation of neurons– By electrical current

or chemicals

Neuropsychological tests

Electrical (EEG) recording

CT Scan

PET Scans and fMRI.

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Studying the Brain: Brain Imaging

Measure Structure: CT Scans & MRI:

Measure Process: Fmri and PET and EEG.

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Brain Structures: The Lobes

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Cortex

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Brain Structures: Cerebral Hemispheres

Left hemisphere: Language and Verbal Processing, analytical thinking

Right hemisphere:– Non verbal

Processing: (spatial skills, visual recognition, music etc)

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Split Brain Studies

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He knows but doesn’t know he knows

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