Biological Psychology and Neurotransmission Module 9 Biological Psychology and Neurotransmission

Neurons- or Nerve Cells The most basic building block of the nervous system

Parts of the Neuron Figure 9.2 A motor neuron David G. Myers: Myers’ Psychology for AP®, Second Edition Copyright © 2014 by Worth Publishers

Nodes of Ranvier

How does a neuron fire? Neurons generate electricity from chemical events Ions (electrically charged atoms) are exchanged Electrical inside Chemical outside

Key Concepts The Neuron is polarized when it is ready to fire, also known as resting potential. As a neuron’s membrane depolarizes the sodium/potassium pumps open and action potential occurs. When the neuron hyperpolarizes, it is returning to its polarized state. This is known as the refractory period.

Resting Potential The Neuron is ready to fire– as the toilet is ready to flush.

Resting Potential At rest the cell is polarized with an interior negative charge of -70 mv. There is about 10X more sodium (Na+) outside and 20 X more potassium (K+) inside.

Figure 9.3 Action potential David G. Myers: Myers’ Psychology for AP®, Second Edition Copyright © 2014 by Worth Publishers

Action Potential When a neuron becomes stimulated, the area of the membrane at the point of stimulation becomes more permeable to Na+ (it is depolarized). This depolarization voltage activates the Na+ gates to open. Na+ rushes inside the cell. At the same time the K+ gates, which were partially open allowing K+ to pass freely all along, open wider and K+ rushes out. This rapid exchange of ions reverses the electrical gradient because the influx of positive ions cancels out the negative interior causing the valence to reach zero. Then the influx of Na+ takes the interior to a slightly more positive state (+20 mv).

Sodium Potassium Pump

Refractory Period Remedial Chemistry Kids… Advanced Chemistry Kids… This hyper-polarization (known as the refractory period) is only momentary as the rapid out flux of K+ returns the interior to a negative state. The sodium/potassium pump is also working to re-establish the resting potential. In other words the out flux of K+ combined with the action of the sodium/potassium pump restores the electrical and concentration gradients. Within milliseconds the polarity is re- established and the neuron is once again ready to fire. Remedial Chemistry Kids… The refractory period-- brief period after 1 millisecond action potential when the neuron is resistant to re-excitation after an action potential. Permeability to sodium ions is low and to potassium ions is higher than normal. Below 50 IQ… The toilet tank is filling

Summary

The All-or None Response The neuron fires or it does not- but there is NO part way firing. Like a gun

How Neurons Communicate Figure 9.4 How neurons communicate David G. Myers: Myers’ Psychology for AP®, Second Edition Copyright © 2014 by Worth Publishers

Neurotransmitters Neurotransmitters are chemical messengers that are released from the vesicles in the axon terminal of the pre-synaptic cell to hook up to a receptor on the dendrite of the postsynaptic cell. Neurotransmitters are like keys which fit into the receptor lock. The receptor will recognize only one type of neurotransmitter. When a neurotransmitter is received by a receptor it either excites (depolarizes) or inhibits (hyperpolarizes) the postsynaptic cell.

Figure 9.5 Neurotransmitter pathways Each of the brain’s differing chemical messengers has designated pathways where it operates, as shown here for serotonin and dopamine (Carter, 1998). Figure 9.5 Neurotransmitter pathways David G. Myers: Myers’ Psychology for AP®, Second Edition Copyright © 2014 by Worth Publishers

Norepinephrine Helps control alertness, arousal, sleeping, dreaming, emotions, and learning. It also can elevate mood and relieve depression Too much… mania Not enough… depressed moods, lethargy How does Wellbutrin, Cymbalta, and Effexor work? It blocks norepinephrine reuptake

Acetylcholine Triggers muscle contraction, stimulates the excretion of some hormones, and plays a vital role in learning and memory Too much… may cause muscle spasms Not enough… may cause paralysis Lack of ACH has been linked to Alzheimer’s disease.

Botulin and Botox

Dopamine influences mood, involved in controlling movement and posture, learning, attention, involved in storing memories Too much… May cause Schizophrenia (over-stimulation of arousal producer) Too little… associated with Parkinson’s Disease which is caused by the deterioration of neurons that manufacture most if the brain’s dopamine

Serotonin Promotes feelings of well being, regulates mood, emotions, anxiety, libido, aggression, sleep, body temperature, appetite, and thinking abilities Too much…seizures, fever, comas Too little…Linked to Depression

Endorphins Natural painkillers, play an important role in control of pain and emotions (anxiety, fear, tension, pleasure) Too much...feel no pain Too little...feel everything We can become addicted to endorphin secreting activities

Why Acupuncture?

Table 9.1 Some Neurotransmitters and Their Functions David G. Myers: Myers’ Psychology for AP®, Second Edition Copyright © 2014 by Worth Publishers

Agonists and Antagonists

Figure 9.6 Agonists and antagonists Curare blocks ACh Curare poisoning paralyzes its victims by blocking ACh receptors involved in muscle movements. Morphine mimics endorphin actions. Which is an agonist, and which is an antagonist? (Art adapted from Higgins & George, 2007.) ANSWER: Morphine is an agonist; curare is an antagonist. Figure 9.6 Agonists and antagonists David G. Myers: Myers’ Psychology for AP®, Second Edition Copyright © 2014 by Worth Publishers

Cocaine blocks dopamine reuptake sites