Biological Psychology

Distribution of the estimated 100 billion neurons in the adult central nervous system. Communication in the Nervous System

Neurons – electrochemical communication (1) Soma – cell body (2) Dendrites – receive transmissions (3) Axon – transmit away Myelin sheath – speeds up transmission Terminal Button – end of axon; secretes neurotransmitters Neurotransmitters – chemical messengers Synapse – point at which neurons interconnect Communication in the Nervous System

Transmissions between neurons

Figure 2.6 When a section of a neuron is stimulated by other neurons, the cell membrane becomes permeable to sodium ions so that an action potential of about 40 millivolts is induced. This action potential is transmitted along the axon. The neuron fires according to the all-or-none principle.

Figure 2.2 FIGURE 2.2 Electrical probes placed inside and outside an axon measure its activity. (The scale is exaggerated here. Such measurements require ultra-small electrodes, as described later in this chapter.) The inside of an axon at rest is about -60 to -70 millivolts, compared with the outside. Electrochemical changes in a neuron generate an action potential. When positively charged sodium ions (Na+) rush into the cell, its interior briefly becomes positive. This is the action potential. After the action potential, positive potassium ions (K+) flow out of the axon and restore its negative charge (see Fig. 2.3 for further explanation).

How many?

How fast? Let’s find out ourselves…

Neurotransmitters

Human Nervous System

The primary motor cortex

The Cerebrum: Two Hemispheres, Four Lobes Four Lobes Occipital Temporal Frontal Parietal

The Cerebrum: Two Hemispheres, Four Lobes Cerebral Hemispheres two specialized halves connected by the corpus collosum Left hemisphere verbal processing: language, speech, reading, writing Right hemisphere nonverbal processing: spatial, musical, visual recognition

In the human visual system (viewed here from above), light from either half of the world crosses through the pupils to strike the opposite side of each retina. Axons from the left half of each retina travel to the left hemisphere of the brain; axons from the right half of each retina travel to the right hemisphere of the brain.

Experience and the brain The two halves of the brain Work with individuals who have had the “split- brain” operation (severing the corpus callosum) to control seizures provides evidence that the two hemispheres are highly specialized. The right hemisphere needs to communicate with the left in order to name the objects in its visual field. The left hemisphere needs the right in order to synthesize details into a whole picture (the parts of a face into a whole recognizable image).

Brain Plasticity

Sympathetic and parasympathetic branches of the autonomic nervous system. Both branches control involuntary actions. The sympathetic system generally activates the body. The parasympathetic system generally quiets it. The sympathetic branch relays its messages through clusters of nerve cells outside the spinal cord.

Sympathetic and parasympathetic branches of the autonomic nervous system. The parasympathetic branch of the ANS generally acts to replenish stores of energy in the body. The sympathetic branch is the most active during activities that expend energy. The two branches of the ANS frequently have antagonistic effects on the organs they service.