Read Psychology for Dummies Online
Authors: Adam Cash
Tags: #Psychology, #General, #Body; Mind & Spirit, #Spirituality
Psychology for Dummies (8 page)
The human nervous system consists of two large divisions: the
central nervous system (CNS)
and the
peripheral nervous system (PNS).
The basic building blocks of the nervous system are nerves, neurons, and neurotransmitters and glial cells. The CNS includes our brain and spinal cord. The PNS includes the nerves outside the CNS; they are in the periphery of the body.
Keep in mind that the nervous system is a living part of our bodies and, therefore, has the same basic needs as any other part of our body (like fuel and immune protection). The components of the nervous system are kept alive and healthy by the circulatory system and other regulatory body functions. The specifics of the support systems for each division of the nervous system are discussed in more detail within each division’s corresponding section in this chapter.
If you remember a little physics, chemistry, or biology, you may remember that the building blocks of life begin with atoms (operating under the laws of physics); atoms grouped in particular ways to make up molecules, that then form compounds, move on up to molecules, then form compounds, then cells, then tissue, then me! So if we really wanted to be reductionistic we’d just study physics and do away with all other branches of science. Or, we could look at human behavior and mental processes from a molecular level. This is the focus of the field of
neurobiology.
Typically, however, biological psychology begins at the cellular level of understanding. Two types of cells appear in the nervous system,
supporting cells
and
neurons.
Of the two divisions of the body’s nervous system, think of the peripheral nervous system (PNS) as a system of connections that make it possible for the brain and spinal cord to communicate with the rest of the body. Two sets of nerves are involved:
Spinal nerves:
These nerves travel from the spinal cord to the muscles and other body parts, carrying neural signals both to and from the spinal cord.
Cranial nerves:
These nerves are involved in the muscular and sensory processes of the head and neck.
In addition to these two sets of nerves, the PNS also contains a subsystem of the overall nervous system known as the
autonomic nervous system
(ANS).
The autonomic nervous system helps regulate two specific types of muscles (smooth and cardiac) and the glands in our body. The ANS is involved in “automatic” or involuntary action. Bodily organs, reflexive muscle contractions, and even the dilation of our pupils are all automatic behaviors governed by the ANS. There are two very important divisions of the ANS:
Sympathetic nervous system:
The sympathetic branch of the ANS is involved in the energetic activation of the body when we need excess energy. For example, then I am confronted with a life-threatening situation, my sympathetic nervous system kicks in and gives me the energy to either take on the challenge or flee the situation.
Parasympathetic nervous system:
The parasympathetic branch of the ANS deactivates the SNS after it has been engaged. This action is sometimes called the
relaxation response
because the activity of the SNS is relaxed, or shut off, and we return to normal functioning.
The CNS consists of both the brain and the spinal cord. There are three main divisions of the brain:
forebrain, midbrain,
and
hindbrain.
Each of these divisions consists of many substructures that are involved in various behaviors and activity.
An important thing to keep in mind about the brain is that it is a complex, integrated system. All of its components work together to produce the complexity of behaviors that each of us is capable of. The concept of
localization
refers to the idea that there are specific parts of the brain for specific components of behaviors. Various parts of the brain work together to produce vision, hearing, speech etc. These divisions have been discovered and established through the use of different neurological techniques such as post-mortem brain examination, CT (co-axial tomography) scans, MRI (magnetic resonance imaging) scans, and PET (positron-emission tomography) scans.
The human forebrain consists of these different subdivisions.
Cerebral cortex:
If you think of the brain as a mushroom, with a top and a stalk, the cerebral cortex is the top of the mushroom. It’s divided into two halves, called
cerebral hemispheres
(the left and the right — pretty creative). These halves are connected by a bundle of nerve fibers known as the
corpus collosum.
Without the corpus collosum, the halves wouldn’t be able to communicate with each other.
The four major divisions of the cerebral cortex are shown in Figure 3-1 and listed below with their corresponding functions:
•
Frontal lobe:
Planning, organizing, coordinating and controlling movements, reasoning, and overall monitoring of the thinking process
•
Parietal lobe:
Sensation
•
Temporal lobe:
Hearing, speaking, and other verbal activity
•
Occipital lobe:
Vision
Limbic system:
Located on the underside of the mushroom top (the cerebral cortex), the limbic system is involved in learning, memory, emotional behavior, and mating or reproduction (see Figure 3-2).
Basal ganglia:
This subdivision is involved in the control of movement.
Thalamus:
This “neural switchboard” is a relay station for the different parts of the brain.
Hypothalamus:
The hypothalamus takes part in the control of the endocrine system and works with the limbic system to control behaviors such as aggression, eating, protection, and mating.
The midbrain consists of the following divisions and their respective areas of responsibility:
Tectum:
Auditory and visual systems
Tegmentum:
Sleep, arousal, attention, muscle tone, and reflexes
The hindbrain also consists of two divisions with their own assigned duties:
Cerebellum:
Motor movement and its coordination
Medulla:
Vital functions of the body such as the cardiovascular system, breathing, and the movement of skeletal muscles
Figure 3-1: |  |
Figure 3-2: |  |
