The Nervous System
Genes & Evolution - notes on genetic instructions:
Fertilization - Process of conception in which the sperm penetrates the egg (ovum).
Zygote - the cell resulting from the union of an ovum and a spermatozoon.
Chromosome - A structure in a cell nucleus that consists of genes. In humans, 23 pairs of chromosomes,
each pair containing one chromosome from each parent, carry the entire genetic code.
DNA is a double-stranded molecule that encodes genetic information.
Genes - A gene is a segment of DNA found on a chromosome that codes for a particular protein; a unit of
heredity; "genes were formerly called factors".
Human Genome Project - Collective name for several projects begun in 1986 to determine the entire nucleotide
sequence of the human chromosomes.
Fragile X syndrome is characterized by mental retardation, autistic-like behavior and other physical abnormalities.
Though it is usually most severe/more common in males (they are more susceptible because they have only one X chromosome
whereas females have two), both males & females can be affected and their karyotype shows a gap (the fragile site) on the long arm
of the X chromosome. The most common form of inherited mental retardation.
Evolution of The Human Brain
* The theory of evolution is a scientific theory of the origin of species of plants & animals. Darwinism is a theory of organic
evolution claiming that new species arise & are perpetuated by natural selection.
* Increases in brain size from early primates to man are well documented.
Studying the Living Brain
* MRI & fMRI brain scans (Magnetic Resonance Imaging) the f stands
for functional in fMRI.
* PET brain scans (Positron Emission Tomography)
* Picturing thoughts is called cognitive neuroscience.
The Nervous System
Divisions of the Nervous System
1. Peripheral Nervous System (PNS) - the section of the nervous system lying outside the brain
& spinal cord.
2. Central Nervous System (CNS)
Subdivisions of PNS
- Somatic nervous system, consciously controlled.
- Afferent (sensory) fibers
- Efferent (motor) fibers
- Autonomic nervous system (ANS), Also categorized as part of the "emotional" nervous system.
- Sympathetic division (arousal)
- Parasympathetic division (calm)
CNS - Control Centers
Cortex - One of the major components of the brain. The cortex is divided into four lobes (frontal, parietal,
temporal, occipital). It also contains the sensory and motor areas. It is the outer layer of gray matter that covers the
surface of the cerebral hemisphere. It is involved in higher brain functions (also referred to as cortical processes)
including visual processing.
Ψ The Four lobes of the Brain
Frontal lobe - The largest area of the brain that lies in the front of the cranial cavity. It is important for
control of voluntary movement or activity, cognition & feelings.
The frontal lobe contains the primary motor cortex (somatomotor cortex), i.e., the portion of the human brain directly
responsible for the movement & exchange of sense & motor information (namely touch: sensitivity, cold, heat, pain etc.)
of the rest of the body.
A cortical homunculus (ho-MONK-you-luss) is a physical representation of the primary motor cortex. The resulting
image is a grotesquely disfigured human with disproportionately huge hands, lips, & face in comparison to the rest of
the body. Because of the fine motor skills & sense nerves found in these particular parts of the body they are represented
as being larger on the homunculus. A part of the body with fewer sensory and/or motor connections to the brain is
represented to appear smaller. The homunculus is a visual representation of the concept of "the body within the brain"
that one's hand or face exists as much as a series of nerve structures or a "neuron concept" as it does a physical form.
This concept relates to many neuro-biological phenomena including "phantom limb" & "body integrity identity disorder".
Because the frontal lobes are involved in paying attention, organizing, deciding, & carrying out thoughts &
social-emotional behaviors, they are said to have an executive function.
Parietal lobe - Area of the brain that lies in front of the occipital lobe that is important in processing
information from the sense of touch & bringing together sensory information.
The somatosensory cortex is a narrow strip of cortex located on the front edge of the parietal lobe & extends down
its side. Like other sensory areas, there is a map of sensory space called a homunculus in this location. For the primary
somatosensory cortex, this is called the sensory homunculus. Areas of this part of the human brain map to certain areas
of the body, dependent on the amount or importance of somatosensory input from that area. For example, there is a
large area of cortex devoted to sensation in the hands, while the back has a much smaller area.
The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense &
navigation. It is involved in language abilities such as writing & speaking a second language.
Temporal lobe - Primary auditory cortex and auditory association area
Aphasia is the inability to use or understand language (spoken or written) because of a brain lesion.
- Broca's area & Broca's aphasia - affects speech but not understanding.
- Wernicke's area & Wernicke's aphasia - affects all understanding.
Occipital lobe - primary visual cortex and visual association area.
- Visual agnosia is the loss of the ability to recognize objects and people.
- Neglect syndrome is the failure to see parts of objects on the side opposite the brain
damage.
Major parts of the brain (other than the cortex):
Forebrain - The paired cerebral hemispheres: the cerebrum.
Midbrain - The brain stem, from which the cranial nerves emerge, consisting of the thalamus & hypothalamus, the
midbrain, the pons, & the medulla oblongata.
Hindbrain - The cerebellum a.k.a. "little brain, plays an important role in the integration of sensory perception &
motor output.
Pons - a band of nerve fibers linking the medulla oblongata & the cerebellum with the midbrain. Makes chemicals
involved in sleep.
Medulla - located at the top of the spinal cord, includes a group of cells that control respiration, heart rate, and blood
pressure.
Cerebellum - a large structure consisting of two halves (hemispheres) located in the lower part of the brain; responsible
for the coordination of movement & balance.
The "Emotional" Nervous System
Emotion involves the entire nervous system, of course. But there are two parts of the nervous system that are especially
significant: The Limbic system & the Autonomic nervous system.
Limbic System: The Old Brain (or how you are like an alligator!)
Four important parts:
Hypothalamus - small structure at the base of the brain that regulates many body functions, including
appetite & body temperature.
Amygdala - an almond-shaped neural structure in the anterior part of the temporal lobe of the cerebrum; intimately
connected with the hypothalamus & the hippocampus & the cingulate gyrus; as part of the limbic system it plays an important
role in motivation & emotional behavior.
Thalamus - Part of the brain through which nearly all sensory input passes to the cerebral cortex.
Hippocampus - An area buried deep in the forebrain that helps regulate emotion & memory. The hippocampus is
a part of the brain located inside the temporal lobe. The name derives from its curved shape, which supposedly resembles that of
a seahorse (Greek: hippocampus).
Autonomic nervous system: (two divisions)
1. The Sympathetic division when triggered increases physiological arousal. The fight-flight response helps
the body too cope with & survive threatening situations.
2. The Parasympathetic division decreases physiological arousal.
Overall the autonomic nervous system seeks to keep the body at an optimum level: homeostasis.
The Endocrine System is a hormonal system.
The Hypothalamus is the control center of the endocrine system.
Endocrine system's glands:
Pituitary gland
- Posterior pituitary - hormones to regulate salt & water balance
- Anterior pituitary - hormones to regulate growth
Pancreas - insulin to regulate sugar levels in the bloodstream.
Thyroid - hormones to regulate metabolism.
Adrenal glands - hormones for stress arousal & return.
Gonads - hormones to regulate sexual development.
Study Questions
1. If you had to give up one part of your brain, which one would you sacrifice?
2. Which brain functions would computers be best & worst at imitating?
3. What would happen if your limbic system were replaced with one from an alligator?
4. What is one reason for the different bodies of football players, soccer players, & jockeys?
5. What is the danger of identifying sex differences in the Brain?
6. If you were supposed to act like a person with a split brain, what would you do differently?
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Topics in Psychology
Robert C. Gates