Neurons and the Nervous System

• Genetics provide the blueprint, while biology supplies the materials.

The Nervous System

• Central Nervous System (CNS) includes the brain and spinal cord
• Peripheral Nervous System (PNS) includes all neural elements outside the brain and spinal cord

Neurons

Neuron Parts

• Dendrites receive messages from other cells
• The cell body (soma) is the neuron's life support center
• The axon passes messages away from the cell body to other neurons, muscles, or glands
• The myelin sheath covers the axon of some neurons and speeds up neural impulses
• Terminal branches of axon form junctions with other cells.

Neural Communication

Action Potential

• A neural impulse, a brief electrical charge, travels down an axon
• Follows an "all or nothing" principle.

Synapse

• A synapse is the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron.

Neurotransmitters

• Neurotransmitters are chemical messengers that cross synaptic gaps between neurons
• Neurotransmitters bind to receptor sites on the receiving neuron.

Types of Neurotransmitters

• Acetylcholine (ACh) enables muscle action, learning, and memory; ACh-producing neurons deteriorate with Alzheimer's disease.
• Dopamine influences movement, learning, attention, and emotion; excess dopamine receptor activity is linked to schizophrenia and a lack of dopamine is linked to Parkinson's disease
• Serotonin affects mood, hunger, sleep, and arousal; undersupply is linked to depression
• Norepinephrine helps control alertness and arousal; undersupply can depress mood
• GABA (gamma-aminobutyric acid) is a major inhibitory neurotransmitter; undersupply is linked to seizures, tremors, and insomnia
• Glutamate is a major excitatory neurotransmitter involved in memory; oversupply can over stimulate the brain, producing migraines or seizures

The Nervous System

Peripheral Nervous System (PNS)

• The Somatic Nervous System controls voluntary movements of skeletal muscles
• The Autonomic Nervous System (ANS) controls self-regulated action of internal organs and glands
  • Sympathetic Nervous System is arousing
  • Parasympathetic Nervous System is calming.

Central Nervous System (CNS)

• The brain is the control center
• The spinal cord connects the brain to the body.

The Endocrine System

• It is a set of glands secreting hormones into the bloodstream.

Hormones

• Hormones are chemical messengers manufactured by the endocrine glands that travel through the bloodstream and affect other tissues.

Glands

• The pituitary gland secretes many different hormones, some of which affect other glands
• The adrenal glands' inner part helps trigger the "fight-or-flight" response
• The thyroid gland affects metabolism, among other things.

Tools to Examine Brain

EEG (electroencephalogram)

• Amplified recording of electrical activity waves across the brain's surface.

CT (computed tomography) scan

• Series of X-ray photos from different angles combined into a composite representation of a body slice.

PET (positron emission tomography) scan

• Visual display of brain activity showing where a radioactive glucose form goes during a task.

MRI (magnetic resonance imaging)

• Uses magnetic fields and radio waves to produce computer-generated images of soft tissue, showing brain anatomy.

fMRI (functional MRI)

• Technique revealing blood flow and brain activity by comparing successive MRI scans, showing brain function.

Brain Structures

The Brainstem

• The oldest part and central core of the brain is also responsible for automatic survival functions
  • Medulla controls heartbeat and breathing
  • Pons helps coordinate movement
  • Reticular formation is a nerve network that plays an important role in controlling arousal

The Thalamus

• The brain's sensory switchboard is located on top of the brainstem
• It directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.

The Cerebellum

• The "little brain" at the rear of the brainstem processes sensory input and coordinates movement output and balance.

The Limbic System

• It is a doughnut-shaped neural system located below the cerebral hemispheres, associated with emotions and drives
  • Amygdala is linked to emotion
  • Hypothalamus directs maintenance activities (eating, drinking, body temperature), governs the endocrine system via the pituitary gland, and is linked to emotion
  • Hippocampus is linked to conscious memory.

The Cerebral Cortex

• The intricate fabric of interconnected neural cells covering the cerebral hemispheres is also the body's ultimate control and information-processing center.

Lobes

• Frontal lobes are involved in speaking and muscle movements and in making plans and judgments
• Parietal lobes include the sensory cortex
• Occipital lobes include the visual areas, which receive information from the opposite visual field
• Temporal lobes include the auditory areas, each receiving information primarily from the opposite ear.

Motor Cortex

• An area at the rear of the frontal lobes controls voluntary movements.

Sensory Cortex

• Area at the front of the parietal lobes that registers and processes body touch and movement sensations.

Association Areas

• Areas of the cerebral cortex not involved in primary motor or sensory functions
• They are involved in higher mental functions such as learning, remembering, thinking, and speaking.

Brain Plasticity

• Brain's capacity for modification, evident in reorganization after damage
• It is is especially prominent in children and in experiments on the effects of experience on brain development.

Our Divided Brain

Corpus Callosum

• Large band of neural fibers connecting the two brain hemispheres and carrying messages between them.

Split Brain

• Condition in which the two hemispheres are isolated by cutting the connecting fibers (mainly those of the corpus callosum).

Nature vs. Nurture

Genes

• Genes are the biochemical units of heredity that make up the chromosomes; segments of DNA capable of synthesizing a protein

Chromosomes

• Chromosomes are threadlike structures made of DNA molecules that contain the genes.

DNA (deoxyribonucleic acid)

• A complex molecule containing the genetic information that makes up the chromosomes.

Genome

• Complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes.

Twin and Adoption Studies

• Identical twins develop from a single fertilized egg that splits in two, creating two genetically identical organisms
• Fraternal twins develop from separate fertilized eggs, with no closer genetic similarity than siblings, but they share a fetal environment
• Adoption studies try to determine if adopted children are more like their adoptive parents or their biological parents.

Heritability

• Proportion of variation among individuals attributable to genes.
• Heritability may vary depending on the populations and environments studied.

Gene-Environment Interaction

• Interplay that occurs when the effect of one factor (such as environment) depends on another factor (such as heredity).

Evolutionary Psychology

• Study of the evolution of behavior and the mind, using principles of natural selection.

Natural Selection

• The principle that, among inherited trait variations, those contributing to reproduction and survival are most likely to be passed on to succeeding generations.