Summary and Key Terms
Human Genetics
Genes are sequences of DNA that code for a particular trait. Different versions of a gene are called alleles—sometimes alleles can be classified as dominant or recessive. A dominant allele always results in the dominant phenotype. In order to exhibit a recessive phenotype, an individual must be homozygous for the recessive allele. Genes affect both physical and psychological characteristics. Ultimately, how and when a gene is expressed, and what the outcome will be—in terms of both physical and psychological characteristics—is a function of the interaction between our genes and our environments.
Cells of the Nervous System
Glia and neurons are the two cell types that make up the nervous system. While glia generally play supporting roles, the communication between neurons is fundamental to all of the functions associated with the nervous system. Neuronal communication is made possible by the neuron’s specialized structures. The soma contains the cell nucleus, and the dendrites extend from the soma in tree-like branches. The axon is another major extension of the cell body; axons are often covered by a myelin sheath, which increases the speed of transmission of neural impulses. At the end of the axon are terminal buttons that contain synaptic vesicles filled with neurotransmitters.
Neuronal communication is an electrochemical event. The dendrites contain receptors for neurotransmitters released by nearby neurons. If the signals received from other neurons are sufficiently strong, an action potential will travel down the length of the axon to the terminal buttons, resulting in the release of neurotransmitters into the synaptic cleft. Action potentials operate on the all-or-none principle and involve the movement of Na+ and K+ across the neuronal membrane.
Different neurotransmitters are associated with different functions. Often, psychological disorders involve imbalances in a given neurotransmitter system. Therefore, psychotropic drugs are prescribed in an attempt to bring the neurotransmitters back into balance. Drugs can act either as agonists or as antagonists for a given neurotransmitter system.
Parts of the Nervous System
The brain and spinal cord make up the central nervous system. The peripheral nervous system is comprised of the somatic and autonomic nervous systems. The somatic nervous system transmits sensory and motor signals to and from the central nervous system. The autonomic nervous system controls the function of our organs and glands, and can be divided into the sympathetic and parasympathetic divisions. Sympathetic activation prepares us for fight or flight, while parasympathetic activation is associated with normal functioning under relaxed conditions.
The Brain and Spinal Cord
The brain consists of two hemispheres, each controlling the opposite side of the body. Each hemisphere can be subdivided into different lobes: frontal, parietal, temporal, and occipital. In addition to the lobes of the cerebral cortex, the forebrain includes the thalamus (sensory relay) and limbic system (emotion and memory circuit). The midbrain contains the reticular formation, which is important for sleep and arousal, as well as the substantia nigra and ventral tegmental area. These structures are important for movement, reward, and addictive processes. The hindbrain contains the structures of the brainstem (medulla, pons, and midbrain), which control automatic functions like breathing and blood pressure. The hindbrain also contains the cerebellum, which helps coordinate movement and certain types of memories.
Individuals with brain damage have been studied extensively to provide information about the role of different areas of the brain, and recent advances in technology allow us to glean similar information by imaging brain structure and function. These techniques include CT, PET, MRI, fMRI, and EEG.
The Endocrine System
The glands of the endocrine system secrete hormones to regulate normal body functions. The hypothalamus serves as the interface between the nervous system and the endocrine system, and it controls the secretions of the pituitary. The pituitary serves as the master gland, controlling the secretions of all other glands. The thyroid secretes thyroxine, which is important for basic metabolic processes and growth; the adrenal glands secrete hormones involved in the stress response; the pancreas secretes hormones that regulate blood sugar levels; and the ovaries and testes produce sex hormones that regulate sexual motivation and behaviour.
Key Terms
- action potential
- electrical signal that moves down the neuron’s axon
- adrenal gland
- sits atop our kidneys and secretes hormones involved in the stress response
- agonist
- drug that mimics or strengthens the effects of a neurotransmitter
- all-or-none
- phenomenon that incoming signal from another neuron is either sufficient or insufficient to reach the threshold of excitation
- allele
- specific version of a gene
- amygdala
- structure in the limbic system involved in our experience of emotion and tying emotional meaning to our memories
- antagonist
- drug that blocks or impedes the normal activity of a given neurotransmitter
- auditory cortex
- strip of cortex in the temporal lobe that is responsible for processing auditory information
- autonomic nervous system
- controls our internal organs and glands
- axon
- major extension of the soma
- biological perspective
- view that psychological disorders like depression and schizophrenia are associated with imbalances in one or more neurotransmitter systems
- Broca’s area
- region in the left hemisphere that is essential for language production
- central nervous system (CNS)
- brain and spinal cord
- cerebellum
- hindbrain structure that controls our balance, coordination, movement, and motor skills, and it is thought to be important in processing some types of memory
- cerebral cortex
- surface of the brain that is associated with our highest mental capabilities
- chromosome
- long strand of genetic information
- computerized tomography (CT) scan
- imaging technique in which a computer coordinates and integrates multiple x-rays of a given area
- corpus callosum
- thick band of neural fibers connecting the brain’s two hemispheres
- dendrite
- branch-like extension of the soma that receives incoming signals from other neurons
- deoxyribonucleic acid (DNA)
- helix-shaped molecule made of nucleotide base pairs
- diabetes
- disease related to insufficient insulin production
- dominant allele
- allele whose phenotype will be expressed in an individual that possesses that allele
- electroencephalography (EEG)
- recording the electrical activity of the brain via electrodes on the scalp
- endocrine system
- series of glands that produce chemical substances known as hormones
- epigenetics
- study of gene-environment interactions, such as how the same genotype leads to different phenotypes
- fight or flight response
- activation of the sympathetic division of the autonomic nervous system, allowing access to energy reserves and heightened sensory capacity so that we might fight off a given threat or run away to safety
- forebrain
- largest part of the brain, containing the cerebral cortex, the thalamus, and the limbic system, among other structures
- fraternal twins
- twins who develop from two different eggs fertilized by different sperm, so their genetic material varies the same as in non-twin siblings
- frontal lobe
- part of the cerebral cortex involved in reasoning, motor control, emotion, and language; contains motor cortex
- functional magnetic resonance imaging (fMRI)
- MRI that shows changes in metabolic activity over time
- gene
- sequence of DNA that controls or partially controls physical characteristics
- genetic environmental correlation
- view of gene-environment interaction that asserts our genes affect our environment, and our environment influences the expression of our genes
- genotype
- genetic makeup of an individual
- glial cell
- nervous system cell that provides physical and metabolic support to neurons, including neuronal insulation and communication, and nutrient and waste transport
- gonad
- secretes sexual hormones, which are important for successful reproduction, and mediate both sexual motivation and behaviour
- gyrus
- (plural: gyri) bump or ridge on the cerebral cortex
- hemisphere
- left or right half of the brain
- heterozygous
- consisting of two different alleles
- hindbrain
- division of the brain containing the medulla, pons, and cerebellum
- hippocampus
- structure in the temporal lobe associated with learning and memory
- homeostasis
- state of equilibrium—biological conditions, such as body temperature, are maintained at optimal levels
- homozygous
- consisting of two identical alleles
- hormone
- chemical messenger released by endocrine glands
- hypothalamus
- forebrain structure that regulates sexual motivation and behaviour and a number of homeostatic processes; serves as an interface between the nervous system and the endocrine system
- identical twins
- twins that develop from the same sperm and egg
- lateralization
- concept that each hemisphere of the brain is associated with specialized functions
- limbic system
- collection of structures involved in processing emotion and memory
- longitudinal fissure
- deep groove in the brain’s cortex
- magnetic resonance imaging (MRI)
- magnetic fields used to produce a picture of the tissue being imaged
- medulla
- hindbrain structure that controls automated processes like breathing, blood pressure, and heart rate
- membrane potential
- difference in charge across the neuronal membrane
- midbrain
- division of the brain located between the forebrain and the hindbrain; contains the reticular formation
- motor cortex
- strip of cortex involved in planning and coordinating movement
- mutation
- sudden, permanent change in a gene
- myelin sheath
- fatty substance that insulates axons
- neuron
- cells in the nervous system that act as interconnected information processors, which are essential for all of the tasks of the nervous system
- neuroplasticity
- nervous system’s ability to change
- neurotransmitter
- chemical messenger of the nervous system
- Nodes of Ranvier
- open spaces that are found in the myelin sheath that encases the axon
- occipital lobe
- part of the cerebral cortex associated with visual processing; contains the primary visual cortex
- pancreas
- secretes hormones that regulate blood sugar
- parasympathetic nervous system
- associated with routine, day-to-day operations of the body
- parietal lobe
- part of the cerebral cortex involved in processing various sensory and perceptual information; contains the primary somatosensory cortex
- peripheral nervous system (PNS)
- connects the brain and spinal cord to the muscles, organs and senses in the periphery of the body
- phenotype
- individual’s inheritable physical characteristics
- pituitary gland
- secretes a number of key hormones, which regulate fluid levels in the body, and a number of messenger hormones, which direct the activity of other glands in the endocrine system
- polygenic
- multiple genes affecting a given trait
- pons
- hindbrain structure that connects the brain and spinal cord; involved in regulating brain activity during sleep
- positron emission tomography (PET) scan
- involves injecting individuals with a mildly radioactive substance and monitoring changes in blood flow to different regions of the brain
- prefrontal cortex
- area in the frontal lobe responsible for higher-level cognitive functioning
- psychotropic medication
- drugs that treat psychiatric symptoms by restoring neurotransmitter balance
- range of reaction
- asserts our genes set the boundaries within which we can operate, and our environment interacts with the genes to determine where in that range we will fall
- receptor
- protein on the cell surface where neurotransmitters attach
- recessive allele
- allele whose phenotype will be expressed only if an individual is homozygous for that allele
- resting potential
- the state of readiness of a neuron membrane’s potential between signals
- reticular formation
- midbrain structure important in regulating the sleep/wake cycle, arousal, alertness, and motor activity
- reuptake
- neurotransmitter is pumped back into the neuron that released it
- semipermeable membrane
- cell membrane that allows smaller molecules or molecules without an electrical charge to pass through it, while stopping larger or highly charged molecules
- soma
- cell body
- somatic nervous system
- relays sensory and motor information to and from the CNS
- somatosensory cortex
- essential for processing sensory information from across the body, such as touch, temperature, and pain
- substantia nigra
- midbrain structure where dopamine is produced; involved in control of movement
- sulcus
- (plural: sulci) depressions or grooves in the cerebral cortex
- sympathetic nervous system
- involved in stress-related activities and functions
- synaptic cleft
- small gap between two neurons where communication occurs
- synaptic vesicle
- storage site for neurotransmitters
- temporal lobe
- part of cerebral cortex associated with hearing, memory, emotion, and some aspects of language; contains primary auditory cortex
- terminal button
- axon terminal containing synaptic vesicles
- thalamus
- sensory relay for the brain
- theory of evolution by natural selection
- states that organisms that are better suited for their environments will survive and reproduce compared to those that are poorly suited for their environments
- threshold of excitation
- level of charge in the membrane that causes the neuron to become active
- thyroid
- secretes hormones that regulate growth, metabolism, and appetite
- ventral tegmental area (VTA)
- midbrain structure where dopamine is produced: associated with mood, reward, and addiction
- Wernicke’s area
- important for speech comprehension