Neuroanatomy

• Neuroanatomy refers to the study of the parts and function of neurons.

• Neurons are individual nerve cells.

• Dendrites—rootlike parts of the cell that stretch out from the cell body.

• Cell body (also called the soma)—contains the nucleus and other parts of the cell needed to sustain its life.

• Axon—wirelike structure ending in the terminal buttons that extends from the cell body.

• Myelin sheath—a fatty covering around the axon of some neurons that speeds neural impulses.

• Terminal buttons (also called end buttons, terminal branches of axons, and synaptic knobs)—the branched end of the axon that contain neurotransmitters.

• Neurotransmitters—chemicals contained in terminal buttons that enable neurons to communicate.

• Synapse—the space between the terminal buttons of one neuron and the dendrites of the next neuron.

Neurotransmitters

• Some neurotransmitters are excitatory, meaning that they excite the next cell into firing.

• Other neurotransmitters are inhibitory, meaning that they inhibit the next cell from firing.

Nervous System

• Afferent Neurons (or Sensory Neurons) - Afferent neurons take information from the senses to the brain. (You can think of afferent nerves as taking information in at the brain.)

• Interneurons - Once information reaches the brain or spinal cord, interneurons take the messages and send them elsewhere in the brain or on to efferent neurons.

• Efferent Neurons (or Motor Neurons) - Efferent neurons take information from the brain to the rest of the body. (You can think of efferent nerves as carrying information that exits the brain.)

Organization of the Nervous System

• Our nervous system is divided into different categories based on function.

• The two main divisions are the central nervous system and the peripheral nervous system.

• The Central Nervous System - The central nervous system (CNS) consists of our brain and spinal cord—all the nerves housed within bone (the skull and vertebrae).

The Peripheral Nervous System

• The peripheral nervous system (PNS) consists of all the other nerves in your body—that is, all the nerves not encased in bone.

• The peripheral nervous system is divided into two categories: the somatic and the autonomic nervous systems.

Somatic Nervous System

• The somatic nervous system controls our voluntary muscle movements.

• The motor cortex of the brain sends impulses to the somatic nervous system, which controls the muscles that allow us to move.

Autonomic Nervous System

• The autonomic nervous system controls the automatic functions of our body—our heart, lungs, internal organs, glands, and so on.

• These nerves control our responses to stress—the fight or flight response that prepares our body to respond to a perceived threat.

Sympathetic Nervous System

• The sympathetic nervous system mobilizes our body to respond to stress.

• This part of our nervous systems carries messages to the control systems of the organs, glands, and muscles that direct our body’s response to stress.

• Parasympathetic Nervous System - The parasympathetic nervous system carries messages to the stress response system that causes our body to slow down after a stress response.

Normal Peripheral Nervous System Transmission

• An example will show how sensory information reaches the brain.

  • You stub your toe on a cast-iron coffee table while late-night snacking.

• Sensory neurons in your toe activate, sending a message up a neuron to the base of your spine (afferent nerves).

  • The message travels up your spinal cord on more afferent nerves to the brainstem and the sensory cortex (see "The Brain"), letting you know you stubbed your toe.

  • Your motor cortex transmits signals down the spinal cord to the leg and foot muscles (efferent nerves), causing you to hop up and down gripping your injured limb and muttering.

Reflexes: An Important Exception

• Most sensory information and muscle movements are controlled by the process.

• However, humans have a few reflexes that work differently.

The Brain

• Possibly the most relevant part of biology to psychologists is the brain.

• As far as we can tell, the brain controls most of human thought and behavior.

• Studying how the brain works is challenging because we cannot simply observe brain function the way we might observe a heart beating.

• Researchers are discovering many new details about how the brain works through experimentation and the use of technology.

Lesions

• Lesioning is the removal or destruction of part of the brain.

• Any time brain tissue is removed (lesioning), researchers can examine behavior changes and try to infer the function of that part of the brain.

• A famous historical example of lesioning is the frontal lobotomy.

• Researchers knew that lesioning part of the frontal lobe would make the patients calm and relieve some serious symptoms.

Electroencephalogram

• An electroencephalogram (EEG) detects brain waves.

• The EEG is widely used in sleep research to identify the different stages of sleep and dreaming.

Computerized Axial Tomography

• A computerized axial tomography (CAT or CT) scan is a sophisticated X-ray.

• The CAT scan uses several X-ray cameras that rotate around the brain and combine all the pictures into a detailed three-dimensional picture of the brain’s structure.

Magnetic Resonance Imaging

• Magnetic resonance imaging (MRI) is similar to a CAT scan in a way: both scans give you pictures of the brain.

• An MRI uses magnetic fields to measure the density and location of brain material.

• Positron Emission Tomography - A positron emission tomography (PET) scan lets researchers see what areas of the brain are most active during certain tasks.

Functional MRI

• Functional MRI (fMRI) is a new technology that combines elements of the MRI and PET scans.

• An fMRI scan can show details of brain structure with information about blood flow in the brain, tying brain structure to brain activity during cognitive tasks.

Brain Structure and Function

• When you study the brain, think about three separate major categories or sections: the hindbrain, midbrain, and forebrain.

• Some evolutionary psychologists organize these categories into two major divisions: the “old brain” (hindbrain and midbrain) and the “new brain” (forebrain).

Hindbrain

• The hindbrain consists of structures in the top part of the spinal cord.

• The hindbrain is our life support system; it controls the basic biological functions that keep us alive.

Medulla

• The medulla is involved in the control of our blood pressure, heart rate, and breathing.

• It is also known as the medulla oblongata and is located above the spinal cord.

Pons

• The pons (located just above the medulla and toward the front) connects the hindbrain with the midbrain and forebrain.

• It is also involved in the control of facial expressions.

Cerebellum

• The cerebellum (located on the bottom rear of the brain) looks like a smaller version of our brain stuck onto the underside of our brain.

• Cerebellum means little brain.

Midbrain

• In general, your midbrain coordinates simple movements with sensory information.

• Different parts of the midbrain are important in various muscle coordinations.

• One specific structure in the midbrain you should be familiar with is the reticular formation.

Forebrain

• The various areas of the forebrain are very important to psychologists.

• Areas of the forebrain control what we think of as thought and reason.

• Specific areas of interest to us in the forebrain are the thalamus, hypothalamus, amygdala, and hippocampus.

Thalamus

• The thalamus is located on top of the brain stem.

• It is responsible for receiving the sensory signals coming up the spinal cord and sending them to the appropriate areas in the rest of the forebrain.

• Hypothalamus - The hypothalamus controls several metabolic functions, including body temperature, sexual arousal (libido), hunger, thirst, and the endocrine system

Amygdala and Hippocampus

• There are two arms surrounding the thalamus.

  • These are called the hippocampus.

• Structures near the end of each hippocampal arm are called the amygdala.

• The amygdala is vital to our experiences of emotion, and the hippocampus is vital to our memory system.

Cerebral Cortex

• When most people think of the human brain, they think of and picture the cerebral cortex.

• The gray wrinkled surface of the brain is actually a thin (0.039-inch [1-mm]) layer of densely packed neurons.

• This layer covers the rest of the brain, including most of the structures we have described.

Hemispheres

• The cerebral cortex is divided into two hemispheres: left and right.

• The hemispheres look like mirror images of one another, but they exert some differences in function.

  • The left hemisphere gets sensory messages and controls the motor function of the right half of the body.

  • The right hemisphere gets sensory messages and controls the motor function of the left half of the body.

• Most of this research in differences between the hemispheres is done by examining split-brain patients—patients whose corpus callosum (the nerve bundle that connects the two hemispheres) has been cut to treat severe epilepsy.

Areas of the Cerebral Cortex

• Think of the cerebral cortex as eight different lobes, four on each hemisphere: frontal, parietal, temporal, and occipital.

• Any area of the cerebral cortex that it is not associated with receiving sensory information or controlling muscle movements is labeled as an association area.

Frontal Lobes

• The frontal lobes are large areas of the cerebral cortex located at the top front part of the brain behind the eyes.

  • The anterior or front of the frontal lobe is called the prefrontal cortex and is thought to play a critical role in directing thought processes.

• Broca’s area (Paul Broca 1824–1880) is in the frontal lobe and is responsible for controlling the muscles involved in producing speech.

• The other area is [Wernicke’s area [Carl Wernicke 1848–1905] and is located in the temporal lobe.

• A thin vertical strip at the back of the frontal lobe (farthest from the eyes) is called the motor cortex.

Parietal Lobes

• The parietal lobes are located behind the frontal lobe but still on the top of the brain.

• The parietal lobes contain the sensory cortex (also known as the somato-sensory cortex), which is located right behind the motor cortex in the frontal lobe.

Occipital Lobes

• Our occipital lobes are at the very back of our brain, farthest from our eyes.

• This is somewhat counterintutive since one of the major functions of this lobe is to interpret messages from our eyes in our visual cortex.

• Temporal Lobes - The temporal lobes process sound sensed by our ears.

Brain Plasticity

• Researchers know some of the functions of different areas of the cerebral cortex, but they have also discovered that the brain is somewhat plastic or flexible.

  • While these cortices and lobes usually perform the functions already mentioned, other parts of the brain can adapt themselves to perform other functions if needed.

Endocrine System

• Another part of human biology relevant to psychology is the endocrine system.

  • This is a system of glands that secrete hormones that affect many different biological processes in our bodies.

• Adrenal Glands - The adrenal glands produce adrenaline, which signals the rest of the body to prepare for fight or flight.

• Ovaries and Testes - Ovaries and testes produce our sex hormones, estrogen for female systems and testosterone for male systems.

Genetics

Twins

• Since identical twins (called monozygotic twins since they develop from one fertilized egg called a zygote) share all the same genetic material, researchers study them in order to examine the influence of genes on human traits.

• Thomas Bouchard found more than 100 identical twins who were given up for adoption and raised in different families.

• The study compared hundreds of traits and made conclusions about the relative influences of genetics and the environment on specific traits.

Chromosomal Abnormalities

• Our sex is determined by our twenty-third pair of chromosomes.

• Male systems have an X and Y chromosome, and female systems have two X chromosomes.

  • Usually a male will contribute either an X or a Y chromosome to a child.

  • Occasionally, chromosomes will combine (or fail to) in an unusual way, resulting in a chromosomal abnormality.

• Other chromosomal abnormalities may cause intellectual disability. The most common type is Down syndrome.

  • Babies with Down syndrome are born with an extra chromosome on the twenty-first pair.