The Biology of Mind Chapter 2

Parts of a Neuron Dendrites: Branching extensions at the cell body. Receive messages from other neurons. Cell Body: Life support center of the neuron. Axon Terminals: Branched endings of an axon that transmit messages to other neurons. Axon: Long single extension of a neuron, covered with a myelin [MY-uh-lin] sheath to insulate and speed up messages through neurons. Dendrites Cell Body Axon Terminals

Parts of a Neuron – Summary Preview Question 1: What are neurons, and how do they transmit information?

Action Potential – Summary Figure 2.3

Refractory Period & Pumps Refractory Period: After a neuron fires an action potential, it pauses for a short period to recharge itself to fire again. It pumps positively charged sodium ions back outside the neuron.

Action Potential Properties Threshold: Each neuron receives excitatory and inhibitory signals from many neurons. When the excitatory signals minus the inhibitory signals exceed a minimum intensity (threshold) the neuron fires an action potential. All-or-None Response: A strong stimulus can trigger more neurons to fire, and to fire more often, but it does not affect the action potentials strength or speed. Intensity of an action potential remains the same throughout the length of the axon.

How Neurons Communicate Synapse [SIN-aps] a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. This tiny gap is called the synaptic gap or cleft. Neurotransmitters are chemical messengers that traverse the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether it will generate a neural impulse.

Neurotransmitters – Summarized

Reuptake Neurotransmitters in the synapse are reabsorbed into the sending neurons through the process of reuptake. This process applies the brakes on neurotransmitter action.

Neurotransmitters Table 2.1

Lock & Key Mechanism Neurotransmitters bind to the receptors of the receiving neuron in a key-lock mechanism.

The Nervous System Figure 2.7

Kinds of Neurons – A Review Sensory Neurons carry incoming information from the sense receptors to the CNS. Motor Neurons carry outgoing information from the CNS to muscles and glands. Interneurons connect the two neurons. Interneuron Neuron (Unipolar) Sensory Neuron (Bipolar) Motor Neuron (Multipolar)

Central Nervous System The Spinal Cord and Reflexes The spinal cord is an information highway connecting the peripheral nervous system to the brain. The neural pathways governing our reflexes, our automatic responses to stimuli, illustrate the spinal cord’s work. Figure 2.10 A Simple Reflex

The Endocrine System The Endocrine System is the body’s “slow” chemical communication system. Communication is carried out by hormones synthesized by a set of glands. Preview Question 4: How does the endocrine system-the body’s slower information system-transmit its messages?

Pituitary Gland The pituitary gland is called the “master gland.” The anterior pituitary lobe releases hormones that regulate other glands. The posterior lobe regulates water and salt balance.

Other Endocrine Glands The pituitary gland is called the “master gland.” The anterior pituitary lobe releases hormones that regulate other glands. The posterior lobe regulates water and salt balance. The thyroid and parathyroid regulate metabolic and calcium rate.

Other Endocrine Glands Adrenal glands consist of the adrenal medulla and the cortex. The medulla secretes hormones (epinephrine and norepinephrine) during stressful and emotional situations, while the adrenal cortex regulates salt and carbohydrate metabolism. Sex glands are located in different places in men and women. They regulate bodily development and maintain reproductive organs in adults.

Techniques to Study the Brain A brain lesion experimentally destroys brain tissue to study animal behaviors after such destruction. An electroencephalogram (EEG) is an amplified recording of the electrical waves sweeping across the brain’s surface, measured by electrodes placed on the scalp. Computerized Axial Tomography (CAT Scan) is a series of X-Ray photographs taken from different angles and combined by computer into a composite representation of a slice through the body. Also called a Computed Tomograph (CT) Scan.

Techniques to Study the Brain A Positron Emission Tomography (PET) Scan is a visual display of brain activity that detects a radioactive form of glucose while the brain performs a given task. Magnetic Resonance Imaging (MRI) uses magnetic fields and radio waves to produce computer-generated images that distinguish among different types of brain tissue. Top images show ventricular enlargement in a schizophrenic patient. Bottom image shows brain regions when a participants lies. Courtesy of National Brookhaven National Laboratories

Brainstem The Medulla [muh-DUL-uh] is the base of the brainstem that controls heartbeat and breathing. Reticular Formation is a nerve network in the brainstem that plays an important role in controlling arousal. The Thalamus [THAL-uh-muss] is the brain’s sensory switchboard, located on top of the brainstem. It directs messages to the sensory areas in the cortex and transmits replies to the cerebellum and medulla. Thalamus Reticular Formation Thalamus Medulla

Cerebellum The cerebellum, or “little brain,” is attached to the rear of the brainstem. It helps us judge time, modulate our emotions, discriminate sounds and textures as well as coordinate voluntary movements and balance.

Amygdala and Hypothalamus The Amygdala [ah-MIG-dah-la] consists of two lima bean-sized neural clusters linked to the emotions of fear and anger. The Hypothalamus lies below (hypo) the thalamus. It directs several maintenance activities like eating, drinking, body temperature, and control of emotions. The hypothalamus helps govern the endocrine system via the pituitary gland. The hippocampus processes memory. Without it, we cannot process new memories of facts and episodes. Thalamus Hypothalamus Pituitary Gland Amygdala Hippocampus

The Cerebral Cortex The cerebral cortex is the intricate fabric of interconnected neural cells that covers the cerebral hemispheres like the bark of a tree. It is the body’s ultimate control and information processing center.

Structure of the Cortex Neurons are like queen bees…they cannot feed or sheathe (protect) themselves. Glial cells are worker bees…they provide nutrients and insulating myelin, guide neural connections, and mop up ions and neurotransmitters. Glial Cells Preview Question 7: What are the four lobes of the cerebral cortex, and where are they located?

Structure of the Cortex The frontal lobe is involved in speaking and muscle movements (motor cortex) and in making plans and judgments The parietal lobe integrates sensory information from various parts of the body and includes the sensory cortex. The occipital lobe includes the visual areas which receive visual information from the opposite visual field. The temporal lobe is concerned with hearing, memory, emotion, and speaking. Frontal Lobe Parietal Lobe Preview Question 7: What are the four lobes of the cerebral cortex, and where are they located? Temporal Lobe Occipital Lobe

Functions of the Cortex The Motor Cortex is the area at the rear of the frontal lobes that control voluntary movements. The Sensory Cortex (parietal cortex) receives information from skin surface and sense organs. Preview Question 8: What are the functions of the cerebral cortex?

Association Areas The sensory and motor cortexes take up about one quarter of the cerebral cortex. Neurons in the other three quarters are called association areas. Association areas are found in all four lobes of the brain and are largest in humans. Electrically probing these areas does not trigger any observable response, so mapping these areas cannot be neatly done. This has led to the erroneous claim that we only use 10% of our brain (but that would mean a bullet would have a 90% chance of hitting an unused area).

Our brain is divided into two hemispheres. Our Divided Brain Our brain is divided into two hemispheres. For more than a century, clinical evidence has shown that the brain’s two sides serve differing functions. Lateralization (hemispheric specialization) is apparent after brain damage. The left hemisphere processes reading, writing, speaking, mathematics, and comprehension skills. In the 1960s, it was termed as the dominant brain.

This surgery was done as a treatment for epileptic seizures. Splitting the Brain A commissurotomy is a procedure in which the two hemispheres of the brain are isolated by cutting the connecting fibers (mainly those of the corpus callosum) between them. This surgery was done as a treatment for epileptic seizures. Corpus Callosum Preview Question 9: What is a split brain, and what does it reveal about brain functioning? Courtesy of Terence Williams, University of Iowa Martin M. Rother

Split Brain Patients With the corpus callosum severed, objects (apple) presented in the right visual field can be named. Objects (pencil) in the left visual field cannot.

Divided Consciousness

“What did you see?” “With your left hand, select the object you saw from those behind the screen.”