Chapter 3: Neurons, Glial Cells, Synapses PDF

What are neurons? What is the cell body? Dendrites? Axons? The path of transmission in a neuron is dendrite, cell body, then axon. What are glial cells? What is the myelin sheath? What is a synapse? o Definition: Neurons are the fundamental units of the nervous system, specialized...

What are neurons? What is the cell body? Dendrites? Axons? The path of transmission in a neuron is dendrite, cell body, then axon. What are glial cells? What is the myelin sheath? What is a synapse? o Definition: Neurons are the fundamental units of the nervous system, specialized cells responsible for transmitting information throughout the body. They communicate via electrical impulses and chemical signals, enabling the functioning of the brain, spinal cord, and peripheral nerves. ▪ Function: Neurons play a critical role in receiving stimuli, processing information, and transmitting signals to other neurons, muscles, or glands. o Definition: The cell body, or soma, is the central part of a neuron that contains the nucleus and organelles. ▪ Function: It is responsible for maintaining the cell's health, processing incoming signals, and integrating information. The cell body generates the necessary electrical impulses to be sent down the axon. o Definition: Dendrites are tree-like structures that extend from the cell body of a neuron. ▪ Function: Their primary role is to receive signals from other neurons or sensory receptors. They increase the surface area of the neuron, allowing it to connect with more cells and receive a greater volume of input. o Definition: Axons are long, thin projections that extend from the cell body of a neuron. ▪ Function: Axons transmit electrical impulses away from the cell body to other neurons, muscles, or glands. o Path of transmission in a neuron: ▪ Dendrites: Receive signals from other neurons. ▪ Cell Body: Processes the signals and integrates information. ▪ Axon: Sends the electrical impulse to the next neuron or target cell. o Definition: Glial cells (or neuroglia) are non-neuronal cells in the nervous system that provide support, protection, and nutrition to neurons. o Definition: The myelin sheath is a fatty layer that surrounds and insulates the axons of some neurons. ▪ It increases the speed of electrical signal transmission along the axon through a process called saltatory conduction, where signals jump between the nodes of Ranvier (gaps in the myelin sheath). This insulation helps prevent signal loss and improves the efficiency of neuronal communication.  o Definition: A synapse is the junction between two neurons, where the axon terminal of one neuron meets the dendrites or cell body of another neuron. ▪ Function: It is the site of neurotransmitter release, where signals are transmitted chemically from one neuron to another. This communication can either be excitatory (promoting the firing of the next neuron) or inhibitory (reducing the likelihood of firing). What are three types of neurons (sensory neurons, motor neurons, and interneurons)? o Definition: Sensory neurons are responsible for transmitting sensory information from sensory receptors (such as those in the skin, eyes, ears, nose, and tongue) to the central nervous system (CNS). ▪ Function: They convert external stimuli into electrical impulses that are sent to the brain and spinal cord for processing. o Definition: Motor neurons transmit signals from the central nervous system to muscles and glands, facilitating movement and physiological responses. ▪ Function: They enable the body to respond to stimuli by triggering muscle contractions or glandular secretions. o Definition: Interneurons are neurons that act as intermediaries between sensory and motor neurons within the central nervous system. ▪ Function: They play a critical role in processing information, integrating sensory input, and coordinating motor output. Be familiar with how electrical signals are conducted within a neuron. What is the resting potential? Is it + or -? When a threshold hold is reached, what happens? What is an action potential – does the charge become + or -? What are nodes of Ranvier? Why is transmission faster in neurons that are insulated with a myelin sheath? What is the refractory period? o Definition: Resting potential refers to the electrical charge difference across a neuron's membrane when the neuron is not actively transmitting a signal. ▪ Charge: It is typically around −70 millivolts (mV), meaning the inside of the neuron is more negatively charged compared to the outside. o Definition: The threshold is the critical level of depolarization that must be reached for an action potential to occur. ▪ Process: When a stimulus causes the membrane potential to reach this threshold (usually around −55 mV), voltage-gated sodium channels open, allowing sodium ions (Na⁺) to rush into the neuron. o Definition: An action potential is a rapid and significant change in the electrical charge of a neuron. ▪ Charge Change: As sodium ions enter the neuron, the charge inside the neuron becomes positive (up to around +30 mV) due to the influx of Na⁺.  This rapid depolarization is followed by repolarization, where potassium ions (K⁺) exit the neuron, returning the charge back to a negative state. o Definition: Nodes of Ranvier are small gaps in the myelin sheath that insulates the axon of a neuron. ▪ Function: They facilitate the rapid conduction of electrical signals along the axon through a process called saltatory conduction, where the action potential jumps from one node to the next. o Definition: The myelin sheath is a fatty layer that surrounds and insulates the axon of many neurons. ▪ Speed of Transmission: The presence of the myelin sheath increases the speed of transmission of electrical signals by preventing the loss of ions and allowing the action potential to jump between the nodes of Ranvier, making it much faster than in unmyelinated axons. o Definition: The refractory period is the time after an action potential during which a neuron cannot fire another action potential. Be familiar with how chemicals transmit messages between neurons. What is a synapse? Is communication between neurons electrical or chemical? What are terminal buttons? What are neurotransmitters? What are the three ways the synapse is cleared? Be familiar with the neurotransmitters dopamine and endorphins. Which is implicated in schizophrenia? What are the ways that drug can influence neurotransmitters? What is an agonist? o Definition: A synapse is the junction between two neurons where communication occurs. It consists of the presynaptic terminal (the terminal button of the sending neuron), the synaptic cleft (the space between the neurons), and the postsynaptic membrane (the receiving neuron). o Type: The communication between neurons is primarily chemical. While electrical signals (action potentials) travel along the axon, the actual transmission across the synapse is mediated by neurotransmitters. o Definition: Terminal buttons (or synaptic terminals) are small knobs at the end of an axon that release neurotransmitters into the synaptic cleft. They contain vesicles filled with neurotransmitters, which are released in response to an action potential. o Definition: Neurotransmitters are chemical messengers released from terminal buttons into the synaptic cleft. They bind to receptors on the postsynaptic neuron, influencing whether it will fire an action potential. o There are three primary ways the synapse is cleared of neurotransmitters after they have exerted their effects: ▪ Reuptake: Neurotransmitters are reabsorbed by the presynaptic neuron through transporters in the membrane. ▪ Enzymatic Degradation: Enzymes in the synaptic cleft break down neurotransmitters into inactive substances.  ▪ Diffusion: Neurotransmitters drift away from the synaptic cleft into surrounding tissue, reducing their concentration. o Dopamine: This neurotransmitter is involved in reward, motivation, and pleasure. It is implicated in several psychiatric disorders, including schizophrenia, where it is thought that excess dopamine activity contributes to symptoms. o Endorphins: These neurotransmitters are natural pain relievers and are associated with feelings of pleasure and euphoria. They play a role in the body's response to stress and pain. o Agonists: Substances that enhance or mimic the action of neurotransmitters. For example, certain medications can increase dopamine levels to help manage symptoms of Parkinson's disease or depression. o Antagonists: Substances that inhibit or block neurotransmitter actions. For example, antipsychotic medications often act as dopamine antagonists to reduce symptoms of schizophrenia. What comprises the central nervous system? The peripheral nervous system? Be able to explain the difference between the somatic and autonomic nervous system and the difference between the sympathetic and parasympathetic nervous system. o Central Nervous System: The central nervous system is comprised of the brain and the spinal cord. ▪ The control center for processing sensory information, regulating bodily functions, and coordinating movement. ▪ A conduit for transmitting signals between the brain and the rest of the body, responsible for reflex actions. o Peripheral Nervous System: The peripheral nervous system consists of all the nerves outside the central nervous system. It includes: ▪ Sensory Nerves: Carry sensory information from the body to the CNS. ▪ Motor Nerves: Convey commands from the CNS to the muscles and glands. o Somatic Nervous System: ▪ Function: Controls voluntary movements by sending signals to skeletal muscles. It is responsible for actions that are consciously controlled, such as walking, talking, and picking up objects. ▪ Components: Comprises motor neurons that innervate skeletal muscles and sensory neurons that relay information about external stimuli to the CNS.  o Autonomic Nervous System (ANS): ▪ Function: Regulates involuntary bodily functions, such as heart rate, digestion, and respiratory rate. It operates automatically without conscious control. ▪ Components: Divided into two main branches: Sympathetic Nervous System: Prepares the body for "fight or flight" responses during stressful situations. It increases heart rate, dilates pupils, and inhibits digestion. Parasympathetic Nervous System: Promotes "rest and digest" activities that occur when the body is at rest. It conserves energy by slowing the heart rate, constricting pupils, and stimulating digestion. Be able to explain the path of a reflex. o Stimulus: A reflex begins with a stimulus, such as touching a hot surface or stepping on a sharp object. o Receptor: Sensory receptors in the skin detect the stimulus. These receptors convert the physical stimulus (e.g., heat, pressure) into an electrical signal. o Sensory Neuron: The electrical signal is transmitted through a sensory neuron. This neuron carries the impulse from the receptor to the spinal cord. o Spinal Cord: The sensory neuron enters the spinal cord, where it synapses with an interneuron (a neuron that processes information within the spinal cord). In simple reflexes, the sensory neuron may directly synapse with a motor neuron. o Interneuron (optional): If present, the interneuron processes the information and may send signals to other neurons. This step is more common in complex reflexes. o Motor Neuron: The motor neuron is activated by the interneuron or directly by the sensory neuron. It carries the impulse away from the spinal cord to the muscles. o Effector: The motor neuron synapses with an effector, typically a muscle. The muscle receives the signal to contract, resulting in a reflex action, such as pulling your hand away from a hot surface. o Response: The body responds quickly to the stimulus, which helps to protect it from harm. The brain - you will not have to label parts on a picture but you will need to know the functions of each part Hindbrain/brainstem: medulla, cerebellum, reticular formation  Medulla Function: The medulla is responsible for regulating vital autonomic functions such as heart rate, blood pressure, and respiration. It acts as a pathway for signals between the brain and spinal cord and controls reflexes like swallowing, coughing, and sneezing. Cerebellum Function: The cerebellum is involved in coordinating voluntary movements, balance, and motor control. It helps fine-tune movements, maintain posture, and ensure smooth, balanced bodily motions. It also plays a role in cognitive functions like attention and language. Reticular Formation Function: The reticular formation is a network of neurons located throughout the brainstem that plays a crucial role in regulating wakefulness and sleep-wake transitions. It helps control alertness and attention and is involved in filtering incoming sensory information. Forebrain: Subcortical structures: thalamus, hypothalamus, hippocampus, amygdala, basal ganglia ▪ Thalamus Function: Often referred to as the "gateway to the cortex," the thalamus processes and relays sensory information (except for smell) to the appropriate areas of the cerebral cortex. It plays a key role in regulating consciousness, sleep, and alertness. ▪ Hypothalamus Function: The hypothalamus regulates homeostasis and various bodily functions, including temperature, hunger, thirst, sleep, and circadian rhythms. It also controls the pituitary gland and plays a critical role in the endocrine system. ▪ Hippocampus Function: The hippocampus is essential for the formation of new memories and learning. It is involved in converting short-term memories into long-term memories and plays a role in spatial navigation. ▪ Amygdala  Function: The amygdala is involved in processing emotions, particularly fear, aggression, and pleasure. It helps form emotional memories and is key in the body’s response to threats. ▪ Basal Ganglia Function: The basal ganglia are a group of nuclei that play a critical role in coordinating movement and motor control. They are involved in various functions, including procedural learning, habit formation, and the regulation of voluntary movements. They also have a role in emotion and cognition. Forebrain: Cerebral cortex: What is the corpus callosum? When you move the left side of you body it was controlled by what side of your brain? Lobes (temporal, occipital, parietal, and frontal): Know their functions. Which lobes contain the auditory cortex? Which lobes contain the visual cortex? What are the motor and sensory cortexes? Which lobes are they in? o Corpus Callosum ▪ Definition: The corpus callosum is a large band of nerve fibers that connects the left and right hemispheres of the brain, allowing communication between the two sides. ▪ Function: It facilitates interhemispheric communication and helps coordinate activities between the left and right sides of the brain. o Lateralization of Motor Control ▪ Fact: When you move the left side of your body, it is controlled by the right side of your brain, and vice versa. This is due to the crossing of motor pathways in the brainstem. Lobes of the Cerebral Cortex and Their Functions 1. Frontal Lobe ○ Function: Responsible for higher-level cognitive functions such as reasoning, problem-solving, planning, impulse control, and judgment. It also houses the primary motor cortex, which is involved in voluntary movement. ○ Motor Cortex Location: The primary motor cortex is located in the posterior part of the frontal lobe. 2. Parietal Lobe ○ Function: Processes sensory information related to touch, temperature, pain, and proprioception (body position). It also plays a role in spatial awareness and coordination. ○ Sensory Cortex Location: The primary somatosensory cortex is located in the anterior part of the parietal lobe. 3. Temporal Lobe ○ Function: Involved in auditory processing, memory, and language comprehension. It plays a key role in recognizing and processing sounds.  ○ Auditory Cortex Location: The primary auditory cortex is located in the superior part of the temporal lobe. 4. Occipital Lobe ○ Function: Primarily responsible for visual processing. It interprets visual stimuli and plays a crucial role in recognizing shapes, colors, and motion. ○ Visual Cortex Location: The primary visual cortex is located in the occipital lobe. Motor and Sensory Cortexes Motor Cortex: ○ Location: Found in the posterior portion of the frontal lobe. ○ Function: Controls voluntary movements by sending signals to the muscles. Sensory Cortex: ○ Location: Found in the anterior part of the parietal lobe. ○ Function: Processes sensory information from the body, allowing perception of touch, pressure, pain, and temperature. Which body parts get more space on the somatosensory and motor cortex? Why? o Fingers and Hands: ▪ Reason: The fingers have a high density of sensory receptors, making them sensitive to touch, texture, and fine motor skills. This requires a larger representation in the somatosensory cortex for detailed sensory processing. o Face and Lips: ▪ Reason: The face, particularly the lips, is rich in sensory receptors and is crucial for communication (speaking) and feeding, necessitating more cortical area for processing sensory information. o Genitalia: ▪ Reason: The genital area also has a high concentration of sensory receptors and is significant in terms of sensory experience, thus requiring a larger representation in the somatosensory cortex. Body Parts with More Space on the Motor Cortex 1. Hands and Fingers: ○ Reason: The fine motor control required for tasks such as typing, playing instruments, and performing delicate tasks necessitates a larger area in the motor cortex dedicated to the hands and fingers. 2. Face and Mouth: ○ Reason: The motor control required for facial expressions, speech, and eating is complex and requires precise movements, warranting greater representation in the motor cortex.  3. Feet: ○ Reason: While not as expansive as the hands, the feet have a dedicated area in the motor cortex for walking and balancing, which is crucial for mobility. Which lobes are involved in planning and making judgments? o Frontal lobe and Parietal Lobe. What is the role of the pituitary gland? 1. Hormone Production The pituitary gland produces and secretes various hormones that regulate critical bodily functions. These hormones influence growth, metabolism, and reproductive processes. 2. Regulation of Other Glands The pituitary gland controls other endocrine glands, such as the thyroid, adrenal glands, and gonads (ovaries and testes). It does this through the release of stimulating hormones: ○ Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones, which regulate metabolism. ○ Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to release cortisol, which helps the body respond to stress. ○ Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH): Regulate reproductive processes in both males and females. 3. Growth and Development Growth Hormone (GH): Promotes growth and development in children and adolescents by stimulating cell growth and reproduction. 4. Water Regulation Antidiuretic Hormone (ADH): Also known as vasopressin, ADH helps regulate water balance in the body by controlling the amount of water reabsorbed by the kidneys. 5. Milk Production Prolactin: Stimulates milk production in breastfeeding women. What are association areas? What is meant by plasticity? o Association areas refer to regions of the cerebral cortex that are involved in higher-level processing and integration of information. Unlike primary sensory or  motor areas, which are primarily responsible for processing specific types of sensory information (like vision or hearing) or controlling voluntary movements, association areas connect and combine information from different modalities and play a crucial role in complex cognitive functions. o Plasticity, or neuroplasticity, refers to the brain's ability to reorganize itself by forming new neural connections throughout life. This capacity allows the brain to adapt to new experiences, learn new information, and recover from injuries. How are identical twins different from fraternal twins? You should understand the logic behind twin studies (E.g., if an effect is all genetics- who should have a higher correlation- identical twins or fraternal twins?) Why do researchers like to study identical twins who have been separated? Identical Twins (Monozygotic Twins): Origin: Identical twins are formed from a single fertilized egg (zygote) that splits into two embryos. This means they share 100% of their genetic material. Genetic Similarity: Because they come from the same zygote, they have identical DNA, which makes them genetically the same. Physical Traits: Identical twins often have very similar physical traits, including appearance, hair color, and eye color, although environmental factors can still lead to some differences. Fraternal Twins (Dizygotic Twins): Origin: Fraternal twins are formed when two separate eggs are fertilized by two different sperm cells during the same pregnancy. As a result, they are genetically similar like regular siblings, sharing about 50% of their genetic material. Genetic Similarity: Fraternal twins have different DNA and can be of the same sex or different sexes. Physical Traits: They may or may not look alike and can have different physical features, reflecting their unique genetic combinations. Twin studies are a powerful tool for understanding the influence of genetics versus environment on human traits and behaviors. The logic behind twin studies is based on the comparison of the similarities between identical twins and fraternal twins. What is the split brain procedure? What hemisphere processes language? Review experiment on p. 84 (shown to right visual field, can name it; shown to left visual field- can only point to it with right hand but not name it). o The split-brain procedure is a surgical intervention that involves severing the corpus callosum, the bundle of nerve fibers connecting the left and right hemispheres of the brain. The experiment referenced on page 84 typically involves visual stimuli presented to either the right or left visual field of split-brain patients. Here’s how it demonstrates hemispheric specialization: 1. Right Visual Field Presentation: When a visual stimulus (such as a word or image) is shown in the right visual field, it is processed by the left hemisphere. Because the left hemisphere is responsible for language, the patient can verbally name the object presented. 2. Left Visual Field Presentation: When the same or a different visual stimulus is presented in the left visual field, it is processed by the right hemisphere. The right hemisphere does not have the same language capabilities as the left. In this case, the patient cannot verbally name the object but may be able to point to it or select it with their left hand (which is controlled by the right hemisphere). Split-Brain Procedure The split-brain procedure is a surgical intervention that involves severing the corpus callosum, the bundle of nerve fibers connecting the left and right hemispheres of the brain. This procedure is typically performed to alleviate severe epilepsy, where seizures originating in one hemisphere can spread to the other. By cutting the corpus callosum, surgeons can isolate the hemispheres, preventing the transfer of seizure activity. Hemispheric Specialization In terms of function, the left hemisphere of the brain is primarily responsible for language processing in most individuals (about 95% of right-handed people and 70% of left-handed people). This includes not just speech production but also comprehension and reading. Experiment Review The experiment referenced on page 84 typically involves visual stimuli presented to either the right or left visual field of split-brain patients. Here’s how it demonstrates hemispheric specialization: 1. Right Visual Field Presentation: When a visual stimulus (such as a word or image) is shown in the right visual field, it is processed by the left hemisphere. Because the left hemisphere is responsible for language, the patient can verbally name the object presented. 2. Left Visual Field Presentation: When the same or a different visual stimulus is presented in the left visual field, it is processed by the right hemisphere. The right hemisphere does not have the same language capabilities as the left. In this case, the patient cannot verbally name the object but may be able to point to it or select it with their left hand (which is controlled by the right hemisphere).  Implications of the Experiment These findings highlight the concept of hemispheric specialization and how the brain's two halves can function independently to some extent. What is an EEG? What are neuroimaging techniques? CT scans and MRIs show the structure of the brain. What procedures show the function of the brain? o An EEG (electroencephalogram) is a neurophysiological monitoring method used to record electrical activity in the brain. It involves placing electrodes on the scalp to detect and measure the electrical impulses generated by neuron activity. The resulting recordings provide insights into brain wave patterns and can help diagnose conditions such as epilepsy, sleep disorders, and other neurological issues. o CT Scans (Computed Tomography): CT scans use X-rays to create detailed cross-sectional images of the brain. They are particularly useful for detecting structural abnormalities, such as tumors, bleeding, or brain injury. o MRI (Magnetic Resonance Imaging): MRI employs powerful magnetic fields and radio waves to produce high-resolution images of brain structures. It provides detailed images of both soft tissue and structural abnormalities in the brain without exposure to radiation. o fMRI (Functional Magnetic Resonance Imaging): fMRI measures brain activity by detecting changes in blood flow and oxygenation levels. This method allows researchers to observe which areas of the brain are active during specific tasks, providing insight into the functional organization of the brain. o PET Scans (Positron Emission Tomography): PET scans use radioactive tracers to visualize brain metabolism and blood flow. By injecting a radioactive substance that emits positrons, this technique can track how glucose is used in the brain, indicating areas of activity.