Exercise 14 Review Sheet Nervous Tissue

Nervous tissue, the intricate network that governs our thoughts, actions, and sensations, is a cornerstone of understanding human biology. This article will dissect the complexities of nervous tissue, offering a comprehensive review that spans its cellular components, functional properties, and organizational structure. We'll explore the building blocks of this vital tissue, unraveling the roles of neurons and glial cells, and shedding light on their collaborative efforts to maintain the body's delicate balance.

Understanding Nervous Tissue

Nervous tissue is primarily responsible for the communication and control within the body. It's composed of two main cell types: neurons and glial cells. Neurons, also known as nerve cells, are specialized for transmitting electrical signals called action potentials. Glial cells, on the other hand, support, protect, and nourish neurons. Together, they form a complex network that allows for rapid communication between different parts of the body.

Neurons: The Communicators

Neurons are the fundamental units of the nervous system, responsible for transmitting information throughout the body. Their unique structure enables them to receive, process, and transmit electrical and chemical signals. Understanding the different parts of a neuron is crucial to understanding how the nervous system functions.

• Cell Body (Soma): The central part of the neuron, containing the nucleus and other essential organelles. It's the neuron's control center, responsible for synthesizing proteins and maintaining the cell's overall health.
• Dendrites: Branch-like extensions that receive signals from other neurons. These signals are transmitted towards the cell body. The more dendrites a neuron has, the more connections it can make with other neurons.
• Axon: A long, slender projection that transmits signals away from the cell body. The axon is responsible for carrying the action potential to other neurons or target cells.
• Axon Hillock: The region where the axon originates from the cell body. This is where the action potential is initiated.
• Myelin Sheath: A fatty insulation layer that surrounds the axons of some neurons. It's formed by glial cells and speeds up the transmission of action potentials.
• Nodes of Ranvier: Gaps in the myelin sheath where the axon is exposed. These gaps allow for the action potential to "jump" along the axon, further increasing the speed of transmission.
• Axon Terminals (Synaptic Terminals): The branched endings of the axon that form connections with other neurons or target cells. These terminals release neurotransmitters, which transmit signals across the synapse.

Glial Cells: The Supporters

Glial cells, often referred to as neuroglia, are the supporting cells of the nervous system. They are more numerous than neurons and play a crucial role in maintaining the health and function of the nervous system. Unlike neurons, glial cells do not transmit electrical signals. Instead, they perform a variety of supporting functions.

• Astrocytes: The most abundant glial cells in the central nervous system (CNS). They provide structural support, regulate the chemical environment around neurons, and form the blood-brain barrier, which protects the brain from harmful substances.
• Oligodendrocytes: Glial cells in the CNS that form the myelin sheath around axons. One oligodendrocyte can myelinate multiple axons, increasing the speed of signal transmission.
• Microglia: The immune cells of the CNS. They act as scavengers, removing debris and pathogens from the brain and spinal cord.
• Ependymal Cells: Line the ventricles of the brain and the central canal of the spinal cord. They produce cerebrospinal fluid (CSF) and help to circulate it throughout the CNS.
• Schwann Cells: Glial cells in the peripheral nervous system (PNS) that form the myelin sheath around axons. Unlike oligodendrocytes, each Schwann cell only myelinates one segment of a single axon.
• Satellite Cells: Surround neuron cell bodies in the PNS. They provide support and regulate the chemical environment around neurons.

Functional Properties of Nervous Tissue

The ability of nervous tissue to transmit and process information depends on its unique functional properties. These properties include excitability, conductivity, and the ability to communicate with other cells.

Excitability

Excitability is the ability of a neuron to respond to a stimulus and generate an electrical signal. This stimulus can be a chemical signal, such as a neurotransmitter, or a physical signal, such as pressure or light. When a neuron is stimulated, its membrane potential changes, potentially leading to the generation of an action potential.

Conductivity

Conductivity is the ability of a neuron to transmit an electrical signal over a distance. This is accomplished through the propagation of the action potential along the axon. The myelin sheath and nodes of Ranvier play a crucial role in speeding up the conduction velocity of the action potential.

Communication

Neurons communicate with each other at specialized junctions called synapses. At the synapse, the presynaptic neuron releases neurotransmitters, which bind to receptors on the postsynaptic neuron. This binding can either excite or inhibit the postsynaptic neuron, influencing its likelihood of generating an action potential.

Organization of Nervous Tissue

Nervous tissue is organized into different structures, each with a specific function. These structures include the brain, spinal cord, nerves, and ganglia.

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord. It's the control center of the body, responsible for processing information and coordinating responses.

• Brain: The brain is the most complex organ in the body. It's responsible for a wide range of functions, including thought, memory, emotion, and motor control. The brain is divided into several regions, each with a specific function.
• Spinal Cord: The spinal cord is a long, cylindrical structure that extends from the brainstem to the lower back. It transmits signals between the brain and the rest of the body. It also controls reflexes, which are rapid, involuntary responses to stimuli.

Peripheral Nervous System (PNS)

The PNS consists of all nervous tissue outside the brain and spinal cord. It connects the CNS to the rest of the body.

• Nerves: Nerves are bundles of axons that transmit signals between the CNS and the rest of the body. They can be either sensory (afferent), carrying signals from the body to the CNS, or motor (efferent), carrying signals from the CNS to the body.
• Ganglia: Ganglia are clusters of neuron cell bodies located outside the CNS. They serve as relay stations for nerve signals.

Histology of Nervous Tissue

Examining nervous tissue under a microscope reveals its intricate structure and cellular components. Staining techniques are often used to highlight specific features of the tissue.

Neurons

Neurons are easily identifiable by their distinct cell body, dendrites, and axon. The nucleus is typically large and centrally located. Nissl bodies, which are clusters of rough endoplasmic reticulum, are also visible in the cell body.

Glial Cells

Glial cells are smaller than neurons and have a more uniform appearance. It can be difficult to distinguish between different types of glial cells without specialized staining techniques.

Myelinated Axons

Myelinated axons appear as thick, dark rings surrounding the axon. The myelin sheath is formed by Schwann cells in the PNS and oligodendrocytes in the CNS.

Clinical Significance

Understanding nervous tissue is crucial for diagnosing and treating a variety of neurological disorders. Damage to nervous tissue can result in a wide range of symptoms, depending on the location and extent of the damage.

Multiple Sclerosis (MS)

MS is an autoimmune disease that affects the myelin sheath in the CNS. The immune system attacks the myelin, leading to inflammation and damage. This can disrupt the transmission of nerve signals, resulting in a variety of symptoms, including muscle weakness, fatigue, and vision problems.

Alzheimer's Disease

Alzheimer's disease is a neurodegenerative disorder that affects the brain. It's characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain, which disrupt neuronal function and lead to cognitive decline.

Stroke

A stroke occurs when blood flow to the brain is interrupted. This can be caused by a blood clot (ischemic stroke) or a ruptured blood vessel (hemorrhagic stroke). The lack of oxygen and nutrients can damage or kill brain cells, leading to a variety of neurological deficits.

Peripheral Neuropathy

Peripheral neuropathy is damage to the nerves in the PNS. It can be caused by a variety of factors, including diabetes, injury, and infection. Symptoms can include pain, numbness, and weakness in the affected area.

Review Questions and Answers

Let's test your understanding of nervous tissue with a few review questions.

Question 1: What are the two main cell types found in nervous tissue?

Answer: Neurons and glial cells.

Question 2: What is the function of the myelin sheath?

Answer: To insulate the axon and speed up the transmission of action potentials.

Question 3: Which glial cell forms the blood-brain barrier?

Answer: Astrocytes.

Question 4: What is the difference between a nerve and a ganglion?

Answer: A nerve is a bundle of axons, while a ganglion is a cluster of neuron cell bodies.

Question 5: What is the function of neurotransmitters?

Answer: To transmit signals across the synapse between neurons.

Advanced Concepts in Nervous Tissue

Delving deeper into the intricacies of nervous tissue reveals advanced concepts crucial for a comprehensive understanding. These concepts include neuroplasticity, neurotransmitter systems, and the role of growth factors in nerve regeneration.

Neuroplasticity

Neuroplasticity refers to the brain's ability to reorganize itself by forming new neural connections throughout life. This remarkable ability allows the brain to adapt to new experiences, learn new skills, and compensate for injury. Neuroplasticity involves changes in the structure and function of neurons and their connections, including the growth of new dendrites, the strengthening or weakening of synaptic connections, and the formation of new synapses.

• Synaptic Plasticity: This is the ability of synapses to strengthen or weaken over time in response to increases or decreases in their activity. Long-term potentiation (LTP) and long-term depression (LTD) are two key mechanisms of synaptic plasticity that play a crucial role in learning and memory.
• Structural Plasticity: This involves changes in the physical structure of the brain, such as the growth of new neurons (neurogenesis) and the remodeling of dendritic trees. Structural plasticity is particularly important in development and recovery from brain injury.

Neurotransmitter Systems

Neurotransmitters are chemical messengers that transmit signals between neurons at the synapse. Different neurotransmitters have different effects on the postsynaptic neuron, and they play a critical role in regulating a wide range of functions, including mood, sleep, appetite, and movement.

• Glutamate: The primary excitatory neurotransmitter in the brain. It's involved in learning, memory, and synaptic plasticity.
• GABA: The primary inhibitory neurotransmitter in the brain. It helps to regulate neuronal excitability and prevent seizures.
• Dopamine: Involved in reward, motivation, and motor control. Dysfunction of the dopamine system is implicated in Parkinson's disease and schizophrenia.
• Serotonin: Involved in mood, sleep, and appetite. Selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat depression.
• Acetylcholine: Involved in muscle contraction, memory, and attention. It's the neurotransmitter used at the neuromuscular junction.

Nerve Regeneration

Nerve regeneration is the process by which damaged nerves repair themselves. While neurons in the CNS have limited ability to regenerate, neurons in the PNS can regenerate under certain conditions.

• Schwann Cells' Role: Schwann cells play a crucial role in nerve regeneration in the PNS. After a nerve injury, Schwann cells proliferate and form a regeneration tube that guides the regenerating axon towards its target.
• Growth Factors: Growth factors, such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), promote the survival and growth of neurons. They play a critical role in nerve regeneration and neuroplasticity.

The Blood-Brain Barrier (BBB)

The blood-brain barrier (BBB) is a highly selective barrier that protects the brain from harmful substances in the blood. It's formed by tight junctions between endothelial cells in the brain capillaries, along with the processes of astrocytes.

• Selective Permeability: The BBB allows essential nutrients, such as glucose and amino acids, to enter the brain while preventing the entry of toxins, pathogens, and large molecules.
• Clinical Implications: The BBB poses a challenge for drug delivery to the brain. Many drugs cannot cross the BBB, limiting their effectiveness in treating neurological disorders. Researchers are developing new strategies to overcome the BBB and deliver drugs directly to the brain.

Emerging Technologies in Nervous Tissue Research

The field of neuroscience is rapidly advancing, with new technologies emerging that are transforming our understanding of nervous tissue. These technologies include advanced imaging techniques, optogenetics, and brain-computer interfaces.

Advanced Imaging Techniques

Advanced imaging techniques, such as functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), allow us to visualize the structure and function of the brain in vivo.

• fMRI: Measures brain activity by detecting changes in blood flow. It's used to study brain function in healthy individuals and in patients with neurological disorders.
• DTI: Measures the diffusion of water molecules in the brain. It's used to map the white matter tracts and study the connectivity of different brain regions.

Optogenetics

Optogenetics is a technique that uses light to control the activity of neurons. It involves genetically modifying neurons to express light-sensitive proteins called opsins. When light is shone on these neurons, the opsins are activated, causing the neurons to either fire or be inhibited.

• Precise Control: Optogenetics allows for precise control over neuronal activity, making it a powerful tool for studying brain circuits and behavior.
• Therapeutic Potential: Optogenetics has potential therapeutic applications in treating neurological disorders, such as Parkinson's disease and epilepsy.

Brain-Computer Interfaces (BCIs)

Brain-computer interfaces (BCIs) are devices that allow communication between the brain and an external device, such as a computer or prosthetic limb. BCIs can be used to restore motor function in paralyzed individuals and to provide new communication pathways for individuals with severe disabilities.

• Neural Decoding: BCIs use algorithms to decode neural signals from the brain and translate them into commands that control the external device.
• Adaptive Learning: BCIs can learn to adapt to the user's brain signals over time, improving their performance and usability.

Conclusion

Nervous tissue is a complex and fascinating tissue that plays a vital role in the function of the body. Understanding its cellular components, functional properties, and organization is crucial for comprehending how the nervous system works and for diagnosing and treating neurological disorders. From the intricate dance of neurons and glial cells to the remarkable plasticity of the brain, nervous tissue continues to be a subject of intense research and discovery. As technology advances, we can expect even greater insights into the complexities of this essential tissue, leading to new treatments and therapies for a wide range of neurological conditions.