26.1 Anatomy of the Nervous System
4 min read•june 18, 2024
The nervous system, comprising the , , and peripheral nerves, is a complex network that controls our body's functions. It's protected by physical barriers like the skull and , as well as chemical defenses like the , making it typically free of normal .
Despite these defenses, pathogens can still invade the nervous system through injuries, adjacent infections, or by crossing the . Infections can lead to serious conditions like or , causing symptoms such as severe headaches, fever, and altered mental status.
Nervous System Anatomy and Infections
Key structures of nervous system
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- consists of the brain and
- Brain includes the (involved in higher cognitive functions), (coordinates movement), and (regulates vital functions like breathing and heart rate)
- Spinal cord transmits signals between the brain and the rest of the body and controls reflexes
- comprises nerves outside the CNS
- (12 pairs) emerge directly from the brain and innervate the head and neck (facial muscles, sensory organs)
- (31 pairs) originate from the spinal cord and innervate the trunk and limbs
- are protective membranes that cover the brain and spinal cord
- is the tough, outermost layer
- is the middle layer with a spider-web-like appearance
- is the delicate, innermost layer that directly adheres to the surface of the brain and spinal cord
- Blood-brain barrier (BBB) is a selective barrier that regulates the passage of substances between the bloodstream and the CNS
- Formed by tight junctions between endothelial cells lining the blood vessels in the brain
- foot processes and basement membrane provide additional support and regulation
Cellular components and communication
- are the primary functional units of the nervous system
- Specialized cells that transmit electrical and chemical signals
- Consist of a cell body, , and an
- are the junctions between neurons where information is transmitted
- are chemical messengers released at synapses to communicate between neurons
- provide support and protection for neurons
- Include astrocytes, , and microglia in the CNS
- Perform various functions such as maintaining homeostasis, providing insulation, and supporting immune responses
Nervous system organization and adaptation
- regulates involuntary bodily functions
- Divided into sympathetic ("fight or flight") and parasympathetic ("rest and digest") branches
- refers to the brain's ability to reorganize and form new neural connections
- Allows for adaptation, learning, and recovery from injuries
Absence of normal microbiota
- Physical barriers protect the CNS from microbial invasion
- Skull and vertebral column provide bony encasement for the brain and spinal cord
- Meninges act as a protective covering, limiting access of microorganisms
- Chemical barriers in the CNS create an inhospitable environment for most microbes
- ###cerebrospinal_fluid_()_0### contains antibodies and immune cells that combat invading pathogens
- Low pH and high osmolarity of CSF inhibit the growth and survival of many microorganisms
- Blood-brain barrier restricts the entry of most microorganisms and toxins from the bloodstream into the CNS
- Tight junctions between endothelial cells prevent the passage of pathogens
- CNS environment is nutrient-poor compared to other body sites
- Lack of readily available nutrients limits the growth and proliferation of microorganisms in the nervous system
Pathogen entry into nervous system
- Penetrating injuries can directly introduce pathogens into the CNS
- Skull fractures or open wounds (traumatic brain injury) allow microorganisms to bypass the physical barriers
- Infections in adjacent tissues can spread to the CNS
- Sinusitis or otitis media (middle ear infection) can lead to if the infection extends to the meninges
- Dental infections (abscesses) can spread to the brain if left untreated
- Hematogenous spread involves pathogens crossing the blood-brain barrier from the bloodstream
- Certain bacteria like Streptococcus pneumoniae and Neisseria meningitidis can penetrate the BBB and cause meningitis
- Fungal pathogens such as Cryptococcus neoformans can also cross the BBB, particularly in immunocompromised individuals
- Retrograde axonal transport allows some viruses to travel along nerve fibers to reach the CNS
- Rabies virus enters peripheral nerves at the bite site and travels to the brain, causing fatal encephalitis
Symptoms of nervous system infections
- Meningitis, inflammation of the meninges, presents with:
- Severe headache due to irritation of the meninges and increased intracranial pressure
- Neck stiffness (inability to flex the neck) caused by meningeal inflammation
- Photophobia (sensitivity to light) resulting from meningeal irritation
- Fever as a systemic response to infection
- Encephalitis, inflammation of the brain tissue, manifests with:
- Headache due to increased intracranial pressure and brain inflammation
- High fever as a result of the body's immune response to the infection
- Altered mental status (confusion, disorientation) due to brain dysfunction
- Seizures caused by abnormal electrical activity in the inflamed brain
- , a localized collection of pus in the brain or spinal cord, causes:
- Localized neurological deficits (weakness, sensory loss) depending on the location of the abscess
- Fever due to the body's immune response to the contained infection
- Headache resulting from increased intracranial pressure
- or , inflammation or dysfunction of peripheral nerves, leads to:
- Pain or sensory disturbances (tingling, numbness) in the area supplied by the affected nerve (facial nerve, sciatic nerve)
- Paralysis or weakness can occur due to damage to motor nerves or CNS structures
- Spinal cord injuries can cause paralysis below the level of the injury
- Brain damage (stroke, trauma) can result in weakness or paralysis on one side of the body ()
Key Terms to Review (62)
Abscess: An abscess is a localized collection of pus and infected material that forms within the body's tissues, often as a result of an infection or injury. It is a common condition that can occur in various parts of the nervous system, including the brain and spinal cord, leading to significant health implications.
Aponeurosis: An aponeurosis is a flat, broad tendon-like structure that connects muscles to the bones or other muscles. It plays a crucial role in muscle movement and stability.
Arachnoid mater: The arachnoid mater is a delicate, web-like middle layer of the meninges that covers and protects the brain and spinal cord. It lies between the dura mater and pia mater.
Arachnoid Mater: The arachnoid mater is one of the three membranes that surround the brain and spinal cord, collectively known as the meninges. It is the middle layer, situated between the outermost dura mater and the innermost pia mater. The arachnoid mater plays a crucial role in protecting the central nervous system and maintaining the cerebrospinal fluid that cushions and supports the brain and spinal cord.
Astrocyte: Astrocytes are a type of glial cell found in the central nervous system (CNS). They are the most numerous and diverse cells in the brain, performing a wide range of critical functions to support and protect neurons.
Autonomic Nervous System: The autonomic nervous system is a division of the nervous system that controls involuntary bodily functions, such as heart rate, blood pressure, digestion, and respiration. It plays a crucial role in maintaining homeostasis, the body's ability to regulate its internal environment and keep it in a stable state.
Axon: An axon is a long, slender projection of a neuron that conducts electrical impulses away from the neuron's cell body. Axons are fundamental to the transmission of neural signals across different parts of the nervous system.
Bacterial meningitis: Bacterial meningitis is an acute inflammation of the protective membranes covering the brain and spinal cord, known as the meninges. It is caused by bacterial infections and can be life-threatening if not treated promptly.
Blood-brain barrier: The blood-brain barrier (BBB) is a selective permeability barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system. It protects the brain from harmful substances while allowing essential nutrients to pass through.
Blood-Brain Barrier: The blood-brain barrier is a highly selective semipermeable membrane that separates the circulating blood from the brain and extracellular fluid in the central nervous system. It acts as a protective barrier, regulating the passage of substances between the bloodstream and the brain.
Blood-spinal cord barrier: The blood-spinal cord barrier is a selective permeability barrier that separates the circulating blood from the extracellular fluid in the spinal cord. It plays a crucial role in protecting the central nervous system from pathogens and toxins.
Brain: The brain is the central organ of the nervous system, responsible for processing sensory information and controlling bodily functions. It is protected by the skull and the blood-brain barrier.
Brainstem: The brainstem is the part of the brain that connects the cerebrum to the spinal cord. It is responsible for regulating many of the body's basic functions, such as breathing, heart rate, and blood pressure, as well as relaying sensory information between the brain and the rest of the body.
Campylobacter jejuni: Campylobacter jejuni is a Gram-negative, spiral-shaped bacterium that is one of the most common causes of bacterial gastroenteritis worldwide. It typically infects the gastrointestinal tract but can sometimes cause more severe systemic infections.
Central Nervous System: The central nervous system (CNS) is the primary control center of the body, consisting of the brain and spinal cord. It is responsible for integrating and coordinating information from the peripheral nervous system to regulate various bodily functions and behaviors.
Central nervous system (CNS): The central nervous system (CNS) consists of the brain and spinal cord, responsible for processing and transmitting information throughout the body. It plays a crucial role in controlling most bodily functions including movements, sensations, and thoughts.
Cerebellum: The cerebellum is a region of the brain located at the back of the skull, below the cerebrum. It is responsible for coordinating voluntary movements, maintaining balance and posture, and facilitating learning of new motor skills.
Cerebrospinal Fluid: Cerebrospinal fluid (CSF) is a clear, colorless fluid that circulates around the brain and spinal cord, providing cushioning and protection for the central nervous system. It is produced in the ventricles of the brain and continuously flows through the subarachnoid space surrounding the brain and spinal cord, before being reabsorbed into the bloodstream.
Cerebrospinal fluid (CSF): Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the brain and spinal cord. It provides cushioning for the brain, removes waste products, and circulates nutrients.
Cerebrum: The cerebrum is the largest and uppermost part of the brain, responsible for a wide range of functions including cognition, perception, motor control, and higher-order processing. It is the primary site of conscious thought and voluntary action in the central nervous system.
Cranial Nerves: Cranial nerves are a set of 12 pairs of nerves that originate directly from the brain, as opposed to the spinal nerves which originate from the spinal cord. These nerves play a crucial role in various sensory, motor, and autonomic functions within the body, connecting the brain to specific regions and organs.
CSF: Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the brain and spinal cord. It cushions the central nervous system and provides vital nutrients while removing waste products.
Dendrites: Dendrites are branched extensions of neurons that receive and integrate synaptic signals from other neurons. They play a crucial role in the transmission of electrical impulses within the nervous system.
Dura mater: The dura mater is the outermost layer of the meninges, which are protective coverings of the brain and spinal cord. It provides a tough barrier against infections and physical impacts.
Dura Mater: The dura mater is the outermost and toughest of the three membranes (meninges) that cover the brain and spinal cord. It serves as a protective layer and provides structural support for the central nervous system.
Dural sheath: The dural sheath is a protective membrane that surrounds the spinal cord and nerve roots. It is part of the dura mater, the outermost layer of the meninges in the central nervous system.
Encephalitis: Encephalitis is the inflammation of the brain, typically caused by viral infections. It can result in symptoms ranging from mild flu-like signs to severe neurological damage.
Epstein-Barr virus: Epstein-Barr virus (EBV) is a herpesvirus that primarily infects B cells and epithelial cells, causing mononucleosis. It is associated with several cancers, including Burkitt's lymphoma and nasopharyngeal carcinoma.
Glial cells: Glial cells, also known as neuroglia, are non-neuronal cells in the central and peripheral nervous systems that provide support and protection for neurons. They play crucial roles in maintaining homeostasis, forming myelin, and providing support and protection for neurons.
Glial Cells: Glial cells are non-neuronal cells in the central nervous system (CNS) and peripheral nervous system (PNS) that provide support and protection for neurons. They are essential for the proper functioning and maintenance of the nervous system.
Guillain-Barré syndrome (GBS): Guillain-Barré syndrome (GBS) is a rare autoimmune disorder where the body's immune system attacks the peripheral nervous system, leading to muscle weakness and paralysis. It often follows an infection and can be life-threatening if not treated promptly.
Hemiparesis: Hemiparesis is a condition characterized by partial paralysis or weakness affecting one side of the body, typically caused by damage or dysfunction in the brain or spinal cord. It is an important term in the context of understanding the anatomy of the nervous system.
Lumbar puncture: A lumbar puncture, or spinal tap, is a medical procedure where a needle is inserted into the lower back to collect cerebrospinal fluid (CSF) for diagnostic testing. It is often used to diagnose infections of the central nervous system.
Meninges: Meninges are three protective membranes that envelop the brain and spinal cord. They consist of the dura mater, arachnoid mater, and pia mater.
Meninges: The meninges are the protective membranes that surround the brain and spinal cord. They play a crucial role in the anatomy of the nervous system and can be affected by various fungal and parasitic diseases.
Meningitis: Meningitis is an inflammation of the protective membranes covering the brain and spinal cord, known as the meninges. It can be caused by bacterial, viral, fungal, or parasitic infections.
Meningitis: Meningitis is an inflammation of the protective membranes covering the brain and spinal cord, known as the meninges. It can be caused by various infectious agents, including bacteria, viruses, and fungi, and can have serious consequences if left untreated.
Microbiota: Microbiota refers to the community of microorganisms, including bacteria, fungi, and viruses, that inhabit a particular environment in or on the body. These microbial communities play essential roles in health and disease.
Myelin sheath: The myelin sheath is a fatty layer that surrounds the axons of neurons, providing insulation and increasing the speed of electrical signal transmission. It plays a crucial role in maintaining the proper functioning of the nervous system.
Neuralgia: Neuralgia is a sharp, stabbing, and often severe pain that follows the path of a nerve. It is typically caused by injury, irritation, or compression of a nerve, leading to abnormal nerve function and pain signaling.
Neuritis: Neuritis is a condition characterized by inflammation of a nerve or group of nerves, leading to pain, numbness, and impaired nerve function. It is often associated with damage or irritation to the peripheral nervous system, which includes the nerves outside the brain and spinal cord.
Neuron: A neuron is a specialized cell in the nervous system that is responsible for transmitting electrical signals throughout the body. Neurons are the fundamental units of the nervous system and are essential for various functions, including sensation, movement, and cognition.
Neurons: Neurons are specialized cells within the nervous system that transmit information through electrical and chemical signals. They play a crucial role in processing and transmitting data throughout the body.
Neuropathy: Neuropathy is a condition characterized by damage or dysfunction of one or more nerves, resulting in numbness, tingling, muscle weakness, and pain. It can be caused by infections affecting the nervous system.
Neuroplasticity: Neuroplasticity is the ability of the brain to adapt and change its structure and function in response to experience and learning. It is the brain's capacity to reorganize and modify its neural pathways, allowing it to compensate for injury and disease, as well as to learn new skills and information.
Neurotransmitters: Neurotransmitters are chemical messengers that transmit signals across synapses from one neuron to another. They play a crucial role in the functioning of the nervous system, including processes like mood regulation, cognition, and muscle movement.
Neurotransmitters: Neurotransmitters are chemical messengers that facilitate communication between neurons in the nervous system. They are responsible for transmitting signals across the synaptic cleft, allowing for the efficient and coordinated functioning of the brain and body.
Oligodendrocytes: Oligodendrocytes are a type of glial cell in the central nervous system responsible for producing myelin, which insulates neuronal axons to facilitate rapid signal transmission. They play a crucial role in maintaining the structural integrity and functionality of neural circuits.
Periosteum: The periosteum is a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints. It plays a crucial role in the growth and repair of bone tissue.
Peripheral Nervous System: The peripheral nervous system (PNS) is the part of the nervous system that lies outside the central nervous system (brain and spinal cord). It consists of the sensory and motor nerves that connect the central nervous system to the rest of the body, allowing communication and coordination between the brain/spinal cord and the various organs, limbs, and tissues.
Peripheral nervous system (PNS): The peripheral nervous system (PNS) consists of all the nerves outside the brain and spinal cord. It connects the central nervous system (CNS) to limbs and organs.
Pia mater: The pia mater is the delicate innermost layer of the meninges that surrounds the brain and spinal cord, providing protection and cushioning. It is highly vascularized, supplying essential nutrients to the nervous tissue.
Pia Mater: The pia mater is the innermost layer of the meninges, the protective membranes surrounding the brain and spinal cord. It is a delicate, vascular membrane that closely adheres to the surface of the central nervous system, playing a crucial role in its protection and nourishment.
Schwann cells: Schwann cells are specialized glial cells in the peripheral nervous system responsible for the formation of myelin sheaths around neuronal axons. They facilitate rapid signal transmission and aid in nerve regeneration following injury.
Soma: The soma, or cell body, is the central part of a neuron containing the nucleus. It is responsible for maintaining the cell's health and metabolic functions.
Spinal cord: The spinal cord is a long, cylindrical structure made of nervous tissue that extends from the brainstem down through the vertebral column. It transmits neural signals between the brain and the rest of the body and plays a crucial role in reflex actions.
Spinal Cord: The spinal cord is a long, cylindrical structure that extends from the base of the brain, known as the medulla oblongata, down through the vertebral column. It is a vital component of the central nervous system, responsible for transmitting sensory information from the body to the brain and motor commands from the brain to the body.
Spinal Nerves: Spinal nerves are the nerves that emerge from the spinal cord and innervate the body. They are responsible for transmitting sensory information from the body to the central nervous system and motor commands from the central nervous system to the muscles.
Subarachnoid space: The subarachnoid space is the interval between the arachnoid membrane and the pia mater in the brain and spinal cord. It contains cerebrospinal fluid (CSF) which cushions the central nervous system.
Synapse: A synapse is a specialized junction between two neurons or between a neuron and another cell, where information is transmitted from one to the other through chemical or electrical signals. It is a crucial structure in the nervous system that facilitates communication and coordination between different parts of the body.
Synapses: Synapses are specialized junctions between neurons that facilitate the transmission of electrical or chemical signals. They play a crucial role in neural communication and overall nervous system function.
Williams: Williams is a reference to a specific researcher or study in microbiology that has contributed significantly to our understanding of nervous system infections. This term often appears in literature discussing the anatomical and pathological effects of such infections.