💀Anatomy and Physiology I Unit 13 – Anatomy of the Nervous System

Key Structures and Functions

• Nervous system consists of the brain, spinal cord, and a complex network of nerves that transmit signals throughout the body
• Primary function involves receiving, processing, and responding to internal and external stimuli
• Facilitates communication between different parts of the body and coordinates voluntary and involuntary actions
• Plays a crucial role in maintaining homeostasis by regulating various physiological processes (heart rate, breathing, digestion)
• Enables sensory perception, including sight, hearing, touch, taste, and smell, allowing organisms to interact with their environment
• Supports cognitive functions such as learning, memory, decision-making, and emotional processing
• Controls motor functions, including movement, balance, and coordination of skeletal muscles

Organization of the Nervous System

• Nervous system is divided into two main components: the central nervous system (CNS) and the peripheral nervous system (PNS)
• CNS comprises the brain and spinal cord, serving as the primary control center for processing information and generating responses
• PNS consists of nerves that extend from the CNS to various parts of the body, transmitting signals to and from the CNS
• PNS is further subdivided into the somatic nervous system, which controls voluntary actions, and the autonomic nervous system, which regulates involuntary functions
  • Somatic nervous system enables conscious control of skeletal muscles and facilitates sensory input from the external environment
  • Autonomic nervous system is divided into the sympathetic and parasympathetic divisions, working together to maintain homeostasis
• Nervous system exhibits a hierarchical organization, with higher-level structures (brain) exerting control over lower-level structures (spinal cord and nerves)
• Nervous tissue is composed of two main cell types: neurons, which transmit electrical and chemical signals, and glial cells, which provide support and protection

Central Nervous System (CNS)

• CNS is the primary control center of the nervous system, consisting of the brain and spinal cord
• Brain is the most complex organ in the body, responsible for processing sensory information, generating thoughts, emotions, and memories, and coordinating motor functions
  • Cerebrum is the largest part of the brain, divided into left and right hemispheres, and is involved in higher-order cognitive functions (reasoning, planning, language)
  • Cerebellum is located at the back of the brain and plays a crucial role in motor control, balance, and coordination
  • Brainstem connects the brain to the spinal cord and regulates vital functions (breathing, heart rate, sleep-wake cycles)
• Spinal cord is a long, thin bundle of nervous tissue that extends from the brainstem and serves as a conduit for signals between the brain and the rest of the body
  • Spinal cord is organized into segments, with each segment corresponding to a specific region of the body
  • Gray matter in the spinal cord contains cell bodies of neurons and is involved in processing sensory input and generating motor output
  • White matter consists of myelinated nerve fibers that transmit signals along the length of the spinal cord
• CNS is protected by the skull and vertebral column, as well as by three layers of meninges (dura mater, arachnoid mater, and pia mater) and cerebrospinal fluid

Peripheral Nervous System (PNS)

• PNS consists of nerves that extend from the CNS to various parts of the body, transmitting signals to and from the brain and spinal cord
• Somatic nervous system is part of the PNS that controls voluntary movements and facilitates sensory input from the external environment
  • Sensory (afferent) nerves carry information from sensory receptors to the CNS for processing
  • Motor (efferent) nerves carry signals from the CNS to skeletal muscles, enabling voluntary movement
• Autonomic nervous system (ANS) is part of the PNS that regulates involuntary functions and maintains homeostasis
  • Sympathetic division of the ANS activates the "fight or flight" response, increasing heart rate, blood pressure, and blood glucose levels in response to stress
  • Parasympathetic division of the ANS promotes "rest and digest" functions, such as slowing heart rate, increasing digestion, and promoting relaxation
• Cranial nerves are 12 pairs of nerves that emerge directly from the brain and innervate various structures in the head, neck, and torso
  • Some cranial nerves (olfactory, optic) are purely sensory, while others (vagus) have both sensory and motor functions
• Spinal nerves are 31 pairs of nerves that emerge from the spinal cord and innervate the trunk and limbs, carrying both sensory and motor information

Neurons and Synapses

• Neurons are the primary functional units of the nervous system, specialized cells that transmit electrical and chemical signals
• Neurons consist of three main parts: the cell body (soma), dendrites, and axon
  • Cell body contains the nucleus and other organelles necessary for cellular function
  • Dendrites are branched extensions that receive signals from other neurons
  • Axon is a long, thin fiber that conducts electrical impulses away from the cell body and towards other neurons or effector cells
• Neurons communicate with each other and with other cells through specialized junctions called synapses
  • Presynaptic neuron releases neurotransmitters into the synaptic cleft, a narrow gap between the presynaptic and postsynaptic cells
  • Neurotransmitters bind to receptors on the postsynaptic cell, triggering changes in the cell's electrical potential and facilitating signal transmission
• Action potentials are the primary means of signal transmission along the length of an axon
  • Action potentials are generated when the neuron's membrane potential reaches a threshold level, triggering a rapid depolarization followed by repolarization
  • Myelin sheath, produced by glial cells, insulates the axon and facilitates rapid signal conduction through saltatory conduction
• Neurons can be classified based on their structure (unipolar, bipolar, multipolar) and function (sensory, motor, interneurons)

Neurotransmitters and Signaling

• Neurotransmitters are chemical messengers released by neurons that facilitate communication between cells in the nervous system
• Neurotransmitters are synthesized in the cell body and stored in vesicles at the presynaptic terminal
• When an action potential reaches the presynaptic terminal, it triggers the release of neurotransmitters into the synaptic cleft through a process called exocytosis
• Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic cell, inducing changes in the cell's electrical potential or intracellular signaling pathways
• Excitatory neurotransmitters (glutamate) increase the likelihood of the postsynaptic neuron generating an action potential, while inhibitory neurotransmitters (GABA) decrease this likelihood
• Neurotransmitters are cleared from the synaptic cleft through reuptake by the presynaptic neuron or degradation by enzymes, terminating the signal
• Examples of neurotransmitters include:
  • Acetylcholine: involved in muscle contraction, memory, and learning
  • Dopamine: plays a role in reward, motivation, and motor control
  • Serotonin: regulates mood, sleep, and appetite
  • Norepinephrine: involved in arousal, attention, and the stress response

Protection and Support Structures

• Nervous system is protected and supported by various structures, including the skull, vertebral column, meninges, and cerebrospinal fluid
• Skull is a bony structure that encases and protects the brain from external damage
• Vertebral column is a series of bones (vertebrae) that surround and protect the spinal cord, providing structural support and flexibility
• Meninges are three layers of protective membranes that cover the brain and spinal cord
  • Dura mater is the outermost layer, a tough, fibrous membrane that adheres to the skull and vertebral column
  • Arachnoid mater is the middle layer, a delicate, web-like membrane that cushions the brain and spinal cord
  • Pia mater is the innermost layer, a thin, highly vascularized membrane that directly adheres to the surface of the brain and spinal cord
• Cerebrospinal fluid (CSF) is a clear, colorless liquid that fills the ventricles of the brain and the subarachnoid space around the brain and spinal cord
  • CSF provides buoyancy and cushioning for the brain and spinal cord, protecting them from mechanical damage
  • CSF also plays a role in maintaining homeostasis by regulating pressure and removing waste products from the CNS
• Blood-brain barrier is a selective barrier formed by tight junctions between endothelial cells of capillaries in the CNS, restricting the passage of substances from the bloodstream into the brain

Clinical Applications and Disorders

• Understanding the anatomy and physiology of the nervous system is crucial for diagnosing and treating various neurological disorders
• Neurodegenerative diseases, such as Alzheimer's and Parkinson's, involve the progressive loss of neurons in specific regions of the brain, leading to cognitive and motor impairments
  • Alzheimer's disease is characterized by the accumulation of amyloid plaques and neurofibrillary tangles, resulting in memory loss and cognitive decline
  • Parkinson's disease is caused by the degeneration of dopaminergic neurons in the substantia nigra, leading to tremors, rigidity, and difficulty with movement
• Traumatic brain injuries (TBI) occur when an external force causes damage to the brain, leading to a range of cognitive, emotional, and physical symptoms
  • Concussions are a type of mild TBI that can result in headaches, dizziness, and difficulty concentrating
  • More severe TBIs can cause long-term disabilities, such as paralysis, speech difficulties, and personality changes
• Spinal cord injuries (SCI) involve damage to the spinal cord, often resulting in loss of sensation and motor function below the level of the injury
  • SCIs can be classified as complete (total loss of function) or incomplete (partial loss of function), depending on the extent of the damage
  • Treatment for SCIs may include surgery, rehabilitation, and assistive devices to help manage symptoms and improve quality of life
• Neuroimaging techniques, such as MRI and CT scans, allow healthcare professionals to visualize the structure and function of the nervous system, aiding in the diagnosis and monitoring of neurological conditions