🤾🏻‍♂️Human Physiology Engineering Unit 4 – Nervous System

Nervous System Basics

• The nervous system is a complex network of cells and tissues that transmits signals and coordinates bodily functions
• Consists of two main divisions: the central nervous system (CNS) and the peripheral nervous system (PNS)
• The CNS includes the brain and spinal cord, while the PNS consists of nerves that extend throughout the body
• Nervous tissue is composed of neurons, the basic functional units of the nervous system, and glial cells that support and protect neurons
• Neurons are specialized cells that transmit electrical and chemical signals called neurotransmitters
• The nervous system enables rapid communication and coordination between different parts of the body
• Plays a crucial role in sensing stimuli, processing information, and generating appropriate responses

Neurons and Synapses

• Neurons are the primary cells responsible for transmitting signals in the nervous system
  • Consist of a cell body (soma), dendrites that receive signals, and an axon that transmits signals to other neurons or effector cells
  • Neurons can be classified into three main types: sensory neurons, motor neurons, and interneurons
• Synapses are specialized junctions between neurons where signal transmission occurs
  • Electrical synapses allow direct transmission of electrical signals between neurons through gap junctions
  • Chemical synapses involve the release of neurotransmitters from the presynaptic neuron, which bind to receptors on the postsynaptic neuron
• The process of signal transmission in neurons involves:
  • Resting potential: the electrical potential difference across the neuronal membrane when the neuron is not actively transmitting signals (typically around -70 mV)
  • Action potential: a rapid, transient change in the membrane potential that propagates along the axon when the neuron is stimulated above its threshold (depolarization followed by repolarization)
• Neurotransmitters are chemical messengers released at synapses that can have excitatory or inhibitory effects on the postsynaptic neuron
  • Examples of neurotransmitters include acetylcholine, dopamine, serotonin, and GABA
• Synaptic plasticity refers to the ability of synapses to strengthen or weaken over time, which is essential for learning and memory formation

Central Nervous System

• The central nervous system (CNS) consists of the brain and spinal cord
• The brain is the control center of the nervous system, responsible for processing sensory information, generating thoughts and emotions, and coordinating motor functions
  • Divided into several regions, including the cerebrum, cerebellum, and brainstem, each with specific functions
  • The cerebrum is the largest part of the brain and is involved in higher cognitive functions, such as perception, reasoning, and decision-making
  • The cerebellum is responsible for coordinating movement, balance, and posture
  • The brainstem connects the brain to the spinal cord and regulates vital functions like breathing, heart rate, and sleep cycles
• The 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
  • Organized into segments, with each segment corresponding to a specific region of the body
  • Contains ascending (sensory) and descending (motor) pathways that transmit signals to and from the brain
• The CNS is protected by the blood-brain barrier, a selective barrier that regulates the passage of substances from the bloodstream into the brain and spinal cord
• Damage to the CNS can lead to various neurological disorders, such as traumatic brain injury, spinal cord injury, and neurodegenerative diseases (Alzheimer's, Parkinson's)

Peripheral Nervous System

• The peripheral nervous system (PNS) consists of nerves that connect the CNS to the rest of the body
• Divided into two main components: the somatic nervous system and the autonomic nervous system
• The somatic nervous system is responsible for voluntary movements and conscious sensations
  • Includes sensory neurons that detect stimuli from the environment and motor neurons that control skeletal muscles
  • Enables actions like walking, grasping objects, and responding to sensory stimuli (touch, pain, temperature)
• The autonomic nervous system regulates involuntary functions and maintains homeostasis
  • Divided into the sympathetic and parasympathetic divisions, which often have opposing effects on target organs
  • The sympathetic division is associated with the "fight or flight" response, increasing heart rate, blood pressure, and glucose release during stress
  • The parasympathetic division is associated with the "rest and digest" response, promoting relaxation, digestion, and energy conservation
• Peripheral nerves are bundles of axons that carry signals between the CNS and the rest of the body
  • Classified as cranial nerves (originating from the brain) or spinal nerves (originating from the spinal cord)
  • Cranial nerves (12 pairs) are involved in various sensory and motor functions of the head and neck (vision, hearing, facial movements)
  • Spinal nerves (31 pairs) emerge from the spinal cord and innervate the trunk and limbs

Sensory Processing

• Sensory processing involves the detection, transduction, and interpretation of stimuli from the environment
• Sensory receptors are specialized structures that detect specific types of stimuli (light, sound, touch, chemicals)
  • Examples include photoreceptors in the retina, hair cells in the inner ear, and mechanoreceptors in the skin
• Sensory transduction is the process by which sensory receptors convert stimuli into electrical signals (receptor potentials) that can be transmitted by sensory neurons
• Sensory pathways carry information from receptors to the CNS for processing and interpretation
  • The somatosensory system processes information related to touch, pressure, temperature, and pain
  • The visual system processes light stimuli and enables visual perception
  • The auditory system processes sound waves and enables hearing
  • The gustatory system processes chemical stimuli related to taste
  • The olfactory system processes chemical stimuli related to smell
• Sensory processing in the CNS involves the integration and interpretation of sensory information
  • Sensory cortices in the brain (primary and secondary) are responsible for processing specific types of sensory information
  • Multisensory integration occurs when information from different sensory modalities is combined to create a unified perception

Motor Control

• Motor control involves the planning, execution, and coordination of movements
• Motor neurons are the final common pathway for the control of movement
  • Upper motor neurons originate in the motor cortex and brainstem and project to lower motor neurons in the spinal cord
  • Lower motor neurons directly innervate skeletal muscles and cause muscle contraction
• The motor cortex, located in the frontal lobe of the cerebrum, is the primary area responsible for the planning and initiation of voluntary movements
• The cerebellum plays a crucial role in motor coordination, precision, and learning of motor skills
  • Receives input from sensory systems and the motor cortex to fine-tune movements and maintain balance
• The basal ganglia are a group of subcortical nuclei involved in the selection and initiation of movements, as well as in motor learning and habit formation
• Reflexes are involuntary, stereotyped responses to specific stimuli that occur without conscious control
  • Examples include the knee-jerk reflex, withdrawal reflex, and pupillary light reflex
• Motor learning involves the acquisition and refinement of motor skills through practice and experience
  • Involves changes in synaptic strength and the formation of new neural connections (neuroplasticity)
• Disorders of motor control can result from damage to various parts of the nervous system
  • Examples include Parkinson's disease (basal ganglia), cerebellar ataxia, and amyotrophic lateral sclerosis (ALS)

Neural Integration and Higher Functions

• Neural integration refers to the processing and combining of information from multiple sources within the nervous system to generate appropriate responses
• The cerebral cortex is the primary site of neural integration and higher cognitive functions
  • Divided into four main lobes: frontal, parietal, temporal, and occipital, each with specific functions
  • The prefrontal cortex is involved in executive functions, such as planning, decision-making, and impulse control
• The limbic system is a group of structures involved in emotion, motivation, and memory formation
  • Includes the amygdala (processing of emotional responses), hippocampus (formation of new memories), and hypothalamus (regulation of homeostasis and neuroendocrine functions)
• Learning and memory are fundamental higher functions of the nervous system
  • Involves changes in synaptic strength (long-term potentiation and depression) and the formation of new neural connections
  • Different types of memory include short-term memory, working memory, and long-term memory (declarative and procedural)
• Language and communication are complex higher functions that involve multiple brain regions
  • Broca's area (speech production) and Wernicke's area (language comprehension) are key language centers in the brain
• Consciousness and self-awareness are emergent properties of the nervous system that arise from the integrated activity of multiple brain regions
  • The neural correlates of consciousness are still not fully understood and are an active area of research

Clinical Applications and Engineering Perspectives

• Understanding the structure and function of the nervous system is crucial for diagnosing and treating neurological disorders
• Neuroimaging techniques, such as MRI, fMRI, and PET, allow for non-invasive visualization of brain structure and function
  • Used in the diagnosis of brain tumors, stroke, neurodegenerative diseases, and psychiatric disorders
• Electrophysiological techniques, such as EEG and MEG, measure the electrical activity of the brain and can be used to study neural oscillations and event-related potentials
• Neuropharmacology involves the development and use of drugs that target the nervous system
  • Examples include antidepressants (SSRIs), antipsychotics, and anticonvulsants
• Neural engineering applies engineering principles to the study and manipulation of the nervous system
  • Includes the development of brain-computer interfaces (BCIs) that enable direct communication between the brain and external devices
  • Neuroprosthetics aim to restore lost sensory or motor functions by interfacing with the nervous system (cochlear implants, retinal implants, robotic prostheses)
• Optogenetics is a technique that uses light to control the activity of specific neurons genetically modified to express light-sensitive ion channels
  • Allows for precise spatial and temporal control of neural activity and is used in research to study neural circuits and behavior
• Computational neuroscience uses mathematical models and simulations to study the function and behavior of the nervous system
  • Helps to understand complex neural processes and to develop new hypotheses for experimental testing
• Advances in our understanding of the nervous system and the development of new technologies have the potential to revolutionize the treatment of neurological disorders and to enhance human performance