🧢Neuroscience Unit 3 – Neuroanatomy and Nervous System Organization

Key Concepts and Terminology

• Neuroscience studies the structure, function, development, and pathology of the nervous system
• Neuroanatomy focuses on the anatomical organization and structure of the nervous system
• The nervous system consists of the central nervous system (CNS) and peripheral nervous system (PNS)
• Neurons are the primary functional units of the nervous system responsible for transmitting electrical and chemical signals
• Glial cells provide support, protection, and maintenance for neurons (astrocytes, oligodendrocytes, microglia)
• Synapses are specialized junctions between neurons that allow for communication and signal transmission
• Neurotransmitters are chemical messengers released by neurons to transmit signals across synapses (glutamate, GABA, dopamine)
• Neuroplasticity refers to the brain's ability to reorganize and adapt in response to experience and learning

Nervous System Overview

• The nervous system is a complex network of cells and tissues that transmits signals and coordinates body functions
• Divided into two main components: the central nervous system (CNS) and the peripheral nervous system (PNS)
• The CNS consists of the brain and spinal cord and serves as the main processing and integration center
• The PNS consists of nerves and ganglia that connect the CNS to the rest of the body
• The nervous system is responsible for receiving sensory input, processing information, and generating appropriate responses
• Neurons are the primary functional units of the nervous system and are specialized for signal transmission
• Glial cells provide support, protection, and maintenance for neurons and outnumber neurons in the brain
• The nervous system communicates through a combination of electrical and chemical signaling

Central Nervous System Structure

• The CNS consists of the brain and spinal cord, which are protected by the skull and vertebral column
• The brain is divided into several major regions: the cerebrum, cerebellum, brainstem, and diencephalon
• The cerebrum is the largest part of the brain and is responsible for higher cognitive functions (perception, memory, language)
• The cerebellum is located at the back of the brain and is involved in motor coordination and balance
• The brainstem connects the brain to the spinal cord and regulates vital functions (breathing, heart rate, sleep)
• The diencephalon includes the thalamus and hypothalamus, which are involved in sensory processing and homeostasis
• The spinal cord is a long, thin bundle of nervous tissue that extends from the brainstem and serves as a conduit for sensory and motor information
  • Divided into cervical, thoracic, lumbar, and sacral regions based on the level of the vertebral column
  • Contains gray matter (cell bodies) and white matter (myelinated axons) organized into specific pathways

Peripheral Nervous System Structure

• The PNS consists of nerves and ganglia 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 sensory information from the skin, muscles, and joints
  • Includes cranial nerves (12 pairs) and spinal nerves (31 pairs) that emerge from the brain and spinal cord
• The autonomic nervous system regulates involuntary functions (heart rate, digestion, respiration)
  • Divided into the sympathetic (fight-or-flight response) and parasympathetic (rest-and-digest) divisions
• Ganglia are clusters of neuronal cell bodies located outside the CNS (dorsal root ganglia, autonomic ganglia)
• Nerves are bundles of axons that transmit signals between the CNS and peripheral targets (muscles, glands, sensory receptors)

Cellular Components of the Nervous System

• Neurons are the primary functional units of the nervous system and are specialized for signal transmission
  • Consist of a cell body (soma), dendrites, and an axon
  • Dendrites receive signals from other neurons, while the axon transmits signals to other cells
• Glial cells are non-neuronal cells that provide support, protection, and maintenance for neurons
  • Astrocytes regulate neurotransmitter levels, maintain the blood-brain barrier, and provide metabolic support
  • Oligodendrocytes (CNS) and Schwann cells (PNS) produce myelin, which insulates axons and enhances signal transmission
  • Microglia are the immune cells of the CNS and respond to injury or infection
• Synapses are specialized junctions between neurons that allow for communication and signal transmission
  • Consist of a presynaptic terminal (axon), synaptic cleft, and postsynaptic membrane (dendrite or cell body)
  • Neurotransmitters are released from the presynaptic terminal and bind to receptors on the postsynaptic membrane

Brain Regions and Functions

• The cerebrum is the largest part of the brain and is divided into two hemispheres connected by the corpus callosum
  • Consists of four lobes: frontal (executive functions, motor control), parietal (sensory processing, spatial awareness), temporal (memory, language), and occipital (visual processing)
  • The cerebral cortex is the outer layer of the cerebrum and is responsible for higher cognitive functions
• The cerebellum is located at the back of the brain and is involved in motor coordination, balance, and learning
  • Consists of two hemispheres and a central region called the vermis
  • Receives input from the vestibular system, proprioceptors, and motor cortex to fine-tune movements
• The brainstem connects the brain to the spinal cord and regulates vital functions
  • Consists of the midbrain (visual and auditory processing), pons (sleep, arousal), and medulla oblongata (cardiovascular and respiratory control)
• The diencephalon includes the thalamus (sensory relay and processing) and hypothalamus (homeostasis, endocrine function)
• The limbic system is a group of structures involved in emotion, memory, and motivation (amygdala, hippocampus, cingulate gyrus)

Spinal Cord Organization

• The spinal cord is a long, thin bundle of nervous tissue that extends from the brainstem and serves as a conduit for sensory and motor information
• Divided into cervical, thoracic, lumbar, and sacral regions based on the level of the vertebral column
• Contains gray matter (cell bodies) and white matter (myelinated axons) organized into specific pathways
  • Gray matter is organized into dorsal (sensory) and ventral (motor) horns
  • White matter is organized into ascending (sensory) and descending (motor) tracts
• Spinal nerves emerge from the spinal cord at each vertebral level and innervate specific dermatomes (skin areas) and myotomes (muscle groups)
• The spinal cord is involved in reflexes, which are rapid, involuntary responses to stimuli (stretch reflex, withdrawal reflex)
  • Reflexes are mediated by simple neural circuits called reflex arcs, which consist of sensory neurons, interneurons, and motor neurons

Neural Pathways and Circuits

• Neural pathways are specific routes along which signals travel in the nervous system
• Sensory pathways transmit information from sensory receptors to the CNS for processing
  • Examples include the spinothalamic tract (pain, temperature) and the dorsal column-medial lemniscus pathway (touch, proprioception)
• Motor pathways transmit signals from the CNS to muscles and glands to initiate movement or secretion
  • Examples include the corticospinal tract (voluntary movement) and the reticulospinal tract (posture, locomotion)
• Neural circuits are interconnected groups of neurons that process specific types of information
  • Examples include the basal ganglia (motor control, learning), the hippocampal formation (memory), and the amygdala (emotion)
• Neuronal oscillations are rhythmic patterns of electrical activity generated by neural circuits
  • Different frequency bands are associated with specific cognitive states (alpha waves: relaxation, theta waves: memory encoding)

Clinical Relevance and Disorders

• Neurological disorders result from damage to or dysfunction of the nervous system
• Neurodegenerative diseases involve the progressive loss of neurons and include Alzheimer's disease (memory, cognition), Parkinson's disease (movement), and amyotrophic lateral sclerosis (motor neurons)
• Stroke occurs when blood flow to the brain is disrupted, leading to cell death and neurological deficits (paralysis, language impairment)
• Traumatic brain injury (TBI) results from external forces causing damage to the brain and can lead to cognitive, emotional, and motor impairments
• Spinal cord injury (SCI) involves damage to the spinal cord, resulting in loss of sensation and movement below the level of injury
• Neuropsychiatric disorders involve abnormalities in brain function and include depression, anxiety, schizophrenia, and bipolar disorder
• Neuroimaging techniques (MRI, CT, PET) allow for the visualization of brain structure and function and aid in the diagnosis and monitoring of neurological disorders
• Neurosurgery involves surgical interventions to treat neurological disorders (tumor removal, deep brain stimulation)