1.4 Neuroanatomy and organization of the nervous system

The nervous system is a complex network divided into central and peripheral components. It processes sensory information, generates thoughts and emotions, and coordinates motor responses. Understanding its structure and function is crucial for grasping how our bodies and minds work together.

Brain regions like the forebrain, midbrain, and hindbrain have specialized functions. The spinal cord connects the brain to the body, while the peripheral nervous system relays information between the central nervous system and the rest of the body.

Nervous System Divisions and Functions

Central and Peripheral Nervous Systems

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• The nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS)
• The CNS consists of the brain and spinal cord
  • Processes and integrates sensory information
  • Generates thoughts and emotions
  • Coordinates motor responses
• The PNS consists of sensory and motor neurons that relay information to and from the CNS
  • Also includes the autonomic nervous system that regulates involuntary functions (heart rate, digestion, respiratory rate)

Somatic and Autonomic Nervous Systems

• The somatic nervous system is part of the PNS
  • Controls voluntary movements
  • Relays sensory information from the skin, muscles, and joints to the CNS
• The autonomic nervous system is divided into the sympathetic and parasympathetic divisions
  • Work in opposition to maintain homeostasis
  • Regulate involuntary functions such as heart rate, digestion, and respiratory rate
  • Sympathetic division activates "fight or flight" response (increases heart rate, dilates pupils)
  • Parasympathetic division promotes "rest and digest" functions (slows heart rate, constricts pupils)

Brain and Spinal Cord Organization

Brain Regions and Functions

• The brain is divided into three main regions: the forebrain, midbrain, and hindbrain
• The forebrain includes:
  • Cerebrum, divided into two hemispheres and four lobes (frontal, parietal, temporal, occipital)
    • Frontal lobe: executive functions, planning, decision-making, motor control
    • Parietal lobe: spatial processing, touch sensation, body awareness
    • Temporal lobe: auditory processing, memory, emotion, language comprehension
    • Occipital lobe: visual processing
  • Thalamus: relay station for sensory and motor information
  • Hypothalamus: regulates hormones, body temperature, hunger, thirst, sleep-wake cycle
• The midbrain connects the forebrain to the hindbrain
  • Involved in visual and auditory processing, motor control
• The hindbrain includes:
  • Cerebellum: balance, coordination, fine motor control
  • Pons: relay station between cerebral cortex and cerebellum, regulates sleep-wake cycle
  • Medulla oblongata: regulates vital functions (breathing, heart rate, blood pressure)

Spinal Cord Structure and Function

• The spinal cord is a long, thin bundle of nervous tissue that extends from the medulla oblongata
  • Protected by the vertebral column
• Organized into segments, with each segment giving rise to a pair of spinal nerves
  • Spinal nerves innervate specific regions of the body
• Gray matter of the spinal cord contains cell bodies of neurons
  • Butterfly-shaped central region
• White matter contains myelinated axons that carry information up and down the spinal cord
  • Surrounds the gray matter
• Ascending tracts carry sensory information from the body to the brain
• Descending tracts carry motor commands from the brain to the body

Peripheral Nervous System Role

• The PNS consists of sensory and motor neurons that relay information between the CNS and the rest of the body
• Sensory neurons in the PNS detect stimuli from the internal and external environment
  • Touch, temperature, pain, proprioception (body position and movement)
  • Transmit this information to the CNS for processing
• Motor neurons in the PNS receive commands from the CNS
  • Innervate muscles and glands to produce movement and other responses
• The PNS is divided into the somatic and autonomic nervous systems
  • Somatic nervous system: controls voluntary functions
    • Includes sensory and motor neurons that innervate skin, muscles, and joints
    • Allows for conscious perception and voluntary movement
  • Autonomic nervous system: regulates involuntary functions
    • Sympathetic division: "fight or flight" response (increases heart rate, dilates pupils)
    • Parasympathetic division: "rest and digest" functions (slows heart rate, constricts pupils)

Hemispheric Lateralization and Functional Localization

Hemispheric Specialization

• The cerebrum is divided into two hemispheres, left and right, connected by the corpus callosum
• Each hemisphere is specialized for certain functions (hemispheric lateralization)
  • Left hemisphere typically dominant for:
    • Language processing (Broca's area, Wernicke's area)
    • Logical reasoning, analytical thinking
  • Right hemisphere typically dominant for:
    • Spatial processing, visual-spatial skills
    • Emotional processing, prosody (tone and rhythm of speech)
    • Creativity, artistic abilities
• Degree of lateralization varies among individuals
  • Both hemispheres work together to perform complex tasks
• Damage to specific hemispheres can result in specific deficits
  • Left hemisphere damage: language impairments (aphasia), difficulty with logic and analysis
  • Right hemisphere damage: spatial neglect, difficulty with emotional processing and creativity

Localization of Brain Functions

• Specific regions of the brain are specialized for certain functions (functional localization)
• Occipital lobe: visual processing
  • Primary visual cortex (V1) receives input from the eyes
  • Higher-order visual areas process color, motion, depth, and object recognition
• Temporal lobe: auditory processing, memory, language comprehension
  • Primary auditory cortex processes sound
  • Hippocampus and surrounding areas involved in memory formation and retrieval
  • Wernicke's area involved in language comprehension
• Parietal lobe: spatial processing, touch sensation, body awareness
  • Primary somatosensory cortex receives touch and proprioceptive information
  • Posterior parietal cortex integrates sensory information to create a body schema
• Frontal lobe: executive functions, planning, decision-making, motor control
  • Prefrontal cortex involved in higher-order cognitive functions
  • Primary motor cortex controls voluntary movements
  • Broca's area involved in speech production
• Damage to specific brain regions can result in specific deficits
  • Occipital lobe damage: visual impairments, blindness
  • Temporal lobe damage: hearing impairments, memory loss, language comprehension difficulties
  • Parietal lobe damage: spatial neglect, impaired touch sensation, difficulty with body awareness
  • Frontal lobe damage: impaired executive functions, difficulty with planning and decision-making, motor deficits