6.1 Neuroanatomy and brain organization

The brain is a complex organ with specialized structures that work together to control our thoughts, emotions, and actions. From the cerebrum's four lobes to the brainstem's vital functions, each part plays a crucial role in our cognitive processes and bodily functions.

Our nervous system is divided into central and peripheral components, allowing for efficient communication throughout the body. Neurons transmit signals using electrical and chemical methods, while neurotransmitters facilitate communication between cells. This intricate system enables our brains to process information and respond to our environment.

Brain Structures and Functions

Structures and functions of the brain

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• Cerebrum contains four lobes responsible for various cognitive functions
  • Frontal lobe involved in executive functions, planning, decision-making, and motor control (Broca's area)
  • Parietal lobe processes sensory information, spatial awareness, and touch perception (somatosensory cortex)
  • Temporal lobe responsible for auditory processing, language comprehension, and memory formation (Wernicke's area, hippocampus)
  • Occipital lobe primarily involved in visual processing and interpretation (primary visual cortex)
• Cerebellum coordinates balance and fine motor control, enabling smooth and precise movements (walking, writing)
• Brainstem consists of three main structures that regulate vital functions
  • Midbrain involved in auditory and visual reflexes, and motor control (superior and inferior colliculi)
  • Pons relays information between the cerebral cortex and cerebellum, and plays a role in sleep regulation (REM sleep)
  • Medulla oblongata controls autonomic functions, such as breathing, heart rate, and blood pressure regulation (cardiovascular center)
• Limbic system comprises structures involved in emotion, memory, and basic drives
  • Hippocampus critical for memory formation and consolidation (episodic memory)
  • Amygdala processes emotions, particularly fear response (fight or flight)
  • Hypothalamus maintains homeostasis, hormonal regulation, and basic drives (hunger, thirst, sleep)
• Basal ganglia involved in motor control, learning, and habit formation (Parkinson's disease)
• Thalamus relays and integrates sensory and motor information, acting as a hub for communication between brain regions (sensory gating)

Nervous System Organization and Communication

Organization of nervous system

• Central nervous system (CNS) consists of the brain and spinal cord
  • Brain serves as the information processing, cognition, and control center (prefrontal cortex)
  • Spinal cord transmits signals between the brain and the body, and contains neural circuits for reflexes (knee-jerk reflex)
• Peripheral nervous system (PNS) includes sensory and motor divisions
  • Sensory (afferent) division transmits sensory information from receptors to the CNS (touch, vision, hearing)
  • Motor (efferent) division transmits motor commands from the CNS to effectors (muscles and glands)
    1. Somatic nervous system controls voluntary movements and receives sensory input from the external environment (skeletal muscles)
    2. Autonomic nervous system regulates involuntary functions and maintains homeostasis (heart rate, digestion)
    • Sympathetic division activates "fight or flight" response, increases alertness and prepares the body for action (increased heart rate, dilated pupils)
    • Parasympathetic division promotes "rest and digest" response, relaxation and energy conservation (decreased heart rate, constricted pupils)

Neurons and neurotransmitters in communication

• Neurons are specialized cells that transmit electrical and chemical signals
  • Dendrites receive signals from other neurons (dendritic spines)
  • Soma (cell body) contains the nucleus and organelles for cellular functions (protein synthesis)
  • Axon conducts electrical signals away from the soma to other neurons or effectors (myelin sheath)
  • Synapse is the junction between two neurons or a neuron and an effector where neurotransmitters are released (synaptic cleft)
• Action potential is an electrical signal that propagates along the axon when the neuron is sufficiently stimulated (threshold potential)
• Neurotransmitters are chemical messengers released from the presynaptic neuron that bind to receptors on the postsynaptic cell
  • Excitatory neurotransmitters (glutamate) increase the likelihood of the postsynaptic neuron firing an action potential (NMDA receptors)
  • Inhibitory neurotransmitters (GABA) decrease the likelihood of the postsynaptic neuron firing an action potential (GABA receptors)
• Synaptic plasticity refers to changes in the strength of synaptic connections, which underlies learning and memory formation
  • Long-term potentiation (LTP) is the strengthening of synaptic connections due to repeated stimulation (Hebbian learning)
  • Long-term depression (LTD) is the weakening of synaptic connections due to lack of stimulation or specific patterns of activity (synaptic pruning)

Lateralization and hemispheric specialization

• Lateralization refers to functional differences between the left and right hemispheres of the brain (hemispheric asymmetry)
• Corpus callosum is a bundle of nerve fibers that connects the two hemispheres and allows for communication between them (interhemispheric transfer)
• Left hemisphere specialization
  • Language processing (Broca's area for speech production, Wernicke's area for language comprehension)
  • Analytical and logical thinking (mathematical reasoning)
  • Sequential processing (reading, writing)
• Right hemisphere specialization
  • Visuospatial processing (facial recognition, mental rotation)
  • Emotional processing (prosody, sarcasm)
  • Holistic and intuitive thinking (creativity, art)
  • Parallel processing (multitasking)
• Hemispheric asymmetry refers to differences in the size, shape, or function of corresponding regions in the left and right hemispheres (planum temporale)
• Split-brain studies involve research on patients with a severed corpus callosum, revealing the specialized functions of each hemisphere (lateralized tasks)