Brain Structure and Function

Brain Structure and Function

• The brain is the nerve center, containing billions of neurons transmitting information from the body and environment, and programming responses (conscious/unconscious actions, thoughts, emotions, memories).
• The brain's multitasking ability stems from specialized regions for specific tasks.

Major Brain Landmarks

• The cerebrum is the largest part, divided into two hemispheres connected by the corpus callosum.
• The cerebral cortex is the deeply folded surface layer, increasing processing power through increased surface area.
• Neuroscientists divide the cerebrum into lobes based on deeper divisions (frontal, parietal, occipital, temporal) each with distinct functions.

Lobes of the Cerebrum

• Frontal Lobes: Located at the front, coordinate voluntary movement, speech, memory, emotion, higher cognitive functions, and personality.
• Parietal Lobes: Located at the top, behind frontal, integrate sensory signals, process taste, and some visual information.
• Occipital Lobes: Located at the back, process visual information, recognizing colors, shapes, and complex visual understanding.
• Temporal Lobes: Located on the sides, carry out some visual processing, interpret auditory information. Include the hippocampus (encodes new memories) and amygdala (integrates memory and emotion).

Limbic System and Forebrain

• The limbic system is a network deep within the brain regulating emotion and motivation.
• Components include the thalamus (integrates sensory input), and hypothalamus (sends hormonal signals).
• The forebrain includes the cerebral cortex and these limbic structures.

Midbrain and Hindbrain

• The midbrain is beneath the thalamus, coordinates eye movements (blinking, focusing), reflexes to sounds (e.g., startle response), inhibits unwanted movements, and coordinates sensory/motor input.
• The hindbrain regulates glucose, sleep, and movement.
• The cerebellum is a deeply folded, two-hemisphere structure, coordinating voluntary movements, learning motor skills, and spatial/temporal perception. Damage can lead to impaired coordination.
• The pons influences breathing and posture.
• The medulla carries nerve pathways connecting the brain to the spinal cord, controlling basic functions like swallowing, heart rate, and breathing.
• The brainstem consists of the midbrain, pons, and medulla.

Brain Evolution

• The human brain evolved from a simple tube-like structure.
• Early vertebrates had brains with specific regions for processing sensory information.
• Over time, regions involved in sensory, motor, and higher level behaviors (e.g. swimming) expanded.

Neural Networks and Circuits

• Information travels through chains of neurons (neural networks), organized into tracts.
• Neural networks analyze and organize information within fractions of a second.
• Movie-watching example illustrates signal pathways from retina through optic nerve and tract to visual cortex.
• Separate processing streams in the temporal and parietal lobe aid in object recognition/spatial location.
• Neural networks can vary depending based location.

Brain Waves

• Brain activity produces rhythmic electrical signals called brain waves.
• Alpha waves are associated with relaxation and closed eyes; beta waves with concentration.
• Theta and delta waves are associated with sleep.
• Wave distinctions are measured by frequency.

Neurons and Glia

• The neuron is the functional unit of neural circuits, with cell bodies, dendrites, and axons.
• Neurons transmit electrical signals between neurons & muscles/glands.
• Glial cells (astrocytes, microglia, ependymal cells, oligodendrocytes) support neurons.
• Glial cells can outnumber neurons depending on location in the brain.

Synapses and Neurotransmission

• Signals pass between neurons at junctions called synapses.
• Neurotransmitters (e.g., amino acids, gases, small organic chemicals, short peptides) are chemical signals crossing the synapse.
• Neurotransmitters bind to receptors on the next neuron, causing voltage changes to open ion channels.
• This process of neurotransmission enables complex brain functions like memory and thought.
• Excitatory and inhibitory neurons have different neurotransmitters.
• Glutamate and GABA are the most common excitatory/inhibitory neurotransmitters

Receptors and Molecular Signaling

• Neurons have receptors for hormones, neuromodulators (e.g., endocannabinoids), and prostaglandins.
• Hormones impact neuronal function by changing cell ion balance or enzyme activity through signal transduction.
• Steroid hormones can affect gene expression by impacting the nucleus.

Neurons, Genes, and Gene Expression

• Neurons can vary in function due to different gene expression.
• Differences may be influenced by chemical changes to chromatin.
• Gene variants affect protein structure/function, which can influence neuronal activity and brain function.
• Tay-Sachs highlights genetic impact on neuronal functioning.