Neuroscience Chapter 4

Brain Structure and Function

• The brain is the nerve center, containing billions of neurons that receive and process information from the body and external world, controlling responses (conscious and unconscious movements, thoughts, emotions, memories).
• The brain performs multiple tasks simultaneously (e.g., throwing a ball and talking, planning dinner while shopping).
• This multitasking is possible due to distinct brain regions specialized for specific tasks.

Major Brain Landmarks

• The cerebrum is the largest part of the human brain, divided into two hemispheres connected by the corpus callosum (a bundle of nerve fibers).
• The cerebral cortex is the deeply folded outer layer of the cerebrum, increasing surface area and processing power.
• Neuroscientists use divisions (lobes) of the cerebrum to identify regions with characteristic functions.

Brain Lobes

• Frontal Lobes: Located above the eyes, coordinating voluntary movements, speech, memory, emotions, higher cognitive skills (planning, problem-solving), and personality aspects.
• Parietal Lobes: Located behind the frontal lobes, integrating sensory signals (from skin), processing taste and some visual information.
• Occipital Lobes: Located at the back of the brain, processing visual information (colors, shapes), integrating visual understanding.
• Temporal Lobes: Located on the sides of the brain, carrying out visual and auditory processing. The hippocampus (encodes new memories) and amygdala (integrates memory and emotion) are components of the temporal lobes.

Limbic System and Forebrain

• The limbic system is a group of structures deep within the brain regulating emotions and motivation.
• The limbic system includes the thalamus (integrates sensory information, relays to other brain parts), and hypothalamus (sends hormonal signals to the body).
• The forebrain comprises the limbic system and the cerebral cortex.

Midbrain and Hindbrain

• The midbrain is beneath the thalamus, coordinating eye movements (blinking, focusing), triggering reflexes (e.g., startled jump), inhibiting unwanted body movements, and coordinating sensory and motor input (fine motor control).
• The basal ganglia, a collection of structures, helps regulate complex body movements, involving parts of the forebrain.
• The hindbrain regulates glucose and sleep, controlling movement. The cerebellum (second-largest brain part, with half the brain's neurons) coordinates voluntary movement, learning motor skills, and has roles in spatial and temporal perception.
• The pons influences breathing and posture.
• The medulla carries nerve pathways to the spinal cord; controls basic functions (swallowing, heart rate, breathing).
• The brainstem comprises the midbrain, pons, and medulla.

Neural Networks

• Information travels through neural networks, consisting of chains of neurons (nerve tracts), connecting brain regions, transmitting signals quickly.
• Examples include the corpus callosum connecting hemispheres and the anterior commissure.
• These networks organize and analyze information within fractions of a second (e.g., watching a movie).
• Visual processing: Starts in the retina, travels through the optic nerve, thalamus to the primary visual cortex, processing shapes, colors, movement, producing a three-dimensional image. Temporal (identifies objects) and parietal lobe (detects spatial location).

Brain Waves

• Brain waves (rhythmic electrical patterns) are created by signaling loops through the thalamus and cortex and are measured by an EEG.
• Four types:
  • Alpha (8-13 Hz), parietal/occipital lobes, relaxation, eyes closed
  • Beta (14-30 Hz), frontal/parietal lobes, sensory processing, concentration
  • Theta (4-7 Hz), slower than alpha
  • Delta (<3.5 Hz), very slow, deep sleep

Neural Circuits

• Neural circuits are interconnected neurons, transforming input into output patterns used for complex information processing (e.g., recognizing faces, planning actions).
• The cerebral cortex contains layers of organized neurons in columns, forming interconnected signal chains.
• Each column is likely dedicated to a specific processing task, but neighboring circuits can influence outputs.

Neurons (Excitatory and Inhibitory)

• Neurons are the functional units of neural circuits.
• Neurons are either excitatory or inhibitory.
• Most brain neurons are excitatory (e.g., pyramidal cells).
• Inhibitory neurons suppress other neurons' activity, regulating circuit activity.
• Imbalances can lead to seizure disorders.

Glia

• Glia are support cells associated with neurons.
• Recent studies suggest a 1:1 ratio of glia to neurons in some brain regions vs. previous estimates of 10:1.
• Four main glial cell types (astrocytes, microglia, ependymal cells, oligodendrocytes).

Synapses and Neurotransmission

• Signals are passed from one neuron to another at synapses.
• Synaptic cleft separates neurons.
• Neurotransmitters (e.g., amino acids, gases, small organic chemicals, short peptides) cross the cleft.
• Action potential triggers neurotransmitter release.
• Neurotransmitters bind to receptors, altering postsynaptic membrane voltage (ionotropic or metabotropic).
• Excess neurotransmitters are removed by glia.
• Neurotransmitter are Broken down or reabsorbed (reuptake).
• Different neurotransmitters induce different effects (e.g., glutamate, GABA).

Receptors and Molecular Signaling

• Neurons have receptors for various molecules (hormones, neuromodulators, prostaglandins) which change neuronal function.
• Signal transduction pathways (cellular reactions) are triggered.
• Steroid hormones (estradiol, cortisol) use intracellular receptors.

Neurons, Genes, and Gene Expression

• Neuorns differ in appearance and function due to differing gene expression.
• All cells have the same DNA; different gene expression (protein building) creates different neurons.
• Chromatin changes regulate gene expression (tightening or spreading out).
• Variants or alleles of genes cause structural differences that affect function (including potential diseases).

Brain Evolution

• Human brains evolved from simple tube-like structures.
• Early vertebrates had basic brain regions (forebrain, midbrain, hindbrain).
• Expansion of regions (e.g., olfactory bulbs, light-sensitive regions) due to sensory and motor reflexes.