Neuroanatomy Overview

Neuroanatomy

• Be able to describe the nervous system's macroscopic anatomy, including major core areas and pathways.
• The brain is divided into sections, such as the telencephalon, diencephalon, brain stem, and spinal cord.
• The corpus callosum is a large bundle of nerve fibers connecting the two hemispheres of the brain.
• The thalamus is a major relay center for sensory information, with the hypothalamus regulating homeostasis.
• The brain stem controls basic life functions and relays information between the brain and spinal cord.
• The spinal cord is a major pathway for sensory and motor information.
• Different regions of the brain have specific functions, such as gyrus precentralis for motor functions, and gyrus postcentralis for sensory functions.
• Broca's area (in the frontal lobe) and Wernicke's area (in the temporal lobe) are crucial for language processing.
• There are association areas in the brain that integrate information from different sensory modalities.
• The cerebellum plays a role in coordination, balance and motor control.
• The basal ganglia are involved in motor control, posture and coordination.
• The limbic system is involved in emotion and memory.

Cerebral Cortex - Division into Lobes

• The cerebral cortex is divided into four lobes: frontal, parietal, temporal, and occipital.
• The frontal lobe is located at the front of the brain and is involved in higher-level cognitive functions such as planning, decision-making, and voluntary movements.
• The parietal lobe is located behind the frontal lobe and is involved in processing sensory information from the body, including touch, temperature, and pain.
• The temporal lobe is located on the sides of the brain and is involved in processing auditory information and language.
• The occipital lobe is located at the back of the brain and is involved in processing visual information.

The Basal Ganglia

• The basal ganglia is a group of subcortical nuclei that play a critical role in motor control, habit learning, and procedural memory.
• Major components of the basal ganglia include the caudate nucleus, putamen, and globus pallidus.
• The basal ganglia are involved in the initiation and execution of movement, as well as the control of posture and muscle tone.
• The basal ganglia work by sending signals through circuits to the thalamus and the cortex.

The Anatomy of Emotions

• The limbic system plays a vital role in emotion and memory.
• Amygdala, hippocampus, and hypothalamus are key structures involved.

The Brainstem

• The brainstem consists of the midbrain, pons, and medulla oblongata.
• The brainstem is responsible for regulating essential bodily functions.
• It serves as a vital relay station for sensory and motor signals.

The Reticular Formation

• The reticular formation is a network of neurons within the brainstem, influencing consciousness and alertness.
• It has ascending and descending pathways that impact various functions.
• The ascending part is associated with awareness and wakefulness, the descending part with motor control.

The Spinal Cord

• The spinal cord serves as a communication pathway between the brain and the peripheral nervous system.
• It contains sensory and motor neurons.
• White and gray matter are present.
• Contains tracts that relay information, either sensory or motor.

The Meninges

• There are three layers: Dura mater, Arachnoid mater, and Pia mater.
• The meninges protect the brain and spinal cord.
• The ventricles are fluid-filled cavities and are apart of the ventricular system.
• The ventricular system contains cerebrospinal fluid (CSF) that cushions and protects the brain.

Axon Growth and Synapse Formation

• Axon growth is guided by attractive and repulsive cues.
• Axon guidance is mediated by different molecules, including those that bind to receptors.
• The growth cone changes its shape to respond to signals.
• The cytoskeleton remodels to adjust to signals in different directions.

Types of Axon Guidance Cues

• Contact-mediated and diffusible cues guide the growth cone in a specific direction.
• Sempahorins bind to plexins and cause repulsion.
• Ephrins bind to Eph receptors to either attract or repel growth.
• Neurtins bind to DCC receptors to cause attraction.
• Slit binds to Robo receptors leading to repulsion.

Types of Neurons

• Bipolar neurons (two extensions), unipolar neurons (one extension), and multipolar neurons (multiple extensions).
• Unipolar and pseudounipolar neurons are common in peripheral sensory systems.
• Motor neurons are a common example of multipolar neurons.

Glial Cells

• Glial cells maintain homeostasis in the nervous system.
• Astrocytes support neurons metabolically and maintain the chemical environment.
• Microglia are immune cells that help defend against pathogens.
• Oligodendrocytes and Schwann cells produce myelin sheaths.

Passive Properties of Nerve Cells

• Passive properties of nerve cells are due to the cell's membrane structure.
• They include properties like capacitance, resistance and membrane time constant.
• Signal passively spreads along the membrane to the next channels.
• Spatial summation is an effect of passive channels

Active Properties of Nerve Cells and Ion Channels

• Ion channels determine the flow of ions in the cell to make it more or less passive.
• Non-gated channels are always open and maintain resting potential.
• Gated channels in the membrane open in response to stimuli affecting the neuron's membrane potential. These channels include voltage-gated, ligand-gated, mechanically-gated and other types.

Steps of an Action Potential

• Membrane depolarization happens as sodium channels open, which increases the inside positivity.
• A stimulus reaches the threshold potential, which starts an action potential.
• During depolarization, voltage-gated sodium channels open and sodium ions rush into the neuron, increasing in positivity.
• Repolarization happens when sodium channels close and potassium channels open allowing potassium ions to rush out.
• Afterhyperpolarization occurs when potassium continues to leave the neuron.
• The sodium-potassium pump restores the original resting potential.

Refractory Periods

• Absolute refractory period: Neuron cannot fire another action potential.
• Relative refractory period: Neuron can fire another action potential, but it needs a stronger stimulus.

Synaptic Transmission

• Action potential depolarizes the axon terminal.
• Voltage-gated calcium channels open.
• Calcium influx triggers neurotransmitter release.
• Neurotransmitters diffuse across the synaptic cleft.
• Neurotransmitters bind to receptors on the postsynaptic neuron or other neurons to generate synaptic potential.

Synaptic Plasticity

• Short-term plasticity: Includes modifications in release, such as facilitation and depression.
• Long-term plasticity: synaptic changes that can influence synaptic strength, and include important neural mechanisms like LTP.

Neurotransmitters

• Small molecule transmitters (acetylcholine, amino acids, biogenic amines, purines)
• Peptide transmitters (endorphins, substance P, somatostatin)

Postsynaptic Receptors

• The binding of a neurotransmitter to a receptor triggers ion channels to open or close.
• Ligand-gated ion channels alter the membrane potential directly.
• G protein-coupled receptors (GPCRs) initiate a cascade of intracellular signaling events.

Signal Transduction in Postsynaptic Receptors

• Different postsynaptic receptors generate different types of signals that trigger different intracellular responses.
• Ligand gated channels are directly connected to ion channels modifying the membrane voltage.
• G-protein coupled receptors (GPCRs) use a second messenger system that triggers a cascade of changes to modify ion currents or other intracellular processes.

Types of Postsynaptic Receptors

• Ionotropic receptors (ligand-gated ion channels): Fast and direct effects, like generating EPSPs or IPSPs directly.
• Metabotropic receptors (GPCRs): Slower and more complex effects, which can cause a cascade of intracellular signaling events.

Chemical Synapse Mechanisms

• Action potential arrives at the axon terminal.
• Calcium channels open, and calcium enters the terminal.
• Neurotransmitter vesicles fuse with the membrane and release neurotransmitters into the synaptic cleft.
• Neurotransmitters bind to receptors on the postsynaptic membrane.
• Postsynaptic response occurs.
• Neurotransmitters are removed from the cleft.

Neural Recording Techniques

• Techniques like patch clamp and intracellular recording allow researchers to measure ion channel activity and membrane potential.
• Patch-clamp technique measures currents flowing through ion channels or cells.
• Techniques allow for an in-depth investigation of the electrical and other properties of cells.

Advantages of Patch Clamp

• Provides high resolution to study single channel activity.
• Enables detailed investigation of ionic channels.
• Allows study of specific ion channels and their behavior.
• Allows study of channel activity from living cells more reliably.

This quiz explores the macroscopic anatomy of the nervous system, detailing major sections such as the telencephalon, diencephalon, brain stem, and spinal cord. It also covers critical functions of specific brain regions and their roles in sensory and motor processing. Test your knowledge on the anatomical pathways and functional areas of the brain.