Notes

Lecturer: Wolfger Von Der Behrens

Types of Neurons Morphology and electrical properties are what characterize neurons.

Terminology

• Axon
• Boutons
• Cleft (gap between two neurons)
• Dendritic spines
• Postsynaptic membrane
• Vesicles (small zones filled with neurotransmitters)
• Transmitter
• Receptors

Axon

Vescicles Lyposomes release the contained neurotransmitter when the action potential arrives.

Neurotransmitter Many different types, the most commons are the Glutamate (excitatory) and GABA (inhibitory). One neuron typically releases just one type of neurotransmitter.

Post-Synaptic Receptor There are two major classes of receptors: Ligand-Gated Ion Channels and G-Protein-Coupled Receptors (neurotransmitters bind to the receptor, which activates the G-Protein that modulates Effector protein) then depending on the ions flowing in, it can depolarize or hyperpolarize.

Dendrites The neuron depolarizes when Glutamate is released, such that it reaches the threshold to generate an action potential. On the other side, if the neuron is hyperpolarized by the release of GABA and Glutamate is released at the same time, we have a mediated effect (orange line) which is probably not reaching the threshold to generate an action potential.

Sequence of Events

1. Neurotransmitter release.
2. Receptor binding.
3. Ion channels open or close.
4. Conductance change causes current flow.
5. Postsynaptic potential changes.
6. Postsynaptic cells excited or inhibited.
7. Summation determines whether or not an action potential occurs.

Central Nervous System (CNS) vs Peripheral Nervous System (PNS) + Enteric Nervous System (ENS). Among the CNS we subdivide in Sympathetic ("Fight or Flight") and Parasympathetic Nervous System ("Feed & Breed").

Gross Anatomy: Protection and Sustenance of the Brain The brain is floating in the cerebrospinal fluid inside the skull.

The Meninges are three layers of tissues: Dura Mater (Hard structure, mechanical protection), Arachnoid Mater (Soft structure) and the Pia Mater.

Ventricular System

Navigating the Central Nervous System

Direction of Orientation in the CNS

• Anterior: toward the front or front-end
• Posterior: toward the back or back-end
• Inferior: toward the bottom of the body, or below
• Superior: toward the top of the head/body, or above
• Medial: toward the middle/midline
• Lateral: away from the middle/midline, toward the side
• Rostral: toward the nose
• Caudal: toward the tail/rear
• Proximal: near the trunk or center
• Ventral: toward the belly
• Ipsilateral: on the same side
• Contralateral: on the opposite side
• Bilateral: on both sides
• Unilateral: on one side.

Neural Development

Major Divisions of the Brain

Cranial Nerves

The Limbic System It was named by Brocas, he hypothesized that it is involved in emotional processing and reactions. Hippocampus is one of the main memory forming structures.

Papez Circuit

Amygdala is strictly connected with the generation and processing of fear.

• Broca's "limbic lobe"
• Papez (1937) more precisely defined it.
• Structure:
  • Structures on medial and basal surfaces of cerebral hemispheres.
  • Cingulate gyrus + parahippocampal gyrus + hippocampal formation + fornix + amygdala + septum + mammillary bodies.
  • Anatomic circuits include basolateral circuit and the Papez circuit.
• Function:
  • Emotional expression.
  • Memory acquisition.
  • Fear conditioning.
  • Violence and aggression.

Hypothalamus and Thalamus On top we have the Thalamus, while the Hypothalamus sits below. The first one is the input structure into the cortex. Most of the sensory inputs are gated into the cortex by the Thalamus. It does not only relay information, but it also performs a processing of information. The Hypothalamus is more part of the endocrine nervous system, it has the control of the epituary gland.

Thalamus Upper Brain Stem: Diencephalon

Thalamus:

• Structure:
  • Relatively large.
  • Two symmetric large nuclei.
  • All thalamic nuclei receive ascending and descending input.
  • Many projections.
• Function:
  • Relay station
  • Domain-specific information processing.

Hypothalamus:

• Structure:
  • Very small.
  • Contains an important collection of nuclei.
• Function:
  • Controls autonomic mechanisms.
  • Link to endocrine system.

Basal Ganglia

It sits below the forebrain, it is strongly interconnected with the cortex and the Thalamus. It is highly involved in movements. In the case of Parkinson's disease we assist at a loss of dopaminergic neurons.

Through Deep Brain Stimulation, i.e., an electrical stimulation of the deep brain tissues, it is possible to reduce the symptoms related to diseases affecting Basal Ganglia and Substantia Nigra.

• Structure:
  • Collection of nuclei embedded deep within cortex.
  • Partially surround the Thalamus.
  • Sensory projection to cerebrum.
  • Efferents to other nervous system structures.
  • Caudate nucleus + putamen + globus pallidus + substantia nigra + subthalamic nucleus.
• Function:
  • Regulate voluntary movement.
  • Integrative or just a relay station?
• Pathology:
  • Movement disorders (e.g., Parkinson's).

Lobes of Cerebral Cortex

Cytoarchitecture The cells are organized in a very systematic and consistent structure made of 6 layers. In the first layer there are mostly projections, very few cells. Cell bodies are stained with Golgi technique even today and in the following picture cell bodies and their projections are shown in the layers 2 - 6. The 2 - 6 layers structure can change depending on the brain cortical area and the functions that they perform.

Cortical Areas

• Frenology
• Phineas Gage (1823 - 1860):
  • Accident in 1848 destroyed the left frontal lobe.
  • "The equilibrium or balance, so to speak, between his intellectual faculties and animal propensities, seems to have been destroyed".

Brodmann's Areas (BA) The cytoarchitecture is not consistent throughout the cortex, Brodmann looked at the composition of layers in different areas in the brain. Hence, he defined a map of the brain based on the histological differences. The map has still some similarities with the actual knowledge of the brain areas, however it was not saying anything about the functions of the various regions.

Extracellular recordings Tungsten microelectrode for recording from single units: an electrode has been developed to fill the need for an easily made, sturdy device capable of resolving single-neuron action potentials at least as well as the commonly used micropipette.

Circuits The basic cortical circuits are either Feedforward or Feedback. In particular, layer 4 of the cortex is the "input layer" of the cortex.