Neuro Sciences Midterm 1

• 1. Central Nervous System (CNS)
•                    - Brain
•                    - Spinal Cord

• 2. Peripheral Nervous System (PNS)
•                    - Cranial nerves
•                    - Spinal nerves

1. Neurons

2. Glia

• Neurons are cells. They have membranes, cytoplasm, nucleus, metabolism, protein synthesis, protein modification and protein transport.
•  

Cell body: contains nucleus and organelles

Dendrites: receive inputs

Axon: Conducts impulses away from the cell body

Axon hillock: an enlarged region where an axon attaches to the cell body.

Node of Ranvier: periodic gap in the insulating sheath (myelin) on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses.

Morphological heterogeneity of neurons



Functional polarity: despite heterogeneity basic structures which is common to most neurons such as dendrites (input) and axons (output).

*Functional polarity: consists of two functions which are polar opposites, but which together entails a larger, more inclusive function, referred to as their common functioning principle.

The Golgi impregnation method is a nervous tissue staining technique discovered by Italian physician and scientist Camillo Golgi.

Impregnate neuron cells with silver chromate (Ag₃)

1 - 10% only turn black.

Step 1: Wash the neurons with 2% aqueous solution of potassium dichromate for two days (incubate)

step 2: Then incubate with 2% aqueous solution of silver nitrate for 2 days

step 3. After 2 days 1 - 10% neurons will be black.

A theory that states the nervous system consists of a large network of tissue, or reticulum, formed by the fused processes of nerve cells. (A continuous pro-plasmatic lanes)

Incorrect!

Neuronal doctrine says neurons are discrete entities communicating at specialized compacts called synapses.

Synapses: A synapse is the junction between the synaptic terminal and another cell.

A dendritic spine (or spine) is a small membranous protrusion from a neuron's dendrite that typically receives input from a single synapse of an axon.

Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body.

Most spines have a bulbous head (the spine head), and a thin neck that connects the head of the spine to the shaft of the dendrite.

The dendrites of a single  neuron can contain hundreds to thousands of spines.

• In addition to spines providing an anatomical substrate for memory storage and synaptic
• transmission, they may also serve to increase the number of possible contacts between neurons.

A neuron contacts its targets through Synapses.

Synapses: In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another cell.

Synapses are essential to neuronal function: neurons are cells that are specialized to pass signals to individual target cells, and synapses are the means by which they do so.

There are two fundamentally different types of synapses:chemical synapse and electrical synapse.

Boutons are axonal swellings or varicosities found typically at the sites where synapses occur.

- Comes from the Greek word 'glue'

- more abandant than neurons (3:1)

- They are not excitable

- They have supportive role and also make signaling faster

• Types of glial cells:
•         - Astrocytes (CNS)
•         - Microglia (CNS)
•         - Oligodendrocytes (CNS)
•         - Schwann cells (PNS)

Oligodendrocytes are types of brain cell whose main function is to produce mylein, laminated lipid rich wrapping along CNS axons (not all axons).

Mylein sheeth: very specialized membranes with specific protein content (PLP).

Ensheeting of axons is a form of electrical isolation that allows action potential to propagate fast along the axon.

Each myelinated segment is called internode (100 - 500 micrometer length).

The gap between is called node of ranvier.

A glial cell found in the CNS named for its characteristic star-like shape.

Constitute between 20-50% of volume in some brain areas

Play scaffolding role during development

Envelop synapses

Cuff Nodes of Ranvier

Cover blood vessels

Essentially they “ fence in” neurons

• These cells provide both mechanical and metabolic support for neurons, regulating
• the environment where they function; they contribute to the blood-brain barrier
• and control transport of substances from the blood to neural tissue; they also
• help coordinate nerve pathway development.

Microglia are extremely small cells of the CNS that remove cellular waste and protect against microorganisms.

Similar to macrophages in other tissues.

Derived from hematopoietic precursors.

• Form mylein sheath in the PNS.
• (similar function as oligodendrocytes)

In contrast to oligodendrocytes, they myelinate one axon only.

Cell body range from 5 to 50 micro meters

Spines = 1 micro meter

Synaptic Cleft = 20 nm

* To see nanometers you need electron microscope which was developed int he 40s.

Resting membrane potential is the difference in voltage of the fluids inside a cell and outside a cell, which is usually between -70 to -80 millivolts (mV).

All cells have this difference, but it is particularly important in relation to nerve and muscle cells, since any stimulus that changes the voltage and makes it different from the resting membrane potential is what allows the cells to transmit electrical signals. If the cells didn't have the voltage difference, then they would be neutral, and wouldn't transmit any information.

The voltage-gated sodium channel has several functional parts. One portion of the channel determines its ion selectivity. This particular channel is quite selective for sodium ions. Even the chemically similar potassium ions cannot pass through the channel.

Another portion of the channel serves as a gate that can open and close. The gate is controlled by a voltage sensor, which responds to the level of the membrane potential.

An inactivation gate: this limits the period of time the channel remains open, despite steady stimulation.

At a typical resting membrane potential (for example, -70 mV) the channel is closed. Then should any factor depolarize the membrane potential sufficiently (for example, to -50 mV), the voltage sensor moves outward and the gate opens.