Transcript Introduction to Cellular and Molecular Neurobiology (and what it`s for).

The Brain: No Moving Parts
Neurons
Neurons come in different shapes and sizes.
Some of the smallest neurons have cell
bodies that are only 4 microns wide, while
some of the biggest neurons have cell
bodies that are 100 microns wide.
Neurons are similar to other cells in the body in some ways such as:
1.
2.
3.
4.
Neurons are surrounded by a cell membrane.
Neurons have a nucleus that contains genes.
Neurons contain cytoplasm, mitochondria and other "organelles".
Neurons carry out basic cellular processes like protein synthesis and energy
production.
However, neurons differ from other cells in the body in that:
1. Neurons have specialized extensions called dendrites and axons. Dendrites
bring information to the cell body and axons take information away from the
cell body.
2. Neurons communicate with each other through an electrochemical process.
3. Neurons contain some specialized structures (for example, synapses) and
chemicals (for example, neurotransmitters).
What Neurons Look Like
Concept of Polarization: Direction of Information Flow
A Morphological Classification:
One way to classify neurons is according to the number of extensions that
originate from the neuron's cell body (soma).
•Bipolar Neurons have two processes
extending from the cell body (examples: retinal
cells, olfactory epithelium cells).
•Pseudounipolar cells (example: dorsal root
ganglion cells). Actually, these cells have 2
axons rather than an axon and dendrite. One
axon extends toward the spinal cord, the other
axon extends toward the skin or muscle.
•Multipolar Neurons have many
processes extending from the cell body,
although only one of these is the axon
(examples: spinal motor neurons, pyramidal
neurons, Purkinje cells).
What’s
Inside?
A neuron has many of the same
"organelles", as other cells in the
body.
•Nucleus - Contains genetic material (chromosomes)
including information for cell development and
synthesis of proteins necessary for cell maintenance
and survival. Covered by a membrane.
•Nucleolus - Produces ribosomes necessary for
translation of genetic information into proteins
•Nissle Bodies - groups of ribosomes used for
protein synthesis.
•Endoplasmic reticulum (ER) - system of tubes for
transport of materials within cytoplasm. Can have
ribosomes (rough ER) or no ribosomes (smooth ER).
With ribosomes, the ER isimportant for protein
synthesis.
•Golgi Apparatus - membrane-bound structure
important in packaging peptides and proteins
(including neurotransmitters) into vesicles.
•Microfilaments/Neurotubules - system of
transport for materials within a neuron and may be
used for structural support.
•Mitochondria - Produce energy to fuel cellular
activities.
Axons & Dendrites:
There are several differences between axons and dendrites:
Axons
Dendrites
•Take information away from the
cell body
• Bring information to the cell body
• Smooth Surface
• Generally only 1 axon per cell
• No ribosomes
• Can have myelin
• Branch further from the cell
body
• Rough Surface (dendritic spines)
• Usually many dendrites per cell
• Have ribosomes, mitochondria
• No myelin insulation
• Branch near the cell body
What neurons Really look like:
What neurons Really look like:
What neurons Really look like:
The cytoskeleton
Principle of dynamic
polarization:
Information (generally) flows in a single direction
Pre-synaptic neuron:
• Generates an action potential which arrives at the
pre-synaptic terminal, causing neurotransmitter
release.
Post –synaptic neuron:
• Neurotransmitter activates the postsynaptic
termninal on dendrites, which transmit a signal to
the cell body.
Terminology:
Afferent = “going to”
Refers to signals that reach the neuronal cell
body (e.g., vie the dendrites).
Efferent = “leaving from”
Refers to signals that leave the cell body (e.g., via
the axon).
The Axon: Efferent component
For communication between
neurons to occur, an electrical
impulse must first travel down
an axon to the synaptic terminal.
Dendrites and their spines:
• The integrative unit of
the neuron
• Contain the majority of
Synapses
• Contain high
concentrations of ion
channels and cell
membrane receptors.
Spines are dynamic objects
Dendrites &
Synapses
Fluorescence staining of a
hippocampal dendrite .
A. After filling with Lucifer
yellow.
B. After staining against
synaptophysin.
The arrows in both images
point to the sites of
spines, and the
arrowheads point to the
site shaft synapses.
The Chemical
Synapse
The Synapse
Electron Micrographs have
shown that synapses can be
either asymmetrical(red
arrow) or symmetrical (green
arrow).
•The Red arrow is pointing to a
synapse that has one dark band
and one lighter band.
•The green arrow is pointing to a
synapse that has two dark bands.
Asymmetrical synapses are thought
to be excitatory synapses and
symmetrical synapse are thought
to be inhibitory synapses.
•The yellow line outlines the
dendrite (D).
Ion Channels
Na+ Channel
K+ Channel
The Knee Jerk Reflex
The
The
The
The
The
Taylor
Krauss
Troemner Berliner Babinski
Hammer Hammer Hammer Hammer /Rabiner
Hammer
The
Queen’s
Square
Hammer
The Knee Jerk Reflex
The Knee
Jerk Reflex
A somatic reflex arc in which the
final element in the chain is skeletal
muscle.
1 Is some sensory transducer in the periphery, for example, a Golgi tendon
organ, a Pacinian corpuscle or other tactile sensor in the skin.
2 The pseudounipolar sensory neuron in the circuit. Its soma is physically
located in a craniospinal ganglion (pictured here as a dorsal root ganglion,
but it could also be on a cranial nerve).
3 An interconnector neuron, whose soma is found in the CNS.
4 Is a motor neuron whose soma is in the ventral horn of the gray H of the
spinal cord.
5 The effector organ, which in the case of this type of arc, will always be
skeletal muscle.
Spinal
cord
injury &
spasticity
Spinal cord injury & spasticity
Although the knee jerk reflex is classically considered to be
“monosynaptic”, it actually is not solely controlled at the
spinal level.
Descending pathways exert excitatory or inhibitory effects
on motor neurons (each of which has over 100,000 synaptic
contacts) either directly, or via interneurones.
Disrupting these descending pathways removes inhibition,
causing spasticity.