Cellular Neurobiology
Albert Cheung-Hoi YU 于常海
北京大學神經科學研究所
Neuroscience Research Institute
Peking University
Department of Neurobiology
Peking University Health Science Center
achy@bjmu.edu.cn
One of the Cajal’s
many drawings of
Brain circuity
The letters label the different
elements Cajal identified in an
area of the human cerebral
cortex that controls voluntary
movement.
Cellular Components
• Neurons: Excitable cells –
“wiring” “Signal Senders”
• Neuroglia: Support, Nurturing,
Insulation
Nerve Cells
Neurons
Neuroglia
Structure of Neurons
• Cell body (soma; perikaryon)
• Axon : only one (branches are collaterals;
terminals are end feet)
• Dendrites : much shorter; one or more than
one; branch extensively into dendritic trees
Axon Hillock
(Axonal end feet)
The Axon
and Axon
Collaterals
Neurons
Structure & Function
• Cell Body (Soma): Life Support
– Protein Synthesis
– Single Nucleus, RER (Nissl Bodies)
• Axon: Longest process transmits messages
away from cell body
• Dendrites: Multiple processes off cell
body – receive messages
What are inside of a neuron?
Neurons are similar to other cells in the
body in some ways such as:
1. Neurons are surrounded by a membrane.
2. Neurons have a nucleus that contains genes.
3. Neurons contain :
Nucleus
Nucleolus
Microfilaments/Neuro
tubules
Endoplasmic Reticulum (ER)
Mitochondria
Golgi Apparatus
Nissl Bodies
Others
Axon and Dendrites
• Dendrites :
– dendrite tree
• Axon :
– axon hillock (axon origination)
– axonal transport system
– initial segment (first myelin sheath)
• action potential generation
– myelin sheath
Differences between Axons and Dendrites
Axons
Dendrites
Take information away
from the cell body
Take information to the cell
body
Smooth surface
Generally only 1 axon per
cell
Rough surface (dendritic
spines)
Usually many dendrites per
cell
No ribosome
Have ribosomes
Can have myelin
No myelin insulation
Branch further from the
cell body
Branch near the cell body
Neuron Classification by Shape
•Multipolar: “multi-” many processes
–Majority: Single axon, many dendrites (motor
neuron and interneuron)
•Bipolar: “bi-” 2 processes
–Found in some sensory organs (retina, taste,
smell, inner ear neuron)
•Unipolar (pseudo-unipolar): “uni -” 1 process (with
branches)
–Sensory afferent neurons (dorsal root ganglia)
Classification of
Neurons by
Morphology
Classification of Neurons
by Axon Length
1. Golgi type I Neurons
• Long axons (longest from the cortex to the
tip of spinal cord, 50-70 cm)
2. Golgi type II Neurons
• Short axons (shortest axons terminate only
a few micron from cell body, interneurons)
3. Amacrine Neurons
• An unusual cell type, lack axons
Functional Classification of Neuron
– Sensory neuron
• from receptor to CNS; receive stimuli and
transmit afferent impulses to CNS
– Interneurons
• communicating between neurons; form
circuits in the CNS
– Motor neuron
• from CNS to effector cells; deliver
efferent impulses out through the PNS to
the effectors to carry out the actions
directed by the CNS
Important Features of Neurons
• EXCITABLE Membrane: Able to
regulate the movement of ions
(charges) across and along
membrane
SIGNAL
TRANSDUCTION
• DO NOT Replicate: Damaged
cells cannot be replaced!
Action
Potential
Four Functional Regions of Model Neurons
Classification of Synapses
• Impulse transmission :
– electrical
– chemical
• Morphology :
–
–
–
–
axodendritic
axonsomatic
axoaxonic
dendrodendritic
Vesicles release
Neurotransmitters
synapse
4
Synapse Structures
• Chemical synapse :
– presynaptic knob (presynaptic component)
• synaptic vesicles
– synaptic cleft
– postsynaptic membrane (postsynaptic
component)
• Electrical synapse :
– gap junctions
Distinguishing Properties of
Electrical and Chemical Synapses
tance
Cytoplasmic
continuity
Ultrastructural
component
Agent of
transmission
Synaptic
delay
Direction
of transmission
Electrical
3.5 nm
Yes
Gap-junction
channel
Ion current
Virtually
absent
Usually
bidirectional
Chemical
20-40 nm
No
Presynaptic
vesicle and
active zone;
postsynaptic
receptors
Chemical
transmitters
Significant: at
least 0.3 ms;
usually 1-5 ms
or longer
Unidirectional
Types
of
synapse
Dis-
At a chemical synapse, neurons transmit information across a cleft.
List of Some Neurotransmitters
1. Small Molecule Neurotransmitter Substances
Acetylcholine (ACh); Dopamine (DA); Norepinephrine
(NE); Serotonin (5-HT); Histamine
2. Amino Acids
Gamma-aminobutyric acid (GABA); Glycine; Glutamate;
Aspartate
3.Neuroactive Peptides - partial list!!
Bradykinin; beta-endorphin; calcitonin; cholecystokinin;
enkephalin; dynorphin; insulin; gastrin; substance P;
glucagon; secretin; vasopressin; oxytocin, etc.
Axonal Transport Systems
• Axonal transport :
– intracellular communication
• Bidirectional mechanism :
– anterograde transport
– retrograde transport
• Classified by transport rates :
– slow transport system (0.2 to 1 mm/day)
– fast transport system (200 to 400 mm/day)
Hitching a
Ride on
“Retrorail”
Nucleus
Membranes of
organelles
involved in
synaptic
transmission are
returned to the
cell body for
reuse or
degradation
Cytoskeleton
(Anterograde transport))
Major Rate Components of Axonal Transport
Component
Rate
Structure and composition
(mm/day)
Fast transport
Anterograde 200-400
Mitochondria 50-100
Retrograde 200-300
Small vesiculotubular structures,
neurotransmitters; membrane proteins
and lipids
Mitochondria
Lysosomal vesicles and enzymes
Slow transport
SCb
2-8
SCa
0.2-1
Microfilaments, metabolic enzymes,
clathrin complex
Neurofilaments and microtubules
Neurons differ from Other Cells
1. Neurons have specialized projections called
dendrites and axons. Dendrites take
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
(like synapses) and chemicals (like
neurotransmitters)
4. Nissl Bodies
5. DO NOT Replicate: Damaged cells cannot be
replaced!