Cellular Neurobiology

Cellular NeurobiologyCellular Neurobiology

Neuroscience Research InstitutePeking University

Department of NeurobiologyPeking University Health Science Center

Albert Cheung-Hoi YU 于常海北京大學神經科學研究所

achy@bjmu.edu.cn

One of the Cajal’s many drawings of

Brain circuity

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.

• Neurons: Excitable cells – “wiring” “Signal Senders”

• Neuroglia: Support, Nurturing, Insulation

Cellular ComponentsCellular Components

Nerve CellsNerve Cells

Neurons Neuroglia

• 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

Structure of NeuronsStructure of Neurons

Axon Hillock(Axonal end feet)

The Axon and Axon Collaterals

The Axon and Axon Collaterals

• 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

Neurons Structure & Function

Neurons Structure & Function

   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 :

What are inside of a neuron?What are inside of a neuron?

Nucleus NucleolusMicrofilaments/

Neurotubules

Endoplasmic Reticulum (ER) Mitochondria Golgi ApparatusNissl BodiesOthers

• Dendrites :– dendrite tree

• Axon :– axon hillock (axon origination)– axonal transport system– initial segment (first myelin sheath)

• action potential generation

– myelin sheath

Axon and DendritesAxon and Dendrites

Axons Dendrites

Take information away from the cell body

Take information to the cell body

Smooth surfaceRough surface (dendritic spines)

Generally only 1 axon per cell

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

Differences between Axons and Dendrites

Neuron Classification by ShapeNeuron 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 Morphology

Classification of Neurons by Axon Length

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

– 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

Functional Classification of NeuronFunctional Classification of Neuron

• EXCITABLE Membrane: Able to regulate the movement of ions (charges) across and along membrane SIGNAL TRANSDUCTION

• DO NOT Replicate: Damaged cells cannot be replaced!

Important Features of NeuronsImportant Features of Neurons

Action PotentialAction

Potential

Four Functional Regions of Model NeuronsFour Functional Regions of Model Neurons

• Impulse transmission : – electrical – chemical

• Morphology : – axodendritic– axonsomatic– axoaxonic– dendrodendritic

Classification of SynapsesClassification of Synapses

synapse4

Vesicles release Neurotransmitters

• Chemical synapse :– presynaptic knob (presynaptic component)

• synaptic vesicles

– synaptic cleft– postsynaptic membrane (postsynaptic

component)

• Electrical synapse :– gap junctions

Synapse StructuresSynapse Structures

Types of

synapse

Dis-tance

Cytoplasmic continuity

Ultrastruct-ural

component

Agent of trans-

mission

Synaptic delay

Direction of trans-mission

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

Uni-directional

Distinguishing Properties of Electrical and Chemical Synapses

Distinguishing Properties of Electrical and Chemical Synapses

At a chemical synapse, neurons transmit information across a cleft.

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.

List of Some NeurotransmittersList of Some Neurotransmitters

• 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)

Axonal Transport SystemsAxonal Transport Systems

Hitching a Ride on “Retrorail”

Membranes of organelles involved in

synaptic transmission are returned to the

cell body for reuse or

degradation

Nucleus

Cytoskeleton

(Anterograde transport))

Component Rate (mm/day)

Structure and composition

Fast transport    

Anterograde 200-400 Small vesiculotubular structures, neurotransmitters; membrane proteins and lipids

Mitochondria 50-100 Mitochondria

Retrograde 200-300 Lysosomal vesicles and enzymes

Slow transport    

SCb 2-8 Microfilaments, metabolic enzymes, clathrin complex

SCa 0.2-1 Neurofilaments and microtubules

Major Rate Components of Axonal TransportMajor Rate Components of Axonal Transport

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!

Neurons differ from Other CellsNeurons differ from Other Cells