Cellular Neurobiology Neuroscience Research Institute Peking University Department of Neurobiology Peking University Health Science Center Albert Cheung-Hoi YU 于常海 北京大學神經科學研究所

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 Components

Nerve 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 Neurons Axon Hillock (Axonal end feet)

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? Nucleus Nucleolus Microfilaments/Neuro tubules Endoplasmic Reticulum (ER) Mitochondria Golgi Apparatus Nissl Bodies Others

Dendrites : –dendrite tree Axon : –axon hillock (axon origination) –axonal transport system –initial segment (first myelin sheath) action potential generation –myelin sheath Axon and Dendrites

Axons Dendrites Take information away from the cell body Take information to the cell body Smooth surface Rough surface (dendritic spines) Generally only 1 axon per cell Usually many dendrites per cell No ribosomeHave ribosomes Can have myelinNo myelin insulation Branch further from the cell body Branch near the cell body Differences between Axons and Dendrites

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 Classification of Neurons by Axon Length 1.Golgi type I Neurons Long axons (longest from the cortex to the tip of spinal cord, 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 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 Neurons

Action Potential

Four Functional Regions of Model Neurons

Impulse transmission : –electrical –chemical Morphology : –axodendritic –axonsomatic –axoaxonic –dendrodendritic Classification of Synapses

synapse 4 Vesicles release Neurotransmitters

Chemical synapse : –presynaptic knob (presynaptic component) synaptic vesicles –synaptic cleft –postsynaptic membrane (postsynaptic component) Electrical synapse : –gap junctions Synapse Structures

Types of synapse Dis - tance Cytoplasmic continuity Ultrastruct- ural component Agent of trans- mission Synaptic delay Direction of trans- mission Electrical3.5 nmYesGap-junction channel Ion currentVirtually absent Usually bidirectional Chemical20-40 nmNoPresynaptic 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

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 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 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))

ComponentRate (mm/day) Structure and composition Fast transport Anterograde Small vesiculotubular structures, neurotransmitters; membrane proteins and lipids Mitochondria Mitochondria Retrograde Lysosomal vesicles and enzymes Slow transport SCb2-8 Microfilaments, metabolic enzymes, clathrin complex SCa0.2-1 Neurofilaments and microtubules Major 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 Cells