Neurobiology of Consciousness 1 Running Head: NEUROBIOLOGY ...
Cellular Neurobiology
description
Transcript of 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
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