•No
•Presyna••ptic
•Chemical •Significant:
•Uni-
l
nm
vesicle and transmitters at least 0.3 directional
active zone;
ms; usually 1-
postsynaptic
5 ms or longer
receptors
•Generally only 1 axon per cell
•Rough surface (dendritic spines) •Usually many dendrites per cell
•No ribosome
•Have ribosomes
•Can have myelin
•Branch further from the cell body
•
•
•Distinguishing Properties of Electrical and Chemical Synapses
•Types of
synapse
•Distance
•Cytoplasmi •Ultrastruct-
c continuity
ural
component
•Agent of transmission
•Component
•Rate
(mm/day)
•Fast transport •
•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)
– 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
– slow transport system (0.2 to 1 mm/day) – fast transport system (200 to 400 mm/day)
•
•Hitching a •Ride on • “Retrorail”
•
•Membranes of organelles involved in synaptic
•
•Cellular Components
• Neurons: Excitable cells – “wiring” “Signal Senders”
• Neuroglia: Support, Nurturing, Insulation
•
•Nerve Cells
•Neurons
•Neuroglia
•
•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
– myelin sheath
•
•Differences between Axons and Dendrites
•Axons
•Dendrites
•Take information away from the cell body
•Take information to the cell body
•Smooth surface
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)
• 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/Neu
rotubules
•Endoplasmic Reticulum (ER) Mitochondria Golgi Apparatus
•Nissl Bodies
•Others
•
•Axon and Dendrites
• Dendrites :
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
• Morphology :
– axodendritic – axonsomatic – axoaxonic – dendrodendritic
•
Vesicles release Neurotransmitters
•4
•synaps e
•
•Synapse Structures
• Chemical synapse :
•Synaptic delay
•Direction of transmission
•Electrica •3.5 nm
•Yes
•Gap-junction •Ion current •Virtually
•Usually
l
channel
absent
bidirectional
•Chemica •20-40
•
•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
•No myelin insulation •Branch near the cell body
•
•Neuron Classification by Shape
•Multipolar: “multi-” many processes
–Majority: Single axon, many dendrites (motor
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.
– presynaptic knob (presynaptic component)
• synaptic vesicles
– synaptic cleft – postsynaptic membrane (postsynaptic
component)
• Electrical synapse :
– gap junctions
•
•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
– dendrite tree