Nervous Tissue Flashcards
What are the two divisions of nervous tissue?
Central Nervous System (CNS) - Brain and spinal cord; derived from the neural tube
Peripheral Nervous System (PNS) - all nervous tissue outside of CNS derived from neural crest cell
Functions of the Nerve Cells
- Irritability: neurons rapidly respond to some stimuli
- Conductivity: transmission of a response spatially and temporally to another part of the body
- Secretion: cells secrete neurotransmitters and other substances that excite or inhibit neighboring cells
Components of Nervous Tissue
- Nervous: nerve cells of the CNS and PNS
- Glial cells: support and protect neurons
- Connective tissue coverings
Peripheral Nervous System (to the left of the CNS)
- afferent neurons
- receive and transmits information from the environment to the CNS
- inputs
Central Nervous System
- brain and spinal cord
Peripheral Nervous System (to the right of the CNS)
- efferent neurons
- transmit information generated in the CNS to the periphery
- outputs
Afferent Neurons
- sensory neurons
- receive stimuli from environment and body
- impulse travels towards CNS
- cell bodies are near CNS
- consist primarily of psuedounipolar neurons
Efferent Neurons
- Motor Neurons
- control effector organs such as muscle fibers
- impulse travels away from CNS
- Cell bodies are within CNS (exception in ANS)
a. further classified
1. somatic - involuntary muscles
2. Autonomic - involuntary smooth muscles -
both sympathetic and parasympathetic
Interneurons
- form functional networks or circuits (e.g. retina)
- impulse travels within CNS
- major function: coordinate all neural activities
- consist mostly of multipolar neurons
Myelinated
formed by schwann’s cells
Non-myelinated
also has schwann cell bu they don’t roll themselves around to protect
Nature of Neurotransmitters Released
- acetylcholine: cholinergic
- norepinephrine: adrenergic
- epinephrine
- serotonin
- glutamate
- GABA (gamma-aminobutyric-acid)
- glycine
- many others
Neuron Structure - Perikaryon
- Cellular Organelles
- Nissl Bodies
- Cytoskeleton
- Lipofuscin
Cellular Organelles of Perikaryon
- Nucleus, RER, Golgi, Mitochondria, protein synthesis machinery
- nucleus note: centrally located, full of euchromatin, usually one nucleolus
Nissl Bodies of Perikaryon
- Regions of RER - in cell body and dendrites, area of extensive protein synthesis, basophilic type of staining
Cytoskeleton of Perikaryon
- Neurofilaments: intermediate filaments provide cellular support 10mm)
- Microtubules: provide intracellular transport and cellular/axonal support 25mm
- Actin: provides some secondary intracellular transport 6-7 mm
Lipofuscin of Perikaryon
residual bodies left over from lysosomal digestion
Neuron Structures - Dendrites
- processes that extend from perikaryon
- lack golgi - but contain most other components of perikaryon
- function - receive stimuli
Neuron Structure - Axon
Structural and Functional Features
- Axon Hillock
- initial segment
- axoplasm
- collateral
- axon terminal
- axonal transport
- oligodendrocyte (CNS)
- Schwann Cell (PNS)
Two types of Axonal Transport
- Anterograde: Kinesin (from perikaryon to axon terminal)
2. Retrograde: Dynesin (from axon terminal to perikaryon)
Axon Hillock
- short segment emanating from perikaryon
- No nissl bodies
- initial site of microtubule bundling
Initial Segment
- region between axon hillock and initial myelinization point
- site of neuron where stimulus is intergregrated - initiates/suppresses signal down the axon
Collateral Branches
also known as axon branches
Neuronal Function - Axonal Transport
- movement of proteins and vesicles within the axon
- vesicles attached via motor proteins move along microtubules
Anterograde Transport
From perikaryon to synapses
a) from slow stream 1-4 mm/day
i. necessary for axon growth
b) fast stream 50-400 mm/day
i. vesicles carrying neurotransmitters and other membrane components needed for synaptic transmissions (e.g. calcium channels)
Primary protein responsible for anterograde motion?
Kinesin
Retrograde Transport
From synapses and axons to perikaryon
a) intermediate stream 10-100 mm/day
i. considered a salvage pathway
b) Transports cytoskeletal components
Primary protein responsible for retrograde motion?
Dynesin
Axon Terminal - Synapses : Types of Synapses
a) Structure behind a Chemical synapse.
b) Structure of an Electrical synapse - composed of transmembrane proteins called connexins
c) Combining both results in a Mixed synapse
Chemical Synapses
Vesicles
• Neurotransmitter vesicles
• Adrenaline secreting
• Acetylcholine secreting
• Hormone vesicles
• Depolarization
-Arrival of a nerve impulse causes an influx of Ca2+
into the axon terminal
-Ca2+ influx triggers exocytosis of neurotransmitter
vesicles into the synaptic cleft
- Adrenaline secreting (sympathetic)
- Acetylcholine secreting (parasympathetic)
Neurotransmitter open or close ion channels to regulate depolarization at the postsynaptic
membrane
Types of Synapses: Depending on the type of synaptic contacts
- Axo-Dendritic
- Axo-somatic
- Dendro-Dendritic
- Axo-Axonic
Membrane structure: Presynaptic membrane
Terminal ending membrane of axon
Membrane structure: Postsynaptic membrane
Membrane of cell juxtaposed to presynaptic membrane
Membrane Structure: Synaptic Cleft
Space between the two membranes
Preganglionic has ____ lines
Postganglionic has ____ lines
Solid;
Dotted
Paravertebral Ganglia is located?
Located immediately outside of spinal column antero-laterally extending from cervical to sacral regions.
Prevertebral Ganglia is located?
in abdomen
Terminal Ganglia is located?
located near the organs to be innervate
Paravertebral Ganglia comprised of mostly?
sympathetic preganglionic axonal endings and postganglionic cell bodies. Few neurons.
Prevertebral Ganglia is the area where?
Preganglion Sympathic axons that bypass the paravertabral ganglion meet postganglionic neurons.
Terminal Ganglia is comprised mostly of?
parasympathetic preganglionic axonal endings and postganglionic cell bodies that give rise to relatively short axons
Neurepinephrine released from sympathetic nerves to the heart ____ heart rate, whereas acetylcholine released from the parasympathetic fibers ____ it.
increase; decrease
