Nervous Tissue II Flashcards
What are the two anatomical subdivisions of the nervous system?
- CNS central nervous system
- PNS peripheral nervous system
The brain and spinal cord are part of which subdivision?
CNS
What does the gray matter of the brain consist of?
- nerve cell bodies
- neuroglia
Describe the cerebral cortex.
“brain bark”
Multiple layers of nerve cell bodies that form a folded sheet on brain surface
How is the cerebellar cortex different from the cerebral cortex?
Location
Cereballar is on the cerbellum; cerebral is on the cerebrum
What are nuclei?
-Collections of nerve cell bodies and neuroglia in the CNS
What does the white matter of the brain consist of?
- Mostly myelinated nerve cell axons
- Some unmyelinated nerve cell axons
- Neuroglia
What are tracts, fasciculi, or lemnisci?
bundles of myelinated and unmyelinated axons and neuroglia in the spinal cord
Why does white matter appear white?
-Because of the lipid content of the myelinated axons
What does the PNS consist of?
All the nervous tissue outside the CNS
Which division of nervous system includes nerves, plexuses, and ganglia?
PNS
What is the function of the PNS?
To convey sensory input from the environment and internal body parts to the CNS, and to convey neural impulses from the CNS to effector organs (muscles and glands)
Define ‘nerves’
Bundles/cables of nerve cell axons
How many cranial nerves exist? spinal nerves?
- 12 pairs of CN
- 31 pairs of spinal nerves
What is a nerve plexus?
- A network of nerves
EX: cervical plexus, brachial plexus, lumbar plexus, sacral plexus, periarterial ANS plexus
What is a ganglion?
-Collection of nerve cell bodies in the PNS
What is the voluntary nervous system? what does it do?
- Somatic nervous system
- Influences skeletal muscles to produce movement
What is the involuntary nervous system? what does it do?
- Autonomic nervous system
- aka visceral nervous system
- Influences smooth muscle, cardiac muscle, and glands
Name the three division of the ANS.
Sympathetic
Parasympathetic
Enteric
Which division is “fight, fright, or flight”?
Sympathetic division
Which division maintains homeostasis?
Parasympathetic division
Why is the sympathetic division called the “thoracolumbar outflow” ?
Because it connects with the thoracic and lumbar region of the spinal cord at T1-L2/3 levels
Which cranial nerves are part of the “cranial outflow” of the parasympathetic division?
CN III, VII, IX, and X
Which spinal nerves are part of the “sacral outflow” of the parasympathetic division?
S2, S3, S4
“S2, 3, 4, keep the penis off the floor”
What is the function of the enteric division?
Controls peristalsis, gland secretions, blood flow through the GI tract through a collection of neurons embedded in the wall of the GI tract
“brain of the gut” *independent of CNS
What is a synapse?
A junction between a neuron (pre-synaptic) and another cell (post-synaptic)
Where are action potentials transmitted from cell to cell?
At synapses
What are the three classifications of synapses based on morphology?
1) axodendritic *most common
2) axosomatic
3) axoaxonic *less frequent
Where are electrical synapses found in humans?
brain stem
retina
cerebral cortex
Which type of synapse has gap junctions?
Electrical synapses
- The junctions allow ions to pass from cell to cell, resulting in a transmission of impulse that is MORE RAPID than chemical impulses
Which type of synapse is associated with neurotransmitters?
chemical synapses
What does the pre-synaptic terminal consist of ? (4 things)
1) presynaptic membrane
2) mictochondria and sER
3) synaptic vesicles
4) presynaptic density
What is presynaptic density?
Cone-shaped structures that represent the active site of the synapse
What is the synaptic cleft?
A narrow extracellular space between the presynaptic and postsynaptic membranes
What does the post-synaptic site consist of? (4 things)
1) post synaptic membrane
2) receptor sites for neurotransmitter
3) postynaptic density
4) ligand-gated Na+ channels
What is the postsynaptic density?
complex of proteins binding neurotransmitter receptors
Review the seven steps of synaptic transmission listed in the handout.
Did you read?
What channels are opened when the action potential reaches the pre-synaptic membrane?
Voltage-gated calcium ion channels
What causes the synaptic vesicles to approach and attach to the inner surface of the presynaptic membrane?
The influx of calcium ions into the presynaptic terminal
Describe “kiss and run” fusion.
Brief fusion of synaptic vesicle to the presynaptic membane where only part of the contents are released into the cleft
The vesicle disconnects and returns to the active site of presynaptic terminal
Describe “collapse” fusion.
Synaptic vesicles attach to the presynaptic membrane and empty all of their contents into the cleft
the empty vesicle fuses with the presynpatic membrane
What do neurotransmitters bind to within the synaptic cleft?
transmitter-gated channels on the post-synaptic membrane
What causes a conformational change s of channel proteins, and thus opening of pores, on the post-synaptic membrane?
neurotransmitters binding to receptors
What opens the voltage-gated sodium channels on the postsynaptic membrane, generating a nerve impulse?
Local depolarization of the postsynaptic membrane caused by an influx of sodium ions through pores
Where is the choroid plexus located?
In the ventricles (hollow cavities) of the brain
What does the choroid plexus consist of?
Fold of pia matter covered by ependymal cells (simple cuboidal epithelial cells, neuroglia)
What are ependymal cells held together by?
tight junctions
What type of capillaries are found in the choroid plexus?
fenestrated (leaky) capillaries
What is the composition of CSF?
low protein, high sodium, potassium and chloride ion concentrations
90% water and ions, a few lymphocytes
How many times a day is CSF replaced?
4 times
Where does the waste of the brian go?
The brain’s metabolic waste products diffuse into the CSF of subarachnoid space
***The brain does NOT contain lymphatic vessels
How is CSF reabsorbed?
By arachnoid villi, it then passes into the bloodstream
How many layers does the cerebellar cortex have?
3 layers
[superficial -> deep]
molecular layer, purkinje layer (unique to cerebellum), granular layer
Where does nerve injury and regeneration occur?
in the PNS
What are the anterograde changes seen in nerve injury and regeneration?
Axonal degeneration and elimination of debris
Occurs distal to the site of injury
What are the four anterograde changes seen in nerve injury and regeneration?
1) distal segment of axon degenerates
2) elimination of debris by phagocytic cells
3) Schwann cells proliferate
4) Schwann cells form tubes along with their external lamina
What are the retrograde changes seen in nerve injury and regeneration?
1) chromatolysis
2) axon grows sprouts
3) Schwann cell guide axon growth toward target cell
4) growing axon grows into the endoneurium
What are the retrograde changes seen in nerve injury and regeneration?
1) chromatolysis
2) axon grows sprouts
3) Schwann cell guide axon growth toward target cell
4) growing axon grows into the endoneurium
*occur proximal to the site of injury
What are the four ESSENTIAL components of regeneration?
1) macrophages
2) fibroblasts
3) basal lamina
4) Schwann cells
Is nerve cell regeneration always successful?
Nope
