Nervous Tissue 2
Terms
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- What layer does nervous tissue develop from?
- ectoderm
- What are the components of the CNS?
- brain & spinal cord
- What are the components of the PNS?
- spinal, autonomic, enteric nerves; ie, all NERVES lie in the PNS
- How are the peripheral nerves classified directionally, and what do these classes do?
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Sensory - afferent info towards CNS
Motor - efferent info away from CNS - What are the effectors for peripheral nerves?
- Muscle, glands
- How are peipheral nerves classified by type of signal?
- Somatic, visceral (autonomic)
- What are the important features of SOMATIC nerves?
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- Conscious perception
- Voluntary
- SINGLE neuron connection from CNS to effector - What are the important features of AUTONOMIC nerves?
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- Sensory/unconscious (proprioception)
- Involuntary (smooth muscle, cardiac, glands)
- 2 neurons b/w CNS and target - How are the autonomic nerves further divided?
- Parasympathetic, sympathetic
- What characterizes SYMPATHETIC nerves?
- Fight/flight, catabolic, mobilize energy stores -- INCREASED ACTIVITY
- What are the characteristics of the parasympathetic division?
- Rest and repose, anabolic, tissue growth and repair -- RESTING FUNCTIONS
- Contrast the origin of nerve cell bodies in para/sympathetic nerves.
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Sympathetic = thoracic + lumbar spinal cord
Parasympathetic = sacral + cervical/cranial - Contrast the 1st synapse location in para/sympathetic nerves.
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Sympathetic = Proximal to CNS
Parasympathetic = Proximal to TARGET - What are the 3 types of cells present in nervous tissue?
- Neurons, Glia, Support Cells
- General function of neurons?
- Excitable cells - info transfer
- General function/origin of glia?
- Non-excitable cells of NEURAL ORIGIN that enhance transmission efficiency
- General function of support cells?
- Cells from blood vessels AND microglia - NON-NEURONAL ORIGIN
- What are microglia?
- Immune cells of CNS (phagocytic)
- What is Nissl substance
- ribosome rich RER found in neuron.
- What are the 4 major parts of neurons?
- Soma, Dendrites, Axon, Axon terminal
- What is the function and an important histological characteristic of DENDRITES?
- Receive impulses, conduct towards cell body. NO GOLGI COMPLEXES.
- What is the function and an important histological characteristic of AXONS?
- Conducts impulses AWAY from cell body. Mitochondria, SER. NO RER! Also contains neurofilaments and microtubules.
- Compare the structure and function of NEUROFILAMENTS and MICROTUBULES
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NF - Smaller, structural. Intermediate filaments
MT - Larger, for transport. Microtubules. - What does anterograde mean wrt axonal transport?
- Towards axon terminal.
- What is histologically characteristic about the synaptic cleft?
- Numerous vesicles at the axon terminal. Space between 2 cells.
- What characterizes neurofilaments?
- - Structural, intermediate filaments. small
- What characterizes microtubules?
- Transport. Larger.
- What are the 6 stages in synaptic transmission?
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1. Vesicle transport
2. Vesicle loading
3. Depolarization
4. Exocytosis
5. Binding of neurotransmitter
6. Depolarization of target - What occurs during the depolarization phase?
- When the signal travels to the axon terminal, the membrane depolarizes, opening Ca2+ channels. The influx of calcium causes the vesicles to fuse with the membrane, releasing their neurotransmitter.
- What occurs on neuronal excitation?
- K+ exits cell, Na+ and Cl- enter.
- What are characteristics of unmyelinated neurons?
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- Leak Na+
- Channels must open along entire length
- Slower - How does myelination occur in the PNS?
- Schwann cells. Wrap around an individual axon. Discontinuous - nodes of ranvier.
- How does myelination occur in the CNS?
- Oligodendrocytes; functionally analagous to schwann cells. 1 oligodendrocyte/>60 axons!
- What would be expected of a heavily myelinated axon?
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Fast
Acute pain
SOMATIC motor - What would be expected of a moderately/unmyelinated axon?
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Slow
Visceral (AUTONOMIC) motor
CHRONIC pain/pleasure - What are the 4 functions of GLIAL cells?
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- Biochemical (speeds up neurotransmission)
- Structural (physical support)
- Nutritive (growth/maintenance)
- Immune (scavenge toxins, depris) - What are the types of neuroglial cells?
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- Protoplasmic + fibrous astrocytes
- Microglia
- Oligodendrocytes - What are the functions of protoplasmic & fibrous astrocytes?
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- Contact blood vessels (blood-brain barrier)
- Maintain local blood flow
- Scavenge IONS - ion homeostasis - What are the staining characteristics of FIBROUS astrocytes?
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- Stained by antibody against Glial Fibrillary Acidic Protein (GFAP)
- The above is an intermediate filament - What are the connective tissue coverings in the PNS?
- - Endoneurium, perineurium, epineurium
- What characterizes the ENDONEURIUM?
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- Surrounds individual NERVE FIBERS (axons)
- Mast cells, fibroblasts, macrophages, capillaries
- Contacts basal lamina of Schwann cells. - What are the characteristics of the perineurium?
- Middle CT layer. Bundles of nerve fibers.
- What are the characteristics of the epineurium?
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- Outermost CT layer: DENSE irregular collagenous CT
- Collagen prevents overstretching
- Continuous with dura - What are the 3 connective tissue coverings of the CNS?
- - Dura mater, arachnoid membrane, pia mater [PAD]
- What characterizes the DURA mater?
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- 2 layers of DENSE irregular collagenous CT
- Fibroblasts, osteoprogenitors, CT connected to skull - What characterizes the ARACHNOID SPACE?
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- AVASCULAR
- Fibroblasts (gap junctioned), collagen, elastic - What characterizes the PIA MATER?
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- Follows brain contours
- Fibroblasts, abundant BLOOD VESSELS
- Macrophages, mast cells, lymphocyts
- Separated from neural tissue by NEUROGLIA - What maintains brain homeostasis?
- - Capillary endothelium and ependymal cells.
- What is the capillary endothelium?
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- Tight lining of blood vessels that maintains BBB
- Does not allow many usually permitted cells out of the blood
- LIPID-soluble substances pass!
- Tight junctions
- Astrocytes cover - What are ependymal cells?
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- Continuous layer of cells lining the brain in pia mater
- Synthesize, Secrete, Excrete CSF into subarachnoid space
- Maintain blood-CSF barrier - What is the choroid plexus?
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- Folds of pia mater with capillaries that makes CSF
- Blood-CSF barrier
- Actively transports ions - What are arachnoid villi?
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- Regions where arachnoid extends to dural venous sinuses
- Returns CSF from subarachnoid space to blood - What is white matter?
- Myelinated axons
- What is gray matter?
- Neuronal cell bodies