DLA 26, 27, 28 & Lecture 35/36: Nerves Flashcards
Peripheral Nervous System
Components:
Connects CNS–> body/organs
- Ganglion = collection of cell bodies
- Peripheral nerve= Collection of axons
Components:
1) Cranial nerves
2) Spinal nerves
3) Ganglia
4) Enteric Plexuses- Digestive
5) Sensory receptor
Functions of Nervous System
1) Sensory Function: Info –> Brain/spinal chord
2) Integrative Function: Processes/stores info
3) Motor Function: Activates muscles/glands
Voluntary and Involuntary Control
Somatic= Voluntary:
-Body sensation (wall/limbs)–> CNS/motor neurons –> Skeletal muscle
Visceral= Involuntary:
-Body sensation (Organs)–> CNS/motor neurons –> cardiac muscle, smooth muscle, glands
Parts of Neuron
1) Cell body/Soma: Nucleus/organelles
2) Dendrite: Carries into into cell body, unmyelinated
3) Axon: Carries info out of cell body, contains mitochondria/microtubules/neurofibrils, myelinated, ENDS AT THE SYNAPTIC END BULB (TERMINAL BOUTON)
Classifications of Neurons by Structure
- Multipolar
- Pseudounipolar (unipolar)
- Bipolar
1) Multipolar: Several dendrites + one axon
2) Pseudounipolar (unipolar): One axon that divides in 2
3) Bipolar: one axon + one dendrite
Classification of Neurons by Function:
Motor (Efferent)
Sensory (Afferent)
Interneurons (Integrative)
Motor (Efferent):
- multipolar
- Somatic: Skeletal muscle
- Viseral: Smooth cardiac muscles, glands found in organs
- CNS–> PNS
Sensory (Afferent):
- Pseudounipolar/bipolar
- PNS–> CNS
- CELL BODIES IN DORSAL ROOT GANGLION (DRG)
- Somatic: 5 senses
- Visceral: Inflammation, Glands, processes of internal organs, blood vessels, etc
Interneurons (Integrative):
- Communication between motor and sensory neurons
- Reflexes
Neuroglial cells Characteristics
Neuroglial cells in CNS
Neuroglial cells in PNS
- Don’t make action potentials
- Can multiple and divide if injured
- Insulate and nourish
CNS: (Central neuroglia)
- Astrocytes
- Oligodendrocytes
- Microglia (macrophages)
- Ependymal cells
PNS: (Peripheral neuroglia)
- Schwann Cells
- Satellite Cells
CNS
Components
- Brain and spinal chord
- White matter= myelinated tracts of axons or nerve cells/glial cells/vessels
- Gray matter= Neuronal cell bodies/axons/dendrites/glial cells
- Nucleus: Collection of cell bodies
- Tract: Collection of axons
Brain:
1) Cerebral hemisphere: Big area, folds=gyri, grooves=sulci, big groove= longitudinal fissure, functions of lobe
2) Thalamus: Relay center for brain
3) Hypothalamus: Homeostasis, growth, reproduction
4) Brainstem: Midbrain, pons, medulla oblongata, Cardio regulation, swallowing, yawning, etc.
5) Cerebellum: Posture, balance, movement
PNS Spinal Nerves
-Axons and neurons forming peripheral nerves exiting the spinal chord segments
- Parasympathetic Nerves = In Cervical and Sacral
- Sympathetic Nerves= In Thoracic and Lumbar
31 Pairs
- 8 Cervical (C1-C8)
- 12 Thoracic (T1-T12)
- 5 Lumbar (L1-L5)
- 5 Sacral (S1-S5)
- 1 Coccygeal (Co1)
PNS Cranial Nerves
- Axons of neurons forming peripheral nerves exiting the cerebral cortex and brainstem
- Can consist of motor, sensory, and parasympathetic fibers
- 12 Pairs
Axonal transport
-Bidirectional movement of material between the cell body and processes
Anterograde:
- Kinesin
- slow or fast
- Towards synapse
Retrograde:
- Dynein
- Fast
- Towards Cell Body
- Clinical importance: route used by toxins and viruses to enter nervous system
Sympathetic Ganglia
Ganglia = clusters of nerve cell bodies outside of the CNS
- Craniospinal (DRG, cranial nerves)
- Pseudounipolar neurons
- Thick fascicles of fibers alternating with bundles of cell bodies
- Central axons
- Pale staining
- No synaptic connection
Autonomic Ganglia (Nerve fibers)
Ganglia = clusters of nerve cell bodies outside of the CNS
- Sympathetic and Parasympathetic
- Large cell bodies
- Random bundles of fibers
- Multipolar neurons
- Diffuse nerve fibers between cell bodies
- Synapsing
Neuroglia of the CNS
1) Oligodendrocytes
- Myelinates axons in the CNS
- Larger Nodes of Ranvier (NR)
- One oligodendrocyte for several axons
2) Ependymal cells
-epithelium lining of the CNS cavities
-cuboid to columnar
-have characteristic of fluid transporting/absorbing
cells (cilia, microvilli, basal infoldings)
-found in choroid plexus- modified ependymal cells
that interact with capillaries and secrete
3) Protoplasmic astrocytes
- In the gray matter
- maintain the blood-CSF barrier
4) Fibrous astrocytes
- In white matter
5) Microglia (Macrophages in brain)
- smallest
- phagocytosis of bacteria, injured tissue and debris
Neuroglia of PNS
1) Schwann cells
- myelinated neurons in PNS
- Several in one axon
- Provides support for both myelinated and unmyelinated axons in PNS
- clean up debris
- scaffolding for regenerating nerve tissue
2) Satellite cells
- small cuboidal cells
- surrounds the cell body of neurons in PNS
- regulate the perineuronal environment
- electrical insulator, DOES NOT MAKE MYELIN
- Regulate metabolic exchange
Formation of Myelin Sheath
1) Schwann cell plasma membrane forms two
distinct polarized domains
-abaxonal plasma membrane
-adaxonal plasma membrane
2) Mesoaxon connects the abaxonal and adaxonal membranes and closes off the extracellular environment
3) Thickness of the myelin sheath is determined by the diameter of the axon regulated by neuregulin (Ngr-1)
Myelination
-lipid rich layer around axons that facilitate rapid conduction of nerve impulses
-Myelin sheaths contain small amounts of
cytoplasm
Myelinating cells
- Schwann cells (PNS)
- Oligodendrocytes (CNS)
Myelinated Vs Unmyelinated Nerves
Myelinated nerves:
- they have multiple concentric layers of myelin sheath around one axon
- The nerves are devoid of myelin at the nodes of Ranvier, axon hillock, and terminal arborizations
Unmyelinated nerves:
-Axon/axons rests in a cleft of Schwann cell
cytoplasm (each with a single mesoaxon)
Synapses
Functions, types
Function:
-Facilitate transmission of impulses
Types:
1) Electrical
2) Chemical = Release of chemical substances (neurotransmitter)
- Pre/post synaptic membranes
- Synaptic cleft
- Axodendritic = between axon and dendrite
- Axosomatic = between axon and soma
- Axoaxonic = between axon and axon
Types of neurotransmitters: How they are made/used and degraded
Acetylcholine
Catecholamines
Serotonin
Acetylcholine:
- Used by cholinergic neurons
- Degraded by acetylcholinterase
Catecholamines
- Precursor = tyrosine
- Used by catecolaminergic neurons in CNS and ENS
- Removed by COMT, MAO
Serotonin
- Precursor = tyrophan
- Used by serotonergic neurons
Blood Brain Barrier
Function, components
Function
-Protects CNS from imbalances (Ex: electrolytes)
Components:
1) Continuous capillaries: Tight junctions, Continuous basal lamina, no fenestrations in cytoplasmic membrane,
2) Surrounded by foot processes of astrocytes (cover around blood vessel, prevent foreign substance from reaching neuron if tight junctions fail), neuronal processing
3) Part of cerebral cortex
4) Can lose function with brain diseases
5) Some parts of CNS have no barrier (Ex: Circumventricular organs)
Multiple Sclerosis
Cause/Symptoms
- Loss of myelin sheath in CNS (Myelin detached from axon and destroyed)
- Damage to Oligodendrocytes
Stages of demyelinating:
1) Myelin breakdown associated w/ lymphocyte and macrophage infiltration
2) Proliferation of astrocytes: Gradual infiltration of astrocytes into demyelinating area
3) Reduced cellularity, astrocyte reduce in size
Guillain-Barre
- Damage to Schwann cells
- Large accumulation of lymphocytes, macrophages, plasma cells
- Loss of muscle coordination and sensation
Response to injury:
Wallerian Degenration (Anterograde)
- PNS
- CNS
Wallerian Degenration (Anterograde) -Degenerative of axon distal to site of injury
PNS
- Degeneration takes a few days
- Dedifferentiation of Schwann cells and alignment
CNS
- Degeneration takes several weeks
- Loss of axon contact = cell death
Some retrograde degeneration also occurs = traumatic degeneration
