Nervous System Histology Flashcards
CNS vs PNS
CNS:
-comprised of the brain and spinal cord as well as the olfactory and optic nerves
PNS:
-includes all parts of the nervous system that are outside of the CNS
functions of CNS vs PNS
CNS:
-receives and processes sensory info
-responds to sensory input with motor output instructions
PNS:
-sends sensory info to the CNS
-transmits motor output instructions from the brain to designated muscles and glands
autonomic nervous system
-involuntary
-comprised of the parasympathetic and sympathetic divisions
somatic nervous system
-voluntary skeletal muscles
-sensory and motor
two types of cell groups in the nervous system
neurons and glial cells
neurons
-conduct APs
-process signals
-contain dendrites, somas and axons
glial cells
-do not generate electrical impulses
-support and protect axons —> form myelin sheath around axon, remove cellular debris, and provide structural support
different types of neurons
-motor (efferent)- control effector organs and are primarily located in the CNS
-sensory (afferent)- receive sensory info and cell body is located in CNS or ganglia
-projection- connect different regions far away and are located in the CNS
-interneurons- create circuits by connecting neurons and are in the CNS or ganglia
types of supporting cells
astrocytes and satellite cells
astrocytes
-supporting cells of the CNS
-star-shaped
-end feet contact capillaries (they interact with blood vessels)
-provide structural support
satellite cells
-supporting cells of the PNS
-surround cell bodies in ganglia
-support and protect neurons
two types of myelinating cells
oligodendrocytes and schwann cells
oligodendrocytes
-located in the CNS
-form and maintain myelin that wrap around axons
-interact with several neurons
schwann cells
-located in the PNS
-wrap myelin around axons
-only surround one neuron
microglia
-guard and protect the CNS
-respond to sites of damage or injury
-phagocytose dying cells or debri
-immune surveillance
-only located in the CNS
ependymal cells
-cuboidal or columnar epithelial cells
-form a simple layer that line ventricles and central canal of spinal cord
-produce CSF
-cilia help circulate CSF
cerebrum
-largest part of the brain
-comprised of white and gray matter
-consists of lobes
-divided into two halves
common cell types of cerebrum
-neurons
-neuroglial cells- astrocytes, oligodendrocytes, and microglia
what neurons make up the gray matter?
-pyramidal cells
-fusiform cells
-cells of martinotti
-horizontal cells of cajal
-stellate cells
cerebellum
-cerebellar cortex (gray matter) with a white matter core
-divided into two halves
-cortex contains 3 layers: molecular layer (outer), purkinje cell layer, and granular layer (inner)
function of cerebellum
-maintain balance and equilibrium
-little brain
-controls posture changes
-coordinates voluntary muscle movements- fine and smooth movements
-cognitive functions like attention, language, and memory
what are the common cell types of cerebellum?
-neurons in the cortex
-neuroglial cells- astrocytes, oligodendrocytes, and microglia in the cortex and white matter
where are unipolar brush cells found?
primarily in flocculonodular lobe and vermis
what types of cells are inhibitory neurons?
-stellate cells
-basket cells
-purkinje cells
-golgi cells
what types of cells are excitatory neurons?
-granule cells
-unipolar brush cells
spinal cord
-thick column of nerves within vertebrae that extend from the brainstem to the lumbar spinal region
-helps communicate info from the PNS to the brain
-31 pairs of spinal nerves radiate from spinal cord: 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve
gray matter
-mainly comprised of neuronal cell bodies and dendrites
-found in center of spinal cord and in layers of cerebral cortex
-processes info
white matter
-features both myelinated and unmyelinated axons
-has very little neuronal cell bodies
-found surrounding gray matter of spinal cord and inside brain
-transmits info
anatomy of a neuron
comprised of dendrites, cell body, and axons
dendrites
-receive and integrate incoming signals
-highly branched
-dendritic spines —> dynamic structures, believed to be involved in learning and memory
cell body
-aka soma or perikaryon
-metabolic and synthetic machinery
-rough endoplasmic reticulum
-round, oval, or triangular (pyramidal)
-large range in size of 5-100 um
axon
-aka nerve fibers
-transmits signals like APs
-constant diameter, usually unbranched
-contains axon hillock which is the site for AP initiation
action potentials
if depolarization reaches threshold potential then:
-voltage gated Na channels will open
-explosive propagation of depolarization
-Na channels inactivate
-delayed K channels open, efflux of K repolarizes the cell
-hyperpolarization and refractory period
myelination
-rich in lipids, which give the white matter appearance
-glial cells perform myelination —> in CNS, oligodendrocytes cover the axons and in the PNS, schwann cells cover only part of an axon
-concentric layers of plasma membrane that fuse together and remove cytoplasm
initiation of myelination in the CNS
-oligodendrocyte progenitor cells (OPCs) differentiate into mature oligodendrocytes
-send limb-like extensions from the cell body —> myelinate multiple nearby axons (up to 50 each)
-nodes of ranvier are unmyelinated regions of the axon
what does myelin do for AP transmission?
-myelin increases conduction speed —> lipids are poor conductors and great insulators
-enables saltatory conduction where the AP jumps between nodes of ranvier
do myelin sheath diameters affect AP speed?
yes, the larger diameters increase the conduction velocity of the AP
synapse
-region between cells and dendrites where electrical or chemical signals are passed
-comprised of three parts: pre-synaptic terminal which contains synaptic vesicles that fuse with the pre-synaptic membrane and release their contents into the synaptic cleft —> bind to receptors on the post-synaptic membrane
neuromuscular junctions (nmjs)
connect nerves to muscles
what happens at an NMJ?
motor neuron connects to muscle —> AP in neuron causes the voltage-gated Ca channels to open and the influx of Ca causes the synaptic vessels containing Acetylcholine to fuse with the pre-synaptic membrane with the help of proteins —> once Acetylcholine is in the synaptic cleft, it binds to the ligand-gated Na channels on the motor end plate
what happens after Ach binds to the Na channels?
influx of Na causes AP that triggers the T tubules to connect with the SR which releases Ca —> Ca binds to the troponin complex, causing a conformational change in the myosin-binding sites —> these sites open for myosin to bind with actin and cause the muscle to contract
what happens during muscle relaxation?
Ca is resorbed and the myosin-binding sites close
post-synaptic membrane effects
-activation of receptors: voltage-gated ion channels with local, immediate effect, ligand-gated io channels with local, immediate effect, and g-protein coupled receptors with more widespread effect
-depolarization
-hyperpolarization
excitatory postsynaptic potential (EPSP)
positively charged ions flow into neuron —> depolarization —> more likely to fire an AP
inhibitory postsynaptic potential (IPSP)
negatively charged ions flow into neuron —> hyperpolarization —> less likely to fire an AP
glutamate
-AP fires and glutamate is released from presynaptic neuron
-binds ligand-gated ion channel NMDA-R and also needs glycine as a co-agonist
-Na and Ca floods into the postsynaptic neuron
-Ca is a secondary messenger and activates kinases
-neuron becomes depolarized
-high levels of glutamate —> seizures
GABA
-AP fires —> GABA is released from presynaptic neuron
-GABA binds ligand-gated ion channel GABAa-R
-Cl floods into postsynaptic neuron
-neuron becomes hyperpolarized
-low GABA levels —> seizures
myasthenia gravis (MG)
-neuromuscular junction disorder
-autoimmune attack on acetylcholine receptors which disrupts neuromuscular transmission
amyotrophic lateral sclerosis (ALS)
-neurodegenerative disorder related to motor neurons
-progressive degeneration of motor neurons impairs muscle control
alzheimer’s dementia
-neurodegenerative disorder related to cognitive function
-accumulation of amyloid plaques and tau tangles disrupts cognitive functions
what are the causes of MG?
production of abnormal antibodies against Acetylcholine receptors, overactive compartment pathway, and disruptions of the thymus
what are symptoms of MG?
muscle weakness and tiredness
histopathology of MG for muscle fibers
normal muscle fibers: striated and uniform
MG muscle fibers: different sized cells and more nuclei and less uniform in appearance
histopathology of MG for NMJ
normal NMJ: has multiple junctional folds
MG NMJ: less junctional folds that are wider and increase the synaptic cleft
what are the causes of ALS?
largely unknown but 5-10% of the cases are genetic
what are the symptoms of ALS?
eye movement abnormalities, progressive weakness, clumsiness, slurred speech, trouble doing daily activities, cognitive, and behavioral impairment
histopathology of ALS
-less gray matter in the sALS group
-loss of myelination and motor neurons in the lateral spinal column
dementia
an umbrella term used to describe a group of symptoms that affect cognitive abilities, memory, thinking, and behavior
alzheimer’s dementia
disease that is the most common cause of dementia, up to 60-70% of dementia cases
what are the causes of alzheimer’s dementia?
largely unknown but a combination of age-related changes in brain, genetic, environmental, and lifestyle factors can contribute —> genetic alterations of APP, PSEN1, PSEN2
what are the symptoms of alzheimer’s dementia?
memory loss, cognitive difficulties, wandering, personality/behavior changes, problems recognizing friends and family, loss of bodily functions like talking, walking, and swallowing
pathology of alzheimer’s dementia
-amyloid plaques- abnormal buildup and clumps of beta-amyloid (AB) protein fragments between neurons
-neurofibrillary tangles- twisted strands of tau fibers inside neurons
-loss of neurons- loss of function and connection to other neurons and die
-brain atrophy- brain tissues shrink
