Cells and general features Flashcards
Neuronal cell body
expanded portion of nruon that contains nucleus. large and leptochromatic. Abundance of RER and polyribosomes (nissl bodies)
Neuronal dendrites
one to many extensions of the cell body specialized to receive input. Nissl bodies proximally. Dendritic spines expand surface area and serve for synaptic contact
Neuronal axon
processes tha project to and synapse with dendrites or cell bodies of other neurons/non neuronal targets. Specialized for conducting regenerative, all or none, electrical action potentials.
Axonal varicosities/boutons
swellins found along the axon or at its terminal branches and typically where synapese occur.
Ganglion
collection of neuron cell bodies situated in PNS
Nucleus
collection of neuronal cell bodies in the CNS (collection of gray matter)
Nerves
bundles of axons that extend out from brain and from spinal cord
Tract
bundle of axons (nerve fibers) within the CNS. Connective tissue is absent around nerve fibers in CNS
Neuronal anatomical classification
unipolar, bipolar, multipolar
neuronal functional classification
motor (efferent), sensory (afferent), interneurons
Unipolar/pseudounipolar
neruon has one process tha bifurcates (found in spinal and cranial ganglia)
bipolar
neuron has 2 processes (rare: retina)
multipolar
neuron has many processes, typically 1 axon and 2 or more dendrites. Most common
Motor/efferent
related to innervation of muscle and glands; activation of these enruons leads to some motor event
sensory/afferent
related to the transfer of sensory information
interneurons
neither motor nor sensory (spinal reflexes)
Glial cells provide
support and protection for neurons.
CNS glial cells
astrocytes, oligodendrocytes, microglia, ependymal
PNS glial cells
lemmocytes (schwann cells)
Astrocytes
star shaped with large leptochromatic nucleus. Influences activity of neurons. Contacts blood vessels and controlling local blood flow in CNS (blood brain barrier)
Oligodendrocytes
form myelin sheaths around brain and spinal cord axons. small pachychromatic nuclei
Microglia
smallest glial cell. Immune effector cells of CNS (brain macrophages)
Ependymal cells
columnar epithelial cells line CSF filled ventricles. Cilia circulate CSF and microvilli absorb CSF. Produce CSF
Lemmocytes
associates with all peripheral nerve fibers. form myelin sheath
Glial cells are capable of
regeneration
Myelin is
highly organized multilamellar structure formed by plasma membrane of oligodendrocytes and lemmocytes.
PNS myelin
chain of lemmocytes provides myelin for one axon. Surrounded by basal lamina and endoneurium
CNS myelin
single oligodendrocyte provides myelin for multiple axons. and each axon myelinated by multiple oligodendrocytes. lacks basal lamina and endoneurium. Does NOT regenerate (several proteins inhibit)
Myelin increases speed of conduction by acting as
an electical insulator.
Nodes of Ranvier
breaks in the continuity of myelin sheath that occur regularly in both P and CNS.
PNS non-myelinated axons
embedded in infoldings of plasma membrans of cahin of lemmocytes. Each lemmocyte encloses 5-20 axons. Surrounded by basal lamina and endoneurium
CNS non-myelinated axons
NOT associated with oligodendrocytes but run free without any ensheathment. Separated by astrocyte processes.
Demyelination refers to the _____. Demyelinated axons transmit nerve implses
destructive removal of myelin. 10X slower than normal myelinated and sometimes stop.
2 peripheral nerve classification schemes
1) based on nerve fiber diameter. 2) derived from the action potential (speed)
Receptor
specialized region on peripheral teminal branch of axon of primary afferent neuron that can serve as a transducer (convert sensory stimuli into nerve signals)
Sense organ
organized collection of receptor cells, with which the dendritic zones of afferent neurons synapse.
Examples of sense organs
retina, cochlea, vestibular apparatus, taste buds, olfactory epithelium. (neurons often SSA or SVA and bipolar)
Receptor classification (morphology)
Free nerve endings, tactile discs, encapsulated
Free nerve endings
terminal branches ramifying among epithelial cells, very common esp in skin
tactile discs
terminal expansions of an afferent axon which are joined to modified epidermal cells (skin and mucous)
encapsulated
each receptor is encapsulated by lemmocytes and perineural epthelium (pacinian corpuscles, muscle spindles)
Location based receptor classification
exteroceptors, proprioceptors, interoceptors
Exteroceptors
associated with skin and SQ tissue (GSA)
Proprioceptors
associated with muscles, tendons, and joints (GSA)
Interoceptors
located in viscera (GVA)
Modality (energy sensitivity) based receptor classification
mechanoreceptors, thermoreceptors, nociceptors, electromagnetic, chemoreceptors
mechanoreceptors
detect mechanical deformation (touch, pressure)
thermoreceptors
detect changes in temperature
nociceptors
detect damage to tissue, and itch
electomagnetic
detect light on the retina of the eye
chemoreceptors
detect chemical molecules (taste, olfactory, arterial blood…)
Endoneurium
surrounds each myelinated axon, ora group of non-myelinated axons
Perineurium
surrounds each nerve fascicle. epithelium and ct. forms blood-nerve barrier
epineurium
surrounds the entire nerve
Dura mater
outermost meningeal layer. consists of coarse, irregular ct composed of collagen and elastic fibers.
Arachnoid
Middle layer. Distinct membrane and numberous fibrous tabeculae on inner surface.
Subarachnoid space
contains CSF and at certain points dilates into cisterns.
Pia Mater
innermost meningeal layer. Thins protective membrane. Flattened fibrocytes superficial to elastic and collagen fine fibers. Very vascular.
