Nervous Tissue Flashcards
2 principal types of cells in nervous system?
- neurons
- supporting cells
Supporting cells in CNS?
Ependymal cells
Neuroglial cells:
- Astrocyte
- Oligodendrocyte
- Microglia
Supporting cells in PNS?
Schwann cells (surround nerve processes) Satellite cells (surround nerve cell bodies in ganglia)
Neuron cell body
- is also called?
- has what type of nucleus?
- contains…?
- called “perikaryon”
- euchromatic nucleus (very active)
- contains: nissel bodies (stacks of rough ER), ## mitochondria, large perinuclear golgi
Where are Nissl bodies & free ribosomes found in neurons?
- extend into dendrites but not into the axon
- NOT in axon hillock
- dependence on cell body for maintenance
Dendrites:
- Carry information towards the cell body
- Greater diameter than axons
- Unmyelinated
- Arborizations = dendritic trees
- greatly increase receptor surface of neuron
- Contain organelles characteristic of cell body
Axons:
- Carry information away from cell body
- 1 axon for each neuron
- Origin = AXON HILLOCK
- NO Nissl and Golgi
- Terminal arborizations (axon terminals)
- Contains: Microtubules, neurofilaments, mitochondria &vesicles
- Plasma membrane =** Axolemma**
- Contents = Axoplasm
Golgi Type 1 Neuron:
- Motor nuclei of CNS
- pyramidal cells = long axons (1 meter+)
- leave gray matter of CNS, traverse white matter, terminate in the periphery
**Golgi Type 2 **Neuron:
- Golgi cells in cerebellum
- stellate neurons = short axon
- Axon branched near target organ
sensory neurons
receptors TO cns
motor neurons
cns/ganglia TO effector cells
interneurons
make up 99.9% of neurons
MULTIPOLAR NEURONS
1 axon + 2 or more dendrites
BIPOLAR NEURONS
1 axon + 1 dendrite
PSEUDOUNIPOLAR NEURONS
1 process (axon) that divides close to cell body into 1 processes
(develop as bipolar but processes fuse, then branch)
ANTEROGRADE transport
AWAY from cell body TO periphery
- Kinesin
RETROGRADE transport
RETURN from axon terminal & dendrites TO cell body
- Dynein
synapses occur between…
neuron –> neuron
neuron –> effector cell (muscle, gland)
Types of SYNAPSES
axosomatic/axodendritic
(axon bouton –> dendrite)
axoaxonic
(axon bouton –> axon)
ELECTRICAL SYNAPSES
gap junctions (ion movement b/t cells)
- smooth muscle (nexus)
- cardiac muscle
NOT skeletal muscle
CHEMICAL SYNAPSES
presynaptic bouton –> synaptic cleft –> postsynaptic membrane
- cleft = 20-30nm
- synaptic vesicles release neurotransmitters
ex. neuromuscular junction
Schwann Cells
- mylenation in PNS
- originate from neural crest cells
- create myelin sheath aroudn axon
- sheath = Schwann cells or neurilemma (Schw.cell cytoplasm)
- neurilemma = nucleus + most organelles
NO MYELINE = axon hillock + axon terminal
- Nodes of Ranvier b/t schwann cells in sheath
Where is cytoplams located in the myelin sheath?
inner collar of cytoplasm
- b/t axon + myelin
Schmidt-Lantermann clefts
- small ilands w/i lamellae of myelin
perinodal cytoplasm
- @ node of ranvier
outer collar fo perinuclear cytoplasm
- around myelin
Unmyelinated nerves (PNS)
- enveloped by Schwann cell cytoplasm
- Single axon or group of axons:
*may be enclosed in a single invagination of Schwann cell surface
* axon rests in a cleft in the cytoplasm of a Schwann cell, with a single mesoaxon
Which type of axon conducts impulses faster?
what is the action of an impulse “jumping” form node to node called?
The speed of transmition is directly related to…
MYELINATED = FASTER
- “Saltatory Conduction”
- speed directly related to myelin thickness + axon thickness
Satellite Cells
- Surround ganglionic neuronal cell bodies
- Cuboidal: complete layer around cell body (only nuclei visible)
- Originate from neural crest cells
- Analogous to Schwann cell
*insulation
*nutrition
Neuroglia
- “GLIAL” cells in CNS
- More numerous than neurons
- Most brain tumors = glial in origin
3 types of neuroglia:
oligodendrocytes
- form myeline in CNS
- 1 cell can myelinate multiple neurons
astrocytes
- physical + metabolic support for CNS neurons
- found attached to blood vessels
microglia
- phagocytic cells of CNS
ASTROCYTES
- Largest of glial cells
- 2 kinds:
- *PROTOPLASMIC** = prevalent in gray matter
- *FIBROUS =** more common in white matter
- have elaborate processes
- extend b/t vessels and neurons
When there is damage to the CNS, which cells form scar tissue?
ASTROCYTES
(fibrous connective tissue)
Which neuroglial cells might have a role in regulating tight junctions of Blood-Brain Barrier?
ASTROCYTES
BLOOD BRAIN BARRIER
- functional barrier w. tight/occluding junctions sealing capilary endothelium
- controls passage of substances fr blood into CNS tissue
= protects neuronal microenvironment
- perivascular feet of astrocytes on basal lamina capillaries helps regulate
= stable composition and constant balance of ions in the interstitial fluid
= Protects neurons + glial cells from potential toxins + infectious agents
NOT in Choroid plexus and posterior pituitary, etc.
OLIGODENDROCYTES
- CNS myelin formed by:
*concentric layers of oligocyte plasma membrane - Aligned in rows between axons
- gives off several tongue-like processes –> wraps around an axon
= internodal segment
- oligodendrocyte forms myelin sheaths for several (3—50) nerve fibers
Microglia
- Part of mononuclear phagocytic system
- Present in small numbers
** (proliferate during injury/disease)**
- Secrete immunoregulatory cytokines = dispose of unwanted cellular debris
Ependyma
- Lines fluid-filled cavities of CNS
- Cuboidal to columnar (fluid-transporting characteristics)
- several locations = specialized to:
produce cerebrospinal fluid
CHOROID PLEXUS
- Modified ependyma (simple cuboidal - produces CSF)
- dialated fenestrated capillaries
- invaginated fold of pia mater (villi)
- lateral, 3rd, 4th ventricles in brain
- removes water from blood + release it as CSF
What are the 3 layers/categories of connective tissue sheaths?
endoneurium
perineurium
epineurium
ENDONEURIUM
- thin layer of reticular fibers produced by the Schwann cells
- surrounds individual nerve fibers
PERINEURIUM
- Surrounds bundles of nerve fibers
- sheath of unique connective tissue cells
- Cells joined by tight junctions
- Form a barrier to passage of most macromolecules
- Protects nerve from aggression
- numerous actin microfilaments = contractile cells
EPINEURIUM
- outermost tissue of peripheral nerve
- typical dense connective tissue:
(binds fascicles together)
- adipose tissue often seen in larger nerve sheaths
- carry blood vessels supplying nerves:
(vessels branch + penetrate perineurium)
SENSORY GANGLIA
- Craniospinal (DRG, cochlear)
- Pseudounipolar neurons:
*larger
*close together - Thick fascicles
AUTONOMIC GANGLIA
- Sympathetic and Parasympathetic
- Multipolar neurons
*smaller
*far apart - Diffuse nerve fibers
Autonomic Nwevous System (ANS)
conducts impulses to:
- smooth muscle
- cardiac muscle
- glandular epithelium
THORACO-LUMBAR OUTFLOW
Sympathetic
- norepinepherine
- postganglionic fibers
CRANIO-SACRAL OUTFLOW
Parasympathetic
- acetylcholine
- preganglionic + postganglionic fibers
Enteric Nervous System
- Confined w/i wall of gut
- 2 sets of Plexus
- *Myenteric (Auerbach)**
- *Submucous(Meissner)**
- unmyelinated nerve fibers intermingled w neuronal cell bodies
- maintain peristaltic movements + secretory function of the gut
Spinal Cord & Spinal Nerves
- Directly continuous with brain
- 31 segments:
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal - Each segment = pair of spinal nerves
- Each spinal nerve is joined to its segment of cord by roots or rootlets
(grouped as posterior (dorsal) or anterior (ventral) roots)
Grey Matter in spinal cord:
- Anterior Grey Horn
- Posterior Grey Horn
- Lateral Grey Horn
- Grey commissure
- surrounds the central canal
has neuron cell bodies, dendrites, axons & glia
White matter in spinal cord:
pheripheral
- contains mainly myelinated fibers
- Arranged in three pairs of funiculus = Anterior, Lateral &Posterior
- Functionally related bundles of axons called TRACTS
CORTEX of brain
**gray matter **
- contains cell bodies, axons, dendrites, and glial cells, synapses
NUCLEI of brain
Islands of gray matter
- found in deep portions of cerebrum and cerebellum
WHITE MATTER of brain
contains mainly:
- myelinated axons of nerve cells
- glial cells
- vessels
Cerebrum
Cerebral cortex + white matter
- Cerebral cortex = 6 layers
- PYRAMIDAL CELLS of cerebral cortex:
- *found in layers III, V**
- *small, medium, large pyramidal cells**
PURKINJE CELLS
IN CEREBELLAR CORTEX
- located between outer molecular layer + inner granular layer
apical numerous dendrites (arborize in molecular layer)
- have a single axon (not visible in H&E)
- *extends into granular layer**
- *beginning of outflow from cerebellum**
3 layers of CNS connective tissue:
MENINGES
COVER BRAIN & SPINAL CORD
Dura Mater:
- outermost
Arachnoid:
- beneath dura
Pia Mater:
- innermost layer; rests directly on brain/spinal cord
- delicate layer
Some parts of CNS have no Blood Brain Barrier:
- Neurohypophysis
- Substantia nigra
- Locus ceruleus
Response to Injury in Nervous Systems:
“Wallerian degeneration”
anterograde
- degeneration of axon distal to site of injury
- *PNS degeneration takes a few days**
- *CNS degeneration takes several weeks**
*Some retrograde degeneration also occurs
(only extends for several internodal segments)
Response to Injury in Nervous Systems:
“Chromatolysis”
- loss of Nissl substance from cell body:
- *1-2 days after injury**
- Changes in cell body are proportionate to:
amount of axoplasm lost from injury
(large amount =CELL DEATH)
Response to Injury:
“Motor fiber cut”
muscles atrophy
