Nervous Tissue II Flashcards
Central Nervous System
- Cerebrum
- Cerebellum
- Spinal Cord
Brain main parts
- Cerebrum
- Cerebellum
- Brain Stem
Cerebrum
Largest part of the brain, it comprises 85% total weight of the brain and looks like large pink/gray walnut
Controls thinking and speaking and is divided into right and left cerebral hemispheres
Cerebral Cortex
Makes up the outside layer of cerebrum composed primarily of gray matter
Basal Ganglia
found at the base of thecerebrum. It consists of a large group of neuron cell bonies. Controls and synchronizes movement
Amygdala
Important for memory and emotional behavior
Hippocampus
Transfers memories from short-term to long-term memory
Cerebellum
The second main part of the human brain.
- Located at the back of the skull
- Size of golfball (cauliflower)
- Coordinates movements, motinos, reflexes, sense of balance
Mid-brain
Lies between cerebrum and cerebellum it is involved in hearing and sight reflexes
Brain Stem
The 3rd major part of the brain. Consists of: Midbrain, medulla, and pons
Medulla
Sits at base of brain, regulates heart rate, breathing, and digestion
Pons
Located as abulge in the brain stem above medulla, responsible for REM sleep
CNS-Spinal Cord Gray Matter
Neuronal cell bodies and support cells called Glial Cells key to gray matter is that the neurons are NOT myelinated. Perikaryons are found throughout sections of gray matter.
-Morphology of gray matter resembles an H resulting in posterior (longer) and anterior (thicker) Horns
-Gray matter is on inside
CNS-Spinal Cord White Matter
No Neuronal cell bodies-Many glial cells. Composed primarily of TRACTS. Morphology of unstained or lightly stained tissues appears clear of white with occasional glial nuclei
-White matter in on OUTSIDE
Tracts
Groups of myelinated axons
CNS-Cerebrum-Cortex
Gray Matter is on OUTSIDE
White Matter is on INSIDE
Cortical Gray Matter:
- Neurons
- Glial Cells
Medullary White Matter:
- Nerve fibers
- Glial Cells
Function: Higher thought processes and coordination of movement
CNS-Cerebrum-Cortex Histology
- White and Gray matter position is reversed from that in spina lchord
- Gray matter has cell bodies/nerve fibers
- At low magnification 6 layers of gray mattter are distinguished
- At high magnification 2 layers-Superficial and Pyramidal cells
CNS-Cerebrum- Superficial Layer
Comprised of few cells (mostly axons
CNS-Cerebrum- Pyramidal Layer
Below Superficial layer
-Axons can reach deep into cortical layers of white matter- some can extend into spinal motor neurons
CNS-Cerebellum
Cortical gray matter:
-Neurons and Glial Cells
Central white matter:
-Nerve fibers and Glial cells
Function: Coordination of movements
CNS-Cerebellum Histology
Position of white and gray matter is reversed to spinal cord
Grey Matter is composed of cell bodies and nerve fibers
-At low mag- 3 layers of gray matter are seen
A. ML-Unmyelinated Nerve Fibers-Few Perikaryons
B. GL-Large flask-shaped cells whose dendrites penetrate ML (Purkinje cells)
C.GrL-Packed with small multipolar neurons
Glial Cells
- Oligodendocytes
- Astrocytes
- Fibrous Astrocytes: Mostly in white matter
- Protoplasmic Astrocytes: Mostly in gray matter
Microglia: Very small- could be compared to immune system of brain
Ependymal Cells
Together, sustain neurons physically, metabolically, and help regulate ionic concentrations in extracellular space
Glial Cells Histology
- Found between myelinated fibers-responsible for forming and maintaining the myeling sheath
- The all important Nodes of Ranview are formed as spaces are left between folds
Glial Cells Histology- Myelination
One Oligodendrocyte cell can myelinate many axons
-myelination is not complete at birth
-Cell division is slow
Histology of Astrocyte
- Starfish shaped, small cells
- Found between tracts of axons/dendrites
- Processes are attached to capillaries, axons, or perikaryons
- When wrapped around capillaries, they engulf them-major players in physical support
- Can take up K+ and spent neurotransmitters
Two types of Astrocytes in Glial Cells
- Fibrous
- Protoplasmic
Protoplasmic Astrocytes
- Found only in gray matter
- Fewer filaments and processes
- Associated with Perikaryons, dendrites, & synapses
Fibrous Astrocytes
Found only in white matter
Upon injury, what happens to Microglia Glial cells ?
They become Reactive Microglia-Actively phaocytic
Histology of Ependymal Cells
- Cells line the ventricles in the brain and central canal of spinal chord
- cells are a single layer of epithelial cells containing desmosomes, adherins junctions, gap junctions, & tight junctions
- Cells can be cuboidal but are mostly pseudostratified columnar epithelia
- Contain microtubule filled cilia that sweep back and forth propelling fluid
- Produce and secrete cerevrospinal fluid
Meninges
- Dura mater
- Arachnoid
- Pia Mater
Dura Mater
- Very dense connective tissue
- Juxtaposed and connected to periosteum of cranial bones by loose connective tissue
- well vascularized
Arachnoid Membranes
- Considered the middle layer conneted to both Dura Mater and Pia Mater
- Specialized netwrok of flat cells and connective tissues called trabeculae
- Subarachnoid space is filled with cerebrospinal fluid
- Loosely conforms to brain folts
Pia Mater
- Innter most layer
- Consists primarily of collagen fibers covered with squamous epithelial cells
- These cells and collage ECM follow the blood vessels, covering them with a sheet of Pia Mater
Blood-Brain Barrier
Endothelial Cells and Neurologlial Cells:
- limit the access of lipid soluble material and other macromolecules from blood to brain and spinal cord - Resides at the level of endothelial cells lining the blood vessels
Protection
Choroid Plexus
Highly vascularized epethelial structure lining portions of the cerebral ventricles responsible
Circulation
Filld ventricles, central spinal canal subarachnoid space and perivascular spaces.
Hydrocephalus
A major problem caused when CSF is blocked from exiting venricles
Peripheral Nervous System (PNS)
Consists of all nerves and supportive cells outside of CNS
- Afferent system (sensory)
- Efferent system (motor)
- Usually seperated anatomically and physiologically into the somatic nervous system (skeletal muscle) and autonomic nervous system (smooth muscle)
Ganglia in PNS
- Dorsal Root Ganglia
- Autonomic Ganglia
Peripheral Nerves
- Axons
- Connective tissue coverings
- Myelination
Dorsal Root Ganglia
Are collections of cell bodies of Afferent Neurons
a) located at the posterior root of spinal nerves and some cranial nerves
b) histologically perikaryons are round and have a wide range in sizes. Nuclei are centralized
c) primarily Pseudounipolar class of neurons
d) 2 processes branch in sperate directions (one proceeds to periphery the other to CNS making up 1 Axon)
e) peripheral branch is dendritic branch
f) impulses bypass perikaryon
g) neurons are seperated from surrounding connective tissue by satelite cells
Autonomic Ganglia
Are collections of cell bodies of Efferent Neurons
- contain multipolar neurons
- 3 types of ganglia are present based on their location in body
Peripheral nerves
- Axons
- Connective tissue coverings
- Myelination
Peripheral Nerves Connective tissue coverings
Epineurium
Perineurium
Endoneurium
Epineurium
Outer most convering-covers most moderate and large nerves
Perineurium
directly covers bundles of nerves
Endoneurium
Vascularized loose connective tissue between individual fibers (outside of Schwann Cells)
Myelination- Schwann Cells
The primary cell type that myelinates axons,
- A single cell myelinates one small segment of axon
- Many cells in a row along an axon form a column with spaces in between called Nodes of Ranvier
Schwann Cells in Non-Myelinated Axons
Loosly wrapped around multiple axons
-Mesaxon is the cleft formed as 2 or more columns of Schwann cells contact each other in a group of neurons .
Regeneration of Nerve Fibers
- Chromatolysis
- Schwann Cell division and column formation
- Penetration by growing Nerve fiber
4 steps of New Fiber Regeneration
- About 2 weeks post trauma changes occur in the body
- After about 3 weeks, myelin sheath completely dissolves; schwann cells increase cell cycling and proliferate
- a continuous column of Schwann cell is formed
- about 3 months, the nerve fiber slowly penetrates the Schwann Cell Column
About 2 weeks post trauma, what changes occur in the body?
it undergoes chromatolysis (nissl bodies dissolve), perikaryon expands, and nuceus moves to one side
Nerve Endings-Peripheral Nerves Function
To convert physical or chemical stimuli into electrical energy. Also convert different instensities of electrical energies
Classified many ways:
- afferent VS efferent
- Cause of stimulation
- Morphology
a. Pacinian corpuscles
b. cause of stimulation
c. Morphology
i. Pacinian Corpuscles
ii. Meissner’s corpuscles
iii. Free endings
iv. Muscle spindles
v. Golgi Tendon Organ
Autonomic Nervous System (ANS)
- Working with direction by CNS
- An effect branch of the PNS
- Ganglia
- Pre- and Para- Vertebral
- Terminal
- Sympathetic and Parasympathetic Brances
- Nerve Endings
ANS-Nerves and Ganglia
Parasympathetic and Sympathetic branches have similar features (PIC)
Paravertebral Ganglia
Located immediately outside of spinal column antero-laterally extending from cervical to sacral regions
Prevertebral Ganglia
In abdomen
Terminal Ganglia
Located near the organs to be innervated
Opposing effects of sympathetic and parasympathetic nerves
Neurepinephrine released from sympathetic nerves to the heart increase heart rate, whereas acetylcholine released from the parasympathetic fibers decrease it
Dorsal, Sympathetic Ganglion
Cell bodies are spaced closely together (PIC)
