NERVOUS TISSUE

Question 1

Nerve cell - structure, types of neurons, synapse

Answer 1

Opening:

• Nerve tissue is one of the 4 main tissues in the body
• It develops from the neuroectoderm, which forms the neural tube and neural crest
• Nerve tissue is the main tissue component of the nervous system and is primarily composed:
  
  • Neurons and supporting glial cells.
• The nervous system is divided into two main components:
  
  • Central nervous system:
    
    • ​Consists of the brain and spinal cord
  • Peripheral nervous system:
    
    • ​Consists of the nerves and ganglia outside the brain and spinal cord,
    • Including the cranial nerves, spinal nerves, and their roots, peripheral nerves, and neuromuscular junctions

Nerve cell, neuron:

• Description:
  
  • Polarized, signal-transmitting cells
  • Structural and functional unit of nervous tissue: central and peripheral nervous system
• Composed of soma (cell body), axon and dendrites
• Do not undergo mitosis, in interphase, G0
• Classified by:
  
  • Number of projections:
    
    • Unipolar, pseudounipolar, bipolar, and multipolar
  • Interconnections and their function:
    
    • Motor, somato sensory, interneurons

Parts of neuron:

• Soma: Cell body
  
  • Axolemma (membrane), axoplasm (cytoplasm)
  • Nucleus: round, center, euchromatic (not well stained)
  • Contains the cell organelles
    
    • Predominant: Golgi complex, ​numerous mitochondria, lysosomes, transport vesicles and inclusions.
  • Pigments: melanin, lipofuscin
    
    • ​Lipofuscin is a fluorescent pigment that accumulates with age in the lysosome
  • Cytoskeleton: microfilaments
    
    • Neurotubules (MT)
    • Neurofilaments (=intermediate filaments) (IMF)
    • Extend through the perikaryon into dendrites and axon.
  • Has Nissl substance/ bodies
    
    • rER and free ribosomes (protien synthetic activity) that are stained basophillicly in cell body and dendrites
• Axon:
  
  • The projection from a neuron’s cell body along which action potentials travel to send intercellular signals
  • Lacks a regular rough endoplasmic reticulum and thus does not contain Nissl substance
  • Connected to the cell body at the axon hillock:
    
    • Which is a trigger zone for initiation of action potentials
    • Part of perikaryon in an area devoid of Nissl bodies
  • Initial segment:
    
    • Site of action potential generation
    • Not covered by mylein sheeth
    • Contains voltage agted Na+ and K+ channels which are important in generation the action potenital
  • Terminal arborization
    
    • Peripheral branching of axon
    • Ending in terminal bouton, the button like ending of axon with synapse
  • Ends in a synapse
  • Cytoskeleton
    
    • Microtubules with associated motor proteins for rapid axonal transport
      
      • Kinesin: anterograde transport (– → +)
      • Dynein: retrograde transport (+ → –)
    • Neurofilaments
      
      • Provide structural support
      • Most abundant in axons and the proximal part of dendrites
      • Neurofilament protein is used as a marker for neuronal cells.
• Dendrites
  
  • Receive input from neighboring neurons and transmit it to the cell body
  • Structure:
    
    • Branching, thin projections from the cell body of neurons
    • Contain spines that increase the number of synapses to other neurons
  • Have Nissl substance
  • Cytoskeleton: microfilaments
  • unmyelinated,????

As I said… Neurons can be classified by:

• Number of projections:
  
  • Unipolar
    
    • Only 1 projection
    • Growing embryonic neuroblasts
    • Amacrine cells of retina
  • Bipolar
    
    • One dentrite and one axon
    • Special sensory cells:
      
      • Olfactory neurons, choclear and vestibular regions (VII cranial nerve)
  • Psuedo-unipolar
    
    • (body does not have to participate in transfer of signal)
    • dorsal root ganglia, somato sensory neurons
  • Multipolar
    
    • One axon, many dendrties
    • Pyramidal cells in brain cortex, purkinje cells (celebellar cortex)
• Interconnections and their function:
  
  • Motor, somato sensory, interneurons
  • Interneurons
    
    • Connect sensory and motor
  • Sensory
    
    • Afferent
    • Psudounipolar neurons of dorsal root ganglion, bipolar neurins in ganglion iof VII cranial nerve, retina
  • Motor
    
    • Efferent
    • Stellate neurons of spinal cord

EXTRA

A-alpha-fibers

• Mylinated
• Afferent: muscle spindles
• Efferent: alpha motoneurons

A-beta fibers

• Mylinated
• Afferent: cutaneous mechanoreceptors

A-gamma fibers

• Mylinated
• Efferent: muscle spindles (gamma motoneurons)

A-delta fibers

• Mylinated
• Afferent: pain (e.g., thermal, mechanical )
• Free nerve endings
• Responsible for the withdrawal response to pain (e.g., rapidly moving the hand when burned)

B fibers

• Moderately mylinated
• Efferent: preganglionic sympathetic fibers

C fibers

• Not mylinated (lack of myelin creates the slow conduction as the saltatory conduction is not present)
• Afferent: pain (e.g., chemical, thermal, mechanical)

Synapse

• Synapses are areas where signals or action potentials are transmitted from a presynaptic to a postsynaptic structure (e.g., neurons, muscle).
• There are different types of synapses according to the synaptic structures:
  
  • Axodendritic synapses: signaling between axons and dendrites
  • Axoaxonic synapses: signaling between axons
  • Axosomatic synapses: signaling between axons and the cell body of neurons
  • Dendrodendritic synapses: signaling between dendrites
• Types of impusle transmission: chemical, electric
  
  • ​​Chemical:
    
    • Example: A type of chemical synapse between alpha motor neurons and skeletal muscle.
    • Description:
      
      • Transfer of signals between neurons with the aid of a neurotransmitter
    • Composed of:
      
      • Presynaptic membrane
        
        • Membrane of presynaptic vessicles with NT contain specific ATP binding protiens which target the presynaptic membrane
        • Presynaptic density (active zones of the presynaptic membrane
      • Synaptic cleft
      • Postsynaptic membrane
        
        • Contain receptors for NT
        • Postsynaptic density: complex of protiens for NT interaction
  • Inhibitory: gamma- amino acid, glycine
  • Excitatory: Achetylcholine, glutamine, serotonin
• Electric
  
  • Characterized by direct flow of current through cells via gap junctions
  • Found in the heart and smooth muscle
  • No chemical synapse is required → no delay during synapsis

Neurohistological methods:

• Nissl’s Method:
  
  • demonstration of Nissl’s substance in the cell body of a neuron. (that is RER and polysomes)
  • Basic dyes, toluidine blue, thionin, methylene blue.
  • Rule number 1 in neurons! Never do a dark nucleus! Each neuron has a completely light nucleus with a darker nucleolus.
• Myelin sheath:
  
  • Sheath around nerve fibers, accumulation of cell membrane.
  • We can demonstrate the phospholipid’s in them:
    
    • ​Luxol blue: light blue color and stained with nuclei red
    • Wiegert ´s method: Brown/black: myelin sheath in a dark brown to black color.
• Impregnation methods: Using salts with silver and salts with gold. Helps us see the processes.
  • Golgi, Cajal, Hirteho, Beilchowskji
  • Impregnation of neurofibrils – processes of neurons – ex. Dendrites of purkyne cells in the cerebellum.
  • Impregnation of neuroglia cells – cells
  • Imunohistochemical methods – can be used in neurohistology/GFAP – astrocytes – neuroglia cells. Neurons and glial cells à Astrocytes. Cytoskeleton, intermediate filaments. The basic protein for the intermediate filaments in a neuron is GFAP. Typical for neuroglial cells

Question 2

Neuroglia – common features, classification and function

The degree of myelination is used to classify the nerve fibers into different subtypes. There are type A fibers that are the thickest, with the highest conduction velocity. Type C fibers that are the thinnest and are unmyelinated, and type B fibers that range in between types A and C with regards to both diameter and myelination.

Answer 2

Opening:

• Nerve tissue is one of the 4 main tissues in the body
• It develops from the neuroectoderm, which forms the neural tube and neural crest
• Nerve tissue is the main tissue component of the nervous system and is primarily composed:
  
  • Neurons and supporting glial cells
• The nervous system is divided into two main components:
  
  • Central nervous system:
    
    • ​Consists of the brain and spinal cord
  • Peripheral nervous system:
    
    • ​Consists of the nerves and ganglia outside the brain and spinal cord,
    • Including the cranial nerves, spinal nerves, and their roots, peripheral nerves, and neuromuscular junctions

Glial cells

• All non-neuronal cells that are associated with neurons in both the central and peripheral nervous systems.
• Glial cells are smaller, more numerous and are morphologically and functionally different from neuronal cells
  
  • Do not propagate action potentials.
• General functions:
  
  • Responsibility of maintaining a homeostatic balance
  • Myelinating neurons
  • Providing structural support for neurons,
  • Protecting them throughout the nervous system.

Classified according to location in PNS and CNS

Glia of the central nervous system

• Surround perikaryon (cells body of neurons) and their processes and occupy spaces between them
• There are four general types of glia in the central nervous system:
  
  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells.

1- Astrocytes

• General:
  
  • Radial glia from neuroepithelium (from neuroectoderm)
  • Star-shaped glial cells that extend numerous processes (end feet)
  • The largest glial cells
  • Made of glial fibrillary acidic protein (GFAP; an astrocyte marker)
• Functions:
  
  • Physical support (“scaffolding” of the CNS)
  • Maintain the ionic environment of neurons:
    
    • Form glial limiting membranes and blood-brain barrier
      
      • Glial limiting membrane:
        
        • Lines the parietal surface of the brain and spinal cord at its interface with the pia mater
        • By joining multiple layers of end feet.
      • Blood-brain barrier consists of:
        
        • (1) endothelial cells joined by tight junctions,
        • (2) endothelial basal lamina, and
        • (3) the foot processes of astrocyt
  • Involved in nervous tissue repair
    
    • Form an astroglial scar (reactive gliosis)
• Types
  
  • Protoplasmic astrocytes
    
    • Located in the grey matter.
    • Have short numerous branches
      
      • ​that wrap around terminal segments of axons, synapses and dendrites.
    • Dense expression of potassium channels:
      
      • Can limit the dissemination of electrical impulses to neighbouring neurons within an axon bundle
  • Fibrous astrocytes
    
    • In bundles of the white matter
    • Few long processes
    • Oriented longitudinally within the plane of the fibre
    • They appear fibrous due to the large amount of GFAP that is found in their cytoplasm.

2- Oligodendrocytes

• Radial glia from neuroepithelium (from neuroectoderm)
• Location:
  
  • These cells are distributed in both the grey and white matter of the central nervous system, but more so in the white matter.
• General structure:
  
  • Lave long cytoplasmic projections extending from their soma.
  • Nuclei:
    
    • “Fried egg” appearance on histology: prominent nucleus and clear, pale cytoplasm
    • Are small and surrounded by a halo of cytoplasm
    • Rich in polyribosomes and granular endoplasmic reticulum.
• Function:
  
  • Produce and maintain myelin sheath
  • Each projection of a cell can myelinate several axons (30 on average, up to 60)
    
    • Unmyelinated axons are not covered by oligodendrocyte cytoplasm.
  • Myelin is an insulating membranous sheath that is wrapped around the axon along its length.
  • The cytoplasmic processes of the cell body form flat cytoplasmic sheets that wrap around several axons forming multiple membrane layers.
  • During wrapping process the cytoplasm is extruded into cell body and apposed membrane layers fuse into myelin sheath.
  • Myelin of CNS contains specific proteolipid protein (PLP) and myelin basic protein (MBP)

3- Microglial cells

• The microglial cell population accounts for roughly 5% of the glial population.
• General:
  
  • Poorly identified with Nissl stain
  • Location:
    
    • The cells are found in both white and grey matter.
• Structure:
  
  • Small, nuclei are elongated and their cytoplasm is sparse.
  • Dark elongated nucleus.
  • Short iregular processes covered with numerous spikes.
• Bone marrow monocytes (mesoderm)
  
  • Originate from the monocyte cell line (specialized macrophage derived from myeloid precursor cells​
• Function:
  
  • Phagocytic cells
    
    • Activated in response to CNS tissue damage
    • Proliferate and migrate to damaged CNS to remove:
      
      • Bacteria, injured cells, and the debris of cells that undergo apoptosis.
    • Release inflammatory mediators and signaling molecules (e,g., nitric oxide and glutamate, respectively)
  • In healthy individuals, they are considered to be dormant.
    
    • Microglia precursor cells enter the CNS from the vascular system.
  • Target cells for the HIV-1 virus: Infected cells fuse to form multinucleated giant cells which are the most specific histological marker of HIV encephalitis and HIV-associated dementia.

4- Ependymal cells

• Radial glia from neuroepithelium (from neuroectoderm)
• General:
  
  • Either be low cuboidal or columnar shape
  • Look like simple columnar but they are not- have no basal membrane!
  • Cover the cerebral ventricular system.
• They are further classified as:
  
  • Ependymocytes
    
    • Most abundant
    • Apical surfaces also contain microvilli, while their bases have cytoplasmic extensions that integrate with the end feet of astrocytes
    • Found throughout the ventricular system and permits communication between the CSF and the nearby nervous tissue
  • Choroidal cells:
    
    • Modified ependymal cells known as the choroid plexus produce cerebrospinal fluid
  • Tanycytes
    
    • In contact with blood vessels:
      
      • Most prominent along the floor of the third ventricle (in the hypothalamus).
      • Their long basal processes extending from the basal surface terminate on the vasculature and pia mater.

Glia of the peripheral nervous system

• The two major cell types in the peripheral nervous system are Schwann cells and satellite cells.
• These cells are homologous to the oligodendrocytes and astrocytes of the central nervous system, with very subtle differences.

1- Schwann cells

• Neural crest cells
• Structure:
  
  • Tubular with stretched nuclei
• Function:
  
  • Produce and maintain myelin sheath
  • Differences between oligodendrocytes and Schwann cells:
    
    • Oligodendrocytes:
      
      • Can myelinate multiple neurons at a time
    • But a single Schwann cell only myelinates one neuron.
      
      • Intimately wrapped around the axons of neurons
      • Is held in place by the mesaxon (double layer of surface membrane).
  • As was the case in the central nervous system:
    
    • Schwann cells in the peripheral nervous system leave small gaps between bundles of myelin along the axon called nodes of Ranvier.

2. Satellite cells

• Envelop cell body of neurons in the nerve ganglia
• Maintain and control microenvironment around neuronal bodies
• Provide electric insulation as well as a pathway for metabolic exchanges
• they are found around the soma of neuronal cells in the central nervous system and the ganglia of the peripheral nervous system.
  
  • also in cns?????

Question 3

Types of nerve fibers, their sheaths and endings

• EXTRA
• A-alpha-fibers
• Mylinated
• Afferent: muscle spindles
• Efferent: alpha motoneurons
• A-beta fibers
• Mylinated
• Afferent: cutaneous mechanoreceptors
• A-gamma fibers
• Mylinated
• Efferent: muscle spindles (gamma motoneurons)
• A-delta fibers
• Mylinated
• Afferent: pain (e.g., thermal, mechanical )
• Free nerve endings
• Responsible for the withdrawal response to pain (e.g., rapidly moving the hand when burned)
• B fibers
• Moderately mylinated
• Efferent: preganglionic sympathetic fibers
• C fibers
• Not mylinated (lack of myelin creates the slow conduction as the saltatory conduction is not present)
• Afferent: pain (e.g., chemical, thermal, mechanical)

Myelin is a membranous sheath that insulates the axon. There are regions of the axon between bundles of myelin that remain bare, which are known as nodes of Ranvier. They promote rapid impulse transmission along the axon in a manner known as saltatory conduction. The rate of conduction increases with the diameter of the axon. Larger axons are typically more heavily myelinated than smaller axons, and consequently neurons with larger axons also transmit impulses faster than those with smaller axons:

Neurons have been grouped into two broad categories: those found in the central nervous system (brain and spinal cord) and those in the peripheral nervous system. In the central nervous system, they are found in clusters referred to as nuclei, or in layers also known as laminae. However, in the peripheral nervous system, they are found in ganglia.

Answer 3

Opening

• Nerve tissue is one of the 4 main tissues in the body
• It develops from the neuroectoderm, which forms the neural tube and neural crest
• Nerve tissue is the main tissue component of the nervous system and is primarily composed:
  
  • Neurons and supporting glial cells.
• The nervous system is divided into two main components:
  
  • Central nervous system:
    
    • ​Consists of the brain and spinal cord
  • Peripheral nervous system:
    
    • ​Consists of the nerves and ganglia outside the brain and spinal cord,
    • Including the cranial nerves, spinal nerves, and their roots, peripheral nerves, and neuromuscular junctions

Neuron:

• Polarized, signal-transmitting cells
• That are the structural and functional unit of nervous tissue
• Composed of soma (cell body), axon and dendrites

Axons

• Are a key component:
  
  • They conduct electrical signals in the form of an action potential from the cell body of the neuron to its axon terminal
  • Where it synapses with another neuron.
• Axons may be myelinated or unmyelinated, depending on their function

Myelin

• Is a membranous sheath that insulates the axon.
• Myelination
  
  • Produced by Schwann cells for peripheral axons
  • Produced by oligodendrocytes for central axons
  • Amount of myelin in the body increases throughout development, from fetal development up until maturity, with the myelination in the prefrontal cortex being the last to complete in the 2nd or 3rd decade.
• Myelin Sheath Function
  
  • Insulates axons allowing for rapid action potential conduction
  • Separates axons from surrounding extracellular components
  • The more myelin and myelination an individual has, the quicker their response is to stimuli because myelin sheaths increase the speed of nerve impulses
• Content:
  
  • Myelin is made up of lipids and proteins, a fatty substance with a whitish appearance.
  • It is made up of many concentric layers of plasma membrane to make up the myelin sheath around axons.

Myelin in CNS

• Fromed by oligodendrocytes
• A single oligodendrocyte has about 15 flat, broad, arm-like processes coming out of the cell body.
• With these they can myelinate multiple axons by spiraling around them to form a myelin sheath.
• The cell body and nucleus of oligodendrocytes remain separate from the myelin sheath, and so there is no neurilemma (that is, a cell body and nucleus enveloping an axon) present in oligodendrocytes
• Nodes of Ranvier
  
  • Are also present on the axons myelinated by oligodendrocytes, but there are far fewer of them.

Myelin in PNS:

• Options of mylination:
  
  • Each Schwann cell myelinates only one axon
    
    • Where one peripheral axon will have multiple Schwann cells myelinating its length
  • A Schwann cell can enclose many (up to 20) unmyelinated axons.
    
    • In this way, the unmyelinated axons go through the Schwann cell, but the Schwann cell does not produce a myelin sheath for these axons.
• Production:
  
  • Schwann cells will first start to myelinate axons during fetal development →
  • Begins with the invagination of a single axon into a Schwann cell→
  • Wrapping its lipid-rich membrane around it many times until there are multiple layers surrounding the axon.
  • As the wrapping continues:
    
    • The nucleus and cytoplasm of the Schwann cell are gradually squeezed out →
  • Once myelination is complete:
    
    • The Schwann cell’s nucleus and cytoplasm finish in the outermost layer.
  • Proteins responsible for compactation:
    
    • Myelin basic protein, myelin protein zero (MPZ, P0), peripheral myelin protein 22
• Myelin sheath is not continuous
  
  • Internodes:
    
    • Segments produced, each by a SC
  • Nodes of Ranvier:
    
    • Regions of the axon between bundles of myelin that remain bare
    • Its axolemma contains numerous voltage gated Na+ channels.
    • Gaps in myelinization ensure rapid transmission of electric impulses
      
      • ​Action potentials “jump“ from node to node
  • Schmidt-Lanterman clefts
    
    • Narrow channels of cytoplasm retained in the myelin sheath
      
      • uncompacted regions of myelin
    • Connecting inner collar of SC cytoplasm with peripheral one.

Larger axons are typically more heavily myelinated than smaller axons, and consequently neurons with larger axons also transmit impulses faster than those with smaller axons:

Axons may be myelinated or unmyelinated, depending on need:

• Non myleniated, “naked”
  
  • Rare
  • Inteaepithelial free nerve endings
  • Cornea of eye
• With glial sheet, non myleinated
  
  • Glial cells do not form multiple wrapping of myelin sheath
  • Each Schwann cell can enclose portions of many axons with small diameters
  • The impulse conduction of these axons is not saltatory and is much slower than that of myelinated axons
• Mylinated
  
  • Oligodendrocyte cytoplasm
  • Schwann cell cytoplasm

NERVE ENDINGS

General characteristics:

• Exteroceptors:
  
  • Help recieve stimuli for outside of body
• Proprioceptors:
  
  • In locomotor system (joints and tendons)
  • Information about mechanical changes
  • Regulation and coordination of movment
• Interoceptiopns
  
  • Stimulation from internal envioemnt

Stimuli: ​Mechanoreceptos, thermoreceptor, nociceptors (pain)

1. Non elncapsuled:

• Free nerve endings
  
  • Lack myleyin or schwann cells- “naked nerve fibers”
  • Afferent fibers
  • Pain and temperature
  • Location:
    
    • Epidermis (all the way to dtratum granulosum), dermis
    • Corneal epithelium
• Merkel disc
  
  • neural crest derived
  • basal layer of epidermis
  • high resolution tactile
  • fingertips and lips
• Palisade: ?
  
  • nerve fibers wrapped arounf of the base of the hair follice, stimulated by hair follicles

2. Encapsuled endings

• Pacinian corpusles
  
  • Lamellae of modified schwann and perineural cells
  • Lymph like fluid bewtween the lamellae
  • Large structures, up to 4 mm in length
  • Deep pressure, pressure change and vibrations
  • Location:
    
    • Hypodermis and deep fascia (mesentary of viseceral organs)
• Meissners corpucles
  
  • Iregular lamellae of schwann cells, spiral pancake
  • Suspended by fibrils which connect to the basal layer of epithelium
  • Mechanoreceptor:
    
    • finner mechanical stimuli
    • shape and texture
    • lower frequency stimuli
  • Location:
    
    • dermal papilla
• Ruffuni corpusles
  
  • Responds to stretching and warmth: redspond to mechanical dispacemt of adjacent collagen fibers
  • Axon ending: mylwn sheet is lost after entrance to corpusle and are dispersed and intertwined in side capsule)
  • Location
    
    • Skin (dermis) and joint capsule (can be considered as proprioceptors)
    • Stratum reticulare
• Karuese end bulb
  
  • Encapsuled thermoreceptor: detects cold
    
    • can also transmit mechanical
  • round sturcture, capsule from perineural cells that encapsule schwann cells with branched nerve endings
  • Location:
    
    • lips and tounge
    • penis and clitoris: genital corpusle

Motor end plate:

• peripheral nrver ending of effernt nerve fibers
• ?????

Muscle spindle and

• afferent and efferent (can be stimulated by gamma motor fiber) endings
• intrafusal (smaller and diffrent morphology that extrafusal)
• contains more neuclei and are thinner
• surroundend by lamellar CT that surounds muscle tissue
• proprioception:
  
  • sensitive to stretch of muscle
  • adapatable senitivity
    
    • more contract- more sensitive to strech

golgi tendon organ

• stimulated by contraction of muscle whuch is transmited to tendon
• located between collagen fibers of tendon

dorsal root ganglion:

• At dorsal root of spinal nrerve
• Pseuodounipolar neurons surround by satellite cells
  
  • T shape

Sympathetic ganglia:

• mutlipolar neurons with many dendrites
• surrounded by saltelite cells
• can be sympathetic: paravertebral ganglia
• parasympathetic: ?

Paraganglia:

• Variable, small up to 3 mm in diameter
• largest: carotid bodies
• aortic sympatheritc ganglia
• small corpuslces consiting of newuroendocrine cells (neural crest origin),
• sympathetic: paraganglion aortic abdomial (childern, chromaffin cells- adrenaline)
• parasympathetic: glomus caroticum, chemorepeption (content of O2 and Cos in bloos)

Structure: PARAGANGLIA

• Cheif cells froming round clupms/nests
• 40% sustenracular cells
• fernistaed capillaries
• *

Question 4

General characteristics of CNS and PNS

• and is primarily composed:
  
  • Neurons and supporting glial cells.

Central Neuroglia

There are four types of central neuroglia:

• Astrocytes are morphologically heterogeneous cells that

provide physical and metabolic support for neurons of the

CNS.

• Oligodendrocytes are small cells that are active in the

formation and maintenance of myelin in the CNS.

• Microglia are inconspicuous cells with small, dark, elongated

nuclei that possess phagocytotic properties.

• Ependymal cells are columnar cells that line the ventricles

of the brain and the central canal of the spinal cord.

Answer 4

Opening:

• Nerve tissue is one of the 4 main tissues in the body
  
  • It develops from the neuroectoderm, which forms the neural tube and neural crest
• Nerve tissue is the main tissue component of the nervous system
• Nervous system:
  
  • Enables body to respond to continuous changes in internal and external enviorment
• The nervous system is divided into two main components:
  
  • Central nervous system:
    
    • ​Consists of the brain and spinal cord
  • Peripheral nervous system:
    
    • ​Consists of the nerves and ganglia outside the brain and spinal cord,
    • Including the cranial nerves, spinal nerves, and their roots, peripheral nerves, and neuromuscular junctions

Nervous system is primarily composed:

• Neurons and supporting glial cells.
  
  • Neurons are similar
  • Variations of glial cells
  • Central Neuroglia: there are four types of central neuroglia:
    
    • Astrocytes
      
      • are morphologically heterogeneous cells that provide physical and metabolic support for neurons of the CNS.
        
        • Protoplasmic astrocytes/ Fibrous astrocytes:
          
          • Short, numerous, branching prosesses vs. fewer processes, straight
    • Oligodendrocytes
      
      • are small cells that are active in the formation and maintenance of myelin in the CNS.
    • Microglia
      
      • are inconspicuous cells with small, dark, elongated nuclei that possess phagocytotic properties.
    • Ependymal cells
      
      • are columnar cells that line the ventricles of the brain and the central canal of the spinal cord.
  • Peripheral Neuroglia:
    
    • Schwann cells
      
      • Produce myelin sheath that surrounds axons
      • isolates axons from enoneurium and ensures rapid conduction of nerve impulses
    • Satellite cells
      
      • Envlope neural bodies,
      • Maintain a controlled microenviorment around neural bodies
      • provide electric insulation as well as a pathway for metabolic exchanges
• Origin of tissue:
  
  • CNS: Neuroectodermal cells of neural tube
    
    • Except microglial cells:mesodermal macrophage percusors. especially from GMP: glanulocyte/monocyte proginator cells in boen marrow
  • PNS: Neural crest cells

​3-Cells assosiated with specific structures

• Mullers cells (in retina)
• enteric neuroglia (assosiated with ganglia in the wall of the alimentary canal
• terminal neuroglia (assosiated woth motor end plate)

CNS characteristics: Brain and spinal cord

• 1- Neurons are seperated from the blood by blood brain barrier
• 2- Covered by menings
• 3- Cavities are filled with cerebrospinal fluid

PNS:

The peripheral nervous system (PNS) consists of peripheral nerves with specialized nerve endings and ganglia containing nerve cell bodies that reside outside the central nervous system.

The peripheral nerve is made up of fasicles and their connective tissue sheaths:

Epineurium: cover the nerve

​External layer

Dense irregular CT surrounding peripheral nerve

Continuous with the dura matter

Forms septa between bundles, containing adipocytes and vascularization

Perineurium: covers the fasicle

A thin layer of flattened connective tissue, fibrous sheath, that encircles a cluster of axons known as a nerve fascicle

Outer layer of collagen connective tissue

Several concentricl layers of perineural cells:

Flat fibrobasts

Joined together with tight junctions and supported by a basal lamina, arranged like epithlium

Important for:

Regulate diffusion into the fascicle

Make up blood nerve barrier (surround blood vessles in the perineurium- with perineural cells), similar to BBB in CNS

Help maintain fibers microenvironment

Endoneurium: covers the nerve fiber

Thin layers of reticular fibres forming loose vascular connective tissue

Surrounds a cluster of unmyelinated axons or a single myelinated axon

Contains mast cells and macrophages

Macrophages mediate immunologic surveillance and also participate in nerve tissue repaire

1- Neurons are seperated from the blood by blood brain barrier

• Function:
  
  • Protects the central nervous system from microorganisms, cells, proteins, and drugs that can cause damage to the brain and other structures.
• Structure:
  
  • made up of four components
  • Capillary endothelial cells → have tight junctions
    
    • Preventing non selective passage of substace though intracellular spaces
  • The basal lamina of endothelial cells
  • Glial limiting membrane:
    
    • Formed by projestion of astrocyte glial cells surrounding the outer surface of the capillary
    • By joining multiple layers of end feet.
• Transport mechanisms: Substances can be transported across the blood-brain barrier via
  
  • Ion channels (e.g., sodium, potassium)
  • Selective transport (amino acids, glucose, vitamin K, vitamin D)
  • Diffusion (lipid soluble substances: oxygen and carbon dioxide)

2- Covered by menings

• Connective tissue layers that provide protection
• In addition to the protection provided by the skull and vertebral column
• Dura mater
  
  • Thick and strong outer layer:
  • Dense irregular CT
  • Adheres to bone
  • The skull and brain contain 2 layers:
    
    • Layer adheing to skull
    • Inner layer that adheres to the arachnid matter
  • Forms the epidural space
    
    • Space between the periosteal layer of the dura mater covering the bones of the cranium/spine and the meningeal layer of the dura mater covering the arachnoid mater
    • Cranial epidural space: a potential space that contains venous sinuses and the meningeal arteries
    • Spinal epidural space: a space that extends from the base of the skull to the sacral hiatus and contains blood vessels, lymphatics, and fat tissue
• Arachnoid mater
  
  • Neural crest
  • Loose CT
  • Adheres to the dura matter
  • Forms the outer layer of the subarachnoid spaceThe space between the arachnoid layer and pia mater that contains cerebrospinal fluid (CSF).
    
    • Contains major arteries of the brain, including the circle of Willis
    • Site for lumbar puncture (diagnostic or therapeutic)
• Pia mater
  
  • Thin and fibrous inner layer
  • Adheres to the brain and the spinal cord
  • Adjacent to the limiting membrane of the superficial glia (astorcytes)

3- Cavities are filled with cerebrospinal fluid

• Description:
  
  • A clear and colorless fluid, dosent contain cells
• Function:
  
  • Has homeostatic function, maintain internal enviorment
  • Provides mechanical support: protects against shock and pressure
  • Transports biochemical compounds
• Production: chorid plexsus
  
  • Produced by ependymal cells of the choroid plexus in the lateral, third, and fourth ventricles → Choroidal cells:
  • Modified ependymal cells: polarized cuboidal secretory cells.
  • Formed the choroid plexus that produce cerebrospinal fluid
  • Apical domain contains microvilli and tight junctions, the basolateral domain form interdigitating folds and contains abundant mitochondria.
  • Subarachnoid space→ reabsorbed in the arachnoid granulations → drains into the dural venous sinuses.
  • Blood-cerebrospinal fluid barrier (BCSFB)
    
    • Function:
      
      • separates cerebrospinal fluid from the main circulation
      • Impermeable to cells, almost all proteins, and toxins (e.g., hydrophilic medications, bacteria)
      • Selectively permeable to substances, including glucose and electrolytes
    • Structure:
      
      • It is formed by the choroid plexus.
      • Modified ependymal cells (choroid epithelial cells) → held by tight junctions
      • Capillary endothelial cells → have fenestrations
      • Basal membrane

Question 5

Peripheral and optic nerve

directly on the axon size and the myelin sheath.

• The satellite cells are small, flat cells that surround the neurons of PNS ganglia. Ganglia
• are collections of neurons that are located outside of the CNS. Peripheral ganglia are located
• parallel to the vertebral column near the junction of the dorsal and ventral roots of the spinal
• nerves and near various visceral organs. Satellite cells provide structural support for the neuronal
• bodies, insulate them, and regulate the exchange of different metabolic substances
• between the neurons and the interstitial fluid

The peripheral nervous system (PNS) consists of peripheral nerves with specialized nerve endings and ganglia containing nerve cell bodies that reside outside the central nervous system.

Neurons of the peripheral nervous system are classified based on their function and structure. Neurons that detect environmental (temperature, touch, proprioception) and visceral (pain) stimuli are known as sensory neurons. The sensory neurons form afferent nerve fibres that take data to the spinal cord and brain to be processed. These neurons have a short stalk projecting from the cell body that shortly thereafter bifurcates; these are pseudo-unipolar neurons. The description given in the previous paragraph represents the multipolar neuron (motor neuron). They deliver motor commands from the brain and spinal cord to the desired end organ; their axons form the efferent fibres.

PERIPHERAL NERVE ORGANIZATION

Whitish, glistening appearance because of myelin and collagen content Endoneurium:

delicate loose CT envelopping individual nerve fibers

Internal layer (Immediately around the external laminae of Schwann cells)

Consist of reticular fibers, scattered fibroblasts, capillaries

Perineurium

Special envelope of CT surrounding a nerve fascicle

Consits of flattened perineural cells which are (sort of CT cells but also similar to epithelium).

they have junctions

and external lamina

between these cells there is ECM with collagen fibrils

Function:

regulate diffusion into the fascicle,

make up blood nerve barrier (surround blood vessles in the perineurium- with perineural cells), similar to BBB in CNS

help maintain fibers microenvironment

Epineurium

External layer

Dense irregular connective tissue, binds nerve bundles together

Extends deeply to fill the space between fascicles

Optic nerve:

• Luxol blue staining
• inside: blue
• CT dosent stain

General:

• cranial nerve
• extension of the CNS
• retina develops as an ouut growth of the diencephalon
• there are meningies surroundiong the optic nerve
• inside there are fibers- mylinaated fibers
• not formed by schwan cells- but oligeindrocytes
• also other glial cells of CNS

ON is composed of the axons of the retinal ganglion cells. These naked axons run through the nerve fiber layer of retina to the optic disc and pierce lamina cribrosa of sclera. Orbital part of ON begins behind lamina cribrosa, here otic nerve fibers become myelinated by oligo- dendrocytes. ON is enveloped by meninges, dura mate (DM) is conti- nuous with sclera (S).

In contrast with the peripheral nerve the optic nerve fibers are not arran- ged into nerve bundles enveloped by the perineurium, but groups of nerve fibers are separated by the irregular pial septa. These septa composed of the loose connective tissue with ves- sels penetrate inside of ON. The ner- ve fibers are enveloped by subpial feet of fibrous astrocytes.

Answer 5

Opening:

• Nerve tissue is one of the 4 main tissues in the body
  
  • It develops from the neuroectoderm, which forms the neural tube and neural crest
• Nerve tissue is the main tissue component of the nervous system and is primarily composed:
  
  • Neurons and supporting glial cells.
• The nervous system is divided into two main components:
  
  • 1- Central nervous system:
    
    • ​Consists of the brain and spinal cord

2- Peripheral nervous system:

• PNS develops from the neural crest.
• PNS is composed of nerve ganglia (contain cell bodies of neurons) and peripheral nerves.
• Supporting (glial) cell of the PNS are satelite cells and Schwann cells.

The peripheral nerve is made up of fasicles and their connective tissue sheaths:

• Epineurium: cover the nerve
  
  • ​External layer
  • Dense irregular CT surrounding peripheral nerve
    
    • Continuous with the dura matter
  • Forms septa between bundles, containing adipocytes and vascularization
• Perineurium: covers the fasicle
  
  • A thin layer of flattened specilized connective tissue,
    
    • Forming a fibrous sheath, that encircles a cluster of axons known as a nerve fascicle
  • Outer layer of collagen connective tissue
  • Several concentric layers of perineural cells:
    
    • Flat fibrobasts
    • Joined together with tight junctions and supported by a basal lamina, arranged like epithlium
    • Important for:
      
      • Regulate diffusion into the fascicle
      • Make up blood nerve barrier (surround blood vessles in the perineurium- with perineural cells), similar to BBB in CNS
      • Help maintain fibers microenvironment
• Endoneurium: covers the nerve fiber
  
  • Thin layers of reticular fibres forming loose vascular connective tissue
  • Surrounds a cluster of unmyelinated axons or a single myelinated axon
  • Contains mast cells and macrophages
    
    • Macrophages mediate immunologic surveillance and also participate in nerve tissue repaire

Embryology:

• The peripheral nervous system is comprised of:
• A cluster of ectodermal cells dorsal to the neural tube in the developing embryo gives rise to the neural crest cells.
  
  • These cells undergo significant morphology during development:
• CN I and CN II are not true nerves, but rather projections of the brain.

Ganglia

• Mass of nerve cell bodies found outside of the central nervous system (CNS) along with some glial cells and connective tissue.
• Ganglia have both afferent and efferent nerve fibers.
• Peripheral ganglia can be divided into two subtypes:
  
  • Sensory ganglia and autonomic ganglia.

Sensory ganglia

• Example: dorsal root ganglia.
  
  • Clusters of sensory nerve bodies found at the base of the spine which can respond to mechanical, chemical, and thermal stimuli.

Autonomic ganglia

• Comprise the cell bodies of postsynaptic neurons conducting impulses to glands, smooth and cardiac muscles.
• Example: Paravertebral ganglia of Sympathetic system
  
  • Form a chain of ganglia on each side of the vertebral column running from the base of the skull to the coccyx, which forms the sympathetic trunk
  • Include: superior cervical, middle cervical, and cervicothoracic (stellate) ganglia , the thoracic (12), lumbar (4), and sacral (4) ganglia, and the ganglion impar (unpaired)

Dorsal Root Ganglion

With Dorsal and Ventral Roots, and Spinal Nerve

• Aggregations of neuron cell bodies that are located outside of the CNS.
• Location:
  
  • Situated on the dorsal (posterior) nerve root which joins the spinal cord.
• Structure:
  
  • Numerous round (pseudo) unipolar neuron or sensory neurons constitute the majority of the ganglion.
  • Numerous fascicles of nerve fibers pass between the unipolar neurons and course either in the dorsal nerve root or the spinal nerve
  • The
• • Enclosed by an irregular connective tissue layer
    
    • Adipose cells, nerves, and blood vessels
• The connective tissue around the ganglion merges with the connective tissue epineurium of the peripheral spinal nerve
• The nerve fibers in the ventral (anterior) root (11) join the nerve fibers that emerge from the ganglion
• (7) to form the spinal nerve (5). The spinal nerve (5) is formed when the dorsal nerve root (9) and
• the ventral (anterior) root (11) unite.
• On emerging from the spinal cord, the dorsal (9) and ventral roots (11) are surrounded by
• pia mater and an arachnoid sheath (8, 10). These become continuous with the epineurium (4) of
• the spinal nerve (5). The connective tissue perineurium around the nerve fascicles (3) and the
• endoneurium around individual nerve fibers in the spinal nerve (5) or in the ganglion (7) are not
• distinguishable at this magnification.

3- Ganglia containing nerve cells bodies that lie outside of the CNS

• Cell bodies in PNS

1-Sensory ganglia:

• Location:
  
  • 3 cranial nerves (V, IX, X)
  • Posterior root of spinal nerves
• Recieve
  
  • Somatosensory information
    
    • (proprioception, pressure, pain, tempature)
  • Viserosensory information
    
    • (blood pressure and pH, interal organ tone etc…)

1-Special sensory ganglia:

• Location:
  
  • in 4 cranial nerves (VII, VIII, IX, X)
• Recieve
  
  • sensory information
    
    • taste: VII, X
    • balance and hearing: VIII

Structure:

• CT sheath
• Neurons
• Neuroglia

Autonomic ganglia

• Neurons transmit viseromotor informatuon (sympathetic and parasympathetic)
• sympathetic
• Parasympathetic

2-Specialized nerve endings

NERVE ENDINGS/ AF sensory receptors

General characteristics:

• Exteroceptors:
  
  • ​help recieve stimuli for outside of body
• Peoprioception:
  
  • in locomotor system (joints and tendons
  • information about mechanical changes
  • regulation and coordination of movment
• Interoceptiopns
  
  • ​stimulation from internal envioemnt
  • Stimuli: ​Mechanoreceptos, thermoreceptor, nociceptors (pain)

1. Non elncapsuled:

• Free nerve endings
  
  • Lack myleyin or schwann cells- “naked nerve fibers”
  • Afferent fibers
    
    • Pain and temperature
  • Location:
    
    • Epidermis (all the way to dtratum granulosum), dermis
    • Corneal epithelium
• Merkel disc
  
  • neural crest derived
  • basal layer of epidermis
  • high resolution tactile
  • fingertips and lips
• Palisade: ?
  
  • nerve fibers wrapped arounf of the base of the hair follice, stimulated by hair follicles

2. Encapsuled endings

• Pacinian corpusles
  
  • Lamellae of modified schwann and perineural cells
  • Lymph like fluid bewtween the lamellae
  • Large structures, up to 4 mm in length
  • Deep pressure, pressure change and vibrations
  • Location:
    
    • Hypodermis and deep fascia (mesentary of viseceral organs)
• Meissners corpucles
  
  • Iregular lamellae of schwann cells, spiral pancake
  • Suspended by fibrils which connect to the basal layer of epithelium
• Mechanoreceptor:
  
  • finner mechanical stimuli
  • shape and texture
  • lower frequency stimuli
  • Location:
    
    • dermal papilla
• Ruffuni corpusles
  
  • Responds to stretching and warmth: redspond to mechanical dispacemt of adjacent collagen fibers
  • Axon ending: mylwn sheet is lost after entrance to corpusle and are dispersed and intertwined in side capsule)
  • Location
    
    • Skin (dermis) and joint capsule (can be considered as proprioceptors)
    • Stratum reticulare
• Karuese end bulb
  
  • Encapsuled thermoreceptor: detects cold
  • can also transmit mechanical
  • round sturcture, capsule from perineural cells that encapsule schwann cells with branched nerve endings
  • Location:
    
    • lips and tounge
    • penis and clitoris: genital corpusle

Motor end plate:

peripheral nrver ending of effernt nerve fibers

?????

Muscle spindle and

afferent and efferent (can be stimulated by gamma motor fiber) endings

intrafusal (smaller and diffrent morphology that extrafusal)

contains more neuclei and are thinner

surroundend by lamellar CT that surounds muscle tissue

proprioception:

sensitive to stretch of muscle

adapatable senitivity

more contract- more sensitive to strech

golgi tendon organ

stimulated by contraction of muscle whuch is transmited to tendon

located between collagen fibers of tendon

dorsal root ganglion:

At dorsal root of spinal nrerve

Pseuodounipolar neurons surround by satellite cells

T shape

Sympathetic ganglia:

mutlipolar neurons with many dendrites

surrounded by saltelite cells

can be sympathetic: paravertebral ganglia

parasympathetic: ?

Paraganglia:

Variable, small up to 3 mm in diameter

largest: carotid bodies

aortic sympatheritc ganglia

small corpuslces consiting of newuroendocrine cells (neural crest origin),

sympathetic: paraganglion aortic abdomial (childern, chromaffin cells- adrenaline)
parasympathetic: glomus caroticum, chemorepeption (content of O2 and Cos in bloos)

Structure: PARAGANGLIA

Cheif cells froming round clupms/nests

40% sustenracular cells

fernistaed capillaries

PERIPHERAL NERVE ENDINGS

Non-encapsulated: (free) nerve ending, Merkel disc

Encapsulated endings - Pacinian corpuscles, Meissner‘s corpuscles, Ruffini‘s corpuscles, Krause‘s end bulb

Question 6

Cerebellum and the spinal cord

Answer 6

Opening:

• Nerve tissue is one of the 4 main tissues in the body
  
  • It develops from the neuroectoderm, which forms the neural tube and neural crest
• Nerve tissue is the main tissue component of the nervous system
  
  • Primarily composed:
    
    • Neurons and supporting glial cells.
• The nervous system is divided into two main components:
  
  • Central nervous system:
    
    • ​Consists of the brain and spinal cord
• Peripheral nervous system:
  
  • ​Consists of the nerves and ganglia outside the brain and spinal cord,
  • Including the cranial nerves, spinal nerves, and their roots, peripheral nerves, and neuromuscular junctions

CNS characteristics: Brain and spinal cord

1- Neurons are seperated from the blood by blood brain barrier

• Function:
  
  • Protects the central nervous system from microorganisms, cells, proteins, and drugs that can cause damage to the brain and other structures.
• Structure: made up of four components
  
  • Capillary endothelial cells → have tight junctions
    
    • Preventing non selective passage of substace though intracellular spaces
  • The basal lamina of endothelial cells
  • Glial limiting membrane:
    
    • Formed by projestion of astrocyte glial cells surrounding the outer surface of the capillary
    • By joining multiple layers of end feet.
• Transport mechanisms: Substances can be transported across the blood-brain barrier via
  
  • Ion channels (e.g., sodium, potassium)
  • Selective transport (amino acids, glucose, vitamin K, vitamin D)
  • Diffusion (lipid soluble substances: oxygen and carbon dioxide)

2- Covered by menings

• Connective tissue layers that provide protection
  
  • In addition to the protection provided by the skull and vertebral column
• Dura mater
  
  • Thick and strong outer layer:
    
    • Dense irregular CT
    • Adheres to bone
  • The skull and brain contain 2 layers:
    
    • Layer adheing to skull
    • Inner layer that adheres to the arachnid matter
  • Forms the epidural space
    
    • Space between the periosteal layer of the dura mater covering the bones of the cranium/spine and the meningeal layer of the dura mater covering the arachnoid mater
      
      • Cranial epidural space: a potential space that contains venous sinuses and the meningeal arteries
      • Spinal epidural space: a space that extends from the base of the skull to the sacral hiatus and contains blood vessels, lymphatics, and fat tissue
• Arachnoid mater
  
  • Neural crest
  • Loose CT
  • Adheres to the dura matter
  • Forms the outer layer of the subarachnoid space
    
    • The space between the arachnoid layer and pia mater that contains cerebrospinal fluid (CSF).
      
      • Contains major arteries of the brain, including the circle of Willis
      • Site for lumbar puncture (diagnostic or therapeutic)
• Pia mater
  
  • Thin and fibrous inner layer
  • Adheres to the brain and the spinal cord
    
    • Adjacent to the limiting membrane of the superficial glia (astorcytes)

3- Cavities are filled with cerebrospinal fluid

• Description:
  
  • A clear and colorless fluid, dosent contain cells
• Function:
  
  • Has homeostatic function, maintain internal enviorment
  • Provides mechanical support: protects against shock and pressure
  • Transports biochemical compounds
• Production: chorid plexsus
  
  • Produced by ependymal cells of the choroid plexus in the lateral, third, and fourth ventricles →
    
    • Choroidal cells:
      
      • Modified ependymal cells: polarized cuboidal secretory cells.
      • Formed the choroid plexus that produce cerebrospinal fluid
      • Apical domain contains microvilli and tight junctions, the basolateral domain form interdigitating folds and contains abundant mitochondria.
  • Subarachnoid space→ reabsorbed in the arachnoid granulations → drains into the dural venous sinuses.
• Blood-cerebrospinal fluid barrier (BCSFB)
  
  • Function: separates cerebrospinal fluid from the main circulation
    
    • Impermeable to cells, almost all proteins, and toxins (e.g., hydrophilic medications, bacteria)
    • Selectively permeable to substances, including glucose and electrolytes
  • Structure: It is formed by the choroid plexus.
    
    • Modified ependymal cells (choroid epithelial cells) → held by tight junctions
    • Capillary endothelial cells → have fenestrations
    • Basal membrane
• Tissue is divided into:
  
  • Grey matter:
    
    • Neuron bodies
      
      • Brain cortex, subcortical basal ganglia, brainstem, spinal cord grey matter
  • White matter:
    
    • Neuronal projections

Spinal cord:

• 1- Neurons are seperated from the blood by blood brain barrier
• 2- Covered by menings
• 3- Cavities are filled with cerebrospinal fluid
• General
  
  • Extends from the medulla oblongata to the conus medullaris
    
    • Entering the spinal canal at the first cervical vertebrae (C1) and terminating between the first and second lumbar vertebra (L1–L2).
  • It is derived from the neural tube.
  • The spinal cord gives rise to 31 pairs of spinal nerves that transfer autonomic, motor, and sensory signals between the CNS and the body.
• Although a basic structural pattern is seen throughout the spinal cord,
  
  • The shape and structure of the cord vary at different levels
  • (cervical, thoracic, lumbar, and sacral)
• White matter
  
  • Peripheral
    
    • Anterior funiculus
    • Lateral funiculus
    • Posterior funiculus
  • Contains bundles of myelinated axons
    
    • Tracts or fasciculi
    • Axons ascend or descend in the spinal cord within the white matter
  • Characteristic features:
    
    • Surrounds the gray matter
    • White color due to myelin
    • Does not contain dendrites
    • Contains glial cells
    • Anterior median fissure
      
      • Groove for the anterior spinal artery
    • Posterior median sulcus
      
      • Separates the posterior columns
• Grey matter
  
  • Central: Butterfly-like shape
  • Contains cell bodies, dendrites and proximal axons of neurons
  • Surrounds the central canal
  • Gray commissure crosses the midline
  • Three regions
    
    • Anterior gray column (anterior horn)
      
      • Cell bodies of motor neurons
        
        • Multipolar cells with a large nucleus and prominent nucleolus
        • Nissl bodies are present in the cell body and dendrites, but not in the axons
    • Posterior gray column (dorsal horn)
      
      • Cell bodies of sensory neurons;
    • Lateral gray column
      
      • Contains the cell bodies of preganglionic sympathetic neurons
• Central canal

Cerebellum

• Overview
  
  • Location
    
    • Posterior cranial fossa above the foramen magnum
  • Covered by the tentorium cerebelli (dura mater)
  • Connected to brainstem via three paired peduncles
  • It consists of three lobes
    
    • (the anterior, posterior, and flocculonodular lobe).
  • Functionally, it is divided into three zones.
• Function
  
  • Control of balance and ocular movements
  • Planning of movements that are about to occur
  • Coordination of complex and sequential movements
  • Maintenance of muscle tone
• Microscopic anatomy
  
  • The cerebellum is composed of the outer gray matter (cerebellar cortex) and inner white matter (cerebellar medulla).
• Cerebellar cortex
  
  • Receives afferent inputs from the cerebrum, spinal cord, and vestibular nuclei
  • Sends neural impulses to the cerebellar nuclei
  • Composed of 5 types of neuronal cells, densely packed and arranged in 3 layers
  • The cortex is primarily an inhibitory structure; all cerebellar cells except granule cells are inhibitory.

1- Molecular layer

• (outermost layer)
• Cells:
  
  • Basket cells: large axons with sparse dendrites (inhibitory)
  • Cerebellar stellate cells: star-shaped neurons with multiple arborizations (inhibitory)
  • Parallel fibers (axons of granule cells) and dendrites of Purkinje cells
• Function:
  
  • Receives excitatory input from parallel fibers
  • Sends inhibitory impulses to Purkinje cells

Molecular layer

The outer molecular layer is synaptic and therefore contains many axons of granule cells and and dendrites of the Purkinje cells with least density of cells.

Superficially located stellate cells and basket cells are found in this layer. The stellate cells usually bear short dendrites in which make contact with small number of Purkinje cell dendrites.

In comparison, basket cells have extensive dendritic processes that can make contact with much larger number of Purkinje cells. Both cells receive excitatory input from the parallel fibers and in turn exhibit inhibitory influence on the Purkinje cells

Question 7

CNS: cyto- and myeloarchitecture of the brain cortex

Layers of the cerebral cortex

Most of the brain is composed of six layers. These areas are referred to as the neocortex. The hippocampus and the olfactory cortex are only composed of three layers and together are referred to as the allocortex. In addition, the cerebral cortex is divided into 47 Brodmann areas.

The neocortex is formed by the following layers (from external to internal)

Molecular layer

External granular layer

External pyramidal layer

Internal granular layer → termination area of thalamocortical projections (form lines of Gennari in the primary visual cortex)

Internal pyramidal layer → area where axons of the corticospinal and corticobulbar tracts form

Multiform layer → composed of polymorphic cells

Answer 7

Opening

• The nervous system is divided into two main components:
  
  • Central nervous system: ​
    
    • Consists of the brain and spinal cord
  • Peripheral nervous system: ​
    
    • Consists of the nerves and ganglia outside the brain and spinal cord, Including the cranial nerves, spinal nerves, and their roots, peripheral nerves, and neuromuscular junction

The central nervous system

• Brain functions to control both conscious and unconscious processes by generating action potentials that travel through axons connected to the spinal cord and the peripheral nervous system.
• Composed of gray and white matter.
• Gray matter
  
  • consists mostly of the neuronal bodies
• White matter
  
  • Consists of the axons of the neurons.
  • The gray matter is found in the cerebral cortex (outer layer of the brain) and in the nuclei (masses of neurons inside the white matter).

Cells of the cortex

The cerebral cortex consists of the hundreds of billions of neurons, and all of them are different variations of only three morphological shapes: pyramidal cells, fusiform cells and stellate (granular cells). Other types of cells seen in the cortex are a modification one of those three. The other cells are horizontal cells of Cajal-Retzius and cells of Martinotti.

Pyramidal cells

• Make up to 75% of the cellular component of the cortex
• and they are the main output neurons of the cerebral cortex.
• They vary in size, going from small to gigantic.
• They usually have one apical dendrite that courses towards the surface of the cortex, and multiple basal dendrites.
• The number of basal dendrites varies widely, but generally there are more than three to four primary dendrites which branch off to the next generations of dendrites (secondary, tertiary etc) which arborize in the vicinity of the cell body. Usually, they have one long axon that leaves the cortex and enters the subcortical white matter. These axons are destined to be:

Question 8

PNS General: IDK whcihc Question

Answer 8

• PNS develops from neural crest
• composed of nerve ganglia (which contain cell bodies aod neurons) and peripheral nerves
• supporting cells: satelite and schwann
• satellite:
  
  • envlope neural bodies, maintain a controlled microenviorment around nrural bodies and provide elecyic insulation as well as a pathway for metabolic exchanges
• schwann:
  
  • produce myelin sheath that surrounds axons
  • isolates wxons from enoneurium and ensures rapid conduction of nerve impulses

peripheral nerve:

endoneurium: indicidual nerve fibers connected by loose CT
perineurium: specilized CT woith cells that contibute to blood nerve barier
epineurium: dense irregular CT, binds fasicles together

Question 9

General characteristics of the sensory organs

Histological structure of the anterior part of the eye

Histological structure of the posterior part of the eye

General structure of the inner ear, structure and function of its vestibular part

Cochlea and the organ of Corti