Histology Flashcards
what are the supporting cells of the nervous system?
Central nervous system:
• Microglia – involved in the immune defence of the CNS
• Ependymal cells – line the ventricles and central canal of the spinal cord
• Oligodendrocytes – produce the myelin sheath for neurons in the CNS
• Astrocytes – provide support to the neurons of the CNS, remove excess neurotransmitter and contribute
Peripheral nervous system:
• Satellite cells – supportive cells found in the ganglia of the PNS
• Schwann cells – produce the myelin sheath for neurons in the PNS
what is the size of nerve cell bodies?
range from 4 - 150 um
what types of neurons are the neurons of the olfactory mucosa?
bipolar
what does the dorsal root ganglia contain? what type of neurons?
nerve cell bodies of unipolar neurons
what is an axon hillock? what happens here? what doesn’t it contain?
- a specialised part of the cell body of a neuron that connects to the axon and is the last site in the cell body
- here membrane potentials propagated from synaptic inputs are summated before transmitted to the axons
- this area doesn’t contain any golgi apparatus or Nissl substance
what are nissl bodies?
Nissl bodies (or Nissl substance) is a combination of stacks of RER interposed with rosettes of free polysomes
Nissl substance = a large granular body found in neurons – these granules are of rough endoplasmic reticulum (rER) with clusters of free ribosomes, and are the site of protein synthesis
proteins synthesised in the nerve cell body are transported to the axon terminal by what?
anterograde transport
what type of neurons are motor neurons?
multipolar
describe the histology of the cerebral cortex
- Divided into 6 layers based on the type of neurone within each layer
- Should be able to identify pyramidal cells (so named because of their shape)
- Pyramidal cells are motor neurones, they vary in size being smallest superficially and increasing in size deeper in the cortex
- The largest of these cells are known as Betz cells (located in the 5th layer)
describe the histology of the spinal cord
- Determine what anterior and what posterior – ventral median fissure will be larger than the dorsal median sulcus and the posterior roots can be seen extending backwards from the dorsal horns
- Identify: grey and white matter, dorsal and ventral horn, central canal, dorsal medial sulcus, ventral median fissure and grey commissure
- In the anterior horn, large pyramidal-shaped nerve cell bodies can be seen, these are the nerve cell bodies of the lower motor neurones – you may be able to see a prominent nucleolus within the nucleus of these cells and Nissl bodies within the cytoplasm (both involved with protein)
- White ventral commissure
- Grey commissure
- Large pyramidal cells (type of multipolar neuron) in the ventral horn
White matter spinal cord:
- Nuclei seen are the nuclei of oligodendrocytes
Grey matter spinal cord:
- Ventral horn – lower motor neurone cell body – producing acetylcholine – big nucleus to produce lots of protein
Less grey matter – not in cervical or lumbar enlargements
describe the histology of peripheral nerves
- Individual axons are ensheathed in a layer of connective tissue termed the endoneurium
- Groups of axons are bundled together to form fascicles, which again are surrounded by connective tissue, the perineurium
- The fascicles are bundled together to form the nerve, which is also wrapped in a layer of connective tissue, termed the epineurium
- The nerves are surrounded by loose connective tissue containing some adipocytes and blood vessels
- Endoneurium – connective tissue layer surrounding a single nerve fibre (neuron)
- Fascicle – bundle of nerve fibres
- Perineurium – connective tissue layer surrounding a fascicle
- Nerve – a group of fascicles
- Epineurium – connective tissue layer surrounding a nerve
what are the three main types of ganglia?
sensory ganglia, sympathetic ganglia and parasympathetic ganglia
- Not motor ganglia – all upper in the CNS and the lower go straight to muscle no need for ganglia
what type of ganglia are dorsal root ganglia? what do they contain?
sensory - they contain unipolar neurons
what type of neurons do the sympathetic ganglia contain?
mutlipolar neurons
describe the histology of a dorsal root ganglion
- Located on the dorsal roots of the spinal cord
- There are large round nerve cell bodies of the sensory neurones
- A centrally located nucleus will be evident in many of them
- The nuclei of satellite cells can be seen surrounding the sensory neurone
- You can also see bundles of sensory axons passing through the ganglion from the periphery
describe the histology of a sympathetic ganglion
- The nerve cell bodies are much more spread out than those seen in the sensory ganglion
- Satellite cells are also present here, but they are dispersed throughout the ganglion rather than surrounding the nerve cell bodies
- See just cell bodies of post-synaptic neurones
- Multipolar nerves – cell bodies much further apart
- Satellite cells around bodies
describe the histology of a parasympathetic ganglion
- Parasympathetic ganglia are located in the gastrointestinal tract between the two layers of the muscularis externa
- They can be difficult to find as they often consist of only a small number of cells
- Where – close to the organs that they’re going to supply
- Long pre-ganglionic and short post-ganglionic
- Oculomotor, facial, vagus, glossopharyngeal nerves (cranial nerves) – associated with parasympathetic ganglia
- Sacral region has parasympathetic ganglia
There are number of ganglia that are associated with the cranial nerves - where are they and what do they contain?
they are located within the head region and contain either sensory or parasympathetic neurones
what are the sensory ganglia associated with cranial nerves?
- Trigeminal
- Superior nucleus of glossopharyngeal
- Inferior nucleus of glossopharyngeal
- Geniculate
- Superior nucleus of vagus
what are the parasympathetic ganglia associated with cranial nerves?
- Inferior nucleus of vagus (nodose)
- Submandibular
- Otic
- Pterygopalatine
- Ciliary
what makes up the peripheral nervous system?
cranial nerves and peripheral nerves
what are bipolar neurones for?
special senses - eye and ear
what are neuroglia?
supportive cells of the nervous system
what do astrocytes do?
maintain chemical environment, provide nutrients, remove excess neurotransmitter and contribute to blood brain barrier
what do microglia do?
engulf invading microorganisms, migrate to areas of nerve injury to clear dead cells
what do ependymal cells do?
line the ventricles of the brain and the central canal of the spinal cord, form cerebrospinal fluid and assist in its circulation
what do Schwann cells do?
produce the myelin sheath around the axons of the PNS neurones, participate in the regeneration of PNS axons
what do satellite cells do?
located in the PNS ganglia, provide metabolic support for the neurones and remove excess neurotransmitters
what is a nerve? what is a tract/fasiculus?
Nerve = a bundle of axons in the PNS Tract/fasiculus = a bundle of axons travelling in the CNS
what are the layers of the cerebral cortex? where are pyramidal cells found?
Pia mater
- Molecular layer – many fibres, few neurons
- External granular layer – small granule cells & neuroglia
- External pyramidal layer – pyramidal cells, some granule cells & neuroglia
- Internal granular layer – granule cells & neuroglia
- Internal pyramidal layer – medium & large pyramidal cells & neuroglia
- Multiform layer – neuroglia & Martinotti cells
White matter
what nerve are the geniculate ganglia associated with?
sensory ganglia for the facial nerve
what else is found in the dorsal root ganglia apart from axons?
satellite cells - supporting nerve cell bodies
what do bone and cartilage consist of?
- Like all connective tissues, bone and cartilage consist of specialised cells suspended in an extracellular matrix
- The matrix is made up of a fluid known as the ground substance in which protein fibres are suspended
what is the extracellular matrix of bone made up of? what does the combination provide?
- The organic component makes up 35% and is called osteoid
- It is made up of type 1 collagen and protein complexes
- It makes the bone strong and flexible but easily compressed
- The remaining 65% is hydroxyapatite, this is the inorganic component that results from the deposition of mineral salts; mainly calcium phosphate and calcium carbonate
- It is hard, relatively inflexible and quite brittle
- The combinations of the organic and inorganic components makes bone strong, flexible and resistant to shattering
what are the four types of cells that exist in bone? what does each do?
- Osteoblast = produces new bone; secretes osteoid and is responsible for mineral deposition
- Osteocyte = mature bone cell; located in a lacuna (nest) – maintains the matrix
- Osteoclast = removes mineral from the matrix, responsible for bone remodelling
- Osteogenic stem cell = found in the periosteum and the endosteum – develops into an osteoblast
what are the two types of bone tissue?
compact bone and cancellous bone
compact bone
- what does it provide
- where is it
- what does it form
- what forms it
- Provides strength for weight bearing & prevents buckling in long bones
- Covers the outer surfaces of flat bones
- Forms a thin layer which covers the outer surfaces of long bones
- Osteons (Haversian systems) form the basic unit of this type of bone
cancellous bone
- what is it made up of
- what does it store
- what does it form
- where is it found
- Made up of trabeculae with spaces in between
- Stores bone marrow
- Forms the core of flat bones
- Found in the epiphyses of long bones
- Trabeculae of cancellous bone arranged haphazardly to from a network of interconnecting struts designed to provide maximum strength for minimum mass
- Spaces between the trabeculae contain bone marrow
- Osteocytes lie in lacunae near the surface of the trabeculae and get nutrients via diffusion
- Trabeculae are orientated along lines of stress
- Trabeculae, osteocytes, bone marrow, periosteum
- Spongy bone does not contain Haversion systems
describe the histology of decalcified compact bone in transverse section
- Numerous holes surrounded by darker stained tissue – osteons and the holes in the centre are Haversian canals
- Stained area which surrounds the canal is made up of many layers of tissue – concentric lamellae
- Small spaces distributed throughout the concentric lamellae – the lacunae
- Nuclei of osteocytes may be seen in some of lacunae
- Tiny canals can be seen radiating out from the lacunae, these are canaliculi which are communicating channels between the osteocytes
describe the histology of skull bone
- In flat bone, such as those of the skull, the spongey bone is sandwiched between two outer layers of compact bone
- Slender bone trabeculae ramify through the central area and enclose the marrow cavity
- The spaces of the marrow cavity contain haemopoietic tissue
- Periosteum surrounds the outer surface of the bone
what can cartilage be classified into?
Can be classified into one of three categories according to the amount, arrangement and type of fibres present in the matrix:
- hyaline cartilage
- elastic cartilage
- fibrocartilage
describe the histology of hyaline cartilage in the ribs
- Shows two rings of costal cartilage separated by intercostal muscle
- Perichondrium containing numerous fibrocytes surround the cartilage
- The inner layer of the perichondrium is the chondrogenic layer and it contains differentiating chondroblasts
- Lacunae can be seen throughout the cartilage, the nuclei of chondrocytes are evident in most lacunae
- The chondrocytes appear singly or in groups, those in groups are in areas where interstitial growth is occurring
- The matrix immediately around lacunae (territorial matrix) appears darker compared to the matrix further away (interterritorial)
- The matrix appears glassy and homogenous
- The fibres of the matrix cannot be seen in hyaline cartilage because they have the same refractive index as the group substance
- Purple blobs are cartilage
- Surrounded by muscle tissue with adipose tissue inside
- Ribs
- Darker around the lacunae because they’re producing the matrix – higher density of matrix (territorial matrix)
- Note the perichondrium – outer & inner layers
- Chondrocytes in lacunae
describe the histology of elastic cartilage in the ear
- E.g. pinna of the ear
- Chondrocytes can be seen in lacunae throughout the tissue
- They are arranged randomly throughout the matrix
Elastic: (e.g. external auditory meatus)
- White empty space = lacunae
- Denser tissue around lacunae – territorial matrix
- Elastic fibres – hyaline you can’t see fibres because of refractive index
- Similar to hyaline – chondrocytes in lacunae
describe the histology of fibrocartilage
- Chondrocytes are small and appear to be organised in rows
- Bundles of fibres and present and they are also arranged in parallel rows
- Annulus fibrosis
- Alternating layers of hyaline cartilage and thick layers of dense collagen fibres
- Chondrocytes are small, few & widely scattered in parallel rows
- No perichondrium
- Layers of dense irregular fibres
- Chondrocytes in parallel layers
- Reduce tearing
- E.g. pubic symphysis, TMJ
where is each cartilage found? give examples
- Auricle of ear – elastic cartilage
- Epiglottis – elastic cartilage
- Intervertebral disc – fibrocartilage
- Meniscus of knee – fibrocartilage
- Symphasis pubis – fibrocartilage
- TMJ - fibrocartilage
- Thyroid cartilage – hyaline cartilage
- Articular cartilage of TMJ – hyaline cartilage
- Articular cartilage of hip joint – hyaline cartilage
what is the function of cartilage? what properties does it have?
- First but flexible, semi-rigid, bears mechanical stress without permanent distortion
- Functions:
- framework in the respiratory tract
- shock absorption and facilitation of joint movement
- covers articular surfaces
- development of long bones
what does cartilage consist of?
- Consists of cartilage cells (CC) suspended in an extracellular matrix (ECM)
- Most cartilage is surrounded by perichondrium (P)
- Cartilage is avascular
- chondrogenic cells
- chondroblasts
- chondrocytes
chondrogenic cells
- what do they do
- where are they located
- Differentiate into chondroblasts
- Located in the perichondrium
chondroblasts
- what are they
- what do they do
- where are they located
- what happens to them
- Metabolically active young cells
- Manufacture the matrix
- Located in the perichondrium
- Become entrapped in lacunae
- Mature in chondrocytes
chondrocytes
- what are they
- what do they do
- Mature cells
- Maintain the matrix
what is extracellular matrix composed of?
- Composed of ground substance and fibres (collagen & elastic)
Major components: - Proteoglycans – regulate movement of molecules through matrix
- Glycosaminoglycans – involved in shock absorption
- Glycoproteins – bind fibres, cells and the ground substance together
what are the two types of cartilage growth?
appositional and interstitial
appositional growth
- where does it occur
- what happens
- how common
- Occurs in perichondrium
- Chondrogenic cells transform into chondroblasts
- Chondroblasts mitotically divide and lay down matrix
- Most growth is appositional growth
interstitial growth
- what is it
- what does it do
- Mitotic division of chondrocytes
- Increases the size of the matrix from within
what does the perichondrium consist of?
- Outer layer – dense irregular connective tissue
- Inner layer – chondrogenic cells & chondroblasts
- Rich in blood vessels and lymphatics
- Afferent nerve fibres for pain transmission
what does bone consist of?
- Organic components (osteoid) – glycoprotein ground substance with type I collagen fibres – strong flexible but easily compressed
- Inorganic component – mineral salts mainly calcium hydroxyapatite
what does the osteon consist of? how are they aligned? what does compact bone consist of?
- Blood vessels
- Haversian canal
- Osteocytes in lacunae
- Canaliculi
- Concentric lamellae
Osteons aligned in same direction to increase unidirectional strength
- Concentric lamellae
- Interstitial lamellae – fill in the gaps
- Circumferential lamellae
- Volkmann canal
what are the interstitial and circumferential lamellae? what are the Volkamnn canals for?
Continuous resorption and redisposition results in new haversian systems being found amongst partially resorbed systems – the remnants of the partially resorbed systems form interstitial lamellae
The lamellar bone that surrounds the outside of the bone is the circumferential lamellae
Blood vessels from the periosteum enter through Volkmann canals and communicate with the vessels in the haversion canal
what are the characteristics of smooth muscle?
- shape
- nucleus
- striations
- location
- innervation
- Short, fusiform cells/spindle-shaped cells (wider in middle and taper as come to an end)
- Single, centrally located nucleus
- No striations
- Location – GI tract, visceral, vascular walls
- Innervation – autonomic
what are the characteristics of cardiac muscle?
- shape
- nucleus
- striations
- location
- innervation
- Short, branched cells
- 1-5 centrally located nuclei
- Striations (muscle tissue that features repeating functional units called sarcomeres)
- Location – cardiac walls
- Innervation – autonomic
what are the characteristics of skeletal muscle?
- shape
- nucleus
- striations
- location
- innervation
- Long, cylindrical cells
- Multiple, peripherally located nuclei
- Striations
- Location – attached to bone
- Innervation – somatic NS
describe the arrangement of skeletal muscle
Endomysium = connective tissue layer surrounding a single muscle fibre Fascicle = bundle of muscle fibres Perimysium = connective tissue layer surrounding a fascicle Muscle = group of fascicles Epimysium = connective tissue layer surrounding a muscle
- Where are the nuclei located?
describe the two different types of fibres
- how do motor units stain
- what is used as stain
- what do different muscle fibre types do
Slow twitch (type I):
- Involved in aerobic respiration
- Generate more ATP for continuous, extended contraction
- Fire more slowly
- Resist fatigue
- Rich in mitochondria & myoglobin – appear dark red in vivo
Fast twitch (type II):
- Use anaerobic respiration
- Good for short bursts of strength or speed
- Fatigue quickly
- Few mitochondria & little myoglobin
- Type IIa – intermediate fast twitch, use both aerobic and anaerobic respiration
- Type IIb – use only anaerobic
Stain (succinate dehydrogenase) more abundant in slow twitch fibres
All muscles have a mixture of slow and fast twitch fibres
- Aerobically respiring cells = dark staining
- Anaerobically respiring cells = pale staining
However, a motor unit will only have one type of fibre
Motor unit = one nerve fibre and all the muscle fibres it innervates
- Succinate dehydrogenase stain – identifies oxidative enzymes and is therefore used to distinguish between type I slow oxidative fibres and type IIB fast glycolytic fibres
- Type I fibres are small, contain many mitochondria and large amounts of myoglobin
- They are slow twitch, fatigue resistant fibres and are found in limb muscles of mammals
- They stain heavily with succinate dehydrogenase
- Type IIb fibres are large fibres that contain less myoglobin and mitochondria, they have high anaerobic activity and are fatigue prone
- They are adapted for rapid contraction and precise movements
- They are therefore located in the extraocular muscles and the intrinsic muscles of the hands
- These fibres appear pale when stained with succinate dehydrogenase
describe the histology of skeletal muscle
- tongue
- Tip of tongue – therefore contains a large portion of skeletal muscle
- Stratifies squamous epithelium forms the edge of the tissue but the remainder consists of skeletal muscle fibres
- The muscle is stained bright pink, the bundles of muscle fibres are running in different directions, so they may be seen in the longitudinal, transverse or oblique plane
- Longitudinal plane – each muscle fibre contains a number of nuclei – the nuclei are located along the edge of the fibre
- Transverse plane – muscle fibres appear as rings of tissue, the nuclei are again seen in the periphery of the rings
- Epithelium surrounding outside
- Parakeratinised epithelium (dorsum of the tongue)
- Non-keratinised stratified squamous epithelium
- Note fibre direction – longitudinal? Horizontal?
describe the transverse section of skeletal muscle
- what different layers can be seen
- what seen in each layer
- Individual muscle fibres are surrounded by a layer of connective tissue – endomysium
- Nuclei can be seen in the periphery of the fibres, just deep to the endomysium
- Bundles of fibres are grouped together and surrounded by another layer of connective tissue – the perimysium
- Fibroblasts can be seen in this layer, you may also see some blood vessels and nerves in this layer
- The whole muscle is surrounded by the epimysium, a dense sheath of connective tissue
muscle spindles
- what are they
- what do they do
- how do they lie
- what consist of
- what response
- innervation
- where found
- what stain
- Sensory receptor – detects fibre length
- Lies parallel to muscle fibres – so if muscle fibres stretch, these will also be stretched
- Consists of:
- spindle cells – nuclear bag fibres (more rounded in the middle) & nuclear chain fibres (just cylindrical) surrounded by an internal capsule
- internal capsule within fluid filled space surrounded by external capsule
- sensory nerve endings wrapped around spindle cells – detect stretch
- Reflex response -> muscle shortening
- Spindle cells also receive motor innervation from CNS by gamma receptors – regulates sensitivity of receptor
- They’re found in the perimysium
- Stained with Trichrome stain which stains connective tissue green
- The perimysium (connective tissue) surrounding the fascicles are clearly seen
- Located in the perimysium are muscle spindles, which are specialised stretch receptors involved in providing proprioceptive information about the degree of stretching and tension in skeletal muscle
- They are located parallel to muscle fibres
- External capsule
- Internal capsule
- Intrafusal muscle fibres (spindle cells)
