Organisation of the Peripheral Nervous System (PNS)
Describe the structural domains of neurons that allow signal integration and conduction of action potentials.
Synpases are neuron junctions, allowing them to communicate with each other.
For signal integration, a single neuron can receive thousands of synapses from many other neurons (both excitatory and inhibitory).
Spatial summation can occur, where multiple postsynpatic potentials from different synpases occur about the same time and are summed together. Goal is to reach potential threshold to send action potential
Temporal summation can also happen, where there is repeated rapid signals from the same synapse, which allows the postsynpatic responses to add together. Goal is to reach potential threshold to start an action potential
Most neurons receive thousands of synaptic inputs. Single synaptic inputs in neurons are small, therefore multiple inputs are needed to reach the threshold. This is reached through temporal and spaital summation of single postsynaptic potential.
Explain the roles of glial cells, myelin sheath, and nodes of Ranvier.
Glial Cells: Essentially support neurons. Involves cells like astrocytes, microglia, oligodendrocytes, ependymal cells in CNS and Schwann Cells in PNS.
Myelin Sheath: Covers axon of some neurons and Increases speed of AP conduction. A myelinated axon can ‘jump’ between Node of Ranviers, as the voltages generated cause spread. AP are generated, and still remain above threshold to continue generating action potential across nodes.
Demyelinated axons have ion leak due to no myelin sheaths. Therefore, spread is nto as far for voltage, and there is failure to produce AP at the next node.
Nodes of Ranvier have ion channels. They allow for the transmission of ions to depolarie and send AP down the axon.
Explain the significance of Na+ channel inactivation and directional action potential conduction in an axon.
Voltage-gated Na⁺ channels open rapidly when the membrane is depolarised.
This allows Na⁺ ions to rush into the neuron, further depolarising the membrane — the rising phase of the action potential.
Shortly after opening, these channels inactivate for a period known as the refractory period, even if the membrane remains depolarised.
As an action potential moves down the axon, Na⁺ channels behind the wavefront become inactivated.
This prevents the action potential from traveling backward (retrograde direction).
Explain how neural action potentials are transduced into chemical signals at the synapse using Ca2+-dependent release of neurotransmitter and how postsynaptic binding of the transmitter regenerates an electrical signal.
AP reaches the axon terminal of presynaptic neuron.
Voltage-gated Ca2+ channels are activated.
Ca2+ enters the synpatic knob in the presynpatic axon terminal.
Neurotransmitter is released by exocytosis into synaptic cleft./
Neurotransmitter binds to receptors which are part of gated channels on postsynaptic neuron.
Binding of neurotransmitter to receptor-channel opens specific ion channels, creating a postsynaptic potential.
Synapse can be:
Excitatory postsynaptic potential (EPSP) – depolarises the membrane (e.g., via Na⁺ or K+ influx).
Inhibitory postsynaptic potential (IPSP) – hyperpolarises the membrane (e.g., via K+ or Cl⁻ channel influx).
The neurotransmitter is quickly cleared by:
Reuptake into the presynaptic terminal.
Enzymatic degradation (e.g., acetylcholinesterase).
Diffusion away from the synaptic cleft
Describe how a mix of fast ligand-gated and slower G protein-coupled receptors found in neurons, allows integration of excitatory and inhibitory information.
Ligand-gated channels (fast) produce fast and localized responses. As neurotransmitter inds, ion channel opens directly, so can quickly excite.
G-protein-coupled receptors (slow) have to activate a G protein before ion channels are opened or closed. These can therefore be more controlled and act as inhibitors.
Explain the excitation-contraction coupling process.
Action potential sent along the motor neuron to NMJ (synapse between neuron and muscle fibre).
Causes presynaptic voltage gated calcium channels to open. Triggers release of acetylcholine (Ach) neurotransmitter in NMJ.
Ach binds to Nicotinic acetylcholine receptors (nAChR). Na+ channels are activated, and depolarisation occurs in sacrolemma and electrical signal sent down T-tubule.
Electrical signal activates dihydropyridine (DHP) receptors in the T-tubule membrane, which opens channels in the adjacent sarcoplasmic reticulum (which stores Ca2+)
SR Ca-release channels release calcium into the cytoplasm.
Describe the essential molecular components and structural organization of the muscle.
Muscle fiber is the muscle cell. Contains contractile structures called myofibrils.
Myofibrils divided into sarcomeres, which have overlapping patterns of thick and thin filaments. Z-lines anchor filaments.
Myosin = Thick Filament
Actin = Thin Filament
Tropomyosin: t
Troponin: Binds to Ca2+. Acts as a switch, and moves tropomyosin to expose the myosin-binding sites for contraction.
Ttransduction of a chemical signal into physical work (contraction),
Ca2+ exposes the active sites for actin binding on the troponin-tropomyosin complex.
Excited:
- Muscle fibre is excited and Ca2+ released.
Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding.
Cross-bridge binding occurs.
Binding of actin and myosin cross bridge triggers power stroke that puls thin filament in during contraction.
and the significance of the length-tension relationship in understanding the mechanics of contraction.
Explain physiological and pathophysiological conditions of shivering, botulism, and rigor mortis.
Understand the overall roles of sensory receptors in the body to maintain homeostasis.
Sensory receptors detect stimuli and carry the information to the CNS through an effe
Understand at a basic level, the transduction and integration of stimulus, receptor, sensation, and perception in the formation, transmission, and adaptation of an action potential to the CNS for higher order processing.
Stimulus occurs (internal or external). It is a change in the environment which elicits response.
Receptor accepts the stimuli, and converts the energy into electrical energy.
Stimulus is converted into an action potential, which travels via afferent pathway (nerve fibre) to the CNS.
CNS converts the stimuli to a perception and processes it as a sensation etc..
Understand the difference between an encapsulated sensory receptor and a bare or free sensory receptor.
Encapsulated sensory receptor:
Characteristics:
High specificity
More complex
Fast adaptation to stimulus
Dendrite is covered by an encapsulation (CT + Layers of collagen)
Sensitive to abrupt changes like stretch, vibration, pressure.
Non-Encapsulated sensory receptor:
Basically a normal dendrite in sensory neuron.
Lower specificity
Less complex
No complex sensory structure
Higher sensitivity to stimulus:
Painful stimuli (Nociceptors)
Thermal (Hot + Cold) Thermoreceptors
Light Touch (Merkel)
Explain the basic structure, function, and location of the 5 main types of mechanoreceptors in the skin and understand that these categories are based on different stimulus modalities (including Meissner's corpuscles, Pacinian corpuscles, Ruffini endings, Merkel's disks and Krause end bulbs).
Mechanoreceptors (Involved in touch + vibration)
Encapsulated mechanoreceptors:
Ruffini Corpuscle
Structure:
Spindle-shaped
Axon terminals of periodontal Ruffini endings have finger-like projections called axonal spines (shaped like a x-cross)
Axon spines project and detect collagen fibre deformation.
Function:
Primary PDL mechanoreceptor
Role in sense and finger control
Detects:
Skin stretch / joint deformation
Sustained pressure
Acting as thermoreceptor
Allows object grip
Location:
Deep layers of skin + PDL
High density around fingernails
Krause end bulb
Structure:
Cylindrical/berry-like shape
Encapsulated with CT
Semifluid media
Function:
Detects cold less than 20 degrees celsius
Location:
Only found in specialised regions
Superficial in skin
Mucosa of lips and tongue, gential regions
Some synovial joints
Pacinian Corpuscles
Structure:
Large + encapsulated
Concentric rings of lamellae
Encircles a single 1˚ (primary) afferent terminal fiber
Fluid deformed with pressure, converted into action potential
Function:
Deep touch, high vibration
Rapidly adapting, large receptive field (holding objects)
Location:
Deep in skin/beneath epithelium
Found in hard palate, gingiva + PDL
Meissner’s Corpuscles:
Structure:
Horizontally elongated, ellipse shape
Schwann Cells + Central Axon
Encapsulated with collagen fibres + well-defined borders
Function:
Rapidly adapting receptor
Responds to fine detail + touch
Location:
High densities in gingiva, tongue + hard palate
Projects into epidermis
Dermal papilla/ papillary ridges
glabrous skin (lips, fingertips, nipples & eye) hairless areas
Unencapsulated Mechanoreceptors:
Merkel Discs
Structure:
Thin projecting microvilli
Dense vesicles
Function:
Sensitive light touch
Slow-adapting
Location:
Glabrous skin (dense in fingertips).
Near base of epidermis
Palms, fingers, feet soles
Also lips, gingiva, buccal mucosa, soft palate, PDL + tongue
• gingiva, tongue & hard palate (high densities)Understand the function, structure, and locations of nociceptors, thermoreceptors, proprioceptors, and chemoreceptors and explain the differences between these receptor types.
Nociceptors (Pain Receptor)
Structure:
Unencapsulated
Has a slow (unmyelinated) and fast (myelinated) pathway
Function:
Detect pain. Different pain receptors for tissue damage, thermal, chemical etc.
Threat signals to CNS
Alert to damage
Little adaptation
Thermoreceptors (Temperature)
Structure:
Non-myelinated (slow fibres) / pathway
Activated by different temperatures
Non-specalised nerve endings
Function:
Thermal regulation (detecting harmful thermal stimuli)
Sensitive to skin temperature changes
Receive multiple stimuli, therefore slow.
Send action potential at baseline rate when skin is at a preferred temperature range
Location:
Dermis, skeletal muscle, GIT, Liver + Hypothalamus
Free-nerve endings
Mechanoreceptor - Proprioreceptors
Detects muscle fibre + tendon tension
Provides information about mechanical forces coming from muscoskeletal system + other body parts.
Highly sensitive to mechanical changes like pressure, stretch, movement.
Proprioceptive fedback derives in large part from specialised mechanorecpetive organs in skeletal muscle.
Proprioreceptors found in golgi tendon organ and muscle spindles, detecting muscle fibre stretch + tendon tension.
In muscle spindles
Structure:
Fusiform shape
Encapsulated intrafusal muscle fibre
Stretch receptors with a fibrous, fluid filled capsule surrounding muscle fibres
Function:
Coordination of limb/joint position + movement
Detecting muscle length through AP discharge to CNS.
Fine muscle movements
Fire AP when muscle lengthens
Location:
Within skeletal muscle core
Found in nearly all skeletal muscles
In Golgi Tendon organ
Structure:
Golgi tendon oran made up of braided collagen strands
Encapsulated proprioceptors
Terminal branches of a large diameter afferent fibre intertwined with collagen bundles
Function:
Sensing muscle tension change
Monitor contraction of motor units
AP to spinal cord. Very low threshold to stimuli
Location
Myo-tendinous (junction or connection between muscle and tendon) of skeletal muscles
Chemoreceptors - Taste
Structure:
Elongated cells with microvilli extending into taste bud pore.
Increased surface area for receptors
Function:
Chemoreceptos for taste called gustatory cell
Dissolved food molecules interact with chemoreceptors
4 distinct gustaphore types (acid, sweet, salt, bitter)
Sodium is stimulus for salt taste, protons for sour. Stimuli opens ion channels, depolarising and therefore sending AP for nerve signalling
Location:
Dorsal surface of tongue
Papillae
Taste buds
Chemoreceptors - Olfaction
Structure:
5-20 cilia per dendrite
Connection to olfactory bulb
Bipolar neurons buried in olfactory mucosa
Function:
Odour molecules breathed in are tiny + airbone and dissolve in mucus.
Substances stick to receptors on cilia, which triggers AP.
AP sent to brain via olfactory bulb
Location
Nasal mucosa
Nasal cavity roof
Olfactory bulb.
Identify the gross and histological nature of the ANS.
Gross:
Sympathetic nervous system (SNS)
Parasympathetic nervous system (PNS)
Preganglionic neurons (from CNS to ganglion)
Ganglia (relay stations)
Postganglionic neurons (from ganglion to target organ)
Histological:
A ganglion is a cluster of neuronal cell bodies that are outside of the CNS
Identify the physiology of receptors and the basics of signal transduction mechanisms.
Preganglionic fiber on the axon releases a preganglionic neurotransmitter that ibds to cell body of postganglionic fiber
Transmits signal.
Variscosities of postganglionic fiber release neurotransmitters which bind to receptor on effector organ for response.
Cell body of first neuron in series is in the CNS. The preganglionic fiber in axon synapses with cell body of second neuron in region called ganglion.
Both SNS and PNS preganglionic fibres secrete ACh, acetylcholine
SNS postganglionic fibres release NAd (Noradrenaline) and Ad (Adrenaline)
PNS postganglionic gibres release ACh
Identify the role of the ANS in maintaining physiological homeostasis.
ANS controls basic organ system functions
e.g., Cardiovascular
Gastrointestinal
Thermoregulation etc..
Elements of other systems
e.g., Respiration (airway resistance)
acts independently
Conscious input negligible (except via pharmacology)
Sympathetic NS
Fight or flight response
Catabolic – breaking things down
Systemic response since life or death
Origin- thoracic and lumbar regions
b) (most) SHORT preganglionic fibres
c) Synapse with postganglionic neurons in Ganglia that lie along the spinal cord – the sympathetic ganglion chain
d) LONG post ganglionic fibres that
terminate in effector organs
Parasympathetic NS
Housekeeping functions (rest and digest)
Anabolic – building things up
Directed response
Parasympathetic (PNS)
a) Origin- CRANIAL and SACRAL regions
b) LONG preganglionic fibres
c) Terminal ganglia are near effector organs
therefore, SHORT postganglionic fibres terminate on effector organs
Typically, there is a dual innervation and control of both SNS + PNS to most visceral organs. This way, there is more control. Organs can increase/decrease activity quizkly. and body can adapt according to pace.
Describe and contrast the main local and long-distance modes of cell-to-cell communication including neural, autocrine, paracrine, and endocrine communication.
Two basic types of physiological signals
1) Electrical - Changes in membrane potential. Electrical depolarisation across heart ( contraction of atria + ventricle)
2) Chemical - In form of hormones + neurotransmitters.
Chemical signals are used for both local and long distance communication. Can be hormones which carry information to target organs (rather than transmitting info via nerves). In endocrine, speed of communication is slower than nervous system, but lasts longer).
Spread of electrical depolarisation (action potential) along nerve axon
Release chemical neurotransmitter from terminal whcih diffuses acros ssyapse and binds to receptors on target cells.
Target cells need specific receptors for chemical substrate.
Neurohormones:
Chemicals released from neurons that diffuse into blood stream. Process is faster and lasts longer.
For sustained function, extensive communication is needed between cells in the body.
Local cell-cell communication
Gap Junctions
Direct cytoplasmic bridge type connections between adjacent cells
Function:
Provide electrical pathways for spread of electrical signal from cell to cell. Permit depolarisation of cardiac muscle cells
Channels open and close to regulate movement of ions.
Contact-Dependent Signals
Involves interaction between membrane molecules on two cells
A adhesion molecule connects the cell to adjacent cell
Function:
Coordinate development + differentiation of tissues
Autocrine + Paracrine Signals
Chemicals secreted from one cell type which then acts on neighbouring cells of a different type (paracrine) OR acts on the original secretory cell (autocrine)
Function:
Help with growth and other processes
Long-distance mode of cell-cell communication
Endocrine
Chemical diffuse into blood stream (hormones) to reach target cells.
Elicit effect over much longer distances
List the main endocrine structures, their hormones, and broad actions.
Pineal Gland, Melatonin, Involved in establishing sleep-wake cycles
Pituitary gland, Various tropic hormones, Regulate hormone release from peripheral glands
Thyroid, T3 + T4, Regulate metabolic rate
Parathyroid, Parathyroid hormoe, Regulate calcium levels in body fluids
Adrenal Gland, Cortisol;aldosterone;adrenaline, Resist stress, H20 balance and metabolism.
Compare and contrast exocrine and endocrine glands.
Endocrine glands are ductless and release hormones into the surrounding fluid
Exocrine glands have ducts and substances (non-hormonal) travel along these to a surface.
Some organs, like pancreas and stomach have both exo + endo functions.
List and describe the main hormone types, their biochemical properties, and modes of action.
Peptide + Protein Hormones:
Amino acid chains
Synthesises like normal proteins (transcription + translation
Stored in secretory vesicles prior to release
Typically have a short half-life (time taken for concentratin to drop by 50%)
Lipophobic (hydrophilic) - transported freely in bood but can not cross plasma membrane
Steroid Hormones:
All derived from cholestrol.
Synthesises in SER of gonads, adrenal glands + placenta.
Largely bound to carrier proteins in blood for extended half-life
Lipophilic (Fat-loving) - Can cross plasma membrane
Alters protein synthesis
Amine hormones:
Amino acids with modified groups
I.E. Thyroid hormones (Acts like steorid)
Hydrophobic
Intracellular receptors
Activates genes
Half-life of a few days
Catecholamines
Hydrophilic
Cell surface receptors
Activate second messengers
Describe the main categories of cell surface and intracellular receptors for first messengers (hormone and neurotransmitter molecules).
The response of a target cell to a signal molecule depends on whether it has the specific receptor for that molecule.
Liphophobic or liphophilic signal molecules bind to receptors on surface of cell membrane
Lipophilic signal molecules diffuse through cell membrane and bind to receptor in cytosol or nucleus.
I.E. Ligand (Molecule that binds to receptors) binds to a cell membrane receptor.
Ligand-receptor complex triggers intracellular response (second messengers) which transmit signal within cell.
I.E. Steroid hormones diffuse and bind to receptor proteins. It is now a ligand-receptor complex.
It attaches to specific sites on DNA and alters transcription of genes. Manufactures new proteins in various different forms.
Different types of cell surface receptors
Receptor channel
Some receptor proteins can form channels
Binding of liand to receptor opens/closes channels
Receptor Enzyme
Ligand binding to a receptor-enzyme activates intacellular enzyme, often involving production of secondary messengers.
G protein-coupled receptor
All the proteins cross cell membrane several times.
Ligand binding to this opens an ion channel or altrrs enzyme activity
Integrin:
Ligand binding to integrin receptors alter cytoskeleton conformation, activates downstream signaling pathways, regulating processes like blood clotting, wound repair, cell adhesion + recognition and immune responses.
Describe how membrane receptors and downstream pathways can produce amplification of a signal.
Receptor-ligand complex activates an amplifier enzyme, resulting in many second messengers. These signals produce responses in target cell by altering activity of enzymes, ion channels, transporters,g enes, etc..
Describe how hormone secretion is stimulated, regulated, and the various patterns of secretion.
Hormone release is stimulated through:
Hormonal:
Stimulation from other hormones (known as tropic hormones)
I.E. Pituitary gland is known as master gland. It releases lots of hormones which bind to and activate receptors located on cells of other endorcine organs, stimulating hormone release
Neural:
Stimulaltion from nerve fibres
Humoral:
Endocrine tissue secretes hormone in response to changes in concentration of substances.
I.E. Parathyroid glands releasing PTH in response to drop in calcium conc in plasma.
Hormone secretion is regulated bv:
Simple endocrine reflex involves a direct hormonal response to a stimulus.
I.E. Low plasma calcium
Parathyroid releases PTH, which increases bone resorption, reabsorbs calcium in kidney, and production of calcitrol leads to intestinal absorption of Ca2+. Increase calcium.
Neuroendocrine reflex:
Not direct. A neural signal occurs first through a neurotransmitter or neurohormone, then triggers the release of one or more hormones, leading to a physiological response.
Patterns of hormone secretion:
Episodic
In response to stimulus
Pulses during day/night
Circadian natural oscillation that repeats roughly every 24 hours
Monthly (periods)
Seasonal (Animals)
Describe examples of negative and positive feedback regulation of hormone secretion.
Negative feedback: I.E. Blood glucose levels are maintained within a narrow range by the opposing actions of hormones insulin + glucagon.
When blood glucose levels rise, beta cells release insulin, facilitating glucose uptake to decrease blood glucose.
When blood glucose levels drop, alpha cells release glucagon, prompting glucose release from liver, increasing blood glucose.
Positive feedback for hormone secretion:
Ferguson reflex, where uterine contraction releases oxytocin, which stimulates further uterine contraction until childbirth is achieved.
List factors affecting hormone concentration in the plasma.
Rate of secretion is the most key influencer of the concentration of active hormone. This isr regulated.
Majority of hormones in blood is bound to plasma proteins. The rate of binding to carrier proteins. Only free active hormones in plasma can interact with receptors.
Rate of metabolism also actives/degrades hormones.
List the varied and important roles of calcium in the body.
Calcium is important for neurotransmitter + hormone release (stimulus-secretion coupling).
Excited cells such as neurons which release transmitters
Maintatining cellular integrity
Cardiac + Skeletal muscle contractility
Bone + Teeth Structure and Strength
Co-factor for blood clotting
Control of calcium channels
Excitability of nerves
When calcium concentration is too low, neural tissue is highly excitable. Easier to trigger action potential and threshold for ap activation is decreased. This can cause hypocalcemia.
Describe and explain (at a basic level) the clinical signs of hypocalcaemia (Chvostek’s & Trousseau’s signs).
When the facial nerve is tapped at the angle of the jaw, the facial muscles on the same side will contract momentarily (like a twitch)
Hypocalcaemia is not always associated with chvostek’s sign.
Chvostek’s sign is absent in about 1/3 of patients with hypocalcemia and present in approximately 10% of people with normal calcium levels.
Trousseau’s signs is seen when a blood pressure cuff is placed around the arm and inflated over the systolic blood pressure. The muscles of the hand and forearm will spasm without control.
This is mostly associated with hypocalcaemia, present in 94% of patients with it. and 1% of patients with normal calcium levels.
Describe the location of the parathyroid glands.
On the posterior surface of the thyroid. Bow-tie shape.
Describe the effects of parathyroid hormone on bone, calcium and phosphate excretion via the kidneys, and calcium absorption via the intestine.
PTH effect on bone:
Moves calcium rapidly from bone canaliculi into plasma through membrane-bound calcium pump.
Activates osteoclast activity and affects mineralised bone stores to slow exhcange calcium into plasma.
Raises plasma calcium by withdrawing it from these ‘bone banks’
PTH effect on kidneys:
Conserves calcium and removes phosphate by altering reabsorption at the level of the distal tubules.
Enables kidneys to pump calcium back into the plasma instead of going out as urine. Done through nephrons which filter blood and reabsorb back into blood stream.
PTH effect on intestine:
Kidneys have enzymes which activate vitamin D (active form called calcitrol)
Vitamin D increases intestinal absorption of calcium
PTH therefore increases enzyme activity to increase vitamin D activation for more absorption.
Describe the mechanism of action of vitamin D with regards calcium absorption.
Vitamin D increases calcium uptake across intestinal epithelia.
1) It increases production of calcium channels, allowing more calcium to enter enterocytes.
2) Increases amount of calbindin, a calcium-bindign transport protein, which moves calciium across cytoplas safely.
3) More calcium pumps, which move calcium out of membrane into bloodstream to be absorbed.
Describe the role of calcitonin in protecting the skeleton in times of extreme calcium demand (pregnancy, breastfeeding etc.).
Inhibits Osteoclast Activity
Calcitonin directly inhibits osteoclasts, the cells that break down bone (bone resorption).
This helps reduce the release of calcium from bone, protecting the maternal skeleton.
Preserves Bone Mass
By suppressing bone breakdown, calcitonin helps maintain bone density, especially during times of high calcium loss.
Acts as a “Brake” on Bone Loss
In conditions like pregnancy and lactation, other hormones (like PTH and PTHrP) promote calcium release from bone.
Calcitonin acts as a counterbalance, limiting excessive bone resorption.
To understand how radiographic images are produced
Latent image:
Analogue - the exposed but undeveloped image formed on a radiographic film as a result of a physical change in silver halide crystals due to their interaction with x-rays
Identify the steps in process, cells involved, and bone types formed via endochondral ossification and intramembranous ossification.
intramembranous ossification = mineralisation of matrix secreted by osteoblasts. Mesenchymal stem cells differentiate into osteoblasts, which lay down bone matrix.
Firstly occurs withn a layer of mesenchyme.
1) Ossification centre - Mesenchymal cells differentiate into osteoblasts (centre of ossification)
2) Calcification - osteoblasts secrete osteoid first (unmineralised matrix) then become calcified. Some osteoblasts become surrounded by matrix and turn into osteocytes.
3) Formation of trabeculae: Spicules of bone are separated by vascular mesenchyme, which unite to form trabeculae network (parts of spongy bone)
4) Development of periosteum: New woven bone is then remodelled to lamellar bone, where compact bone forms.
Endochondral ossification = Bone matrix deposited on cartilage matrix.
1) Cartilage changes. Growth, calcification and then degeneration
2) Ossification. Bone-forming tissue invades spaces left by cartilagnous degeneration.
1) Mesenchymal cells differentiate into chondrocyte to form hyaline cartilage.
2) Cartilage increases in length via interstitial growth and width via appositional growth
3)Chondrocytes grow in size, calcify, and then die as nutrients cannot go through calcified matrix,
4) Voids are left behind and blood vessel grow in them.
5) Osteoblasts come in and form bone on the calcified cartilage,, leading to bony formation of trabeculae.
6) Osteoclasts break down some bone to form the medullary cavity.
7) Secondary ossification centres form in the epiphyses (end of bones). These replace cartilgage.
8. Layer of epiphyseal cartilage forms between epiphysis and diaphysis, which allows bone to grow in length during childhood.
Understand the role of epiphyseal cartilage and changes that occur within the epiphyseal plate (histologically), that allow long bones to grow in length.
Epiphyseal cartilage needed for growth of long boens.
There aere five layers of cells
Resting Zone - Chondrocytes are present and produce matrix.
Proliferative Zone - Chondrocytes divide and produce more matrix
Hypertrophic Zone - Chondrocytes increase in size
Calcification Zone - Cartilage matrix becomes calcified.Chondrocytes die due to lack of nutrients. Forms a scaffold for new bone
Ossification Zone - Osteoblasts swarm up and deposit bone over left-over cartilage
Describe the growth of upper limbs, lower limbs, and the mandible, including the processes involved and how they change with age.
Epiphysis enlarges by growth of cartilage and replacement with bone.
upper limb
• growth at wrist and shoulder
• (proximal end of humerus;
distal ends of radius & ulna)
lower limb
• growth at knee
• (distal end of femur; proximal
ends
of tibia & fibula)
Mandible:
A) Newborn:
Thin bone with tooth sockets
Two halves joined by fibrous mandibular symphysis, which is replaced by bone every second year.
Cartilage present at future condyle of madible is ‘growth plate’
B) 6 year old
Body of mandible grows via intramembranouse ossification
Ramus height achieved by encochondral ossification of condylar cartilage
C) Adult
Growth stops at around 20 years.
Condylar cartilage replaced by bone.
Demonstrate an understanding of:
how complex organisms and structures have come into existence;
Natural selection and evolution. Living things changed or evolved over time and turned into complex organisms.
what forces have operated to mold adaptive characteristics; and
Changes in environment have meant that organisms have possessed adaptive features specifically designed to flourish in the environment lived in.
Species change as climate changes, and there are variations of the same species as climate changes.
E.G. Humans closer to the equator have become darker, shorter and more robust, while at the poles, it is the opposite.
how diversity originates in the living world, and how it is maintained.
Can be through:
Non-random mating (inbreeding)
Random genetic drift
Gene flow (allele flow between populations)
Mutation - ultimate source of all genetic variation
Random, non-adaptive, recurrent.
Germinal changes in:
Chromosome number or structure
Individual gene structure (point mutation) {Single Nucleotides}
Changes in nucleotide sequence causes allelic variation.
Mutations can result in more favourable cahracteristics. ‘Survival of the fittest’, meaning more likely to produce progeny with these favourable characteristics in high frequencies. Easily adapt to environment.
Appreciate the development of modern evolutionary theory.
Modern evolutionary theory is called ‘The Origin of Species’ by Charles Darwin.
It combines three prior theories:
Malthus ‘Principles of Population’ - Most organism populations grow exponentially in absence of resource competition. Species expansion is limited by local resources.
Lamarck ‘Evolution of acquired characters’ - Favourable characteristics allowing organs to better compete for resources were adapted over time E.G. Giraffe necks kept stretching to reach higher for tree leaves in diet.
Lyell ‘Principles of Geology’ - Earth was old and constantly changing through volcanic activity + tectonic plate shift. Earth is never static, and constantly changes.
Charles Darwin’s theory
Recognised vast age of the Earth
Rejected the idea that the Earth has largely been shaped by sudden, short-lived, violent events instead of gradual changes.
Rejected the idea of a ‘perfect’ organism. (No-one is perfect, always undergoes changes for environment adaptation)
Rejected the idea of special creation (that there is one creator of the world).
Replaced typological thinking (static + unchanging organisms) with population thinking (organisms adapt and change in environment).
Abolished anthropocentrism (idea that man was the perfect organism/creator of all natural variation in environment)
Only some organisms survive as there is a struggle for existence among individuals within a population, largely due to limitation of natural resources.
Individuals with favourable variation more likely to survive and reproduce. Favourable characteristics are inherited over generations to continuously adapt.
Accumulation of variation/adaptation over many generations is evolution.
Understand how natural selection (amongst other things) acts to change allele frequencies in populations, allowing adaptation to environmental change.
Natural selection acts indirectly through phenotype to alter genotype frequencies.
Type of selection
Stabilising selection
Average (intermediate) traits are favored.
Extremes are selected against.
Reduces variation, maintains status quo.
I.E. Children born underweight or overweight less likely to survive
Directional selection
One extreme trait is favored over others.
Causes allele frequency to shift in one direction.
Example: Agriculture - Low wheat yield to maximum amount.
Disruptive selection
Both extremes are favored over the average.
Can lead to speciation, meaning species diverges into two distinct species.
Example: Birds with either very short or very long beaks do better than those with medium-length beaks.
Demonstrate a basic understanding of the modes of speciation.
Speciation creates new biological species
Biological Species Definition: A population of individuals that are genetically similar enough to be capable of interbreeding viable, fertile offspring.
Genetic differences can act:
Indirectly through phenotype - Two individuals who look or behave too differenly may not recognise each other as mates
Directly during fertilisation/embryogenesis - Egg and sperm cannot combine, or embryo fails to develop due to genetic differences.
Morphological similarity does not imply genetic similarity:
Just because two organisms look alike, doesn’t mean they are genetically similar.
Some species evolve similar features independently.
Modes of Speciation:
Phyletic
A single species gradually changes over time into a new species, without branching. due to slow environmental changes. Original population accumulates small genetic changes to the point that it becomes a new species. Old species is replaced.
Cladogenic
A species splits into two or more distinct species — a branching proces
Each population becomes genetically isolated and the groups evolve separately.
A branching tree — species A → species A + species B.
Allopatric Speciation (Different place)
A population becomes geographically separated and become different species.
Peripatric Speciation (Separation)
Group of animals or plants breaks off from the main population.
This small group moves to a new, isolated place and become a new species, different from original big group.
Parapatric Speciation (Next to each other)
Speciation occurs between populations that are adjacent, but experience different environments, but no physical barrier.
I.E. Plants growing on contaminated vs. normal soil gradually diverge.
Sympatric Speciation (Same Place)
Speciation occurs within the same geographic area, without physical separation.