BIO 224
Physiology- the scientific study of how various parts (cells to organs) of an organism function
Anatomy- the scientific study of body structure
A structure without a function has no relevance, therefore physiology and anatomy are connected.
January 8- evolutionary aspects of the animal kingdom
What is an animal?
- Colloquial use for word refers to non-human animals
- Biological definition refers to all members of the animal kingdom
- Having breath or having soul
Characteristics
- Multicellular eukaryote that lacks cell wall (not a plant cell, and contain a nucleus)- red blood cells do not have nucleus (smaller, more oxygen intake), still considered eukaryote
- Heterotroph
- Motile at least at some time in their lives
- Reproduces asexually or sexually (in most)
- Most have nerves and muscles
Diversity
There are more then 1 million known animal species
-diverse species, habitats, and characteristics
Evidence of animal species
-Biologists agree the common ancestor was a colonial flagellated protist in the Precambrian (700 million years ago MYA)- all animals come from single common
- like a modern colonial flagellated species- the choanoflagellates
-supported by morphological and molecular evidence
-Some cells may have taken on specialized functions
There are 35 recognized animal phyla
- Phyla can be grouped into clades, based on shared characteristics
Cells in these protists gradually became more specialized and layered. Hypothesized evolution of a two layered animal body plan
Cell walls and central vacuole are used to keep plant cells stable, in animals the extra cellular matrix and the cell junctions keep the tissue stable. The resistance to change, the proteins within the matrix (proteoglycans, collagen fibers, polysaccharide molecule, integrin, and fibronectin) help with structure strength, and support. They attach to other proteins to keep structure.
Collagen fibers-
Cell junctions-
Anchoring- connects the cytoskeleton to the other cells and the matrix
Tight- extremely tight, hold cells so close that things can’t pass through
Gap- hold cells together, but have openings allowing for ions to move between cells
Function of esophagus cells- stratified squamous epithelial cells
- For protection, when you swallow cells from the layer also get swallowed
Function of stomach cells-
- Need for secretion of hydrochloric acid (for digestion)
January 10th
Classifying animals
Animal body plans are influenced by:
1. Embryonic development pattern (protostomes vs deuterostomes)- single to multi- cellular organisms
- Most animals will undergo some form of sexual reproduction (asexual or sexual)
Asexual: budding in hydra, fragmentation inn echinoderms and parthenogenesis in insects and some reptiles
- Germ line cells undergo meiosis to produce haploid and gametes
- Gametes fuse during fertilization to form a diploid gamete
Zygote cleavage- follows fertilization, the division of cells in the early embryo
- Zygotes undergo rapid cell cycles with no significant growth
- Zygote develops into a compact mass of cells termed morula
- Morula derives into a hallow sphere of a single layer of cells, termed Blastula (only animals)
- Protostomes and deuterostomes have different cleavage patterns
- Animal pole develops faster than the vegetal pole
Cilia- movement, move liquid around to move nutrients
- Protostomes exhibit spiral cleavage- newly produced cells lie in the space between the cells immediately below them
- Each cells development path is determined as the cell is produced
Determinant cleavage- meaning that each blastomere is unable to develop into a complete organism by itself
- Deuterosotrmes exhibit radial cleavage- newly produced cells lie directly above and below other cells of the embryo
- Developmental fates of the first few cells are not determined
Indeterminant cleavage- meaning a cell removed from the morula will go on to form a complete organism
Gastrulation follows cleavage
- Begins at the vegetal pole
- Blastula invaginates and undergoes further differentiation into 2 or 3 (most animals) germ layers:
- Ectoderm, mesoderm, and endoderm
- Trying to crate digestive tract, formed before other organs in the body
- Germ layers differentiate to form tissues and organs
2. Germ cell layers (diploblasts vs. triploblasts)
Diploblastic animals (jellyfish, corals, anemones)- Have 2 germ layers (ecto and endo)
Triploblastic animals (flatworms, chordates)- Have 3 germ layers (ecto, meso and endo)
Endoderm
- Innermost layer that forms lining of the gut
- Digestive tract
Mesoderm
- All the organs but the nervous system
- Middle layer between the others
- Forms muscles of body wall and most other structures between gut and external covering
- Muscle and skeleton
Ectoderm
- Outermost layer
- Forms external covering and nervous system
- Skin and nervous system
Tissues- groups of similar differentiated cells specialized for particular functions, usually isolated from other tissues by membrane layers.
Polarity of the digestive system-
-blastopore develops first, another opening at the opposite end of the embryo develops. The second opening transforms the pouch-like gut into a digestive tube
Coelom- scientific term for body cavity
Protostomes- mesoderm differentiates near the blastopore (near the bottom)
- Coelom originates as a split in the mesoderm (schizocoelum (split)
- The mouth forms fist, then anus
- triploblastic
Deuterostomes- mesoderm originates from outpocketings of the archenteron (primitive gut)
- Coelom develops from space within the outpocketings (enterocoelom (“intestine)
- Anus forms first than mouth
- Triploblastic
Lecture 3 slide 17 (good comparative)
3. Body Symmetry
Radial symmetry- can be divided equally by any longitudinal plane passing through the central axis (sea star)
- All are diploblastic
- Do not have a left or right side, have a top and a bottom
- Often circular or tubular in shape with a mouth at one end
-
Bilateral symmetry- can be divided along a vertical plan at the middle to create two identical halves (Humans)
- Triploblastic
- Balanced supplicate distribution of most body parts (not too livers)
Specialized head with feeding and sensory organs(cephalization)
Digestive chamber with two openings, mouth and anus
- Most animals with bilateral symmetry contain segmentation (not just mammals, also annelids, arthropods, chordates)
Segmentation- repeated structures along the anterior-posterior axis. Advantages in movement and specialization
4. Body Cavity Types
Deuterostomes Body Cavity (COELOM)
- In most bilaterally symmetrical, animals, a body cavity (coelom) separates the gut form the body
- A fluid-filled cavity between the intestines and the body wall (formed within the mesoderm of the embryo)
- Most animals are coelomate (Eucoelomate)
Protostomes Body cavity
Acoelomate (not hallow)
- No body cavity
- Flat worms (phylum Platyhelminthes)
Pseudocoelomate (false)
- Pseudocoelom: fluid-filled or organ-filled space between endoderm and mesoderm
- Roundworms (phylum Nematoda)
Why do we study animal diversity and evolution?
- Animals and animal body systems have a common evolutionary history
- Help us to learn common principles
- Animals occupy very diverse types of environments
- Helps us understand environment
The physiological phenotype is a product of the genotype and the environment
Respiratory system adaptation
Human- tidal flow Fish- floe through Bird- circular flow
Challenges for animals
- Extract nutrients and O2/ energy from the environment
- Eliminate toxic metabolic wastes from the body
- Sense the environmental changes and respond favourably
- Maintain near constant body condition
Unifying Concepts
Animals are diverse, yest some common principles apply to all animals
Physiological processes must:
- Obey the laws of physics and chemistry
- Usually tightly regulated (homeostasis)
Homeostasis- regulation of the body’s internal environment at or near a stable level, homeostatic mechanism result in only small internal changes compared to the outside environment that changes a lot.
Goal- to have an optimal physiological performance by maintaining:
Temperature, nutrient concentration, O2 concentration, CO2 concentration, concentration of waste chemicals, pH, water and NaCl concentration
Homeostasis regulates a physiological variable within a narrow range around a set point
Regulatory mechanisms include
Negative feedback (primary method)
- Variable rises above the set point
- Negative feedback mechanisms return the variable back towards the set point
- Ex) minimize difference between actual level and the set point
Positive feedback
- Moves variable away from set point ex) amplifies difference between actual level and the set point
- Used to quickly increase (or decrease) a process
- Amplification effect eventually shut off negative feedback
Ex) childbirth- brains triggers the release of hormones, which enter blood and increase the strength
- Membrane potential, rising phase of the nerve action potential (AP)
Feedforward
- Future needs are anticipated
- Physiology is adjusted in advance
- Often involves learning and complex behaviours
Thermoregulation
Thermogenesis- heat production through physiological processes
Endotherms- get heat from internal physiological sources (mouse)
- Physiological processes happen at the same time
- Can create own body heat
- Need to maintain high metabolic rate (eat food)
- As environmental temperature decreases, animals metabolic rate increases causing body temperature to increase
Ectotherms- get heat from external environment (lizards)
- don’t need as many nutrients (less food)
-less effective because of slower body processes
- body temperature decreases as environmental temperature decreases
- causes biochemical and physiological processes to slow down
(Neither is truly more superior to the other, it is about adapting
-Constant vs variable body temperature
Homotherms-maintain a body temp at a constant level/range
e.g.) mammals, birds, dinosaurs
Heterotherms- Vary between self-regulating their body temperature and allowing the surrounding environment to affect it
e.g.) reptiles and amphibians
Are all endotherms, homotherm? No, many birds are not both, as well as squirrels
Ectotherms in all invertebrate groups
- Most aquatic invertebrates are limited thermoregulators
-but some use behavioural responses to regulate body temperature
- Terrestrials’ invertebrates regulate body temperatures more closely
- Some use a combination of behavioural and heat-generating physiological mechanisms
Fishes
- Body temperature of most fishes remains within one or two degrees of the aquatic environment
- Many fishes use behavioural mechanisms to regulate temperature
- Deeper down = colder
Amphibians and reptiles
- Body temperatures closely match environmental temperature
- Can move to different locations to regulate
- More pronounced among terrestrial reptiles
Endotherms: birds and mammals
Physiological and behavioural responses to changes in skin and core body temperature- signal to the brain saying core temp has changed
Use of negative feedback loops (like a thermostat)
- Maintains a balance between the heat loss and the heat gain
Sheep’s response to warm environments- sweating and panting, loss heat in spots without fur(legs), shade
Rats response to warm environments- stay underground, tail loses heat, use saliva to help cool
Giraffes’ response to warm environment
coloured skin (dark areas get hotter) larger surface areas
January 15th
Thermoregulation- animals maintain body temperature at a level that provides optimal physiological performance
Organismal performance- the rate and efficiency of an animals biochemical, physiological and whole-body processes
Ecto= external, obtain heat energy primarily from the external environment (fish amphibians, reptiles)
Thermal acclimatization- a structural or metabolic change in the limits of tolerable temperature as the environment alternates between warm and cool seasons
- Allows animal to attain good physiological performance at both winter and summer temperature
- Could be an increase in specific enzymes that work better at different temperatures
- Could be a change in phospholipids saturation and cholesterol levels (from bio-120)
Surviving freezing-
As the body gets colder it formed ice crystals, the anti-freeze proteins stop their systems from forming the ice crystals
Endo- internal, heat energy primarily from internal reactions, balance internal heat production against heat loss from the body surface
Temperature regulation- skin temperature causes changes in core temperature and the body’s attempt to thermoregulate
- Thermoreceptors detect the change in temperature
- The hypothalamus is referred to as the body’s thermostat
- **
Hypothalamus
- Maintains core homeostatic functions
- Thyroid- front of the throat, wide range of effect through hormones
- TRH- thyroid-releasing hormone
- TSH- thyroid stimulating hormone
- T3- triiodothyronine
- T4- thyroxine
- Iodine needed for thyroid to produce T3 and T4. Too little and thyroid grows larger to make more thyroid hormones
Effect of Iodine deficiency
Hyper- too much
Hypo- too little
Hypo or hyperthyroidism refers to T3 and T4 production, not thyroid size
Do low levels of T3 and T4 causes hypothyroidism? Yes
- Iodine defiency result in hypothyroidism
- Without iodine, thyroid cannot make T3 and T4 in response to stimulation by TSH
- Low T3 and T4 remain but TSH continues to be secreted, overstimulating the thyroid and making it grow in size while still not being able to make T3 and T4
Skin and Endothermy
- Organ of heat transfer
- Blood vessel of the skin regulate heat loss by constricting (vasoconstriction) or dilating (vasodilation)
- Skin is water-impermeable (hard to get water across) reducing heat loss by direct evaporation of body fluid
- An insulating fatty tissue layer under blood vessels limits losses to heat carried by blood
- Cells on skin surface are dead because of lack of nutrients
Keeping warm-
- When thermoreceptors signal a fail in core temperature below the set point. The hypothalamus trigger compensating responses by sending signals through the autonomic nervous system
- Immediate responses include the constriction of the arterioles in the skin (vasoconstriction) which reduces the flow of blood to the skins capillary network
- Ex) many mammals have uneven distribution of fur, birds and mammals have veins and arteries to their legs, whales and seals have adjustments of blood flow
Keeping cool
- When core temperature rises above the set point, the hypothalamus sends through the automic system to trigger that lower body temperature
- As an immediate response, the signals relax smooth muscles of arteries in the skin (vasodilation), increasing blood flow and with it the heat loss from the body surface
- Ex) birds fly with their legs extended
- Ex) elephants dissipate heat from their large ears
Temperature Variations
- The temperature set point in many birds and mammals varies in daily and seasonal patterns
- during cooler conditions, a lowered set point is accompanied by Torpor
- torpor- a state of physical or mental inactivity; lethargy
What happens during a fever?
- Temporary increase in body temperature, from an infection within the immune system
- Foreign bodies signal hypothalamus to increase internal temperature
- Turns on the immune system to help fight infection
- Mild fever is ok, high fever shuts down organs
January 17th
Organization of animal bodies and introduction to nervous systems
Why it matters?
- Multicellular organisms- cells differentiate into different tissues which combine indifferent ways to form organs and organ systems with their own unique functions
- Such specialization allows multicellular organisms to establish a steady-state internal environment able to be maintained independent of the external environment
Cells- specialized and organized into tissues
Tissue- A group of cells with the same structure and function, working as a unit to carry out one or more activities
Organ- an assembly of tissues integrated into a structure that carries out a specific function. body structure that integrates different tissues and carries out a specific function.
Organ system- a group of organs that carry out related steps in a major physiological process. set of organs that interact to carry out a major body function.
A group of cells with the same structure and function. Working as a unit to carry out one or more activities
Coordination of tissues in organ and organ systems
Organ systems preform vital tasks
- Acquiring nutrients and other required substances
- Coordinating their processing, distribution, and disposal
- Synthesizing molecules
- Sensing and responding to the environment
- Protecting the body from injury, disease, and attack
- reproducing
There is 11 different organ systems (need to know main functions and structures)
1. Repository system
Main structure- lungs, diaphragm, trachea, and other airways
Main Functions- exchanges gases with the environment, including uptake of oxygen and release of carbon dioxide
2. Digestive system
Main function- converts ingested matter into molecules and ions that can be absorbed into body; eliminates undigested matter; helps regulate water content
Main structures- oral cavity, pharynx, esophagus, stomach, intestines, liver, pancreas, rectum, anus
3. Reproductive system
Main structures- female: ovaries, oviducts, uterus, vagina, mammary glands, Male: testes, sperm ducts, accessory glands, penis
Main functions- maintains the sexual characteristics and passes on genes to the next generation
4. Excretory system
Main structures- kidneys, bladder, ureter, urethra
Main functions- removes and eliminates excess water, ions, and metabolic wastes from body; helps regulate internal osmotic balance and pH helps regulate blood pressure
5. Muscular system
Mian structures- skeletal cardiac, and smooth muscles
Main functions- moves body parts; helps run bodily function, generates heat, moves intestinal lumen contents
6. Skeletal system
Main structures- Bone, tendons, ligaments, cartilage
Main functions- supports and protects body parts, provides leverage for body movements, stores minerals
7. Integumentary system
Main structures- skin, sweat glands, hair, nails
Mian functions- covers external body surfaces and protects against injury and infection, helps regulate water content and body temperature
8. Circulatory system
Mian structures- heart, blood vessels, blood
Main functions- distributes water, nutrients, oxygen, hormones and other substances throughout the body and carries carbon dioxide and other metabolic waste, helps stabilize internal temperature and pH
9. Immune system,
Main structures- lymph nodes, lymph duct, spleen thymus, bone marrow, and white blood cells
Main functions- defends against disease- causing microorganisms and viruses (pathogens)
10. Nervous system
main structures- Brian, spinal cord, peripheral nerves, sensory organs
Main functions- principal regulatory system, monitors changes in internal and external environments and formulates compensatory responses, coordinates body activities
11. Endocrine system
Main structures- pituitary, hypothalamus, thyroid, adrenal, pancreas and other hormone- secreting glands
Main functions- regulate and coordinates body activities through secretion of hormones
Organizations- Properties of cells in tissues determine the tissues structures and functions
Epithelial tissue- protection, transport, secretion, and absorption of nutrients released by digestion of food
- Consists of sheetlike layers of cells
- Covers surfaces of body and internal organs
- Lines cavities and ducts with the body
- 5 main types of epithelial tissue-
1. simple squamous (single layer of flattened cell, good for diffusion), blood vessels inner lining, air sacs in the lungs
2. Stratified squamous, good for protection against abrasion of food, (mouth esophagus and vagina)
3. Cuboidal epithelium- part of secretion and absorption (single layer), in the kidneys
4. Single columnar epithelium (single layer) secretion and absorption, in the lining of the gut, cervical canal and gallbladder
5. Simple pseudostratified columnar epithelium, protection and secretion, moves mucus across surface, nasal cavities, trachea, upper digestive tract
Glands- secretory structures derived from epithelia
Exocrine glands- connected to an epithelium by a duct that empties on the epithelial surface
Endocrine glands- ductless; no direct connection to an epithelium
Connective Tissue- (structural support) consist of cell networks or layer and the extracellular matrix
- Supports other body tissues
- Transmits mechanical and other forces
- Sometimes acts as a filter
6 types:
Loose connective tissue- support, elasticity, diffusion
Cartilage- Support, flexibility, low friction surface for joint movement
Adipose tissue- energy reserves insulation, padding
Fibrous connective tissue- strength and elasticity
Bone- movement, support, protection,
blood- transport of substance
Muscle tissue- (movement) vertebrates
- Skeletal muscles
Long contractile cells (muscle fibres)
Moves body parts and maintains posture
- Cardiac muscle
Short contractile cells with a branched structure
Forms the heart
- Smooth muscle
Spindle-shaped contractile cells
Forms layers surrounding body cavities and tubes
Nervous tissue- neurons communicate information between body parts (electrical and chemical signals)
Gilal cells
- Support and provide nutrients to neurons
- Provide electrical, insulation between them
- Scavenger cellular debris and foreign matter
Types of neurons
Afferent Neurons (sensory neurons)
- Conducts information from sensory receptors neurons
Interneurons
- Integrates the information into a response
Efferent Neurons (motor neuron)
- Carry response signals to effectors, which carry out the response (muscles)
Neuron Structure
- The dendrites, and often the cell body, receive signals and integrate and transmit them towards the spike initiation zone
Axons- conduct signals away from the spike initiation zone to another neuron or an effector
Steps in processing of information in single neurons
1. Incoming signals are received and converted to a change in membrane potential
2. A change in membrane potential initiates action potentials
3. Action potentials are conducted to the axon terminals
4. Neurotransmitter release transmits a signal to the target cell
A basic neuron circuit
- An afferent neuron, an interneuron and efferent neuron make up a basic circuit
- Circuits combine into network that interconnect the peripheral and central nervous systems
Animal nervous systems
- Functions of the nervous system result from the activities of only two major cell types: neurons and glial cells
- In most animals, these are organized into complex networks called nervous systems
- In the peripheral nervous system (PNS), the long slender projection of neurons(axons) is bundled into cablelike projections(nerves)
- Nerves provide a common pathway between structures and the central nervous system (CNS)
- In the CNS, networks are organized into ganglia and brains
Four functions of the animal nervous system
1. Reception- detection of a stimulus
2. Integration- integrates information to formulate appropriate response
3. Transmission- conducts message along neurons
4. Response- transmits signal to effector organs to produce a response
Glial Cells
Astrocytes- help maintain ion balance surrounding neurons
Oligodendrocytes, Schwann cells- form insulating layers around axons (myelin)
Electrochemical potentials in neurons
Organ systems must be coordinated within the animal and with the environment
Two major systems involved are the nervous system and endocrine system
Both act together- allows for complex homeostasis control
Nervous system: in all animals except sponge, a very rapid coordination/Regulation system
Has 3 major roles:
1. Collect information- from internal or external environment using modified neurons (sensory) receptors)
2. Process and integrate information- evaluates based on experience and/or genetics
3. Transmits information- coordinates/ regulates effector organ/cells.
Neuron- individual cell
Nerve- a bundle of axons (a few to a million)
Axon- also called a nerve fiber
Synapse- connection between axon terminal and effector cell
Effector- can be a neuron, muscle cell, any other cell
Electrical Terminology
Bioelectricity- it all happens in the membrane
Potential- difference in electrical charge between regions
- Measured in volts (V) or millivolts (mV)
Current- flow of electrical charge between regions
- Opposites attract, like repel
Membrane potential- unequal charge distribution across a cell membrane
ALL living cells are electrically polarized
- Have a membrane potential
- Inside of membrane is negative to exterior side
- Size of MP ranges from -10 to -90 mV
Excitable cells- neurons and muscles cells are specially adapted, they have:
- Large membrane potential
- Special mechanisms to regulate membrane potentials and currents
- Membrane potentials and currents depend on inorganic ions
Three type of membrane potential
1. Resting membrane potential (RMP)
- All cells have resting membrane potential ( measured when the cell is inactive)
- The membrane potential of a cell results from the unequal distribution of positive and negative charges on either side of the membrane
- This establishes a potential difference in resting potential, across the membranes
- Principle ions involved are Na+ and K+
Extracellular fluid always has high Na+ and low K+
Intracellular fluid always has high K+ and low Na+
Sodium outside cell, potassium inside the cell
Ion Gradient in all cells
- Ion gradients maintained by active transport
- Na+/ K+ ATPase
- Moves 3 Na+ out and 2K+ in
- Is an electrogenic pump that generates -10mV potential
- All cells anionic proteins generate a -5-mV potential
- By passive diffusion of k+ through an open K+ channel
- ATPase and the leak channels together create a electrochemical gradients (leaks are always open)
- Na+/K+ active transport pump- sets up concentration gradients of Na+ ions and K+ ions
- Open channel allows K+ to flow out freely
- Negatively charged molecules (proteins) inside cells can’t past through membrane
Membrane ion channels
- Ion gradients maintained by active transport
- Na+/ K+ ATPase
- Moves 3 Na+ out and 2K+ in
- Is an electrogenic pump that generates -10mV potential
- All cells anionic proteins generate a -5-mV potential
- By passive diffusion of k+ through an open K+ channel
- ATPase and the leak channels together create a electrochemical gradients (leaks are always open)
- Na+/K+ active transport pump- sets up concentration gradients of Na+ ions and K+ ions
- Open channel allows K+ to flow out freely
- Negatively charged molecules (proteins) inside cells can’t past through membrane
Polarization in cells
The cell is now polarized (negative inside)
- But cell can be depolarized (more positives inside) or hyperpolarized (more negative inside)
Happens during electronic potentials or action potentials
EP- small changes in membrane potentials
AP- large and rapid changes in membrane potentials
Graded Potentials
- Changes in membrane potential due to changes in membrane permeability to ions are called graded potentials
- In neurons, graded potentials are part of the integration that takes place in dendrites and cell bodies
- Electronic potentials are one type of graded potential
2. Electronic potentials (EP)
- Current (ions) travels along surface of membrane
- Small (only a few mV)
- Can depolarize or hyperpolarize
- Only travel a short distance along membrane
-used to initiate an action potential in axon hillock
- also to conduct AP along axon
3. Action potential (AP)
- Initiated at axon hillock region
- Found only in axons
- Carries the signal from axon hillock to terminals
Special features of APs
- Depolarizes membrane (from -70 to + 35 mV)
- Are all or nothing but transient
- Once started, conducted along entire axon
- Rely on ion currents through membrane via voltage-gated ions channels
Generation of action potential
- Generated when stimulus pushes resting potential to threshold value
Voltage-gated Na and K channels open in the plasma membrane
- Inward flow of NA changes membrane potential from negative to positive peak
- Potential falls to resting value as gated K channels allow ions to flow out
Depolarization- the rising phase of ATP
AP depends on ion currents and voltage-gated channels
The falling phase of AP- k channels open (repolarization), K flows out, K channel closes (hyperpolarization)
Repolarization-
Hyperpolarization
Refractory period-
January 22, 2025
The Hodgkin-Huxley cycle- initial polarizationà opening of Na channels increases permeability to Na à increased Na flow à further membrane depolarizationà again
AP propagation Along Axon
Propagation of Action Potential
- AP move along an axon as the ion flows generated in one segment depolarize the potential in the next segment
- Will look at this for both unmyelinated axons and myelinated axons
Unmyelinated axons
- Reduced threshold at axon hillock
- Concentration of Na channels
- Current spreads along membrane towards terminals(new AP)
- Adjacent (downstream) Na channels reach threshold from large depolarization
- Refractory period prevents back propagation
- Next adjacent Na channels reach threshold
- Axon diameter determines speed of conduction(up to 40 m/s)
- Typical of most invertebrates
Saltatory conduction
- In myelinated axons, ions can flow across the plasma membrane only at nodes where the myelin sheath is interrupted
- Action potentials skip rapidly from node to node
- Saltatory conduction allows thousands to millions of fast- transmitting axons to be packed into a relatively small diameter
Myelinated Axons
- Myelin (protein and lipid) insulation prevention ions from crossing the membrane reduces current loss
- Concentration of Na and K at nodes, allows ions to cross membrane
- Axon hillock similar to unmyelinated neuron
- Similar conduction process but current spreads quickly between nodes
- Saltatory conduction from node to node to reach terminals
- Higher conduction velocities
Synaptic Transmission
Synapses- site where a neuron communicates with another neuron or effector
Presynaptic cell- neuron that sends a signal
Postsynaptic cell- neuron that receives a signal
Electrical synapse- impulse pass directly from presynaptic cell to postsynaptic cell
Examples: cardiac muscle cells, neurons in a few invertebrate animals
- Gap junction directly connect cytoplasm of each cell
- Ions flow between cells
- Rapid flow of current
- Synchronous activity- escape responses
- Cannot be modulated
- Excitatory only
Chemical synapse- neurotransmitter released by presynaptic cell diffuses across synaptic cleft. Binds to receptors in the plasma membrane of postsynaptic cell
Examples: majority of neurons
- Pre and postsynaptic neurons separated by synaptic cells
- Neurotransmitter is stored in vesicles within the axon terminals of presynaptic neurons
Vesicles release neurotransmitter
- AP cause Ca influx through voltage gated Ca channels
- Ca causes vesicles to move to the plasma membrane, fuse, and release neurotransmitter into the cleft
Postsynaptic Binding
- Neurotransmitter binds to postsynaptic receptors- channels open- depolarization (excitatory) or hyperpolarization (inhibitory)
Transmitters work in two ways
- Some transmitters bind directly to ligand-gated ion channels in the postsynaptic membrane (binding opens or closes the channel gate)
- Others work more slowly, acting as first messenger, binding to G-protein-coupled receptors in postsynaptic membrane (triggers second messenger)
Transmitters
- Many different kinds
- Diverse effects
- All bind to a receptor protein in post-synaptic membrane
- Each neurotransmitter has several different receptors and thus can stimulate or inhibit an effector cell (depending on the receptors present)
Acetylcholine
- Stimulates skeletal muscle contraction
- Inhibits cardiac muscle contraction
Ionotropic receptors
- Ligand-gated ion channels
- Post-synaptic response depends on ion current
- The binding of two acetylcholine molecules opens the ion channel permitting ions to flow through the membrane
- Causes depolarization
Metabotropic receptors
- Influences post-synaptic cell indirectly
- Post-synaptic response depends on ion current
- Connects to a g-protein
- Acts via an intracellular
- Complex cell biochemistry
January 24
Post-synaptic electrophysiology, The ANS, and the evolution of nervous system
Post-synaptic electrophysiology
- Ions move across post-synaptic membrane due to neurotransmitter binding to receptor
- Cause an electrotonic potential (EP) in dendrites of post-synaptic neuron
- Flows along membrane surface to axon hillock if it is strong enough= action potential
- * EP from the dendrites called a post-synaptic potential (PSP)
Neurons will line up and connect at the synapse
At the hillock, the PSP will.
- Depolarize or hyperpolarize the membrane (depends on the type of receptor? Ion channel in the dendrite:)
- A Na channel will let Na flow inward, causes a depolarizing to excitatory PSP (EPSP)
- A K channel will let k flow outward- causes a hyperpolarizing or inhibitory PSP (IPSP)
- A Cl channels will let Cl flow inward- causes a hyperpolarizing or inhibitory PSP (IPSP)
PSPs are graded potentials
- EPSPs and IPSPs are called graded potentials (not all or none like APs)
- Size of PSP at each receptor depends on amount of neurotransmitter released
a. did not reach so no action potential
b. axon hillock releases new EPSP before the other one dies down (same presynaptic neuron with EPSP coming quick enough to add)
c. different pre-synaptic neuron (many different neurons connect), arrive at the same time and add together
d. neurotransmitter can be depolarized or hyperpolarized, and if you get both, they cancel each other out
- Summation can involve EPSP and IPSP, summation occurs at axon hillock
- Occurs in time and space
- Important for processing inputs, learning, memory
Psot synaptic regulation
All neurons have the same basic electrophysiology, but diversity of post-synaptic regulation possible through:
- Many, many synaptic inputs per effector
- A wide variety of neurotransmitters
- Different receptor proteins
- Several intracellular signaling pathways
Allows a nervous system to regulate/coordinate virtually all cellular physiology
all these activities depend on bioelectricity
bioelectricity- the electrical activity that occurs within living organisms
it’s a result of the movement of charged particles called ions in and out of cells
somatic- voluntary control
autonomic- involuntary control
- Sympathetic- whole body, ‘flight or fight’. It is more widespread effects
- Parasympathetic- organ specific, ‘rest and digest’. Has more organ specific effects (neurons coming out will go to organs)
Most tissues innervated by both divisions are two efferent neurons and peripheral ganglia
Integration also occurs in ganglia, so in the brain (groups of neurons together)
Preganglionic neuron- connects to spinal cord
Postganglionic neuron
Functions of the ANS
Sympathetic- relaxes airways, increases the heartbeat and force of contraction (STIMULATES), inhibits digestion and stomach activities
Parasympathetic- constricts airway, slows heartbeat
Stimulates digestion and stomach activity
*Tissue specific response depends on neurotransmitter and type of receptor in effector cell
Sympathetic system- preganglionic fibers: acetylcholine/nicotinic receptor, postganglionic fibers: norepinephrine/adrenoreceptor
Parasympathetic system- preganglionic fibers: acetylcholine/nicotinic receptor, postganglionic fibers: acetylcholine/ muscarinic receptors
ANS divisions have antagonistic (opposing) effects
- Both divisions are always activated
- Overall effect depends on which divisions is more active
ANS Summary
- A major source of integration in body
- Used to regulate and coordinates majority of organ systems
- Extensive feedback loops maintain body homeostasis
Pressure on the nervous system development
- Nervous system of all animals is designed to provide optimum functioning
- Organization of nervous systems indifferent groups of invertebrates and vertebrates reflects differences in lifestyle and habitat
Nervous system evolution
Sponges- no neurons but still have basic cell physiology
Nerve nest, limited processing abilities
Cephalization- concentration of neurons/ganglia in ‘head’ region
The mammalian nervous system, brain is divided into functional regions
The Neuromuscular Junction (NMJ)
Acetylcholine causes a muscle fibre depolarization
Depolarization results in muscle action potential
Sliding filament theory of muscle contraction- filaments slide past each other to shorten a sarcomere
Cross bridge binding-sliding due to cross bridge binding between filaments
Actin and myosin (protein polymers)
Have respective binding sites
Change in myosin shape after bridge formation moves filaments past each other
ATP required for detachment
In presence of high sarcoplasmic CA, cycle of binding and unbinding continues
ATP required to detach myosin/actin
No ATP than filaments remain bound- rigor mortis
ATP also needed for CA++ pump on sarcolemma
Crossbridge cycling- overall muscle contraction due to; continual crossbridge cycling plus the formation of many many cross bridges per sarcomere
Generating force and movement
Small molecular movement translate into overall muscle shortening
Sarcomere length- 2.5
Distance shortened per sarcomere- .25
Neural regulation of skeletal muscles- reflex arc, motor unit recruitment and tetanus and stretch activation
Reflex Arc
Stretch receptors and motor neurons connect in CNS
Important arcs operate automatically
Important in posture, coordinating limb movements
Integrated with conscious motor control by CNS
Neural stimulation always shorten skeletal muscles
Muscles usually found in antagonistic pairs
Motor unit recruitment and tetanus
Adjust muscle force
Motor unit- one neuron plus all muscle fibers it contacts
Tetanus- multiple action potentials will lead to tetanus (a form of summation)
Produces much more force than a twitch
Opsins and colour vision
Colour vision depends on cones in retina
Most mammals- 2 types of cones
Humans and other primates- 3 types of cones
Each cone cell contains 1-3 photopsins in which retinal is combined with different opsins
Photoreceptors of the retina
Rods- specialized for detecting low intensity light, night vision
Cones- specialized for detecting light of different wavelengths (colours)
Both are linked to neurons in the retina
Preform initial integration and precessing of visual info
Converting signals to electrical impulses
Photoreceptors have three parts:
Outer segment of stacked, flattened, membranous discs
Inner segment where metabolic activities occur
Synaptic terminal where neurotransmitter molecules are stored and released
Photoreceptors of different animals contain different forms of retinal, light-absorbing pigment.
Photopigment:Rhodopsin
Found in discs of rods
Consists of the opsin protein retinal
In response to light, retinal changes from a bent to a straight structure
Neural Pathways for vision
Half of axons carried by the optic nerves cross over at the optic chiasma
Leading to the left half of the field seen by both eyes being transmitted to the visual cortex in the right hemisphere (and reverse for the right half of visual field)
Results in right hemisphere seeing objects to the left of the centre of vision and left hemisphere seeing objects to the right of the centre of vision
Sensory cell membrane proteins respond to stimuli
Chemoreceptors
Provide info about taste (gustation) and smell (olfaction)
Measure intrinsic levels of specific molecules in the environment (oxygen, carbon dioxide, hydrogen)
Work through membrane receptor proteins
Stimulated when they bind with specific molecules
Generate action potentials leading to CNS
Taste-involves the detection of potential molecules in objects touched by receptor
Smell- involves the detection of airborne molecules
Invertebrates
In many invertebrates, same receptors for sensing smell and taste
May be around mouth (hydra) or distributed over body surface (earthworm)
Terrestrial invertebrates- some terrestrial invertebrates have clearly differentiated receptors for taste and smell
Insects
Taste receptors occur inside hollow sensory bristles called sensilla usually located on the antennae, mouthparts, or feet
Pores in the sensilla admit molecules from potential food to the chemoreceptors
Specialized to detect sugars, salts, amino acids or other chemicals
Use of Pheromones
Chemicals used in communication in both animals and plants
Insects are excellent examples that make extensive use of pheromones
male/female attraction
Ants, bees, and wasps use odour to identify members of the same hive or nest or to alert nestmates to danger
Taste and smell in vertebrates
Taste and smell receptors have hairlike extensions containing proteins that bind environmental molecules
Hairs of taste receptors are derived from microvilli and contain microfiliments, processed in parietal lobes of the brain
Hairs of smell receptors are derived from cilia and contain microtubules, processed in olfactory bulbs and temporal lobes
Taste receptors form part of a structure called a taste bud, a small, pear-shaped capsule with a pore at the top opening to the exterior
Taste transduction
Taste- relies on contact chemoreception
Salt and sour simple- cation inflow depolarizes cell- neurotransmitter release
Sweet, bitter and umami complex- 2nd messenger pathway
Each receptor has a preferred chemical sensitivity
Odors as signals
Smell is a powerful receptor fro memories
Many mammals communicate with odors
Family or colony identification, attraction of mates, territory and trail marking
Smell in water dwelling vertebrates (fishes and amphibian tadpoles)
Detects chemical in surrounding water
Receptor found inside the nasal sac
Opens to the water through nares
Blind ending
Not used for breathing
Smell in air breathing vertebrate
Detects volatile (airborne) chemicals
Receptors located in nasal cavities
Used for both smell and breathing
One end has 10-20 sensory hairs projecting into layer of mucus covering the olfactory area of the nose
Molecules dissolve in the watery molecule solution
Other end has olfactory receptor cells synapse with interneurons in the olfactory bulb
Communicate directly with cerebral cortex
Humans- 107 olfactory neurons
Dogs- 20 times more
Moth- 1000 more sensitive than a dog
Nociceptors
Detect damaging stimuli interpreted by brain as pain
In mammals and possibly other vertebrates
Located on body surface and interior
Pain receptors adapt very little, if at all, as part of their protective function
Protective mechanisms
Prompts us to do something immediately to remove or decrease the damage being done
Pain circuits
Neurons involved are part of the somatic nervous system of PNS
Synapse with interneurons in the grey matter of the spinal cord
Causes these interneurons to release either glutamate or substance P
Glutamate releasing axons sharp, prickly sensations localized to a specific body part
Substance P releasing axons produce dull, burning or aching sensations more wide spread
Electroreception- ancient trait in vertebrates
Electroreceptors detect electrical currents and fields (sharks, bony fishes, some amphibians)
Electrorepetors detect distortion of electric fields
Also produce large fields for prey capture
Magnetoreception
Detects and uses earth's magnetic field as source of directional information
butterflies , beluga whales, sea turtles, homing pigeons and foraging honey bees
Adaption of receptors with constant stimuli
In many sensory system, the effects of a stimulus is reduced if it continues at a constant level, this reduction is called sensory adaptation
Some receptors adapt quickly and broadly, other receptors adapt only slightly
Perception- the conscious awareness of our external and internal environments derived from the processing of sensory input
action potentials from sensory receptors are the signals the brain uses to generate an interpretation( the perception) of the external and internal environments.
Jan 31st
Animal skeletons- for body support, locomotion, protection
Three broad types:
Hydrostatic
Structure consisting of a muscles surrounded by a compartment or compartments filled with fluid under pressure
Contraction and relaxation of muscles change the shape fo the animal
ex) flatworms, roundworms
Exoskeleton
Rigid external body covering
Can protect delicate internal tissues
Incompressible
Force of muscle contraction is applied against the covering
Exoskeleton is formed by secretions from the underlying epidermis
Functions- protect against dehydration, act as armour against predators, provides levers against which muscles work.
Muscle attached to an exoskeleton
Arthropod exoskeleton has moveable joints, flexed and extended by muscles
Most muscles attach directly to the cuticle by extension od the myofibrils
Extend front the inside surface of one section of cuticle to the inside surface of another section
Since the sections are separated by flexible cuticle, contraction results in movement about the joint
ENdoskeleton
Supports the body by rigid structures (bones) within the body
Also protects delicate internal tissues
Force of muscle contraction is applied against supporting structures
In vertebrates, endoskeletons is the primary skeletal system
Two types of endoskeletons
Echinoderms- calcium carbonate and protein fibers
Easily dissolved in acid
Vertebrates- calcium phosphate and protein fibers
Internal store of CA and PO4
More resistant to acid
The human skeleton
Axial skeleton- skull, vertebral column, sternum, and ribcage
Appendicular skeleton- shoulder, hip, leg and arm bones
Bone tissues
Complex organs built from multiple tissues (nerves, blood vessels, bone tissue)
Compact bone regions (outer surface)
No space except microscopic canals of the osteons
Spongy bone regions- open into larger spaces, spaces filled by marrow
Red (primary source of new red blood cells) or yellow ( adipose tissue)
Mineral storage
Calcium and phosphate ions are constantly deposited and withdrawn from bones
Hormonal controls maintain a concentration of CA2 ions at optimal levels in blood and extracellular fluids
Calcium Regulation
Vertebrate skeleton relies on CA homeostasis
Blood CA++ tightly regulated by endocrine negative feedback loop
Muscle
Responsible for movement of body
Contractile cells are found in all animals
True muscle evolved first in cnidarians
Contraction (shortening) based on interaction between: supporting filaments (actin) and a motor unit (myosin)
Three types of vertebrate muscles
Striated muscle unstriated muscle
Skeletal muscle cardiac muscle smooth muscles
Voluntary muscle involuntary muscle
Neurogenic myogenic
All muscle is bioelectric (produces a membrane action potential)
Skeletal muscle
Most vertebrates have more than 600 skeletal muscles
Consist of bundles of elongated, cylindrical cells called muscles fibres that run the entire length of the muscle
Formed by a fusion of cells called myoblasts
Contains multiple nuclei
Cells held in parallel bundles by sheaths of connective tissue
Sheaths merge with the tendons
Have an extensive network of blood vessels
Skeletal muscle structure- within each muscle fibre are longitudinal bundles of contractile proteins called myofibrils
Orderly protein arrangement produces striated appearance
Contraction stimulated by motor neurons (from somatic nervous system)
Actin, myosin, and other proteins
Physiology of vertebrate skeletal muscle
ex) rotator cuff muscle in human shoulder
Skeletal muscle actively shortens but passively relaxes
sliding filament theory explains muscle contraction
Shortening of a muscle generate a force and movement
Muscles generally grouped as antagonistic pairs around joints
Working as a lever
Muscles can be attached proximal to the joint or distal from the joint
Proximal insertion favours speed; distal insertion favours strength
The fulcrum can also vary in position, favouring either speed or strength
Sarcomere structure
1 myofibril= many sarcomeres
Myofilaments:
Thick filaments (myosin)- A band
Thin filament (actin)- I band
H zone- myosin only, bisected by M line
Z disk anchors actin, M line anchors myosin
Sliding filament theory- troponin and tropomyosin (actin) regulate interactions with myosin
Sliding filament model of contraction