BIO 224 FINAL

Physiology

The scientific study of how various parts (cells and organs) of an organism function.

Anatomy

The scientific study of body structure.

What can phyla be grouped into?

Clades. (monophyletic groups that share a common ancestor)

What characteristics attribute an animal?

• multicellular eukaryote that lacks a cell wall

• heterotroph

• motile at least at some time in their lives

• reproduces sexually or asexually

  • most have nerves and muscles

Tissue stability

Achieved through the extracellular matrix and cell junctions.

Gap junctions

Create channels allowing for cell to cell communication.

Tight junctions

Act as seals that prevent the leakage of materials between cells, acting as a diffusion barrier.

Anchoring junctions

Connect cells together to resist shearing, stretching, or abrasive forces.

Animal body plans are influenced by:

• patterns of embryonic development

• development of different tissues (germ cell layers)

• type of body symmetry

• body cavity types

Asexual reproduction occurs as:

• budding in hydra

• fragmentation in echinoderms

• parthenogenesis in insects and some reptiles

Zygote cleavage

Follows fertilization.

The division of cells in early embryo.

The zygote undergoes rapid cell cycles with no significant growth.

Morula

Zygote develops into a compact mass of cells.

Blastula

Morula derives into a hollow sphere of a single layer of cells. Unique to animals.

Protostomes

Mouth forms first.

Exhibit spiral cleavage.

Mesodermal differentiates near blastopore.

Coelom (body cavity) originates as a split in the mesoderm (schizocoelom).

Deuterostomes

Anus forms first.

Exhibit radial cleavage.

Mesoderm originates from outpocketings of the archenteron (primitive gut).

Coelom develops from space within the outpocketing (enterocoelom).

Spiral cleavage

Newly produced cells lie in the space between the cells immediately below them. Each cells developmental path is determined as the cell is produced.

Radial cleavage

Newley produced cells lie directly above and below other cells in the embryo. Developmental fates of the first few cells are not determined. A cell removed from the morula will go on to form a complete organism.

Gastrulation

Follows cleavage.

Begins at the vegetal pole.

The blastula invaginates and undergoes further differentiation into two or three germ laters.

Germ layers

• ectoderm - skin and nervous system

• mesoderm - muscle and skeleton

• endoderm - digestive tract

Diploblastic

Two germ layers: ectoderm and endoderm.

Triploblastic

Three germ layers: ectoderm, mesoderm, endoderm.

Radiata (radial symmetry)

Can be divided equally by any longitudinal plane passing through the central axis. (multiple lines)

Bilateria (bilateral symmetry)

Can be divided along a vertical plane at the middle to create two identical halves. (one line)

Animals with radial symmetry:

• diploblastic

• exhibit no left or right sides, instead have a top and a bottom

• often circular or tubular in shape with a mouth at one end

Animals with bilateral symmetry:

• triploblastic

• balanced duplicate distribution of most body parts

• have a specialized head with feeding and sensory organs

• have digestive chamber with two openings, mouth and anus

• segmentation

Cephalization

An organism with a specialized head with feeding and sensory organs.

Segmentation

Repeated body structures along the anterior-posterior axis.

Coelom

A body cavity separates the gut from the body wall.

Acoelomate

No body cavity, no circulatory/respiratory system - rely on diffusion.

Pseudocoelomate

Fluid-filled or organ-filled space between endoderm and mesoderm.

Why do we study animal diversity and evolution?

• animals and animal systems have a common evolutionary history - helping is to learn common principles

• animals occupy very diverse types of environments - helping us understand environmental adaptations

• the physiological phenotype is a product of genotype and the environment

What challenges must animals overcome to be able to survive and reproduce?

• extract nutrients and O2/energy from the environment

• eliminate toxic metabolic wastes from the body

• sense environmental changes and respond favourably

• maintain near constant internal body conditions

Unifying concepts (all physiological processes must):

• obey the laws of physics and chemistry

• electrical laws describe membrane function of all cells, including excitable cells

• usually tightly regulated - homeostasis

Homeostasis

Regulation of the bodily (internal) environment at or near a stable level. Dynamic process where internal adjustments are made continuously to compensate for changes in the internal or external environment.

Goal of homeostasis

Allow organism to reach optimal physiological performance.

Osmoregulator

Homeostatic efforts to maintain stable internal conditions despite external environmental changes. Osmotic pressure of body fluids is homeostatically regulated and usually different from the external environment.

• maintain extracellular osmolarity and ion composition constant

• cells and tissues are not able to cope with changes in extracellular osmolarity and ion concentration

Osmoconformer

Homeostatic efforts allow internal conditions to change to meet external environmental conditions. Body fluids and cells are equal in osmotic pressure to the environment.

• do not activity control osmotic conditions of extracellular environment

• high degree of cellular osmotic tolerance

• cells and tissues can cope with high extracellular osmolarities by increasing intracellular osmolarities with compatible osmolytes to maintain cell volume

• most common strategy by marine invertebrates

• energetically less expensive then osmoregulation

Negative feedback

Returns a variable towards a set point. Minimizes the difference between actual level and the set point.

Most common in homeostasis.

Examples: body temperature, osmoregulation.

Process of negative feedback and body temperature

Occurs in endothermic animals. Maintains the balance between heat loss and heat gain. Keeps physiological variables stable, but not constant.

Positive feedback

Moves variable away from the set point. Amplifies the difference between actual level and set point. Used to quickly increase or decrease a process. Amplification effect eventually is shut off by negative feedback.

Examples: child birth, nerve action potential.

Feedforward

Future needs are anticipated. Physiology is adjusted in advance. Often involves learning and complex behaviours.

Example: race horses, large-scale migration movements.

What is a fever?

A state of elevated core body temperature above its normal range in a defence response against invading pathogens or lesions.

What happens during a fever?

• temporary increase in body temperature, usually due to infection

• foreign bodies signal hypothalamus to increase internal set point

• turns on the immune system to help fight infection

• high temperature increases performance of immune system helping to weaken pathogens

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.

Organ system

A group of organs that carry out related steps in a major physiological process.

Types of tissue:

• epithelial - protection, transport, secretion, and absorption of nutrients released by digestion of food

• connective - structural support

• muscle - movement

• nervous - communication, coordination, and control

Epithelial tissue

Sheet-like layer of cells, covers surfaces of body and organs and lines cavities and duct within the body.

Functions: diffusion, secretion, absorption, and protection.

Types: simple squamous, stratified squamous, cuboidal, simple columnar, simple pseudostratified.

Epithelial tissue - glands

Secretory structure derived from epithelia.

Exocrine - connected to an epithelium by a duct the empties on the epithelial surface.

Endocrine - ductless, no direct connection to an epithelium.

Connective tissue

Cell networks or layers and an extracellular matrix. Supports other body tissues, transmits mechanical and other forces, sometimes acts as a filter.

Functions: support, flexibility, elasticity, insulation, transport.

Types: loose connective tissue, cartilage, adipose tissue, fibrous connective tissue, bone, blood.

Muscle tissue (vertebrates)

Function: contraction and the movement of organs.

Types: skeletal, cardiac, smooth.

Nervous tissue

Function: communicate signals and provide support/enhance signals.

Types: neurons and glial cells.

Neurons

Generate bioelectric signals, transmit information to other cells.

Function: receiving and transmitting signals.

Dendrites and cell body deal with receptions.

Axons deal with signal conduction.

Axon terminals transmit signals.

Types: motor, sensory, interneuron.

Nervous tissue - neurons terminology

• neuron - individual cell

• nerve - a bundle of axons

• axon - also called a nerve fibre

• synapse - connection between axon terminal and effector cell

• effector - can be a neuron, muscle cell, or any other cell

Basic neuron circuit

An afferent neuron, interneuron, and efferent neuron.

Combine into networks that interconnect the peripheral and central nervous systems.

Glial cells

“Supporting” cells, assist neuronal signalling, maintain environment for neurons, acting as insulation, scavenge cellular debris and foreign matter.

Function: supporting or insulating tissues.

Types: astrocytes (maintain ion balance surrounding neuron) and oligodendrites (form insulating layers around axons).

Organ systems perform 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

Controlling homeostasis:

• organ systems must be coordinated within the animal and within an environment

• two major systems involved: nervous system and endocrine system

• both must act together, allowing for complex homeostatic control

Major functions of the nervous system:

A very rapid coordination and regulation system in all animals except sponges.

1. collects information - detect stimulus from internal and external environment

2. processes and integrates information - integrates information to formulate appropriate response

3. transmits information - conducts message along neurons

4. response - transmits signals to effector organs to produce a response

Bioelectricity

Electrical phenomenon within living animals due to uneven distribution of ions and charged molecules across membranes.

Potential

Difference in electrical charge between regions. Measured in volts or millivolts.

Membrane potential

Unequal charge distribution across a cell membrane.

Current

Flow of electrical charge between regions. Opposites attract and like repels.

Size of MP (membrane potential) ranges from…

-10 to -90 mV.

Neurons and muscle cells are specially adapted to:

• have large membrane potentials and

• have special mechanisms to regulate membrane potentials and currents.

Types of membrane potentials:

• resting

• electrotonic

• action

Membrane potentials and currents depend on…

inorganic ions.

Resting membrane potential (RMP)

Measure when neuron is inactive.

About -70mV in neurons and muscle cells.

Due to unequal distribution of ions across membranes.

Main ions involved are Na+ and K+.

Sodium is high outside cells and potassium is high inside cells.

Ion gradients maintained by active transport via Na+/K+ATPase.

Ions flow through membrane channels passively and a chemical gradient for K+.

EP (electrotonic potentials)

Small changes in membrane potential.

Current travels along surface of membrane.

Only travels a short distance along membrane.

Can depolarize or hyperpolarize.

AP (action potential)

Large and rapid changes in membrane potential.

Initiated in axon hillock region.

Found only in axons.

Carries signal from axon hillock to terminals.

Depolarizes membrane from -70 mV to +35 mV.

All or nothing, transient. Once started conducted along the entire axon.

Rely on ion currents through membrane via voltage-gated ion channels.

Threshold

Voltage at which AP is initiated.

Saltatory conduction

Jumping from node to node to reach terminals creating higher conduction velocities.

Speed of conduction is dictated by axon diameter.

Repolarization

Returns membrane potential back to resting potential.

Hyperpolarization

Prevents back propagation of signal.

The process of a neural signal:

• incoming signals are received and converted to a change in membrane potential

• a change in membrane potential initiates action potentials

• action potentials are conducted to the axon terminals

• neurotransmitter release transmits a signal to the target cell

Two types of synaptic transmission:

• electrical

• chemical

Electrical synaptic transmission

• actual ions flow from cell to cell with a rapid flow current

• occurs via gap junctions directly connecting the cytoplasm of each cell

• synchronous activity - escape responses

• cannot be modulated, excitatory only

• examples: cardiac muscle cells, neurons in a few invertebrate animals

Chemical synaptic transmission

• another molecule carries signal neurotransmitters from presynaptic cell

• pre and post synaptic neurons are separated by a synaptic cleft

• neurotransmitter stored in synaptic vesicles

• AP cause Ca2+ influx into presynaptic neuron

• vesicle binds to presynaptic membrane and neurotransmitter is released into the cleft

• neurotransmitter binds to postsynaptic receptors

• channels open, leading to depolarization or hyperpolarization

• allowing for the integration of multiple presynaptic inputs

• summed postsynaptic excitation or inhibition

• example: the majority of neurons

Classes of neurotransmitters

Acetylcholine, biogenic amines, amino acids, neuropeptides, and gases.

Neurotransmitters

• diverse effects

• can stimulate or inhibit an effector cell

• all bind to a receptor protein in post-synaptic membrane

• each has several different receptors

Classes of receptor proteins:

• ionotropic

• metabotropic

Ionotropic receptors

• ligand gated ion channels

• postsynaptic response depends on ion current

• example: the nicotinic receptor is a Na+ channel - acetylcholine stimulates by depolarization, the GABA receptor is a Cl- receptor - GABA inhibits by hyperpolarization

Metabotropic receptors

• influence post-synaptic cell indirectly

• acts via an intracellular signal (2nd messenger)

• complex cell biochemistry

• diversity of effects on cell

Post-synaptic electrophysiology

• ions move across post-synaptic membrane due to neurotransmitter binding to receptor

• cause an electrotonic potential (EP) in dendrites, called a postsynaptic potential (PSP)

• flows along membrane surface to axon hillock

• at the hillock, the PSP will depolarize or hyperpolarize the membrane, depending on the type of receptor/ion channel in the dendrite

• postsynaptic neurons receive many inputs, up to 1000

• summation of subthreshold PSPs occurs in axon hillock

• occurring in relation to time and space, important for processing inputs, learning, memory

Graded potentials

EPSP and IPSP.

The size is dependant on the amount of neurotransmitter released.

Temporal summations

When PSPs come from the same presynaptic neuron and occur close together in time.

Spatial summation

PSPs from different presynaptic neurons that occur close in time.

Diversity of post synaptic regulation is possible through:

• many synaptic inputs per effector

• a wide variety of neurotransmitters

• different receptor proteins

• several intracellular signalling pathways

Somatic nervous system

• voluntary control

• motor neurons carry signal to skeletal muscle

• dendrites and cell bodies in the spinal cord (CNS)

• axon extends directly to muscle

Autonomic nervous system

• involuntary control

• two-neuron pathway - preganglionic and postganglionic

• ganglia are in the PNS acting as a relay point with clusters of nerve cell bodies

• tissue-specific response depends on the neurotransmitter and the type of receptor in effector cells

• major source of integration in the body

• used to regulate and coordinate majority of organ systems

• extensive feedback loops maintain body homeostasis

Preganglionic neuron

Cell body in CNS with axons to autonomic ganglia.

Postganglionic neuron

Cell body in autonomic ganglia with axons to effectors.

Two divisions of the autonomic nervous system

• sympathetic nervous system

• parasympathetic nervous system

Both are always active and have opposing effects on organs to maintain precise control.

Sympathetic nervous system

• whole body effects

• fight or flight response

• more active when body energy stores need to be used

• relaxes and opens airways

• increases heartbeat and force of contraction

• inhibits digestion and stomach activity

Parasympathetic nervous system

• organ-specific effects

• rest and digest response

• more active when body energy stores are being conserved/restored

• constricts airways

• slows heartbeat

• stimulates digestion and stomach activity

Nervous system evolution in animals

• designed to provide optimum functioning

• organization of nervous systems in difference animals reflects differences in lifestyle and habitat

• sponges - no neurons but still have basic cell physiology

• ganglia - collections of neuronal cell bodies as sites of integration

• cephalization - concentration of neurons/ganglia in a “head” region

Animals ability to detect the environment

• detect a wide variety of variable contributing to the environment

• important in the context of homeostasis

• basic neuronal physiology applies in all animals, some with specializations

Sensory receptors

Detect sensory information from internal and external environments, convert to neural activity, and pass the information to the CNS.

These receptors can be dendrites/free nerve endings in afferent neurons or specialized receptor cells.

How is stimulus transmitted/transduced?

• stimulus causes changes in membrane potentials in sensory receptors

• this results in positive ions crossing the membrane