Biology Stage 1 - Animal Physiology

What is homeostasis?

Property in which variables are regulated so that internal conditions remain stable and relatively constant

What are the key components of a homeostatic circuit?

Regulated variable, controlled variable, set point, sensor, error detector, controller and effector

What is regulated variable?

Physiological variable for which sensors are present in the homeostatic circuit and is maintained at a stable level (set point) by a negative feedback system

What is controlled variable?

Physiological variable that is manipulated in order to maintain the regulated variable within normal values

What is set point?

Range of values of a regulated variable that the homeostatic circuit attempts to maintain

What is an error detector?

Component that determines the difference between set point value and actual value

What is a controller?

Component that receives information from the error detector and sends output signals to increase or decrease activity of effectors

What are effectors?

Components activated by controller to change value of the regulated variable

What is the fundamental mechanism that maintains regulated variable at set point?

Negative feedback

What is negative feeback?

Reaction in which system responds in such a way as to reverse direction of change, maintaining stability

What is positive feedback?

Self-amplifying cycle where physiological change leads to even greater change in the same direction, rather than producing corrective effects

One example of positive feedback in physiological processes

Childbirth: pressure on cervix induces release of oxytocin, which stimulates uterine contraction which creates more pressure on the cervix continuing until baby is born

Why can positive feedback be harmful?

Can quickly change regulated variable far from its homeostatic set point, creating a vicious circle that can be life threatening

What is the extracellular fluid (ECF)?

Internal environment of the body, consisting of all body fluids outside the cells, including plasma and interstitial fluid

What is simple diffusion?

Movement of particles from place of high conc to lower conc without energy expenditure

What is osmosis?

Type of passive transport, exclusively the movement of water across cell membrane through channel proteins (aquaporins)

What is filtration in cell membrane transport?

Process in which water and solutes are driven through cell membrane by hydrostatic pressure (high to low pressure)

What is facilitated diffusion?

Carrier-mediated transport of a solute through the cell membrane down its concentration gradient, without energy expenditure

What is active transport?

Carrier-mediated transport of a solute through cell membrane against the concentration gradient using ATP

How does the Na+/K+ pump work?

Pumps 3 Na+ ions out of the cell for every 2 K+ ions it pumps in, using ATP. Creating and maintaining concentration gradients of these ions across membrane

What is vesicular transport?

Movement of large particles, droplets of fluid or numerous molecules at once through the cell membrane, contained in bubble-like vesicles of membrane

What are the different types of endocytosis?

Phagocytosis (cell eating), pinocytosis (cell drinking) and receptor-mediated

What is autocrine signalling?

Chemical messenger diffuses short distance through ECF and binds to a receptor on the same cell that released it

What is paracrine signalling?

Chemical messenger diffuses short distance through the ECF and binds to receptor on nearby cell

What is endocrine signalling?

Hormone is released into bloodstream and binds to specific target cell receptor

What is neuroendocrine signalling?

Release of hormone from nerve cell and transport of that hormone by the blood to a distant target cell

What is nervous signalling?

Rapid transmission of action potentials, often over long distances and the release of a neurotransmitter at a synapse

What are gap junctions in cell signalling?

Direct connections between adjacent cells that allow passage of ions and small molecules, facilitating electrical and metabolic coupling between cells

What is the resting membrane potential?

Electrical potential difference across the cell membrane when the cell is not undergoing an electrochemical change, typically around -70mV

What causes the resting membrane potential?

Difference in permeability of the cell membrane to Na+ and K+ as determined by leak channels, along with the concentration gradients of these ions across the membrane maintained by the Na+/K+ pump

What are the types of ion channels in cell membranes?

Leak channels, chemically-gated channels, voltage-gated channels and mechanically gated channels

What are leak channels?

Ion channels that open and close at random, having an intrinsic rate of switching between open and closed states without triggering an event

What are chemically-gated channels?

Ion channels that open in response to specific chemical messengers that bind to the extracellular region of the chennal. AKA ligand-gated channels

What are voltage-gated channels?

Ion channels that open in response to changes in membrane potential (electrical)

What are mechanically gated channels?

Ion channels that open in response to physical distortion of the membrane surface

What is graded potential?

Change in membrane potential that can have several values and does not travel far from area of stimulation as it decreases as it goes

What is an action potential?

Rapid rise then fall in membrane potential across a cellular membrane with a characteristic pattern, occurring when the balance of Na+ and K+ is disrupted

What is the threshold for action potential?

Membrane potential value (typically around -55mV) must be reached for action potential to be initiated

What is the all or none principle of action potentials?

Either depolarisation reaches threshold and elicits an action potential or it does not reach threshold and no potential triggered. Strength of stimulus does not affect amplitude of the action potential

What happens during the repolarisation phase?

Na+ channels close, K+ channels open and K+ leaves the cell, taking positive charge with it and returning the membrane potential toward a resting value

What is hyperpolarisation?

Period when the membrane potential goes below resting potential due to K+ channels remaining open slightly longer

What is the refractory period?

Period after action potentials when the membrane is not excitable, divided into absolute refractory period (no new action potential can be generated) and relative refractory period (only a strong stimulus can generate)

What is the difference between continuous propagation and saltatory propagation?

Continuous occurs in unmyelinated axons and is slower, while saltatory occurs in myelinated axons, with action potentials “jumping” between nodes of Ranvier, making it faster

What are the two main divisions of nervous system?

Central nervous system (CNS), consisting of the brain and spinal cord and the peripheral nervous system (PNS), consisting of all neural tissue outside the CNS

What are the two divisions of the PNS?

Sensory (afferent) division, which carries information to the CNS from the receptors and the motor (efferent) division, which carries motor commands from CNS to peripheral tissues and organs

What are the two subdivisions of the motor division?

Somatic nervous system, which controls skeletal muscle contractions and the Autonomic nervous system, which provides automatic regulation of smooth muscle, cardiac muscle, glands and adipose tissue

What are the two divisions of the autonomic nervous system?

Sympathetic nervous system and parasympathetic nervous system

When is the sympathetic nervous system most active?

During periods of stress (fight or flight) or physical activity

When is the parasympathetic nervous system most active?

Periods of rest (resting and digesting)

What are the main types of neurons based on their structure?

Multipolar neurons, bipolar neurons, pseudounipolar neurons and unipolar neurons

What are the main types of neuroglia in the CNS?

Astrocytes, oligodendrocytes, microglia and ependymal cells

What are the functions of astrocytes?

Maintain blood-brain barrier, provide structural support, regulate ions and nutrients, recycle neurotransmitters and form scar tissue

What are the functions of oligodendrocytes?

Myelinate axons in the CNS and provide structural support

What are the functions of microglia?

Remove cell debris, wastes and pathogens by phagocytosis

What are the functions of ependymal cells?

Line the central canal of the spinal cord and brain ventricles, help circulate CSF, produce CSF in some areas and monitor CSF composition

What is the blood-brain barrier?

Protective barrier separating brain’s interstitial fluid from blood, isolating the central nervous system from potentially harmful substance + pathogens

What is cerebrospinal fluid (CSF) and its functions?

Clear, colourless fluid circulating around the brain and spinal cord, providing cushioning, delivering nutrients and removing waste products

What are the main types of neuroglia in the PNS?

Schwann cells and satellite cells

What are the functions of Schwann cells?

Surround axons in the PNS, responsible for myelination of peripheral axons and participate in the repair process after injury

What are the functions of satellite cells?

Surround cell bodies of neurons and regulate O2, CO2, nutrients and neurotransmitter levels around neurons

What is a synapse?

Specialised site where a neuron communicates with another cell, involving a presynaptic cell that sends the message and postsynaptic cell that receives it

What are the two main types of synapse?

Chemical- which use neurotransmitters to carry information

Electrical- transfer electrical currents through gap junctions

What is the enteric nervous system (ENS)?

Network of neurons and glia located in the gut wall that can control gastrointestinal function independently of the CNS

Can neurons regenerate?

No, neurons do not have the ability to divide as they lack centrioles and cannot be replaced

Can peripheral nerves regenerate?

Yes, Schwann cells play a key role in the process by proliferating, migrating, producing trophic factors and forming Büngner bands

What is a sensory receptor?

Transducer that converts a stimulus into an intracellular signal, changing the membrane potential

What are the main categories of sensory receptors based on location?

Interoceptors (monitoring internal systems), exteroceptors (provide information about the external environments) and proprioceptors (monitoring position and movement of skeletal muscles and joints)

What are chemoreceptors?

Sensory receptors that can detect small changes in the concentration of specific chemicals or compounds dissolved in body fluids

What are noiceptors?

Pain receptors that are sensitive to extremes of temperature, mechanical damage and injury-related chemicals

What are mechanoreceptors?

Sensory receptors to stimuli that can distort their plasma membrane, containing mechanically-gated ion channels

What are thermoreceptors?

Temperature receptors that are free nerve endings located in the dermis, skeletal muscles, liver and hypothalamus. Cold receptors are more abundant than warm receptors

What are photoreceptors?

Sensory receptors that convert photons of light into membrane potentials

What is a receptive field in sensory pathways?

Area where stimuli can affect a particular sensory neuron or sensory unit

How is a physical or chemical stimulus converted into a membrane potential?

Stimulus opens or closes ion channels in the receptor membrane either directly or through transmitter, creating a graded potential called a receptor potential

What are the basic properties of muscle tissue?

Excitability, contractility, extensibility and elasticity

What are the three types of muscle tissue?

Skeletal, cardiac and smooth muscle

What are the main functions of skeletal muscle?

Skeletal movement, posture maintenance, organ support, control of entries and exits, body temp regulation and serving as a nutrient reserve

How do skeletal muscle cells form?

Fusion of mesodermal cells called myoblasts, resulting in multinucleated skeletal muscle fibres

Can skeletal muscle cells regenerate?

Yes, through myosatellite cells, which are normally quiescent but can initiate proliferation in response to stress or injury

What is muscle hypertrophy?

Increase in individual muscle fibre size

What is muscle hyperplasia?

Increase in number of muscle fibre

What is muscle atrophy?

Decrease in size of a mucle

What are the main characteristic of cardiac muscle cells?

One nucleus, branched and connected by intercalated discs

How is cardiac muscle controlled?

Contraction is involuntary, initiated by specialised pacemaker cells and can be modulated by the nervous system and hormones

Can cardiac cells regenerate?

No, there is no counterpart to myosatellite cells in cardiac muscle. Dead cells are replaced by fibrous non-contractile scar tissue

What are the main characteristics of smooth muscle cells?

One nucleus, small and spindle-shaped and do not have organised sarcomeres

What are the two types of smooth muscle?

Single-unit (visceral) smooth muscle, where cells are joined by gap junctions and contract as a unit and multi-unit smooth muscle, with no gap junctions and contraction confined to the stimulated cell

Can smooth muscles regenrate?

Yes, smooth muscle cells can divide after injury

What is the sliding filament of muscle contraction?

During muscle contraction, the sarcomere shortens as thin filaments are pulled and slide past the thick filaments

What are the stages of the contractile cycle in skeletal muscle?

1) ATP binding and myosin detachment

2) ATP hydrolysis and cocking of myosin head

3) Cross-bridge formation between myosin and actin

4) Power stroke as myosin pulls actin

5) Either ATP binding to release myosin for another cycle or myosin remaining attached in rigor if ATP is exhausted

How does calcium trigger muscle contractions in skeletal muscle?

Calcium released from the sarcoplasmic reticulum binds to troponin C, causing a conformational change that moves tropomyosin away from actin’s binding sites, allowing myosin to bind to actin and initiate contraction

How does smooth muscle contraction differ from skeletal muscle?

Lacks organised sarcomeres, uses calmodulin instead of troponin-tropomyosin, has slower contraction onset, may contract without action potentials and the depolarisation phase involves calcium rather than sodium entry

What is myogenic contraction of smooth muscle?

Contraction triggered when stretch-activated calcium channels open due to pressure or other force distorting the cell membrane, without requiring neural or hormonal stimulation

What causes cardiac muscle to contract rhythmically without external stimulus?

Specialised pacemaker cells in the SAN have unstable membrane potentials with funny current channels that automatically trigger depolarisations

What are the basic components of the skeletal system?

Bones, cartilage, ligaments (connect bone to bone) and tendons (connect muscle to bone)

What are the two major divisions of the skeleton?

Axial skeleton (bones in skull, vertebral column and thoracic cage) and the appendicular skeleton (bones of the thoracic and pelvic limbs)

What are the main types of bones in the skeletal system?

Long bones, short bones, flat bones, irregular bones, sesamoid bones, splanchnic bones and pneumatic bones

What are the three types of fibrous joints?

Sutures (immovable, found in skull), syndesmosis (slightly movable), and gomphosis (immovable, connects tooth to mandible)

What are the two types of cartilaginous joints?

Synchondrosis (immovable, disappear during growth) and symphysis (slightly movable, contains fibrocartilage)

What are the main types of synovial joints?

Ball and socket, hinge, pivot, plane, saddle and condylar joints