Unit 8

Question 1

Define physiology

Answer 1

Physiology is the study of biological function –of how the body works, from molecular mechanisms within cells to the actions of tissue, organs and systems, and how the organism as a whole accomplishes tasks essential for life

Question 2

What is the relationship between physiology and anatomy

Answer 2

The study of physiology focuses on the mechanisms of action, looking at how the body acts, whereas anatomy is concerned with the description of structures within the body. Studies of physiology can be combined with anatomy to provide a bigger picture of the body.

Question 3

Define and give examples of homeostasis

Answer 3

Homeostasis is a term coined by Walter Cannon to describe the dynamic constancy of the internal environment as compared to variations in the external environment. Examples include our ability to maintain body temperature, blood pressure and glucose metabolism.

Question 4

Discuss the relationships between the external and internal environments as they relate to homeostasis

Answer 4

Homeostasis involves keeping the internal environment constant while the external environment changes. For example, body temperature (internal) is kept around 37 C, while the external temperature varies.

Question 5

Identify the components of a homeostatic feedback loop

Answer 5

The homeostatic feedback loop involves a sensor, an integrating centre and an effector. Sensors send information to the integrating centre to allow for detection in changes from a set point. Changes from a set point then send signals from the integrating centre to the effector to counter the deviation from the set point

Question 6

Discuss the relationship between the nervous and endocrine systems and their control over homeostasis

Answer 6

The nervous and endocrine systems are able to extrinsically maintain homeostatic regulation. Endocrine regulation is through chemical regulators known as hormones. Hormones can act on a given organ to produce a change. Nervous system regulation is done via innervation of a target organ. The endocrine and nervous systems can also interact as the nervous system can control hormone release, and some hormones can affect nervous system function.

Question 7

Discuss and give examples of negative and positive feedback loops

Answer 7

Negative feedback loops maintain a state of dynamic constancy around a give set point. Negative feedback loops are important for maintaining body temperature as well as blood glucose levels. Positive feedback loops aim to amplify a response. Positive feedback loops are important for blood clotting as well as preovulatory surge in luteinizing hormone in females.

Question 8

CNS

Answer 8

The brain and spinal cord

Question 9

PNS

Answer 9

Everything outside the CNS (nerves, ganglia and nerve plexuses)

Question 10

SNS

Answer 10

A division of the nervous system responsible for the control of skeletal muscles

Question 11

Discuss the structural classification of neurons and identify anatomical features of a neuron

Answer 11

Neurons contain a cell body, dendrites and an axon. The cell body is the nutritional centre of the neuron. Dendrites are thin, branched process that transmit signals from their ends to the cell body. The axon is a long process that conducts impulses away from the cell body. Three structural classifications exist. Pseudounipolar neurons have a single short process that branches like a T to form a pair of longer processes. Bipolar neurons have two processes, one at either end. Multipolar neurons have several dendrites and one axon extending from the cell body

Question 12

nucleus

Answer 12

A grouping of neuron cell bodies within the CNS

Question 13

ganglion

Answer 13

A grouping of neuron cell bodies located outside the CNS

Question 14

tract

Answer 14

A grouping of axons that interconnect regions of the CNS

Question 15

somatic neuron

Answer 15

A nerve the stimulates contraction of skeletal muscles

Question 16

motor neuron

Answer 16

conduct impulses out of the CNS to effector organs (ie. Muscle)

Question 17

sensory neuron

Answer 17

conduct impulses from sensory receptors into the CNS

Question 18

afferent

Answer 18

conducts nerve impulses from organ into CNS (ie. Sensory neuron)

Question 19

efferent

Answer 19

transmits impulses from CNS to effector organ (ie. Motor neuron)

Question 20

nerve

Answer 20

Cable-like collection of many axons in the PNS, can contain both sensory and motor fibers

Question 21

Identify and briefly describe the function of specialty receptors located on dendrites

Answer 21

Receptors exist on dendrites (of the postsynaptic cell) for neurotransmitters, which are released from the axon of the presynaptic cell into the synapse. These receptors allow for signals to be sent from one cell (presynaptic) to another cell (postsynaptic).

Question 22

oligodendrocytes

Answer 22

Responsible for the myelin sheath around axons in the CNS

Question 23

Schwann cells

Answer 23

Also known as neurolemmocytes, are responsible for the myelin sheath around myelinated axons in the PNS

Question 24

astrocytes

Answer 24

A cell type in the CNS that covers capillaries and induces the blood-brain barrier as well as interacts metabolically with neurons

Question 25

microglia

Answer 25

A cell type in the CNS that phagocytoses pathogens and cellular debris

Question 26

Ependymal cells

Answer 26

A cell type in the CNS that forms the epithelial lining of brain cavities (ventricles) and the central canal of the spinal cord; covers tufts of the choroid plexuses

Question 27

Describe myelin and identify its role in the nervous physiology.

Answer 27

he myelin sheath encases the axon and is formed by Schwann cells in the PNS and oligodendrocytes in the CNS. Myelinated axons are able to conduct nerve impulses more rapidly than unmyelinated axons.

Question 28

Define ‘node’ and ‘antinode’ and describe their formation.

Answer 28

A node is a site of no myelination on a myelinated axon. An antinode is the opposite of a node and is the region of the axon that is myelinated. Schwann cells in the PNS and oligodendrocytes in the CNS form antinodes. Nodes are formed where gaps are left between the myelin sheath.

Question 29

simple diffusion

Answer 29

The net movement of ions or molecules from regions of higher concentration to regions of lower concentration

Question 30

ion channels

Answer 30

Channels in the membrane that permit the movement of ions; channels can be open or gated

Question 31

gating of integral membrane proteins

Answer 31

Many channels have gates that can open or close and channel. In this way, particular stimuli can open an otherwise closed channel.

Question 32

facilitated diffusion

Answer 32

the net movement of ions or molecules from regions of high to regions of low concentration through the aid of a transmembrane protein (carrier-mediated transport)

Question 33

primary active transport

Answer 33

The movement of molecules and ions against their concentration gradients where hydrolysis of ATP is the source of energy

Question 34

secondary active transport

Answer 34

The movement of an ion or molecule against its concentration gradient where the energy is obtained through the movement of an ion or molecule with its concentration gradient (coupled transport)

Question 35

pinocytosis

Answer 35

Also known as ‘cell drinking’; invagination of the cell membrane to form narrow channels that pinch off into vacuoles. This permits cellular intake of extracellular fluid and dissolved molecules.

Question 36

exocytosis

Answer 36

Bulk transport of large molecules out of the cell through the fusion of a membrane-bound vesicle with the plasma membrane

Question 37

endocytosis

Answer 37

Bulk transport of large molecules into the cell through the formation of a membrane-bound vesicle from the plasma membrane

Question 38

Describe the Nernst equation

Answer 38

The Nernst equation allows for the theoretical equilibrium potential to be calculated for a particular ion when its concentrations are known.

Question 39

Define the resting membrane potential. List conditions that result in a resting membrane potential.

Answer 39

The resting membrane potential is the membrane potential of a cell that is not producing impulses. The resting membrane potential depends on 1) the ratio of the concentrations of each ion on the two sides of the plasma membrane and 2) the specific permeability of the membrane to each different ion.

Question 40

Describe the movement of K+ and Cl- ion across the plasma membrane to restore resting membrane potentials.

Answer 40

Potassium (K+): If the cell potential were to become more negative than its equilibrium potential (-90mV), K+ would be draw into the cell to restore the potential. If the cell potential were to become less negative, K+ would diffuse out of the cell to restore the membrane potential.

Chloride (Cl-): Chloride remains in the cell as a fixed anion population. It is responsible for drawing positively charged ions into the cell to restore membrane potential if it becomes more negative than the resting potential.

Question 41

Describe the ‘patch clamp’ technique.

Answer 41

Patching clamping of a neuron allows for detection of the cell’s membrane potential. One electrode is placed outside the cell membrane near the area being recorded and a second electrode is placed inside the cell. The voltage difference can be visualized by connecting the electrodes to a computer. Deflections up or down represent changes in membrane potential with an upward deflection indicating the inside of the cell has become more positive compared to the outside and a downward deflection indicating the cell has become more negative compared to outside.

Question 42

graded potential

Answer 42

A change in membrane potential with amplitudes that are varied, or graded, by gradations in stimulus intensity. Ie. The amount of neurotransmitter released determines the amount of depolarization or hyperpolarization on the postsynaptic neuron.

Question 43

action potential

Answer 43

An all-or-none electrical event in an axon or muscle fiber in which the polarity of the membrane is rapidly reversed and reestablished

Question 44

resting potential

Answer 44

The potential across a plasma membrane when the cell is in an unstimulated state

Question 45

all or none law

Answer 45

Action potentials are an all-or-none event: if the threshold potential is not met, no action potential will occur, but if the threshold potential is exceeded an action potential will occur. The size of the action potential dose not change depending on how the threshold potential is exceeded.

Question 46

threshold potential

Answer 46

The potential at which an action potential will occur. Generally -55 mV in neurons

Question 47

depolarization

Answer 47

The loss of membrane potential in which the inside of the cell becomes less negative compared to the outside of the membrane

Question 48

repolarization

Answer 48

The reestablishment of the resting membrane potential after depolarization has occurred

Question 49

hyperpolerization

Answer 49

An increase in the negatively of the inside of the cell membrane with respect to the resting membrane potential

Question 50

Describe the three states of the Na+ channel during rest, depolarization and repolarization of an excitable cell.

Answer 50

At rest, the Na+ channels are closed. During depolarization, Na+ channels are open allowing the membrane to become permeable to Na+ and Na+ flows into the cell. During repolarization, the Na+ channels are inactivated.

Question 51

Describe how an action potential is propagated down the length of an axon and explain the refractory period.

Answer 51

Action potentials (APs) are conducted down the length on an axon due to the cable properties. Depolarization in one region of the axon allows for the depolarization of the region next to it. The AP can’t “bounce backwards” up the axon because of the refractory period, which immediately follows. Axons also make use of the myelin sheath to allow for conduction over long distances. A refractory period is the period of time during which a region of axon (or muscle) cell membrane cannot be stimulated to produce an action potential (absolute refractory period), or when it can only be stimulated by a very strong stimulus (relative refractory period).

Question 52

Define and describe saltatory conduction.

Answer 52

Saltatory conduction involves the “leaping” of action potentials from one node to the next in myelinated axons. Instead of depolarization along the whole length of the axon, depolarization only occurs at the nodes of Ranvier allowing for faster conduction of action potentials.

Question 53

Describe the differences in myocyte action potentials.

Answer 53

In skeletal muscle, rapid opening of sodium channels causes the action potential, but the resting membrane potential and recovery are driven largely by chloride permeability. This is why defects in chloride channels can give rise to myotonia, associated with a failure of the muscle to relax after contraction. (Notes: Propagation of the action potential)

Question 54

Describe the differences in impulse characteristics between large and small axon and myelinate and unmyelinated axons

Answer 54

1) Action potentials are conducted faster is large axons versus small axons due to a reduction in resistance in the large axon.
2) Action potentials are conducted faster in myelinated axons versus unmyelinated axons because the myelin sheath allows for saltatory conduction of action potentials.

Question 55

ANS

Answer 55

A division of the nervous system responsible for the control of involuntary effectors such as smooth muscle, cardiac muscle and glands. The ANS is further divided into the sympathetic and parasympathetic nervous systems.

Question 56

ENS

Answer 56

a complex network of neurons involved in the intrinsic control of the gastrointestinal system