UNIT 8- HOMEOSTASIS

Question 1

What is the role of skin and mucous membranes?

Answer 1

• Form barrier between internal and external environments. Provide first line of defense from infectious agents
• Skin provides an insulation layer and limit heat energy loss

Question 2

What is the role of musculo-skeletal system?

Answer 2

Acquisition, consumption of food and water, avoiding predation, avoiding extremes of climate change, processes related to reproduction

Question 3

What 2 systems are primarily involved in regulating homeostasis?

Answer 3

Nervous system and endocrine system

Question 4

What are the 2 main cell types of the CNS and what function do they provide? Which can divide and what can’t divide?

Answer 4

Neurons- conduct electrical signals, release chemical signals (CANNOT DIVIDE)
Glia- support cells of neurons (CAN DIVIDE)

Question 5

What is the role of sensory neurons?

Answer 5

transmit impulses from sensory receptors to CNS (PNS to CNS)

Question 6

What is the role of motor neutrons? What are the 2 subtypes?

Answer 6

transmit impulses from CNS to target organs (CNS to PNS)
Autonomic motor neurons - innervate target organs
Somatic motor neurons - reflexes and voluntary control of skeletal muscle

Question 7

What is the role of association/interneurons?

Answer 7

located within CNS contribute to functions of the NS

Question 8

Match the function to the correct neuron:
1. large dendritic tree, one main output axon
2. one axons branches into 2
3. 2 axons
4. no obvious axon
5. one axon

A. Anaxonic
B. Unipolar
C. Bipolar
D. Pseudounipolar
E. Multipolar

Answer 8

1. Large dendritic tree, one main output axon = Multipolar
2. One axon branches into 2 = Pseudounipolar
3. 2 axons = Bipolar
4. No obvious axon = Anaxonic
5. One axon = Unipolar

Question 9

What are the 2 types of glia found in the PNS and what are role do they each have?

Answer 9

1. Schwann cells- myelinate
2. Satellite cells- support function in sensory and autonomic ganglia

Question 10

What are the 4 main types of glia found in the CNS and what role do they each have?

Answer 10

1. Oligodendrocytes- myelinate
2. Astrocytes- surround capillaries, part of BBB
3. Microglia- phagocytose pathogens and cellular debris
4. Ependymal cells- form epithelial layer of ventricles and central canal of spinal cord

Question 11

What does the membrane potential represent?

Answer 11

difference in ion electric potential

Question 12

Why is the RMP negative? (-70mV) What influences the distribution of cations?

Answer 12

Anions are fixed within the cell as they cannot penetrate the plasma membrane. These anions will attract cations which are capable of bypassing the plasma membrane to raise the membrane potential. Distribution of cations is influenced by the fixed anions within the cell

Question 13

What do we mean when we say each cell acts as a tiny battery?

Answer 13

There is a positive pole outside the plasma membrane and a negative pole inside the cell

Question 14

What does the Nernst equation allow us to determine?

Answer 14

The membrane equilibrium potential for a particular ion

Question 15

What does membrane potential of -90mV represent? What would a more neg or more pos MP cause?

Answer 15

-90mV represents the equilibrium membrane potential of potassium, where the intracellular and extracellular potassium concentrations are kept STABLE.
Fixed anions inside the cell attract potassium (can easily bypass the plasma membrane) causing the extracellular conc. of potassium to be lower and the intracellular conc. to be higher.
In order to make reach stable concentrations:
More negative MP would cause K+ influx
Less negative MP would cause K+ efflux

Question 16

RMP=EK true or false?

Answer 16

FALSE

Question 17

What MP once reached causes Na+ channels to close?

Answer 17

MP of +30mV is the peak of depolarization, this is when Na+ channels will close and K+ channels will open in order for repolarization to occur and return to RMP

Question 18

Does the size of depolarization affect the size or duration of the AP?

Answer 18

NO
size of depolarization DOES NOT affect the duration or size of the AP
ALL APs have the same amplitude
The AP will always reach +30mV then Na+ channels will close no matter the size of the stimulus

Question 19

What is different about the AP of skeletal muscle? What causes myotonia?

Answer 19

depolarization is still driven by Na+ channels BUT the RMP is driven by Cl- permeability
Deficits in Cl- give rise to myotonia- muscles can’t relax after contraction

Question 20

What role do myelinated axons play in the AP current?

Answer 20

myelinated axons allow AP current to jump between nodes of ranvier and therefore speeds up the transmission. They also save energy as the total ion influx is much LESS

Question 21

During the absolute refractory period…

Answer 21

neuron is unable to respond to a stimulus of any intensity

Question 22

What does cascade imply in homeostasis? What are the 3 steps of homeostasis? What are the similarities and differences between extrinsic and and intrinsic pathways?

Answer 22

Cascade implies step-wise procedure where one component activates the next. Cascade results in activation of clotting factors
3 steps of homeostasis:
1. vasoconstriction / vascular spasm
2. formation of platelet plug (reduce blood loss)
3. production of a web of fibrin proteins which penetrate and surround platelet plug (coagulation)
Similarities: both pathways convert fibrinogen into fibrin. Both are biochemical pathways that activate clotting factors. Both converge to common pathway at thrombin
Differences: initiation of intrinsic pathway occurs when factors inside blood are exposed to extracellular matrix outside blood vessels. Initiation of extrinsic pathway occurs due to factor release by damaged tissues (shorter pathway)