Physiological Control

Question 1

Endocrine System

Answer 1

• Releases hormones (chemical substances) into the blood stream to exert influence on distant cells
• Response is slow and widespread
• negative feedback loop

Question 2

Endocrine Cells

Answer 2

• Typically organized into endocrine glands
• Glands are ductless - hormones released into capillaries among cells
• target cells have a receptor that binds to the hormone
• needs a receptor, cannot be injected into cell

Question 3

The nervous system

Answer 3

• Made up of neurons
• stimuli received by dendrites

Question 4

Resting Membrane Potential

Answer 4

• voltage difference between inside and outside of cell
• negatively charged inside
• NaK pump moves 3Na+ out and 2K in (primary active transport)
• More K inside, leaks out through K channels creating negative inside
• can be measured by glass electrode
• usually at -70 to -55mV

Question 5

Polarization

Answer 5

• When a neuron is excited, in inside become less negative (depolarized)
• starts in dendrites and travels to cell body
• if depolarization at the axon hillock exceeds threshold, action potential is fired

Question 6

Depolarization and repolarization

Answer 6

• Summed input depolarizes the cell membrane at the axon hillock above the threshold potential, from resting
• Voltage gated Na+ channels open, Na+ rapidly enters the cell, K channels open slower
• Voltage increases to +40mV, Na channels close, K channels remain open, potential becomes more negative
• Overshoot of K leaving cell results in hyperpolarization, starts a refractory period
• returns to resting as K+ is returned through NaK pumps

Question 7

Refractory Period

Answer 7

• Inside voltage falls bellow and then returns to resting
• A neuron cannot fire a second action potential

Question 8

Action Potentials

Answer 8

• propagated along axon by opening and closing adjacent Na and K channels
• travel in one direction
• water will dilute ions, making it harder to reach an action potential

Question 9

Saltatory propagation

Answer 9

• Myelin sheath insulates axon, potentials jump from node to node increasing conduction speed
• gaps are node of ranvier, buildup of +ve charges inside and -ve charges outside axon

Question 10

Synaptic transmission

Answer 10

• Begins with action potential conduction to the axon terminal
• depolarization of the axon terminal opens Ca2+ channels, Ca flows into cell
• vesicles fuse with presynaptic membrane, releasing neurotransmitters into synaptic cleft
• ACH binds with post-synaptic ligand gated channels, allowing in ions
• ACH is actively reabsorbed into the presynaptic terminal

Question 11

Signals

Answer 11

• Can be excitatory or inhibitory
• Effect of ACH binding depend on type of postsynaptic cell
• If depolarized - potential is excitatory (EPSP), more likely to reach an action potential
• If hyperpolarized - potential is inhibitory (IPSP), harder to reach and action potential

Question 12

Sensory Transduction

Answer 12

• sensory receptor cells:
• Chemoreceptors - chemical signals, become depolarized
• mechanoreceptors - pressure opens cell
• photo receptors - response to light, hyperpolarization