physiology notes: neurophysiology

Chapter 11

1. a. Cell body: contains the nucleus; control center; carries out metabolism

b. Dendrite: thin branched processes that project from cell body; receives

impulses from other neurons

c. Axon hillock: narrow region where axon begins; nerve impulse originates

here

d. Axon and axonal terminals: axon is a long process that conducts impulses away

from the cell body; axonal terminals are the enlarged ends of the axon.

2. Myelin sheath in peripheral system: from Schwann cells; leaves exposed patches

(Nodes of Ranvier)

Myelin in central nervous system: from oligodendrocytes (neuroglia)

3. Nodes of Ranvier: gaps in the myelin sheath; rapid ion exchange area.
4. Membrane potential: when cells have an electrical charge across their membrane due to negative proteins and K+ inside the cell and Na+, Ca² and Cl- outside the cell; it is about -70mv.
5. a. Depolarization: when the membrane potential becomes less negative (more positive); can be caused by Na+ moving into the cell±

b. Repolarization: when membrane potential moves back toward -70mv; can be

caused by K+ moving out of the cell or Cl- moving in.

c. Hyperpolarization: when membrane potential becomes more negative than

-70mv; can be caused by K+ moving out of the cell or Cl- moving into cell

6. Gated ion Channels: found in axons; open due to a certain stimulus; will stay open a

fraction of a second before being blocked; there are ion channels for Na+, K+,

and Cl-

7. Voltage gated: channels that open at a certain membrane potential; axon terminals have Ca+² voltage gated channels

Ligand gated ion channels: open when a certain molecule binds to a receptor

the membrane surface

8. Action potential: rapid changes in membrane potential across a small section of

the axon membrane caused by ion movement cross the membrane

9. Na+ movement: depolarization below -50mv opens voltage gated Na+ channels to

Open; Na+±the cell; membrane potential rises to +30mv and then blocks Na+

channels and Na+ movement stops.

K+ movement: after Na+ channels open, gated K+ channels open letting K+ out of the cell; membrane potential drops to -90mv;

10. Na+/K+ pump: moves Na+ back out of the cell and K+ into the cell, resetting the

proper ion gradient

11. Myelinated axons: the myelin sheath will not allow ions to cross the membrane;

at the nodes of Ranvier, the axon is bare and here ions can cross at these areas; this is called saltatory conduction.

Non-myelinated axons: have no sheath of myelin; action move down the entire

length of the axon; every stretch of the axon will experience depolarization and

repolarization; the action potential moves like a wave.

12. All or None Law: voltage gated channels will open all the way once the membrane potential reaches the threshold; therefore, every action potential has

same strength.

13. Refractory period: time period during an action potential in which the axon

cannot respond to a new change in the membrane potential.

14. Absolute refractory period: when Na+ ion channel is opened it can not respond to

another depolarization until it moves from the active state to the closed state.

Relative refractory period: if a 2^nd depolarization occurs while the K+ channels are open , it takes a more intense depolarization to overcome the effect of the

K+ leaving through the open K+ channels.

15. Synapse: junction point between two neurons or between a neuron and an effector

cell (muscle or gland).

16. Neurotransmitters: chemicals stored in vesicles in the axon terminal of the

pre-synaptic cell.

Function: when an action potential moves down the axon to the terminal, the

membrane depolarization opens voltage gated Ca+² channels;

-Ca+² enters the cell causing the vesicle to fuse with the presynaptic membrane

releases neurotransmitters in the synaptic cleft

- neurotransmitters cross the synaptic cleft and bind to receptors on the

post-synaptic membrane.

17. Excitatory postsynaptic potential: depolarization; more neurotransmitters= more

Depolarization; no refractory period; several EPSP’s can be summed to create

a greater depolarization

Inhibitory postsynaptic potential: hyperpolarization; lessens the chance for

depolarization due to increased outward diffusion of K+ ions and > increase

of positive charge outside the membrane.

18. Describe:
    1. Acetylcholine: excitatory neurotransmitter in the CNS and neuromuscular

junction; can be excitatory or inhibitory

18. 2. Ligand-gated channels: nicotinic acetylcholine receptors: acetylcholine binds to receptors and opens channels that let Na+ in and K+ out; more

Na+ comes in so they produce EPSPs in neuromuscular junction

18. 3. G-protein mediated channels: muscarinic acetylcholine receptors: binding

of acetylcholine to these receptors activate a G-protein; one type of G protein opens K+ channels letting K+ out causing an IPSP; another type

closes K+ channels causing an EPSP; therefore, two different cells can have opposite response to muscarinic stimulation.

d. Acetylcholinesterase: enzyme in the synaptic cleft that degrades

acetylcholine.

e. Monoamines: neurotransmitters derived from amine groups; similar in

action to acetylcholine

f. Second messenger mediation: rather than activating ion channels directly,

monoamines work through a 2^nd messenger, Cyclic AMP

which is the second messenger; cyclic AMP±ion channels to open

g. Monoamine inactivation: monoamines are reabsorbed by the pre-synaptic

cell and degraded by the enzyme monamine oxidase

h. Serotonin: involved in mood, behavior, appetite, cerebral circulation.

i. Dopamine: two separate systems: one involved in control of movements

and one involved in behavior and reward

j. Norepinephrine: involved in general arousal

k. Amino acids as neurotransmitters: some create EPSP’s and others, IPSP’s by opening voltage gated Cl- channels (glycine, glutamate, GABA)

l. Polypeptides: analgesics, opioids; (endorphins)

m. Nitric oxide: diffuses out of pre-synaptic cell and into postsynaptic cell and causes muscle relaxation in target organ; can produce engorgement of spongy tissue with blood in males

19. Signal integration: all the EPSP’s and IPSP’s that occur on the dendrites of the

post-synaptic cell will add together to alter membrane potential of axon hillock

20. Spatial summation: occurs when IPSP’s and EPSP’s from several synapses

combine to alter the membrane potential

21. Temporal summation: occurs when several EPSP’s or IPSP’s are generated from

the same synapse in a very short period of time and the collected effect is added

together to alter the membrane potential