The nervous system and the action potential

Question 1

the nervous system allows for rapid and direct communication between specific parts of the body resulting in …

Answer 1

changes in muscular contractions or glandular secretions.

Question 2

what is included within the nervous system?

Answer 2

brain, spinal cord, nerves and neural support cells and sense organs like eye and ear

Question 3

what is the functional unit of the nervous system?

Answer 3

neuron (can transmit signals via electrical or chemical means)
- so highly specialized that it can’t replicate.
it depends almost entirely upon glucose for its chemical energy - it depends highly on the efficiency of the aerobic respiration.
- neurons DO NOT depend on insulin to obtain glucose.

Question 4

what are the parts of the neuron?

Answer 4

dendrites : receive a signal to be transmitted.
axon hillock: generate an axon potential in all directions including down the axon.
the signal travels from the dendrites to the axon hillock, where an action pot is generated and moves down the axon to the synapse.

Question 5

what is the action pot?

Answer 5

disturbance in the electrical field across the mem of the neuron.

Question 6

what is the resting potential?

Answer 6

eat mainly by an equilibrium between passive diffusion of ions across membrane and the NA/K pump. the pump moves 3 NA out and brings in 2 K. So the positive charge outside is more then inside. also , the electrochemical gradient of NA increases, and there’s a force that pushes the NA back into the cell . eventually, the rate at which the na is pulled in = rate at which its pushed out. when all rates reach equilibrium, the inside of the mem has a negative potential diff compared to the outside. this potential difference is called the resting mem potential.

Question 7

the mem of the neuron also has integral mem proteins called ?

Answer 7

voltage gated sodium channels. these proteins change conformation when voltage across the mem is disturbed. they allow NA to flow thru the mem for a fraction of second as the confirmation is being changed. more na comes in due to positive feedback. now the inside is positive ( depolarization has occurred)

Question 8

the neuronal mem also has voltage gated ____ channels

Answer 8

voltage gated potassium channels- these are less sensitive to voltage change so they take longer to open. by the time they start to open most of the NA channels are closing. now the K moves out fo the cell, making inside of the cell negative and this is called depolarization. the potassium channels are so slow to close that for a fraction of a second, the inside becomes even more negative then the resting potential and this is called hyper polarization.

Question 9

the action potential is a

Answer 9

all or nothing process

Question 10

in order to create an action potential the stimulus to the membrane must be greater then the …

Answer 10

threshold stimulus.

Question 11

what is the absolute refectory period?

Answer 11

once an action potential has begun, there is a short period of time called the absolute refractory period in which no stimulus will create another action potential.

Question 12

what is the relative refectory period?

Answer 12

the time during which only an abnormally large stimulus will create an action potential.

Question 13

which other cells conduct action potentials?

Answer 13

cardiac and skeletal muscle cells

although these action potentials are slightly diff in duration, shape, and even in the types of ions.

Question 14

how are neural impulses transmitted from one cell to another ?

Answer 14

chemically or electrically via a synapse

this transmission is the slowest part !

Question 15

electrical synapses

Answer 15

are uncommon! they are composed of gap junctions between cells. cardiac muscle, visceral smooth muscle and a very few neutrons in the CNS contain electrical synapses.
- they transmit signals much faster then chemical synapses and in both directions

Question 16

chemical synapse

Answer 16

more common! , it is unidirectional!
small vesicles with neurotransmitters rest in the presynaptic membrane, the membrane near the synapse contains an unusually large amounts of ca voltage gated channels. when an action potential arrives at a synapse, these channels are activated and allows ca to flow into the cell . sudden influx of ca ions causes some of the neurotransmitter vesicles to be released through exocytosis into the synaptic cleft.

Question 17

what does the post synaptic mem have?

Answer 17

it has neurotransmitter receptor proteins, to which the neurotransmitter will attach to and this will make the post synaptic mem more permeable to ions– completing the transfer of the neural impulse.

Question 18

neurotransmitter

Answer 18

the neurotransmitter attaches to its receptor for only a fraction of a second and is released back to the synaptic cleft if it remains there , the post synaptic cell may be stimulated over and over. the cells deals with this by: destroying the neurotransmitter by an enzyme, it may be also absorbed directly by the presynaptic cell via active transport. it may also diffuse out of the synaptic cleft.

Question 19

a single synapse can …

Answer 19

only release one type of neurotransmitter and is designed to either inhibit or excite but not both.
on the other hand, some neurotransmitters are capable of inhibitor or excitation depending upon the type of receptor in the postsynaptic membrane.

Question 20

receptors on the post synaptic mem can be…

Answer 20

ion channels themselves which open when a respective neurotransmitter attaches or they can act via second messenger system activating another molecule inside the cell to make changes.

Question 21

what do we know about second messenger systems?

Answer 21

they are preferred for prolonged changes such as in memory. G proteins commonly start second messenger systems. A G protein is attatched to the receptor protein along the inside of the postsynaptic membrane . When the receptor is stimulated by a neurotransmitter, part of the G protein called the alpha subunit breaks free.

Question 22

what does the alpha subunit that breaks away from the G protein do?

Answer 22

it may : 
activate separate specific ion channels 
activate a second messenger (cAMP, cGMP)
activate intracellular enzymes
active gene transcription

Question 23

what do synapses attach to ?

Answer 23

most synapses contact dendrites, but some may directly contact other cell bodies, other axons, or even other synapses.

Question 24

besides neurons , nervous tissue contains many support cells called?

Answer 24

glial cells or neuroglia

neuroglia are the ones that are capable of cellular division

Question 25

what are the 6 types of glial cells?

Answer 25

1) microglia - phagocytize microbes and cellular debris in the CNS.
2) ependymal cells - are epithelial cells and they line the space containing the CSF. These cells use cilia to circulate the CSF
3) satellite cells - these support ganglia
4) astrocytes- give physical support to neurons
5) oligodendrocytes- wrap many times around the axon in the CNS - create myelin in the CNS
6) neurolemmocytes or Schwann cells. - MYELIN in PNS

Question 26

What is the function of the myelin

Answer 26

increases the rate at which an axon can transmit signals.

gaps between the myelin are nodes of ranvier.

Question 27

what is saltatory conduction?

Answer 27

when an action potential jumps from one node of ranvier to the next