Nervous System

Question 1

What is the Nervous System and the Endocrine System

Answer 1

The nervous system works in conjunction with
the endocrine system to respond to both
internal and external environmental change,
thereby maintaining homeostasis within the
body.
○ The nervous system responds via
electrochemical messages relayed from the
brain
○ The endocrine system responds via
chemical messengers relayed through the

Question 2

Two main types of nerve cells found in the nervous
system:

Answer 2

1. Glial Cells
   ○ used for structural and
   nutritional support
2. Neurons
   ○ conduct nerve impulses
   throughout the body
   ○ supported by glial cells

Question 3

Neurons

Answer 3

Neurons are the basic unit of the
nervous system

Question 4

Dendrites, Axons, myelin sheath

Answer 4

Dendrites - branches which
accept nerve impulses from
other neurons and carry them
towards the cell body
➢ Axons - longer branches which
carry nerve impulses away from
the cell body
➢ A fatty myelin sheath
surrounds each axon, insulating
the neuron and speeding up
the rate of impulse transmission

Question 5

Schwann Cells, nodes of Ranviersaltatory
conduction), axon
terminal

Answer 5

Schwann Cells, a type of glial cell, are
responsible for producing the myelin around
each axon
➢ Gaps between Schwann cells are referred to
as the nodes of Ranvier. Electrical impulses
“jump” from node to node (saltatory
conduction)
➢ Once the electrical signal reaches the axon
terminal, it is passed on to the dendrites of
an adjoining neuron.

Question 6

Myelination

Answer 6

The myelination of neurons is vital for proper signal
transduction within the nervous systems.

• Myelinated
  Neurons

Unmyelinated
Neurons
Make up the white
matter of your
brain, which is
responsible for
conducting nerve
impulses

• Unmyelinated
  Neurons
  Make up the grey
  matter of your brain,
  which is responsible
  for processing
  information and
  generating nerve
  impulses
  Can regenerate
  after injury
  Cannot regenerate
  after injury

Question 7

Multiple Sclerosis

Answer 7

MS is a genetic disorder which causes hardened tissue
to form on top of the myelin sheath, affecting nerve
transmission. ➢ Symptoms: numbness/tingling
of limbs, muscle spasms, loss of balance and coordination

➢ The more scar tissue that builds
up along the nerve, the worse
the symptoms become. As a
result, MS gradually worsens with
age

Question 8

Types of Neurons

Answer 8

1. Sensory Neurons (afferent)
   ● Gather information from sensory receptors (i.e.
   touch/sight/sound/taste receptors) and
   transmit these impulses to the brain
2. Interneurons
   ● Process and integrate incoming sensory info
   from sensory neurons and relay outgoing
   information to motor neurons
3. Motor Neurons (efferent)
   ● Transmit information from the brain to muscles
   (effectors), glands, and other organs

Question 9

Neural Circuits

Answer 9

answer it on your own

Question 10

Reflex Arc

Answer 10

A neural circuit that passes through interneurons in
the spinal cord for immediate response

Question 11

Summation

Answer 11

The sum of multiple neurons
can lead to greater
stimulation
* Example: One postsynaptic
neuron (D) is excited/inhibited
by more than one presynaptic
neuron (A, B, C

Question 12

Conduction of Nerve Impulses (Electrical
Event)

Answer 12

A nerve impulse or action potential has both a
chemical and electrical component (hence the
term electrochemical impulse)

Four stages of a nerve
impulse:
1)Polarized/resting
state
2)Depolarization
3)Repolarization
4)Refractory Period

Question 13

Resting State

Answer 13

The difference in charge across the membrane
of a resting neuron is called resting membrane
potential.➢ The inside of a neuron
has a slight negative
charge at rest, whereas
the outside has a slight
positive charge
➢ This results in a resting
potential of -70 mV

Question 14

Resting State & the Sodium-Potassium
Pump

Answer 14

Inside the resting cell, there
exists a higher concentration of
potassium (K+) than sodium
(Na+); outside the cell, the
opposite is true
ii. Potassium ions are able to
passively diffuse out of the cell
more easily than sodium ions
can diffuse into the cell to
counteract this concentration
gradient (K+ = “leaky” ion
channels)

3. In an attempt to balance this
   difference, the sodium-
   potassium pump along the
   membrane surface will
   exchange three sodium ions
   from inside the cell for two
   potassium ions from outside
   the cell

As a result, as excess of
positive charge accumulates
outside of the cell membrane.
A constant membrane
potential of -70 mV is

Question 15

Depolarization

Answer 15

Action potentials occur when a neuron is
stimulated by an electrical impulse

.a. An impulse causes sodium
gates to fully open, thus
allowing Na+ to diffuse
freely across the membrane

b. Na+ rushes into the cell
(down their concentration
gradient), leading to a slight
positive charge on the
inside relative to the outside

c. This reverses the
membrane potential from
-70 mV to +40 mV; the
membrane is now said to
be depolarized

d. Once Na+ reaches
equilibrium, the
membrane once again
becomes impermeable to
them, and the gates close

Question 16

Depolarization & Threshold Potential

Answer 16

An action potential is considered to be an “all-or-none”
event because any stimulus that fails to achieve a
membrane potential of at least -55 mV will have no effect
● Note that increasing the
stimulus strength does not
increase the impulse
strength; a neuron will
either fire or not fire
● The intensity of a stimulus
is instead experienced as
an increased frequency
(number) of nerve impulses

Question 17

Repolarization

Answer 17

Once an action potential has peaked, Na+ gates close, and K+
gates open so K+ rushes out of the axon.
➢ This restores the positive charge outside the
membrane; however, Na+ and K+ concentrations are
briefly reversed compared to at the resting state (Na+
is higher inside the membrane)
➢ The sodium-potassium pumps kicks in and exchanges
Na+ for K+, restoring the initial resting potential of -70
mV. This process is called repolarization.
➢ Occurs in a wavelike motion down an axon

Question 18

Refractory Period
(Hyperpolarization)

Answer 18

he sodium-potassium pump often overshoots -70 mV and
the cell becomes hyperpolarized (-90 mV). Until the
resting potential of the neuron has been properly restored,
a second action potential cannot be conducted along the
axon; this is referred to as the refractory period
➢ During this time, the
membrane cannot be made
permeable to Na+, so a
second wave of
depolarization cannot occur
➢ The stronger the impulse, the
longer it takes for the nerve
to recover

Question 19

Signal Transduction Across a Synapse
(Chemical Event)

Answer 19

Once the impulse has traveled down the entire length of
the axon, it reaches the axon terminal.
➢ The axon terminal is in close
contact with the dendrites of
another neuron
➢ For the signal to move to the
next neuron, it must cross
the space between the axon
terminal and the dendrites
of the subsequent cell; this
space is referred to as the
synapse

Question 20

Neurotransmitter Release and Binding

Answer 20

1.An action potential reaches
the axon terminal

2.Calcium channel “gates”
within the axon terminal
open, causing calcium ions
to flow into the cell and
trigger the movement of
neurotransmitter vesicles
towards the presynaptic
membrane

Vesicles fuse to the
membrane and
neurotransmitters
are released into the
synapse

4. Neurotransmitters
   diffuse across the
   synaptic cleft to the
   post-synaptic
   membrane
5. Once neurotransmitters have
   reached the post-synaptic
   membrane, they bind with
   receptors embedded in the
   membrane
6. Binding induces or inhibits an
   action potential in the
   corresponding neuron
7. Neurotransmitters are then
   released by the receptors and
   either return to the presynaptic
   neuron or are broken down by
   an enzyme on the post-synaptic

Question 21

Neurotransmitter Types: Excitory

Answer 21

There are two types of neurotransmitters:
1) Excitatory

Causes the Na+ channels of the post-synaptic
membrane to open, resulting in depolarization and
continuing the action potential
● e.g. Acetylcholine is an excitatory neurotransmitter
found in muscle cells; causes contraction of the
muscle fibre
● Cholinesterase is the enzyme required to break
down acetylcholine after the action potential has
occurred
● Insecticides and nerve gas block the release of
cholinesterase, causing muscles to remain in a state
of constant contraction

Question 22

Neurotransmitter Types: Inhibitory

Answer 22

2. Inhibitory
   ● Trigger K+ channels to open, causing
   K+ to flow out and thus lowering the
   membrane potential.
   ● This leads to hyperpolarization,
   making it more difficult to generate
   an action potential
   ● e.g. GABA (gamma-aminobutyric
   acid): Problems with GABA are often
   associated with epilepsy and
   Huntington’s disease