Neurons, action potential, synapses, neurotransmitters, divisions of the nervous system, and sense organs

1. The Nervous System
Ch. 37/38

2. Objectives
Content
Label and describe the
major divisions of the
nervous system and of
neurons
Skill
Use models and
representations

3. The command
center of the body
The brain contains over 100 billion neurons (nerve
cells)
Each one of those connected to 100s of others
Incredibly complex
MRIs have allowed scientists to “see” into the brain
Have found that certain regions dedicated to certain tasks

4. Evolution of the Nervous System
All animals
(except
sponges) have
some sort of
nervous system
The
arrangement of
neurons is what
is different
between them
Greater complexity
of the nervous
system evolved with
cephalization

5. Quick Think
The Unity of Life is an important theme in
BIOLOGY
All living things are able to RESPOND TO
THEIR ENVIRONMENT
With a partner – come up with at least 3With a partner – come up with at least 3
different organisms and how theydifferent organisms and how they
respond to their environmentrespond to their environment
Be prepared to share

8. hibernation
estivation
migration

11. https://www.youtube.com/watch?v=bkVhLJLG7ug
this is so beautiful

13. The mammalian nervous system
has 2 parts
1. Central Nervous
System (CNS)
1. Brain + spinal cord
2. Peripheral
Nervous System
(PNS)
1. All the nerves that run
throughout the body

14. Nervous system is made up of
neurons & support cells

15. Neurons
The cells of the nervous system
Cell body – contains nucleus & organelles
Dendrites – extensions of the cell body that
receive incoming messages from other cells
Axon – conveys message to the next cell

16. Axon – many are covered in a fatty
layer called the myelin sheath
This insulates the axon and helps the
message travel faster

17. Synaptic terminal –
the end of the axon
Synapse – where the
message is relayed from
one neuron to the next
Message is sent via a
chemical messenger
called a
neurotransmitter

19. 3 main types of neurons
Sensory neurons –
collect info from inside
(blood pressure, blood
CO2 levels, etc) &
outside the body (light,
temperature, taste, etc)

20. Interneurons
– neurons in
CNS that
analyze &
interpret the info
from the
sensory neuron
and connect to
motor neurons
to elicit a
response

21. Motor neurons – send signals
from the CNS to the body
Messages sent to effector cells
Effector cells are muscle cells or
gland cells that carry out a particular
response

22. An example of a nerve circuit
The reflex arc – a
reflex is a body’s
automatic response
to stimuli
Sensory neuron
receives info
Passes message to
spinal cord
(interneurons)
Message passed to
motor neuron
Motor neuron signals
an effector cell
Response is initiated

23. Dendrites, cell body, axon,
sensory neuron, interneuron,
motor neuron, stimulus, effect

24. Glia – support cells for
neurons
3 kinds:
Astrocytes – provide support to neurons
Oligodendrocytes – form the myelin
sheath in the CNS
Schwann cells – form the myelin sheath
in the PNS

25. Stop and Process – read
description & color as you go
A bracket – red
B bracket – yellow
C & D– pink
E1 & E2 – orange
F1 – blue
F2 – green
F3 – light green
G bracket – gray
Background of G
area – gray
Cell bodies and
dendrites in G area –
pink
H bracket – white
Axons in H area -
purple

26. How neurons send messages
Part 1: Electrical message within
the neuron

27. Q: What is membrane potential?

28. All cells maintain an
electrical potential
difference (voltage)
across their plasma
membrane
The membrane
potential is maintained
by a difference in ionic
composition on either
side of the membrane
For neurons- the
resting potential is the
membrane potential
when the cell is not
transmitting a signal

29. Q: What is membrane potential?
A: A difference in charge between the
inside and outside of the cell
membrane

30. Q: How is this membrane potential created?

31. Neurons have ion
channels in the membrane
The sodium/potassium
pump protein (Na+
/K+
) uses
active transport (ATP) to
maintain the resting
potential

32. Q: How is this membrane potential created?
A: by proteins in the cell membrane called
sodium/potassium (Na+
/K+
) pumps

33. Q: Why “potential”? I get “membrane”…but
what does the “potential” part mean?
A: It refers to potential energy – the
potential to do work for the cell

34. Q: So how do Na+
/K+
pumps work?
A: they move 3 Na+
out of cell and 2 K+
into cell so there is an overall negative
charge inside the cell

35. Q: What is “resting” potential?
A: normal voltage (~-70 mV) when a
neuron is inactive

36. A stimulus of some
sort affects the
permeability of the
membrane to
certain ions
This gives rise to a
nerve impulse we
call an action
potential

37. Q: What is an “action” potential?

38. The Action PotentialAction Potential (aka
nerve impulse)
They are the signals
conducted by the
axons
An all or none
reaction
It starts with a
stimulus that causes
the depolarization
of the neuron
Na+
ion channels
open and Na+
enters
the cell
This reverses the
charges (+ inside
and – outside)

39. The action
potential ends as
Na+
channels are
closed and K+
channels are
opened
This helps return
the neuron to its
resting potential

40. Action potentials move down the axon
Saltatory conduction is the jumping
of the nerve impulse between the
nodes of Ranvier
This speeds up nerve impulses

41. Q: What is an “action” potential?
A: a stimulus opens ion
channels in cell
membrane that allow Na+
to rush into cell, reversing
electrical potential. This
impulse jumps from node
of Ranvier to node of
Ranvier until it reaches
the synapse

42. Q: How does it all go back to normal?
A: The Na+
/K+
pump

43. So…
bioflix

44. How the message is passed
to the next neuron
From the axon of one
cell to the dendrites of
then next through the
synapse
Electrical
synapse (a few) -
electrical current
flows from cell to cell
via gap junctions
Chemical synapse
(most) - the release
of a neurotransmitter

45. The Chemical Synapse
Neurotransmitter
binds to receptors on
the plasma
membrane of the next
neuron
This triggers an
action potential in the
next neuron

46. Neurotransmitters are then broken down
by enzymes, diffuse away, or are taken up
by neighboring cells
Bioflix

47. 2 types of neurotransmitter
response
1. Excitory postsynaptic potential
(EPSP) - binding of neurotransmitter
causes electrical charge (depolarization) of
postsynaptic membrane - action potential
can now be generated in this cell
2. Inhibitory postsynaptic potential
(IPSP) - binding of neurotransmitter causes
an electrical charge that makes it harder for
the next neuron to generate an action
potential

48. Acetylcholine - reduces the strength
& rate of contraction of cardiac
muscles
Epinephrine & norepinephrine -
“fight or flight”
Important neurotransmitters
Serotonin &
Dopamine -
affect sleep,
mood,
attention,
learning

49. The Central and Peripheral
Nervous Systems

50. Peripheral Nervous System
Somatic nervous
system - carries
signals to skeletal
muscles
Autonomic
nervous system -
regulates automatic
functions of smooth &
cardiac muscle
Sympathetic
division - increased
heart rate, adrenaline,
fight-or-flight
Parasympathetic
division - opposite
effect, calming

51. The Brain
Cerebrum - 2 hemispheres,
regulates learning, language,
personality, etc.
Contains a thick band of axons that
connects the 2 sides called the corpus
callosum

52. Each side has 4 lobes:
Frontal Temporal
Occipital Parietal

53. Cerebellum - coordination, decision
making, consciousness, awareness of
surroundings

54. Brainstem - medulla oblangata +
pons + midbrain
Controls breathing rate, arousal & sleep,
swallowing, digestion

55. Diencephalon - epithalamus,
thalamus, and hypothalamus
Main center through which sensory and
motor info passes to & from cerebrum
Hypothalamus controls feeding, fighting,
fleeing, reproduction, circadian rhythms

56. Sensory & Motor Mechanisms
Ch. 49

57. Types of sensory receptors
Mechanoreceptors - get info from physical
stimuli (pressure, touch, motion, sound)
Thermoreceptors - heat & cold , maintain
body temp
Chemoreceptors - solute concentration,
taste, smell
Electromagnetic receptors - detect
electromagnetic light, electricity,
magnetism
Pain receptors - respond to excess
stimuli

58. Mechanoreceptors for hearing detect
settling particles & moving fluid
Ear
Outer ear - external pinna & auditory
canal
Collect sounds & direct them to tympanic
membrane (eardrum)

59. Middle ear - vibrations conducted through 3
small bones (malleus, incus, stapes)
Inner ear - contains cochlea - organ for
hearing
Organ of Corti - in cochlea, has hair cells that
transduce vibrations into action potentials

60. Taste
Tastebuds are
modified epithelial
cells on tongue &
mouth

61. Eyes
Compound eyes
(insects,crustaceans) - have 1000s of
light detectors and lenses
Single lens eye (vertebrates, some
inverts)

62. Eyeball - 2 outer layers
Sclera & choroid
Sclera becomes cornea - allows light in
Pupil - hole in center of iris
Retina - contains photorecptor cells
Rods - very light sensitive cells
Cones - cells that distinguish color
Aqeuous humor -
fills anterior of eye
Vitreous humor -
fills posterior of eye
Rhodopsin - light
absorbing pigment
that triggers signal
transduction
pathways that lead to
sight

63. Skeleton
Exoskeleton - hard encasement on
surface of animal
Endoskeleton - hard parts buried
within soft tissue

64. Skeletal
muscle
Attached to bone,
responsible for
movement
Made up of long fibers
that are the muscle
cells
Muscle fibers are
made up of bundles of
myofibrils
Myofibrils have 2
kinds of
myofilaments: thick

65. Basic contractile
unit is sarcomere
During contraction,
the sarcomere
length is reduced
Sliding filament
model - thick &
thin filaments slide
past each other
Actin & myosin
molecules in thick
& thin filaments
interact to cause
the sliding

66. Slow twitch
muscle fibers - slow,
long lasting
contractions
(endurance)
Fast twitch
muscle fibers - fast,
powerful contractions
(speed)