1. Biology Sylvia S. Mader Michael Windelspecht
Chapter 37
Neurons and Nervous Systems
Lecture Outline
See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1

2. Evolution of the Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
eyespot
auricle
ventral nerve
cord with ganglia
cerebral
ganglia
nerve
brain
nerve net
lateral
nerve
cords
transverse
nerves
a. Hydra
b. Planarian
c. Earthworm

3. Evolution of the Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cerebrum
in forebrain
hindbrain
giant
nerve
fiber
spinal
cord
brain
eye
brain
thoracic
ganglion
tentacle
d. Crab
e. Squid
f. Cat 3

4. Evolution of the Nervous System
Division of Nervous System:
The Central nervous system (CNS)
Includes the brain and spinal cord
The peripheral nervous system (PNS)
Consists of all nerves that lie outside the CNS
Somatic nervous system
Sensory and motor functions that control skeletal muscle
Autonomic nervous system
Controls smooth muscle, cardiac, muscle, and gland
Divided into sympathetic and parasympathetic divisions

5. Organization of the Human Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
brain
cranial nerves
cervical nerves
thoracic
nerves
spinal cord
lumbar
nerves
radial nerve
median nerve
sacral
nerves
ulnar nerve
sciatic nerve
tibial nerve
common fibular
nerve a.

6. 37.2 Nervous Tissue Neurons (nerve cells)
Cell body contains nucleus and organelles
Dendrites receive signals from sensory receptors or other neurons
Axon conducts nerve impulses to another neuron or to other cells
Covered by myelin sheath

7. Nervous Tissue Types of Neurons Motor (efferent) neurons
Accept nerve impulses from the CNS
Transmit them to muscles or glands(away)
Sensory (afferent) neurons
Accept impulses from sensory receptors
Transmit them to the CNS
Interneurons
Convey nerve impulses between various parts of the CNS

8. Neuron Anatomy cell body dendrite myelin sheath direction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cell body
dendrite
myelin
sheath
direction
of conduction
axon
terminal
node of Ranvier
axon
a. Motor neuron (multipolar)
muscle
a: © M.B. Bunge/Biological Photo Service

9. Neuron Anatomy axon cell body direction of conduction sensory receptor
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
axon
cell body
direction of
conduction
sensory
receptor
axon
b. Sensory neuron (unipolar)
myelin sheath
skin 9

10. c: © Manfred Kage/Peter Arnold, Inc.
Neuron Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
axon
cell body
dendrite 10
c. Interneuron (multipolar)
c: © Manfred Kage/Peter Arnold, Inc.

11. Nervous Tissue Transmission of Nerve Impulses Resting Potential
The membrane potential (voltage) when the axon is not conducting an impulse
The inside of a neuron is more negative than the outside, around -70 mV
Due in part to the activity of the sodium-potassium pump

12. Nervous Tissue
An action potential is a rapid change in polarity across a portion of an axonal membrane
An action potential is generated only after a stimulus larger than the threshold (-55mV)
Gated channel proteins
One channel protein suddenly allows sodium to enter the cell
Another channel protein allows potassium to leave the cell

13. Resting and Action Potential of the Axonal Membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
+60
+40
Na+ moves
to inside
axon
K+ moves
to outside
axon
action
potential
+20
repolarization
depolarization
Voltage (mV)
–20
–40
threshold
–60
resting
potential 1 2 3 4 5 6
Time (milliseconds) 13
d. An action potential can be visualized if voltage changes are
graphed over time.

15. Nervous Tissue Propagation of Action Potentials
In nonmyelinated axons, the action potential travels down an axon one small section at a time
In myelinated fibers, an action potential at one node causes an action potential at the next node
Saltatory (jumping) Conduction
Conduction of a nerve impulse is an all-or-nothing event
Intensity of signal is determined by how many impulses are generated within a given time span

16. Nervous Tissue Transmission Across a Synapse
A synapse is a region where neurons nearly touch
Small gap between neurons is the synaptic cleft
Transmission across a synapse is carried out by neurotransmitters
Sudden rise in calcium in the axon terminal of one neuron
Calcium stimulates synaptic vesicles to merge with the presynaptic membrane
Neurotransmitter molecules are released into the synaptic cleft

17. Nervous Tissue Synaptic Integration
A single neuron is on the receiving end of
Many excitatory signals, and
Many inhibitory signals
Integration
The summing of excitatory and inhibitory signals

18. End of Nervous system Notes PT. 1

19. 37.3 The Central Nervous System
Consists of the brain and spinal cord
Three specific functions:
Receives sensory input
Performs integration
Generates motor output

20. The Central Nervous System
Consists of the brain and spinal cord
Spinal cord and brain are wrapped in three protective membranes called meninges
Spaces between meninges are filled with cerebrospinal fluid
Fluid is continuous with that of central canal of spinal cord and the ventricles of the brain

21. The Central Nervous System
The Spinal Cord
Two main functions
Center for many reflex actions
Means of communication between the brain and spinal nerves
Composed of grey matter and white matter
Cell bodies and short unmyelinated fibers give the gray mater its color
Myelinated long fibers of interneurons running in tracts give white mater its color

22. The Central Nervous System
The Brain
The cerebrum is the largest portion of the brain in humans
Communicates with, and coordinates the activities of, the other parts of the brain
Longitudinal fissure divides the cerebrum into left and right cerebral hemispheres

23. The Human Brain Cerebrum (telencephalon) opening to lateral ventricle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cerebrum
(telencephalon)
opening to lateral
ventricle
third ventricle
skull
Diencephalon
thalamus
(surrounds the
third ventricle)
meninges
corpus
callosum
hypothalamus
pineal gland
pituitary gland
fourth ventricle
Brain stem
midbrain
Cerebellum
pons
medulla
oblongata
spinal cord
a. Parts of brain
b. Cerebral hemispheres

24. The Lobes of a Cerebral Hemisphere
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
central sulcus
Frontal lobe
Parietal lobe
primary motor area
primary somatosensory area
somatosensory
association area
premotor area
leg
motor speech
(Broca’s) area
trunk
primary taste area
arm
prefrontal
area
hand
general interpretation area
face
tongue
Occipital lobe
primary
visual area
lateral sulcus
visual
association
area
Temporal lobe
auditory association area
primary auditory area
sensory speech (Wernicke’s) area

25. The Central Nervous System
Cerebral Cortex
A thin but highly convoluted outer layer of gray matter
Covers the cerebral hemispheres
Contains motor areas and sensory areas as well as association areas
Primary motor area is in the frontal lobe, just ventral to the central sulcus
Primary somatosensory area is in the parietal lobe, just dorsal to the central sulcus

26. The Central Nervous System
Basal nuclei
Integrate motor commands
Ensures that the proper muscle groups are either activated or inhibited

27. The Central Nervous System
Other Parts of the Brain
Diencephalon
A region encircling the third ventricle
Includes three structures
Hypothalamus
Forms the floor of the third ventricle
Integrating center that maintains homeostasis
Controls the pituitary gland

28. The Central Nervous System
Other Parts of the Brain
Diencephalon (continued)
Thalamus
Consists of two masses of gray matter located in the sides and roof of the third ventricle
Receives all sensory input except smell
Integrates sensory information and sends it to the cerebrum
Pineal gland
Secretes melatonin

29. The Central Nervous System
Other Parts of the Brain
Cerebellum
Separated from the brain stem by the fourth ventricle
Largest portion of the brainstem
Receives sensory input from the eyes, ears, joints, and muscles
Sends motor impulses out the brain stem to the skeletal muscles

30. The Central Nervous System
Other Parts of the Brain
Brain Stem
Contains the midbrain, pons, and the medulla oblongata
Midbrain
Acts as a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum
Pons
Contains axons that form a bridge between the cerebellum and the rest of the central nervous system
Medulla Oblongata
Contains reflex centers for vomiting, coughing, sneezing, hiccupping, and swallowing

31. The Central Nervous System
The Reticular Activating System (RAS)
A complex network of:
Nuclei (masses of gray matter)
Nerve fibers that extend the length of the brain stem
The reticular formation is a major component of the RAS
The RAS arouses the cerebrum via the thalamus and causes a person to be alert

32. The Reticular Activating System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
radiations
to cerebral
cortex
thalamus
reticular
formation
ascending sensory
tracts (touch, pain,
temperature)

33. The Central Nervous System
Limbic System
Complex network of tracts and “nuclei”
Incorporates
Medial portions of the cerebral lobes,
The basal nuclei, and
The diencephalon
Integrates higher mental functions and primitive emotions
Important structures in the limbic system are
The hippocampus and the amygdala

34. The Limbic System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
corpus callosum
thalamus
hypothalamus
hippocampus
olfactory bulb
amygdala
olfactory tract

35. The Central Nervous System
Learning and Memory
Memory
The ability to hold a thought in mind or recall events from the past
Learning
Takes place when we retain and use past memories
Short term memory is associated with the prefrontal area of the frontal lobe
Long term memory is associated with the hippocampus

36. 37.4 The Peripheral Nervous System
Somatic system
Includes cranial nerves and spinal nerves
Gather information from sensors and conduct decisions to effectors
Controls the skeletal muscles
Voluntary
Autonomic system
Controls the smooth muscles, cardiac muscles, and glands
Innervates all internal organs
Usually involuntary
Divided into two divisions
Sympathetic division
Parasympathetic division
Utilizes two neurons and one ganglion for each impulse

37. Cranial and Spinal Nerves
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
spinal cord
gray matter
vertebra
white matter
frontal lobe
olfactory bulb
dorsal root
olfactory tract
dorsal root
ganglion
optic nerve
optic chiasma
spinal
nerve
ventral root
vertebra b.
temporal lobe
central canal
cerebellum
gray matter
medulla
white matter a. c.
c: © Karl E. Deckart/Phototake

38. The Peripheral Nervous System
Reflex Arc
Sensory receptors generate a nerve impulse that moves along sensory axons through a dorsal root ganglion toward the spinal cord
Sensory neurons pass signals on to many interneurons in the gray matter of the spinal cord
Nerve pulses travel along motor axons to an effector, which brings about a response to the stimulus

39. A Reflex Arc Showing the Path of a Spinal Reflex
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pin
dorsal root ganglion
central canal
white matter
sensory
receptor
(in skin)
dendrites
Dorsal
gray matter
dorsal
horn
cell body of
sensory neuron
axon of sensory neuron
interneuron
dendrites
cell body of
motor neuron
axon of motor neuron
effector
(muscle)
ventral root
ventral horn
Ventral

40. The Peripheral Nervous System
Sympathetic division
Especially important during fight or flight responses
Accelerates heartbeat and dilates bronchi
Parasympathetic division
Promotes all internal responses associated with a relaxed state
Promotes digestion and retards heartbeat

41. Autonomic System Structure and Function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
inhibits tears
stimulates tears
constricts pupils
dilates
pupils
ganglion
inhibits salivation
Sympathetic Division
stimulates
salivation
Parasympathetic Division
cranial
nerves
slows heart
speeds
heart
dilates air
passages
constricts
bronchioles
vagus nerve
cervical
nerves
stimulates liver to
release glucose
stimulates gallbladder
to release bile
stimulates
adrenal
secretion
increases activity
of stomach and
pancreas
thoracic
nerves
inhibits activity
of kidneys,
stomach, and
pancreas
increases
intestinal
activity
decreases
intestinal activity
lumbar
nerves
inhibits
urination
ganglion
stimulates
urination
sacral
nerves
causes
orgasmic
contractions
causes
erection
of genitals
sympathetic ganglia
Acetylcholine is neurotransmitter.
Norepinephrine is neurotransmitter.

42. Comparison of Somatic Motor and Autonomic Motor Pathways

43. Drugs of Abuse
Drug abuse - person takes a drug at a dose level that increases the potential for a harmful effect.
Addiction - when more of the drug is needed to get the same effect
Withdrawal - when the user stops taking the drug
Alcohol, drugs, and tobacco can all adversely affect the developing embryo, fetus, or newborn.

44. Drug Use: Brain Activity Before and After the Use of Cocaine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
brain activity
Before cocaine use,
brain is less active.
After cocaine use, brain is more active.
© Science VU/Visuals Unlimited

45. End Nervous system Notes PT. 2

46. Evolution of the Nervous System
Vertebrate Nervous-System Organization
Central nervous system
Vertebrate brain is organized into three areas
Hindbrain
Midbrain
Forebrain

47. 37.1 Evolution of the Nervous System
Invertebrate Nervous System Organization
Hydras
Nerve net composed of neurons in contact with one another
Also in contact with contractile cells in the body wall
Planarians
Ladderlike nervous system
Cephalization - a concentration of ganglia and sensory receptors in the head
Annelids, Arthropods and Molluscs
Complex animals
True nervous systems

48. Organization of the Human Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Central Nervous
System
brain and
spinal cord
Peripheral Nervous
System
somatic motor
fibers (to skeletal
muscles)
somatic sensory
fibers (skin,
special senses)
autonomic motor
fibers (to cardiac
and smooth
muscle, glands)
visceral sensory
fibers (internal
organs)
sympathetic
division
parasympathetic
division 48 b.

49. Resting and Action Potential of the Axonal Membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
recording
electrode
inside axon
reference
electrode
outside axon + + + + + + + + + + – – – – – – – – – –
axonal
membrane – – – – – – – – – + + + + + + + + +
inside axon K+
Na+
gated K+
channel
gated Na+
channel
outside axon
a. Resting potential: more Na+ outside the axon and more K+ inside
the axon causes polarization.

50. Resting and Action Potential of the Axonal Membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – – + + + + + + + + + + – – – – – – – –
direction of impulse + + – – – – – – – – – – + + + + + + + +
open Na+
channel 50
b. Action potential begins: depolarization occurs when Na+ gates open and Na+ moves to inside the axon.

51. Resting and Action Potential of the Axonal Membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + + – – – – – – – – – – + + + + + + + +
direction of impulse – – + + + + + + + + + + – – – – – – – –
open K+
channel 51
c. Action potential ends: repolarization occurs when K+ gates open and
K+ moves to outside the axon.

52. Synapse Structure and Function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
path of action potential
1. After an
action
potential
arrives at an
axon terminal,
Ca2+ enters,
and synaptic
vesicles fuse
with the
presynaptic
membrane.
Ca2+
axon
terminal
synaptic vesicles
enclose neuro-
transmitter
cell body of
postsynaptic
neuron
synaptic cleft
2. Neuro-
transmitter
molecules
are released
and bind to
receptors
on the
postsynaptic
membrane.
presynaptic
membrane
neurotransmitter
postsynaptic
membrane
3. When an
excitatory
neuro-
transmitter
binds to a
receptor,
Na+ diffuses
into the
postsynaptic
neuron, and
an action
potential
begins.
neuro-
transmitter
receptor
Na+
postsynaptic
neuron