1. CHAPTER 28 Nervous Systems
Modules 28.1 – 28.9

2. Can an Injured Spinal Cord Be Fixed?
The spinal cord is the central communication conduit between the brain and the body
It consists of a bundle of nerves

3. Spinal cord injury disrupts communication between the central nervous system and the rest of the body
Paraplegia is paralysis of the lower half of the body
Quadriplegia is paralysis from the neck down
Research on nerve cells is leading to new therapies

4. NERVOUS SYSTEM STRUCTURE AND FUNCTION
28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands
The nervous system has three interconnected functions
Sensory input
Integration
Motor output

5. Peripheral nervous system (PNS) Central nervous system (CNS)
SENSORY INPUT
INTEGRATION
Sensory receptor
MOTOR OUTPUT
Brain and spinal cord
Effector
Peripheral nervous system (PNS)
Central nervous system (CNS)
Figure 28.1A

6. The nervous system can be divided into two main divisions
The central nervous system (CNS) : the brain the spinal cord (in vertebrates)
The peripheral nervous system (PNS) : nerves ganglia (carry signals into/out of the CNS)

7. Central nervous system
Peripheral nervous system
B1. Somatic nervous system
B2. Autonomic nervous system
1. Cerebrum
2. Brainstem
3. Cerebellum
4. Spinal cord

8. Three types of neurons correspond to the nervous system’s three main functions
Sensory neurons convey signals from sensory receptors into the CNS
Interneurons integrate data and relay signals
Motor neurons convey signals to effectors

9. 1 2 3 4 Sensory receptor Sensory neuron Brain Ganglion Motor neuron
Spinal cord
Quadriceps muscles 4
Interneuron
CNS
Nerve
Flexor muscles
PNS
Figure 28.1B

10. 28.2 Neurons are the functional units of nervous systems
Neurons are cells specialized to transmit nervous impulses
They consist of
a cell body
dendrites (highly branched fibers)
an axon (long fiber)

11. Supporting cells protect, insulate, and reinforce neurons
The myelin sheath is the insulating material in vertebrates
It is composed of a chain of Schwann cells linked by nodes of Ranvier
It speeds up signal transmission
Multiple sclerosis (MS) involves the destruction of myelin sheaths by the immune system

12. Signal direction
Dendrites
Cell body
Cell body
Node of Ranvier
Myelin sheath
Signal pathway
Axon
Schwann cell
Nucleus
Nucleus
Nodes of Ranvier
Schwann cell
Myelin sheath
Synaptic knobs
Figure 28.2

13. FIGURE 38-1 A nerve cell, showing its specialized parts and their functions

14. 28.3 A neuron maintains a membrane potential across its membrane
NERVE SIGNALS AND THEIR TRANSMISSION
28.3 A neuron maintains a membrane potential across its membrane
The resting potential of a neuron’s plasma membrane is caused by the cell membrane’s ability to maintain
a positive charge on its outer surface
a negative charge on its inner (cytoplasmic) surface
Voltmeter
Plasma membrane
Microelectrode outside cell
–70 mV
Microelectrode inside cell
Axon
Neuron
Figure 28.3A

15. Resting potential is generated and maintained with help from sodium-potassium pumps
These pump K+ into the cell and Na+ out of the cell
OUTSIDE OF CELL K+
Na+ K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+ channel
Na+
Plasma membrane K+
Na+ - K+ pump
K+ channel
Na+ K+ K+ K+
Protein K+ K+ K+ K+ K+ K+ K+
INSIDE OF CELL
Figure 28.3B

16. 28.4 A nerve signal begins as a change in the membrane potential
A stimulus alters the permeability of a portion of the plasma membrane
Ions pass through the plasma membrane, changing the membrane’s voltage
It causes a nerve signal to be generated

17. An action potential is a nerve signal
It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential

18. Neuron interior Neuron interior Figure 28.4 3 4 5 2 1 1 Na+ K+ Na+ K+
Additional Na+ channels open,
K+ channels are closed; interior of cell becomes more positive. 4
Na+ channels close and inactivate. K+ channels open, and K+ rushes out; interior of cell more negative than outside.
Na+
Action potential 3 4 2
The K+ channels close relatively slowly, causing a brief undershoot.
Na+
Threshold potential 5 2
A stimulus opens some Na+ channels; if threshold is reached, action potential is triggered. 1 1 5
Resting potential
Neuron interior
Neuron interior 1
Resting state: voltage gated Na+ and K+ channels closed; resting potential is maintained. 1
Return to resting state.
Figure 28.4

19. 28.5 The action potential propagates itself along the neuron
Axon
Action potential
Axon segment 1
Na+ K+
Action potential 2
Na+ K+ K+
Action potential 3
Na+ K+
Figure 28.5

20. An action potential is an all-or-none event
Its size is not affected by the stimulus strength
However, the frequency changes with the strength of the stimulus

21. FIGURE 38-5 Signaling stimulus intensity
The intensity of a stimulus is signaled by the rate at which individual sensory neurons produce action potentials and by the number of sensory neurons activated. In this example, increasing pressure on the skin first causes faster firing and then causes an adjacent receptor to be activated.

22. 28.6 Neurons communicate at synapses
The synapse is a key element of nervous systems
It is a junction or relay point between two neurons or between a neuron and an effector cell
Synapses are either electrical or chemical
Action potentials pass between cells at electrical synapses
At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell

23. 1 2 3 4 5 6 SENDING NEURON Action potential arrives
Axon of sending neuron
Vesicles
Synaptic knob
SYNAPSE 2 3
Vesicle fuses with plasma membrane
Neurotransmitter is released into synaptic cleft
SYNAPTIC CLEFT 4
Receiving neuron
Neuro- transmitter binds to receptor
RECEIVING NEURON
Neurotransmitter molecules
Ion channels
Neurotransmitter
Neurotransmitter broken down and released
Receptor
Ions 5
Ion channel opens 6
Ion channel closes
Figure 28.6

24. FIGURE 38-4 (part 1) Structure and operation of the synapse
A synaptic terminal contains many neurotransmitter-filled vesicles. When an action potential enters the synaptic terminal, the vesicles release their neurotransmitter into the space between the neurons. The neurotransmitter diffuses rapidly across the gap and binds to receptors on the postsynaptic cell. In many cases, transmitter binding to receptors causes a change in the resting potential of the postsynaptic cell, called a postsynaptic potential (PSP).

25. 28.7 Chemical synapses make complex information processing possible
Excitatory neurotransmitters trigger action potentials in the receiving cell
Inhibitory neurotransmitters decrease the cell’s ability to develop action potentials
The summation of excitation and inhibition determines whether or not the cell will transmit a nerve signal

26. A neuron may receive input from hundreds of other neurons via thousands of synaptic knobs
Dendrites
Synaptic knobs
Myelin sheath
Receiving cell body
Axon
Synaptic knobs
Figure 28.7

27. 28.8 A variety of small molecules function as neurotransmitters
Most neurotransmitters are small, nitrogen-containing organic molecules
Acetylcholine
Biogenic amines (epinephrine, norepinephrine, serotonin, dopamine)
Amino acids (aspartate, glutamate, glycine, GABA)
Peptides (substance P and endorphins)
Dissolved gases (nitric oxide)

28. 28.9 Connection: Many drugs act at chemical synapses
Drugs act at synapses and may increase or decrease the normal effect of neurotransmitters
Caffeine
Nicotine
Alcohol
Prescription and illegal drugs
Figure 28.9

29. NERVOUS SYSTEMS
Nervous system organization usually correlates with body symmetry
Radially symmetrical animals have a nervous system arranged in a nerve net
Example: Hydras
Nerve net
Neuron
A. Hydra (cnidarian)
Figure 28.10A

30. B. Planarian (flatworm)
Most bilaterally symmetrical animals exhibit
cephalization, the concentration of the nervous system in the head end
centralization, the presence of a central nervous system
Eye
Brain
Brain
Brain
Brain
Ventral nerve cord
Ventral nerve cord
Nerve cord
Transverse nerve
Ganglia
Giant axon
Segmental ganglion
B. Planarian (flatworm)
C. Leech (annelid)
D. Insect (arthropod)
E. Squid (mollusk)
Figure 28.10B-E

31. 28.11 Vertebrate nervous systems are highly centralized and cephalized
CENTRAL NERVOUS SYSTEM (CNS)
PERIPHERAL NERVOUS SYSTEM (PNS)
Brain
Cranial nerve
Spinal cord
Ganglia outside CNS
Spinal nerves
Figure 28.11A

32. The brain and spinal cord contain fluid-filled spaces
Dorsal root ganglion (part of PNS)
Gray matter
Meninges
BRAIN
White matter
Central canal
Spinal nerve (part of PNS)
Ventricles
Central canal of spinal cord
SPINAL CORD (cross section)
Spinal cord
Figure 28.11B

33. 28.12 The peripheral nervous system of vertebrates is a functional hierarchy
Sensory division
Motor division
Sensing external environment
Sensing internal environment
Autonomic nervous system (involuntary)
Somatic nervous system (voluntary)
Sympathetic division
Parasympathetic division
Figure 28.12A

34. Referred pain is when we feel pain from an internal organ on the body surface
This happens because neurons carrying information from the skin and those carrying information from the internal organs synapse with the same neurons in the CNS
Heart
Lungs and
diaphragm
Lungs and
diaphragm
Liver
Gallbladder
Heart
Stomach
Liver
Pancreas
Small intestine
Appendix
Ovaries
Kidney
Colon
Urinary bladder
Ureters
Figure 28.12B

35. The motor division of the PNS
The autonomic nervous system exerts involuntary control over the internal organs
The somatic nervous system exerts voluntary control over skeletal muscles

36. 28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment
The autonomic nervous system consists of two sets of neurons that function antagonistically on most body organs
The parasympathetic division primes the body for activities that gain and conserve energy
The sympathetic division prepares the body for intense, energy-consuming activities

37. PARASYMPATHETIC DIVISION
Brain
Eye
Constricts pupil
Dilates pupil
Salivary glands
Stimulates saliva production
Inhibits saliva production
Lung
Constricts bronchi
Relaxes bronchi
Accelerates heart
Slows heart
Heart
Adrenal gland
Stimulates epinephrine and norepi- nephrine release
Liver
Spinal cord
Stomach
Stimulates stomach, pancreas, and intestines
Pancreas
Stimulates glucose release
Inhibits stomach, pancreas, and intestines
Intestines
Bladder
Stimulates urination
Inhibits urination
Promotes erection of genitals
Promotes ejacu- lation and vaginal contractions
Genitals
Figure 28.13

38. THE HUMAN BRAIN
The vertebrate brain develops from three anterior bulges of the neural tube
The vertebrate brain evolved by the enlargement and subdivision of three anterior bulges of the neural tube
Forebrain
Midbrain
Hindbrain
Cerebrum size and complexity in birds and mammals correlates with sophisticated behavior

39. Embryonic Brain Regions Brain Structures Present in Adult
Cerebrum (cerebral hemispheres; includes cerebral cortex, white matter, basal ganglia)
Forebrain
Diencephalon (thalamus, hypothalamus, posterior pituitary, pineal gland)
Midbrain
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Hindbrain
Medulla oblongata (part of brainstem)
Diencephalon
Cerebral hemisphere
Midbrain
Midbrain
Pons
Hindbrain
Cerebellum
Medulla oblongata
Spinal cord
Forebrain
Embryo one month old
Fetus three months old
Figure 28.14

40. 28.15 The structure of a living supercomputer: The human brain
Table 28.15

41. Cerebrum
Forebrain
Thalamus
Cerebral cortex
Hypothalamus
Pituitary gland
Midbrain
Pons
Hindbrain
Medulla oblongata
Spinal cord
Cerebellum
Figure 28.15A

42. Most of the cerebrum’s integrative power resides in the cerebral cortex of the two cerebral hemispheres
Left cerebral hemisphere
Right cerebral hemisphere
Corpus callosum
Basal ganglia
Figure 28.15B

43. 28.16 The cerebral cortex is a mosaic of specialized, interactive regions
The motor cortex sends commands to skeletal muscles
The somatosensory cortex receives information about pain, pressure, and temperature
Several regions receive and process sensory information (vision, hearing, taste, smell)

44. The association areas are the sites of higher mental activities (thinking)
Frontal association area (judgment, planning)
Auditory association area
Somatosensory association area (reading, speech)
Visual association area

45. FRONTAL LOBE
PARIETAL LOBE
Somatosensory association area
Somatosensory cortex
Motor cortex
Speech
Frontal association area
Taste
Reading
Speech
Hearing
Smell
Visual association area
Auditory association area
Vision
TEMPORAL LOBE
OCCIPITAL LOBE
Figure 28.16

46. In lateralization, areas in the two hemispheres become specialized for different functions
“Right-brained” vs. “left-brained”

47. 28.17 Connection: Injuries and brain operations have provided insight into brain function
Much knowledge about the brain has come from individuals whose brains were altered through injury, illness, or surgery
The rod that pierced Phineas Gage’s skull left his intellect intact but altered his personality and behavior
Figure 28.17A

48. A radical surgery called hemispherectomy removes almost half of the brain
It demonstrates the brain’s remarkable plasticity
Figure 28.17B

49. 28.18 Several parts of the brain regulate sleep and arousal
Sleep and arousal are controlled by
the hypothalamus
the medulla oblongata
the pons
neurons of reticular formation
Input from ears
Eye
Motor output to spinal cord
Reticular formation
Input from touch, pain, and temperature receptors
Figure 28.18A

50. Two types of deep sleep alternate
An electroencephalogram (EEG) measures brain waves during sleep and arousal
Two types of deep sleep alternate
Slow-wave (delta waves) and REM sleep
Awake but quiet (alpha waves)
Awake during intense mental activity (beta waves)
Delta waves
REM sleep
Delta waves
Asleep
Figure 28.18B, C

51. 28.19 The limbic system is involved in emotions, memory, and learning
The limbic system is a functional group of integrating centers in the cerebral cortex, thalamus, and hypothalamus
It is involved in emotions, memory (short-term and long-term), and learning
The amygdala is central to the formation of emotional memories
The hippocampus is involved in the formation of memories and their recall

52. Thalamus
CEREBRUM
Hypothalamus
Prefrontal cortex
Smell
Olfactory bulb
Hippocampus
Amygdala
Figure 28.19

53. 28.20 The cellular changes underlying memory and learning probably occur at synapses
Memory and learning involve structural and chemical changes at synapses
Long-term depression (LTD)
Long-term potentiation (LTP)

54. 1 2 2 4 3 3 Repeated action potentials Sending neuron Sending neuron
Synaptic cleft 2 2 4
Ca2+
Cascade of chemical changes 3
Ca2+ 3
Receiving neuron
LTP
Figure 28.20