Nervous and Sensory Systems

1
Chapter 38

• Nervous and Sensory Systems

2
Overview Command and Control Center

• The human brain contains about 100 billion
  neurons, organized into circuits more complex
  than the most powerful supercomputers
• A recent advance in brain exploration involves a
  method for expressing combinations of colored
  proteins in brain cells, a technique called
  brainbow
• This may allow researchers to develop detailed
  maps of information transfer between regions of
  the brain

3
Figure 49.1
How do scientists identify individual neurons in
the brain?
4
Nervous systems consist of circuits of neurons
and supporting cells

• Each single-celled organism can respond to
  stimuli in its environment
• Animals are multicellular and most groups respond
  to stimuli using systems of neurons

5

• The simplest animals with nervous systems, the
  cnidarians, have neurons arranged in nerve nets
• A nerve net is a series of interconnected nerve
  cells
• More complex animals have nerves

6

• Nerves are bundles that consist of the axons of
  multiple nerve cells
• Sea stars have a nerve net in each arm connected
  by radial nerves to a central nerve ring

7
Figure 49.2
Eyespot
Brain
Brain
Radialnerve
Nervecords
Ventralnerve cord
Nervering
Transversenerve
Nerve net
Segmentalganglia
(a) Hydra (cnidarian)
(d) Leech (annelid)
Brain
Ganglia
Brain
Anteriornerve ring
Spinalcord(dorsalnervecord)
Brain
Ventralnerve cord
Sensoryganglia
Ganglia
Longitudinalnerve cords
Segmentalganglia
(e) Insect (arthropod)
(f) Chiton (mollusc)
(g) Squid (mollusc)
8

• Bilaterally symmetrical animals exhibit
  cephalization, the clustering of sensory organs
  at the front end of the body
• Relatively simple cephalized animals, such as
  flatworms, have a central nervous system (CNS)
• The CNS consists of a brain and longitudinal
  nerve cords

9

• Annelids and arthropods have segmentally arranged
  clusters of neurons called ganglia

10

• Nervous system organization usually correlates
  with lifestyle
• Sessile molluscs (for example, clams and chitons)
  have simple systems, whereas more complex
  molluscs (for example, octopuses and squids) have
  more sophisticated systems

11

• In vertebrates
• The CNS is composed of the brain and spinal cord
• The peripheral nervous system (PNS) is composed
  of nerves and ganglia

12
Organization of the Vertebrate Nervous System

• The spinal cord conveys information from and to
  the brain
• The spinal cord also produces reflexes
  independently of the brain
• A reflex is the bodys automatic response to a
  stimulus
• For example, a doctor uses a mallet to trigger a
  knee-jerk reflex

13
Figure 49.3
Cell body ofsensory neuron indorsal
rootganglion
Gray matter
Quadricepsmuscle
White matter
Hamstringmuscle
Spinal cord(cross section)
Sensory neuron
Motor neuron
Interneuron
14

• Invertebrates usually have a ventral nerve cord
  while vertebrates have a dorsal spinal cord
• The spinal cord and brain develop from the
  embryonic nerve cord
• The nerve cord gives rise to the central canal
  and ventricles of the brain

15
Figure 49.4
Central nervoussystem (CNS)
Peripheral nervoussystem (PNS)
Brain
Cranial nerves
Spinal cord
Ganglia outsideCNS
Spinal nerves
16
Figure 49.5
Gray matter
Whitematter
Ventricles
17

• The central canal of the spinal cord and the
  ventricles of the brain are hollow and filled
  with cerebrospinal fluid
• The cerebrospinal fluid is filtered from blood
  and functions to cushion the brain and spinal
  cord as well as to provide nutrients and remove
  wastes

18

• The brain and spinal cord contain
• Gray matter, which consists of neuron cell
  bodies, dendrites, and unmyelinated axons
• White matter, which consists of bundles of
  myelinated axons

19
Glia

• Glia have numerous functions to nourish, support,
  and regulate neurons
• Embryonic radial glia form tracks along which
  newly formed neurons migrate
• Astrocytes induce cells lining capillaries in the
  CNS to form tight junctions, resulting in a
  blood-brain barrier and restricting the entry of
  most substances into the brain

20
Figure 49.6
CNS
PNS
Neuron
VENTRICLE
Astrocyte
Cilia
Oligodendrocyte
Schwann cell
Microglial cell
Capillary
Ependymal cell
50 ?m
LM
21
Figure 49.6a
CNS
PNS
Neuron
VENTRICLE
Astrocyte
Cilia
Oligodendrocyte
Schwann cell
Microglial cell
Capillary
Ependymal cell
22
Figure 49.6b
50 ?m
LM
23
The Peripheral Nervous System

• The PNS transmits information to and from the CNS
  and regulates movement and the internal
  environment
• In the PNS, afferent neurons transmit information
  to the CNS and efferent neurons transmit
  information away from the CNS

24

• The PNS has two efferent components the motor
  system and the autonomic nervous system
• The motor system carries signals to skeletal
  muscles and is voluntary
• The autonomic nervous system regulates smooth and
  cardiac muscles and is generally involuntary

25
Figure 49.7
Central NervousSystem(information processing)
Peripheral NervousSystem
Efferent neurons
Afferent neurons
Autonomicnervous system
Motorsystem
Sensoryreceptors
Control ofskeletal muscle
Sympatheticdivision
Parasympatheticdivision
Internaland externalstimuli
Entericdivision
Control of smooth muscles,cardiac muscles, glands
26

• The autonomic nervous system has sympathetic,
  parasympathetic, and enteric divisions
• The sympathetic division regulates arousal and
  energy generation (fight-or-flight response)
• The parasympathetic division has antagonistic
  effects on target organs and promotes calming and
  a return to rest and digest functions

27

• The enteric division controls activity of the
  digestive tract, pancreas, and gallbladder

28
Figure 49.8
Sympathetic division
Parasympathetic division
Action on target organs
Action on target organs
Constricts pupilof eye
Dilates pupil of eye
Inhibits salivarygland secretion
Stimulates salivarygland secretion
Sympatheticganglia
Constrictsbronchi in lungs
Relaxes bronchiin lungs
Cervical
Slows heart
Accelerates heart
Stimulates activityof stomach andintestines
Inhibits activity ofstomach and intestines
Thoracic
Stimulates activityof pancreas
Inhibits activityof pancreas
Stimulates glucoserelease from liverinhibits
gallbladder
Stimulatesgallbladder
Lumbar
Stimulatesadrenal medulla
Promotes emptyingof bladder
Inhibits emptyingof bladder
Sacral
Promotes erectionof genitalia
Promotes ejaculationand vaginal contractions
Synapse
29
Figure 49.8a
Parasympathetic division
Sympathetic division
Action on target organs
Action on target organs
Constricts pupilof eye
Dilates pupil of eye
Inhibits salivarygland secretion
Stimulates salivarygland secretion
Sympatheticganglia
Constrictsbronchi in lungs
Cervical
Slows heart
Stimulates activityof stomach andintestines
Stimulates activityof pancreas
Stimulatesgallbladder
30
Figure 49.8b
Parasympathetic division
Sympathetic division
Relaxes bronchiin lungs
Accelerates heart
Inhibits activity ofstomach and intestines
Thoracic
Inhibits activityof pancreas
Stimulates glucoserelease from liverinhibits
gallbladder
Lumbar
Stimulatesadrenal medulla
Promotes emptyingof bladder
Inhibits emptyingof bladder
Sacral
Promotes ejaculationand vaginal contractions
Promotes erectionof genitalia
Synapse
31
The vertebrate brain is regionally specialized

• Specific brain structures are particularly
  specialized for diverse functions
• These structures arise during embryonic
  development

32
Figure 49.9a
33
Figure 49.9b
Embryonic brain regions
Brain structures in child and adult
Cerebrum (includes cerebral cortex, whitematter,
basal nuclei)
Telencephalon
Forebrain
Diencephalon (thalamus, hypothalamus,epithalamus)
Diencephalon
Mesencephalon
Midbrain (part of brainstem)
Midbrain
Metencephalon
Pons (part of brainstem), cerebellum
Hindbrain
Myelencephalon
Medulla oblongata (part of brainstem)
Diencephalon
Cerebrum
Mesencephalon
Metencephalon
Midbrain
Midbrain
Diencephalon
Myelencephalon
Hindbrain
Pons
Medullaoblongata
Spinal cord
Forebrain
Cerebellum
Telencephalon
Spinal cord
Child
Embryo at 5 weeks
Embryo at 1 month
34
Figure 49.9ba
Mesencephalon
Metencephalon
Midbrain
Diencephalon
Myelencephalon
Hindbrain
Spinal cord
Forebrain
Telencephalon
Embryo at 5 weeks
Embryo at 1 month
35
Figure 49.9bb
Diencephalon
Cerebrum
Midbrain
Pons
Medullaoblongata
Cerebellum
Spinal cord
Child
36
Figure 49.9c
Left cerebralhemisphere
Right cerebralhemisphere
Cerebral cortex
Corpus callosum
Cerebrum
Basal nuclei
Cerebellum
Adult brain viewed from the rear
37
Figure 49.9d
Diencephalon
Thalamus
Pineal gland
Brainstem
Hypothalamus
Midbrain
Pituitary gland
Pons
Medullaoblongata
Spinal cord
38
Arousal and Sleep

• The brainstem and cerebrum control arousal and
  sleep
• The core of the brainstem has a diffuse network
  of neurons called the reticular formation
• This regulates the amount and type of information
  that reaches the cerebral cortex and affects
  alertness
• The hormone melatonin is released by the pineal
  gland and plays a role in bird and mammal sleep
  cycles

39
Figure 49.10
Eye
Input from nervesof ears
Reticular formation
Input from touch,pain, and temperaturereceptors
40

• Sleep is essential and may play a role in the
  consolidation of learning and memory
• Dolphins sleep with one brain hemisphere at a
  time and are therefore able to swim while asleep

41
Figure 49.11
Key
Low-frequency waves characteristic of sleep
High-frequency waves characteristic of wakefulness
Time 1 hour
Location
Time 0 hours
Lefthemisphere
Righthemisphere
42
Biological Clock Regulation

• Cycles of sleep and wakefulness are examples of
  circadian rhythms, daily cycles of biological
  activity
• Mammalian circadian rhythms rely on a biological
  clock, molecular mechanism that directs periodic
  gene expression
• Biological clocks are typically synchronized to
  light and dark cycles

43

• In mammals, circadian rhythms are coordinated by
  a group of neurons in the hypothalamus called the
  suprachiasmatic nucleus (SCN)
• The SCN acts as a pacemaker, synchronizing the
  biological clock

44
Figure 49.12
RESULTS
Wild-type hamster
? hamster
Wild-type hamster withSCN from ? hamster
? hamster with SCNfrom wild-type hamster
24
23
22
Circadian cycle period (hours)
21
20
19
After surgeryand transplant
Beforeprocedures
45
Emotions

• Generation and experience of emotions involve
  many brain structures including the amygdala,
  hippocampus, and parts of the thalamus
• These structures are grouped as the limbic system
• The limbic system also functions in motivation,
  olfaction, behavior, and memory

46
Figure 49.13
Thalamus
Hypothalamus
Olfactorybulb
Amygdala
Hippocampus
47

• Generation and experience of emotion also require
  interaction between the limbic system and sensory
  areas of the cerebrum
• The structure most important to the storage of
  emotion in the memory is the amygdala, a mass of
  nuclei near the base of the cerebrum

48
Figure 49.14
Amygdala
Nucleus accumbens
Happy music
Sad music
49
Figure 49.14a
Nucleus accumbens
Happy music
50
Figure 49.14b
Amygdala
Sad music
51
The cerebral cortex controls voluntary movement
and cognitive functions

• The cerebrum, the largest structure in the human
  brain, is essential for awareness, language,
  cognition, memory, and consciousness
• Four regions, or lobes (frontal, temporal,
  occipital, and parietal), are landmarks for
  particular functions

52
Figure 49.15
Motor cortex(control ofskeletal muscles)
Somatosensory cortex(sense of touch)
Frontal lobe
Parietal lobe
Prefrontal cortex(decision making,planning)
Sensory associationcortex (integration
ofsensory information)
Visual associationcortex (combiningimages and
objectrecognition)
Brocas area(forming speech)
Temporal lobe
Occipital lobe
Auditory cortex (hearing)
Visual cortex(processing visualstimuli and
patternrecognition)
Cerebellum
Wernickes area(comprehending language)
53
Language and Speech

• Studies of brain activity have mapped areas
  responsible for language and speech
• Brocas area in the frontal lobe is active when
  speech is generated
• Wernickes area in the temporal lobe is active
  when speech is heard
• These areas belong to a larger network of regions
  involved in language

54
Figure 49.16
Max
Hearingwords
Seeingwords
Min
Speakingwords
Generatingwords
55
Lateralization of Cortical Function

• The two hemispheres make distinct contributions
  to brain function
• The left hemisphere is more adept at language,
  math, logic, and processing of serial sequences
• The right hemisphere is stronger at pattern
  recognition, nonverbal thinking, and emotional
  processing

56

• The differences in hemisphere function are called
  lateralization
• Lateralization is partly linked to handedness
• The two hemispheres work together by
  communicating through the fibers of the corpus
  callosum

57
Information Processing

• The cerebral cortex receives input from sensory
  organs and somatosensory receptors
• Somatosensory receptors provide information about
  touch, pain, pressure, temperature, and the
  position of muscles and limbs
• The thalamus directs different types of input to
  distinct locations

58

• Adjacent areas process features in the sensory
  input and integrate information from different
  sensory areas
• Integrated sensory information passes to the
  prefrontal cortex, which helps plan actions and
  movements
• In the somatosensory cortex and motor cortex,
  neurons are arranged according to the part of the
  body that generates input or receives commands

59
Figure 49.17
Frontal lobe
Parietal lobe
Shoulder
Upper arm
Trunk
Elbow
Trunk
Head
Forearm
Knee
Neck
Leg
Hip
Hip
Wrist
Elbow
Hand
Forearm
Fingers
Hand
Fingers
Thumb
Thumb
Eye
Neck
Nose
Brow
Eye
Face
Genitalia
Lips
Toes
Face
Teeth
Gums
Lips
Jaw
Jaw
Tongue
Pharynx
Tongue
Primarysomatosensorycortex
Primarymotor cortex
Abdominalorgans
60
Figure 49.17a
Shoulder
Knee
Elbow
Trunk
Forearm
Hip
Wrist
Hand
Fingers
Thumb
Neck
Brow
Eye
Toes
Face
Lips
Jaw
Tongue
Primarymotor cortex
61
Figure 49.17b
Upper arm
Trunk
Head
Neck
Leg
Hip
Elbow
Forearm
Hand
Fingers
Thumb
Eye
Nose
Face
Lips
Genitalia
Teeth
Gums
Jaw
Tongue
Pharynx
Primarysomatosensorycortex
Abdominalorgans
62
Frontal Lobe Function

• Frontal lobe damage may impair decision making
  and emotional responses but leave intellect and
  memory intact
• The frontal lobes have a substantial effect on
  executive functions

63
Figure 49.UN01
64
Evolution of Cognition in Vertebrates

• Previous ideas that a highly convoluted neocortex
  is required for advanced cognition may be
  incorrect
• The anatomical basis for sophisticated
  information processing in birds (without a highly
  convoluted neocortex) appears to be the
  clustering of nuclei in the top or outer portion
  of the brain (pallium)

65
Figure 49.18
Human brain
Cerebrum (includingcerebral cortex)
Thalamus
Midbrain
Hindbrain
Cerebellum
Avian brainto scale
Cerebrum(including pallium)
Avian brain
Cerebellum
Hindbrain
Thalamus
Midbrain
66
Changes in synaptic connections underlie memory
and learning

• Two processes dominate embryonic development of
  the nervous system
• Neurons compete for growth-supporting factors in
  order to survive
• Only half the synapses that form during embryo
  development survive into adulthood

67
Neural Plasticity

• Neural plasticity describes the ability of the
  nervous system to be modified after birth
• Changes can strengthen or weaken signaling at a
  synapse

68
Figure 49.19
N1
N1
N2
N2
69
Memory and Learning

• The formation of memories is an example of neural
  plasticity
• Short-term memory is accessed via the hippocampus
• The hippocampus also plays a role in forming
  long-term memory, which is stored in the cerebral
  cortex
• Some consolidation of memory is thought to occur
  during sleep

70
Long-Term Potentiation

• In the vertebrate brain, a form of learning
  called long-term potentiation (LTP) involves an
  increase in the strength of synaptic transmission
• LTP involves glutamate receptors
• If the presynaptic and postsynaptic neurons are
  stimulated at the same time, the set of receptors
  present on the postsynaptic membranes changes

71
Figure 49.20
PRESYNAPTICNEURON
Ca2?
Na?
Mg2?
Glutamate
NMDA receptor (open)
NMDAreceptor(closed)
StoredAMPAreceptor
POSTSYNAPTICNEURON
(a) Synapse prior to long-term potentiation (LTP)
(b) Establishing LTP
Actionpotential
Depolarization
(c) Synapse exhibiting LTP
72
Figure 49.20a
PRESYNAPTICNEURON
Ca2?
Na?
Mg2?
Glutamate
NMDAreceptor(closed)
NMDA receptor (open)
StoredAMPAreceptor
POSTSYNAPTICNEURON
(a) Synapse prior to long-term potentiation (LTP)
73
Figure 49.20b
Mg2?
NMDA receptor
AMPAreceptor
Na?
Ca2?
(b) Establishing LTP
74
Figure 49.20c
NMDA receptor
AMPAreceptor
Actionpotential
Depolarization
(c) Synapse exhibiting LTP
75
Stem Cells in the Brain

• The adult human brain contains neural stem cells
• In mice, stem cells in the brain can give rise to
  neurons that mature and become incorporated into
  the adult nervous system
• Such neurons play an essential role in learning
  and memory

76
Figure 49.21
77
Nervous system disorders can be explained in
molecular terms

• Disorders of the nervous system include
  schizophrenia, depression, drug addiction,
  Alzheimers disease, and Parkinsons disease
• Genetic and environmental factors contribute to
  diseases of the nervous system

78
Figure 49.22
50
Genes shared with relatives ofperson with
schizophrenia
12.5 (3rd-degree relative)
40
25 (2nd-degree relative)
50 (1st-degree relative)
100
30
Risk of developing schizophrenia ()
20
10
0
Child
Fraternaltwin
Parent
Identicaltwin
Individual,generalpopulation
Nephew/niece
Uncle/aunt
Full sibling
Grandchild
Half sibling
First cousin
Relationship to person with schizophrenia
79
Schizophrenia

• About 1 of the worlds population suffers from
  schizophrenia
• Schizophrenia is characterized by hallucinations,
  delusions, and other symptoms
• Available treatments focus on brain pathways that
  use dopamine as a neurotransmitter

80
Depression

• Two broad forms of depressive illness are known
  major depressive disorder and bipolar disorder
• In major depressive disorder, patients have a
  persistent lack of interest or pleasure in most
  activities
• Bipolar disorder is characterized by manic
  (high-mood) and depressive (low-mood) phases
• Treatments for these types of depression include
  drugs such as Prozac

81
Drug Addiction and the Brains Reward System

• The brains reward system rewards motivation with
  pleasure
• Some drugs are addictive because they increase
  activity of the brains reward system
• These drugs include cocaine, amphetamine, heroin,
  alcohol, and tobacco
• Drug addiction is characterized by compulsive
  consumption and an inability to control intake

82

• Addictive drugs enhance the activity of the
  dopamine pathway
• Drug addiction leads to long-lasting changes in
  the reward circuitry that cause craving for the
  drug

83
Figure 49.23
Nicotinestimulatesdopamine-releasingVTA
neuron.
Inhibitory neuron
Opium and heroindecrease activityof
inhibitoryneuron.
Dopamine-releasingVTA neuron
Cocaine andamphetaminesblock removalof
dopaminefrom synapticcleft.
Cerebralneuron ofrewardpathway
Rewardsystemresponse
84
Alzheimers Disease

• Alzheimers disease is a mental deterioration
  characterized by confusion and memory loss
• Alzheimers disease is caused by the formation of
  neurofibrillary tangles and amyloid plaques in
  the brain
• There is no cure for this disease though some
  drugs are effective at relieving symptoms

85
Figure 49.24
20 ?m
Neurofibrillary tangle
Amyloid plaque
86
Parkinsons Disease

• Parkinsons disease is a motor disorder caused by
  death of dopamine-secreting neurons in the
  midbrain
• It is characterized by muscle tremors, flexed
  posture, and a shuffling gait
• There is no cure, although drugs and various
  other approaches are used to manage symptoms

87
Figure 49.UN03
PNS
CNS
VENTRICLE
Astrocyte
Ependy-malcell
Oligodendrocyte
Cilia
Schwanncells
Capillary
Neuron
Microglial cell