1. Nervous and Sensory Systems38
Nervous and Sensory Systems

2. Aim: How can we describe the peripheral and central nervous system
Aim: How can we describe the peripheral and central nervous system? Do Now: Describe the main differences between the peripheral and central nervous system. Homework: Read chapter 38 and complete concept questions.

3. Concept 38.1: Nervous systems consist of circuits of neurons and supporting cells
The ability to sense and react originated billions of years ago in prokaryotes
Hydras, jellies, and cnidarians are the simplest animals with nervous systems
In most cnidarians, interconnected nerve cells form a nerve net, which controls contraction and expansion of the gastro-vascular cavity

4. (b) Planarian (flatworm)
Figure 38.2
Eyespot
Brain
Nerve
cords
Transverse
nerve
Nerve net
(a) Hydra (cnidarian)
(b) Planarian (flatworm)
Brain
Brain
Ventral
nerve cord
Spinal
cord
(dorsal
nerve
cord)
Figure 38.2 Nervous system organization
Sensory
ganglia
Segmental
ganglia
(c) Insect (arthropod)
(d) Salamander (vertebrate) 4

5. In more complex animals, the axons of multiple nerve cells are often bundled together to form nerves
These fibrous structures channel and organize information flow through the nervous system
Animals with elongated, bilaterally symmetrical bodies have even more specialized systems

6. Cephalization is an evolutionary trend toward a clustering of sensory neurons and interneurons at the anterior
Nonsegmented worms have the simplest clearly defined central nervous system (CNS), consisting of a small brain and longitudinal nerve cords

7. Annelids and arthropods have segmentally arranged clusters of neurons called ganglia
In vertebrates:
The CNS is composed of the brain and spinal cord
The peripheral nervous system (PNS) is composed of nerves and ganglia

8. Glia
Glia have numerous functions to nourish, support, and regulate neurons:
Embryonic radial glia form tracks along which newly formed neurons migrate
Astrocytes (star-shaped glial cells) induce cells lining capillaries in the CNS to form tight junctions, resulting in a blood-brain barrier

9. CNS PNS VENTRICLE Neuron Cilia Oligodendrocyte Schwann cell
Figure 38.3
CNS
PNS
VENTRICLE
Neuron
Cilia
Oligodendrocyte
Schwann cell
Microglial cell
Capillary
Ependymal
cell
Astrocytes
Figure 38.3 Glia in the vertebrate nervous system
Intermingling of
astrocytes with
neurons (blue)
50 m LM 9

10. Astrocytes Intermingling of astrocytes with neurons (blue) 50 m LM
Figure 38.3a
Astrocytes
Intermingling of
astrocytes with
neurons (blue)
Figure 38.3a Glia in the vertebrate nervous system (LM)
50 m LM 10

11. Organization of the Vertebrate Nervous System
The spinal cord runs lengthwise inside the vertebral column (the spine)
The spinal cord conveys information to and from the brain
It can also act independently of the brain as part of simple nerve circuits that produce reflexes, the body’s automatic responses to certain stimuli

12. Central nervous Peripheral nervous system (CNS) system (PNS) Brain
Figure 38.4
Central nervous
system (CNS)
Peripheral nervous
system (PNS)
Brain
Cranial
nerves
Spinal cord
Ganglia
outside
CNS
Spinal
nerves
Figure 38.4 The vertebrate nervous system 12

13. The brain and spinal cord contain:
Gray matter, which consists mainly of neuron cell bodies and glia
White matter, which consists of bundles of myelinated axons

14. The CNS contains fluid-filled spaces called ventricles in the brain and the central canal in the spinal cord
Cerebrospinal fluid is formed in the brain and circulates through the ventricles and central canal and drains into the veins
It supplies the CNS with nutrients and hormones and carries away wastes

15. 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

16. The PNS has two efferent components:
The motor system carries signals to skeletal muscles and can be voluntary or involuntary
The autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary

17. The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions
The enteric division controls activity of the digestive tract, pancreas, and gallbladder
The sympathetic division regulates the “fight-or-flight” response
The parasympathetic division generates opposite responses in target organs and promotes calming and a return to “rest and digest” functions

18. Aim: How can we describe the various parts of the brain and how they function? Do Now: Describe the different functions of the left and right hemispheres of the brain?

19. Concept 38.2: The vertebrate brain is regionally specialized
The human brain contains 100 billion neurons
These cells are organized into circuits that can perform highly sophisticated information processing, storage, and retrieval

20. Embryonic brain regions Brain structures in child and adult
Figure 38.6b
Embryonic brain regions
Brain structures in child and adult
Cerebrum (includes cerebral cortex,
white matter, basal nuclei)
Telencephalon
Forebrain
Diencephalon (thalamus,
hypothalamus, epithalamus)
Diencephalon
Midbrain
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Hindbrain
Myelencephalon
Medulla oblongata (part of brainstem)
Mesencephalon
Cerebrum
Diencephalon
Metencephalon
Midbrain
Diencephalon
Myelencephalon
Hindbrain
Figure 38.6b Exploring the organization of the human brain (part 2: brain development)
Midbrain
Pons
Medulla
oblongata
Spinal
cord
Forebrain
Telencephalon
Cerebellum
Spinal cord
Embryo at 1 month
Embryo at 5 weeks
Child 20

21. Adult brain viewed from the rear
Figure 38.6c
Left cerebral
hemisphere
Right cerebral
hemisphere
Cerebral
cortex
Corpus
callosum
Cerebrum
Basal
nuclei
Figure 38.6c Exploring the organization of the human brain (part 3: cerebrum and cerebellum)
Cerebellum
Adult brain viewed from the rear 21

22. Diencephalon Thalamus Pineal gland Brainstem Hypothalamus Midbrain
Figure 38.6d
Diencephalon
Thalamus
Pineal gland
Brainstem
Hypothalamus
Midbrain
Pituitary gland
Pons
Figure 38.6d Exploring the organization of the human brain (part 4: diencephalon and brainstem)
Medulla
oblongata
Spinal cord 22

23. Arousal and Sleep
Arousal is a state of awareness of the external world
Sleep is a state in which external stimuli are received but not consciously perceived
Arousal and sleep are controlled in part by clusters of neurons in the midbrain and pons

24. Sleep is an active state for the brain and is regulated by the biological clock and regions of the forebrain, which regulate the intensity and duration of sleep
Some animals have evolutionary adaptations that allow for substantial activity during sleep
For example, in dolphins, only one side of the brain is asleep at a time

25. 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, a molecular mechanism that directs periodic gene expression
Biological clocks are typically synchronized to light and dark cycles and maintain a roughly 24-hour cycle

26. The SCN acts as a pacemaker, synchronizing the biological clock
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 26

27. 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
Generation and experience of emotion also require interaction between the limbic system and sensory areas of the cerebrum
The brain structure that is most important for emotional memory is the amygdala 27

28. The Brain’s Reward System and Drug Addiction
The brain’s reward system provides motivation for activities that enhance survival and reproduction
The brain’s reward system is dramatically affected by drug addiction
Drug addiction is characterized by compulsive consumption and an inability to control intake

29. Addictive drugs such as cocaine, amphetamine, heroin, alcohol, and tobacco enhance the activity of the dopamine pathway
Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug

30. Functional Imaging of the Brain
Functional imaging methods are transforming our understanding of normal and diseased brains
In positron-emission tomography (PET) an injection of radioactive glucose enables a display of metabolic activity

31. In functional magnetic resonance imaging, fMRI, the subject lies with his or her head in the center of a large, doughnut-shaped magnet
Brain activity is detected by changes in local oxygen concentration
Applications of fMRI include monitoring recovery from stroke, mapping abnormalities in migraine headaches, and increasing the effectiveness of brain surgery

32. Concept 38.3: The cerebral cortex controls voluntary movement and cognitive functions
The cerebrum is essential for language, cognition, memory, consciousness, and awareness of our surroundings
The cognitive functions reside mainly in the cortex, the outer layer
Four regions, or lobes (frontal, temporal, occipital, and parietal), are landmarks for particular functions 32

33. (comprehending language) Cerebellum
Figure 38.11
Somatosensory cortex
(sense of touch)
Motor cortex (control
of skeletal muscles)
Parietal lobe
Frontal lobe
Sensory association
cortex (integration
of sensory
information)
Prefrontal cortex
(decision
making,
planning)
Visual association
cortex (combining
images and object
recognition)
Broca’s area
(forming speech)
Occipital lobe
Figure The human cerebral cortex
Temporal lobe
Visual cortex
(processing visual
stimuli and pattern
recognition)
Auditory cortex
(hearing)
Wernicke’s area
(comprehending language)
Cerebellum 33

34. Language and Speech
The mapping of cognitive functions within the cortex began in the 1800s
Broca’s area, in the left frontal lobe, is active when speech is generated
Wernicke’s area, in the posterior of the left frontal lobe, is active when speech is heard

35. Lateralization of Cortical Function
The left side of the cerebrum is dominant regarding language, math, and logical operations
The right hemisphere is dominant in recognition of faces and patterns, spatial relations, and nonverbal thinking
The establishment of differences in hemisphere function is called lateralization
The two hemispheres exchange information through the fibers of the corpus callosum
Severing this connection results in a “split brain” effect, in which the two hemispheres operate independently

36. 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

37. 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”

38. Evolution of Cognition in Vertebrates
In nearly all vertebrates, the brain has the same number of divisions
The hypothesis that higher order reasoning requires a highly convoluted cerebral cortex has been experimentally refuted
The anatomical basis for sophisticated information processing in birds (without a highly convoluted neocortex) appears to be a cluster of nuclei in the top or outer portion of the brain (pallium)

39. Aim: How can we explain how organisms maintain equilibrium
Aim: How can we explain how organisms maintain equilibrium? Do Now: What human structure/organ contributes to maintaining equilibrium the most?

40. Neural Plasticity
Neural plasticity is the capacity of the nervous system to be modified after birth
Changes can strengthen or weaken signaling at a synapse
Autism, a developmental disorder, involves a disruption of activity-dependent remodeling at synapses
Children with autism display impaired communication and social interaction, as well as stereotyped and repetitive behaviors

41. (a) Synapses are strengthened or weakened in response to activity.
Figure 38.14 N1 N1 N2 N2
(a) Synapses are strengthened or weakened in response to
activity.
Figure Neural plasticity
(b) If two synapses are often active at the same time, the strength
of the postsynaptic response may increase at both synapses. 41

42. Memory and Learning
Neural plasticity is essential to formation of memories
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

43. Concept 38.4: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system
Much brain activity begins with sensory input
A sensory receptor detects a stimulus, which alters the transmission of action potentials to the CNS
The information is decoded in the CNS, resulting in a sensation

44. Sensory Reception and Transduction
A sensory pathway begins with sensory reception, detection of stimuli by sensory receptors
Sensory receptors, which detect stimuli, interact directly with stimuli, both inside and outside the body
Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor
This change in membrane potential is called a receptor potential
Receptor potentials are graded; their magnitude varies with the strength of the stimulus 44

45. (a) Receptor is afferent neuron.
Figure 38.15
(a) Receptor is afferent neuron.
(b) Receptor regulates afferent neuron.
To CNS
To CNS
Afferent
neuron
Afferent
neuron
Receptor
protein
Neurotransmitter
Sensory
receptor
Figure Neuronal and non-neuronal sensory receptors
Stimulus
leads to
neuro-
transmitter
release.
Stimulus
Sensory
receptor
cell
Stimulus 45

46. Transmission
Sensory information is transmitted as nerve impulses or action potentials
Neurons that act directly as sensory receptors produce action potentials and have an axon that extends into the CNS
Non-neuronal sensory receptors form chemical synapses with sensory neurons
They typically respond to stimuli by increasing the rate at which the sensory neurons produce action potentials 46

47. The response of a sensory receptor varies with intensity of stimuli
If the receptor is a neuron, a larger receptor potential results in more frequent action potentials
If the receptor is not a neuron, a larger receptor potential causes more neurotransmitter to be released 47

48. Perception Perception is the brain’s construction of stimuli
Action potentials from sensory receptors travel along neurons that are dedicated to a particular stimulus
The brain thus distinguishes stimuli, such as light or sound, solely by the path along which the action potentials have arrived
Amplification is the strengthening of stimulus energy by cells in sensory pathways
Sensory adaptation is a decrease in responsiveness to continued stimulation 48