1. Neural Control and the Senses
Chapter 25

2. Neurons Communication units of nervous systems
Detect information about internal and external conditions
Issue commands for responsive actions

3. interneurons of brain, spinal cord
Types of Neurons
stimulus
(output)
receptors
Sensory neurons
Detect and relay information
Interneurons
Receive and process information
Motor neurons
Transmit signals from interneurons to effectors
sensory neurons
integrators
interneurons of brain, spinal cord
motor neurons
effectors
muscles,
glands
response
(output)

4. Structure of a Neuron dendrites INPUT ZONE cell body axon OUPUT ZONE
TRIGGER ZONE
CONDUCTING ZONE
axon endings

5. Fig. 25-1b, p.423

6. Neuroglia
Cells that metabolically assist, structurally support, and protect neurons
Make up more than half the volume of the vertebrate nervous system

7. Resting Membrane Potential
Electrical gradient across membrane
About -70 mV
Maintained by sodium-potassium pump
Potassium (K+) higher inside
Sodium (Na+) higher outside
more Na+ flows
into the neuron
more gated channels
for Na+ open
neuron becomes
more positive inside

8. Na+ K+
outside
plasma membrane
inside K+
Na+
p.424a

9. How Ions Move across Membrane
interstitial fluid
cytoplasm
Na+/K+ pump
passive transporters with open channels
passive transporters with voltage-sensitive gated channels
active transporters
lipid bilayer of neuron membrane

10. Action Potential Brief reversal in membrane potential
Voltage change causes voltage-gated channels in membrane to open
Inside of neuron briefly becomes more positive than outside

11. Action Potential 1 2 3 4 Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+

12. interstitial fluid
cytoplasm
Fig. 25-4a, p.425

13. Na+
Na+
Na+
Fig. 25-4b, p.425

14. K+ K+ K+
Na+
Na+
Na+
Fig. 25-4c, p.425

15. Na+/K+
pump K+ K+ K+
Na+
Na+
Na+ K+
Fig. 25-4d, p.425

16. Positive Feedback more Na+ ions flow into the neuron
more gated channels
for Na+ open
neuron becomes
more positive inside

17. All or Nothing All action potentials are the same size
If stimulation is below threshold level, no action potential occurs
If stimulation is above threshold level, cell always depolarizes to same level

18. Repolarization
Once action potential peak is reached, Na+ gates close and K+ gates open
Movement of K+ out of cell
The inside of the cell once again becomes more negative than the outside

19. Recording of Action Potential
+20
-20
Membrane potential (millivolts)
threshold
-40
resting membrane potential
-70 1 2 3 4 5
Time (milliseconds)

20. Propagation of Action Potentials
Action potential in one part of an axon brings neighboring region to threshold
Action potential moves from one patch of membrane to another
Can only move one direction

21. Chemical Synapses Action potentials cannot jump from cell to cell
Signal is transmitted from axon end, across a synaptic cleft, by chemical signals called neurotransmitters

22. Chemical Synapse
Gap between the terminal ending of an axon and the input zone of another cell
plasma membrane of axon ending of presynaptic cell
plasma membrane of postsynaptic cell
synaptic vesicle
synaptic cleft
membrane receptor

23. Synaptic Transmission
Action potential in axon ending triggers release of neurotransmitter from presynaptic cell into synaptic cleft
vesicle inside presynaptic cell
synaptic cleft
postsynaptic cell

24. Synaptic Transmission
Neurotransmitter diffuses across cleft and binds to receptors on membrane of postsynaptic cell
Binding of neurotransmitter to receptors opens ion gates in membrane of postsynaptic cell

25. Ion Gates Open neurotransmitter ions receptor for neurotransmitter
gated channel protein

26. Synaptic Integration Many signals reach a neuron at the same time
Signals may suppress or reinforce one another
Whether or not an action potential occurs depends on the sum of the signals the neuron receives

27. Neuromuscular Junction
Synapse between motor neuron and skeletal muscle fiber
Neuron releases chemical neurotransmitter acetylcholine (ACh)

28. A Neuromuscular Junction
motor neuron axons from spinal cord to skeletal muscle fibers
transverse slice of spinal cord
part of a skeletal muscle
Fig. 25-6a, p.427

29. A Neuromuscular Junction
muscle fiber
axon ending
Fig. 25-6b, p.427

30. Neurotransmitters Acetylcholine (ACh) Norepinephrine Epinephrine
Dopamine
Serotonin
GABA

31. Cleaning Up
After neurotransmitter has acted, it is quickly removed from synaptic cleft
Molecules diffuse away, are pumped out, or broken down

32. Information Flow
interneuron
motor neuron
sensory neuron

33. Organization Neurons are bundled in nerves
Nerves are organized in circuits and reflex pathways
Information from sensory neurons is relayed to interneurons in spinal cord and brain
Motor neurons carry signals to body

34. Nerve A bundle of axons enclosed within a connective tissue sheath
myelin sheath
A bundle of axons enclosed within a connective tissue sheath
many neurons
inside a connective tissue sheath

35. Myelin Sheath Sheath blocks ion movements
Action potential must “jump” from node to node
Greatly enhances speed of transmission

36. Multiple Sclerosis A condition in which nerve fibers lose their myelin
Slows conduction
Symptoms include visual problems, numbness, muscle weakness, and fatigue

37. Reflexes Automatic movements in response to stimuli
In simplest reflex arcs, sensory neurons synapse directly on motor neurons
Most reflexes involve an interneuron

38. Stretch Reflex STIMULUS Biceps stretches. sensory neuron motor neuron
RESPONSE
Biceps contracts.

39. Invertebrate Nervous Systems
All animals except sponges have some sort of nervous system
Nerve cells interact with one another in signal- conducting and information-processing highways

40. Bilateral Nervous System
rudimentary brain
branching nerve
nerve
cord
ganglion (one in most body segments)

41. Vertebrate Development
Earliest fishlike vertebrates had a hollow, tubular nerve cord
Modification and expansion of nerve cord produced spinal cord and brain
Nerve cord persists in vertebrate embryos as a neural tube

42. Central and Peripheral Nervous Systems
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system
Nerves that thread through the body

43. Vertebrate Nervous Systems

44. Major Nerves Brain cervical nerves cranial nerves (eight pairs)
(twelve pairs)
Spinal Cord
thoracic nerves
(twelve pairs)
ulnar nerve
(one in each arm)
lumbar nerves
(five pairs)
sacral nerves
(five pairs)
sciatic nerve
(one in each leg)
coccygeal nerves
(one pair)
Fig , p.431

45. Peripheral Nervous System
Somatic nerves
Motor functions
(Shown in green)
Autonomic nerves
Visceral functions
(Shown in red)

46. Two Types of Autonomic Nerves
Sympathetic
Parasympathetic
Most organs receive input from both
Usually have opposite effects on organ

47. eggs optic nerve midbrain medulla oblongata salivary glands heart
vagus nerve
cervical nerves (8pairs)
larynx
bronchi
lungs
stomach
liver
spleen
pancreas
thoracic nerves (12 pairs)
kidneys
adrenal glands
small intestine
upper colon
lower colon
rectum
lumbar nerves (five pairs)
(all ganglia in walls of organs)
(most ganglia near spinal cord)
bladder
sacral nerves (five pairs)
uterus
pelvic nerve
genitals
Autonomic Nervous System
Fig , p.432

48. Sympathetic Nerves
Originate in thoracic and lumbar regions of spinal cord
Ganglia are near the spinal cord
Respond to stress or physical activity (fight-or-flight response)

49. Parasympathetic Nerves
Originate in brain and sacral region of spinal cord
Ganglia are in walls of organs
Promote housekeeping responses such as digestion

50. Opposing Systems
Most organs receive both sympathetic and parasympathetic signals
Example: Sympathetic nerves signal heart to speed up; parasympathetic stimulate it to slow down
Synaptic integration determines response

51. Structure of CNS White matter Gray matter Meninges
Tracts with myelin sheaths
Sensory and motor neurons
Gray matter
Unmyelinated
Cell bodies, dendrites, neuroglia
Meninges
Protective coverings

52. Table 25-1, p.434

53. Function of Spinal Cord
Expressway for signals between brain and peripheral nerves
Sensory and motor neurons make direct reflex connections in spinal cord
Spinal reflexes do not involve brain

54. Spinal Cord ventral dorsal spinal cord meninges (protective coverings)
spinal nerve
vertebra
location of intervertebral disk
Spinal Cord
Fig , p.433

55. The Brain corpus callosum hypothalamus thalamus pineal gland location
part of optic nerve
midbrain
cerebellum
pons
medulla oblongata
Fig , p.434

56. Development of the Brain
Brain develops from a hollow neural tube
Forebrain, midbrain, and hindbrain form from three successive regions of tube
Most evolutionarily ancient nervous tissue persists as the brain stem

57. Divisions of Brain Division Main Parts Forebrain Cerebrum
Olfactory lobes
Thalamus
Hypothalamus
Limbic system
Pituitary gland
Pineal gland
Midbrain
Tectum
Hindbrain
Pons
Cerebellum
Medulla oblongata

58. Cerebrospinal Fluid Surrounds the spinal cord
Fills ventricles within the brain
Blood-brain barrier controls which solutes enter the cerebrospinal fluid

59. Anatomy of the Cerebrum
Largest and most complex part of human brain
Outer layer (cerebral cortex) is highly folded
A longitudinal fissure divides cerebrum into left and right hemispheres

60. Lobes of the Cerebrum parietal frontal occipital temporal
primary somatosensory cortex
primary motor cortex
parietal
frontal
occipital
temporal

61. Limbic System Controls emotions and has role in memory
(olfactory tract)
cingulate gyrus
thalamus
amygdala
hypothalamus
hippocampus

62. Sensory Receptors Mechanoreceptors Thermoreceptors Pain receptors
Convert stimulus into action potentials
Mechanoreceptors
Thermoreceptors
Pain receptors
Chemoreceptors
Osmoreceptors
Photoreceptors

63. Stimulus Strength Which pathway carries the signal
Action potentials don’t vary in size
Brain integrate information by
Which pathway carries the signal
Frequency of action potentials along each axon
Number of axons recruited

64. Touch Pressure Temperature Pain Motion Position
Somatic Sensations
Touch Pressure Temperature Pain Motion Position

65. The Somatosensory Cortex

66. Receptors in Skin Free nerve ending Ruffini ending Pacinian corpuscle
Bulb of Krause
Meissner’s corpuscle

67. Smell A special sense Olfactory receptors
Receptor axons lead to olfactory lobe
olfactory
bulb
receptor
cell

68. Taste A special sense Chemoreceptors Five primary sensations:
sweet, sour, salty, bitter, and umami

69. Vision Sensitivity to light is not vision Vision requires Eyes
Capacity for image formation in the brain

70. The Eye Perceives visual field Lens collects light
Image formed on retina
Contains visual pigments
Stimulate photoreceptors

71. Human Eye sclera retina choroid iris fovea optic lens disk pupil
cornea
part of
optic
nerve
aqueous
humor
ciliary muscle
vitreous body

72. Pattern of Stimulation
Image on retina is upside down and reversed right to left compared with the stimulus
Brain corrects during processing

73. Organization of Retina
Photoreceptors at back of retina, in front of pigmented epithelium
For light to reach photoreceptors, it must pass layers of neurons involved in visual processing

74. Organization of Retina
Signals from photoreceptors are passed to bipolar sensory neurons, then to ganglion cells
Axons of ganglion cells form the two optic nerves
Cone
Rod
Ganglion cell
Bipolar sensory neuron

75. The Photoreceptors Rods Cones Contain the pigment rhodopsin
Detect very dim light, changes in light intensity
Cones
Three kinds; detect red, blue, or green
Provide color sense and daytime vision

76. Rods and Cones cone cell stacked, pigmented membrane rod cell
Fig , p.443

77. Eye Diseases Macular degeneration Cataract Glaucoma fovea
start of an optic nerve in back of the eyeball

78. Hearing
Outer ear
Middle ear
Inner ear
new

79. Properties of Sound Ear detects pressure waves
Amplitude of waves corresponds to perceived loudness
Frequency of waves (number per second) corresponds to perceived pitch

80. Anatomy of Human Ear stirrup anvil auditory nerve hammer
auditory canal
eardrum
cochlea

81. Sound Reception Sound waves make the eardrum vibrate
Vibrations are transmitted to the bones of the middle ear
The stirrup transmits force to the oval window of the fluid-filled cochlea

82. Sound Reception hair cells in organ of Corti lumen of cochlear duct
tectorial
membrane
basilar membrane
to auditory nerve
lumen of scala tympani

83. Organ of Corti
Hair cells

84. Balance and Equilibrium
Mechanoreceptors located in the inner ear
Maintains body position
semicircular canals
vestibular apparatus