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Neural Control and the Senses

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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

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

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