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Chapter 25. Communication units of nervous systems Detect information about internal and external conditions Issue commands for responsive actions.

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Presentation on theme: "Chapter 25. Communication units of nervous systems Detect information about internal and external conditions Issue commands for responsive actions."— Presentation transcript:

1 Chapter 25

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

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

4 dendrites cell body TRIGGER ZONE INPUT ZONE CONDUCTING ZONE OUPUT ZONE axon axon endings

5 Fig. 25-1b, p.423

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

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

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

9 passive transporters with open channels passive transporters with voltage-sensitive gated channels active transporters lipid bilayer of neuron membrane interstitial fluid cytoplasmNa + /K + pump

10 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 Na + K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K

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

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

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

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

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

17 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 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 action potential threshold resting membrane potential Time (milliseconds) Membrane potential (millivolts)

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

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

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

24 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 ions neurotransmitter receptor for neurotransmitter gated channel protein

26 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 Synapse between motor neuron and skeletal muscle fiber Neuron releases chemical neurotransmitter acetylcholine (ACh)

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

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

30 Acetylcholine (ACh) Norepinephrine Epinephrine Dopamine Serotonin GABA

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

32 interneuronmotor neuron sensory neuron

33 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 A bundle of axons enclosed within a connective tissue sheath axon myelin sheath many neurons inside a connective tissue sheath

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

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

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

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

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

40 ganglion (one in most body segments) nerve cord branching nerve rudimentary brain

41 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 nervous system (CNS) Brain Spinal cord Peripheral nervous system Nerves that thread through the body


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

45 Somatic nerves Motor functions (Shown in green) Autonomic nerves Visceral functions (Shown in red)

46 Sympathetic Parasympathetic Most organs receive input from both Usually have opposite effects on organ

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

48 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 Originate in brain and sacral region of spinal cord Ganglia are in walls of organs Promote housekeeping responses such as digestion

50 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 White matter 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 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 spinal nerve vertebra meninges (protective coverings) Fig , p.433 ventraldorsal location of intervertebral disk Spinal Cord

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

56 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 DivisionMain Parts Forebrain Midbrain Hindbrain Cerebrum Olfactory lobes Thalamus Hypothalamus Limbic system Pituitary gland Pineal gland Tectum Pons Cerebellum Medulla oblongata

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

59 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 temporal frontal parietal occipital primary motor cortex primary somatosensory cortex

61 Controls emotions and has role in memory (olfactory tract)cingulate gyrusthalamus amygdala hippocampus hypothalamus

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

63 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


66 Free nerve ending Ruffini ending Pacinian corpuscle Bulb of Krause Meissner’s corpuscle

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

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

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

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

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

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

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

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

78 Outer ear Middle ear Inner ear

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

80 cochlea auditory nerve eardrum auditory canal hammer anvil stirrup

81 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 hair cells in organ of Corti tectorial membrane lumen of cochlear duct basilar membrane lumen of scala tympani to auditory nerve

83 Hair cells

84 Mechanoreceptors located in the inner ear Maintains body position vestibular apparatus semicircular canals

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