Chapter 11: Nervous System - PowerPoint PPT Presentation

Loading...

PPT – Chapter 11: Nervous System PowerPoint presentation | free to download - id: 7146d2-YzU4Y



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Chapter 11: Nervous System

Description:

Chapter 11: Nervous System 17-* – PowerPoint PPT presentation

Number of Views:38
Avg rating:3.0/5.0
Slides: 95
Provided by: Preferr513
Learn more at: http://www.stjohnbrebeuf.ca
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Chapter 11: Nervous System


1
Chapter 11 Nervous System
2
  • Function of the Nervous System
  • To coordinate the actions of your body
  • To ensure effective behaviour
  • To maintain the internal environment within safe
    limits (homeostasis)
  • Messages are relayed throughout the body via
    electrochemical messages from the brain or
    through chemical messengers hormones (hormones
    require more time than nervous transmission but
    are long lasting)
  • There are more nerve cells in the body than there
    are visible stars in the Milky Way!
  • 1 cm3 of brain tissue houses several million
    neurons with each connecting with several
    thousand others

3
Nervous Tissue
  • The nervous system is divided into a central
    nervous system (CNS), consisting of the brain and
    spinal cord, and a peripheral nervous system
    (PNS), consisting of nerves carrying sensory and
    motor information between the CNS and muscles and
    glands.
  • Both systems have two types of cells neurons
    that transmit impulses and neuroglial cells that
    support neurons.

4
(No Transcript)
5
Organization of the nervous system
6
Neuron Structure
  • Neurons are composed of dendrites that receive
    signals, a cell body with a nucleus, and an axon
    that conducts a nerve impulse away.
  • Sensory neurons take information from sensory
    receptors to the CNS.
  • Interneurons occur within the CNS and integrate
    input (nonmyelinated).
  • Motor neurons take information from the CNS to
    muscles or glands.

7
Types of neurons
8
  • dendrites receive information (either from
    receptor cells or other nerve cells), conducting
    towards the cell body (200 dendrites/cell body)
  • cell body location of the nucleus, high
    metabolic rate (so contains mitochondria)
  • axon may be 1m long, very thin, conducts the
    impulse towards other neurons or effectors,
    starts at axon hillock, the smaller the neuronal
    diameter, the faster the neuronal transmission

9
  • nodes of Ranvier the unmyelinated sections of a
    myelinated neuron, impulses jump between the
    nodes of Ranvier
  • neurilemma a thin layer encompassing neurons in
    the peripheral nervous system, promoting their
    regeneration

10
  • Schwann cell responsible for the myelin
    synthesis, type of glial cell (supporting and
    nourishing cell found in the nervous system)
  • Axon Bulb either at a synaptic bulb or end
    plate to muscle, contains neurotransmitter

11
Myelin Sheath
  • Myelination covers long axons with a protective
    myelin sheath (made by neuroglial cells called
    Schwann cells).
  • The sheath contains lipid myelin which gives
    nerve fibers their white, glistening appearance.
  • The sheath is interrupted by gaps called nodes of
    Ranvier.
  • Multiple sclerosis is a disease of the myelin
    sheath.

12
Myelin sheath
13
  • FYI
  • Nerves are generally comprised of many neurons
    together (like fibre optic cable)
  • Myelinated neurons in the brain are termed white
    matter (the myelin makes them look white)
  • White matter may regenerate after injury, whereas
    grey matter (unprotected) will not

14
The Nerve Impulse
  • The nervous system uses the nerve impulse to
    convey information.
  • The nature of a nerve impulse has been studied by
    using excised axons and a voltmeter called an
    oscilloscope.
  • Voltage (in millivolts, mV) measures the
    electrical potential difference between the
    inside and outside of the axon.

15
Membrane Polarization (Resting Potential)
  • When an axon is not conducting a nerve impulse,
    the inside of an axon is negative (-70mV)
    compared to the outside(40mV) this is the
    resting potential.
  • To establish the 70mV potential in the cell
  • Na is actively pumped out of the cell
  • K is actively pumped into the cell

Sodium pump
16
Membrane Polarization (Resting Potential)
  • Na and K diffuse down the concentration
    gradient, but K diffuses faster due to an
    increased number of ion channels (gates) open to
    K ions
  • Since there is a net loss of positive ions to the
    outside of the cell, -70 mV is established inside
    the neuron
  • There are also large negative proteins inside the
    neuron that contribute to the negative charge

17
Resting potential
18
Membrane Depolarization
  • When the nerve cell is excited, the membrane
    DEPOLARIZES (Action Potential)
  • The membranes polarity changes
  • Na channels open, Na rushes in, K gates
    close
  • The positive ions flowing in causes a charge
    reversal to 40 mV inside the neuron
  • (gated channel proteins)

19
Action potential
20
Membrane Repolarization
  • Once the charge becomes positive, the Na gates
    close, K gates open, eventually restoring the
    charge inside the neuron to 70 mV (but the Na
    excess is inside and K excess is outside!)
  • The Na/K Pump restores the ion concentrations
    inside and outside the cell

21
Membrane Repolarization
  • During the repolarization, the nerve cannot be
    reactivated this is called the refractory
    period (1 to 10 ms) and is a recovery time for
    the neuron
  • The pump requires ATP in order to operate

22
The Na/K Pump
  • To be ready for another action potential, the
    membrane re-establishes the proper concentration
    gradient for sodium and potassium
  • Three sodium ions are actively transported across
    the membrane and to the ECM
  • Two potassium ions are then carried across to the
    cytoplasm

23
Movement of the Action Potential
  • The action in the neuron adjacent to an area of
    resting membrane causes that area to depolarize,
    moving the action potential along (due to
    attraction of opposite charges)
  • Since the area from which the action potential
    came is still in recovery, the action potential
    will only move in one direction

24
(No Transcript)
25
(No Transcript)
26
Propagation of an Action Potential
  • The action potential travels the length of an
    axon, with each portion of the axon undergoing
    depolarization then repolarization.
  • A refractory period ensures that the action
    potential will not move backwards.
  • In myelinated fibers, the action potential only
    occurs at the nodes of Ranvier.
  • This jumping from node-to-node is called
    saltatory conduction.

27
Fig. 48-13
Schwann cell
Depolarized region (node of Ranvier)
Cell body
Myelin sheath
Axon
28
The All-or-None Response (Threshold Potential)
  • All neurons provide an all-or-none response
  • - in response to a stimulus, they either
    activate (fire) and provide a certain level of
    response, or dont fire at all
  • A neuron will only fire if it is stimulated with
    an intensity of at least threshold level
  • Every action potential for a neuron is identical
    in strength and duration (regardless of how much
    beyond threshold the stimulus is)

29
Threshold Potential
  • All neurons differ in their threshold level
  • To inform the brain of the intensity of a
    stimulus
  • - the frequency of firing is increased (not
    speed, which is constant for each neuron)
  • - the number of neurons that respond to that
    level of stimulus can increase (neurons may have
    different threshold)

30
Transmission Across a Synapse
  • The junction between neurons or neurons
    effectors is called the synapse.
  • Transmission of a nerve impulse takes place when
    a neurotransmitter molecule stored in synaptic
    vesicles in the axon bulb is released into a
    synaptic cleft between the axon and the receiving
    neuron.

31
  • When a nerve impulse reaches an axon bulb,
    calcium channels open and Ca2 flow into the
    bulb.
  • This sudden rise in Ca2 causes synaptic vesicles
    to move and merge with the presynaptic membrane,
    releasing their neurotransmitter molecules into
    the synapse
  • The binding of the neurotransmitter to receptors
    in the postsynaptic membrane causes either
    excitation or inhibition.

32
Synapse structure and function
33
Synaptic Summation
  • Many synapses per single neuron is not uncommon.
  • Excitatory signals have a depolarizing effect,
    and inhibitory signals have a hyperpolarizing
    effect on the post- synaptic membrane.
  • Summation is the summing up of these excitatory
    and inhibitory signals.

34
Summation
35
Summation
36
Neurotransmitter Molecules
  • Out of 25, two well-known neurotransmitters are
    acetylcholine (ACh) and norepinephrine (NE).
  • Neurotransmitters that have done their job are
    removed from the cleft the enzyme
    acetylcholinesterase (AChE) breaks down
    acetylcholine.
  • Neurotransmitter molecules are removed from the
    cleft by enzymatic breakdown or by reabsorption,
    thus preventing continuous stimulation or
    inhibition.

37
  • FYI
  • most synapses involve more than just 2 neurons
    (or neuron/effectors)
  • neurotransmitters move only by diffusion, so
    synaptic transmission is MUCH slower than axonal
    transmission.
  • insecticides interfere with enzymes that break
    down neurotransmitters causing their hearts to
    remain contracted,
  • whereas LSD and other hallucinogens are believed
    to bind to the receptor sites for
    neurotransmitters

38
  • Lidocaine, an anesthetic works by stabilizing the
    neuronal membrane so it cant depolarize
  • Endorphins and enkephalins are natural
    painkillers produced in the CNS, blocking the
    pain transmitter that usually attaches to the
    injured organ allowing the perception of pain
  • opiates (heroin, codeine, morphine) block the
    production of the pain transmitter. Since they
    act to decrease the production of natural
    painkillers, the amount of opiate taken must be
    increased or at least maintained to maintain the
    effect

39
  • Valium and other depressants are believed to
    enhance the action of inhibitory synapses
  • Alcohol acts to increase the polarization of the
    membrane, increasing the threshold
  • Since many neurons will connect to a postsynaptic
    neuron, it is the summation of the effects of the
    presynaptic neurons that determine whether or not
    the postsynaptic neuron or effector will
    depolarize

40
  • Neural Circuits includes neuronal and synaptic
    transmission
  • There are two types of neural circuits
  • complicated neural circuits, involving conscious
    thought
  • reflex arcs without brain coordination
  • often unconscious, involuntary and faster than
    when thought is required (why are these useful?)

41
  • Nervous Control (in general)
  • Stimulus?Receptor?SensoryNeuron?Interneuron?
  • Brain?Interneuron?MotorNeuron?Effector?Response
  • Reflex Arc (see diagram the reflex arc)
  • Stimulus?Receptor?SensoryNeuron?Interneuron
  • (spinal cord)?MotorNeuron?Effector?Response
  • When the response is made at the spinal cord
    level (information does not have to go to the
    brain to be processed), the response is quick
    (and always correct given the circumstances)
  • Reflexes protect the body from injury

42
The Central Nervous System
  • The central nervous system (CNS) consists of the
    spinal cord and brain.
  • Both are protected by bone, wrapped in protective
    membranes called meninges, and surrounded and
    cushioned with cerebrospinal fluid that is
    produced in the ventricles of the brain.

43
  • The ventricles are interconnecting cavities that
    produce and serve as a reservoir for
    cerebrospinal fluid.
  • The CNS receives and integrates sensory input and
    formulates motor output.
  • Gray matter contains cell bodies and short,
    nonmyelinated fibers white matter contains
    myelinated axons that run in tracts.

44
The Brain
  • consumes more oxygen and glucose than any other
    part of the body
  • meninges outer layers (protection) dura
    mater, arachnoid and pia mater
  • cerebrospinal fluid between the inner, middle
    meninges central canal of s.cord, carries
    nutrients, acts as a shock absorber, relays waste
    by diffusion fac. diffusion, flows within
    ventricles four spaces in the brain

45
The human brain
46
Fig. 49-15
Frontal lobe
Parietal lobe
Somatosensory cortex
Motor cortex
Somatosensory association area
Speech
Frontal association area
Taste
Reading
Speech
Hearing
Visual association area
Smell
Auditory association area
Vision
Temporal lobe
Occipital lobe
47
Fig. 49-17
Max
Hearing words
Seeing words
Min
Generating words
Speaking words
48
Fig. 49-1
49
The Cerebral Cortex
  • The cerebral cortex is a thin, highly convoluted
    outer layer of gray matter covering both
    hemispheres.
  • The primary motor area is in the frontal lobe
    this commands skeletal muscle.
  • The primary somatosensory area is dorsal to the
    central sulcus or groove.

50
  • Forebrain (cerebrum)
  • contains two hemispheres for coordinating sensory
    and motor information speech,
  • reasoning, memory, personality, which may be
    located on one side only
  • the outer layer is called the cerebral cortex
    (only 1 mm thick), deeply folded into fissures(to
    increase surface area)

51
Cerebral hemispheres
52
Forebrain Continued
  • - the two hemispheres are connected by the corpus
  • callosum allowing info to be shared between the
  • hemispheres (a collection of nerve fibres)
    which are
  • sometimes severed to control epilepsy leading
    to
  • interesting results
  • - the cerebrum can be subdivided into 4 lobes
  • Frontal (walking, speech, intellect,
    personality),
  • temporal (hearing,vision, memory,
    interpretation),
  • parietal (interpreting sensory info receptors,
    long term memory) and
  • occipital (vision) lobes
  • Brocas area - a part of the left hemisphere
    usually where
  • speech centre is located

53
The lobes of a cerebral hemisphere
54
Forebrain Continued
  • thalamus- below cerebrum, coordinates and
    interprets sensory info
  • hypothalamus below the thalamus, related to
    pituitary,
  • connects endocrine to the nervous system,
    receives sensory info, instincts, temperature
    control (ANS)
  • pituitary gland influenced by the hypthalamus,
    part of the endocrine system (master gland)
  • pineal gland part of the endocrine system
    melatonin production

55
  • midbrain - less developed in humans than the
    forebrain, 4 spheres relay centre for some eye
    and ear reflexes
  • Hindbrain - located behind the midbrain, connects
    brain to spinal cord
  • contains cerebellum (coordinates movement,
    balance, muscle tone), The cerebellum is involved
    in learning of new motor skills, such as playing
    the piano.
  • pons (relay station between cerebellum areas, and
    cerebellum medulla)
  • medulla oblongata (connection between peripheral
    and CNS, involuntary movements heart rate,
    breathing (ANS), crossover of control)

56
  • FYI
  • much brain research takes place during brain
    surgery after people have strokes
  • epileptics also provide insight into brain
    differentiation when they undergo severing of the
    corpus callosum to relieve extremely serious
    seizures
  • although the brain must control the entire body,
    the volume of brain allocated to each part of the
    body is not proportional to that body parts size
    the face and hands account for the majority of
    the motor cortexs attention

57
Fig. 49-16
Parietal lobe
Frontal lobe
Upper arm
Shoulder
Trunk
Head
Knee
Leg
Neck
Trunk
Hip
Elbow
Forearm
Hip
Elbow
Wrist
Forearm
Hand
Hand
Fingers
Fingers
Thumb
Thumb
Eye
Neck
Nose
Brow
Face
Eye
Lips
Genitals
Toes
Face
Teeth Gums Jaw
Lips
Jaw
Tongue
Tongue
Pharynx
Primary motor cortex
Primary somatosensory cortex
Abdominal organs
58
Language and Speech
  • Language and speech are dependent upon Brocas
    area (a motor speech area) and Wernickes area (a
    sensory speech area) that are involved in
    communication.
  • These two areas are located only in the left
    hemisphere the left hemisphere functions in
    language in general and not just in speech.

59
Language and speech
60
Organization of the nervous system
61
The Spinal Cord
  • The spinal cord extends from the base of the
    brain through the vertebral canal.
  • Structure of the Spinal Cord
  • A central canal holds cerebrospinal fluid.
  • Gray matter of the spinal cord forms an H and
    contains interneurons and portions of sensory and
    motor neurons.
  • White matter consists of ascending tracts taking
    sensory information to the brain and descending
    tracts carrying motor information from the brain.

62
  • ventral root (towards front of body) carries
    motor neuron messages to muscles
  • dorsal root (towards back) carries sensory neuron
    messages from the body

63
Spinal cord
64
(No Transcript)
65
Functions of the Spinal Cord
  • The spinal cord is the center for many reflex
    arcs.
  • It also sends sensory information to the brain
    and receives motor output from the brain,
    extending communication from the brain to the
    peripheral nerves for both control of voluntary
    skeletal muscles and involuntary internal organs.
  • Severing the spinal cord produces paralysis.

66
The Peripheral Nervous System
  • The peripheral nervous system (PNS) contains
    nerves (bundles of axons) and ganglia (cell
    bodies).
  • Sensory nerves carry information to the CNS,
    motor nerves carry information away
  • Humans have 12 pairs of cranial nerves and 31
    pairs of spinal nerves.

67
Nerve structure
68
Cranial nerves
69
  • The dorsal root of a spinal nerve contains
    sensory fibers that conduct sensory impulses from
    sensory receptors toward the spinal cord.
  • Dorsal root ganglia near the spinal cord contain
    the cell bodies of sensory neurons.
  • The ventral root of a spinal nerve contains motor
    fibers that conduct impulses away from the spinal
    cord to effectors.

70
Spinal nerves
71
Somatic System
  • The somatic system serves the skin, skeletal
    muscles, and tendons.
  • The brain is always involved in voluntary muscle
    actions but somatic system reflexes are automatic
    and may not require involvement of the brain.
  • nerves running to skeletal muscle system (under
    voluntary control)
  • motor neurons ? voluntary effectors (skeletal
    muscle)
  • control exists in the cerebrum cerebellum
    (coordination)

72
Homeostasis and the Autonomic Nervous System
  • All autonomic nerves are motor nerves that
    regulate the organs of the body without conscious
    control involuntary
  • Control exists in the medulla
  • Effectors are smooth muscle (digestive system),
    cardiac muscle (heart) and glands (exocrine
    endocrine)
  • Responsible for maintaining homeostasis during
    times of rest and during emergencies

73
  • Consists of two parts
  • Sympathetic
  • prepares the body for stress, including fight or
    flight response
  • short preganglionic nerve (Ach), long
    postganglionic nerve (NEp)
  • originate in the thoracic vertebrae (ribs) or
    lumbar vertebrae (small of back)
  • Parasympathetic
  • restores normal balance times of relaxation
  • long preganglionic nerve (Ach), short
    postganglionic nerve (ACh)
  • originate in the brain (cranial nerves) or the
    spinal cord

74
(No Transcript)
75
(No Transcript)
76
Fig. 49-8
Parasympathetic division
Sympathetic division
Action on target organs
Action on target organs
Dilates pupil of eye
Constricts pupil of eye
Inhibits salivary gland secretion
Stimulates salivary gland secretion
Sympathetic ganglia
Constricts bronchi in lungs
Relaxes bronchi in lungs
Cervical
Slows heart
Accelerates heart
Stimulates activity of stomach and intestines
Inhibits activity of stomach and intestines
Thoracic
Inhibits activity of pancreas
Stimulates activity of pancreas
Stimulates glucose release from liver inhibits
gallbladder
Stimulates gallbladder
Lumbar
Stimulates adrenal medulla
Promotes emptying of bladder
Inhibits emptying of bladder
Sacral
Promotes ejaculation and vaginal contractions
Promotes erection of genitals
Synapse
77
Autonomic nervous system
78
Disorders Associated With the Nervous System
  • Parkinsons Disease inadequate production of
    dopamine in the brain causes involuntary muscle
    contractions and tremors can be partially
    alleviated with L-dopa (synthetic dopamine)

79
  • Alzheimers Disease decrease in CNS levels of
    acetylcholine
  • Multiple Sclerosis degeneration of the Myelin
    sheath Many symptoms, partial paralysis, double
    vision,speech problems
  • Amyotrophic lateral sclerosis (Lou Gehrig's
    disease (ALS) genetic disease causing motor
    neurons to die muscle control is lost, increased
    salivation, cramping, twitching

80
  • Epilepsy brain injury or lack of oxygen to the
    brain Seizures grand mal or petit mal
    transient loss of muscle control
  • Spinal Cord Injuries through injury or disease,
    the spinal neurons are damaged, Results in loss
    of motor control -degree of which depends on
    where the damage occurred

81
  • Hydrocephalus water on the brain excess
    cerebrospinal fluid in the brain Increased
    pressure may lead to brain damage
  • Cerebral Palsy Usually caused by oxygen
    deficiency before/during birth, reduced muscle
    coordination (cerebral damage)

82
Drug Abuse
  • Stimulants increase excitation, and depressants
    decrease excitation either can lead to physical
    dependence.
  • Each type of drug has been found to either
    promote or prevent the action of a particular
    neurotransmitter.
  • Medications that counter drug effects work by
    affecting the release, reception, or breakdown of
    dopamine, a neurotransmitter responsible for mood.

83
Drug actions at a synapse
84
  • A drug can affect a neurotransmitter in these
    ways
  • cause leakage out of a synaptic vesicle into the
    axon bulb
  • prevent release of the neurotransmitter into the
    synaptic cleft
  • promote release of the neurotransmitter into the
    synaptic cleft
  • prevent reuptake by the presynaptic membrane
  • block the enzyme that causes breakdown of the
    neurotransmitter or
  • bind to a receptor, mimicking the action or
    preventing the uptake of a neurotransmitter.

85
Drug use
86
Alcohol
  • Alcohol may affect the inhibiting transmitter
    GABA or glutamate, an excitatory
    neurotransmitter.
  • Alcohol is primarily metabolized in liver and
    heavy doses can cause liver scar tissue and
    cirrhosis.
  • Alcohol is an energy source but it lacks
    nutrients needed for health.
  • Cirrhosis of the liver and fetal alcohol syndrome
    are serious conditions associated with alcohol
    intake.

87
Nicotine
  • Nicotine is an alkaloid derived from tobacco.
  • In the CNS, nicotine causes neurons to release
    dopamine in the PNS, nicotine mimics the
    activity of acetylcholine and increases heart
    rate, blood pressure, and digestive tract
    mobility.
  • Nicotine induces both physiological and
    psychological dependence.

88
Cocaine
  • Cocaine is an alkaloid derived from the shrub
    Erythroxylum cocoa, often sold as potent extract
    termed crack.
  • Cocaine prevents uptake of dopamine by the
    presynaptic membrane, is highly likely to cause
    physical dependence, and requires higher doses to
    overcome tolerance.
  • This makes overdosing is a real possibility
    overdosing can cause seizures and cardiac arrest.

89
Heroin
  • Derived from morphine, heroin is an alkaloid of
    opium.
  • Use of heroin causes euphoria.
  • Heroin alleviates pain by binding to receptors
    meant for the bodys own pain killers which are
    the endorphins.
  • Tolerance rapidly develops and withdrawal
    symptoms are severe.

90
Marijuana
  • Marijuana is obtained from the plant Cannabis
    sativa that contains a resin rich in THC
    (tetrahydrocannabinol).
  • Effects include psychosis and delirium and
    regular use can lead to dependence.
  • Long-term marijuana use may lead to brain
    impairment, and a fetal cannabis syndrome has
    been reported.

91
Chapter Summary
  • The nervous system consists of two types of
    cells neurons and mesoglia.
  • Neurons are specialized to carry nerve impulses.
  • A nerve impulse is an electrochemical change that
    travels along the length of a neuron fiber.
  • Transmission of signals between neurons is
    dependent on neurotransmitter molecules.

92
  • The central nervous system is made up of the
    spinal cord and the brain.
  • The parts of the brain are specialized for
    particular functions.
  • The cerebral cortex contains motor areas, sensory
    areas, and association areas that are in
    communication with each other.
  • The cerebellum is responsible for maintaining
    posture the brainstem houses reflexes for
    homeostasis.

93
  • The reticular formation contains fibers that
    arouse the brain when active and account for
    sleep when they are inactive.
  • The limbic system contains specialized areas that
    are involved in higher mental functions and
    emotional responses.
  • Long-term memory depends upon association areas
    that are in contact with the limbic system.

94
  • There are particular areas in the left hemisphere
    that are involved in language and speech.
  • The peripheral nervous system contains nerves
    that conduct nerve impulses toward and away from
    the central nervous system.
  • The autonomic nervous system has sympathetic and
    parasympathetic divisions with counteracting
    activities.
  • Use of psychoactive drugs such as alcohol,
    nicotine, marijuana, cocaine, and heroin is
    detrimental to the body.
About PowerShow.com