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Title: Neurophysiology Part 3


1
Neurophysiology Part 3
  • Structural Functional Organization of the
    Nervous System
  • Chapter 8

2
Main Functions of Neurons
  • Sensory reception
  • Central processing
  • Motor output
  • Predictable organized connected integrated
    from diffuse distribution (e.g. Hydra where
    different regions of body respond to environment
    independently) to complex integration with brain
    spinal cord (most neurons in CNS most
    receptors effectors in PNS)

3
Flow of Information
  • Into NS via sensory receptor neurons
  • Through complicated central processing network
    (brain and/or spinal cord)
  • Out to Motor neurons (to muscles or glands)
  • Simplest example Reflex Arc (primordial type
    may have been receptor cell directly innervated
    an effector cell) basic operating unit
  • Monosynaptic reflex arc 3 elements sensory
    neuron, motor neuron effector (cell, tissue or
    organ that acts to change the condition of an
    organism I.e. contact a muscle, secrete a hormone
    in response to neuronal or hormonal signal)

4
Flow of Information cont
  • Most reflex arcs include gt 1 synapse
    polysynaptic consist of at least 1 interneuron
    between sensory motor neurons
  • Evolutionarily speaking, as animals became more
    complex (including greater behavioral
    complexity), number of interneurons increased
    enormously greater behavioral flexibility
    learning?
  • Information can converge diverge
  • Parallel Processing ability of neurons to carry
    out different operations on one set of
    information simultaneously permits system to
    analyse info rapidly efficiently

5
Principles of Evolution of NS
  • Neuron is functional unit of NS of all organisms
  • Organization of NS evolved through 1 fundamental
    pattern reflex arc
  • Trend in evolution toward gathering of neurons
    into a CNS
  • Complex organisms have more neurons than simple
    organisms
  • As NS more complex, new structures added
  • Relative size of each region in brain how NB
    sensory input is or motor control out for
    survival of species
  • In vertebrates regions of brain organized into
    topographical maps

6
Organization of Vertebrate NS
  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
  • CNS contains most somata encompassing entire
    structure of all interneurons contains somata
    of most neurons that innervate muscles other
    effectors collections of somata with similar
    function nuclei bundles of axons extending
    from somata tracts
  • PNS includes nerves which are bundles of axons
    from sensory motor neurons, ganglia that
    contain somata of some autonomic neurons
    ganglia containing somata of most sensory neurons
    (retina is an exception as in CNS)
  • Afferents efferents most nerves are mixed Fig
    8-6 p. 284

7
Efferent Output 2 main pathways
  • Somatic NS (voluntary system) motor neurons
    control skeletal muscles under animals voluntary
    control
  • Autonomic NS efferent neurons modulating
    contraction of smooth cardiac muscle
    secretory activity of glands (e.g. heartbeat,
    digestion, temp regulation while autonomic,
    are integrated controlled connections between
    SNS ANS allow each to influence the other
    further divided into sympathetic
    parasympathetic differing both anatomically
    physiologically

8
The Spinal Cord
  • Enclosed protected by vertebral column
  • Site of reflex action can act independently of
    brain but also receives input from higher centers
    in brain
  • 4 regions cervical, thoracic, lumbar sacral
    within each, receives info from sends info to a
    particular body part

9
The Spinal Cord cont
  • Cross-section ascending (sensory) descending
    (motor) axons grouped around outside surface of
    cord organized into tracts outer region
    white matter (shiny white appearance of myelin
    central region gray matter contains somata
    dendrites of interneurons motor neurons axons
    presynaptic terminals of neurons that synapse
    onto these spinal neurons (mostly unmylinated)
  • Spinal canal fluid-filled central cavity
    continuous with fluid-filled cavities in brain
    (cerebral ventricles) containing cerebrospinal
    fluid (composition similar to plasma)

10
The Spinal Cord cont
  • Afferents enter via dorsal root
  • Efferents leave via ventral root (some exceptions
    to this)
  • Somata of spinal motor neurons located in ventral
    gray matter ventral horn
  • Somata of interneurons that receive transmit
    sensory info located in dorsal gray matter
    dorsal horn

11
The Spinal Cord cont
  • Afferent axons that synapse onto sensory
    interneurons within cord arise from sensory
    receptor neurons whose somata are located in
    dorsal root ganglia outside CNS
  • Segregation of sensory motor axons into dorsal
    ventral roots makes it possible to selectively
    stimulate afferent or efferent neurons in a
    single spinal segment
  • Many neuronal connections that produce relfex
    behaviors re located in spinal cord e.g stretch
    reflex, withdrawal reflex

12
The Brain - Structure
  • Vestigial segmental organization
  • While differences exist across phylogenic levels
    complexity organization increases as go up,
    similarities from caudal (back) to rostral
    (front)
  • Medulla oblongata where brain meets spinal cord
    contains controls centers for respiration
    autonomic function groups of neurons that
    receive relay sensory info from several
    modalities (e.g. organs of equilibrium hearing)
    other clusters that receive relay info from
    motor centers

13
The Brain Structure cont
  • Cerebellum dorsal (above) medulla pair of
    hemispheres smooth surface in lower vert
    convoluted in higher (increases surface area)
    coordination of motor output compares
    integrates info arriving from semicircular canals
    neurons that provide info about muscle stretch
    position s of joints (together called
    proprioceptors) from visual auditory systems
    help maintain posture, orienting an animal in
    space producing accurate limb movements size
    varies with species

14
Cerebellum cont
  • lacks direct connection to spinal cord can not
    directly control movement but sends signals to
    regions of brain that do directly control
    movement
  • Participates in learning motor skills (recent
    work abnormalities with cerebellar neurons may
    contribute to challenges with autism)
  • Research also suggesting involvement with
    regulating behavior

15
The Brain Structure cont
  • The pons (lying ventral slightly anterior to
    cerebellum) consists of fiber tracts that
    interconnect many different regions of the brain
    e.g. connecting cerebellum and the medulla with
    the cerebrum biological clock mediate
    sleep-wake cyclesleep
  • Tectum (optic lobe in mammals superior
    culliculus) located within the pons receives
    integrates visual, auditory sensory inputs
    role it plays varies with species for some it
    is more NB than others

16
Cerebral Cortex
  • In higher vertebrates, cerebral cortex
    (multilayered collection of cells on the outer
    surface of the cerebrum) takes over many of
    functions of the tectum in lower animals most
    enlarged elaborated in humans yet still typical
    of all mammals subdivided into functional
    regions (more later)

17
Additional Regions of Importance
  • Thalamus major coordinating center for sensory
    motor signaling relay station for sensory
    input, providing some info processing also in
    mammals, sensory info sent by neurons of thalamus
    to sensory regions of cerebral cortex motor
    info is received from motor regions of cortex by
    thalamus relayed to other centers NB cortex
    not only receives info from thalamus it can also
    modify thalamic function to change the nature
    amt of info the thalamus relays such feedback
    between parts of brain are common can
    powerfully modify brain function

18
Additional Regions of Importance
  • Amygdala medial temporal lob, (few inches from
    ear humans) almond-shaped structure involved
    in producing responding to nonverbal signs of
    anger, avoidance, defensiveness fear i.e.
    processes info organizes output related to
    emotions (phylogenetically old structure
    involved in protecting organisms moving away from
    noxious stimuli)
  • coordinates the actions of the autonomic
    endocrine systems
  • Working through the hypothalamus, it releases
    excitatory hormones Perts work

19
Additional Regions of Importance
  • Hypothalamus includes of centers controlling
    functions related to survival of individual
    species eg. BT regulation, eating, drinking
    sexual appetite also participate in expression
    of emotional reaction e.g excitement, pleasure
    rage neuroendocrine cells here control water
    electrolyte balance secretory activity of
    pituitary gland

20
Organization of the Mammalian Cerebral Cortex
  • 2 hemispheres of cerebrum prominent folds
    increases surface area increases total
    neurons
  • Surface covering gray matter organized into
    sub-layers paralleling the surface each having
    recognizable pattern of input output
  • further organized into functional regions
  • Some areas purely sensory (receive info, process
    it pass it on) some purely motor (primitive
    mammals, cortex primarily sensory motor) in
    humans/higher NHPs, regions neither clearly
    sensory nor clearly motor association cortex
    inter-sensory associations, memory, planning
    future behavior, thought communication

21
Organization of the Mammalian Cerebral Cortex
cont
  • Areas sensory in function auditory,
    somatosensory visual cortical areas
  • CNS has no pain receptors why much research can
    be performed on a conscious person which have
    supported hypothesis that all sensory perception
    occus in CNS in sensory association areas

22
Divisions of Cerebrum
  • four (or five depending on ones view)
    arbitrary divisions or lobes
  • four lobes on the surface
  • Frontal
  • Parietal
  • Occipital
  • Temporal
  • fifth lobe is underneath the surface lobes
    called the limbic lobe or limbic system
    (amygdala, hipp

23
Frontal Lobe rearmost
  • areas that control motor functions
  • body areas controlled are mapped onto that
    portion of the cortex, with some parts, (in
    humans, notably the hands and lips), having more
    corical dedication than other parts, (like the
    torso in humans) I.e. the map is asymmetric
    with respect to the body
  • contralateral organization I.e. stimulating the
    left motor area will result in a movement on the
    right side of the body

24
Parietal Lobe frontmost
  • areas that monitor sensory information
  • areas are directly across a deep sulcus, or
    division, from the motor areas
  • body is also mapped onto the sensory areas of the
    parietal lobe, but that map (or homunculus) is
    not exactly like the map of the motor areas
  • contralateral organization

25
Temporal Lobe
  • receives sensory input from the ears
  • sounds are analyzed and interpreted (as language
    in humans)

26
Occipital Lobe
  • receive sensory input from the eyes
  • analyzes interprets visual stimuli
  • analysis interpretation of vision is extremely
    complex accounts for the largest percentage of
    the brain's activity in many species

27
Somatosensory
  • Ea. Separate location receives input from
    specific area of body info received from
    adjacent areas of body is transmitted to adjacent
    cortical regions fig. 8-14 p. 291
  • amt dedicated to each area varies with species
    their needs e.g. humans ½ somatosensory
    cortex receive input from face hands while
    remaining ½ responsible for entire remainder of
    body surface

28
Examples of purely Sensory Areas
  • Auditory cortex of temporal lobe
  • Visual cortex of occipatal lobe
  • Similar to somatosensory areas, sensory areas are
    organized in a highly ordered fashion

29
Motor Cortex
  • Adjacent to somtosensory cortex
  • Organized into a map corresponding to rest of
    body i.e. spatial distribution of neurons in
    motor cortex correlates with location of muscles
    that are controlled by those neurons
  • Takes more neurons to control muscles making
    precise movements than those controlling muscles
    making large, imprecise movements

30
Control of Movement
  • Control of movement arises from activity in motro
    cortx based on input fromother areas of cortex
    brain
  • Motor control signal travels to muscles by
    several parallel pathways including corticospinal
    tract (in vertebrates, tracts are named by where
    the somata is located and where synapses located)

31
Autonomic Nervous System
  • Visceral function in vertebrates regulated
    largely without conscious control
  • Sympathetic parasympathetic pathways act
    continuously in opposition to each other
    i.e. at rest/sleep (i.e. low stimulation level)
    parasym in charge low HR, RR, diverting
    metabolic energy to low/house-keeping
    activities like digestion vs. active/frightened
    (higher stimulation level) sym in charge
    higher HR, RR, increase blood flow to muscles,
    inhibiting housekeeping
  • Deep sleep vs intense physical activity
    continuum - sym/parasym keeps this in balance
    table 8-1 p. 295

32
Autonomic Reflex Arc Functional Unit of ANS
  • Afferent side of auto reflex arc similar to
    somatic reflex arc but sensory neurons respond to
    different stimuli i.e. concentration glucose, O2
    content
  • Unlike somatic reflex arc (where all necessary
    neurons located in spinal cord) autonomic
    reflexes typically processed through brain

33
Autonomic Reflex Arc Functional Unit of ANS
cont
  • Efferent side different from somatic reflex arc
    motor output carried by chain of 2 neurons in
    sympathetic NS soma of 1st neuron located in
    CNS (preganglionic neuron) soma of 2nd neuron
    lies in sympathetic ahin ganglion (postganglionic
    neuron which lie entirely outside CNS synaping
    onto target cell of that reflex
  • Fig. 8-17 p. 294

34
Sympathetic/Parasympathetic Divisions - Structure
  • Somata of sympathetic preganglionic neurons
    located in thoracic lumbar regions of spinal
    cord many synapse onto postgang neurons in sym
    chain ganglia (containing somata of
    postganglionic neurons) axons of postgang
    neurons extend to target organs may lie far from
    gang (celiac gang exception stomach, liver,
    splee pancread, kidney and adrenal gland located
    in abdomen)
  • Fig 8-18 p. 296

35
Sympathetic/Parasympathetic Divisions Structure
cont
  • Pregang neuron of parasym synapse onto post gang
    neurons in gang that lie near (or even in) walls
    of target organs axons of pregang neurons may
    be very long axons of post gang neurons are
    very short somata of parsym pregagn neurons are
    located in brain in sacral spinal cord

36
ANS Neurotransmitters divisions differ
chemically
  • All pregang neurons cholinergic i.e. NT is ACh
  • Post gang NT of parasym is ACh but postgang NT of
    sympathetic is norepinephrine (some exceptions)
  • Postgang neurons of both divisions typically
    innervate same target organ exerting opposite
    effects e.g pacemaker activity is slowed by ACh
    release by para vs. it is accelerated by
    norepinephrine released by sympathetic post gang
    these activities are reversed in digestive
    tract (i.e. ACh from para stim intestinal
    motility secretions vs. norepinephrine from sym
    inhibits these functions)

37
NT Receptors
  • ACh norepinephrine bind to 2 specific kinds of
    receptors nicotinic muscarinic
  • Receptors in postgang of both divisions
    nicotinic
  • Receptors in target tissue are alpha or beta
    adrenergic receptors in sympathetic muscarinic
    ACh receptor in parasym
  • table 8-2 p. 297
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