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