Sensory, Motor and Integrative Systems

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Sensory, Motor and Integrative Systems
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Sensation

• The conscious or subconscious awareness of
  external or internal stimuli
• Perception means the conscious awareness and
  interpretation of a stimulus

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Sensory Modalities

• Each type of sensation is called a modality,
  e.g., touch, hearing
• A given sensory neuron only handles one modality
• There are two classes of modalities

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Classes of Modalities

• General senses (somatic and visceral)
• Tactile
• Thermal
• Pain
• Proprioception
• Visceral sensations
• Special senses
• Smell
• Taste
• Hearing
• Vision
• Equilibrium

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Process of Sensation

• Stimulation of receptor (either a dendrite or a
  specialized receptor cell)
• Transduction of the stimulus into graded impulses
• Generation of impulses into action potentials by
  first order neurons (those that carry impulses
  from PNS to CNS)
• Integration of sensory input

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Receptor Classification Based on Anatomy

• Free nerve endings (dendrites)- itch, tickle,
  some touch
• Encapsulated nerve endings (dendrites)-deep touch
• Separate cells-merkle cells, gustatory receptors,
  hair cells of cochlea, photoreceptors
• Produce receptor potentials

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Potentials

• Generator potential
• Graded potential produced by a free or
  encapsulated nerve ending of a first order
  neuron.
• Receptor potential
• A potential generated in a special receptor cell
  that causes exocytosis of a neurotransmitter that
  diffuses across the synapse and produces a graded
  potential in the first order neuron.

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Receptor Classification Based on Location

• Exteroreceptors
• Interoreceptors
• Proprioreceptors

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Receptor Classification Based on Stimuli

• Mechanoreceptors
• Thermoreceptors
• Nocioreceptors
• Photoreceptors
• Chemoreceptors

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Adaptation in Sensory Receptors

• The amplitude of the generator or receptor
  potential decreases with time, even though the
  stimulus remains constant.
• Perception may decrease or cease.
• Receptors vary in how quickly they adapt.
• Those associated with pain, body position, and
  blood chemistry adapt more slowlya good
  protective mechanism.

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Somatic Sensations

• From receptors in skin (cutaneous) or
  subcutaneous layer, mucous membranes, muscles,
  tendons, joints, inner ear.
• Unequal distribution highest density in finger
  tips, lips, tip of tongue.

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Modalities of Somatic Sensation

• Tactile
• Thermal
• Pain
• Proprioceptive

LETS CONSIDER EACH ONE SEPARATELY
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Tactile sensations

• Touch
• Pressure
• Vibration
• Itch
• Tickle

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Touch

• Crude
• Discriminative
• Receptors
• Meissners corpuscles (corpuscles of touch)
• Hair root plexuses
• Merkle discs
• Ruffini corpuscles-in deep dermis, tendons,
  ligament respond to stretching of digits or
  limbs

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Meissners corpuscle
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Pressure

• Felt over a larger area than touch
• Receptors
• Pacinian corpuscles
• Ruffinian

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Pacinian corpuscle
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Vibration

• Vibration perceived from repeated signals from
  Meissner or Pacinian corpuscles

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Itch and Tickle

• Free nerve endings
• You cannot tickle yourself! Someone has to do it
  for you!

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Thermal Sensations

• Free nerve endings detect cold (10o-40o C,
  50o-105o F -includes paradoxical cold) and warm
  (32-48o C,90-118o F )
• Very cold or very warm temps (below 10oC or above
  48oC) elicit a pain response.
• Rapidly adapting, then slowing

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Pain Sensations

• The receptors are called nocioreceptors
• Little, if any, adaptation
• Stimulated by chemicals released during tissue
  damage
• Prostaglandins
• Kinins
• K

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Types of Pain

• Fast-type medium diameter fibers
• Acute
• Not felt in deeper areas of the body
• Slow-type C fibers
• throbbing
• Begins about 1 second after fast
• Diminishes slowly
• Found in superficial and deep regions of body

THINK ABOUT WHAT HAPPENS WHEN YOU STUB YOUR TOE
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Location of Pain

• Superficial somatic
• Deep somatic
• Visceral

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Perception of Pain

• Fast pain is precise
• Slow pain is more diffuse
• Localized visceral
• Referred visceral
• Phantom limb sensation

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DISTRIBUTION OF REFERRED PAIN
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Pain relief

• Block action potential-lidocaine
• Block prostaglandins-nsaids
• Block perception-morphine

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Proprioceptive Sensations

• Monitor amount of muscle contraction
• Monitor amount of tension in the tendons and
  joints
• Monitor position of head
• Receptors are called proprioceptors
• Slow adaptation

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Types of Proprioceptors

• Muscle spindles
• Monitor stretch
• Used by brain to set muscle tone
• Tendon organs
• Initiate tendon reflexes
• Reduce damage to muscle and tendons through
  feedback reflexes
• Joint kinesthetic receptors in synovial capsules
  (Ruffini and Pacinian)
• Monitor joint position and movement
• Initiate protective reflexes

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Somatic Sensory Pathways

• Relay of information from the receptors to the
  cortex and cerebellum

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Types of Neurons Involved

• First order
• From receptor to brain stem or spinal cord
• Second order
• From brain stem or spinal cord to thalamus
  decussate in brain stem or spinal cord
• Third order
• From thalamus to primary somatosensory areas of
  cortex on same side

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Types of Pathways

• Posterior column-medial lemniscus pathway to the
  cortex
• Anterolateral pathway to cortex

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Posterior Column-Medial Lemniscus Pathway

• Discriminative (fine) touch
• Stereognosis
• Proprioception
• Weight discrimination
• Vibratory sensation

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Decussation occurs in medulla
Note the first, second and Third order neurons
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Anterolateral Pathway (Spinothalmic)

• Pain
• Temperature
• Tickle
• Itch
• Crude touch and pressure
• Vibration (travels through either posterior
  columns or anterolateral pathways)

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Anterolateral (spinothalmic) pathways
Note first, second and third order neurons
Decussation occurs in cord
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Trigenimothalmic pathway to cortex

• Tactile, thermal and pain
• From face, nasal cavity, oral cavity and teeth
• First order neurons extend from receptor in head
  to pons where cell bodies are located
• Synapse occurs in pons for some neurons and in
  medulla for others.
• Decussation occurs in pons or medulla
• Second order neurons enter trigenminothalmic
  tract to thalamus
• Third order from thalamus to cerebral cortex

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Mapping of Somatic Sensory and Motor Cortex

• Note relative amounts of brain devoted to
  different body parts. Amounts can increase with
  learning!

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Somatic Pathways to the Cerebellum

• Two neuron pathways
• Do not usually reach consciousness
• Posterior spinocerebellar
• Anterior spinocerebellar
• Cuneocerebellar and rostralcerebellar
• From upper limbs

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Information of Cerebellar Pathways

• Convey information related to
• Posture
• Balance
• Coordinated movement

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Somatic Motor Pathways
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Neurons of Somatic Motor Pathways

• Upper motor
• 60 of cell bodies in precentral gyrus and 40
  in postcentral gyrus
• 90 decussate in the medulla 10 in cord
• Lower motor
• Extend from motor nuclei of cranial nerves to
  skeletal muscles of the face, head
• Extend from anterior horn of each spinal cord
  segment to skeletal muscle of the trunk and limbs

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Lower Motor Neurons

• Cell bodies in cord or brain stem
• Extend from CNS to skeletal muscle of body
• Called final common pathway because of input from
  4 distinct sources is integrated, determining if
  an action potential will generate in the lower
  motor neuron, which synapses with a muscle.

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Circuits Influencing Lower Motor Neuron

• 1. Local circuits- input from nearby interneurons
  to lower motor neurons in cord or brain stem
• Coordinate rhythmic activities
• 2. Upper motor neurons-input to local circuits
  and lower motor neurons. Cell bodies in cortex
  and motor areas of brain stem, including red
  nucleus, vestibular nucleus, superior colliculus,
  reticular formation.
• Planning, initiating directing sequences of
  voluntary movement (cortex)
• Muscle tone, posture, balance, head and body
  orientation (brain stem)

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• 3. Basal ganglia neurons
• Assist U.M.N.,
• Help initiate, terminate, and suppress movements
• Muscle tone
• 4. Cerebellar neurons
• Coordinates body movements
• Balance and posture

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Types of Somatic Motor Pathways

• Direct (pyramidal)
• Indirect (extrapyramidal)

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Direct (pyramidal)

• Simplest
• Impulses for voluntary movements
• Precise movements
• Cell bodies located in cortex

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Direct Pathways

• Corticospinal pathways
• Lateral corticospinal
• Synapse with lower motor neurons to distal parts
  of limbs
• Decussation in medulla (90 of all decussation)
• Anterior corticospinal
• Synapse with lower motor neurons to skeletal
  muscle of trunk and proximal parts of limbs
• Decussation in cord (10 of all decussation)
• Corticobulbar
• Synapse with lower motor neurons, which are
  C.N.s III, IV, V, VI, VII, IX, X, XI, XII to
  skeletal muscles in head
• Not all axons decussate

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Direct (pyramidal) pathways serve skeletal muscle
Three main tracts Lateral corticospinal -Serves
limbs, hands, feet Anterior corticospinal -Serves
neck and trunk Axial muscles Corticobulbar
-Serves skeletal muscles from head and neck
through cranial nerves pass through
internal capsule to cerebral peduncles to C.N
3-7,9-12
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Direct Pathways in Cord
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Indirect Pathways-extrapyramidal

• All other tracts
• Control tone of skeletal muscle, posture, and
  precise movements of distal part of upper limb
• Upper motor neurons from various parts of brain
• Complex pathways
• 5 main tracts
• Rubrospinal
• Tectospinal
• Vestibulospinal
• Lateral reticulolspinal
• Medial reticulospinal

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INDIRECT PATHWAYS
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Indirect Pathways in Cord
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Paralysis

• LMN-flaccid, ipsilateral
• UMN-spastic, contralateral

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Roles of the Basal Ganglia

• Connect with many parts of the brain
• Program habitual or automatic movements
• Set up muscle tone
• Damage results in abnormal movements, rigidity,
  or tremor
• Parkinsons loss of dopamine results in
  increased tone and stiffness
• Huntingtons chorea hereditary loss of ACH and
  GABA results in jerky, purposeless movements,
  mental deteriation, death. Symptoms may not
  appear until age 30-40

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Roles of the Cerebellum

• Monitors intentions for movements
• Monitors actual movements
• Compares the two
• Sends out signals to adjust movements as needed
• Involved in learning and executing movements
• Damage results in
• Ataxia jerky, uncoordinated movement
• Intention tremor-shaking before deliberate
  movement

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Integrative Functions of the Cerebrum

• Wakefulness and sleep
• Learning and memory

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Wakefulness and Sleep

• Circadian rythum is established by the
  hypothalamus
• Reticular activating system increases cortical
  activity (consciousness)
• RAS also plays a role in arousal from sleep

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Sleep

• Sleep
• Rem 3-5 episodes/night
• Non-rem 4 stages

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Learning and Memory

• The brain produces changes when it is used in
  learning and memorythis is plasticity.
• Production of different proteins
• Production of new dendrites
• Memory may be classified as short-term,
  intermediate or long-term.
• The hippocampus plays a vital role in memory

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The End