Download Sensory, Motor, and Integrative Systems

Zoology 142
Sensory, Motor, and Integrative Systems – Ch 15
Dr. Bob Moeng
Sensory, Motor, and Integrative Systems
Sensation vs. Perception
• Sensation encompasses both conscious and subconscious response to external and
internal stimuli
• Only if the sensory information reaches the thalamus is it consciously perceived in a
general way
• Only if the sensory information reaches the cerebral cortex is it identified, localized
and interpreted
• Modality - type of sensation or perception
– Any one neuron can carry info from only one
Elements of Sensory Input
• Stimulus - change in internal or external environment
• Sensory receptor(neuron or specialized cell) or organ - responds to a particular type
of stimulus and transduces information (ultimately to a potential change – graded
potential)
• First-order sensory neurons - generate and conduct APs centrally
• CNS - integrates incoming sources of APs for type, characteristic and appropriate
response
Structures of Sensory Reception (graphic)
Sensory Receptors
• Somatic senses - touch, pressure, vibration, heat, cold, pain, and proprioception
• Visceral senses - status within organs
• Special senses - smell, taste, vision, hearing, and equilibrium
– Complex sensory apparatus
• Classification by location
– Exteroceptors - stimuli from without
– Interorceptors - stimuli from within
– Proprioceptors - (in muscles, tendons, joints & inner ear) body position
• Classification by type of stimulus
– Mechanoreceptors, thermoreceptors, photoreceptors, nociceptors,
chemoreceptors
• Receptor potentials (vision, hearing, equilibrium, & taste) - cause release of synaptic
vesicles
• Generator potentials (others) - act directly to cause APs in primary sensory neurons
• Classification based on adaptation
– Rapidly adapting (phasic) - sensitive to change – pressure, touch, smell
– Slowly adapting (tonic) - those sensitive to chemical levels, body position, or pain
Cutaneous Sensations
• Regions include skin, connective tissue below skin, mucous membranes, mouth, &
anus
1
Zoology 142
Sensory, Motor, and Integrative Systems – Ch 15
•
Dr. Bob Moeng
Usually composed of dendritic nerve ends that are free or enclosed in epithelial or
connective tissue structures
• Tactile
– Touch, pressure, vibration, itch and tickle
• Thermal
• Pain
Cutaneous Receptors (graphic)
Touch
• Crude touch vs. discriminative touch
• Corpuscles of touch (Meissner) - connective tissue enclosure in dermal papillae, for
discriminative touch, adapt rapidly
– 40% of tactile receptors in hands and also tongue, lips, nipples, clitoris & penis
• Hair root plexuses - dendrite wrapped around follicle, respond to hair movement,
adapt rapidly
• Type I mechanoreceptors (Merkel discs) - free dendrite below Merkel cells, slow
adapting, important for discriminative touch
– Concentrated in finger tips, lips & external genitalia, 25% of tactile receptors in
hands
• Type II mechanoreceptors (Ruffini corpuscles) - limited structure around dendrites in
dermis (also ligaments & tendons), slow adapting, sensitive to stretching of tissue(?)
– 20% of tactile receptors in hands and also soles of feet
Other Tactile
• Pressure - sustained, heavy, distributed touch
– Corpuscles of touch (Meissner)
– Type I mechanoreceptors (Merkel discs)
– Lamellated corpuslces (Pacinian) - layered connective tissue enclosure in
subcutaneous layer, submucosal layer, and below serous membranes (thus
various regions), adapt rapidly
• Vibration - repetitive stimuli
– Corpuscles of touch - low frequency
– Lamellated corpuscle - high frequency
• Itch and tickle
– Free nerve endings, unmyelinated C fibers
– Itch - localized inflammation
– Tickle - also involves lamellated corpuscle
Pacinian Corpuscle (graphic)
Thermal
• Separate free nerve endings for heat and cold, rapidly adapting
• Cold receptors in stratum basale - usually myelinated type A fibers
– Respond to 50-105 degrees F (Why above 98.6? – result paradoxical cold)
• Warm receptors in dermis - unmyelinated type C fibers
2
Zoology 142
Sensory, Motor, and Integrative Systems – Ch 15
Dr. Bob Moeng
– Respond to 90-118 degrees F
•
Below 50 and above 118 degrees F - nociceptors are stimulated instead
Pain
• Nociceptors - free nerve endings that respond to extreme thermal, mechanical or
chemical stimuli, also surrounding tissue damage which release chemicals like kinins,
prostaglandins & K+
– little or no adaptation
• Somatic pain - associated with skin or underlying muscles, joints, tendons or fascia,
usually localized
– Acute - fast (.1 sec), sharp sensation, carried via medium-sized A-delta fibers
– Chronic - slow (1 sec), growing, burning, aching or throbbing pain, carried via
unmyelinated C fibers, more diffuse than acute pain
• Visceral pain - usually not localized
– Referred pain - visceral pain that is experienced superficially(common spinal cord
segment)
• Phantom sensation or pain (itching, pressure, tingling, or pain)
• Analgesics
– Aspirin & ibuprofen - block formation of prostaglandins
– Local anesthetics - block nerve conduction
– Opiates - alter brain’s interpretation of pain
Referred Pain (graphic)
Proprioceptive Sensations
• Also kinesthetic sense
• Sensation of body position and movement - tendon, joints, muscles
• Sensors include muscle spindles, tendon organs, and joint kinesthetic receptors and
hair cells (vestibular)
• Slow adaptation
• Connections from spinal cord to thalamus and on to cerebral cortex (somatosensory
area of parietal lobe) and to cerebellum
Muscle Spindles
• 3-10 intrafusal muscle fibers - specialized muscle fibers anchored in endomysium
and perimysium
• Enclosed in connective tissue capsule
• Little or no actin and myosin except at ends of fibers
• More concentrated in muscles for controlled movement
• Innervation
– Motor - gamma motor neurons (as opposed to larger alpha motor neurons of
normal fibers) - alters sensitivity
– Sensory - type Ia and type II fibers wrap around central portion of spindle and
respond to stretch
3
Zoology 142
Sensory, Motor, and Integrative Systems – Ch 15
•
Dr. Bob Moeng
Manages muscle tone and limits overstretching of muscles
Anatomy of Muscle Spindle (graphic)
Tendon Organs
• Collagen fibers wrapped with type Ib sensory fibers enclosed in connective tissue
• Located in tendon near muscle
• Monitor force of contraction and limit muscle & tendon damage
Anatomy of Tendon Organ (graphic)
Joint Kinesthetic Receptors
• Three similar to previously described receptors
– Free nerve endings & type II cutaneous mechanoreceptors (Ruffini corpuscles) in
articular capsule of synovial joints - pressure sensitive
– Lamellated corpuscles in connective tissue around capsules - increasing or
decreasing movement of joint
– Receptors similar to tendon organs in articular ligaments - sense force and strain
Somatic Sensory Pathways
• Ascending
• First order neurons - neurons contained within spinal or cranial nerves to cord or
brain stem respectively
• Second order neurons - neurons from cord or brain stem to thalamus, decussation
occurs in pathway
• Third order neurons - neurons from thalamus to somatosensory area of cortex (5 & 7)
• 2 major pathways to cortex - conscious
• Posterior column - medial lemniscus - cortex
– 1st order - from sensory apparatus to medulla (same side) making up posterior
column including:
• fasiculus gracilis from trunk and lower limbs to nucleus gracilis in medulla
• fasciculus cuneatus from neck, upper limbs and upper chest to nucleus
cuneatus in medulla
– 2nd order - from nucleus gracilis or cuneatus cross to contralateral medial
lemniscus and on to thalamus (ventral posterior nucleus)
– 3rd order - thalamus to cortex
– Sensations for this pathway include discriminative touch, stereognosis,
proprioception, weight discrimination, and vibratory sensations
– Syphilis, a bacterial STD causes degeneration of posterior column
• Anterior & lateral spinothalamic - cortex
– 1st order - from sensory apparatus to spinal cord
– 2nd order - from spinal cord, cross to other side, ascends via either spinothalamic
tract to thalamus
– 3rd order - thalamus to cortex
– Sensations for this pathway include pain, temperature (lateral), tickle, itch, crude
touch and pressure (anterior)
4
Zoology 142
Sensory, Motor, and Integrative Systems – Ch 15
•
Dr. Bob Moeng
Other pathways to cerebellum - subconscious proprioception
• Anterior and posterior spinocerebellar and others
Cortical Mapping (graphic)
Somatic Sensory Tracts (graphic)
Sensory Pathway (graphic)
Sensory Pathway (graphic)
Somatosensory Cortex
• Mapped sensory input from different parts of the body
– Spatial organization
– Density of receptors in region
Cortical Mapping (graphic)
Somatic Motor Pathways
• Descending
• Primary motor area (4) and in part the premotor area (6) and somatosensory area
contribute to motor neurons
• Mapped primary motor area of cortex
– Spatial organization
– Number of motor units in region
Cortical Mapping (graphic)
Direct Pathways
• Or pyramidal pathways - found in the swellings on ventral side of medulla
• Precise control of voluntary skeletal muscle movements primarily in face, vocal cords,
hands and feet
• Upper motor neurons descend from cortex to cranial nerve nuclei or anterior horn of
spinal cord and most decussate in between
– Damage causes spastic paralysis
• Lower motor neurons innervate skeletal muscle
– Damage cause flaccid paralysis
• Lateral corticospinal tracts
– Supply limbs, hands and feet
– Cortex decussate in medulla (90%) lateral corticospinal tracts in spinal cord
lower motor neurons (possibly via interneurons)
• Anterior corticospinal tracts
– Supply neck & part of trunk (axial movement)
– Cortex anterior corticospinal tracts in spinal cord may decussate in cord
lower motor neurons (possibly via interneurons)
• Corticobulbar tracts
– Supply eyes, tongue, and neck (chewing, facial expression, speech)
– Cortex nuclei of various cranial nerves in pons and medulla (may decussate)
lower motor neurons
Motor Tracts (graphic)
5
Zoology 142
Sensory, Motor, and Integrative Systems – Ch 15
Dr. Bob Moeng
Lateral and Anterior Corticospinal Pathways (graphic)
Indirect Pathways
• Or extrapyramidal pathways - all other descending pathways
• Interneuronal connections much more variable - may occur at basal ganglia, limbic
system, thalamus, cerebellum, reticular formation & brain stem nuclei
• Input to lower motor neurons from interneurons and may be excitatory or inhibitory
• Basal ganglia appears to loop information possibly for programming of movements
– Cortex basal ganglia via globus pallidus  thalamus cortex
– Parkinson and Huntington disease related to degeneration of this circuit
• Cerebellum
– Monitoring intentions - what movements are planned by higher centers
– Monitoring actual movement - proprioception, equilibrium and eye input
– Comparing sensory feedback and commands
– Providing corrective feedback - to higher brain centers
• Pathways include rubrospinal, tectospinal, vestibulospinal, lateral and medial
reticulospinal tracts
Indirect Motor Pathways (graphic)
Cerebellar Motor Control (graphic)
Learning and Memory
• Learning - ability to acquire knowledge or skills
• Memory - storage of knowledge gained or skills developed over time
• Plasticity - changes in the nervous system that are reflected in behavioral changes to
stimuli (i.e. learning and memory)
– Changes may include altered cell synthesis of protein molecules, dendrites and
their connections, synaptic activity
– Areas known for memory - cortex, limbic system (hippocampus and amygdala)
and diencephalon
• Short-term vs. long-term memory
– Short-term - likely to be mediated by electrical or chemical actions (i.e.
reverberating circuits)
– Long-term - likely to be anatomical and synaptic enhancement changes
• Increased # and size of presynaptic terminals, inc. postsynaptic dendrites, inc.
in neurotransmitter
Consicousness
• Active reticular activating system(part of reticular formation) which stimulates cortex
via thalamus
• Sensory input to RAS (olfaction has little or no effect)
• Coma - frequently related to RAS inactivity
Reticular Activating System (graphic)
Sleep
• Evidence of sleep-inducing chemicals
6
Zoology 142
Sensory, Motor, and Integrative Systems – Ch 15
Dr. Bob Moeng
– e.g. adenosine (through specific receptors, inhibits ACh neurons in RAS)
– Caffeine blocks receptors
•
•
Changes in EEG
Non-rapid eye movement sleep vs. rapid eye movement sleep
– Alternate between types every 90 min. through the night starting with progressive
stages of NREM
– REM sleep totals 90-120 min. per night
• Active dreaming period
• Increased autonomic activity, time of penile erections
• Period reduced by sedatives
• REM 25% of sleep period in adults, 35% in 2 yr olds, 50% in infants
Stages of Sleep (graphic)
7