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

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Zoology 142

Sensory, Motor, and Integrative Systems – Ch 15

Dr. Bob Moeng

Cutaneous Sensations • Regions include skin, connective tissue below skin, mucous membranes, mouth, & anus • 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)

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Zoology 142

Sensory, Motor, and Integrative Systems – Ch 15

Dr. Bob Moeng

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 – 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

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Zoology 142

Sensory, Motor, and Integrative Systems – Ch 15

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Dr. Bob Moeng

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 • 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

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Zoology 142

Sensory, Motor, and Integrative Systems – Ch 15

Dr. Bob Moeng

– 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) • 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

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Zoology 142

Sensory, Motor, and Integrative Systems – Ch 15

Dr. Bob Moeng

– 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) 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

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Zoology 142

Sensory, Motor, and Integrative Systems – Ch 15

Dr. Bob Moeng

– 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 – 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)

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