Sensory, Motor and Integrative Systems - 2024 PDF

Sensory, Motor and Integrative Systems  Learning Objectives Differentiate the classes of sensory receptors Describe the organization of sensory and motor pathways from the brain to the spinal cord Sensory Modalities each receptor responds to only one kind of stimulus senses...

Sensory, Motor and Integrative Systems  Learning Objectives Differentiate the classes of sensory receptors Describe the organization of sensory and motor pathways from the brain to the spinal cord Sensory Modalities each receptor responds to only one kind of stimulus senses classified as general or special  General Senses receptors widely distributed –touch, vibration, temperature, pain, etc. receptors throughout skin and body structures –proprioceptors in muscles and joints  Special Senses receptors in specialized organs respond to specific stimuli all located in the head taste, smell, vision, hearing, equilibrium  Structural Classification of Receptors Free nerve endings bare pain, temperature, tickle, itch, light touch Encapsulated nerve endings dendrites enclosed in connective tissue capsule pressure, vibration, deep touch Separate sensory cells specialized cells that respond to stimuli vision, taste, hearing, balance Classification of Receptors by Location Classification by Location: exteroreceptors near surface of body receive stimuli hearing, vision, smell, taste, touch, pressure, pain, vibration, temperature Classification by Location: interoreceptors monitor environment not conscious except pain, pressure Classification by Location: proprioceptors in muscle, tendon, joint, inner ear sense body position and movement  Classification of Receptors by nature of Stimulus Detected Classification by Stimulus: Mechanoreceptors pressure or stretch (touch, pressure, vibration, hearing, proprioception, equilibrium, blood pressure) Thermoreceptors temperature Classification by Stimulus: Nociceptors tissue damage Photoreceptors light (vision) Chemoreceptors specific molecules (detect taste, smell, changes in body fluids)  Sensory Adaptation (adaptation of receptors) sensitivity to sustained stimulation (e.g, odours disappear, water temp. feels less extreme) ability to adapt varies – smell, pressure, touch receptors are fast – pain, body position receptors are slow  Somatic Tactile Sensations Touch onset of touch (crude) –perception something has touched the skin continuous touch (discriminative) –provides location, texture of source  Somatic Tactile Sensations Pressure - sustained sensation over a large area Vibration - rapid, repetitive sensory signals Itch - chemical irritation of free nerve endings Tickle - stimulation of free nerve endings  Skin receptors Nonecapuslated sensory nociceptor corpuscle (pain) (continuous touch) Tactile corpuscle hair root plexus (vibration, onset (movement of of touch) hair) lamellar Bulbous corpuscle corpuscle (high freq. (pressure, stretch) vibration) © John Wiley & Son Inc  Thermal Sensations cold receptors respond to 10-35C warm receptors respond to 30-45C adapt rapidly, but continue to generate impulses at a low frequency < 10 or >45C → receptors  Nociceptors free nerve endings in all tissues except stimulated by excessive distension, muscle spasm, inadequate blood flow slow adaptation occurs  Types of Pain Fast (acute) pain sharp, rapid onset (.1 sec) pain (e.g., needle puncture, cut) felt in superficial tissues only  Types of Pain Slow (chronic) pain slower onset (1 sec.) aching or throbbing pain felt in superficial and deep tissues increases in intensity  Proprioceptive/ Kinesthetic Sense sensory information sent from muscles, tendons, joint capsules, receptors in ear, to cerebellum, cerebral cortex → proprioception (awareness of body position), Kinesthetic sense (awareness of movement) Sensory Pathways from peripheral receptors to the primary sensory area of the cerebrum consist of three neurons  sensory cortex 3rd order neuron thalamus 2nd order neuron 1st order neuron First order sensory neuron neuron cell body in spinal ganglion carries impulses from receptors in skin, joints, and muscles to the spinal cord or brainstem  Second order sensory neuron cell body in the grey matter of the spinal cord or brainstem carries impulses to the and cerebellum Recall… Sensory tracts Posterior Spinothalamic Spinocerebellar funiculi Third order sensory neuron cell body in carries impulses from the thalamus to the primary sensory area of the cerebral cortex Primary Sensory Cortex postcentral gyrus input from 3rd order sensory neurons  Primary Motor Cortex precentral gyrus initiates voluntary movement cells are called upper motor neurons 1 million UMN in cerebral cortex Motor Neurons upper motor neurons (UMNs) extend from primary motor cortex to ventral horn of spinal cord CNS neurons with cell bodies in brain terminate on LMNs lower motor neurons (LMNs) peripheral neurons cell bodies in ventral horn of s.c. terminate on effectors  Direct Motor Pathways direct tract neurons extend uninterrupted from primary motor cortex to ventral horn of the s.c. in action control muscle tone, precise, voluntary movements on contralateral side of the body © John Wiley & Son Inc Direct Motor Pathways 90% decussate in medulla then descend as the lateral corticospinal tracts 10% descend uncrossed as anterior corticospinal tracts then cross in spinal cord  Direct Motor Pathways lateral corticospinal tract precise, skilled movements of limbs, hands, feet  Direct Motor Pathways anterior corticospinal tract neck and trunk muscles  Motor Pathways indirect pathways direct pathways (extrapyramidal tracts) (pyramidal tracts) Final Common Pathway there are several pathways from the brain to ventral horn, but the LOWER MOTOR NEURON is the only pathway from the ventral horn to the effector LMN is final common pathway