Receptive Field and Sensory Pathways

Receptive Field

Area monitored by a single receptor cell; larger fields make stimulus localization difficult

Types Of Stimuli

Include physical force, dissolved chemicals, sound, and light

Tonic Receptors

Always active receptors providing info on stimulus intensity and change rate

Phasic Receptors

Normally inactive receptors becoming active briefly when change occurs

Adaptation

Reduction in sensitivity to constant stimuli; nervous system quickly adapts

Major Receptor Types

Nociceptors (pain), thermoreceptors (temperature), mechanoreceptors (physical distortion), chemoreceptors (chemical concentration)

Pain Receptors

Nociceptors common in skin, joint capsules, bones, and blood vessel walls

Myelinated Type A Pain Fibers

Carry fast pain sensations to CNS, trigger reflexes, reach sensory cortex

Type C Pain Fibers

Carry slow pain sensations, cause generalized activation, less specific area awareness

Thermoreceptors

Detect temperature changes, located in dermis, muscles, liver, and hypothalamus

Mechanoreceptors

Sensitive to membrane distortions, contain ion channels responding to membrane changes

Tactile Receptors

Sensitive receptors providing touch, pressure, and vibration sensations

Baroreceptors

Detect pressure changes in blood vessel walls and digestive, reproductive, and urinary tracts

Proprioceptors

Monitor joint and muscle positions, including muscle length and external tension

Chemoreceptors

Respond to water and lipid-soluble substances, located in carotid and aortic bodies

Spinal Cord Anatomy

Central canal, white matter for conduction tracts, gray matter for cell bodies, sensory and motor neuron horns

Somatic Sensory Pathways

Carry sensory info from skin and muscles, with sensory neuron cell bodies in dorsal horns

Posterior Column Pathway

Transmits pressure, vibration, and proprioception sensations, synapse in dorsal horn

Anterior Spinothalamic Tract

Carries crude touch and pressure sensations, synapse in ventral horn

Somatic Motor Pathways

Involve upper and lower motor neurons for voluntary muscle control

Upper Motor Neuron

Synapses on lower motor neuron, innervates skeletal muscle units

Lower Motor Neuron

Triggers muscle contractions, extends outside CNS

Corticospinal Pathway

Voluntary control over skeletal muscles, descending tracts from primary motor cortex

Lateral Corticospinal Tract

Descending tracts visible as pyramids, control skeletal muscles of trunk and limbs