Concrete is pumped from a cement mixer to the place it is being laid, instead of being carried in wheelbarrows. The flow rate is 200.0 L/min through a 50.0-m-long, 8.00-cm-diameter hose, and the pressure at the pump is 8.00×106 N/m2 . (a) Calculate the resistance of the hose. (b) What is the viscosity of the concrete, assuming the flow is laminar? (c) How much power is being supplied, assuming the point of use is at the same level as the pump? You may neglect the power supplied to increase the concrete’s velocity.
Ch 14: The Cutaneous Senses Somatosensory System ● Three Parts ○ Cutaneous Senses perception from the skin ○ Proprioception position of body and limbs ○ Kinesthesis movement of body and limbs Cutaneous System ● Skin heaviest organ in the body ○ Protects keeps agents from penetrating body ○ Epidermis outer layer of skin ■ dead skin cells ○ Dermis below epidermis ■ Mechanoreceptors ● Shallow ○ Merkel Receptor ■ fires continuously while stimulus is present ■ respon sible for sensing fine details ○ Meissner Corpuscle ■ fires when stimulus is first applied and removed ■ respon sible for controlling hand grip ● Deeper ○ Ruffini Cylinder ■ fires continuously to stimulation ■ perceiv es stretching of skin ○ Pacinian Corpuscle ■ fires when stimulus first applied and removed ■ associ ated with sensing rapid vibrations and fine texture ○ Pathways from Skin to Cortex ■ nerve fibers travel in bundles to the spinal cord ■ Two major Pathways ● Medial Lemniscal Pathway: large fibers carry proprioceptive (where body is) and touch information ● Spinothalamic Pathway: smaller fibers carry temperature and pain information ● they cross over to the opposite side of the body and synapse in the thalamus ■ Somatosensory Cortex ● signals travel from the thalamus to the somatosensory receiving area (S1) and the secondary receiving area (S2) in the parietal lobe ● body map (homunculus) allocation of senses ○ plasticity in neural functioning leads to multiple homunculi ○ changes allocation of cortical cells Perceiving Details ● Measuring Tactile Acuity ○ TwoPoint Threshold: minimum separation between points to perceive as separate ○ Grading Acuity: indicate the orientation of the rating ○ Raised Pattern Identification: using patterns to determine the smallest size that can be identified ● Receptor Mechanism for Tactile Acuity ○ high density of Merkel receptors in the fingertips ■ densely packed on the fingertip ○ body areas with high acuity have larger areas of cortical tissues devoted to them ■ also smaller receptive fields on the skin Perceiving Vibration ● Pacinian Corpuscle (PC) primarily responsible for sensing vibration ○ fibers without the PC only respond to continuous pressure Perceiving Texture ● Katz proposed that perception of texture depends on two cues ○ Spatial Cues: size, shape, and distribution of surface elements ○ Temporal Cues: rate of vibration as skin is moved across finely textured surfaces ● Two receptors may be responsible for this process: called the duplex theory of texture perception Perceiving Objects ● active touch to interact with the environment ● Haptic Perception: active exploration of 3D objects with the hand ○ Three Systems ■ Sensory System ■ Motor System ■ Cognitive System ● Psychophysical Research ○ people can identify objects haptically in one to two seconds ○ Klatzky et al. ■ shown that people use Exploratory Procedures (EPs) ● Lateral Motion ● Contour Following ● Pressure ● Enclosure ● Physiology ○ firing pattern of groups of mechanoreceptors signal shape ○ neurons further upstream, more specialized Pain ● multimodal phenomenon containing sensory component and emotional component ● Three Types ○ Inflammatory Pain: damage to tissues and joints or by tumor cells ○ Neuropathic Pain: damage to the central nervous system ■ brain damage caused by stroke ■ repetitive movements ● carpal tunnel syndrome ○ Nociceptive: signals of impending damage to the skin ■ transmit pain signals to the spinal cord and brain ■ some respond to heat, chemicals, pressure, cold ■ threshold of receptor warns of damage, but not affected by normal activity ● the Brain and Pain ○ Pain Matrix ■ Subcortical Areas ● hypothalamus, limbic system, thalamus ■ Cortical Areas ● S1, insula, anterior cingulate, prefrontal cortices ○ Hoffauer et al ■ presented with potentially painful stimuli and asked to rate ● pain intensity ● unpleasantness ■ brain activity measured while hands in hot water ■ hypnosis used to increase or decrease sensory and affective component ■ Results: ● suggestions to change subjective intensity changed ratings and S1 activity ● suggestions to change unpleasantness did not change subjective ratings, but did change ratings of unpleasantness ○ Endorphins ■ evidence that endorphins reduce pain ● injecting naloxone blocks the receptor sites causing more pain ● naloxone also decreases the effectiveness of placebos ● individuals who release more endorphins can withstand higher pain levels ● Direct Pathway Model (Early Model) ○ nociceptors are stimulated and send signals to the brain ○ Problems ■ pain can be affected by mental state and attention ■ pain can occur with no stimulation ■ phantom limbs ● Gate Control Model ○ “gate” consists of substantia gelatinosa cells in the spinal cord (SG and SG+) ○ input into the gate comes from ■ Large Diameter (L) Fibers: information from tactile stimuli (mechanoreceptors) ■ Small Diameter (S) Fibers: information from nociceptors ■ Central Control: information from cognitive factor from the cortex ● Cognition and Pain ○ Expectation ■ patients and pain medication ■ placebos ○ Shifting Attention ■ virtual reality ○ Content of Emotional Distraction ■ keep hands in cold water longer when shown positive pictures ○ Derbyshire ■ investigate hypnotically induced pain ■ thermal stimulator attached to the palm ■ 3 Conditions ● Physically induced pain ● hypnotically induced pain ● control: imagined pain ■ Results: ● subjective reports & fMRI showed hypnosis produced pain perception The Effects of Observing Touch and Pain in Others ● Keyser et al. ○ being touched vs. watching people or objects being touched ○ similar brain areas activated ● Meyer et al. ○ showed films of hands haptically exploring objects ○ both visual and S1 areas activated ● Singer et al. ○ romantically involved couples participated ○ woman’s brain activity measured by fMRI ○ the women either received shocks or she watched partner receive shocks ○ Results: ■ similar brain areas activated in both conditions Congenital Insensitivity to Pain ● Hereditary Sensory and Autonomic Neuropathy ● Mutations in the SCN9A gene ○ SCN9A gene provides instructions for making a sodium channel (NaV1.7) ○ NaV1.7 found in nociceptors: cause congenital insensitivity to pain ■ production of nonfunctional alpha subunits that cannot be incorporated into NaV1.7 channels ■ as a result, the channels are not formed