SA Medical - General Medicine And Imaging of Disease

General Organisation; the tactile and Position senses The somatic senses can be divided into three main components Mechanoreceptors  Thermoreceptors Nociception - pain and damage discriminative - precisely localised touch  Crude - poorly localised - proprioception - touch, pressure, vibration and the senses of static body position and movement Exterioceptive sensation  Visceral sensations Detection and Transmission of Tactile Sensation Even though touch, pressure and vibration are often classified as separate and distinct sensations, they are each detected by the same general class of tactile receptors: the Mechanoreceptors Free nerve endings - skin and in the cornea of the eye Meissner's corpuscule -    The   tactile corpuscles of Wagner and Meissner   (Fig. 936)   are oval-shaped bodies.   These tactile corpuscles occur in the papillæ of the corium of the hand and foot, the front of the forearm, the skin of the lips, the mucous membrane of the tip of the t

SENSORY RECEPTORS Five basic types of Sensory Receptors Mechanoreceptors Thermoreceptors Nocioreceptors Photoreceptors Chemoreceptors Sensory Receptors are highly sensitive to one particular type of stimulus - "the labeled line" priciple. sensory modality anteriolateral system (spinothalamic tract) - pain Receptors transduce a physico-chemical stimulus into a Nerve Impulse The Sensory fiber linked to each receptor exhibits "threshold phenomena" The receptor potential is proportional to stimulus intensity frequency Sensory receptors adapt their stimuli either partially or completely over time accomodation Receptors are classified as slowly adapting or rapidly adapting Slowly adapting receptors Tonic receptors Rapidly adapting receptors rate receptors or movement receptors Physiological Classification of receptors Two different schemes have been devised to classify the entire range of peripheral nerve fibers Types A and C  Fiber diameter and c

The general design of the Nervous system: The Nervous system includes both sensory and motor systems interconnected by complex integrative mechanisms neuron Soma several dendrites single axon sensory receptors sensory neuron motor response Motor response memory Function of the Central Nervous System This is based upon interactions that occur between neurons at specialised junctions called synapses synaptic terminals or synaptic boutons synaptic cleft synaptic vesicles neurotransmitter agent Chemical synapses and electrical synapses are the two most prevalent types of synapses in the brain chemical synapses presynaptic element - releases neurotransmitter agent that bind to the postsynaptic neuron - which is excited or inhibited electrical synapse gap junctions Neurotransmitter Release is Calcium Dependent voltage gated calcium channels calcium moves into the terminal Action of a Neurotransmitter is Determined by its Postsynaptic Receptor Rec