What are the five classes of sensory receptors in the skin?
Ruffini’s endings (Free nerve ending), Merkel’s disk, Meissner’s Corpuscle, Pacinian corpuscle, Hair follicle receptor.
What is meant by slow or fast adapting receptors?
Fast adapting receptors are those that fire only a few or one AP in response to touch. Slow adapting receptors are those that keep firing as long as the skin is being touched.
What is indicated by the receptive field size of a receptor?
The receptive field is the total area in which a mechanical stimulus elicits a response from that receptor/cell. There are two broad classes of receptors when classified by receptive field: small fields, 2-8mm diam, w/ sharp borders; large fields (entire finger), w/ poorly defined borders.
How are the four primary mechanoreceptors classified by adaptation and receptive field size?
Which sensors detect vibration?
Pacinian corpuscles.
Which receptors detect steady touch?
Ruffini’s endings (Free nerve endings), shearing or slipping between an object and the hand, or between the skin and deeper tissues, results in stretch of the Ruffini endings.
How does sensory information flow along the medial lemniscal system to the first synapse?
Stimulus is detected at receptor and transmitted through the DRG. Axon enters the dorsal horn and travels up the fasciculus gracilis/cuneatus) to the nucleus gracilis/cuneatus in the caudal medulla. First synapse is in the nucleus gracilis/cuneatus in the caudal medulla.
How does sensory information flow along the medial lemniscal pathway after the first synapse?
The secondary order neuron leaves the nucleus gracilis/cuneatus and cross over the midline to form the medial lemniscus. They are joined by trigeminal fibers at the midbrain and travel up to the ventro-basal complex in the thalamus. Trunk and limb cells synapse in the Ventral-Posterior-Lateral (VPL) nucleus and head cells synapse in the Ventral-Posterior-Medial (VPM) nucleus. Tertiary neurons then project to areas 3,1, and 2 on the posterior central sulcus/post central gyrus.
How does sensory information flow through the Trigeminal lemniscal system?
Stimulus is detected at the receptor -> trigeminal ganglion -> principal nucleus of the trigeminal complex/mid pons -> 2ary neuron crosses midline -> medial lemniscus tract -> Ventral Posterior Medial nucleus in thalamus -> cerebral cortex
Define Somatotopy
Somatotopy is the mapping of different body regions to specfici areas of the cerebral cortex. Creates the homunculus.
Describe cortical barrels
Cortical Barrels are columnar sections of the cerebral cortex that correspond to specific sensory modalities and receptor fields.
Describe the columnar organization of the cortex including the general role of each layer
There are six horizontal layers within the cortex. These are then divided into coritcal barrels, with each layer serving a specific funciton in the barrel. Layers II & III project to other areas of the cortex, layer IV recieves input from the thalamus, layer V projects to other subcortical structures, and layer VI projects back to the thalamus.
What sort of stimuli do the cells in the different Broadman’s areas (1, 2, 3a, 3b) respond to?
Broadman area 1: Orientation and direction; Area 2: Shape, orientation and direction; Area 3b: Skin (slowly and rapidly adapting receptors); Area 3a: Deep tissue (muscle stretch receptors)
