Exam 3 Neuro II Flashcards
Why is the S shaped curve of receptor response significant
If the curve were linear, the sensory range of the receptor would be narrower.
What are the group sensory nerve fibers?
A and C fibers?
Group 1a - found in muscle spindles.
Group 1b - found in Golgi tendon organs.
Group II - cutaneous tactile receptors, flower-spray endings of muscle spindles.
Group III - temperature, pricking pain, crude touch.
Group IV - unmyelinated fives carrying pain, itch, temp.
A fibers - large to medium sized myelinated fibers of spinal nerve.
C fibers - small, unmyelinated nerve fibers, make up half of the sensory fibers in peripheral nerves and make up all the post-ganglionic autonomic fibers.
First order neurons and 2nd order neurons
1st order - primary afferent, the peripheral endings form receptors (or receive input from accessory). Cell body in DRG.
2nd order - usually in braid stem or cord, crosses midline. Receives info from 1st order and sends it to the thalamus.
Third and fourth order/higher order neurons.
Third order - usually in thalamus, projects to celebrate cortex.
Fourth order/higher order - these neurons process info. They communicate between the cortex and subcortical areas. They allow for the eventual conscious sensory experience produced.
Basic seq of travel areas from 1st order neurons to the higher order neuron
- Input/stimulus
- Peripheral ending receptors
- Brain stem or cord.
- Crosses midline.
- Thalamus.
- Cerebral cortex.
- Info processing.
Basic seq of travel of signals into the spinal cord
- Sensory info received by dorsal roots of the spinal nerves.
- Dorsal roots send signal to spinal cord.
- Dorsal column-medial lemniscal system > brain.
OR 4. Anterolateral system > brain.
What sensations does the dorsal column-medial lemniscal system receive? (6) What kinds of fibers do they use?
Large, fast myelinated fibers. Enter the spinal cord and divide into medial and lateral.
- Touch sensations req a high degree of localization of the stimulus. 2. Touch sense req transmission of fine gradations of intensity. 3. Phastic sensations eg vibratory sensations. 4. Sense that spinal movement against skin. 5. Position sense from joints. 6. Pressure sense that req fine degrees of judgement of pressure intensity.
What sensations does the anterolateral system receive? (5)
- Pain 2 thermal (hot and cold) 3 crude touch and pressure sensations (only capable of crude localizing ability) 4 tickle and itch 5 SEXUAL sensations
Pacian corpuscle description
Mechanoreceptor on skin, work via central unmyelinated fiber that upon deformation will change ionic perm of the membranes and create a receptor potential.
Describe the paths taken by the nerve signals after they arrive at the medial and lateral branches of the DC-ML system.
How are fibers entering the DC-ML spatially maintained? Upper vs lower body?
Medial > travels medial and upward in the dorsal column > dorsal branch divide and synapses on local neurons in the gray matter. These local cells then: 1. Send projections up the column to the brain. 2. Send short fibers locally to cause local spinal cord reflexes. 3. Make up the spinocerebellar tracts.
Spatially maintained meaning the first fibers are medial, new fibers are laid on top of those and will become more lateral to the midline. Thus fibers from lower body are medial and fibers from upper body are lateral.
Describe DC-ML primary, secondary, and tertiary neurons.
Primary - project to fasciculus gracilis (lower body) and T7 & caudal, or fasciculus cuneatus (upper body) and T6 & rostral.
Secondary - N. Grascilis & Cuneatus (caudal medulla) = “Dorsal column nuclei”, they project to ventral postereolateral (VPL) N. of thalamus via medial lemniscus. These cells responds similarly to primary neurons (eg adaptation), have a larger receptive field, and there is some convergence of classes of receptors.
Tertiary - thalamic neurons that project to somatosensory cortex.
Describe the neurons in the trigeminal portion of the DC-ML
Primary - mechanoreceptor in face, synapse on sensory n. of trigeminal nerve (Cranial Nerve #3)
Secondary - project to contra thal (trigeminothalamic t.) & ipsi VPM thal N.
Tertiary - project to somatosensory cortex.
Describe the spinocervical tract, postsynaptic dorsal column pathway, and dorsal spinocerebellar tract of the DC-ML.
spinocervical tract - mechanoreceptors. Axons ascend in the dorsal horn of the spinal cord to the LATERAL CERVICAL NUCLEUS (spinal) and then to the contralateral VPL nucleus of the thalamus.
postsynaptic dorsal column pathway - mechano. Axons ascend in the dorsal horn of the spinal cord to the DORSAL COLUMN NUCLEI (spinal) and then to the contralateral VPL nucleus of the thalamus.
dorsal spinocerebellar tract - muscle receptors. The main destination of this tract is the CEREBELLUM and the NUCLEUS Z in the medulla.
What areas of the brain maintain the spatial or topographical order of the fibers?
Maintained at the thalamic level and on to the projections on the somatosensory cortex. So essentially a map of the body is reproduced on the cortex.
Describe the layers of the cerebral cortex
Layer 1 - molecular layer. Very few/zero cell bodies, mostly apical dendrites from lower pyramidal cells and axons projecting to those dendrites.
2 - external granular layer. Receives inputs from other cortical areas, has small densely-packed pyramidal cells»_space; giving it its granular appearance.
3 - external pyramidal layer. Medium sized pyramidal cells which project to other cortical areas. *layers 2&3 are seen as where he communications with other cortical areas originates.
4- internal granular layer. Receives inputs from outside the cortex, sensory input project to this layer.
5 - internal pyramidal layer. Contains largest pyramidal cells. Sends outputs to brainstorm and spinal cord. Especially well developed motor areas.
6- multiform layer. Made up of pyramidal cells and spindle-shaped neurons. * most cortical outputs leading to the thalamus originate in layer 6, while outputs to other subcortical nuclei/targets originate in layer 5.
(So non-cortical projects originate in 5&6).
