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In 1926 Charles Sherrington proposed a classification of sensation that divided the sensory receptors into three sections.
Describe the sensations that each of these classes mediate, and provide examples
- a) exteroceptors
- Mediates sight, sound, smell, and cutaneous sensations (Cutaneous superficial skin sensations include: touch, superficial pain, temperature, itching, and tickling)
- b) proprioceptors
- mediates deep somatic sensation from receptors beneath the skin, muscles, joints and the inner ear. Primarily targets the cerebellum.
- Proprioception includes the following senses: pressure, movement, vibration, deep pain, and equilibrium
- c) interoceptors
- Mediates sensation from viscera, as well as visceral pain and pressure or distention
- Pain receptors, either from cellular or tissue injury, are know as nonciceptive receptors
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In 1926 Charles Sherrington proposed a classification of sensation that divided the sensory receptors into three broad classes
Describe the sensations of the EXTERNOCEPTORS ans provide examples
- exteroceptors Mediate:
- sight,
- sound
- smell
- cutaneous sensations (Cutaneous superficial skin sensations include: touch, superficial pain, temperature, itching, and tickling)
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In 1926 Charles Sherrington proposed a classification of sensation that divided the sensory receptors into three broad classes
Describe the sensations of the PROPRIOCEPTORS and provide examples
- Proprioceptors mediate:
- Deep somatic sensation from receptors beneath the skin, in muscles and joints, and in the inner ear. Primarily targets the cerebellum
- Proprioception Senses:
- Pressure
- movement
- vibration
- deep pain
- equilibrium
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In 1926 Charles Sherrington proposed a classification of sensation that divided the sensory receptors into three broad classes Describe the sensations of the INTROCEPTORS and provide examples
- Interoceptors mediate
- Sensation from viscera
- (visceral pain and pressure or distention)
Pain receptors either from cellular or tissue injury, are known as nocicepitive receptors
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Define the type of sensory information that LATERAL SPINOTHALMIC TRACT mediate, and describe their pathways from periphery to the cortex (i.e. first order neurons, second-order neurons, third-order neurons)
- The lateral spinothalmic tract is the crossed ascending sensory pathway in the spinal chord that transmits the sensations of pain and temperature (hot and cold).
- The Pathway begins at the nociceptive (pain-related) receptors in the skin
- the first order fibers, with their nuclei in the dorsal root gangalia, carry sensations from the skin and enter the dorsal lateral spinal chord.
- Sensation enters the periphery via sensory axons. All sensory neurons have their cell bodies sitting outside the spinal chord in a clump called a dorsal root ganglion.
- There is one such ganglion for every spinal nerve.
- The sensory neurons are unique because unlike most neurons, the signal does not pass through the cell body.
- Instead the cell body sits off to one side, without dendrites, and the signal passes directly from the distal axon process to the proximal process.
- The fibers enter the spinal chord through the spinal root ganglion, travel up or down a few spinal segments in the dorsolateral fasciculus (Lissauer's tract) before penetrating the dorsal spinal gray matterAfter penetrating the dorsal spinal gray matter, these fibers terminate in the substantia gelatinosa and the nucleus proprius in the dorsal spinal column.
- The Second Order fibers cross the midline in the ventral white commissure to ascend in the lateral spinothalmic tract.
- fibers carrying pain and temp sensation from the entire body level in the lateral spinothalmic tract and ascend toward the brain steam on the to the thalamus
- Other fibers are given off as the lateral spinothalmic tract ascends and terminate on the reticular nuclei in the brainstem.
- Fibers from the reticular nucleui then project to the thalamus, hypothalamus and hippocampus.
- Somatic and visceral responses to pain, such as changes in respiration a and heartbeat, as well as nausea and fainting, are mediated through descending fibers from these structures.
- After traveling through the medulla, the ventrolateral pons, and the midbrain tegmentum, the second order fibers terminate on the third-order neurons in the ventral posterolateral nucleus of the thalamus. Thalamocortical fibers travel through the internal capsule and corono radiata, then project to the upper 2/3 of the postcentral gyrus in the parietal lobe.The primary sensory cortex is responsible for a finer analysis of sensation and determines its quality and source.
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Define the type of sensory information that ANTERIOR SPINOTHALMIC TRACT mediate, and describe their pathways from periphery to the cortex (i.e. first order neurons, second-order neurons, third-order neurons)
- The anterior (or vental) spinothalmic tract carries sensory information of
- 1) light touch
- 2) light pressure and touch
- 3) tactile location
- The light touch fiber synapse within the dorsal gray horn cells in the spinal chord and ascend in the anterior spinothalmic tract to the brainstem and the posterior ventral nucleus of the midbrain.
- The tract also ends up in the post central gyrus of the parietal lobe.
- The first-order sensory fibers transmit general touch sensations from the receptors in the skin and enter the dorsal lateral spinal chord
- After the fibers enter the spinal chord through the spinal root ganglion, they disperse longitudinally in the dorsolateral fasciculus of Lissauer.
- They then travel up or down a few spinal segments in the dorsolateral fasciculus (Lissauer's tract) before terminating in the substantia gelatinosa and the nucleus proprius in the dorsal horn.
- The majority of the second order fibers cross the midline in the ventral spinal gray matter and turn upward to form the anterior spinothalmic tract.
- The third order fibers from the thalamus ascends through the internal capsule, and reaches the upper 2/3 of the post central cortical gyri in the parietal lobe (Broamann 3, 2 & 1)
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Define the type of sensory information that DORSAL COLUMN PATHWAY mediate, and describe their pathways from periphery to the cortex (i.e. first order neurons, second-order neurons, third-order neurons)
- Conscious propioception, two-point discrimination, and formperception have been called the sensory modalities of the dorsal, or posterior columns of the spinal cord. The axons of the dorsal columns enter the spinal cord after entering the peripheral nerves of the spinal chord with the first order neuron at the dorsal root ganglion.
- The axons then ascend ipsilaterally in the dorsal white columns to the medulla
- Axons entering the cord at the sacral lumbar regions, which mediate proprioception from the leg and lower body, are found in the medial dorsal columns, called the fasciculus gracilis.
- The second order neurons leave the nucleus graclius and nucleus cuneatus, cross over the over to the other side of the medulla.
- At this point, they form a bundle called the medial lemniscus, which ascends to the third-order neuron at the thalamus, and then proceeds to the parietal lobe.
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I. Define the type of sensory information that the spinocerebellar tract mediates
II. Describe its ventral and dorsal pathway to the cerebellum (i.e. first-order neurons, second-order neurons).
- The spinocerebellar tract mediates
- A) unconscious perception of already learned motor patterns are thought travel along the other tract called the spinocerebellar tract.
- The sensation of limb and joint positon as well as range and direction of limb movements
B) Unconscious perception involves multiple afferent inout into the cerebellum, and is important in the acquisition and maintenance of skilled motor activities such as walking, speaking, writing, swallowing, and eye movement.
- II.The spino cerebellar tract is a two-order neuron system (rather than a three-order nervous system) It consists of 2 tracts (Dorsal and Ventral)
- A) Both tracts arise from the posterior and medial gray matter of the spinal cord (first order).
- B) The dorsal tract ascends ipsilaterally, but the ventral tract crosses at the spinal chord (second order).
- C)Both tracts terminate in the cerebellum, and allow proprioceptive impulses from all parts of the body to be integrated in the cerebellum
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Damage to the Postcentral Gyrus of the parietal lobe, the dorsal columns, or the dorsal root ganglion may produce a loss of proprioception, astereognosis (ability to recognize object in ones hand), loss of vibratory sense, and loss of two-point discrimination in the trunk or extremities. In general, describe the side of the body involved when damage occurs in the following areas, and explain your rationale.
- Dorsal columns below the medulla
- - the loss in proprioception is on the same side of the injury. The nerve has not decussated yet (ipsilateral)
- Dorsal columns above the medulla
- - The loss in proprioception is on the contralateral side of the injury because the nerve has decussated or crossed the midline (contralateral)
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Name the three tracts that make up the corticofungual pathways of the pyramid tract, and describe the primary function of the fibers for each these tracts.
(pyramid tract= major voluntary pathway for all movement, including the voluntary movement of the muscles of speech)
- A) corticospinal tract
- - 2 parts (Anterior and Lateral)
- -controls the skilled movements in the distal muscles of the limbs and digits- permit extremely rapid voluntary motor responses in the nervous system
- B) corticobulbar tract- controls the cranial nerves, many of which directly innervate the muscles of speech, except respiration
- - Bilaterally symmetry
- - Contralateral
- - Unilateral innervation
- C) Corticopontine tract
- - goes to the pontine nuclei, which in turn, projects to the cerebellum
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Clinical lesions in the nervous system have been been classically divided into upper and lower motor neuron lesions
A)A hallmark of an upper motor neuron lesion is the clasp knife spasticity. Describe this condition and lany other signs that are representative of of an upper motor neuron lesion
B)Types of paralysis
A) Clasp Knife reaction:Occurs when the examiner feels increased tone or resistance to movement in the muscle after the joint has been briskly flexed and than feels the resistance fade.
This reaction identifies HYPERTONICITY and is analogous to the resistance felt when a knife blade of a clasp knife is first opened, followed by the reduction of resistance when the blade is straightened out. (usually during extension of the elbow)
- B)Types of paralysis
- -spasticity is also associated with exaggerated muscle stretch reflexes, resulting in hyperrflexia
- - reflex action is tested at joints by outting stretch tendons, which elicits the exaggerated muscle stretch reflex
- -Spastic paralysis, hypertonia, and hyperreflexia have most often been associated with pyramidal tract damage, particularly lesions of the corticospinal tract
- -the corticobulbar tracts are often also involved when a lesion interrupts the cortico spinal tract. the signs of spasticity may be found in the midline speech muscles as well as the distal limb muscles.
- - Spastic speech muscles maybe weak, slow, and limited in range or movement.
- -Hypertonia may decrease muscle flexibility of the articulators and limit the ability to achieve a full range of motion of the speech muscles.
- *clasp knife spasticity
- *hypertonia
- *hyperflexia
- *babinski skin
- *clonus
- *superficial abdominal
- *cremasteric reflexes
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