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SENSORY SYSTEMS

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SOMATIC SENSATION

TRANSDUCTION: The process by which a physical stimulus is converted into a neural signal and sent to the CNS.

FIBER DIAMETER AND MODALITY SPECIFICITY:

CLASS DIAMETER

VELOCITY

ELECTRICAL

STIMULATION

SENSATION
II (A-beta) Relatively large diameter

Fast conduction velocity

Lowest

threshold

i.e. first to be stimulated

Cutaneous Sensation
III (A-delta) Small diameter

Slow conduction velocity

Medium

threshold

Fast Pain

Crude Touch

Some temperature

IV (C) Smallest diameter

Slowest conduction velocity

Highest

threshold

i.e. last to be stimulated

Slow Pain

Crude Touch

Some temperature

FREE NERVE ENDINGS: Pain and temperature both end in free nerve-endings in the skin.

SPECIALIZED NERVE ENDINGS: They mediate tactile sensation: flutter, vibrations, and pressure.

ADAPTATION: "A decrease in neural response to sustained stimulation." Meissner's and Pacinian corpuscles both show adaptation.

DORSAL-COLUMN MEDIAL-LEMNISCAL PATHWAY: Proprioception and Discriminative Touch run parallel with each other but actually have separately named paths.

Labelled Line Theory: There are separate pathways for each modality of sensation, and these all run into the CNS in a parallel fashion.

RECEPTIVE FIELDS: The area of skin which, when appropriately stimulated, causes a neuron to discharge.

PHANTOM LIMB SYNDROME: People who have had a severed limb still retain sensation that the limb is there (proprioception) when other parts of the body are stimulated, such as the face.

HIERARCHICAL PROCESSING: As one ascends through the CNS, more complex types of sensations are processed.

NEGLECT SYNDROME: Lesion of posterior Tempero-parietal area. Extinction occurs in the Neglect Syndrome. Extinction is failure to recognize a specific stimulus (either visual, somatic, and/or auditory) on one side of the body, contralateral to the lesion.

PAIN:

TRIPLE RESPONSE OF LEWIS (AXON REFLEX):

THALAMIC (CENTRAL PAIN) SYNDROME: Spontaneous pain, and exaggerated responses to pain stimuli, resulting from a vascular lesion in the Thalamus.

Mechanisms of ANALGESIA:

RADICULAR PAIN: Pain localized to the dermatome of a dorsal root.

REFERRED PAIN: Visceral injury will send afferent pain information on the same nerves that also serve a cutaneous region. Because the brain is more used to getting sensory input from the cutaneous region of the nerve, the CNS will interpret the pain as originating from the cutaneous region.


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VISION

CONVEX LENS: Converging rays. They shorten the focal length and can be used to correct for farsightedness.

CONCAVE LENS: Diverging rays. They lengthen the focal lengthy and can be used to correct for nearsightedness.

LENS POWER: It indicates how much the lens can converge or diverge the light rays. The stronger the power, the shorter the focal length. A short focal length means the light is being bent a lot.

EMMETROPIC EYE: Normal vision, in which the light rays form an image on the retina.

MYOPIA, NEARSIGHTEDNESS: You can see things up close just fine but have difficulty seeing into the distance.

HYPEROPIA, FARSIGHTEDNESS: You can see things far away just fine but have difficulty seeing things up close.

ASTIGMATISM: A problem in which the cornea has two different radii of curvature (one horizontal and one vertical) and two different focal points. Essentially, the cornea is deformed such that the horizontal and vertical focal lengths don't match up with each other.

VISUAL ACUITY: The minimal angular resolution of the eye.

OPTICAL AXIS: Straight through the lens. It is slightly medial to the Visual Axis, which is where the fovea is located.

THE RETINA: From the back of the eye (outer limit of eye) to the inner most layer...

OPTIC DISK: Region of retina where the optic nerve and blood vessels enter. The optic disc is a blind-spot, but it is in a different part of the visual field for each eye so normally (with both eyes open) the blind-sport is not evident.

FOVEA: Contains no vessels, no inner-nuclear layer, no ganglion cell layer, and no rods. Just a high concentration of cone-photoreceptors.

PRIMARY PHOTO TRANSDUCTION:

SECONDARY CELLS: They receive signals from the photoreceptors.

VISUAL FIELDS:

LATERAL GENICULATE NUCLEUS:

PRIMARY VISUAL (STRIATE) CORTEX: Area 17.

EXTRA STRIATE CORTEX: Visual Association cortices.

Other Retinal Projections: Retinal projection that go somewhere other than the LGN.


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HEARING

Measuring Frequency and Volume:

EXTERNAL EAR, Pinna:

MIDDLE EAR: Air-filled cavity. Malleus ------> Incus ------> Stapes

COCHLEA:

ORGAN OF CORTI: It is located in the Scala Media, a top the Basilar Membrane.

FREQUENCY SELECTIVITY: Sound is mapped to different parts of the Cochlea according to frequency. Each part of the cochlea is most sensitive to a small range of frequencies, i.e. it has the lowest threshold.

ENDOLYMPHATIC POTENTIAL: +80mV Potential. The Scala Media is positive with respect to the hair cells, and with respect to the perilymphatic compartments.

HEARING LOSS:

COCHLEAR IMPLANTS: Put in an implant that can provide direct stimulation to VIIIth-Nerve afferents. This can be done even if there is hair-cell deafness.

MENIERE'S DISEASE:

CENTRAL AUDITORY PATHWAYS:

AUDITORY EVOKED POTENTIALS: Place electrodes on head to measure the actual electrical activity generated by signals in the Auditory pathway.


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TASTE AND SMELL

TASTE BUDS:

ENSEMBLE ENCODING: Taste is perceived as a combination of the four basic tastes.

OLFACTION:


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SLEEP AND WAKEFULNESS

ELECTROENCEPHALOGRAM (EEG): Electrodes are placed in five general regions bilaterally, over the five cortices.

Rhythm Dominant Freq Amplitude State of Arousal
Beta 20 Hz

High Frequency

Low Amplitude Alertness

REM Sleep

Alpha 10 Hz

high frequency

High Alertness but with eyes closed;

Relaxed wakefulness

Theta 3 - 7 Hz High Slow-Wave Sleep
Delta 0.5 - 3 Hz

Low Frequency

High Slow-Wave Sleep

SLEEP STAGES:

Alpha Waves: Relaxed Wakefulness with the eyes closed.

Synchronized -vs- Desynchronized:

Definitions:

CONSCIOUSNESS: Awareness of environment and self. It involves two systems.

EPILEPSY: Two or more unprovoked seizures.

SLEEP APNEA:


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THE HYPOTHALAMUS

Anatomy of Hypothalamus: The Hypothalamus forms the walls of the Third Ventricle.

CONNECTIONS to Hypothalamus: Most of the neural connections with the Hypothalamus are part of the Limbic System.

POSTERIOR PITUITARY PATHWAY: Paraventricular Nucleus ------> Superoptic Nucleus ------> (Arcuate Nucleus ------> Infundibulum) ------> Neurohypophysis

NUCLEI, PARTS, and FUNCTIONS OF THE HYPOTHALAMUS:

Functions of Hypothalamus:


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HIGHER CORTICAL FUNCTION

ALLOCORTEX: All cortical structures below the Rhinal (Collateral) Sulcus. It contains the following (The neocortex is everything else)

CORTICAL NEURONS:

CORTICAL LAMINA: Layers of the Cerebral Cortex

CYTOARCHITECTURE:

BRODMANN'S AREAS

Area 3a, 3b, 1, 2 Primary and secondary somatosensory cortices
Area 17 Primary Visual (Striate) Cortex
Area 41 Primary Auditory Cortex
Area 42 Secondary Auditory Cortex (Wernicke's Area)
Area 4 Primary Motor Cortex
Area 6 Premotor Cortex
Area 8 Frontal Eye Fields
Area 5, 7 Posterior Parietal Cortices

ASSOCIATION CORTICES: The sign of higher intelligence. There are three association cortices.

CORTICAL HEMISPHERES:

Language:

LEARNING AND MEMORY:


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THE LIMBIC SYSTEM

Anatomical Structures of the Limbic System:

PAPEZ CIRCUIT: The fundamental interaction between higher sensory input from the cortex and more primitive functions from the sub-cortex and the rest of the body.

KLÜVER-BUCY SYNDROME: Hypersexual horniness. Lesion of the Amygdala and Hypothalamus.

SCHIZOPHRENIA: A splitting of the cognitive with the emotional aspects of behavior.


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Copyright 1999, Scott Goodman, all rights reserved