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| Specialized cells or cell processes that monitor specific conditions in the body or the external environment. |
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A sensory receptor detects an arriving stimulus and translates it into an action potential that can be conducted to the CNS.
Begins when stimulus changes transmembrane potential receptor cell |
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| The link between peripheral receptor and cortical neuron, consists of axons carrying information about one type (modality) of stimulus. |
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| The translation of complex sensory information into meaningful patterns of action potentials. |
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A reduction in sensitivity in the presence of a constant stimulus.
-Nervous system quickly adapts to stimuli
that are painless and constant |
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When the level of receptor activity changes.
-Reduces the amount of information that reaches CNS |
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Sensory neurons that are always active. Also called slow-adapting receptors.
Provide information on duration of stimulus |
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Sensory neurons that are usually not active, also called fast-adapting receptors.
Provide information on intensity and rate of stimulus.
-Pressure receptor or temperature receptor |
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| 3 types of receptors for the general senses |
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Definition
1. Exteroceptors: provide information about the external environment
2. Proprioceptors: report the positions and movements of skeletal muscles and joints. No proprioceptors in the visceral organs of the thoracic and abdominopelvic cavities.
3. Interoceptors: monitor visceral organs and functions. |
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| 4 types of natures of stimulus |
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Definition
1. nociceptors (pain)
2. thermoreceptors (temperature)
3. mechanoreceptors (physical distortion)
4. chemoreceptors (chemical concentration) |
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arriving information from these senses
-Sensory information interpreted by frequency of action potentials
-Harder pressure-high frequency of action potentials |
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| Conscious awareness of a sensation |
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Each receptor has a characteristic sensitivity
-taste receptor: dissolved chemicals, not pressure |
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Branching tips of sensory neurons
-simplest receptors, little receptor sensitivity
-respond to tissue damage, sensation Pain-chemical, pressure, temperature, trauma |
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-receptors
-sensory neurons
-sensory pathways
Going TO CNS |
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-nuclei (cell body)
-motor tracts (bundles of axons)
-motor neurons
Exiting FROM CNS |
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The area monitored by a single receptor cell
-the larger the receptive field, the more difficult it is to localize a stimulus
-general body surface: larger field
-fingertip: smaller field |
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Arriving stimulus may take many forms:
physical force (such as pressure), dissolved chemical, sound, light
Form doesn't matter: information always sent as action potential (electrical event) |
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| "Change", graded depolarization or graded hyperpolarization in receptor cell |
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| A depolarizing receptor potential in a neural receptor |
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-Smell receptors accustomed to scent
-Involved inhibition of nuclei along sensory pathway
-Restrict amount of detail arriving at cerebral cortex |
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-Common in superficial portions of skin, joint capsules, within periostea of bones, around walls of blood vessels
-Few nociceptors in deep tissue, visceral organs
-Sensitive to: temperature extremes, mechanical damage, dissolved chemicals, ie chemicals released by injured cells
Nociceptors are free nerve endings with large receptive fields
2 types of axons, type A (fastest) and type C (slowest) |
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Definition
Carry sensations of FAST pain (prickling), i.e. deep cut or injection
Sensations reach CNS quickly and often trigger somatic reflexes
Also relayed to primary sensory cortex (cerebrum) and receive conscious attention |
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Definition
Carry sensations of SLOW pain, burning and aching
Cause a generalized activation of reticular formation and thalamus
Aware of the pain but have only a general idea of the area affected |
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| Nociceptors-tonic receptors |
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Definition
-Peripheral adaptation does not occur
-Receptors continue to respond as long as painful stimulus occurs
-The sensory neurons that bring pain sensations into the CNS release glutamate and/or substance P as neurotransmitters
-hyperexcitable interneurons can continue to generate pain sensations |
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Definition
Free nerve endings located in: dermis, skeletal muscles, liver, hypothalamus
Sent along the same pathways as pain sensations: reticular formation, thalamus, primary sensory cortex (to a lesser extent)
Phasic receptors: active if temperature changes, quickly adapt to a stable temperature |
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| 3 classes of mechanoreceptors |
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Definition
1. Tactile receptors
2. Baroreceptors
3. Proprioceptors |
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-Sensitive to stimuli that distort the plasma membrane
-Contain mechanically gated ion channels whose gates open/close in response to:
stretching
compression
twisting
other distortions of the membrane |
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Provide sensations of touch, pressure, vibration
-touch: shape or texture
-pressure: indicates degree of mechanical distortion
-vibration: indicate pulsing or oscillating pressure |
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| -Detect pressure changes in walls of blood vessels, and in digestive, reproductive, and urinary tracts |
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| Monitor positions of joints and muscles, most structurally and functionally complex |
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| Tactile receptors, fine touch and crude touch |
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Definition
Fine touch and pressure receptors-extremely sensitive, relatively narrow receptive field
-provide detailed information: exact location, shape, size, texture, movement
Crude touch and pressure receptors-provide poor localization, relatively large receptive fields
-Give little information about the stimulus |
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| 6 types of tactile receptors in skin |
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Definition
1. Tactile discs (Merkel discs)
2. Free nerve endings
3. Root hair plexus nerve endings
4. Tactile corpuscles (Meissner corpuscles)
5.Lamellated corpuscles (Pacinian corpuscles)
6. Ruffini corpuscles |
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Definition
-Sensitive to touch and pressure
-Situated between epidural cells
-Tonic receptors with small receptive fields |
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| Root hair plexus nerve endings |
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Definition
-Monitor distortions and movements across body surface wherever hairs are located
-Adapt rapidly,best at detecting initial contact and subsequent movements |
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| Tactile discs (Merkel discs) |
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Definition
-Fine touch and pressure receptors
-Extremely sensitive to tonic receptors
-Have very small receptive fields |
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| Tactile corpuscles (Meissner corpuscles) |
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Definition
-Perceive sensations of fine touch, pressure, low-frequency vibration
-Adapt to stimulation within 1 second after contact
-Fairly large structure
-Most abundant in the eyelids, lips, fingertips, nipples, external genitalia |
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| Lamellated corpuscles (Pacinian corpuscles) |
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Definition
-Sensitive to deep pressure
-Fast adapting receptors
-Most sensitive to pulsing or high-frequency vibrating stimuli |
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-Sensitive to pressure and distortion of skin
-Located in the reticular (deep) dermis
-Tonic receptors, show little if any adaptation |
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-Monitor change in pressure
-Consist of free nerve endings that branch within elastic tissues in wall of distensible organ (such as a blood vessel)
-Respond immediately to a change in pressure but adapt rapidly
-Trigger urination and defecation reflexes, as well as monitor lung expansion |
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Definition
-Monitor position of joints, tension in tendons and ligaments, state of muscular contraction
-Muscle spindles: monitor skeletal muscle length, trigger stretch reflexes
-Golgi tendon organs: located at junction between skeletal muscle and its tendon, stimulated by tension in tendon, monitor external tension developed during a muscle contraction
-Receptors in joint capsules: free nerve endings detect pressure, tension, movement at the joint |
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Definition
Respond only to water-soluble and lipid-soluble substances that are dissolved in body fluids (interstitial fluid, blood plasma, and CSF)
Exhibit peripheral adaptation over a period of seconds; central adaptation may also occur
Located in the carotid bodies (near origin of internal carotid arteries on each side of neck) and in aortic bodies (between major branches of aortic arch)
Receptors monitor pH, carbon dioxide, and oxygen levels in arterial blood |
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Definition
First-order neuron: sensory neuron that delivers sensations to the CNS
-cell body located in dorsal rot ganglion or cranial nerve ganglion
Second-order neuron:what the 1st order sensory neuron connects to in the CNS
-located in spinal cord or brain stem
Third-order neuron: if sensation is to reach our awareness, the 2nd-order neuron synapses on a 3rd-order neuron in the thalamus |
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| The crossing of an axon from the left side to the right side, or from the right side to the left side |
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Definition
Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs
3 major somatic sensory pathways:
Posterior column pathway
Spinothalamic pathway
Spinocerebellar pathway |
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| Tract names give clues to their function |
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Definition
Starts "spino", it originates in the spinal cord and is heading TO CNS (ascending tract)
Ends "spinal" it originates in brain and is heading TO the spinal cord (descending tract) |
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Carries sensations of highly localized touch, pressure, vibration, proprioception
-Begin peripheral receptor, end primary sensory cortex cerebral hemispheres
-Spinal tracts involved:
left and right fasciculus gracilis
left and right fasciculus cuneatus |
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| Posterior column pathway-first order neurons |
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Definition
1st-order axons reach CNS in dorsal roots of spinal nerves and sensory roots of cranial nerves
Axons ascending within the posterior column (2nd-order interneurons
-inferior body half: ascend within fasciculus gracilis, synapse in gracilis in medulla oblongata
-Superior body half: ascend within the fasciculus cuneatus, synapse in the nucleus cuneatus |
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| Posterior column pathway-2nd order neurons |
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Definition
decussation-once on opposite sides of brain axons enter tract-medial lemniscus
Medial lemniscus axons synapse on 3rd order neurons in one of ventral nuclei of thalamus
Nuclei sort the arriving information according to:
-nature of the stimuli
-region of the body involved |
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| Posterior column pathway-processing |
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Definition
| Processing in the thalamus determines whether you perceive a given sensation as fine touch, as pressure, or as vibration Ability to determine where the stimulus originated depends on the projection of information from the thalamus to the primary sensory cortex Sensory information from the toes arrives at one end of primary sensory cortex, from head arrives at the other When neurons in one portion of your primary sensory cortex are stimulated, you become aware of sensations originating at a specific location |
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Functional map of the primary sensory cortex
Area of sensory cortex devoted to particular body region is not proportional to region's size, but to the number of sensory receptors it contains.
Lips, tongue, hand-large areas
back-little area |
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Definition
Provides conscious sensations of poorly localized (crude) touch, pressure, pain, and temperature
Axons of 1st-order sensory neurons enter spinal cord and synapse on 2nd-order neurons within the posterior gray horns
2nd-order neurons cross to opposite side of spinal cord before ascending within anterior or lateral spinothalamic tracts.
-anterior tracts carry crude touch and pressure sensations
-lateral tracts carry pain and temperature sensations |
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| Spinothalamic pathway-2nd order |
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Definition
2nd-order neurons synapse to 3rd-order neurons in ventral nucleus group of thalamus. After sensations have been sorted and processed, they are relayed to primary sensory cortex.
Perception of stimulus (cold? hot? vibration?) depends on 2nd and 3rd order neurons that are stimulated.
Ability to localize the sensation depends on area of primary sensory cortex that is stimulated |
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| Injury/abnormality along spinothalamic pathway |
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Definition
| Results in inappropriate sensations or inaccurate localization of the source. |
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Definition
| Caused by activity in the sensory neurons or interneurons along the spinothalamic pathway. |
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A person can feel pain in an uninjured part of the body when the pain actually originates in another part of the body.
Ex. heart attack: felt in left arm
Ex. appendicitis: felt first in area around the navel, then in the RLQ |
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Definition
Cerebellum receives proprioceptive information about position of skeletal muscles, tendons, and joints.
-This information does NOT reach our awareness!
Axons of 1st-order neurons synapse on interneurons in dorsal gray horns of spinal cord
Axons of 2nd-order neurons ascend in 2 tracts:
posterior spinocerebellar tracts
anterior spinocerebellar tracts |
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| Posterior spinocerebellar tracts |
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Definition
2nd-order axons do NOT cross over to opposite side of spinal cord
Axons reach cerebellar cortex via inferior cerebellar peduncle of that side |
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| Anterior spinocerebellar tracts |
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Definition
Most 2nd-order axons cross over to opposite side of spinal cord, contain significant number of uncrossed axons as well
Sensations reach cerebellar cortex via superior cerebellar peduncle
Many axons that cross over, ascend to cerebellum then cross over again within the cerebellum, synapsing on the same side as original stimulus |
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| Visceral sensory pathways |
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Definition
Collected by interoceptors monitoring visceral tissues and organs, primarily within thoracic and abdominopelvic cavities
Interoceptors not as numerous as in somatic tissues, include:
nociceptors, thermoreceptors, tactile receptors, baroreceptors, and chemoreceptors
Usually 1st-order neurons travel with autonomic motor fibers in same structures |
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| Visceral sensory pathways-cranial nerves |
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Definition
Carry visceral sensory information from mouth, palate, pharynx, larynx, trachea, esophagus, associated vessels and glands to SOLITARY NUCLEUS (large nucleus in medulla oblongata)
Major processing and sorting center for visceral sensory information
Extensive connections with various cardiovascular and respiratory centers and reticular formation
1st-order neurons deliver visceral sensory information to interneurons who ascend within spinothalamic pathway.
We remain unaware of these sensations |
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| SNS (Somatic motor system) |
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Definition
| controls contractions of skeletal muscles |
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| ANS (visceral motor system) |
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Definition
| Controls visceral effectors, such as smooth muscle, cardiac muscle, and glands |
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Definition
Always involve at least 2 motor neurons:
-upper motor neuron, whose cell body lies in a CNS processing center
-lower motor neuron, whose cell body lies in a nucleus of the brain stem or spinal cord |
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Definition
Synapses on lower motor neuron which innervates a single motor unit in a skeletal muscle
Activity in the upper motor neuron may facilitate or inhibit the lower motor neuron.
Destruction of or damage to a lower motor neuron eliminates voluntary and reflex control over the innervated motor unit |
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Term
| 3 integrated motor pathways |
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Definition
Corticospinal pathway
Medial pathway
Lateral pathway
Conscious and subconscious motor commands control skeletal muscles by traveling over them
Activity within these motor pathways adjusted by basal nuclei and cerebellum
Output stimulate/inhibit activity of
1. motor nuclei or
2. primary motor cortex |
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Definition
Sometimes called the pyramidal system
Provides voluntary control over skeletal muscles
-system begins at pyramidal cells of primary motor cortex
-Axons of these upper motor neurons descend into brain stem and spinal cord to synapse on lower motor neurons that control skeletal muscles
Contains 3 pairs of descending tracts:
Corticobulbar tracts
Lateral corticospinal tracts
Anterior corticospinal tracts |
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Definition
Provide conscious control over skeletal muscles that move the eye, jaw, face, some muscles of the neck and pharynx
Innervate motor centers of medial and lateral pathways |
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| Corticospinal tracts (lateral and anterior) |
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Definition
Axons synapse on lower motor neurons in the anterior gray horns of the spinal cord.
As they descend, lateral corticospinal tracts are visible along the ventral surface of medulla oblongata as a pair of thick bands, the pyramids.
At spinal segment it targets, an axon in anterior corticospinal tract decusses in anterior white commissure before synapsing on lower motor neurons in anterior gray horns. |
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Definition
Primary motor cortex corresponds point by point with specific regions of the body
Cortical areas have been mapped out in diagrammatic form
Homunculus provides indication of degree of fine motor control available:
hands, face, and tongue, which are capable of varied and complex movements are very large, while the trunk is relatively small.
Proportions similar to sensory homunculus. |
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Definition
Help control gross movements of trunk and proximal limb muscles.
Upper motor neurons of medial pathway are located in:
vestibular nuclei
superior and inferior colliculi
reticular formation |
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Definition
| Helps control distal limb muscles that perform more precise movements |
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Term
| Medial and lateral pathways |
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Definition
Several centers in cerebrum, diencephalon, and brain stem may issue somatic motor commands as a result of processing performed at the subconscious level.
These nuclei and tracts are grouped by their primary functions:
medial pathways-gross movements of proximal limb muscles and trunk
lateral pathway-distal limb muscles that perform more precise movements |
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| Medial pathway-vestibular nuclei |
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Definition
Receive information over vestibulocochlear nerve (VIII) from receptors in inner ear that monitor position and movement of the head.
-primary goal is to maintain posture and balance
-descending fibers of spinal cord constitute vestibulospinal tracts |
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| Medial pathway-superior and inferior colliculi |
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Definition
-located in roof of mesencephalon (tectum)
-Colliculi receive visual (superior) and auditory (inferior) sensations
-Axons of upper motor neurons in colliculi descend in tectospinal tracts
-These axons cross to opposite side before descending to synapse on lower motor neurons in brain stem or spinal cord.
-detect reflexive changes in position of the head, neck, and upper limbs in response to bright lights, sudden movements, or loud noises |
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Term
| Medial pathway-reticular formation |
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Definition
| A loosely organized network of neurons that extends throughout the brain stem. Axons of upper motor neurons in reticular formation descend into reticulospinal tracts without crossing to the opposite side. -Effects of reticular formation stimulation determined by region stimulated. |
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Definition
Primarily concerned with control of muscle tone and more precise movements of distal parts of limbs.
Axons of upper motor neurons in red nuclei cross to opposite side of brain and descend into spinal cord in rubrospinal tracts. |
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| Basal nuclei and cerebellum |
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Definition
| Responsible for coordination and feedback control over muscle contractions, whether contractions are consciously or subconsciously directed. |
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Definition
Provide background patterns of movement involved in voluntary motor activites.
ex. may direct rhythmic cycles of movement as in walking or running
-Do not exert direct control over lower motor nuclei; they adjust the activities of upper motor neurons in the various motor pathways based on input from all portions of the cerebral cortex, as well as from the substantia nigra
The basal nuclei adjust or establish patterns of movement by 2 major pathways:
1.one group synapses on thalamic neurons, whose axons extend to the premotor cortex. This arrangement creates a feedback loop that changes the sensitivity of the pyramidal cells and alters the pattern of instructions carried by the corticospinal tracts.
2. A second group of axons synapses in the reticular formation, altering the excitatory or inhibitory output of reticulospinal tracts. |
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| 2 distinct groups of neurons exist in basal nuclei |
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Definition
1.one that stimulates neurons by releasing acetylcholine
2. one that inhibits neurons by releasing
gamma aminobutyric acid (GABA).
Normal conditions, excitatory interneurons kept inactive, tracts leaving basal nuclei have an inhibitory effect on upper motor neurons. |
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Definition
| the excitatory neurons become more active, leading to problems with the voluntary control of movement. |
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Definition
Monitors:
Proprioceptive (position) sensations-from spinocerebellar tracts.
Visual information from the eyes-from superior colliculi
Vestibular (balance) sensations from inner ear as movements are underway-from vestibular nuclei
The output of the cerebellum affects upper motor neuron activity in the corticospinal, medial, and lateral pathways. |
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