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NEU 302: EXAM 1
Motor Unit |
A single alpha motor neuron and all the muscle fibers that innervate it.
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Motor Pool |
All the alpha motor neurons that innervate a single muscle.
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Alpha Motor Neuron Input |
Spinal Interneurons
Sensory input from muscle spindles
Upper Motor Neurons in brain
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Somatotopic Organization |
Refers to Alpha Motor Neuron arrangement in ventral horn of the spinal cord. Organized from Medial to Lateral.
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Fast Fatiguable Motor Unit |
Dunking Basketball or sprinting down field.
Highest threshold.
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Fast Fatigue-Resistant Motor Unit |
Walking or Jogging.
High threshold.
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Slow Fatigue-Resistant Motor Unit |
Sitting upright with a straight back in class.
Low threshold.
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Fast Muscle Fiber Characteristics |
Few mitochondria.
Pale color (less myoglobin).
Large Alpha Motor Neurons.
High threshold for activation.
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Slow Muscle Fiber Characterisitics |
Many mitochondria.
Red color (due to myoglobin).
Small Alpha Motor Neurons.
Low threshold for activation.
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Excitation-Contraction Coupling |
Action potential excites membrane of muscle fiber to threshold, leading to release of Ca2+ from the SR, causing the muscle fiber to contract.
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Relaxation of Muscle Fiber |
Occurs when Ca2+ levels are lowered by reuptake into the organelle.
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Myofibrils |
Contract in response to an action potential down the sarcolemma.
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Sarcolemma |
Excitable membrane that surrounds the muscle fiber.
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Sarcoplasmic Reticulum (SR) |
Surrounds myofibrils and contains intracellular stores of Ca2+.
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T-Tubules |
Conducts electrical activity from surface of membrane into depths of muscle fiber.
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Tetrad |
Voltage-sensitive cluster of 4 Ca2+ channels within T-Tubule membrane.
Responsible for Ca2+ release into myofibril.
Undergoes conformational change with action potential.
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Muscle Fiber Action Potential |
ACh release from Alpha Motor Neuron.
ACh binds to nicotinic receptors on muscle fiber membrane.
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Myofibril Contraction Events |
Ca2+ binds to troponin.
Tropomyosin shifts position and myosin binding sites on actin are exposed.
Myosin heads bind actin.
Myosin heads pivot.
ATP bind to myosin head and disengages from actin.
Myosin head is activated again with hydrolyzation of ATP.
Continues as long as Ca2+ and ATP are present.
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Alpha Motor Neurons |
Innervate extrafusal muscle fibers.
Important for muscle contraction.
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Gamma Motor Neurons |
Innervate intrafusal muscle fibers.
Important for regulating desired set point of contraction or length of muscle.
Keep muscle spindle stretched, allowing for 1a afferents to detect muscle length changes.
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1a Afferents |
Respond to rate of change in muscle length.
Wrapped around muscle spindle.
Enter via dorsal roots of spinal cord.
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1b Afferents |
In Golgi Tendon Organ.
Axon contacts both excitatory and inhibitory interneuron.
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Crossed Innervation Experiment |
Concluded that type of motor neuron dictates phenotype.
Eccles.
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Muscle spindle |
Located in parallel with extrafusal skeletal muscle fibers.
Detects changes in muscle length.
1a sensory afferents.
Monosynaptic Synapse.
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Golgi Tendon Organ |
Located in series with skeletal muscle between muscle and tendon.
Detects changes in muscle tension (safety measure).
1b sensory afferents.
Allows for activation of inhibitory interneurons that inhibit the Alpha Motor Neurons to cause muscle relaxation.
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A Delta Afferents |
Transmit information regarding noxious stimuli to spinal cord.
Important for Flexion-Crossed Extension Reflex.
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Corticospinal Tract |
Originates in neocortex (motor cortex).
Pathway goes through base of cerebral peduncle (white matter) and synapse on lateral white matter and medial white matter in the spinal cord.
Decussates between medulla and spinal cord (pyramidal decussation).
Travels through pyramidal neurons in the medulla.
Upper Motor Neurons synapse on ventral horn of spinal cord.
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Vestibulospinal Tract |
Provides compensatory feedback responses to lower motor neurons concerned with postural activity/maintaining balance.
Vestibular nuclei orginiate in the medulla.
Has both medial and lateral tracts.
Medial pathway travels from medulla down to the venture horn of the upper cervical spinal cord .
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Medial Vestibular Tract |
Concerned with head position, and rotational movement of the head.
Receives input from semicircular canals.
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Lateral Vestibular Tract |
Concerned with antigravity (extensor) muscles, and deviations from stable balance.
Receives input from otolith organs.
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Reticulospinal Tract |
Extrapyramidal pathway that initiates feedforward adjustments during movements.
Involved in locomotion and postural control.
Upper Motor Nuerons originate in the pontine reticular formation and medullary reticular formation.
Similar pathway to Vestibulospinal Tract and terminates in the same area (cervical spinal cord).
Receives input from cortex and brainstem, but NOT from vestibular organs.
Pathways have strong influence on muscle tone.
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Bilateral Pyramidodotomy |
Bilateral lesions of the corticospinal tract at the level of the pyramids.
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Lawrence and Kuypers (1968) |
Performing bilateral pyramidodotomies on monkeys demonstrated major deficits in the shoulders, arms, hands, and wrists (fine precision grip) but very little deficit in their ability to stand and walk.
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Motor Cortex |
Located in the caudal (rear) portion of the frontal lobe, just before the central sulcus.
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Neurons of the Motor Cortex |
Primarily made up of Betz cells and Non-Betz pyramidal neurons.
Betz cells are located in Layer V of the motor cortex and they provide output to the spinal cord.
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Hughlings Jackson |
Preliminary map of motor cortex by observing seizure patterns.
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Ed Evarts |
Neurophysiology in behaving monkeys.
Found that firing rate of the corticospinal neuron was related to the force exerted during movement and not displacement of the wrist.
Active neurons fired before movements.
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Wilder Penfield |
Mapped the human motor cortex to create the Homonculus.
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Charles Sherrington |
Small amounts of current used to generate muscle twitches in primates.
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Apostolos Georgopoulis |
Motor cortex neurons also code individual directions.
Recorded from single neurons & coded movement.
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Fritsch & Hitzig |
Movement caused by electricity.
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Spike-Triggered Averaging |
Demonstrates relationship between upper motor neuron and lower motor neurons that contract one particular muscle.
Muscle field.
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Direction Vector |
The preferred direction of movement for a particular motor neuron.
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Population Vector |
The sum of preferred direction movements of a group of local motor neurons.
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Graziano Findings |
Suggest that mapping from cortex to muscles is not fixed but rather is dynamic and based upon feedback control from upper motor neurons.
Behavior can influence motor cortex mapping fluidity.
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Ischemic Stroke of Left Anterior Cerebral Artery |
Damage to Medial Motor Cortex. Motor deficit in left arm movement.
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Ischemic Stroke of Right Medial Cerebral Artery |
Impairs motor speech and swallowing functions.
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Premotor Cortex |
Located rostral to the primary motor cortex.
Involved in initiation and preparation of the movement.
These neurons can be identified as mirror motor neurons.
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Premotor Neuron Firing |
They fire before movement, during movement, and slightly after.
They fire even when it is a different individual making the movement.
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fMRI Study of Mirror Neurons - Icoboni |
Two contexts: Before tea and After tea
Demonstrated activity in visual cortex with synchronous activity in mirror neurons.
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Action Condition |
No context for action in trial.
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Intention Condition |
Context implies intention.
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Basal Ganglia Function |
Important for voluntary movement.
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4 Basal Ganglia Nuclei |
Striatum
Globus Pallidus
Subthalamic Nucleus
Substantia Nigra
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Basal Ganglia Central Nucleus |
Striatum:
Caudate & Putamen
Only provides output to other Basal Ganglia structures.
When activated, Striatum tonically inhibits Globus Pallidus to allow thalamus to excite motor cortex.
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Direct Pathway |
Cortex -> Caudate/Putamen -> Globus Pallidus internal -> Thalamus -> Motor Cortex
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Indirect Pathway |
Cortex -> Caudate/Putamen -> Globus Pallidus external -> Subthalamic Nucleus -> Globus Pallidus internal -> Thalamus -> Motor Cortex
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D1 |
Dopamine Direct Pathway
Greatly inhibits GPi.
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D2 |
Dopamine Indirect Pathway
Can slightly excite GPi, opposing action of direct pathway.
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Parkinson's Symptoms |
Bradyinesia
Akinesia
Rigidity
Tremors
Stooped Posture
Cognitive deficits
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Huntington's Symptoms |
Mood Changes
Personality Changes
Memory & Attention Deficits
Dyskinesias
Chorea
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Parkinson's Etiology |
Degeneration of Striatum and Substantia Nigra (dopaminergic neurons).
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Huntington's Etiology |
Degeneration of caudate neurons that project to GPe.
DNA polymorphism (CAG repeats).
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V1 |
Striate Cortex
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Temporal Lobe Lesions |
Monkeys could not recognize the objects.
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Parietal Lobe Lesions |
Monkeys could not figure out the well to drink from.
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What Pathway |
Ventral Stream.
V1 -> V2 -> V4 -> Inferotemporal Lobe.
Neurons have high spatial resolution and sustained responses to stimuli (Parvocellular).
Respond to shape/color/texture as well as face/specific objects.
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Where Pathway |
Dorsal Stream.
V1 -> V2 -> MT -> Parietal Lobe.
Neurons have low spatial resolution and transient responses to stimuli (Magnocellular).
Respond to motion and positional relationships between objects.
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Lesions of Inferotemporal Cortex |
Impairs recognition and color vision.
Spares ability to do spatial tasks.
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Lesions of Parietal Cortex and MT |
Impairs motion perception.
Spares ability to recognize.
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MT Neurons |
Important for perception and behavior.
They have preferred directional movement.
Discovered in monkeys through microsimulation of MT areas.
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STS |
Neurons respond to biological motion.
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Cerebral Achromatopsia |
Jonathon Case.
Color-blindness caused by damage to the cerebral cortex of the brain.
Neurons can slowly reestablish connection ("heal") following trauma.
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Cerebral Akinetopsia |
LM Case.
Visual motion blindness where she would not see the movement, object or people would just appear in places.
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MST |
Neurons respond to complex optical flow field: rotation, expansion, contraction.
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Optic Flow |
Refers to motion detection and navigation.
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Cortical Lamination of Neocortex |
I: Axons and dendrites of other layers
II/III: Cortico-Cortical
IV: Input (from periphery)
V:Output
VI: Output
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Pyriform/Archicortex |
Has 3-4 layers
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Association Cortex |
Lies in similar regions to the primary sensory/motor cortices.
Subcortical input is not from nuclei that receive information from the periphery.
Has more cortico-cortical connections.
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Parietal Cortex (Cognitive Role) |
Attention
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Temporal Cortex (Cognitive Role) |
Identification
Important for recognition of faces (inferior temporal)
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Frontal Cortex (Cognitive Role) |
Planning |
Hemineglect/Contralateral Neglect Syndrome |
Individuals cannot pay or perceive either the left or right side of objects, even if asked to draw object they will not realize a side is missing unless someone else draws their attention to it. You perceive less of one visual field.
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Face Patches |
Patches of neurons in the temporal cortex are attuned to recognize objects that look like faces, some patches also are important for recognizing particular faces, while face patches still are focused on particular facial feature recognition.
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Prosopagnosia |
Individual as inability to identify faces of familiar individuals. |