Human Nervous System

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  • Created by: gec114
  • Created on: 07-04-16 10:47
Rostral
Towards the nose
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Caudal
Towards the tail
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Dorsal
Towards the back
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Ventral
Towards the belly
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Superior
Upper
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Inferior
Lower
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Medial
In the middle
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Lateral
At/towards the side
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Sulci
Grooves found within the folded structure of the brain
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Gyri
Elevated areas within the folded region of the brain
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Lateral Sulcus
Separates the frontal lobe and the temporal lobe
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Central Sulcus
Separates the frontal lobe from the parietal lobe
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Cingulate Sulcus
Separates the frontal lobe from the parietal lobe
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Increased cortex folding........
Increases the brain surface area and therefore means more computing power.
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Golgi Stain
Causes individual cells to show up. can see the axon and dendroid of each cell. only some cells are visible, unpredictable which ones.
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Nissi Stain
Shows only the cell bodies but of almost all of the cells.
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Weigert Stain
Shows only the axon and dendoids (no cell bodies) it works for almost all cells
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Local Interneuron
Inhibitory. Information signals are not passed are not passed on. prevent over excitation and the same signals passing around a loop of neurons multiple times. GABA binds to channel receptors causing Cl- to enter reducing excitability.
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Projection Neuron
Excitatory. When they get excited they are activated and excite further surrounding neurons spreading the signal. Glutamate binds to receptors in the cell membrane activating the cell.
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Soma
The cell body of a neuron. It contains the nucleus and other organelles meaning protein synthesis and energy production happens here.
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Dendrites
Collect inputs from other cells and can change the state of the cell from passive to active generating an action potential.
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Axon
Transmits information and signals through the cell.
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Synaptic Terminals
The signal leaves the cell and is passed on to other neurons
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Potassium Concentrations
Inside the cell: 400mM, Outside the cell: 20mM
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Sodium Concentrations
Inside the cell: 50mM, Outside the cell: 440mM
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Chlorine Concentrations
Inside the cell: 52mM, Outside the cell: 560mM
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Nernst Equation
Ex = (R T) /(z F) ln([Xo]/[Xi]) ; Ex - equilibrium potential, R- gas constant, T- absolute temperature, [Xo] - outer ion concentration, [Xi] - inner ion concentration, F -Faraday constant, z - valence of electron
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Chemical Driving Force
Wa = R T ln([Xo]/[Xi]) ; R- gas constant, T- absolute temperature, [Xo] - outer ion concentration, [Xi] - inner ion concentration, Wa - work done because of the chemical driving force
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Electrical Driving force
Wb = Ex z F ; Ex- equilibrium potential, Wb- work done because of electrical driving force, F -Faraday constant, z - valence of electron
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Resting Membrane potential
-75mV
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Goldman Equation
Takes into account all contributing ion species and their relative permeability, Px. Vm=(RT/F) ln{(Pk[Ko]+Pna[Nao]+Pcl[Cli])/(Pk[Ki]+Pna[Nai]+Pcl[Clo])} ; Vm - membrane potential, [Xi] - inner ion concentration, [Xo] - outer ion concentration,
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Active Membrane potential
+55mV
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Sodium - Potassium pump
Requires ATP, maintains the concentration gradient preventing an equilibrium from being reached. Pumps 3 sodium out for every 2 potassium in
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Modelling Ion Channels
Act like a battery and resistor in series. The battery has the same voltage as the equilibrium potential for that ion.
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Electrical Equivalent Circuit for the Cell Membrane
Vm = {(Ena x Gna)+(Ek x Gk)+ (Ecl x Gcl)}/(Gna+Gk+Gcl) ; Gx is the conductance of the ion channel, Ex is the equilibrium potential for the ion , Vm is the membrane potential
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Function of the Myelin Sheath
Provide additional insulation so increase the propagation speed of the action potential
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Electrical Synapses
Occur at GAP JUNCTIONS. Directly conduct current flow between the pre and post synaptic cells via a CHANNEL MOLECULE. There is a decrease in amplitude of the signal. Virtually instantaneous.
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Chemical Synapses
Neurotransmitters diffuse through the synaptic cleft, activate LIGAND GATED ion channels in the postsynaptic membrane generating a postsynaptic potential (PSP). Takes 1-3ms.
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Type 1 Chemical Synapse
Found in the dendrites of the postsynaptic cell. The transmitter is Glutamate and has an excitary effect on the cell.
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Type 2 Chemical Synapse
Found in the soma of the postsynaptic cell. The transmitter is GABAnand is inhibitory. Normally it hyper polarizes the cell.
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Directly Gated Chemical Synapse
Opens when a transmitter molecule binds to the receptor. Need one molecule per gate. Very quickly reacts to the binding. The molecule is later released.
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Indirectly Gated Chemical Synapse
To open a G protein binds to Guanosine Triphosphate and stimulates Adenylyl Cyclase which produces cAMP. This activates cAMP-dependent-cAMP-kinase which phosphorylates the channel. Used to modulate synpatic transmission. Can change signal gain.
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Reversal Potential
The membrane potential of the motor neuron where there is no net current flow (not dominated by sodium or potassium ions) during synaptic activation. The membrane potential does not change, it is at the equilibrium potential of the PSP, (Epsp).
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Post Synaptic Integration
The number and amplitude of excitatory and inhibitory inputs determines the PSP spread down the soma. Linear summation of excitatory and inhibatory signals. If the result exceeds a threshold then an action potential starts at the trigger zone.
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Trigger Zone
An area high in voltage gated sodium channels that generates action potentials should the PSP depolarise the membrane enough. long time constants increase the chance of triggering a potential.
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Time Constant of a Cell Membrane
Proportional to the capacitance of the membrane multiplied by Resistance caused by the ion channels. A short time constant means two signals have to be applied simultaneously to both have an effect. Long time constants allow signals to accumulate.
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Auricle
Part of the outer ear that collects, funnels and filters sound waves.
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External Auditory Meatus
A tube running from the outer to middle ear.
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Topic Maps
Neighbouring values in space (e.g. sound waves) are encoded by neighbouring elements in the nervous system.
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Outer Hair Cells
Recieve information from the central nervous system. Change length according to membrane potential which alters the signal amplitude and signal strength. Useful for damping out background noise.
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Inner Hair Cells
Stimulated by the outer hair cells. They send information to the central nervous system.
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Cochlea to cortex pathways
there are three major pathways: dorsal acoustic stria, intermediate acoustic stria, trapezoid body
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Delay Line Mechanism
An interneuron only fires if the acoustic signal from the right ear and the one from the left ear coincide. The position of the neuron that fires allows the location of the sound to be identified. The delay line causes simultaneous signals.
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Vestibular System
Monitors linear and angular accelerations of the head and body. It is located next to the cochlea.It is made of two parts, the utricle and saccule which are tubes filled with endolymph.
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Utricle
Part of the vestibular system. Contains hair cells which measure head tilt as they get sheared by the otholithic membrane. Tilting in one direction in excitatory and the other is inhibitory. Every cell has some noise but averages out as none.
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Effect of the Vestibular System on Vision
Generates complimentary eye movements to stabilize the retinal image. It avoids motion blur by the lateral eye muscles contracting and the eyes counter rotating.
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Fovea
An area of the retina that has the highest density of photoreceptors and gives the highest spatial resolution of the visual surroundings.
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Rhodopsin
A visual pigment found in the photoreceptors. It causes a change in the shape of the outer membrane when it is hit by a photon. This triggers phototransduction
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Rods
The photoreceptor that is highly sensitive to light. It triggers action potentials frequently
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Cones
The photoreceptor responsible for colour vision. A high light intensity is required to trigger an action potential
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Dark Current
In low light intensity levels, there is an inward sodium current (-50pA) created by ions moving through cGMP gated channels in the outer segment of the membrane. Light causes the sodium channels to close and the photoreceptor membrane hyperpolarizes.
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Bipolar Cells
Collect information from rods and cones and integrates the signals.
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Retinal Ganglion Cells
The axons of these build the optic nerve. Each ganglion cell only triggers when the exact rod and cone are hit. When the cell depolarises an action potential is sent to the brain.
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Receptive Field of a Ganglion Cell.
The area within the visual field that light has to hit in order to trigger the ganglion cell. A change in firing rate of the ganglion cell indicates a change in light intensity. It is made of two concentric circles.
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On-Center Ganglion Cell
Shining light in the center increases the firing rate of the cell. Shining light off center is inhibitory.
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Off-Center Ganglion Cell
Shining light in the center decreases the firing rate of the cell. Shining light off center is excitory.
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Receptive Field in the Primary Visual Cortex
The cells have elongated receptive fields of a specific orientation that respond best to light bars of the same orientation. The receptive field is bigger than that of a ganglion cell and the individual cells have larger degrees of variability.
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Inferior Temporal Cortex
Responsible for face recognition. Relies upon mouth, eyes and face shape to trigger the action potential.
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Nociceptors
They are bare nerve endings that sense Pain. Turn physical energy into neural signals. They are located in the skin.
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Merkel Disk Receptors
Detect pressure/touch and the size and shape of the object creating it. Sharper points produce a higher firing rate.
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Myelinated Axons
innervate the bare nerve endings of the mechanoreceptors. They convey information to the spinal cords via action potentials.
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Dorsal Root Ganglion Cells
Transmits action potentials from the skin to the spinal cord. Information is locally processed and sent to the brain. The cell bodies are in the dorsal root ganglia, the axon splits in the dorsal horn and enters the spinal cord through dorsal roots.
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Human Detection Threshold
The combined effect of the Meissners and Pacinian corpuscles (pressure sensors with different receptive fields). the receptor types complement each others dynamic response ranges and together form what we actually perceive.
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Dorsal Column- Medial Lemniscal system
Sends information about texture and the position of the joints to the thalamus.
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Anterolateral System
Sends information about pain and temperature to the somatosensory cortex.
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Mapping the Body Parts to the Somatosensory Cortex
This is in two parts; sensory and motor. The body is not mapped linearly. Senory section - regions with more mechanoreceptors (e.g. fingers) are more represented. Motor part - similar but with fewer body parts as not all sensing regions have muscles.
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Convergent Excitation
The second order neuron is connected to multiple first order neurons hence increasing the receptive field. The signal to noise ratio is increased.
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Surround Inhibition
The central primary neuron sends an excitatory signal to the second order neuron. Peripheral receptors send inhibitory signals and receptors in between are a mixture or excitatory and inhibitaory. This allows the location of small stimuli.
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Lateral Inhibition
There is a row of excitatory signals and a row of inhibitory signals. This is used for edge detection.
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Proprioception
the body's ability to sense movement within joints and joint position. This ability enables us to know where our limbs are in space without having to look.
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Ipsilateral
On the same side of the body.
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Contralateral
On the opposite side of the body.
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Muscle Spindle Arrangement
They are orientated in parallel to the contractile parts of the efferint fibers and are enclosed by a capsule. when stretched the ion channels are opened and the afferent fibers are triggered.
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Role of Gamma Motor Neurons Alongside Muscle Spindles
Keeps the muscle spindles in the operating range. When an alpha neuron is stimulated the muscle contracts unloading the spindle so it stops firing. The gamma neuron controls the contraction of the interfusal muscle fiber maintaining sensitivity.
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Servo- Mechanism
Automatically controls muscle force independent of external load. External loads counteract muscle force so the length change of the muscle is not the desired one. Deviation is sensed by muscle spindles and corrected by alpha and gamma neurons.
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Goldi Tendon Organ
Found between contractile muscle fibers and tendons attached to skeletal muscle. The muscle contracts & the tension causes collagen fibers to straighten, squeezing the axon. Ion channels open generating an action potential in afferent fibers.
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Saccadic System
moves eyes from one point to another at a very high speed. We perform saccadic eye movement to analyse feature in the visual environment. Subconsciously we perform micro movements directing the primary visual axis towards the most important details.
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Smooth Pursuit System
In charge of slow movements and taking in details of a moving object.
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Vergence System
Merges the information from the left and right eye.
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Vestibulo Ocular Reflex (VOR)
Compensatory eye movements are induced by the vestibular system. e.g. when a subject is rotated on a chair the eye focuses on one point so the velocity of the eye is the opposite of the chair to remain focused on that point. Eyes flick at field edge.
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Optokinetic Reflex
Compensatory eye movements induced by the visual system. Occurs when the subject remains stationary and the visual field moves
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Motorneuron encoding of the duration of the eye movement
Indicated by the duration of increased spike rate.
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Motorneuron encoding for the velocity of eye movement
encoded by the instantaneous spike rate during the movements - PHASIC ACTIVITY
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Motorneuron encoding for the angular position
encoded by the spike rate in between eye movements - TONIC ACTIVITY
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Neuonal Pathway in the VOR
excitary: vestibular nucleus -> CROSS MIDLINE to abducens nucleus -> CROSS MIDLINE to medial longitudinal fasciculus -> eye muscle. Inhibitory : vestibular nucleus -> abducens nucleus -> eye muscle.
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Posterior Parietal Cortex
involved in visual attention.
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Supplementary Eye Fields
Involved in eye movements to specific parts of a visual target.
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Head- Eye Movements for Small Gaze Shifts
Eyes move first to bring the object into foveal vision. Head then moves, eyes also move to keep the object in foveal vision. Eyes and head move with opposite velocities.
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Head- Eye Movements for Large Gaze Shifts
Eyes and head move simultaneously. Initially eyes move in the opposite direction to the head to stabilize gaze. Eyes then move with head. As the head movement ends the eyes are still and then reverse direction to stabilize gaze.
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Thalamus
Part of the brain responsible for passing sensory information to higher cortical areas in the brain e.g. to the somatosensory cortex.
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Ascending Pathway
dorsal root ganglion -> sensory decussation -> medial lemniscus -> thalamus -> somatosensory cortex
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Premotor Cortex
plans a motor action based on the information sent by the somatosensory cortex. It is all about the planning of the movement rather than executing the movement itself.
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Descending Pathway
motor cortex -> cerebral preduncle -> pyramid -> pyramidal decussation ->corticospinal tract -> motor neurons in the ventral horn
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Cortical Plasticity
The motor cortex is arranged somatotopically. If the part of the motor cortex stops working, it can rearrange itself causing regions of the cortex to be responsible for different parts of the body compensating for function loss of part of the cortex.
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Detecting the Direction of Limb Movements
Neurons in the motor cortex have a preferred direction, the limb moving this way largely increases activity. They are inhibitory when moving the other way. There are 8 clusters of neurons, the summed activity (population vector) is the direction.
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Flocculonodal Lobe
Part of the cerebellum responsible for sending information to the vestibular nuclei. It is involved in balance and eye movements
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Lateral Hemisphere
Part of the cerebellum that sends information to the motor and premotor cortex. It is involved in motor planning.
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Inputs to the Cerebellum - Unspecific Purkinje cell
Unspecific Purkinje cells get information from the spinal cord, higher senses and cerebal cortex via mossy fibers.
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Inputs to the Cerebellum - Specific Purkinje cell
Specific Purkinje cells get input from the spinal cord, auditory & visual systems and the cerebal cortex via climbing fibers. Each climbing fiber wraps around a purkinje cell in a 1:1 ratio. There is an output to the deep nuclei.
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Affect of Lesions in the Cerebellum
SImple motor tasks need to be executed consciously. Movements become more inaccurate and less smooth.
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Fractured Somatotopic Maps
Found in the cerebellum. There are multiple representations of the same body part found in different locations . There is a topic mapping system where for motor programs involving multiple body parts, they are represented next to each other.
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Long-Term Potentiation
Patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons. If the membrane is already depolarized the magnesium blocking the glutamate-gated NMDA channels is released and calcium enters the cell.
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The Cerebellum and Motor Learning
1) the first time you have to consciously think about what you do 2) repeat many times. movement generates sensory feedback which coincides with generating further movements. A chain of coincident feedback and movement makes a motor programme.
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Correcting the Motor Programme
Feedback on the success of the motor action occurs late during the motor sequence or after it has been completed. Analysis is then carried out and the action corrected for.
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