Lecture 7-9: Straub Flashcards
What are the basic properties of a reflex?
Involuntary stereotypic response trigged by a stimulus Can be mono or polysynaptic
What are the advantages of having reflex?
Fast response to a fixed stimulus Can produce a complex behaviour e.g. egg retrieval - Due to fixed action potentials (FAPs) / behavioural pattern
What are fixed action potentials?
A behavioural pattern which once triggered is performed to completion. Innate and species specific behaviour e.g. egg retrevial, eyebrow raise, emotion display.
How are fixed action potentials controlled?
Hypo 1: peripheral control hypothesis Reflex 1 –> Reflex 2 (reflex 1 acts as the stimulus Hypo 2: Central control hypothesis
Please describe the central control hypothesis.
Central pattern generator (CPG) produces a sequence of motor behaviours. Set the pattern which must be completed.
How was it proved that the central hypothesis was correct?
If you remove the stimulus i.e. egg for egg retrieval then the pattern will still be completed
How does the central pattern generator (CPG) produce rhythmic activity?
Contains a pacemaker Emergent network property
Explain how a pacemaker helps the CPG produce a rhythm
Single neuron or group of neurons which oscillate between active and inactive. - mechanism? post-inhibitory rebound, spontaneous, constant excitation? Imposes the state of activity on network
Explain how an emergent network helps produce a rhythm.
Control is imposed by a network, depending on the interaction of neurons Half-centre generator model: - two neurons coupled by an inhibitory synapse -> stable oscillation as post-inhibitory rebound sustains oscillation. - flexor and extensor alternatively active (one fires, the other is inhibited) - excitatory synapse would be unstable.
What does a sea angel use to move?
Wings which are like feet of a snail Simple but large movement
What are the underlying mechanisms of swimming in a sea angel?
2 phases: dorsal and ventral Few 1000 neurons clustered in a central ganglia (diagram) Left and right wing movement is coordinated - Left wing movement is intrinsically generated
Where are the swim moto-neurons located?
Able to identify the neurons with axons in a specific nerve, by backfilling the neuron. - Inserting dye from the end of the neuron and watching it migrate to the cell body.
How do the swim motoneurons generate a behavioural pattern.
2 large neurons, 1 innervating left wing, 1 innervating right wing. Inactivation of individual or all motoneurons does not change rhythm - motoneurons do not generate the activity.
What generates the activity responsible for the swimming behaviour of the sea angel (clione)
Inter-neurons identified by systematic search with intracellular electrodes. - Inactivation of inter-neuron leads to disruption of rhythm - neurons fire on the rebound of inhibition (propagation)
Which groups of inter-neurons are responsible for the movement?
Two groups (7 and 8) 7= up beat of wing = dorsal phase 8= down beat of wing = ventral phase The two groups are connected by an inhibitory synapse
How would you summarise the movement mechanisms of the sea angel (clione)
Half-centre oscillator with a twist - swim inter-neurons with intrinsic bursting properties - rhythm generation is due to to intrinsic cellular properties and network properties (endogenous oscillator / pacemaker)
How do tadpoles swim?
Propagation of a wave movement from head to tail - Controlled by the spinal cord
Please describe the neuroanatomy of the tadpole.
100um spinal cord 8 types of spinal neurons: motoneurons, commissural interneuron, descending interneuron, dorsolateral interneuron, dorsolateral commissural interneuron, Rohon-Bear neurons. Neurons are organised into segments and are symmetrical on either side of the spinal cord.
Describe the basic of a tadpoles swim motoneurons:
Motoneurons show rhythmic pattern when applied with a tail stimulus –> swimming episode. Strict corrdination of left and right motoneurons (alternating)
How is the movement of a tadpole controlled.
Central pattern generator: descending, commissural and motoneurons which produce a basic swimming pattern - creates a half-centre oscillator - alternation of activation and inhibition is controlled by commissural inter-neurons - A.P’s fired during swimming, tonically excited, recieve mid-cycle inhibition
How is the swim CPG activated?
Small short stimulus from Rohon-Beard neurons –> dorsolateral and dorsolateral commissural sensory interneurons –> activation of CPG - After activation, rebound continues propagation and activity decreases over time.
How is the wave of activity propagated through the tadpole?
Head to tail (rostral –> caudal) can be seen by progression in motoneuron activity Hypo 1: single oscillator Hypo 2: chain of unitary oscillator, leading oscillator
How would a single oscillator work in a tadpole?
CPG close to brain, closet segments activated first –> delay increases with distance Unlikely because: CPGs over length of spinal cord Rhythmic activity can be seen in some stretches in isolation
Why is a chain of unitary oscillators with a leading oscillator more likely.
-Each CPG generates its own rhythm, the one which is fastest sets overall frequency –> coordinates other CPGs -More rostral CPGs operate at a faster frequency because the regions are more depolarisation and receive larger mid-cycle inhibitions -Manipulating the excitability of regions changes the delay. Possible to artificially increase the excitability of caudal regions –> shortens or reversal of delay (can lead to caudal –> rostral propagation)
Describe the swimming CPG of a Lamprey.
Increased complexity due to organism complexity. - Insert structure diagram Sensory feedback is therefore not required, just CPG
How does the Lamrey follow the leading oscillator hypothesis?
Spinal cord can be ‘divided’ into rostral, middle and caudal pools. - pool with the highest frequency coordinates other pool - Rostral fastest: rostral –> caudal propagation (forwards) - Caudal fastest: caudal –> rostral propagation (backwards) - This is a behavioural adaptation allowing reversing - Middle pool fastest –> 2 propagation waves.
How can locomotion in mammals be observed?
Kinematic analysis - observing animal using photography
How are the key observations of walking?
Two phases- stance and swing Three joints involved: hip, knee, ankle Speed related changes in step cycle
What is the purpose of the two phases of walking?
Stance phase: anterior to posterior (limb moves back) - Supports weight : loaded Swing phase: posterior to anterior
What is the purpose of the three joints involved in walking?
Flexion and extension Hip performs 1 cycle, Knee and ankle 2 (body stays at same height)
How does the step cycle change with speed?
Stance phase decreases with increased speed Swing phase stays constant Cycle becomes shorter Locomotor pattern changes with increased speed - Walk –> Trot –> Pace –> Gallop
Describe the four different locomotor patterns
Walk: 4 limbs out of phase, 3 always touching floor Trot: Diagonal limbs are in phase, opposite are antiphase Pace: one side moves then the other Gallop: pairs of limbs in phase (front then back)
How is walking neurally controlled?
Each limb has its own controller due to variation in stepping rhythm and stride length Various gaits (movement based on speed) controlled by a single neuronal network
How do by know that gaits are controlled by a single network?
Gradual shift in movement over wide range Basic pattern remains constant at various speeds Changes in gait controlled by single parameters - CPG extension
Where is the neural network located?
Diagram Level of superior colliculus: Caudal (left) of transect cannot recover Rostral side (right) can recover ability to walk Identification of Mesencephalic Locomotor region
What is the purpose of transecting this section of the brain?
See how movement recovers Creates mesencephalic cat - able to machine like walk
How does walking work in a mesencephalic cat?
Neuronal behaviour the same but no actual movement. Stimulation of MLR required for triggering movement Destruction of MLR doesnt prevent walking
What is the purpose of the Mesencephalic Locomotor Region (MLR)?
Used for determining intensity of muscle contraction Affects muscle force and limb coordination
What is the role of the spinal cord in walking?
Limb controller is present in spinal cord If you transect the thoracic section –> weak movement and a lack of coordination - Lack of excitatory drive, compensated for by application of NA agonist.
Is walking / stepping controlled by a CPG?
Removal of sensory feedback (muscle relaxant / input removal) –> no disturbing in pattern –> suggests no need for feedback
Could one rhythm be generated by multiple CPGs
L2-L4 and L5-L7 = CPG - Cooling of L5 –> no propagation of rhythm to caudal areas e.g. ankles
How is walking controlled by CPGs?
Local oscillator networks which are coordinated into one single rhythm generator.
What are the neuronal elements of limb CPGs?
Insert diagram Identified by genetic approaches, activity dependent labelling, electrophysiology
Explain the Unit Burst model:
Each joint has an individual CPG They are coupled to form a network which coordinates the entirity of limb movement
Explain the two level CPG model
Two tiered CPG - Rhythm generation occurs at the top - pattern generation occurs below - Information is coordinated and transmitted to joints
How do endogenous bursters contibution to the CPG
Pacemaker properties displayed by Hb9 interneurons –> oscillation –> initiation?
