Lecture 7-9: Straub

Question 1

What are the basic properties of a reflex?

Answer 1

Involuntary stereotypic response trigged by a stimulus Can be mono or polysynaptic

Question 2

What are the advantages of having reflex?

Answer 2

Fast response to a fixed stimulus Can produce a complex behaviour e.g. egg retrieval - Due to fixed action potentials (FAPs) / behavioural pattern

Question 3

What are fixed action potentials?

Answer 3

A behavioural pattern which once triggered is performed to completion. Innate and species specific behaviour e.g. egg retrevial, eyebrow raise, emotion display.

Question 4

How are fixed action potentials controlled?

Answer 4

Hypo 1: peripheral control hypothesis Reflex 1 –> Reflex 2 (reflex 1 acts as the stimulus Hypo 2: Central control hypothesis

Question 5

Please describe the central control hypothesis.

Answer 5

Central pattern generator (CPG) produces a sequence of motor behaviours. Set the pattern which must be completed.

Question 6

How was it proved that the central hypothesis was correct?

Answer 6

If you remove the stimulus i.e. egg for egg retrieval then the pattern will still be completed

Question 7

How does the central pattern generator (CPG) produce rhythmic activity?

Answer 7

Contains a pacemaker Emergent network property

Question 8

Explain how a pacemaker helps the CPG produce a rhythm

Answer 8

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

Question 9

Explain how an emergent network helps produce a rhythm.

Answer 9

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.

Question 10

What does a sea angel use to move?

Answer 10

Wings which are like feet of a snail Simple but large movement

Question 11

What are the underlying mechanisms of swimming in a sea angel?

Answer 11

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

Question 12

Where are the swim moto-neurons located?

Answer 12

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.

Question 13

How do the swim motoneurons generate a behavioural pattern.

Answer 13

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.

Question 14

What generates the activity responsible for the swimming behaviour of the sea angel (clione)

Answer 14

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)

Question 15

Which groups of inter-neurons are responsible for the movement?

Answer 15

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

Question 16

How would you summarise the movement mechanisms of the sea angel (clione)

Answer 16

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)

Question 17

How do tadpoles swim?

Answer 17

Propagation of a wave movement from head to tail - Controlled by the spinal cord

Question 18

Please describe the neuroanatomy of the tadpole.

Answer 18

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.

Question 19

Describe the basic of a tadpoles swim motoneurons:

Answer 19

Motoneurons show rhythmic pattern when applied with a tail stimulus –> swimming episode. Strict corrdination of left and right motoneurons (alternating)

Question 20

How is the movement of a tadpole controlled.

Answer 20

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

Question 21

How is the swim CPG activated?

Answer 21

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.

Question 22

How is the wave of activity propagated through the tadpole?

Answer 22

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

Question 23

How would a single oscillator work in a tadpole?

Answer 23

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

Question 24

Why is a chain of unitary oscillators with a leading oscillator more likely.

Answer 24

-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)

Question 25

Describe the swimming CPG of a Lamprey.

Answer 25

Increased complexity due to organism complexity. - Insert structure diagram Sensory feedback is therefore not required, just CPG

Question 26

How does the Lamrey follow the leading oscillator hypothesis?

Answer 26

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.

Question 27

How can locomotion in mammals be observed?

Answer 27

Kinematic analysis - observing animal using photography

Question 28

How are the key observations of walking?

Answer 28

Two phases- stance and swing Three joints involved: hip, knee, ankle Speed related changes in step cycle

Question 29

What is the purpose of the two phases of walking?

Answer 29

Stance phase: anterior to posterior (limb moves back) - Supports weight : loaded Swing phase: posterior to anterior

Question 30

What is the purpose of the three joints involved in walking?

Answer 30

Flexion and extension Hip performs 1 cycle, Knee and ankle 2 (body stays at same height)

Question 31

How does the step cycle change with speed?

Answer 31

Stance phase decreases with increased speed Swing phase stays constant Cycle becomes shorter Locomotor pattern changes with increased speed - Walk –> Trot –> Pace –> Gallop

Question 32

Describe the four different locomotor patterns

Answer 32

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)

Question 33

How is walking neurally controlled?

Answer 33

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

Question 34

How do by know that gaits are controlled by a single network?

Answer 34

Gradual shift in movement over wide range Basic pattern remains constant at various speeds Changes in gait controlled by single parameters - CPG extension

Question 35

Where is the neural network located?

Answer 35

Diagram Level of superior colliculus: Caudal (left) of transect cannot recover Rostral side (right) can recover ability to walk Identification of Mesencephalic Locomotor region

Question 36

What is the purpose of transecting this section of the brain?

Answer 36

See how movement recovers Creates mesencephalic cat - able to machine like walk

Question 37

How does walking work in a mesencephalic cat?

Answer 37

Neuronal behaviour the same but no actual movement. Stimulation of MLR required for triggering movement Destruction of MLR doesnt prevent walking

Question 38

What is the purpose of the Mesencephalic Locomotor Region (MLR)?

Answer 38

Used for determining intensity of muscle contraction Affects muscle force and limb coordination

Question 39

What is the role of the spinal cord in walking?

Answer 39

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.

Question 40

Is walking / stepping controlled by a CPG?

Answer 40

Removal of sensory feedback (muscle relaxant / input removal) –> no disturbing in pattern –> suggests no need for feedback

Question 41

Could one rhythm be generated by multiple CPGs

Answer 41

L2-L4 and L5-L7 = CPG - Cooling of L5 –> no propagation of rhythm to caudal areas e.g. ankles

Question 42

How is walking controlled by CPGs?

Answer 42

Local oscillator networks which are coordinated into one single rhythm generator.

Question 43

What are the neuronal elements of limb CPGs?

Answer 43

Insert diagram Identified by genetic approaches, activity dependent labelling, electrophysiology

Question 44

Explain the Unit Burst model:

Answer 44

Each joint has an individual CPG They are coupled to form a network which coordinates the entirity of limb movement

Question 45

Explain the two level CPG model

Answer 45

Two tiered CPG - Rhythm generation occurs at the top - pattern generation occurs below - Information is coordinated and transmitted to joints

Question 46

How do endogenous bursters contibution to the CPG

Answer 46

Pacemaker properties displayed by Hb9 interneurons –> oscillation –> initiation?