Chapter 19: Control of Movement: The Motor Basis of Animal Behavior Flashcards
Invertebrates vs. Vertebrates
- Invertebrate neural circuits contain fewer neurons
- Arthropod muscle is innervated by a small number of neurons
- Vertebrate muscle is controlled by hundreds of neurons
- Invertebrate neurons can be uniquely identified
- C. elegans
- Aplysia
- One invertebrate neurons may play a functional role, while several vertebrate neurons may be required for the same behavior
Information Processing in the Nervous System
The nervous system evolved from a simple reflex arc that can be divided into 3 parts:
- Stimulus (sensory reception)
- Processing (sensory filtering/past experience/other input/patterned neuronal activity)
- Behavior (motor output)
Types of Reflex Arcs
A reflex is a simple, graded response to a specific stimulus.
Muscle Spindles (proprioceptor)
- γ motor neurons stimulate contraction of the intrafusal fibers
- How does this alter AP firing?
- What is the significance?
Stretch Reflex
- AKA knee-jerk
- Important for posture and coordination of movements
Flexion Reflex
Allows withdrawal from damaging stimulus
(cross withdrawl; contralateral)
Activation of Motor Neurons
Primary input to spinal cord from brain and spinal central circuits
Secondary input from reflexes
Therefore, major role of sensory input to spinal cord is to control responses to central circuits
Activation of Motor Neurons prt 2
If no load, whole muscle contracts
Shortening of intrafusal fibers prevents activity of spindle stretch receptor
Activation of Motor Neurons prt 3
With load that stops shortening…
Intrafusal fibers contract and activate the afferent neuron
This neuron then activates the alpha motor neuron
This is load compensation
Rhythmic Behavior
- Most behaviors involve a sequence of actions
- Scientists study rhythmic behavior to learn about sequences
- Stereotyped, repetitive sequences that are stable, repeatable, and predictable
- Walking, swimming, flying
- Stereotyped, repetitive sequences that are stable, repeatable, and predictable
Flying Locusts
Flying involves a patterned contraction of the depressor and levator muscles
Flying Locusts – Two Hypothesises
- Peripheral Control – feedback from proprioceptors triggers contraction of a muscle
- If true, deafferntation of sensory nerves should abolish activity – but it doesn’t, activity continues at a slower frequency
- Central Control – A central pattern generator in the CNS controls the contractions
- This is not a chained reflex
- Stimulation of nerve stumps restores wingbeat frequency
- Sensory stimulation excites the CNS, but the CNS is needed for timing information
- Sensory feedback can entrain the CPG
Central Pattern Generation
- CPGs producing patterns that look like sine waves are called oscillators
- Cellular oscillator- a single neuron generates the pattern
- Synaptic interaction is not needed
- Does not have to produce action potentials
- Network oscillator – neurons interact to produce a temporary pattern
CPGs
- Hybrid oscillators contain at least one neural oscillator working within a network
- The crustacean stomatogastric ganglion is one example
- Only requires 30 neurons!
- Behavior similar to chewing
- Ganglion located on outside of lobster, crayfish, and crab stomach
- The stomach has a cardiac chamber containing teeth to grind food and a pylorus that allows small food particles to pass through
- AB pacemaker (neuron) sets the rhythm
- Electrically coupled to 2 pyloric dilator neurons (PD)
- All 3 neurons fire together
- Inhibit the other cells
- LP cells recover quickly following the burst and generate Aps
- PY neurons fire next and inhibit LP
- Many oscillators may be modulated
- At least 15 modulators in the reflex above
- Modulators usually initiate and continue rhythm
- Alter membrane properties
- Alter synaptic transmission
Control & Coordination of Vertebrate Movement
- Cat movement
- Simplify system
- Brain, spinal cord, and sensory input is used for control
- Spinal cord motor neurons control muscles
- Get info from:
- Brain
- Proprioceptors
- Intrinsic spinal circuits
- Get info from:
Spinal CPG
- Cat locomotion requires a spinal CPG
- Cats can walk on a treadmill after spinal cord transection (no brain control)
- Brain does not provide timing
- In brain transected cats, electrical stimulation of the mesencephalon stimulates walking
- Cats can walk on a treadmill after spinal cord transection (no brain control)
- Increasing frequency, increases speed
- Brain may initiate and modulate walking, but isn’t needed to generate the locomotor rhythm
- Cats with cut dorsal roots can still walk
- What does this say about the role of proprioception in walking?
- Any medical implications of these studies?
Cerebral Cortex
- Electrical stimulation of the primary motor cortex causes movements of particular body parts
- These are pyramidal cells
- The amount of activity of some neurons is related to force of contraction
- Others cause a change in force
- Others predict the direction of independent muscles
- Axons go to brainstem motor nuclei
- Axons of these cells go to the spinal cord
- These are pyramidal cells
- Premotor cortex is involved in planning, executing, and organizing purposeful movement
Cerebellum
- Coordinates movement
- Lesioning creates clumsy and uncoordinated tremoring movement
- Provides error correction during movement
- Two parts
- Cortex
- All output goes to 2nd part
- Deep cerebellar nuclei
- Output to: vestibulocerebellum, medial spinocerebellum, lateral cerebrocerebellum
- Cortex
- No clear understanding of how it functions
Basal Ganglia
- Select movements, suppress unwanted movement, initiate selected movement
- ex: parkinson and huntington
Many Areas Interact
