Lecture 14 + 15 (Reflexes) Flashcards
Reflex
Coordinated within spinal cord or brain stem; either simple or complex automatic behaviours; higher brain centers can influence response
Neuronal pools
functional groups of interconnected neurons; limited input and output; stimulates or depresses parts
Steps in a Neural Reflex
- receptor activation
- activation sensory neuron (graded depolarisation)
- integration (info processing by postsynaptic cell)
- activation of motor neuron
- response of peripheral effector (triggered by NTs)
Classifications of Reflexes
- early development (innate or acquired)
- type of motor response (somatic or visceral)
- complexity of neural circuit (monosynaptic or poly synaptic)
- site of information processing (spinal or cranial)
Spinal reflex
- monosynaptic (20 - 40 msec)
- polysynaptic
- intersegmental reflex arcs
Myotactic reflex
Monosynaptic stretch reflex; patellar knee-jerk
Muscle Spindles
Receptors in stretch reflexes; bundles of small, specialised intramural muscle fibers; surrounded by extramural muscle fibers
Sensory Region of Muscle Spindle
Central region of intramural fibers that are wound with anulospiral endings and have flower spray endings attached; innervated by gamma efferent fibers
Anulospiral endings
Dendrites of sensory neurons; stimulated by rate and degree of stretch
Flower spray endings
- Formed by smaller axons that supply spindle ends
- Stimulated by degree of stretch
Gamma Efferents in Muscle Spindle
- Axons of motor neurons
- synapse back onto intramural fibers
- important in voluntary muscle contractions
- allow CNS to adjust sensitivity of muscle spindles
Polysynaptic Reflexes
Interneurons control more than one muscle group; produce either EPSPs or IPSPs
1. Involve pools of neurons
2. Are intersegmental in distribution
3. Involve reciprocal inhibition
4. Have reverberating circuits
5. Several reflexes cooperate
Tendon Reflex
- Monitors external tension produced during muscle contraction
- Prevents developing too much tension and tearing or breaking tendons
Golgi tendon organ (GTO)
- Where muscle fibers of skeletal muscle meet tendons
- Strands of collagen
Flexor Reflexes
- Withdrawal reflexes
- Move body parts away from stimulus
- Strength and extent of response depends on intensity and location stimulus
Reciprocal Inhibition
For flexor reflex to work, antagonistic (extensor) muscle must be inhibited by interneurons in spinal cord
Ipsilateral reflex arcs
occur on same side of body as stimulus; stretch, tendon and withdrawal reflexes
Crossed extensor reflexes
involves contralateral reflex arc; occurs on the side opposite to stimulus; simultaneously coordinated with flexor reflex
Voluntary Movements and Reflex Motor Patterns
higher centers of brain incorporate lower, reflexive motor patterns; automatic reflexes can be activated by brain as needed, use few nerve impulses for complex motor functions, walking running jumping
Reinforcement of Spinal Reflexes
Higher centers reinforce spinal reflexes by
- stimulating excitatory neurons in brain stem or spinal cord
- creating EPSPs at reflex motor neurons
- facilitating postsynaptic neurons
Inhibition of Spinal Reflexes
Higher centers can inhibit spinal reflexes
- stimulating inhibitory neurons
- creating IPSPs at reflex motor neurons
- suppressing postsynaptic neurons
