General organization

1. General organization • Sensory neurons • Deliver information to CNS • Motor neurons • Distribute commands to peripheral effectors • Interneurons • Interpret information and coordinate responses

2. Neuronal pools • Neuronal Pools- Functional group of interconnected neurons. • There are 5 Neural circuit patterns: • Divergence- Spread of information from one neuron to several neurons, or from one pool to multiple pools. • Permits the broad distribution of a specific input. • Convergence- Several neurons synapse on the same postsynaptic neuron. • Several patterns of activity in the presynaptic neurons can have the same effect on the postsynaptic neuron. • The same motor neurons can be subject to both conscious and subconscious control. • Ex.: Ribs and diaphram motion.

3. 5 Neural circuit patterns, continue • -Serial processing- Occurs when information is relayed in a stepwise fashion, from one neuron to another or from one neuronal pool to the next. • -Occurs as sensory information in relayed from one part of the brain to • another. • -Parallel processing- Occurs when several neurons or neuronal pools process the same information at one time. • -Divergence must take place first. • -Due to parallel processing many responses can occur at the same time. • -Ex.: Stepping on a nail and subsequent, simultaneous response • of moving your foot, shifting your weight, pain, and yelling. • -Reverberation- A positive feedback along a chain of neurons such that they remain active once stimulated. • -Will continue to function until synaptic fatigue or inhibitory stimuli • break the cycle. • -May involve a single neuronal pool or a series of interconnected pools.

4. Figure 13.15 The Organization of Neuronal Pools Figure 13.15

5. An introduction to reflexes • Reflexes are rapid automatic responses to stimuli • Neural reflex involves sensory fibers to CNS and motor fibers to effectors

6. Reflex arc • Wiring of a neural reflex • Five steps • Arrival of stimulus and activation of receptor • Activation of sensory neuron • Information processing • Activation of motor neuron • Response by effector

7. Figure 13.16 Components of a Reflex Arc Figure 13.16

8. Reflex classification • Reflexes are classified according to: • 1). Development • 2). Site of information processing • 3). Nature of resulting motor response • 4). Complexity of neural circuit involved

9. Figure 13.17 Methods of Classifying Reflexes Figure 13.17

10. reflex classifications • Innate reflexes • Result from connections that form between neurons during development • Acquired reflexes • Learned, and typically more complex motor patterns. • Ex.: A professional skier makes quick adjustments in body positioning while racing.

11. More reflex classifications • Cranial reflexes • Reflexes processed in the brain • Spinal reflexes • Interconnections and processing events occur in the spinal cord

12. still more reflex classifications • Somatic reflexes • Control skeletal muscle • Visceral reflexes (autonomic reflexes) • Control activities of other systems • See chapter 16.

13. and more reflex classifications • Monosynaptic reflex • Sensory neuron synapses directly on a motor neuron • Polysynaptic reflex • At least one interneuron between sensory afferent and motor efferent • Longer delay between stimulus and response • Length of delay is proportional to the number of synapses involved. • Can produce far more complicated responses than monosynaptic reflexes as the interneurons can control several muscle groups.

14. Figure 13.18 Neural Organization and Simple Reflexes Figure 13.18

15. Spinal Reflexes • Range from simple monosynaptic reflexes (single segment of spinal cord) to polysynaptic reflexes that involve many segments • In the most complicated spinal reflexes, called intersegmental reflex arcs, many segments interact to produce a coordinated, highly variable motor response. • Many segments interact to form complex response

16. Monosynaptic Reflexes • Stretch reflex automatically monitors skeletal muscle length and tone • Patellar (knee jerk) reflex • Sensory receptors are muscle spindles • Postural reflex maintains upright position

17. Figure 13.19 Components of the Stretch Reflex Figure 13.19

18. Figure 13.20 The Patellar Reflex Figure 13.20

19. Figure 13.21 Intrafusal Fibers Figure 13.21

20. Polysynaptic reflexes • Produce more complicated responses • Tendon reflex • Withdrawal reflexes • Flexor reflex • Crossed extensor reflex

21. Figure 13.22 The Flexor and Crossed Extensor Reflexes Figure 13.22

22. Polysynaptic reflexes, continue • Involve pools of interneurons • Occurs in pools of interneurons before motor neurons are activated. • Result may be excitation or inhibition. • Are intersegmental in distribution • Interneuron pools extend across spinal segments and may activate muscle groups in many parts of the body. • Involve reciprocal inhibition • Coordinates muscular contractions and reduces resistance to movement. • Have reverberating circuits to prolong the motor response • Several reflexes may cooperate to produce a coordinated response

23. Control of spinal reflexes • Brain can facilitate or inhibit motor patterns based in spinal cord • Motor control involves a series of interacting levels • Monosynaptic reflexes are the lowest level • Brain centers that modulate or build on motor patterns are the highest

24. Reinforcement and inhibition • Reinforcement = facilitation that enhances spinal reflexes • Spinal reflexes can also be inhibited • Babinski reflex replaced by planter reflex

25. Figure 13.23 The Babinski Reflexes Figure 13.23

26. You should now be familiar with: • The structure and functions of the spinal cord. • The three meningeal layers that surround the CNS. • The major components of a spinal nerve and their distribution in relation to their regions of innervation. • The significance of neuronal pools. • The steps in a neural reflex. • How reflexes interact to produce complicated behaviors.