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General organization. Sensory neurons Deliver information to CNS Motor neurons Distribute commands to peripheral effectors Interneurons Interpret information and coordinate responses. Neuronal pools. Neuronal Pools - Functional group of interconnected neurons.
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General organization • Sensory neurons • Deliver information to CNS • Motor neurons • Distribute commands to peripheral effectors • Interneurons • Interpret information and coordinate responses
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.
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.
Figure 13.15 The Organization of Neuronal Pools Figure 13.15
An introduction to reflexes • Reflexes are rapid automatic responses to stimuli • Neural reflex involves sensory fibers to CNS and motor fibers to effectors
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
Figure 13.16 Components of a Reflex Arc Figure 13.16
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
Figure 13.17 Methods of Classifying Reflexes Figure 13.17
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.
More reflex classifications • Cranial reflexes • Reflexes processed in the brain • Spinal reflexes • Interconnections and processing events occur in the spinal cord
still more reflex classifications • Somatic reflexes • Control skeletal muscle • Visceral reflexes (autonomic reflexes) • Control activities of other systems • See chapter 16.
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.
Figure 13.18 Neural Organization and Simple Reflexes Figure 13.18
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
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
Figure 13.19 Components of the Stretch Reflex Figure 13.19
Figure 13.20 The Patellar Reflex Figure 13.20
Figure 13.21 Intrafusal Fibers Figure 13.21
Polysynaptic reflexes • Produce more complicated responses • Tendon reflex • Withdrawal reflexes • Flexor reflex • Crossed extensor reflex
Figure 13.22 The Flexor and Crossed Extensor Reflexes Figure 13.22
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
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
Reinforcement and inhibition • Reinforcement = facilitation that enhances spinal reflexes • Spinal reflexes can also be inhibited • Babinski reflex replaced by planter reflex
Figure 13.23 The Babinski Reflexes Figure 13.23
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.