General organization

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

• Sensory neurons

• Deliver information to CNS

• Motor neurons

• Distribute commands to peripheral effectors

• Interneurons

• Interpret information and coordinate responses

General organization


• 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.

Neuronal pools


-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.

5 Neural circuit patterns, continue

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.15

Figure 13.15 The Organization of Neuronal Pools


• Reflexes are rapid automatic responses to stimuli

• Neural reflex involves sensory fibers to CNS and motor fibers to effectors

An introduction to reflexes


• 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

Reflex arc


Figure 13.16 Components of a Reflex Arc

Figure 13.16


• Reflexes are classified according to:

• 1). Development

• 2). Site of information processing

• 3). Nature of resulting motor response

• 4). Complexity of neural circuit involved

Reflex classification


Figure 13.17 Methods of Classifying Reflexes

Figure 13.17


• 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.

reflex classifications


• Cranial reflexes

• Reflexes processed in the brain

• Spinal reflexes

• Interconnections and processing events occur in the spinal cord

More reflex classifications


• Somatic reflexes

• Control skeletal muscle

• Visceral reflexes (autonomic reflexes)

• Control activities of other systems • See chapter 16.

still 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.

and more reflex classifications


Figure 13.18 Neural Organization and Simple Reflexes

Figure 13.18


• 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

Spinal Reflexes


• Stretch reflex automatically monitors skeletal muscle length and tone

• Patellar (knee jerk) reflex

• Sensory receptors are muscle spindles

• Postural reflex maintains upright position

Monosynaptic Reflexes


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


• Produce more complicated responses

• Tendon reflex

• Withdrawal reflexes

• Flexor reflex

• Crossed extensor reflex

Polysynaptic reflexes


Figure 13.22 The Flexor and Crossed Extensor Reflexes

Figure 13.22


• 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

Polysynaptic reflexes, continue


• 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

Control of spinal reflexes


• Reinforcement = facilitation that enhances spinal reflexes

• Spinal reflexes can also be inhibited

• Babinski reflex replaced by planter reflex

Reinforcement and inhibition


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.

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General organization