Phyl 1000

Topics: Muscle, Nervous system, Muscular system Pages: 9 (2040 words) Published: May 23, 2013
Neural Reflexes
* all neural reflexes begin with stimulus that activates sensory receptor * receptor sends info in form of AP through sensory neurons to CNS * CNS: integrating center that evaluates all incoming info and selects appropriate response * Initiates AP in efferent neurons to direct response of muscles or glands (effectors) * Negative feedback:

* Feedback signals from muscle or joint receptors keep CNS continuously informed of changing body position * Feedforward:
* Component that allows body to anticipate stimulus and begin response

Neural Reflex Pathways Can Be Classified in Different Ways
* reflex pathways in NS consist of chains or networks of neurons that link sensory receptors to muscle or glands * classified in several ways:
1. efferent division of NS that controls the response/effector a. somatic motor neurons control skeletal muscles
b. autonomic neurons control smooth and cardiac muscles, glands, and adipose tissue 2. CNS location where reflex is integrated (integrating region within CNS) c. Spinal reflexes don’t require input from brain – may be modulated by higher input from brain but integrated in spinal cord d. Cranial reflexes are integrated within brain

3. Whether reflex is innate or learned (time at which reflex develops) e. Innate (inborn) reflexes are genetically determined
Ex. Knee jerk rxn
f. Learned (conditioned) reflexes are acquired through experience
Ex. Pavolv’s dogs
4. Number of neurons in reflex pathway
g. Monosynaptic reflexes – have only 2 neurons: one afferent (sensory) and one efferent. Only somatic motor reflexes can be monosynaptic h. Polysynaptic reflexes include 1+ interneurons between afferent and efferent neurons. All autonomic reflexes are polysynaptic because they have 3 neurons: one afferent and 2 efferent * divergence: of pathways allows single stimulus to affect multiple targets * convergence: integrates input from multiple sources to modulate the response * maybe involved in excitation of inhibition

* aka visceral reflexes: often involved internal organs of body * some are spinal reflexes: urination and defecation
* often modulated by excitatory or inhibitory signals from brain carried by descending tracts from higher brain centers * ex. Urination: voluntarily initiated by conscious through or may be inhibited by emotion or stressful situation * often higher control of a spinal reflex is learned response * ex. Toilet training

* other autonomic reflexes are integrated in brain, primarily in hypothalamus, thalamus and brain stem * contain centers that coordinate body functions need to maintain homeostasis: HR, BP, breathing, eating, water balance, body temp * brain stem:

* contains integrating centers for autonomic reflexes * salivating, vomiting, sneezing, coughing, swallowing, gagging * interesting type of autonomic reflex = conversion of emotional stimuli into visceral responses * limbic system-site of primitive drives: sex, fear, rage, aggression and hunger- has been called “visceral brain” due to role in emotionally driven reflexes * ex. Gut feelings, butterflies in stomach

* urination, defecation, blushing, blanching, piloerection: tiny muscles in hair follicles pull shaft of hair erect * all polysynaptic, with at least 1 synapse in CNS between sensory neuron and preganglionic autonomic neuron and additional synapse in ganglion between perganglionic and postganglionic neurons * characterized by tonic activity: continuous stream of AP that creates ongoing activity in effectors * ex. Tonic control of blood vessels

* receptors that sense changes in joint movements, muscle tension, muscle length fee this info to CNS which...
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