Figure 14.17b

Figure 14.17b

Table 14.5

Figure 14.18

Concept 14.4Reflexesand SNS Reflex Arcs

Reflexes • somatic reflexes involve contraction of skeletal muscles • autonomic reflexes • not consciously perceived • responses of smooth muscle, cardiac muscle, and glands • reflex arc • pathway followed by nerve impulses that produce reflex • may be monosynaptic or polysynaptic

Reflexes • fast involuntary, unplanned sequence of actions that occurs in response to a particular stimulus • some present from birth • some are learned or acquired • cranial reflex • integration occurs in brain • spinal reflex • integration occurs in spinal cord • SNS reflexes are always excitatory

SNS Reflex Arc Components • sensory receptor • dendrite or associated sensory structure • sensory neuron • axon and axon terminals • integrating center • interneuron(s) that relay impulses • motor neuron • impulse triggered by integrating center • effector • body part that responds to impulse

Stretch Reflexes • Triggered by tapping on tendons attached to muscles at elbow, wrist, knee, and ankle joints • Monosynaptic • muscle spindles detect slight stretch • muscle spindle generates impulse(s) to sensory neuron to posterior root of spinal nerve • sensory neuron synapses with motor neuron in gray matter of spinal cord • strong enough impulse triggers AP of motor neuron • ACh at NMJ triggers contraction of skeletal muscle

Figure 14.20

Stretch Reflexes • Monosynaptic reflexes are called ipsilateral reflexes • propagate into and out of the same side of spinal cord • reflex helps prevent injury by preventing overstretching of muscles • reciprocal innervation • polysynaptic reflex arc to antagonistic muscles operates at the same time • three neurons and two synapses

Flexor Reflexes • Triggered by painful AKA withdrawal reflex • Polysynaptic or intersegmental reflex arc • pain-sensitive sensory neuron stimulated • impulse propagates into spinal cord • sensory neuron activated interneuron and signal sent to several segments • several motor neurons activated and motor impulse propagates toward several NMJs • ACh released into synaptic cleft causes flexor muscles to contract withdrawing body part from painful stimulus

Figure 14.21

Flexor Reflexes • reciprocal innervation occurs as in stretch reflex

Concept 14.5ANS Reflexes

ANS versus SNS SNS • produces voluntary movements • in response to consciouslyperceived sensory input ANS • produces involuntary movements in • cardiac muscle • smooth muscle • glands • in response to unconscious sensory input

ANS Reflex Arcs • regulates activity of smooth, cardiac muscle, and many glands • continual flow of nerve impulses from autonomic sensory neurons in visceral organs and blood vessels propagates into integrating centers of CNS • impulses in autonomic motor neurons propagate to various effector tissues • can excite or inhibit activities of effector tissues • ANS activity is regulated by hypothalamus and brain stem of CNS

ANS Divisions sympathetic division parasympathetic division • most organs have dual innervation by both sympathetic and parasympathetic divisions • transmit opposing nerve impulses enteric division • enteric plexuses • network of neurons that extend throughout GI tract walls • contain • sensory neurons • interneurons • motor neurons

Figure 14.22a

Figure 14.22b

Table 14.6

Concept 14.6Anatomy of the ANS

Components of ANS • Preganglionic Neurons • Autonomic Ganglia • Postganglionic Neurons • Effectors

Preganglionic Neurons • cell body in CNS • sympathetic division • in gray matter segments T1-T12, L1 and L2 • parasympathetic division • in nuclei of four cranial nerves in brain stem • in gray matter segments S2-S4 • small-diameter myelinated fiber • extends to an autonomic ganglion • synapses with postganglionic neuron

Figure 14.23

Figure 14.24

Ganglia • Sympathetic ganglia • sympathetic trunk ganglia • vertical row on either side of vertebral column • prevertebral ganglia • celiac ganglion • superior mesenteric ganglion • inferior mesenteric ganglion • Parasympathetic ganglia • terminal ganglia • located close to or actually within wall of visceral organ • longer than most axons of sympathetic preganglionic neurons

Figure 14.25

Autonomic Plexuses • many lie along major arteries • may contain sympathetic ganglia and axons of autonomic sensory neurons • often named after associated artery • thoracic plexuses • cardiac plexus • pulmonary plexus • abdominal and pelvic plexuses • celiac plexus • superior and inferior mesenteric plexus • hypogastric plexus • renal plexus

Figure 14.25

Postganglionic Neurons • Sympathetic neurons connect with postganglionic neurons by • synapse with first ganglion it reaches • may ascent or descent to higher or lower ganglion before synapsing with postganglionic neurons • without synapsing it may continue through sympathetic trunk ganglion • end at prevertebral ganglion • synapse with postganglionic neurons there

Figure 14.26

Postganglionic Neurons Sympathetic effectors • some preganglionic sympathetic axons directly innervate adrenal medullae • each has many axon collaterals • single sympathetic preganglionic fiber may synapse with 20 or more postganglionic neurons • example of divergence • explains why responses affect almost entire body simultaneously Parasympathetic effectors • preganglionic neurons pass to terminal ganglia near or within a visceral effector • can be localized to single effector

Concept 14.7ANS Signal Transmission

ANS Signal Transmission Classification based on neurotransmitter released • Cholinergenic neurons • release acetylcholine • Adrenergenic neurons • release norepinephrine

Cholinergenic neurons • release acetylcholine • preganglionic • both sympathetic and parasympathetic • sympathetic postganglionic that innervate most sweat glands • all parasympathetic postganglionic neurons

Adrenergenic neurons • release norepinephrine • most sympathetic postganglionic neurons • receptors • bind both neurotransmitter norepinephrine and hormone epinephrine • four classifications • alpha 1, alpha 2, beta 1, and beta 2 • alpha 1 and beta 1 are generally excitatory receptors • alpha 2 and beta 2 are generally inhibitory receptors

Figure 14.27a

Figure 14.27b

Figure 14.27c

Table 14.7

Concept 14.8Sympathetic and Parasympathetic Responses

Sympathetic • dominates during extreme physical or emotional stress • favors activities that can support high production of ATP and high physical activity • fight or flight response • pupil dilation • increased heart function • dilation of airways • reduced blood flow to viscera • increased blood flow to heart, skeletal muscles, liver and adipose tissue • increased glycogen and fatty acid breakdown • release of glucose from liver • inhibition of processes not essential for emergency response

Parasympathetic • enhances rest and digest activities • favors activities that can support body functions that conserve and restore energy during times of rest and recovery • SLUDD • salivation • lacrimation • urination • digestion • defecation • three decreases • heart rate • diameter of airways • diameter of pupils

Table 14.9 pt 1

Table 14.9 pt 2

Table 14.8

Concept 14.9ANS Reflex Arcs

Autonomic Reflexes Components: • Receptor • Sensory neuron • Integrating center • Motor Neuron • Effector

Hypothalamus • control and integration center of ANS • receives sensory input regarding • visceral function • olfaction • gustation • blood, temperature, osmolarity, and substance concentration • emotions from limbic system • output via reticular formation to • brain stem • spinal cord • posterior and lateral control sympathetic activities • anterior and medial control parasympathetic activities

Figure 14.17b

Figure 14.17b

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