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Chapter 11

Chapter 11 Study Guide

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Biological Sciences

CHAPTER 11 EFFERENT DIVISION: AUTONOMIC AND SOMATIC MOTOR CONTROL Pages 377 391 - efferent division of peripheral nervous system can be subdivided into somatic motor neurons, which control skeletal muscles, and autonomic neurons, which control smooth muscle, cardiac muscle, many glands, and some adipose tissue - somatic and autonomic divisions are sometimes called the voluntary and involuntary divisions of the nervous system, respectively THE AUTONOMIC DIVISION - its functions not under voluntary control - control over internal organs - divided into sympathetic and parasympathetic branches - if you are resting quietly after a meal, the parasympathetic branch is dominant, taking command of the routine, quiet activities of day-to-day living, such as digestion. Its 30:7438,7084209L2088,L/94.43974O7089 ,3//LJ0891:3.9L438 - in contrast, sympathetic branch is dominant in stressful situations, such as the potential threat from the snake - fight-or-flight response brain triggers massive simultaneous sympathetic discharge throughout the body; as the body prepares to fight or flee, the heart speeds up; blood vessels to muscles of the arms, legs, and heart dilate; and the liver starts to produce glucose to provide energy for muscle contraction. The discharge during fight-or-flight situations is mediated through the hypothalamus and is a total-body response to a crisis Autonomic reflexes are important for homeostasis - works closely with endocrine and behavioural state system to maintain homeostasis in the body - sensory info from somatosensory and visceral receptors goes to homeostatic control centres in hypothalamus, pons, and medulla. These centres monitor and regulate important functions such as BP, temp regulation, and water balance - hypothalamus has neurons that act as sensors, such as osmoreceptors, which monitor osmolarity, and thermoreceptors, which monitor body temp - motor output from hypothalamus and brain stem creates autonomic responses, endocrine responses, and behavioural responses such as drinking, food-seeking, and temp regulation - sensory info integrated in cerebral cortex and limbic system can create emotions that influence autonomic output - some can place without input from brain. These spinal reflexes include urination, defecation, and penile erection bodily functions that can be influenced by descending pathways from the brain but do not require this input Antagonistic control is a hallmark of the autonomic division - sympa and parasympa display all 4 properties of homeostasis: o preservation of fitness of internal environment o up-down regulation by tonic control, o antagonistic control o chemical signals with diff. effects in diff. tissues - most internal organs are under antagonistic control, one autonomic branch is excitatory and one the other is inhibitory. Exception: sweat glands and smooth muscel in most blood vessels innervated only by sympa branch and rely strictly on tonic (up-down) control www.notesolution.com- para and sympa work cooperatively on diff. tissues to achieve a common goal - in some autonomic pathways, neurotransmitter receptor determines the response of the target tissue. Most blood vessels contain one type of adrenergic receptor that causes smooth muscle contraction (vasoconstriction). However, some blood vessels also contain a second type of adrenergic receptor that causes smooth muscle to relax (vasodilation) Autonomic pathways have 2 efferent pathways in series - preganglionic neuron originates in CNS and projects to an autonomic ganglion outside the CNS. There, the preganglionic neuron synapses with the second neuron in the pathway, the postganglionic neuron has its cell body in ganglion and projects its axon to the target tissue. ( A ganglion is a cluster of nerve cell bodies that lie outside the CNS. The equivalent in the CNS is a nucleus - divergence single signal from the CNS can affect a large number of target cells simultaneously - ganglia contain interneurons that lie completely within them. These interneurons enable the autonomic ganglia to act as miniintegrating centres, receiving sensory input from periphery of body and modulating outgoing autonomic signals to target tissues Sympathetic and parasympathetic branches exit the spinal cord in different regions - anatomical differences: o where the pathways originate in CNS and o the location of autonomic ganglia - most sympathetic pathways originate in thoracic and lumbar regions of the spinal cord. Sympathetic ganglia found primarily in 2 chains that run along either side of spinal column, with additional ganlia along the descending aorta - long nerves (axons of postganglion neurons) project from ganglia to the target tissues. Since ganglia lie close to the spinal cord, sympa pathways generally have short pregangl
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