BIO217.02 Focus Outline Peripheral Nervous System 217 PDF

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BIO 217 Focus Outline Peripheral Nervous System Chapter 13 Marieb

The majority of the information you need to complete this outline is in your textbook. Use other online textbooks and reliable sources, such as those identified in your syllabus, to find the remaining information. This outline is not collected but is to be used in place of lecture notes. The Peripheral Nervous System Define peripheral nervous system and list its components. -Peripheral nervous system: includes all neural structures outside the brain and spinal cord. It provides these links from and to the world outside the bodies. Ghostly white nerves thread through every part of the body, enabling the CNS to receive information and carry out its decisions. -Its components: sensory receptors, afferent nerves, efferent nerves, their association ganglia, and motor-endings. Sensory Receptors What are sensory receptors? Sensory receptors: are specialized to respond to changes in their environment, which are called Stimuli Identify the subclasses for each of the following classifications type of stimulus detected - mechanoreceptors: respond to mechanical force (touch, pressure (BP), vibration, and stretch - thermoreceptors: respond to temperature changes - photoreceptors: those of the retina of the eye, respond to light - chemoreceptors: responds to chemicals in solution (molecules smelled or tasted, changes in blood) - Nociceptors : respond to potentially damaging stimuli that result in pain. (searing heat, extreme cold, excessive pressure, inflammatory chemicals) body location - Exteroreceptors: are sensitive to stimuli arising outside the body, so most exteroceptors are near or at the body surface. (touch, pain, temperature receptors in the skin and most receptors of special senses: vision, hearing, equilibrium, smell, and taste) -

Interoceptors: (visceroceptors) respond to stimuli within the body ( from internal viscera and blood vessels, chemical changes, tissue stretch, and temperature) (feel pain, discomfortable, hunger, or thirst) : unawareness

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Prioprioceptors: respond to internal stimuli. their location are more restricted.

occur in skeletal muscles, tendons, joints, and ligaments, and in Connective tissue coverings of bones and muscles) structure - Nonencapsulated: Free nerve endings of sensory neurons; modified free nerve endings: epithelial tactile complexes (Merkel cell and discs); hair follicle receptors -

Encapsulated:

Tactile ( Meissner’s ) corpuscles; Lamellar (Pacinian) corpuscles; Bulbous corpuscles (Ruffini endings); Muscle spindles; tendon organs; joint kinesthetic receptors

Outline the events that lead to sensation and perception. - The events that lead to sensation: 1. Receptor level: sensory receptors 2. Circuit level: processing in ascending pathways 3. Perceptual level: processing in the cortical sensory areas

- The events that lead to perception: -Pain receptors are activated by extremes of pressure and temperature as well as a veritable soup of chemicals released from injured tissue -Histamine, K+, ATP, acids, and bradykinin are the most potent pain-reducing chemicals. -All of these chemicals act on small-diameter fibers. - Impulses travel on fibers that release neurotransmitters glutamate and substance P -Some pain impulses are blocked by inhibitory endogenous opioids (endorphins) Describe receptor and generator potentials - Receptor can produce one of two types of graded potentials. - when the receptor region is part of a sensory neuron (free dendrites or encapsulated receptors), the graded potential is called generator potential because it generates action potentials in a sensory neuron What is sensory adaptation? Sensory adaptation is a change in sensitivity in presence of constant stimulus What are the main aspects of perceiving sensory information? - perceptual detection: the ability to detect that a stimulus has occurred. this is the simplest level of perception. -

Magnitude estimation: the ability to detect how intense the stimulus is.

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Spatial discrimination: allow us to identify the site or pattern of stimulation.

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Feature abstraction: the mechanism by which a neuron or a circuit is tuned to one feature, or property of a stimulus in preference to others. Quality discrimination: the ability to differentiate to submodalities of a particular sensation. Pattern recognition: the ability to take in the scene around us and recognize a familiar pattern , an unfamiliar one, or one that has special significance for us.

Why does the body sense pain? Because the brain makes the body feel pain How does the body sense pain? Sensory receptor detects a stimulus, then sends it to the central nervous system is the brain through afferent neuron. The brain integrate information , so then the brain makes the body feel brain Compare and contrast visceral pain with somatic pain. Visceral pain

Somatic pain

from noxious stimulation of receptors in the organs of the thorax and abdominal cavity: dull aching, grawing, or burning.

pain generated from skin and musculoskeletal system (including joints)

Nerves and Ganglia Describe the general structure of a nerve. - each axon (nerve fiber) is surrounded by endoneurium - The perineurium binds groups of axons into bundles called fascicles - A tough fibrous sheath, the epineurium, encloses all the fascicles to form the nerve What is a ganglion? Ganglion are collections of neuron cell bodies associated with nerves in the PNS. Ganglia associated with afferent nerve fibers contain cell bodies of sensory neurons (dorsal root ganglia) (sensory, somatic) Ganglia associated with efferent nerve fibers mostly contain cell bodies of autonomic motor neurons (motor, visceral) Where do you find ganglia in the body? outside of Central nervous system, in the PNS Under what conditions can nerve fibers regenerate? If the cell body remains intact, axon of peripheral nerves can regenerate Can fibers in both the PNS and CNS regenerate? No. Fibers of the central nervous system can never regenerate

Outline process of nerve regeneration. 1. T  he axon fragments: - The cut axon ends seal themselves off. - Axon transport is interrupted, causing the cut ends to swell - Without access to the cell body, the axon (and its myelin sheath) begins to disintegrate distal to the injury. - Degeneration of the distal end of the cut axon, called Wallerian degeneration, spreads down the axon 2. Schwann cells and macrophages cleans out the dead axon distal to the injury: - Surviving Schwann cells engulf the myelin fragments and secrete chemicals that recruit macrophages. - Macrophages help dispose of the debris and release chemicals that stimulate Schwann cells to divide 3. Axon filaments grow through a regeneration tube: - Schwann cells release growth factors and express cell adhesion molecules (CAMs) that encourage axon growth - Schwann cells line up along the tube of remaining endoneurium, forming a regeneration tube that guides the regenerating axon “sprouts” across the gap to their original contacts 4. The axon regenerates and a new myelin sheath forms: - The Schwann cells protect and support the regenerating axon and ultimately produce a new myelin sheath.

Motor Endings Describe the structure and function of motor endings -motor endings are PNS elements that activate effectors by releasing neurotransmitters. Structure of motor ending

Function of motor endings

-Each motor neuron branches many times near the muscle which it supplies - Axons lead to the motor end plates; - each of these branches ends in a motor end plate on the surface of muscle fiber, - These branches are covered by a myelin sheath for most of their length, but absent near the motor end plate

Sensory nerve endings detect stimuli from the environment and send impulses toward the central nervous system in response to these stimuli. Efferent nerve endings carry impulses from the central nervous system to effector organs and muscles

What differences are there between the motor endings of somatic and autonomic nerve fibers?

The motor endings of somatic nerve fibers

The motor endings of autonomic nerve fibers

- innervate voluntary muscles form elaborate neuromuscular junctions with their effector cells;

- simpler - branch repeatedly, each branch forming synapses en passant with its effector cells

-the ending splits into a cluster of axon terminals that brach treelike over the junctional folds of sarcolemma of the muscle fiber.

- an axon ending serving smooth muscle or gland has a series of varicosities

- they release the neurotransmitter acetylcholine

- release either acetylcholine or epinephrine as their neurotransmitters

Reflexes What are the components of a reflex arc? - Receptor - Sensory neuron - Integration center - Motor neuron - Effector How do autonomic and somatic reflexes differ? Autonomic reflexes

Somatic reflexes

- the output: a two-step pathway starting with the preganglionic fiber emerging from a lateral horn neuron in the spinal cord, or the cranial nucleus in the brain stem, to a ganglio.

- the output: motor neuron in the ventral horn of the spinal cord that projects directly to a skeletal muscle to cause contraction

Define Spinal Reflexes. -Spinal reflexes: are somatic reflexes mediated by the spinal cord Compare and contrast the following reflexes stretch reflexes:- makes sure that the muscle stays at that length. - is important for maintaining muscle tone and adjusting it reflexively and in the large extensor muscles that sustain upright posture and in the postural muscles of the trunk

flexor reflexes : - a painful stimulus initiates the flexor which causes autonomic withdrawal of the threatened body part from the stimulus. -

are ipsilateral and polysynaptic

-are protective and important to our survival, they override the spinal cord pathways and prevent any other reflexes from using them at the same time. crossed-extensor reflexes : often accompanies the flexor reflex in weight-bearing limbs and is particularly important in maintaining balance. - is complex spinal reflex consisting of an ipsilateral withdrawal reflex and contralateral extensor reflex tendon reflexes: the polysynaptic tendon reflexes produce exactly the opposite effect: Muscle relax and lengthen in response to tension - when muscle tension increases during contraction or passive stretching, high-threshold tendon organs may be activated....