the Peripheral nervous system and reflex activity Flashcards


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Chapter 13 its almost everything in chapter 13
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1

Peripheral nervous system

the PNS includes all neural structures outside the brain and spinal cord that is sensory receptors, peripheral nerves and their associated ganglia, and eferent motor endings.

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Sensory (afferent) divison

Towards

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Motor (efferent) Division

Away

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Somatic nervous system

voluntary

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Autonomic nervous system (ANS)

automatic

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Sympathetic divison

Fight or Flight

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Parasympathetic divison

Rest and digest

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sensory receptors

are specialized to respond to changes in their enviornment, which are called stimuli

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Mechanoreceptors

respond to mechanical force such as touch, pressure, including BP, vibration and stretch

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Thermoreceptors

are sensitive to temperature changes

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Photoreceptors

such as those of the retina of the eye, respond to light energy

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Chemoreceptors

respond to chemicals in solution(molecusle smelled or tasted, or changes in blood or interstitial fluid chemistry.

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Nociceptors (HARM)

respond to potentiall damagin stimuli that result in pain
EX: searing heat, extreme cold, excessive pressure, and inflammotry chemicals
these signals stimulate subtypes of thermo, mechano, and chemo receptors.

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exteroceptors (OUTSIDE)

are sensitive to stimuli arising outside the body
LOC: near or at the body surface

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Interoceptors (INSIDE)

respond to stimuli within the body
EX: internal viscera and blood vessels

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proprioceptors

respond internal stimuli
LOC:they occur in Skeletal muscles, tendons, joints, and ligamnets and in cunnective tissu coverings of bones and muslces.

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Simple receptors

are modified dendritic endings of senosyr neuron
* found throught the body
*the monitor most types of general sensory information

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Complex receptors

*they are sense organs
*associated with special sense(vision, hearin,equilibrium, smell and taste)

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Unencapsulated
free nerve endings of sensory neurons

L: exteroceptors, interoceptors, and proprioceptors
S: thermoreceptors(warm and cool) chemoreceptors (itch, PH, ETC.) Mechanoreceptor (Presssure), nociceptors (pain, hot, cold, pinch, and chemicals)
BL: most body tissues; most dense in connective tissues (ligaments, tendons, dermis, joint capsules, periostea) and epithelia (epidermis, conea, mucosae, and glands

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unencapsulated
modified free nerve endings: tactile discs (markel discs)

L: exteroceptors
S:mechanoreceptors (light pressure) slowly adaptic
BL: basal layer of epidermis

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Unencapsulated
Hair follicle receptors

L: exteroceptors
S: mechanoreceptors (hair deflection); rapidly adapting
BL: In and surrounding hair follicles

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Encapsulated
Meissner's corpuscles (tactile corpuscles)

L: exteroceptors
S: mechanoreceptors (light pressure, discriminative touch, vibration of low frequency); rapidly adapting
BL: dermal papilae of hairless skin, particularly nipples, external genitalia, fingertips, soles of feet, eyelids

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encapsulated
Pacinian corpuscles (lamellated corpuscles

L: exteroceptors, interoceptors, and some proprioceptors
S: mechanoreceptors (deep pressure, strech, vibraition of high frequency:; rapidly adapting
BL: dermis and hypodermis; periostea, mesentery, tendons, ligaments, joint capsule, most abundant on fingers, soles of feet external genitalia, nipples

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encapsulated
Ruffin i endings

L: exteroceptors and propriceptors
S: mechanoreceptors (deep pressure and stretch); slowly or nonadapting
BL: deep in dermis, hypodermis and joint capsules

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Encapsulated
Muscle spindles

L: proprioceptors
S: mechanoreceptors (muscle stretch, lenghth
BL: skeletal muscle, particularly those of the extermities

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Golgi tendon organs

L: proprioceptors
S: mechanoreceptors (tendon stretch, tension)
BL: Tendons

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Joint Kinesthetic receptors

L: proprioceptors
S: mechanoreceptors and nociceptors
BL: joint capsules of synovial joints

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Receptor potential

its like graded potential that can be depolarizing or hyperpolarizing they are similar to the EPSPs or IPSPs which are generated at postsynaptic membranes in response to neruotransmitter binding

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generator potentials

membran depolarization that summate and directly lead to generation of anction potentials in an afferent fiber are GP

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Adaptation

a change in sensitivity and nerve impulse generation in the presence of a constant stimulus

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Phasic receptors

are fast adapting, often giving bursts of impulses at the beginning and at the end of the stimuls the just work to report the changes inside or outside the body

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Tonic receptors

provide a sustained response with little or no adaptation, Nociceptors and most proprioceptors are tonic receptor because of the protective importance of their information

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perceptual detection

ability to detect a stimulus (requires summation of impulses)

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Magnitude estimation

intensity is coded in the frequency of impulses

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Spatial discrimination

identifying the site or pattern of the stimulus (studied by the two-point discrimination test)

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First-order neurons

Conduct impulses from the receptor level to the

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second-order neurons in the CNS
Second-order neurons

Transmit impulses to the thalamus or cerebellum

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Third-order neurons

Conduct impulses from the thalamus to the somatosensory cortex (perceptual level)

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Feature abstraction

identification of more complex aspects and several stimulus properties

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Quality discrimination

the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)

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Pattern recognition

ecognition of familiar or significant patterns in stimuli (e.g., the melody in a piece of music)

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Perception of Pain

Warns of actual or impending tissue damage
Stimuli include extreme pressure and temperature, histamine, K+, ATP, acids, and bradykinin
Impulses travel on fibers that release neurotransmitters glutamate and substance P
Some pain impulses are blocked by inhibitory endogenous opioids

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:
Endoneurium

loose connective tissue that encloses axons and their myelin sheaths

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PERINEURIUM

coarse connective tissue that bundles fibers into fascicles

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Epineurium

tough fibrous sheath around a nerve

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REGENERATION OF A NERVE FIBER INA PERIPHERAL NERVE

1. the axon becomes fragmented at the injury site.
2. macrophages clean out the dead axon distal to the injury
3. axon sprouts, or filaments, grow through a regeneration tube formed by schwann cells
4. the axon regenrates and a new myelin sheath forms.

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I: The Olfactory Nerves

Arise from the olfactory receptor cells of nasal cavity
Pass through the cribriform plate of the ethmoid bone
Fibers synapse in the olfactory bulbs
Pathway terminates in the primary olfactory cortex

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II: The Optic Nerves

Arise from the retinas
Pass through the optic canals, converge and partially cross over at the optic chiasma
Optic tracts continue to the thalamus, where they synapse
Optic radiation fibers run to the occipital (visual) cortex

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III: The Oculomotor Nerves

Fibers extend from the ventral midbrain through the superior orbital fissures to the extrinsic eye muscles
Functions in raising the eyelid, directing the eyeball, constricting the iris (parasympathetic), and controlling lens shape

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IV: The Trochlear Nerves

Fibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle
Primarily a motor nerve that directs the eyeball

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V: The Trigeminal Nerves

Largest cranial nerves; fibers extend from pons to face
Three divisions
Ophthalmic (V1) passes through the superior orbital fissure
Maxillary (V2) passes through the foramen rotundum
Mandibular (V3) passes through the foramen ovale
Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

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VI: The Abducens Nerves

Fibers from the inferior pons enter the orbits via the superior orbital fissures
Primarily a motor, innervating the lateral rectus muscle

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VII: The Facial Nerves

Fibers from the pons travel through the internal acoustic meatuses, and emerge through the stylomastoid foramina to the lateral aspect of the face
Chief motor nerves of the face with 5 major branches
Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands
Sensory function (taste) from the anterior two-thirds of the tongue

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VIII: The Vestibulocochlear Nerves

Afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla border
Mostly sensory function; small motor component for adjustment of sensitivity of receptors

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IX: The Glossopharyngeal Nerves

Fibers from the medulla leave the skull via the jugular foramen and run to the throat
Motor functions: innervate part of the tongue and pharynx for swallowing, and provide parasympathetic fibers to the parotid salivary glands
Sensory functions: fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors

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X: The Vagus Nerves

Fibers from the medulla exit the skull via the jugular foramen
Most motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal viscera
Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx

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XI: The Accessory Nerves

Formed from ventral rootlets from the C1–C5 region of the spinal cord (not the brain)
Rootlets pass into the cranium via each foramen magnum
Accessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid muscles

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XII: The Hypoglossal Nerves

Fibers from the medulla exit the skull via the hypoglossal canal
Innervate extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speech

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Segmental Level

The lowest level of the motor hierarchy
Central pattern generators (CPGs): segmental circuits that activate networks of ventral horn neurons to stimulate specific groups of muscles

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Projection Level

Consists of:
Upper motor neurons that direct the direct (pyramidal) system to produce voluntary skeletal muscle movements
Brain stem motor areas that oversee the indirect (extrapyramidal) system to control reflex and CPG-controlled motor actions

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Precommand Level

Neurons in the cerebellum and basal nuclei
Regulate motor activity
Precisely start or stop movements
Coordinate movements with posture
Block unwanted movements
Monitor muscle tone

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Reflexes

Inborn (intrinsic) reflex: a rapid, involuntary, predictable motor response to a stimulus
Learned (acquired) reflexes result from practice or repetition,

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Spinal Reflexes

Spinal somatic reflexes
Integration center is in the spinal cord
Effectors are skeletal muscle
Testing of somatic reflexes is important clinically to assess the condition of the nervous system

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Stretch and Golgi Tendon Reflexes

For skeletal muscle activity to be smoothly coordinated, proprioceptor input is necessary
Muscle spindles inform the nervous system of the length of the muscle
Golgi tendon organs inform the brain as to the amount of tension in the muscle and tendons

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Muscle Spindles

Composed of 3–10 short intrafusal muscle fibers in a connective tissue capsule
Intrafusal fibers
Noncontractile in their central regions (lack myofilaments)
Wrapped with two types of afferent endings: primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers

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Excited in two ways:
External stretch of muscle and muscle spindle
Internal stretch of muscle spindle:
Activating the  motor neurons stimulates the ends to contract, thereby stretching the spindle
Stretch causes an increased rate of impulses in Ia fibers

Muscle Spindles

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Stretch Reflexes

Maintain muscle tone in large postural muscles
Cause muscle contraction in response to increased muscle length (stretch)
How a stretch reflex works:
Stretch activates the muscle spindle
IIa sensory neurons synapse directly with  motor neurons in the spinal cord
 motor neurons cause the stretched muscle to contract
All stretch reflexes are monosynaptic and ipsilateral

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Golgi Tendon Reflexes

Polysynaptic reflexes
Help to prevent damage due to excessive stretch
Important for smooth onset and termination of muscle contraction

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Produce muscle relaxation (lengthening) in response to tension
Contraction or passive stretch activates Golgi tendon organs
Afferent impulses are transmitted to spinal cord
Contracting muscle relaxes and the antagonist contracts (reciprocal activation)
Information transmitted simultaneously to the cerebellum is used to adjust muscle tension

Golgi Tendon Reflexes

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Flexor and Crossed-Extensor Reflexes

Flexor (withdrawal) reflex
Initiated by a painful stimulus
Causes automatic withdrawal of the threatened body part
Ipsilateral and polysynaptic

Crossed extensor reflex
Occurs with flexor reflexes in weight-bearing limbs to maintain balance
Consists of an ipsilateral flexor reflex and a contralateral extensor reflex
The stimulated side is withdrawn (flexed)
The contralateral side is extended