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Flashcards in Chapter 16 Deck (92):
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sensation

conscious or subconscious awareness of changes in the external or internal environment

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perception

conscious awareness and interpretation of sensations; primarily a function of the cerebral cortex

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sensory modality

each unique type of sensation i.e. touch, pain, vision or hearing

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general senses

refers to both somatic and visceral senses

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somatic senses

includes tactile senses (touch, pressure, vibration, itch, tickle), thermal sensations (warm and cold), pain sensations and proprioceptive sensations (perception of static and moving positions of the body)

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visceral senses

provide info about conditions within internal organs (i.e. pressure, stretch, chemicals, nausea, hunger and temperature)

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special senses

include the sensory modalities of smell, taste, vision, hearing and equilibrium/balance

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process of sensation (4 steps)

1. Stimulation of a sensory receptor
2. Transduction of the stimulus (converts energy into a stimulus into a graded potential)
3. Generation of nerve impulses
4. Integration of sensory input

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3 ways to classify sensory receptors

1. microscopic structure
2. location of the receptors and origin of stimuli that activate them
3. type of stimulus detected

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3 classifications based on microscopic structure

1. free nerve endings of first order sensory neurons
2. encapsulated nerve endings of first order sensory neurons
3. separate cells that synapse with first order sensory neurons

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free nerve endings

bare dendrites; lack any structural specializations that can be seen under a microscope; i.e. pain, temperature, tickle, itch and some touch sensations

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encapsulated nerve endings

dendrites enclosed in connective tissue capsule ; a distinctive microscopic structure; i.e. somatic and visceral sensations (pressure, vibration and some touch sensations)

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separate cells

synapse with sensory neurons; i.e. hair cells for hearing and equilibrium in the inner ear; gustatory receptor cells in taste buds and photoreceptors in the retina in the eye for vision

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generator potential

a potential created by stimulation of dendrites of free nerve endings, encapsulated nerve endings and receptive part of olfactory receptors; if the potential is big enough to reach threshold, it triggers one or more nerve impulses in the axon of a first order sensory neuron

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receptor potential

produced by sensory receptors that are separate cells; the potential triggers release of NT through exocytosis of synaptic vesicles

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3 classifications based on location

Exteroceptors, Interoceptors and Proprioceptors

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Exteroceptors

located at or near the external surface of the body; sensitive to stimuli originating outside the body; provide info about external environment; i.e. hearing, vision, smell, taste, touch, pressure, pain etc.

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interoceptors/ visceroceptors

located in blood vessels, visceral organs, muscles and nervous system; monitor conditions of internal environment; nerve impulses produced by interoceptors are not consciously received unless strong stimuli (can be felt as pain or pressure)

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proprioceptors

located in muscles, tendons, joints and the inner ear; provide info about body position, muscle length and tension and the position and movement of joints

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6 classifications based on type of stimulus detected

Mechanoreceptors, thermoreceptors, nociceptors, photoreceptors, chemoreceptors and osmoreceptors

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mechanoreceptors

detect mechanical stimuli; provide sensations of touch, pressure, vibration and proprioception and hearing and equilibrium; monitor stretching of blood vessels and internal organs

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thermoreceptors

detect changes in temperature

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nociceptors

respond to painful stimuli resulting from physical or chemical damage to tissue; free nerve endings; found in every tissue of the body except the brain

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photoreceptors

detect light that strikes the retina of the eye

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chemoreceptors

detect chemicals in the mouth (taste), nose (smell) and body fluids

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osmoreceptors

sense osmotic pressure of body fluids

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rapidly adapting receptors/ phasic receptor

adapt very quickly; specialized for signaling changes in a stimulus; i.e. receptors associated with pressure, touch, and smell

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slowly adapting receptors/ tonic receptor

adapt slowly; continue to trigger nerve impulses as long as the stimulus persists; monitor stimuli associated with pain, body position and chemical composition of the blood

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tactile sensations

include touch, pressure, vibration, itch and tickle

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touch

result from stimulation of tactile receptors in the skin or subcutaneous layer

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Meissner Corpuscles

rapidly adapting touch receptor; located in the dermal papillae of hairless skin; consists of egg shaped mass of dendrites enclosed by a capsule of connective tissue; abundant in fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles, clitoris and tip of the penis

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hair root plexuses

rapidly adapting touch receptors; found in hairy skin; consist of free nerve endings wrapped around hair follicles; detect movements on the skin that disturb hairs

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Type I cutaneous mechanoreceptor or Merkel disc

slowly adapting touch receptor; saucer shaped, flattened free nerve endings that make contact with Merkel cells of the stratum basale; plentiful in fingertips, hands, lips and external genitalia

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type II cutaneous mechanoreceptor or Ruffini corpuscle

slowly adapting touch receptor; elongated, encapsulated receptors; located deep in the dermis and in ligaments and tendons; found in hands, abundant in soles; most sensitive to stretching that occurs when digits or limbs are moved

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pressure

sustained sensation felt over a larger area than touch; occurs with a deformation of deeper tissues; receptors: meissner corpuscles, merkel discs and pacinian corpuscles

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lamellated or Pacinian corpuscle

rapidly adapting receptor; large oval structure composed of a multilayered connective tissue capsule that encloses a dendrite; found in dermis and subcutaneous layer, submucosal tissues that underlie mucous and serous membranes, around joints, tendons and muscles, in the periosteum, mammary glands, external genitalia, certain viscera (i.e. pancreas and urinary bladder)

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vibration

result from rapidly repetitive sensory signals from tactile receptors; receptors: meissner corpuscles (detect lower frequency vibrations), pacinian corpuscles (detect higher frequency vibrations)

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itch

sensation resulting from stimulation of free nerve endings by certain chemicals (i.e. bradykinin or antigens in mosquito saliva)

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tickle

arises only when someone else touches you

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phantom limb sensation

patients who have had a limb amputated may still experience sensation such as itching, pressure, tingling or pain as if the limb were still there; severed nerve endings of sensory axons are still present in the remaining stump, if these are activated, the cerebral cortex interprets the sensations as coming from sensory receptors in the non existing limb

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cold receptors

rapidly adapting receptor; located in the stratum basale of the epidermis; temperatures between 10 and 40 degrees celsius

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warm receptors

rapidly adapting receptor; not as abundant as cold receptors; located in dermis; activated by temperatures between 32 and 48 degrees celsius

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2 types of pain

fast pain and slow pain

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fast pain

peception occurs very rapidly; occurs within 0.1 of a second after stimulus is applied; aka acute, sharp or prickling pain; not felt in deeper tissues of the body

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slow pain

perception is slow; occurs a second or more after the stimulus is applied; gradually increases in intensity over a period of several seconds or minutes; aka chronic, burning, aching or throbbing pain; can occur in both the skin and in deeper tissues or internal organs

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superficial somatic pain

pain that arises from stimulation of receptors in the skin

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deep somatic pain

pain that arises from stimulation of receptors in skeletal muscles, joints, tendons and fascia

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visceral pain

results from stimulation of nociceptors in visceral organs

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localization of pain

fast pain is precisely localized to the stimulated area; somatic slow pain is well localized but more diffuse (involves larger areas)

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referred pain

in many instances of visceral pain, the pain is felt in or just deep to the skin that overlies the stimulated organ, or in a surface area far from the stimulated organ

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kinesthesia

perception of body movement

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proprioceptor

embedded in muscles and tendons; inform us of the degree to which muscles are contracted, the amount of tension in tendons and the positions of joints

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muscle spindle

proprioceptors in skeletal muscles that monitor changes in length of skeletal muscles and participate in stretch reflexes; consists of several slowly adapting sensory nerve endings wrapped around 3-10 specialized muscle fibres

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intrafusal muscle fibres

specialized muscle fibres

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gamma motor neurons

motor neurons contained within muscle spindles

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extrafusal muscle fibres

skeletal muscle fibres surrounding muscle spindles

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alpha motor neurons

large diamter A fibres that supply extrafusal muscle fibres

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tendon organ

located at the junction of a tendon and a muscle

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joint kinesthetic receptor

present within and around the articular capsules of synovial joints; receptors: free nerve endings, Pacinian Corpuscles, tendon organs and Ruffini Corpuscles; function: joint position and movement; rapid adapting

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somatic sensory pathways

relay info from the somatic sensory receptors to the primary somatosensory area in the cerebral cortex and to the cerebellum

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first order neurons

conduct impulses from somatic receptors to the brain stem or spinal cord;

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second order neurons

conduct impulses from the brain stem and spinal cord to the thalamus

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third order neurons

conduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side

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posterior column—medial lemniscus pathway to the cortex

The name of the pathway comes from the names of two white-matter tracts that convey the impulses: the posterior column of the spinal cord and the medial lemniscus of the brain stem

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anterolateral or spinothalamic pathways to the cortex

Nerve impulses for pain, temperature, itch, and tickle from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex

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upper motor neuron

synapse with local circuit neurons, which in turn synapse with lower motor neurons; voluntary movements of the body; originate motor centres of the brain stem; page 620 diagram

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lower motor neuron

receive input directly from local circuit neurons and upper motor neurons in the cerebral cortex; page 620 diagram

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primary motor area

located in precentral gyrus of the frontal lobe of the cerebral cortex; major control region for the execution of voluntary movements

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direct motor pathways or pyramidal pathways

provide input to lower motor neurons via axons that extend directly from the cerebral cortex; page 624

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indirect motor pathways or extrapyramidal pathways

provide input to lower motor neurons from motor centres in the basal nuclei, cerebellum and cerebral cortex page 624

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roles of the basal nuclei with regard to movement

initiation and termination of movements; suppress unwanted movements by their inhibitory effects on the thalamus and superior colliculus; influence muscle tone; influence many aspects of cortical function (sensory, limbic, cognitive and linguistic function)

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roles of the cerebellum with regard to movement

monitoring intentions for movement; monitoring actual movement; comparing command signals with sensory information; sending out corrective feedback

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circadian rhythm

24 hour sleep and wake cycle for humans; established by the suprachiasmatic nucleus of the hypothalamus

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reticular activating system (RAS)

When this area is active, many nerve impulses are transmitted to widespread areas of the cerebral cortex, both directly and via the thalamus. The effect is a generalized increase in cortical activity.

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arousal

awakening from sleep; involves increased activity in the RAS; RAS must be stimulated (by nociceptors, touch and pressure on the skin, movements of the limbs, bright light, sound)

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consciousness

a state of wakefulness that is the result of arousal

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sleep

state of altered consciousness/ partial unconsciousness from which an individual can be aroused; consists of NREM sleep (non rapid eye movement) and REM sleep

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4 stages of NREM sleep

non rapid eye movement;
1. transition stage between wakefulness and sleep (lasts between 1-7 mins)
2. light sleep (fragments of dreams, more difficult to awaken)
3. moderately deep sleep (body temp and blood pressure decrease; difficult to awaken; occurs 20 mins after falling asleep)
4. deep sleep (brain metabolism decreases significantly; if sleep walking occurs, it's during this stage)

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REM sleep

rapid eye movements; 3-5 episodes of REM sleep per 7-8 hour sleep

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learning

ability to acquire new info or skills through instruction or experience

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memory

process by which info acquired through learning is stored and retrieved

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plasticity

capability for change associated with learning

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immediate memory

ability to recall ongoing experiences for a few seconds

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short term memory (STM)

temporary ability to recall a few pieces of info for seconds to minutes; can be transferred to LTM

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LTM

lasts days to years; more permanent memory; can be retrieved for use when needed

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memory consolidation

reinforcement that results from the frequent retrieval of a piece of info

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long term potentiation (LTP)

transmission at some synapses within the hippocampus is en- hanced (potentiated) for hours or weeks after a brief period of high-frequency stimulation

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Parkinson Disease

progressive disorder of the CNS that typically affects its victims around the age 60

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Cerebral Palsy (CP)

motor disorder that results in the loss of muscle control and coordination; caused by damage of the motor areas of the brain during fetal life, birth or infancy

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insomnia

difficulty falling asleep or staying asleep; causes: stress, excessive caffeine, disruption of circadian rhythms and depression

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narcolepsy

condition in which REM sleep cannot be inhibited during waking periods resulting in involuntary periods of sleep that last about 15 mins throughout the day

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sleep apnea

disorder where a person repeatedly stops breathing for 10 or more seconds while sleeping; cause: loss of muscle tone in pharyngeal muscles allows the airway to collapse