Chapter 4 Pns - Afferent Division: Receptor Physiology

Front 1

The PNS consists of nerve fibres that

Back 1

carry information between the CNS and other parts of the body

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Afferent division

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Sends information from internal and external environment to CNS

Front 3

What are the 3 types of afferent division?

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1. visceral afferent

2. sensory afferent

3. special senses

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Visceral afferent

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incoming pathway for information from internal viscera (organs and body cavities)

Front 5

Sensory afferent

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Somatic (body sense) sensation - sensation arising from body surface and proprioception

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Special senses include

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vision, hearing, taste, smell

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What is perception?

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Conscious interpretation of external world created by the brain from a pattern of nerve impulses delivered to it from sensory receptors

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Two types of sensory information, describe each

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1. somatic (body) sensation: arises from body surface

2. Special senses: vision, hearing, taste, smell, touch

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Types of somatic (body) sensation:

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1. somatic sensation: awareness of sensory as touch, pressure, temp, pain from body surface

2. proprioception: awareness of body input in relation to each other and surrounding

Front 10

Describe what receptors are (3)

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- structures at peripheral endings of afferent neurons

- detect stimuli (change detectable by the body)

- convert forms of energy into electrical signals (action potentials)

Front 11

Converting forms of energy into electrical signals (actions potentials) is a process called

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Transduction

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6 types of receptors and describe each?

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1. photorecpetors: responsive to visible wavelengths of light

2. mechanorecptors: sensitive to mechanical energy

3. thermoreceptors: sensitive to heat and cold

4. osmoreceptors: detect changes in concentration of solutes in body fluids and resultant changes in osmotic activity

5. chemoreceptors: sensitive to specific chemicals

6. nociceptors: pain receptors that are sensitive to tissue damage or distortion of tissue

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Chemoreceptors include receptors for:

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smell and taste and receptors that detect O2 and CO2 concentrations in blood and chemical content of digestive trate

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Processing of sensory input by reticular activating system (RAS) in brain stem is critical for

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cortical arousal and consciouness

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Use of information detected by receptors (3)

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- afferent input essential for control of efferent output

- sensory input by RAS is critical for cortical arousal/consciousness

- selected info delivered to CNS can be stored for further reference

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What is adaption?

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despite the sustained or same intensity of stimulus, some receptors have the ability to diminish their depolarization

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Types of receptors according to their speed of adaption,briefly describe each

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1. tonic

2. phasic

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Characteristics of Tonic receptors

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1. do not adapt to the stimulus at all of adapt slowly

2. receptors play an important role in situations where maintained information about a stimulus is valuable

3. despite of non-adaption, they continue to generate action potentials to relay information to the CNS

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Examples of tonic receptors

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1. stretch receptors: monitors muscle and joint strength

2. proprioceptors: measures degree of joint flexion (provides CNS with degree of muscle length)

Front 20

What does the CNS do to maintain posture and balance

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Continuously informs the degree of muscle length and joint position

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Slow adapting receptors are

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tonic

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Fast adapting receptors are

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phasic

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Characteristics of phasic receptors (3)

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- no longer respond to maintained stimulus

- upon removal of stimulus, receptors respond with slight depolarization as off response

- useful in situation where it's important to signal the change in stimulus intensity rather than to relay status quo information

Front 24

Give an exampled of off response

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Due to rapid adaptation of phasic receptors, person is not aware of wearing items such as watch, rings and clothing. When items are taken off, person is aware of its removal due to off response

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Example of phasic receptor

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touch (tectile): located on the skin and respond to change pressure change in skin

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Characteristics of the RAS (4)

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- network of interconnected neurons spread throughout the entire brainstem and into thalamus

- consists of ascending and descending fibres that carry signals upward to arouse and activate the cerebral cortex

- controls overall degree of cortical alertness and directs attention

- centers within RAS are responsible for sleep

Front 27

The cerebral cortex(3)

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- thin outer shell of gray matter of each hemisphere

- composed of thick central core white matter

- contains basal nuclei within white matter

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4 lobes of cerebral cortex

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frontal, parietal, occipetal, temporal

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Functions of the cerebral cortex: (5)

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1. sensory perception

2. voluntary control movement

3. language

4. personality traits

5. sophisticated mental events: thinking, memory, decisions making, creativity adn self conciousnes

Front 30

How much of the cerebral cortex areas account for motor, sensory and language? What are the remaining ares called?

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50%, the remaining areas are called the association areas

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Association areas includes

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1. prefrontal association cortex

2. parietal-temporal-occipetal associatio cortex

3. limbic association cortex

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1. Location of the prefrontal association cortex

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located in frontal lobe, just anterior of premotor cortex

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Functions of the prefrontal association cortex(5)

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- planning for voluntary activity

- decision making

- creativity

- personality traits

- serve as a "working memory" temporarily stores and actively manipulates information used inreasoning and planning

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Location of the parietal-temporal-occipetal association cortex?

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found at the interface of 3 lobes

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Functions of the parietal-temporal-occipetal association cortex (2)

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1. pools and integrates somatic, auditory and visual sensations for processing

2. combines the complete picture of the various parts of the bodies with the external world (ex:integrates visual information on position of bottle)

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Location of limbic association cortex:

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mostly on the bottom and adjoining inner portion of each temporal lobe

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Functions of the limbic association cortex (2)

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1. concerned with motivation, emotion and memory

2. integrates diverse information for purposeful action

Front 38

Conversion of receptor potential into action potential

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chemical messenger released from a separates receptor initiates an action potential in the fibre by opening chemically gated Na+ channels

Front 39

Conversion of generator potentials into action potentials

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local current flow between the depolarized receptor ending and the afferent fibre initiates an action potential in the fibre by opening voltage-gated Na+ channels