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Mammalian Physiology I > The Peripheral Nervous System > Flashcards

The Peripheral Nervous System Flashcards

1
Q

what are afferent neurons

A

neurons that carry nerve impulses from the peripheral receptors and special sense organs to the CNS

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2
Q

where are afferent nerve cell bodies found

A

in clusters called ganglia immediately external to the spine

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3
Q

what is transduction

A

the conversion of an environmental signal to an electrical signal

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4
Q

what four properties do afferent neurons use to differentiate incoming signals from the PNS

A
  • modality: each type of receptor is specialized to respond to a different stimulus
  • intensity: stronger signals have increased frequency of action potentials
  • location: the site of sensory stimulation
  • duration: length of time action potentials were firing
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5
Q

what are the four types of receptors

A
  • photoreceptors
  • mechanoreceptors
  • thermoreceptors
  • chemoreceptors
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6
Q

what are the three ways neurons can encode the location of a stimulus

A
  • receptive field: each neuron has a region of the environment it is sensitive to
  • multiple receptors: comparing inputs from more than one sensor
  • gradients: intensity increasing towards source
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7
Q

what is a receptor potential and how does it differ from a generator potential

A

receptor potentials are caused by an alteration of membrane permeability in specialized receptor cells causing the opening of nonselective cation channels, generator potentials occur in the ending of an afferent neuron

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8
Q

how do receptor potentials occur in separate receptor cells

A

when receptor potential is strong enough it releases a chemical messenger that diffuses to the afferent neuron opening chemically gated sodium channels , when threshold is achieved the nerve fibre initiates an action potential

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9
Q

what receptors are able to adapt, and how?

A
  • tonic receptors slowly adapt (if at all) and are important in situations with a near-constant stimulus (eg muscle stretching)
  • phasic receptors rapidly adapt after the initial stimulus to stop generating rapid action potentials in the presence of a stimulus, until the stimulus is removed (wearing a watch)
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10
Q

what are the three groups of nociceptors (pain receptors)

A
  • mechanical: respond to physical damage (eg cutting)
  • thermal: respond to temperature (eg heat)
  • chemical: respond to noxious chemicals (internal/external)
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11
Q

what are the differences between fast and slow pain fibres?

A
  • fast pain fibres (A-delta fibres) respond to stimuli causing acute/sharp/stabbing pain
  • slow pain fibres (C-fibres) are unmyelinated and can activate polymodal receptors causing burning/aching/throbbing sensations
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12
Q

what is bradykinin

A

a chemical activated by enzymes released from damaged cells that directly stimulate nociceptors

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13
Q

how does the brain process pain

A
  • the action potential triggers a release of neurotransmitters (substance P and glutamate)
  • the reticular formation increases alertness to painful stimulus
  • the thalamus processes and perceives pain
  • the hypothalamus/limbic system allow for behavioural and emotional response
  • the cortex (cortical somatosensory) localizes pain to a discrete body region
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13
Q

how does the brain process pain

A
  • the action potential triggers a release of neurotransmitters (substance P and glutamate)
  • the reticular formation increases alertness to painful stimulus
  • the thalamus processes and perceives pain
  • the hypothalamus/limbic system allow for behavioural and emotional response
  • the cortex (cortical somatosensory) localizes pain to a discrete body region
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14
Q

what is glutamate and explain the difference between AMPA and NMDA receptors

A

an amino acid that also functions as a neurotransmitter with two actions depending on the type of receptor that is activated
AMPA receptors generate action potentials in the dorsal horn neuron and send the signal to higher centres
NMDA receptors activate a second messenger pathway resulting in a more excitable neuron (highly sensitive to stimuli)

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15
Q

how does the perception of pain change when taking an exogenous opioid

A

the opioid activates the receptors resulting in a suppression of neurotransmitters (from A-delta fibres) being released decreasing the perception of pain

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16
Q

explain the key differences between pupillary constriction and pupillary dilation

A
  • pupillary constriction is caused by parasympathetic stimulation smooth muscles in a circular shape constrict the pupil
  • pupillary dilation is caused by sympathetic stimulation smooth muscles in a radial organization contract to dilate the pupil
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17
Q

what happens when light passes through transparent media that has a different density from air

A

the wavelength decreases, and unless it enters perpendicularly it will refract (change direction)

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18
Q

what are the two refractive structures of the eye

A
  • the cornea has a large density difference (air-cornea boundary) that contributes to its significant refractive ability (constant)
  • the lens is a convex structure allowing it to further focus light rays on the retina (adjustable)
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19
Q

what controls the eye’s ability to adjust and focus

A

the ciliary muscle and suspensory ligaments (relaxed muscle = less convex)

20
Q

what are the three layers of excitable cells in the retina

A
  • the photoreceptors are rods (vision in low light) and cones (sensitive to colour)
  • bipolar cells transmits signals from rods/cones to ganglion cells
  • ganglion cells are the neurons at the inner surface of the retina (axons are the optic nerve)
21
Q

what are the three ways we define sound waves

A

pitch, intensity, and timbre (quality)

22
Q

what are the three structures of the external ear

A
  • pinna is cartilage that collects sound wave
  • the ear canal conducts the sound waves to the tympanic membrane
  • the tympanic membrane stretches across the entrance to the middle ear and vibrates when hit by sound waves
23
Q

what are the three bones of the middle ear

A

the malleus, incus, and stapes

24
Q

what are the key anatomical structures of the inner ear

A
  • the cochlea (responsible for the perception of hearing) is spiral-shaped to help determine pitch
  • the Organ of Corti (sense organ) and the basilar membrane contain hair cells (when deformed generate neuronal signals)
  • the inner hair cells transform fluid vibrations into action potentials sending auditory messages to the cortex (changes in membrane pot. match frequency)
  • the outer hair cells DO NOT TRANSMIT SOUND TO BRAIN they modify electrical signalling of the inner hair cells enhancing their response
25
Q

what allows us to discriminate pitch

A

the shape of the basilar membrane

26
Q

what is the function of the vestibular apparatus

A

detect changes in head movement which is essential for equilibrium and coordination (sensitive vestibular apparatus causes motion sickness) helps maintain balance and posture, allows eyes to remain fixed when turning head, perceives motion and orientation

27
Q

where are signals from the vestibular apparatus sent

A

to vestibular nuclei in the brainstem and to the cerebellum

28
Q

what senses rely on chemoreceptors

A

taste and smell (unique because they can trigger appetite and the release of digestive juices) are very important as they act as quality control system for ingestion

29
Q

where are the chemoreceptors that sense taste housed?

A

the tongue, oral cavity, and throat

30
Q

what are taste buds?

A

clusters of nerve endings on the tongue that exists in groups of a hundred taste buds (papillae) each taste bud is made of about 50 taste receptor cells (and supporting cells)

31
Q

what occurs in taste receptor cells when you consume something?

A

ion channels create a depolarizing potential which can initiate an action potential in the nerve endings of afferent neurons

32
Q

describe the process of olfaction

A

chemicals that can be smelled (odourants) dissolve in the mucous layer and interact with cilia on the olfactory receptor cells (activated G proteins and mobilizes the second messenger cAMP causing depolarizing - action potential

33
Q

what two neurotransmitters are used in the efferent division of the PNS

A

acetylcholine and norepinephrine

34
Q

what are the two subcategories of the efferent division of the PNS

A

the autonomic and somatic nervous systems

35
Q

what structures are influenced by the somatic nervous system compared to the autonomic nervous system

A
  • somatic: skeletal muscles
  • autonomic: smooth/cardiac muscle exo/endocrine glands (not all)
36
Q

what are the two divisions of the autonomic nervous system

A
  • sympathetic: fight or flight response (adrenal medulla produces hormones ie epinephrine)
  • parasympathetic: rest and digest
37
Q

describe the autonomic nerve pathway

A

two neuron chain connecting the CNS to the effector

38
Q

For both the sympathetic and parasympathetic nervous systems answer each of these
a) is the preganglionic fibre short or long?
b) is the postganglionic fibre short or long?
c) what neurotransmitter is released from pre - fibre?
d) what neurotransmitter is released from post - fibre?
e) what is the fibre type?

A

Sympathetic Parasympathetic
a) short long
b) long short
c) ACh ACh
d) NE and E ACh
e) adrenergic cholinergic

39
Q

what is dual innervation

A

almost all effector organs receive input from both the sympathetic and parasympathetic systems

40
Q

what is the role of the adrenal glands in the ANS

A

when stimulated the adrenal medulla releases hormones into the blood to be circulated

41
Q

what are the two main classes of receptors for the ANS

A
  • cholinergic receptor is on the membrane of cells that respond to acetylcholine
  • a G-protein coupled receptor in the membrane of cells that respond to nor/epinephrine (catecholamine neurotransmitters)
42
Q

what are the two types of cholinergic receptors?

A
  • muscarinic receptors are activated by ACh and muscarine and create a depolarizing potential
  • nicotinic receptors are activated by nicotine and ACh
43
Q

what are the two types of adrenergic receptors?

A
  • alpha receptors have sensitivity to both E and NE
  • beta receptors (B2) has a greater affinity for E but (B1) responds equally to both
    -adrenergic receptors activate G proteins
  • epinephrine is circulated through the system and is classified as a2, B1, and B2 receptors
  • norepinephrine is released locally and is classified as a1 and a2 receptors
44
Q

what are the key differences between the Alpha and Beta-adrenergic receptors?

A
  • a1 are excitatory and expressed in smooth muscle cells of blood vessels causing contraction, a2 are the smooth muscles of the digestive tract and cause decreased contraction
  • b1 receptors are excitatory and found in heart muscle, b2 receptors are inhibitory and found in smooth muscle cells of the respiratory airway
45
Q

describe the pathway of motor signals

A

muscle - lower motor neuron (ventral horn) - lateral column - upper motor neuron - motor cortex

46
Q

describe steps of the neuromuscular junction

A
  • an action potential in a motor neuron is propagated to the terminal button
  • causes voltage Ca channels to open (Ca enters button) triggering the exocytotic release of acetylcholine
  • Ach binds to nicotinic receptors on the motor plate opening cation channels depolarizing the membrane potential
  • the depolarizing effect influences the muscle membrane opening voltage-gated Na channels until the muscle fibre reaches the threshold and contracts
47
Q

what are three ways the neuromuscular junction can be compromised

A
  • black widow spider venom causes a prolonged depolarization due to the explosive release of ACh which inactivates the Na channels so no muscle contraction can occur
  • the botulinum toxin blocks ACh release so skeletal muscles cannot be excited
  • curare binds to the ACh receptors so that the muscle can not accept ACh and therefore the muscle cannot be excited

Mammalian Physiology I (3 decks)

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