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Physiology Flashcards

1
Q

Give examples of some of the viruses that exploit retrograde transport to infect neurones

A

Herpes, polio, rabies

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2
Q

What are the 4 functional regions of a neuron?

A

Input

Integrative

Conductile

Output

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3
Q

What ions are responsible for the AP in neurones?

A

Na is responsible for the upstroke

K is responsible for the downstroke

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4
Q

How can passive current spread be increased?

A

By decreasing the axon resistence- possible by increasing axon diameter

Increasing membrane resistence- done by adding an insulating material (myelin)

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5
Q

What is Saltatory conduction?

A

The propagation of action potentials along myelinated axons from one node of ranvier to the next, this increases the conduction velocity of APs

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6
Q

How might synapses be classified?

A

Morphologically- by the location of the presynaptic terminal upon the postsynaptic cell

Functionally- excitatory or inhibitory

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7
Q

What are some of the morphological classifications of synapses?

A
  • Axodendritic
  • Axosomatic
  • Axoaxonic
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8
Q

What are the major amino acid neurotransmitters in the CNS?

A

Glutamate, GABA and Glycine

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9
Q

What is excitatory post-synaptic potential EPSP?

A

An excitatory synapse e.g. Glutamate, causes the activation of poststynaptic receptors which then generates a local, depolarizing response.

Glutamate synapses leading to influx of Na which brings the membrane to threshold making an AP more likely

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10
Q

What is an inhibitory synapse?

A

Most commonly in the CNS are GABA or Glycine

The activate postsynaptic receptors which generate a graded inhibitory (hyperpolarizing) response.

  • Cl- ions influx causing the neurone to move further from threshold
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11
Q

What is spatial summation?

A

The effect of triggering an AP in a neurone from one or more presynaptic neurones

Many inputs converge upon a neuron to determine its output

Excitation occurs when more than 1 ESPS originate simultaenously at different points of the neurone

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12
Q

What is temporal summation?

A

A single input may modulate output by variation in AP frequency of that input

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13
Q

What a metatropic receptors?

A

Subtype of membrane receptors that do not form an ion channel pore but use signal transduction mechanisms- often G proteins

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14
Q

What are some dymylinating disorders and what do they do?

A

Examples include- MS and Guillain-Barre

Cause slowing or even the cessation of nerve conduction

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15
Q

What is Pruriception?

A

Itch

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16
Q

What is mechanosensation?

A

Fine discrimatory senasation- light touch, pressure, vibration, flutter and stretch

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17
Q

What is proprioception?

A

Joint and muscle position sense

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18
Q

Describe a somatosensory pathway

A

Composed of 3 neurons in a sequence- 1st, 2nd and 3rd order neuron

  • 1st- the primary sensory afferent. Picks up the sense then transports it to 2nd
  • 2nd- projection neuron. Usually in the dorsal horn of the spinal cord or brainstem nuclei.
  • 3rd- found in the thalmic nuclei and then project to the somatosensory cortex
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19
Q

What is sensory adaptation?

A

The change in sensitivity of your perception of a sensation

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20
Q

What are Tonic receptors?

A

Slow adapting receptors

Respond to the stimulus for as long as it persists and will produce a continous, high frequency of APs

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21
Q

What are phasic receptors?

A

Rapidly adapting receptors

Quickly respond to stimuli but stop responding upon continual stimulation. AP frequncy decreases during prolonged stimulation

Receptor still remains sensitive to a change in stilulus energy or removal of the stimulus

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22
Q

Describe conduction velocity

A

The rate at which an AP is conducted along an axon

There are 2 important contributing factors to conduction velocity

  • Diamter of axon
  • Insulating myelin

Large diameters and myelin favour conduction

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23
Q

What is a receptive field?

A

The target territory from which a sensory unit can be excited

RF size varies greatly and is inverseyly related to innervation density

Sensory acuity correlates inversley with RF size

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24
Q

How is 2 point discrimination tested?

A

Applying simultaenously 2 sharp point stimuli separated by a variable distance at different sites on the body.

Patient reports whether 1 point or 2 are sensed and a threshold distance between the 2 is established

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25
Q

What cutaneous receptors sense pressure?

A

Pacinian Corpuscles

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26
Q

What are Laminae of Rexed?

A

The grey matter of the spinal cord is subdivided into dorsal and ventral horns as well as 10 distinct Laminae of Rexed

The laminae are layers of neurons that perform specific functions

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27
Q

Describe the somatotopic organisation of the dorsal columns

A

The columns are made up of the medial gracile tract (fasciculus gracilis) and the lateral cuneate tract (fasciculus cuneatus)

Input to T6 and below (legs and lower trunk) travel in the gracile tract

Input from above T6 (arms and upper trunk) travel in the cuneate tract

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28
Q

What is the major route by which touch and concious proprioceptive information are carried to the cerebral cortex?

A

The Dorsal Column Medial Lemniscal Pathway

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29
Q

What is stereognosis?

A

The ability to recognise an object by feeling it

To test the patient is asked to identify a familiar object by touch alone

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30
Q

What is contrast enhancement?

A

As information is conveyed from one neurone to the next in a sensory pathway, differences in the activity of adjacent neurones is amplified

This produced contrast enhancement

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31
Q

Describe lateral inhibition

A

When one neurone is active it inhibits the activity of its neighbouring neurones via inhibitory interneurones

This works to sharpen stimulus perception

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32
Q

How is sensory information from the anterior head relayed to the brain?

A

Via the trigeminal system. Impulses originate at the terminals of CNV

The soma of the sensory neurones are located in the trigemenial sensory ganglion

The central terminals of CNV then synapse onto 2nd order neurones in the cheif sensory nucleus or spinal nucleus

These then descussate and project to the VPM nucleus of the thalamus

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33
Q

Describe the somatosensory cortex

A

Located in the post central gyrus of the parietal cortex, immeadiatley posterior to the central sulcus (SI) and adjacent to the posterior parietal cortex (SII)

SI contains Brodmann Areas (BA) 1, 2, 3a and 3b

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34
Q

How many layers does the somatosensory cortex have?

A

6 layers

Thalmic inputs to SI terminate mainly on neurones in level IV which in turn project to cells towards the surface of the cortex and deeper layers

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35
Q

What is the role of the posterior parietal cortex (SII)?

A

It recieves and integrates the information from SI and other cortical areas (visual, auditory) and sub-cortical areas (thalamus)

It deciphers the deeper meaning of the information of SI

(A key has a defined shape, size, weight, texture etc. when we feel for one in our pocket we immediately recognise it as a key not e.g. a coin without analysing it individual characteristics)

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36
Q

What are LMNs composed of?

A
  • Alpha-MNs= innervate the bulk of fibres within a muscle that generate force
  • Gamma-MNs= innervate a sensory organ within the muscle known as a muscle spindle
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37
Q

True or False?

Motor Neurones are distributed evenly within the spinal cord

A

False

There is a greater number in the cervical enlargement (C3-T1) that supplies the arm and in the lumbar enlargement (L1-L3) supplying the leg

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38
Q

What is a motor unit?

A

The alpha-MN and all the skeletal muscle fibres that it innervates forms a motor unit- the smallest functional component of the motor system

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39
Q

What is a motor neurone pool?

A

The collection of alpha-MNs that innervate a single muscle

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40
Q

What are the 3 sources of input to alpha-MN that regulate its activity?

A
  1. Central terminals of dorsal root ganglion cells whose axons innervate the muscle spindles
  2. UMNs in the motor cortex and brain stem
  3. Spinal interneurones
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41
Q

What does muscle strength depend on?

A
  • Activation of the muscle fibres
    • The firing rate of LMNs involved
    • Number of LMNs simulatenously active
    • Co-ordination of the movement
  • Force production by innervated muscle fibres
    • Fibre size (hypertrophy)
    • Fibre phenotype (fast or slow twitch)
42
Q

Describe slow-oxidative (Type 1) muscle fibres?

A

The ATP is derived from oxidative phosphorylation

Slow relaxation and contraction- fatigue resistant

43
Q

What are the subtypes of Fast (type II) muscle fibres?

A
  • Type IIa- ATP mostly from oxidative phosphorylation. Fast contraction and relaxation. Fatigue resistent
  • Type IIb, IIx- ATP from glycolysis. Fast contraction but not fatigue resistent. (Type IIb isnt in mammals)
44
Q

What is the Henneman Size Principle?

A

The susceptability of an alpha-MN to discharge APs is a function of its size.

Smaller alpha-MNs (part of slow motor units) have a lower threshold than larger ones. Slow motor units are more easily activated and ‘trained’ by any training that activates the muscle.

45
Q

What is the myotatic reflex?

A

Also called the stretch reflex- a muscle contraction in response to stretching within the muscle.

The change in length is registered by a sensory organ within the muscle- the muscle spindle.

46
Q

What is the jendrassik manouver?

A

Reinforces the myotatic reflex

Patient interlocks fingers and trys to pull their hands apart strongly when instructed. Tap patellar tendon immediately- reflex usually will be exagerated

May be employed when the reflex is apparently absent

47
Q

True or False?

The intrafusal muscle fibres are innervated by alpha-MN?

A

False

Gamma-MN innervate the intrafusal fibres (motor)

Also contain afferent neurons

The alpha-MN innervate the extrafusal fibres

48
Q

What are the subdivisions of muscle spindles?

A
  • Nuclear Bag fibres
    • Bag 1/Dynamic- very sensitive to the rate of change of muscle length. Innervated by dynamic Gamma-MNs
    • Bag 2/Static- more sensitive to the absolute length of the muscle. Innervated by static gamma-MNs
  • Chain fibres
    • Sensitive to the absolute length of the muscle. Innervated by static gamma-MNs
49
Q

What are the afferent fibres that innervate the intrafusal fibres?

A
  • Ia fibres- primary annulospiral nerve ending, winding around the centre of all intrafusal fibres
  • II fibres- more slowly conducting, form flowerspray endings on the intrafusal fibres except bag 1 dynamic types

Both sets respond to stretch but Ia are more sensitive to rate of change of stretch whereas II are more sensitve to absolute length

50
Q

Where are golgi tendon organs located?

A

At the junction of the muscle and the tendon

51
Q

What is the role of the golgi tendon organs?

A

Monitor changes in muscle tension, working in series with the extrafusal muscle fibres. Act to regulate muscle tension to;

  • Protect the muscle from overload (in extreme circumstances like weight lifting)
  • More generally regulate muscle tension to an optimal range
52
Q

What is the innervation of the golgi tendon organs?

A

Innervated by group Ib sensory afferents- myelinated, slightly slower conducting than Ia

They enter the spinal cord and synapse upon inhibitory interneurons which in turn synapse on the alpha motor neurones of the homonymous muscle, forming the basis of the reverse motonic reflex

53
Q

What does proprioceptive information arise from? (3)

A

Muscle spindles

Golgi tendon organs

Joint receptors

54
Q

What are joint receptors?

A

Proprioceptive axons found in the connective tissue of joints. Mix of fast or slow acting with either high or low thresholds for activation.

55
Q

Give examples of joint receptors (4)

A
  • Golgi type endings- found in ligaments. High threshold and slow acting. Protective role?
  • Free nerve endings- capsule and connective tissue. Most numerous. HT, SA. Noicereceptive function
  • Paciniform endings- periosteum near articular attachments and fibrous part of joint capsule. LT, SA, acceleration detectors
  • Ruffini endings- joint capsule. LT, SA, static position and speed of movements
56
Q

What do inhibitory interneurons mediate?

A

The inverse myotatic response

Reciprocal inhibition between extensor and flexor muscles

57
Q

What do excitatory interneurones mediate?

A

The flexor reflex

The crossed extensor reflex

58
Q

What is the flexor reflex?

A

Noxious stimuli cause the limb to flex by;

  • contraction of the flexor muscles via excitatory interneurones
  • Relaxation of the extensor muscles via excitatory and inhibitory interneurones
59
Q

What is the crossed extensor reflex?

A

Noxious stimuli causes the limb to extend by;

  • Contraction of the extensor muscles via excitatory interneurones
  • Relaxation of the flexor muscles via excitatory and inhibitory interneurones

This reflex enhances postural support during withdrawl of foot from a stimulus- you do not fall over

60
Q

What is a central pattern generator (CPG)?

A

A neuronal network in which interconencted inhibitory and excitatory neurones produce an oscilitating, rhythmic output in the absense of sensory feedback.

61
Q

What are the 3 levels of the motor control heirarchy?

A
  • Strategy- What is the aim of the movement? How is it best achived?
    • Neurocortical association areas, basal ganglia
  • Tactics- What sequence of muscle contractions and relaxations will fulfil the aim?
    • Motor cortex, cerebellum
  • Execution- Activation of motor pools and interneuron pools that command the desired movement and makes postural adjustments
    • Brain stem, spinal cord
62
Q

What are the pathway divisions of the descending spinal tract?

A
  • Lateral Pathways
    • Controlled by cerebral cortex
    • Voluntary control of distal musculature, particularly discreete, skilled movements
  • Venteromedial Pathways
    • Controlled by brainstem
    • Controls posture and locomotion
63
Q

What is the major lateral pathway?

A

Corticospinal (pyramidal) tract

Cell nodies are located in the motor cortex and somatosensory areas of the parietal cortex

64
Q

Where do the axons of the corticospinal tract terminate?

A

In the dorsolateral region of the ventral horn and intermediate grey, the location of the LMNs and interneurons controlling the distal muscles, particularly flexors

65
Q

What does the rubrospinal tract control?

A

Limb flexor muscles, exciting the LMNs of those muscles

66
Q

What are lesions to the lateral pathways associated with?

A
  • Loss of fractioned movement (shoulders, elbow, wrist and fingers cannot be moved independently)
  • Slowing and impairment of accuracy of voluntary movements
  • Little effect on normal posture (e.g. standing, sitting)
67
Q

What occurs if only the corticospinal tract is damaged?

A

Initially the patient will have deficits just as profound as a lesion to the lateral columns. Over time, major recovery can occur - although weakness of distal flexors and inability to independently move fingers persist.

However, such recovery is reversed if the rubospinal tract is also lesioned.

The rubospinal tract is capable of compensating significantly if the corticospinal tract is damaged

68
Q

What do the axons of the vestibulopsinal tract do?

A
  • Axons from the lateral vestibular nucleus descend ipsilaterally as the lateral vestibulospinal tract as far as the lumbar spinal cord
    • Helps to hold upright and balanced posture by facilitating extensor MNs of antigrav muscles
  • Axons from the medial vestibular nucleus descend as the medial vestibulospinal tract as far as the cervical spinal cord
    • Activate cervical spinal circuits that control neck and back muscles guiding head movements
69
Q

What does the tectospinal tract do?

A

Originated in the superior collicus which acts as a map of the external world guiding, e.g. the head and eyes to a new, important visual stimulus

70
Q

Describe the reticulospinal tracts?

A

Made up of the Pontine (medial) and medullary (lateral) reticulospinal tracts

Both arise from the reticular formation, a diffuse mesh of neurones located along the length and at the core of the brainstem

71
Q

Describe the Pontine (medial) reticulospinal tract

A
  • Descends ipsilaterally
  • Enhances the antigravity reflexes of the spinal cord
  • Helps manintain standing posture by facilitating contraction of the extensors of the lower limb
72
Q

Describe the medullary (lateral) reticulospinal tract

A
  • Descends bilaterally
  • Opposes the action of the medial tract
  • Releases antigravity muscles from reflex control
73
Q

What are the 3 organs of the inner ear that detect different sensory modalities?

A
  • Cochlea
  • Otolith organs= Saccule and Utricle (tilt and acceleration)
  • Semicircular canals (rotational movements)
74
Q

What are the 3 mechanisms for impedence matching in the middle ear?

A
  1. Area ratio of the ear drum to staped footplate (20:1)
  2. Lever action of the osiciles
  3. Buckling of the ear drum
75
Q

What are the membranes of the inner ear?

A

Reissner’s membrane- separates the scala vestibuli from the scala media

Basilar membrane- separated the scala media from the scala tympani

Organ of corti sits on basilar membrane

76
Q

True or False?

The perilymph in the scala tympani and scala vestibuli is continous

A

True

ST and SV connect at the helicotrema and so the perilymph is contious

ST meets oval window whilst the SV meets the round window

77
Q

What is unusual about the K+ current of the hair cell?

A

The K+ current is inwards

78
Q

What is Tonotopy?

A

The ability of the brain to recognise sounds of different frequency (pitch)

79
Q

What in the ear processes tonotopy?

A

The Basilar membrane- it is flexable and vibrates in sync with fluid motion

The width and flexability of the basilar membrane determines the distance a particular freqeuncy travels

80
Q

What lights do rods and cones see in?

A

Rods- see in dim light

Cones- see in normal daylight

81
Q

What is centre-surround organisation in the retina?

A

Also called lateral inhibition

Serves to emphasise areas of difference (contrast) - it sharpens the boundary between objects of different luminence

82
Q

Define pain

A

An unpleasent sensory and emotional experience, associated with actual tissue damage or described in terms of such damage

83
Q

What are the 3 forms that pain can be classified in?

A
  • Nociceptive pain- adaptive, an immediate protective response that is short lived
  • Inflammatory pain- adaptive, assists in healing and persists over days/weeks
  • Pathological pain- maladaptive, no physiological purpose and persists for months/years/lifetime
84
Q

What are some drug classes used to treat chronic pain?

A

Antidepressents, anticonvulsants, local anesthetics

85
Q

How does Nociceptive pain begin?

A

Nociceptors are specific peripheral primary sensory afferent neurones that are normally activated preferentially by an intense stimuli (e.g. thermal, mechanical, chemical) that are noxious

First order neurones that relay information to 2nd order neurones in the CNS

86
Q

What are the subtypes of nociceptor?

A

Adelta and C fibres

87
Q

Describe Adelta nociceptors

A

Mechanical/thermal nociceptors that are thinly myelinated

Repsond to noxious mechanical or thermal stimuli

Mediate first/fast pain

88
Q

Describe C-fibre Nociceptors

A

Unmyelinated nociceptors that collectively respond to all noxious stimuli (polymodal)

Mediate second or slow pain

89
Q

Describe the Nociceptive pathway

A
  • Noxious stimuli, stimulates nociceptor
  • Synapses onto 2nd order neuron in the dorsal (posterior) horn of the spinal cord
  • Travel to CNS via the Spinothalamic and Spinoreticulothalamic tracts
90
Q

True or False?

Peptidergic Noiceptor C-fibres have only afferent fibres

A

False

Have both afferent and efferent fibres

The afferent fibres transmit noiceptive information to the CNS
Efferent fibres release pro-inflammatory mediators from the peripheral terminals which contributes to neurogenic inflammation

91
Q

What is allodynia?

A

A condition where pain is caused by a stimulus that does not normally elicit pain

92
Q

Breifly outline neurogenic inflammation

A
  1. Peptides (SP and CGRP) are released from the free nerve endings of peptidergic nociceptors due to tissue damage or inflammatory mediators
  2. SP and CGRP initiate an inflammatory response leading to vasodilation, release of mediators and sensitive surrounding nociceptors
  3. Leads to primary and secondary hyperalgesia and allodynia
93
Q

Describe the character of visceral pain

A

Poorly localised with a dull, aching, throbbing character

94
Q

Where does visceral pain originate and what is it caused by?

A

Originated from receptors that cover tissues (e.g. the peritoneum or the pleura) or the walls of hollow organs

Originates from twisting, stretching, inflammation and ischaemia- but not cutting or burning

95
Q

Describe reffered pain

A

Visceral afferents from nociceptors follow sympathetic pathways before entering the dorsal horn

Some visceral and skin afferents converge upon the same spinothalamic neurones

The brain then interperets the nociceptive information arising from the viscera as originating from an area of skin, that may be distant to the internal organ

96
Q

What might visceral pain be associated with?

A

Autonomic features such as nausea, vomiting, sweating, pallor

97
Q

Describe the character of viscerosomatic pain

A

Sharp and well localised pain

98
Q

What is the gate control theory of pain?

A

The theory suggest that the spinal cord has a neurological gate that either blocks pain signals or allows them to travel to the brain

It suggests that non-painful input closes the gate, preventing pain sensation travelling to the brain

Describes how non-painful sensations can override and reduce painful sensations

99
Q

What are the major nociceptive tracts?

A

The spinothalamic tract (pain perception)

The spinoreticular tract (autonomic responses to pain, arousal, emotional responses, fear of pain)

100
Q

Describe thermosensation at the skin

A

Thermoreceptors are neurones that are sepcialised to respond to small changes in termperature

Separate neurones and their associated receptors/channels must exist to encode between warm and cold

Neurology (6 decks)

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