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Physiology Flashcards

1
Q

List all regions of a neurone

A 
Dendrites 
Cell body - soma 
Axon hillock 
Axon 
Synapse
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2
Q

What are the functions of the dendrites

A

Receive inputs from other neurones and convey graded electrical signals passively to the soma

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3
Q

What are the functions of the cell body

A

Contains the nucleus, mitochondria, ribosomes etc

Integrates the incoming electrical signals and conducts them passively to the axon hillock

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4
Q

What is the function of the axon hillock

A

Site of initiation of the ‘all or none’ action potential

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5
Q

What is the function of the axon

A

Conducts the action potentials to the presynaptic terminal

Mediates transport of materials between the soma and presynaptic terminal

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6
Q

What is the function of the synapse

A

It is the point of chemical communication between neurones

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7
Q

Describe unipolar neurones

A

Has one process (neutrite) arising from the cell body

Peripheral autonomic neurones have this structure

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8
Q

Describe pseudounipolar neurones

A

One process from the cell body but it bifurcates and can supply different areas
Dorsal root ganglion neurones have this structure

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9
Q

Describe bipolar neurones

A

Has two processes from the cell body - receiving and outgoing
Retinal bipolar neurones are an example

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10
Q

Describe multipolar neurones

A

Have 3 or more processes contacting the cell body
Larger neurones that integrate info from larger areas
Lower motor neurones have this structure

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11
Q

Describe the initiation of an action potential

A

All neurones have a resting potential
A depolarising stimulus occurs which makes the potential more positive
If it reaches the threshold the AP is triggered
Rapid sodium influx occurs = depolarization and upward stroke
Then K+ channels allow K efflux and the potential becomes negative again - downstroke
The neurone then rebalances itself to resting potential

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12
Q

Action potentials have constant amplitudes - true or false

A

TRUE

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13
Q

What governs the distance travelled by an AP

A

The strength of the signal which is itself determined by the ion movement
Membrane resistance must be high and axial resistance must be low in order to increase the length the signal travels

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14
Q

What causes the change in membrane potential as you travel further from the source

A

Current leaking back out into the extracellular space
This is a passive process and occurs exponentially
The further away, the less the difference in charge

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15
Q

Longer AP’s travel slower - true or false

A

False

Increased length potential means the signal will travel at a greater speed

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16
Q

What factors can increase the speed of nerve conduction

A

Thicker axons - less axial resistance

Insulate the axons - myelin sheath

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17
Q

Which cells produce the myelin sheath

A

Schwann cells in the PNS

Oligodendrocytes in the CNS

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18
Q

What are the nodes of ranvier

A

Unmyelinated regions along the axons

Sodium channels cluster here

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19
Q

Describe how neurotransmitters are released and returned

A

Calcium enters the presynaptic area and triggers the fusion of the neurotransmitter vesicles with the membrane
This allows the neurotransmitters to be released into the cleft
They bind to receptors to the other side and trigger either efflux or influx which can create an impulse
NT’s are taken back up into the neurone or broken down to ensure that the signal only lasts as long as it needs to

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20
Q

How do the pre and post synaptic membranes stay close to each other

A

A matrix of fibrous extracellular protein within the cleft holds them in place

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21
Q

List the different classes of synapse

A

Axodendritic - from axon of one neurone to dendrite of another
Axosomatic - from axon of one to soma of another
Axoaxonic - from axon of one to another axon

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22
Q

What is the most common excitatory neurotransmitter

A

Glutamate

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23
Q

Describe the action of glutamate as an excitatory neurotransmitter

A

It is released and activates postsynaptic, selective receptors
This generates an excitatory depolarising response e.p.s.p

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24
Q

What are the most common inhibitory neurotransmitters in the CNS

A

GABA and glycine

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25
Q

Describe the action of inhibitory neurotransmitters

A

GABA or glycine bind to selective post-synaptic receptors
This generates a hyperpolarising response so that an AP is not produced
For GABA it does this by causing Cl- influx

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26
Q

Describe summation

A

A neuron can receive multiple influences from different neurones – must compute all inputs at the axon hillock
These inputs are added together to determine the response

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27
Q

List the different classes of NT

A

Amino acids - e.g. glutamate
Amines - e.g. dopamine and NA
Peptides - CCK

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28
Q

What is an ionotropic receptor

A

This receptor is itself the channel - opens when NT binds

Direct gating

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29
Q

What is a metabotropic receptor

A

The receptor influences a nearby channel (signals it to open, usually via G-proteins)
This path is triggered when the NT binds

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30
Q

Describe the action of ACh on ionotropic and metabotropic receptros

A

Can bind to both
The ionotropic receptor causes a fast response– Na/K channel opens
The metabotropic has a slower response - triggers closure of K+ channel

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31
Q

How can glutamate have an inhibitory effect

A

If it acts on metabotropic receptors

This has a role in modulation of neurotransmission

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32
Q

What type of channels can glutamate act on

A

Non-NMDA - mediate fast transmission to CNS

NMDA - contribute a slow component to the excitatory potential

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33
Q

What are the functions of the somatosensory system

A 
Mediates sensory modalities of: 
Fine touch 
Proprioception
Temperature 
Pain - nociception 
Itch  - pruriception
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34
Q

What is the function of the exteroceptive division of the somatosensory system

A

It registers info from the surface of the body from numerous types of receptor

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35
Q

What are the 3 divisions of the somatosensory system

A

Exteroceptive
Proprioceptive
Enteroceptive

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36
Q

What is the function of the proprioceptive division of the somatosensory system

A

Monitors posture and movement

Has sensors in the muscles, tendons and joints

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37
Q

What is the function of the enteroceptive division of the somatosensory system

A

Reports upon the internal state of the body

Closely related to autonomic functions

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38
Q

Describe the general somatosensory pathway

A

Usually 3 neurons in sequence
1st has its cell body in the dorsal root ganglia (body) or a cranial ganglia (head)
2nd order has cell body in dorsal horn of spinal cord or brainstem nuclei
3rd has cell body in thalamic nuclei
This neuron synapses with the somatosensory cortex

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39
Q

What acts as a receptor in the somatosensory pathway

A

The peripheral terminal of the first order neurons

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40
Q

How is a receptor potential created

A 
The stimulus (mechanical, thermal, or chemical) opens cation-selective ion channels in peripheral terminal of primary sensory afferent 
Causes a depolarizing response
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41
Q

What is the amplitude of a potential dependant upon

A

It is proportional to the intensity of the stimulus

It is graded

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42
Q

What is the frequency of a potential dependant upon

A

Proportional to the amplitude of the stimulus
The greater the amplitude the higher the frequency
This is known as frequency coding

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43
Q

What is meant by modality of a neuron

A

The neurons are tuned to respond to a specific type of energy/stimulus to excite them
Can be touch/pressure, proprioception, temperature, pain, itch

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44
Q

What is meant by the threshold of a neuron

A

The intensity of a stimulus needed to excite the sensory unit

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45
Q

What are low threshold receptors responsible for

A

Low intentisty ‘normal’ sensations
Fine discriminatory touch (can never cause pain)
Cold through to hot temperatures (not extremes)

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46
Q

What are high threshold receptors responsible for

A

Noxious stimuli
Pain
Extreme temperatures
Inflammation in response to chemical insult

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47
Q

Describe adaption of a sensory unit

A

Some units can change their firing rate if the stimuli changes strength
This is called a fast adapting response

Slower adapting responses will not change and rate remains constant for the duration of stimulus

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48
Q

How do rapidly adapting sensory units work

A

An abrupt change in stimulus will cause an AP to be fired
Gradual change has no effect
Used to detect vibration

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49
Q

How does axon diameter affect conduction velocity

A

The bigger the diameter the faster the conduction

Largest are the A-alpha fibres

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50
Q

How does degree of myelination affect conduction velocity

A

The greater the myelination, the faster the conduction

Again A-alpha have the greater velocity

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51
Q

List the classes of axons

A 
A-alpha (proprioceptors)
A-beta  (mechanoreceptors)
A-delta (pain and temp)
C fibres (temp, pain, itch)

Listed in order of conduction velocity (therefore size and myelination)

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52
Q

what is the receptive field

A

The area of the skin from which a particular sensory unit can be excited
It varies across the body and some may overlap
Related to the density of innervation inversely

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53
Q

How does sensory acuity relate to receptive field

A

It correlates inversely

A small RF gives high acuity as there is a greater density of innervation

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54
Q

How and why do we test 2 point discrimination

A

It measures somatosensory function - checks if their RF are average or not
Apply 2 sharp point stimuli simultaneously and ask patient if they feel one or 2

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55
Q

Describe free nerve endings

A

type of sensory receptor found in the skin
Found in all areas
Sensitive to pain and temperature

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56
Q

Describe Meissner’s corpuscles

A

Highly sensitive to touch
Found superficially and in areas where discrimination is highest (e.g. hands)
Small RF
Not found in hairy skin

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57
Q

Describe Merkel’s discs

A

Type of cutaneous receptor Consist of the terminals of a sensory axon and a Merkle cell
Similar to Meissner’s
Sensitive to touch and found in hairy skin as well as normal

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58
Q

Describe Ruffini endings

A

Cutaneous receptors found deep in the dermis and in joint capsules
Respond to deep pressure

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59
Q

Describe Pacinian corpuscles

A 
Found in the dermis and fascia 
Surrounded by a capsule of non-neurological tissue 
Anatomically they are large receptor
Sensitive to pressure 
Larger RF
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60
Q

Describe Krause end bulbs

A

Receptors that are found at the border of dry skin and mucous membrane
Sensitive to touch

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61
Q

How can low threshold mechanoreceptors be classified

A

By rate of adaption (fast or slow)
By size of receptive field (small=1 wide=2)
Combined to give the following groups

Fast acting small field – FA1
Fast acting wide field – FA2
Slow acting small field – SA1
Slow acting wide field – SA2

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62
Q

Which type of receptors are A-beta fibres associated with

A 
Follicular nerve endings 
Merkel cells 
Meissner corpuscles
Ruffini endings 
Pacinian corpuscles
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63
Q

Which type of receptors are A-delta fibres associated with

A

Free nerve endings

Follicular nerve endings

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64
Q

Which type of receptors are C fibres associated with

A

Free nerve endings

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65
Q

What forms a dermatome

A

The area of skin innervated by the left and right dorsal roots of a spinal segment

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66
Q

List the location of the sensory afferent terminals in the grey matter dorsal horn

A

Horn is divided into 10 laminae of Rexed
Nociceptors terminate in 1 and 2
LTM - terminate in 3-6
Proprioceptors in 7-9

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67
Q

Describe the dorsal column lemniscal pathway

A

Carries touch, pressure, vibration and proprioception
Uses A-a/b fibres
First order carries from sensory receptor to medulla
Second order decussates and then synapses in thalamus
3rd order carries to cortex

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68
Q

Describe the spinothalamic tract

A

Carries pain, temp, itch and crude touch
Uses A-delta and C fibres
First order carries from receptors to spinal cord
Synapses and decussates in cord (second order)
2nd carries up to thalamus and synapses
3rd to cortex

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69
Q

How is the dorsal column of the spinal cord organised

A

Split into the medial gracile tract and the more lateral cuneate tract
Sensory info from T6 and below (inc. lower limb) travels in gracilis (runs whole length of cord)
Input above T6 travels in cuneate tract

Frome lateral to medial: cervical, thoracic, lumbar, sacral

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70
Q

What does the DCML pathway allow us to do

A

Stereognosis - recognise objects by feeling them
Detect vibration - activates Pacinian and Meissner’s corpuscles
Fine touch - inc. 2 point discrimination
Conscious proprioception

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71
Q

Which tuning fork is used for testing vibration detection on the body surface

A

128Hz

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72
Q

What is lateral inhibition

A

The process by which an activated neurone can inhibit the activity of its neighbours
This is done via inhibitory interneurons
It sharpens the perception of the important stimuli - gets rid of ‘background noise’

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73
Q

Which nerves are responsible for the sensation to the anterior head

A

The 2 trigeminal nerves - each with 3 divisions

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74
Q

Describe the path of the trigeminal nerves

A

Receptors are found in the skin of the head and face
The cell bodies are found in the trigeminal sensory ganglion
The 1st order synapse with 2nd in the principle sensory or spinal nucleus
2nd order then decussate and project to the thalmus (VPM nucleus)
3rd order relay info to the cortex

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75
Q

Where is the somatosensory cortex found

A

The post central gyrus of the parietal cortex

Immediately behind central sulcus

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76
Q

How is the somatosensory cortex divided

A

Into Brodmann areas

3a, 3b, 1 and 2

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77
Q

What type of information is received in Brodmann area 3a

A

Proprioception

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78
Q

What type of information is received in Brodmann area 3b

A

Cutaneous sensation from Merkel cells or Meissner’s

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79
Q

What type of information is received in Brodmann area 1

A

Cutaneous sensation from fast acting mechanoreceptors or area 3b

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80
Q

What type of information is received in Brodmann area 2

A

Deep pressure and joint position

Comes from joint afferents and tendons

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81
Q

Describe the somatotopic map of the body

A

Each area of the somatosensory cortex correlates to an area of the body
Represented by the homunculus
Toes are at the top of the brain and tongue at the lower end

82
Q

How is the somatosensory cortex organised

A

Into 6 layers of cells
Input from thalamus mainly comes in at level 4
Also split into vertical columns which extend across all layers

83
Q

Can the somatosensory map of the body change

A

YES
Change with life, activity and injury
For example if you lose a digit, the somatosensory area from can change and become responsible for other digits
This is also responsible for phantom pain

84
Q

What is the function of the posterior parietal cortex

A

It receives and integrates information from the somatosensory areas and others such as visual, auditory and thalamus
Allows us to determine deeper meaning of the info

85
Q

what can damage to the posterior parietal cortex lead to

A

Bizarre neurological defects
Agnosia - unable to recognise sensory info such as objects, smells, people
Hemispatial neglect - patients cannot perceive the existence of one side of their body/world

86
Q

Where are the upper motor neurons found

A

Within the brain

87
Q

Where are the lower motor neurons found

A

Cell bodies are in the brain stem and ventral horn of the spinal cord
Axons exit the cord via the ventral roots or by cranial nerves
Joins with the posterior/dorsal root to form a mixed spinal nerve
Carries signals to effector cells

88
Q

What is the function of an upper motor neuron

A

They supply input to the lower motor neurons to modulate their activity

89
Q

What is the function of a lower motor neuron

A

Command muscle contraction
Form the final common pathway
Receive input from the UMN, proprioceptors and interneurons

90
Q

What do alpha motor neurons do

A

Innervate the bulk of fibres within a muscle that generate force
Found in LMN

91
Q

What do gamma motor neurons do

A

Innervate a sensory organ within a muscle = muscle spindle

Found in LMN

92
Q

What is meant by synergistic muscles

A

Muscles that work together to produce a movement

e.g. biceps brachii and the brachialis

93
Q

What is meant by antagonist muscles

A

Those which have opposite effects - flexors vs extensors

94
Q

What do axial muscles do

A

Control movement of the trunk - maintain posture

95
Q

What do proximal muscles do

A

Also called girdle muscles
Found in the shoulder, elbow, pelvis and knee
They mediate locomotion

96
Q

What do distal muscles do

A

Move the hands, feet and digits

Allows fine movement and manipulation of objects

97
Q

Where are the greatest number of spinal nerves found

A

At the cervical and lumbar enlargements of the spinal cord

These areas supply the arms and legs so need more nerves

98
Q

What is a motor unit

A

The smallest functional component of the motor system

The group of muscle fibres innervates by one alpha-motor neuron

99
Q

What name is given to the group of alpha motor neurons that innervate a signal muscle

A

Motor neuron pool

100
Q

What decides the force of a muscle contraction

A

Frequency of action potential discharge of the α-MN - more AP’s = stronger
The number of LMN that are simultaneously active - more motor units = stronger
The coordination of the movement - recruiting synergistic muscles
The fibre size and fibre phenotype

101
Q

Describe the somatotopic organisation of LMN

A

The LMN innervating axial muscles are found medial to those innervating distal ones
The LMN innervating flexors are found posterior to those innervating extensors

102
Q

A single AP does what to a muscle fibre

A

Causes it to twitch - sudden contraction then relaxation

Need several AP’s to generate a continuous contraction

103
Q

What are the differences between small and large motor units

A

Small - few fibres, used for fine movement, innervated by small aMN

Large - many fibres, used in large antigravity muscles and innervated by large aMN

104
Q

Motor units contain only one ‘speed type’ of fibre- true or false

A

True

Only contain either fast or slow twitch fibres

105
Q

Describe Slow (type 1) fibres

A 
Slow contraction and relaxation 
Fatigue resistant 
Get ATP from oxidative phosphorylation 
Red fibres - due to high myoglobin
Lots of capillary
106
Q

Describe fast (type 2) fibres

A

Type 2a - fast contraction and relaxation, fatigue resistant
Get ATP mostly from oxidative phosphorylation
Red fibres - well vascularised

Type 2b - fast contraction and relaxation, not resistant to fatigue
Get ATP from glycolysis
Poorly vascularised - white fibres

107
Q

What activities are type 2b fast fibres used for

A

Sudden bursts of high energy movement

e.g. weightlifting

108
Q

What activities are type 2a fast fibres used for

A

Sustained locomotion
Need some resistance to fatigue
Longer runs

109
Q

What activities are type 1 slow fibres used for

A

Antigravity/posture

Sustained movement

110
Q

What is the Henneman Size principle

A

The susceptibility of a aMN to discharge an AP is related to its size
Smaller ones have a lower threshold
Slow fibres are more easy to activate

111
Q

In which order are motor units activated

A

In order of their size as the smaller ones haver a lower threshold
This allows for finer control of muscle force
Slow ones also recruit first and build up towards the fast ones to build up to the maximal force

112
Q

What is the myotatic reflex

A

When a skeletal muscle is pulled, it pulls back - e.g. knee jerk
The change in length is registered by the muscle spindle (sensory organ) and triggers reflex
Non-conscious proprioception

113
Q

What forms a muscle spindle

A

A fibrous capsule
Intrafusal muscle fibres
Sensory afferents that innervate these fibres
Gamma motor neurones

114
Q

For each of the main myotactic reflexes, state the spinal level being assessed

A 
Biceps - C5-6 
Supinator - C5-6 
Triceps - C7 
Knee - L3-4 
Ankle - S1
115
Q

How can you reinforce a reflex

A

Get the patient to interlock their fingers and pull apart as you hit the tendon
Or get them to hold something and squeeze it
Jendrassik manoeuvre

116
Q

Stimulation of gamma motor neurons does what

A

Causes the intrafusal fibres of the muscle spindle to contract
They are activated by higher centres in the CNS

117
Q

Intrafusal and extrafusal contract simultaneously - true or false

A

True
This prevents the spindle from going slack when the extrafusal ones contract
If it was to go slack the neurons wouldn’t be stimulated and the contraction wouldn’t be maintained

118
Q

When are dynamic gamma motor neurons activated

A

When there is a lot of active movement that means the muscle lengths will be changing rapidly
A low levels of activity there is no dynamic activity

119
Q

What are the Golgi tendon organs

A

Organs which are found at junction of muscle and tendons
Monitor changes in muscle tension and regulate it to prevent overloading the muscle
They also help with fine grip – prevent it being too hard

120
Q

What innervates the Golgi tendon organs

A

Group Ib sensory afferents

121
Q

What are the functions of proprioceptive axons within joints

A

Found in the connective tissue of a joint
Respond to changes in angle, direction and velocity of movement of a joint.
Also prevent excessive flexion, or extension

122
Q

What forms a proprioceptive axon

A

Mixture of different units - both fast and slow acting
Lots of different receptor types are there as well to carry all types of information (free endings, Golgi, paciniform, ruffini)
e.g. pain, acceleration, position

123
Q

Where do spinal interneurons receive their input from

A

Primary sensory axons
Descending axons from the brain
Branches of the lower motor neurons
Other interneurons

124
Q

What is the function of the interneurons

A

They can send excitatory or inhibitory signals to muscles
Involved in the inverse myotatic response - cause the muscle opposite the one contracting to relax
Reciprocal inhibition between extensors and flexors - ensures they are peforming opposite actions

125
Q

What is reciprocal inhibition

A

When a muscle contracts, inhibitory interneurons cause the opposing ones to relax so that the movement is unopposed
Initiated by the motor cortex
Occurs between extensors and flexors

126
Q

Which reflexes do excitatory interneurons mediate

A

The flexor reflex

The crossed extensor reflex

127
Q

What is the flexor reflex

A

When noxious stimuli cause a limb to flex - to move it further away from source
Excitatory interneurons cause contraction of the muscle
Inhibitory ones cause the extensors to relax

128
Q

What is the crossed extensor reflex

A

Noxious stimulus causes the limb to extends - this prevents us falling over when we withdraw (flexor reflex in other limb)
Excitatory interneurons cause contraction of the extensor muscle
Inhibitory ones cause the flexors to relax

129
Q

How can interneurons help us walk

A

excitatory ones need to fire rhythmically to cause repeated flexion then extension when they are inhibited
Fire, then inhibited over and over

130
Q

what are the 3 levels of motor coordination and control

A

Strategy - what’s the aim of the move (controlled by basal ganglia etc)
Tactics - what sequence of muscle movements are needed (motor cortex and cerebellum)
Execution - activation of the motor pools (brain stem and cord)

131
Q

How are signals passed through the retina

A

Vertically - photoreceptors receives signal then pass back up to bipolar cells then the ganglion cells

Some horizontal pathways exist to spread signals to other cells

132
Q

What is the function of the horizontal cells in the retina

A

Receive input from photoreceptors and project to other photoreceptors and bipolar cells
The greater the signal, the further they project by releasing more GABA

133
Q

What is the function of the amacrine cells in the retina

A

Receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells

134
Q

Describe the dark current

A

There is a flow of sodium in cells that keeps potential steady
When exposed to light the cell is hyperpolarised and a signal can be created

135
Q

What is the basis of colour vision

A

Different opsins present in the cone cells are sensitive to different wavelengths of light

136
Q

Which type of retinal cell can see in dim light

A

The rods

Cones see in normal daylight

137
Q

What facilitates high acuity vision

A

The distribution of rods and cones
Higher density of cone in the fovea increases the acuity

In the periphery there is larger spacing between rods and more cells acting on one ganglion - increased sensitivity but less acuity

138
Q

Describe the rod cells of the eye

A 
Don't see colour 
Found in the peripheral retina 
High convergence 
High light sensitivity 
Low acuity
139
Q

Describe the cone cells

A 
See colour 
Found in the central retina (fovea)
Low convergence 
Low light sensitivity 
High acuity
140
Q

What is the function of lateral inhibition in the visual pathway

A

Inhibits signals in neighbouring neurons to exaggerate the difference in stimulus intensity
Helps with localisation

141
Q

What signals are sent from the retina to the brain

A 
Simultaneous input from two eyes
Depth and distance 
Light vs dark - centre ganglion cells 
Movement
Form and colour
142
Q

Do the visual fields of the left and right eyes overlap

A

YES
Forms the binocular visual field
Peripheral vison is monocular

143
Q

How is the visual field mapped in the visual cortex

A

Different regions of the retina are mapped into the cortex - each region has an area in the cortex
Larger than proportional area is dedicated to the fovea - this is why it has high acuity

144
Q

Which nucleus does visual information pass through to reach the visual cortex

A

Lateral geniculate nucleus

145
Q

How are the hair cells responsible for generating AP’s

A

They have cation channels at the top of them
Open when tilted one way and closed in the other
Sound moves the hair cells and changes the channel
The hair cells release glutamate in response which is passed to nearby nerve cells creates the AP

146
Q

What is sound

A

A change in the pressure/density in the air
Often created by an object vibrating
Can measure the frequency and amplitude

147
Q

Describe how we hear sound (pathway through the ear)

A

Vibration in the air travels up canal and causes drum to vibration
This spreads through the ossicles to the cochlea(via oval window)
This is caught by the hair cells in the cochlea
They transduce the vibration into an AP
Travels to the auditory cortex via cohlear nerve

148
Q

Where and why is sound amplified in the ear

A

It is amplified by the bones in the ear - ossicles

This is because the inner ear is fluid filled which is denser than air - needs to be louder to be received

149
Q

Describe the structure of the cochlea

A

Made up of 3 fluid filled cavities
Scala vestibuli, scala media and scala tympani
Separated by membranes

150
Q

Which cavity of the cochlea meets the oval window

A

Scala tympani

151
Q

Which cavity of the cochlea meets the round window

A

Scala vestibuli

152
Q

Which cavity of the cochlea contains the organ of corti

A

Scala media

153
Q

How is the basilar membrane in the cochlea affected by pitch

A

It differs in thickness/rigidity along its length - allows us to identify pitch
Higher pitch sounds have more energy so is able to move the membrane easier
Lower pitch will have to travel further along the membrane before it is able to move it

154
Q

How do hair cells allow us to determine pitch

A

Different frequencies of sound waves activate hair cells maximally at different locations
Wherever they bend the most will fire the most nerve signals - we hear this frequency

155
Q

What is the importance of K+ channels in hair cells

A

K+ moves into the cells

Mutations in these channels can lead to deafness

156
Q

How are hair cells innervated

A

The inner hair cells are innervated by many ganglions (more fibres)
The outer hair cells can be innervated by just one ganglion

Inner cells send signals out via multiple afferents whilst multiple outer HC will send via same single afferent

157
Q

What effect can furosemide have on hair cells

A

It inactivates the motor component of the outer hair cells

No longer get their amplifying effect

158
Q

Is tonotopy present in the auditory cortex

A

YES

Areas of the brain will also respond to particular pitch

159
Q

Describe the path of an auditory signal to the brain

A

Signal arises in the organ of corti in the cochlea
This travels to the spiral ganglion (cochlea) before going either to the dorsal or ventral cochlear nucleus (brainstem)
The ventral one passes to the superior olivary nucleus and then to the inferior colliculus via the lateral lemniscus
The dorsal one goes straight to the inferior colliculus via the lateral lemniscus
Both paths pass to the medial geniculate nucleus of the thalamus before finally reaching the auditory cortex

160
Q

How do we localise sound

A

The superior olivary nucleus helps us do this
If the sound is louder on one side, this area will generate the signal but also an inhibitory signal to block/dampen the other side

161
Q

What are the functions of the vestibular system

A

Integrates information about body position and movement - gravity, rotation and acceleration
Communicates with somatosensory and visual systems
Allows for stability and orientation

162
Q

How does the vestibular system detect position and movement

A

Head angular acceleration and rotation - semi-circular canal
Head linear acceleration (moving forward and back) - saccule and utricle

163
Q

What are the different functional areas of the vestibular system

A

Peripheral sensory apparatus - found in the vestibular organ and detects and relays info about head postion/movement
Central processing system
Motor output - generates the compensating eye and body movement

164
Q

What are the otolith organs

A

The saccule and utricle

They sense linear acceleration and gravity

165
Q

How do the otolith organs detect movement

A

Have small crystals called otoconia which move within the organ
This moves the hair cells leading on to NT release
Detects the movement and leads to the change in head position relative to the movement

166
Q

What are the 3 vestibular reflexes

A

Vestibulo-ocular – keep the eyes still when the head moves.
Vestibulo-colic – keeps the head still or at least level when you walk
Vestibular-spinal – adjusts posture for rapid changes in position.

167
Q

What are the 3 forms of pain

A

Nociceptive - immediate and short lived
Inflammatory - days/weeks, assists healing
Pathological - no physiological purpose, long term

168
Q

How does inflammatory pain aid healing

A

It forces us to protect the damaged area until it is healed – will get pain if you touch/used the damage tissue

169
Q

Which drugs are used to treat pain

A

NSAIDs and paracetamol for mild
Opioids for mod/severe
Some antidepressants, anticonvulsants and local anaesthetics can be used

170
Q

What are nociceptors

A

Specific peripheral primary sensory afferents that are activated by an intense and noxious stimuli (pain)
Includes thermal, mechanical and chemical

171
Q

Where are nociceptors found

A

The have free nerve ending in a peripheral location
Central terminal is in the dorsal horn of the spinal cord
From here it can release glutamate to excite a 2nd order neurone
These travel in the spinothalamic or spinoreticulothalamic tracts

172
Q

Describe A-delta nociceptive fibres

A

Respond to mechanical and thermal stimuli
Thinly myelinated so moderate speed conduction
Responsible for ‘first/fast;’ pain - stabbing

173
Q

Describe C type nociceptive fibres

A

Unmyelinated fibres so slow to conduct
Respond to all types of noxious stimuli
Mediate slow pain - achy or inflammatory

174
Q

What is allodynia

A

Pain arising when there is not a noxious stimuli

175
Q

What is hyperalgesia

A

Where a painful stimulus becomes even more painful (enhanced pain response)

176
Q

How can nociceptors affect their surrounding area

A

They can cause efferent affects by releasing pro-inflammatory mediators
Contributes to neurogenic inflammation in the area

177
Q

How does neurogenic inflammation occur

A

Peptides are released from the nociceptors due to tissue damage or inflammation
Get local vasodilation, release of histamine etc and sensitization of nearby nociceptors = inflammation

178
Q

What is the primary NT in the nociceptor pathway

A

Glutamate - causes an excitatory potential

179
Q

What receptors does glutamate act on in the pain pathway

A

AMPA - activated first

NMDA - activated by intense stimuli

180
Q

Where do nociceptors synapse In the spinal cord

A

In laminae I and II of the dorsal horn
They synapse with nociceptor specific cells that are only activated by noxious stimuli
Can also synapse with an interneuron which travels deeper and activates a wider reaching neuron

181
Q

Where does visceral pain come from

A

From nociceptors in the coverings of internal organs - e.g. peritoneum
Caused by twisting/stretching sensations or inflammatory or ischemia
Tends to be dull/achy

182
Q

Why is visceral pain sometimes referred to a distant area of skin

A

Some visceral and skin afferent converge upon the same spinothalamic neurones
Pain will be in one dermatome
Brain cannot differentiate where the pain is so you get referred pain

183
Q

Visceral pain is often associated with autonomic symptoms - true or false

A

True

May get vomiting, nausea, sweating and pallor

184
Q

What is viscerosomatic pain

A

Occurs when inflammation from a diseased organ reaches a somatic/body wall structure
Becomes a sharp, well localised pain
e.g. shifting pain in appendicitis

185
Q

Are pain and nociception the same

A

NO
Pain involves the awareness of sufferings
Nociception can occur without pain

186
Q

How can pain caused by activity in nociceptors be reduced

A

By simultaneous activity in low threshold mechanoreceptors
e.g. rubbing an injured area
Gate control theory

187
Q

Describe the gate control theory

A

If the mechanical stimulus is stronger it ‘closes the gate’ by inhibiting the nociceptor and the pain is not passed on
If the pain fibres have a stronger signal it opens the gate and we feel it

188
Q

What are the major nociceptive tracts

A

Spinothalamic tract - carries a-delta fibres, fast pain

Spinoreticular tract - carries C fibres, slow pain

189
Q

What are thermoreceptors

A

Neurons that are specialised to respond to small changes in temperature

190
Q

Is sensitivity to temperature uniform across the body

A

Nope

There are areas that are sensitive to heat and those that are sensitive to cold (wont respond to both)

191
Q

What is the neuromuscular junction

A

The connection between the neurons and the muscle

192
Q

What neurons innervate skeletal muscle

A

Motor neurons
Their cell bodies arise in the ventral horn of the spinal cord
The terminal portions give rise to fine projections which run along the muscle cell

193
Q

What are the motor end plates

A

The synapses formed between motor neurons and muscle

194
Q

A single motor neuron may control many muscle cells - true or false

A

True

However each muscle cell will only respond to one motor neuron

195
Q

Describe the transmission of nerve impulses by acetylcholine

A

Action potential moves along the nerve
Voltage gated calcium channels open allowing influx of calcium
Vesicles of acetyl choline released into synaptic cleft
Acetyl choline diffuses across the synaptic cleft
The acetylcholine receptor opens and renders the membrane permeable to Na / K ions
The depolarisation starts an action potential at the motor end plate
Causes muscle to contract

196
Q

What happens if you block acetylcholine receptors

A

You get no muscle contraction and therefore no respiration
This will kill you
Certain nerve toxins act this way

197
Q

Describe how botulinum toxin works

A

Cleaves presynaptic proteins involved in vesicle formation and blocks vesicle docking with the presynaptic membrane
Leads to rapid onset weakness
It will eventually wear off but need to support breathing during the paralysis or it will be fatal

198
Q

How can botulinum toxin be used clinically

A

Can temporarily paralyse over active muscles in spasticity
Can be used on overactive sweat glands
Some cosmetic uses - Botox

199
Q

What surrounds a skeletal muscle fibre

A

A thin layer called the endomysium

200
Q

What forms a fascicle

A

Groups of skeletal muscle fibres surrounded by a perimysium

201
Q

Describe the structure of smooth muscle

A

Cells are not striated and have a single central nucleus
Gap junctions between cells
Lots of connective tissue around them
More actin than myosin

Neurology (18 decks)

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