Neuroscience Flashcards

1
Q

Regardless of function, what four function regions do most neurons have?

A

Input, integrative, conductive and output

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2
Q

At rest, is the concentration for K+ and Na+ higher inside or outside the cell?

A

K+ is higher inside, and Na+ is higher outside

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3
Q

Describe the stages of an AP:

A

1) Signal comes and triggers K+ efflux to increase, causing depolarisation (less negative)
2) Reaches threshold and causes Na+ channels to open, driving towards Na+ equilibrium (+54mV)
3) Overshoot occurs as causes the polarity of membrane to switch, resulting in inactivation of Na+ (refractory period)
4) As Na+ channels close and K+ efflux continues, cell replolarisis, and may hyper polarise as driven towards K+ equilibrium (-74mV)
5) Then resumes normal resting potential

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4
Q

What is the length constant? And how do you increase it?

A

length constant (λ) is used to quantify the distance that a graded electric potential will travel along a neurite via passive electrical conduction. It = square root of membrane resistance Rm / axial resistance Ri. To increase the length constant, you want to decrease the axial resistance (by having a wider diameter of axon) and increase the membrane resistance (by providing an insulation to the axon e.g. myelin)

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5
Q

*What is the difference between the myelin-producing cells in the CNS and PNS - i.e. name and quantity ratio to axons?

A
CNS = oligodendrites, where there is one oligodendrite to many axons. 
PNS = Schwann cells, where there are many schwann cells to one axon
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6
Q

What effect do demyelinating conditions such as MS (CNS) and Guillian Bare Syndrome (PNS) have on nerve conduction?

A

Reduce speed of conduction by reducing myelination, and slowing saltatory conduction

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7
Q

*What are the different types of synapse?

A

Synapses can be classified functionally (excitatory or inhibitory) or morphologically by the location of the presynaptic terminal upon the postsynaptic cell:

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8
Q

In the CNS, what is the excitatory transmitter most commonly?

A

Glutamate - activates postsynaptic, cation selective, ionotropic, glutamate receptors generating a local, graded, excitatory (depolarizing) response: the excitatory postsynaptic potential (e.p.s.p.)

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9
Q

In the CNS, what is the inhibitory transmitter most commonly, and what response does it have?

A

GABA - activates postsynaptic, anion selective, ionotropic, GABAA, or glycine, receptors generating a local, graded, inhibitory (hyperpolarizing) response: the inhibitory postsynaptic potential (i.p.s.p.)

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10
Q

What is spatial and temporal summation?

A

Summation helps determine whether an AP will be triggered either by several different, simultaneous inputs (spatial) or several repeated inputs (temporal)

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11
Q

Where are glycine, glutamate, GABA and amines made?

A

Glycine and glutamate occur in all cells as they are amino acids, while GABA and amines must be specifically synthesized by the neurones that release them, requiring specific enzymes

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12
Q

What do lower motor neurone receive input from?

A

Upper motor neurones, proprioceptors and interneurons - then send commands to muscle fibres

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13
Q

What are the 2 main types of lower motor neuron, and what do they innervate?

A

α-motor neurons - innervate bulk of muscle fibres causing contraction. gamma(γ)-motor neurons innervate sensory organ in the muscle - muscle spindles (there are also beta motor neurone but not as important)

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14
Q

Where are upper and lower motor neurone each found?

A

UMN = brain and LMN = brainstem and ventral horn of spinal cord

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15
Q

How do axons of LMNs exit the spinal cord?

A

In the ventral roots (or via cranial nerves)

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16
Q

True or false: motoneurons are distributed equally throughout the spinal cord

A

False, greater number in the cervical enlargement (C3-T1) supplying the arm and lumbar enlargement (L1-S3) supplying leg

17
Q

At what spinal levels are the cervical and lumbar enlargements?

A

Cervical = C3-T1 and Lumbar = L1-S3

18
Q

What makes up a motor unit?

A

An α-motoneuron and all of the skeletal muscle fibres that it innervates

19
Q

What makes up a motor neurone pool?

A

The collection of α-motor neurones that innervate a single muscle

20
Q

What 2 mechanisms of α-MNs grade the force of muscle contraction?

A

o frequency of action potential discharge of the α-MN (note: each AP causes a muscle ‘twitch’ which summate)
o the recruitment of additional, synergistic, motor units

21
Q

What is the somatotrophic distribution in the ventral horn of LMNs?

A

Those innervating axial muscles are medial to those innervating distal muscles, and those innervating flexors and dorsal to those supplying extensors

22
Q

What factors do muscle strength rely on?

A

Neuromuscular activation (firing rates of LMNs, number of LMNs that innervate them and co-ordination i.e. agonist vs antagonist) and force production by innervated fibres (fibre size and type i.e. fast vs low)

23
Q

What does a single AP in a α-MN cause, and how do these cause a contraction?

A

These cause a twitch, and the summation of these cause a contraction

24
Q

What size of motor units are those for fine movements and those for large postural muscle such as leg muscles?

A

Fine movements have small motor units, and large postural fibres have large units made up of hundreds of fibres

25
Q

What are the 2 main types of skeletal muscle fibre, and what makes them different?

A

Fast (Type II), subdivided into Type II and IIb, and Slow-oxidative (Type I). Differ in how fast myosin ATPase splits ATP to provide energy for cross bridge cycling. Reflected in time to develop peak tension.

26
Q

Where do each type of skeletal muscle fibre get their ATP? What are the implications of this in terms of fatigue?

A

Type I (slow) and type IIa from oxidative phosphorylation. Type IIb from glycolysis. This means that Type I and Type IIa are fatigue resistant, but Type IIb fatigues quickly, although it is much faster

27
Q

What is the Henneman Size Principle?

A

The susceptibility of an α-MN to discharge action potentials is a function of its size. Smaller α-MNs (part of slow motor units) have a lower threshold than larger ones.

28
Q

What is the myotatic reflex?

A

When a skeletal muscle is pulled, it pulls back (tendon jerk reflex - a monosynaptic reflex arc)

29
Q

What do muscle spindles consist of?

A

Intrafusal muscle fibres, sensory afferents (Ia class), gamma motor neurone and a fibrous capsule

30
Q

What are the stages of the knee jerk as a myotatic/monosynaptic reflex arc?

A

1) When the patellar tendon is tapped, the muscle spindle in the quadriceps detects the stretch 2) This activates the Ia afferent which travels to the L3 and L4 nerve roots 3) Excitatory synaptic transmission, releasing glutamate onto alpha- motor neuron 4) This causes the contraction of the quadriceps muscle, leading to extension of the lower leg at the knee

31
Q

What types of infrafusal fibres in muscles spindles are there?

A

Nuclear bag fibres:
♣ Bag 1 or dynamic – very sensitive to the rate of change of muscle length. Innervated by dynamic γ-MNs
♣ Bag 2 or static – more sensitive to the absolute length of the muscle. Innervated by static gamma motor neurones
Chain fibres – sensitive to the absolute length of the muscle. Innervated by static γ-MNs

32
Q

What is the function of golgi tendon organs?

A

Monitor changes in muscle tension to protect muscle from overstretch and regulate tension to an optimal range

33
Q

What is the location of golgi tendon organs?

A

Junction of muscle and tendon

34
Q

What innervates golgi tendon organs?

A

group Ib sensory afferents (myelinated, slightly slower conducting than Ia fibres)

35
Q

What is the reverse myotonic reflex?

A

Group Ib afferents enter the spinal cord and synapse upon inhibitory interneurones which, in turn, synapse upon the alpha motor neurones of the homonymous muscle - this prevents excessive movement and power when carrying out a function

36
Q

Where are proprioceptive axons present in joints?

A

In the connective tissue e.g. joint capsule and ligaments

37
Q

What kind of nerve endings are found in the proprioceptive axons in joints and where?

A

Free nerve endings in the capsule and connective tissue; Golgi-type endings in the ligaments; Paciniform endings in the periosteum and fibrous joint capsule; Ruffini endings in the joint capusle

38
Q

Where does proprioceptive information arise from in joints?

A

Muscle spindles, golgi tendon organs and joint receptors

39
Q

How do different types of units in joint receptors help generate proprioceptive information for the CNS?

A

Mixture of rapidly adapting (RA) and slowly adapting (SA) units that have either high threshold (HT), or low thresholds (LT) for activation thus information concerning movement and the static, or resting, positon of a joint is transmitted to the CNS