Neuroscience

Question 1

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

Answer 1

Input, integrative, conductive and output

Question 2

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

Answer 2

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

Question 3

Describe the stages of an AP:

Answer 3

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

Question 4

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

Answer 4

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)

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

*What are the different types of synapse?

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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.)

Question 10

What is spatial and temporal summation?

Answer 10

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

Question 11

Where are glycine, glutamate, GABA and amines made?

Answer 11

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

Question 12

What do lower motor neurone receive input from?

Answer 12

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

Question 13

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

Answer 13

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)

Question 14

Where are upper and lower motor neurone each found?

Answer 14

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

Question 15

How do axons of LMNs exit the spinal cord?

Answer 15

In the ventral roots (or via cranial nerves)

Question 16

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

Answer 16

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

Question 17

At what spinal levels are the cervical and lumbar enlargements?

Answer 17

Cervical = C3-T1 and Lumbar = L1-S3

Question 18

What makes up a motor unit?

Answer 18

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

Question 19

What makes up a motor neurone pool?

Answer 19

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

What factors do muscle strength rely on?

Answer 22

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)

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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.

Question 26

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

Answer 26

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

Question 27

What is the Henneman Size Principle?

Answer 27

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.

Question 28

What is the myotatic reflex?

Answer 28

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

Question 29

What do muscle spindles consist of?

Answer 29

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

Question 30

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

Answer 30

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

Question 31

What types of infrafusal fibres in muscles spindles are there?

Answer 31

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

Question 32

What is the function of golgi tendon organs?

Answer 32

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

Question 33

What is the location of golgi tendon organs?

Answer 33

Junction of muscle and tendon

Question 34

What innervates golgi tendon organs?

Answer 34

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

Question 35

What is the reverse myotonic reflex?

Answer 35

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

Question 36

Where are proprioceptive axons present in joints?

Answer 36

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

Question 37

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

Answer 37

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

Question 38

Where does proprioceptive information arise from in joints?

Answer 38

Muscle spindles, golgi tendon organs and joint receptors

Question 39

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

Answer 39

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