CNS: structure and function

Question 1

What are the functions of the nervous system?

Answer 1

• control of the internal environment
• voluntary control of movement
• spinal cord reflexes

Question 2

Describe the peripheral nervous system

Answer 2

Neurons outside the CNS

Question 3

Describe the sensory division

Answer 3

afferent fibres transmit impulses from receptors to CNS

Question 4

Describe the motor division

Answer 4

efferent fibres transmit impulses from the CNS to effector organs

Question 5

What 2 types of input make up sensory nervous system?

Answer 5

somatic sensory
visceral sensory

Question 6

What 2 types of input make up motor nervous system?

Answer 6

somatic motor
autonomic motor

Question 7

What does the axon (nerve fibre) do?

Answer 7

• carries APs away from cell body
• covered by Schwann cells (forms discontinuous myelin sheath)

Question 8

What does it mean if the axon diameter is larger or there is increased myelin sheath?

Answer 8

greater speed of neural transmission

Question 9

When a cell is polarised, does it have a positive or negative charge?

Answer 9

Negative.
–5 to –100 mv
-40 to –75 mv in neurons

Question 10

What is the magnitude of a resting membrane potential determined by?

Answer 10

1. Permeability of plasma
   membrane to ions.
2. Difference in ion concentrations
   across membrane
   * Na+, K+, C, and Ca+2

Question 11

What ions plays most important role in generating resting membrane potential?

Answer 11

Na+ (greater conc on outside of cell) and K+ (greater conc on inside of cell)

Question 12

How is resting membrane potential achieved?

Answer 12

Maintained by sodium-potassium pump
–Potassium tends to diffuse out
of cell
–Na+/K+ pump moves 2 K+ in
and 3Na+out

Question 13

AP occurs when a stimulus of sufficient strength depolarizes the cell, how?

Answer 13

Opens Na+ channels, Na+ diffuses into cell (inside becomes more positive)

Question 14

What is the all-or-none law?

Answer 14

Once a nerve impulse is initiated, it will travel the length of the neuron

Question 15

What are the 2 ways in which excitatory postsynaptic potentials can promote depolarization?

Answer 15

1) Temporal summation - Rapid, repetitive excitation from a single excitatory presynaptic neuron
2) Spatial summation - Summing EPSPs from several different presynaptic neurons.

Question 16

What do inhibitory postsynaptic potentials cause?

Answer 16

Hyperpolarization (more negative resting memb potential)..
- Neurons with more negative memb potential resist depolarization

Question 17

What are the 2 types of mechanoreceptors?

Answer 17

• Muscle spindles
• Golgi tendon organs

Question 18

Define propriception

Answer 18

The sense of the body’s position in space based on specialized receptors that reside in the muscles, tendons and joint.

Question 19

What are proprioreceptors?

Answer 19

sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give information about the position of the
limb in space.

Question 20

What do muscle spindles respond to, and consist of?

Answer 20

Respind to changes in muscle length.
Consist of:
- Intrafusal fibres
- Gamma motor neurons

Question 21

What is the function of the muscle spindle?

Answer 21

To assist in the regulation of movement and maintain posture.

Question 22

What do Golgi tendon organs do?

Answer 22

Monitors force development in muscle
- prevents muscle damage during excessive force generation

Question 23

Stimulation of GTO does what?

Answer 23

Results in reflex relaxation of muscle
- inhibitory neurons send inhibitory postsynaptic potentials to muscle alpha motor neurons

Question 24

What may the ability to voluntarily oppose GTO inhibitioin be related to?

Answer 24

Gains in strength with training due to increased tendon stiffness

Question 25

What is the innervation ratio?

Answer 25

Number of muscle fibres innervated by a single motor unit
- low ratio involved in fine motor control
- high ratio in muscles requiring power/less fine motor control

Question 26

What is motor unit recruitment?

Answer 26

Recruitment of additional muscle fibres by activting more motor units

Question 27

What is the size principle?

Answer 27

The orderly and sequential recruitment of larger motor units during exercise (smaller MU recruited 1st)

Question 28

What 3 components is the brain stem made out of?

Answer 28

• Midbrain
• Medulla Ob
• Pons

Question 29

What is ‘spinal tuning’?

Answer 29

Refers to intrinsic neural networks within spinal cord that refine voluntary movements after receiving messages from higher brain centres.

Question 30

How do astrocytes prevent prolonged (unwanted) effects at synapses?

Answer 30

If more glutatmate released from presynaptic terminal than required, most is removed by astrocytes surrounding synaptic cleft. Glutamate converted to glutamine and then released to neuron which converts back to glutamate and stores it in vesicles ready for next AP.

Question 31

Describe convergence and divergence

Answer 31

Convergence - when a neuron receives input from many other neurons
Divergence - when a neuron synapses with many other neurons

Question 32

Can neurons receive multiple presynpatic inputs?

Answer 32

Yes! excitatory and inhibitory. Inputs closer to axon hillock have greater effect than those further away