Central and Peripheral Nervous System

Question 1

Describe the functions of the; Cell body, Dendrites, Axon, Neurilemma, Schwann cell, Myelin sheath, Nodes of Ranvier, Axon terminal and synaptic bulb.

Answer 1

Cell body => Controls all functioning of the cell.
Dendrites => Receive impulses and transfer them to the cell body.
Axon => Transfers impulses away from the cell body.
Neurilemma => Neuron membrane that helps in the repair of injured fibres
Schwann Cell => Produce Myelin
Myelin Sheath => Insulates, thickens, protects against damage and speeds up movement.
Nodes of Ranvier => Saltatory Transmission (jumping + speed up impulses)
Axon Terminal => Connects with next neuron, site of neurotransmitter release.

Question 2

Synapses

Answer 2

The junction is where nerve impulses are passed from neuron to neuron where the axon terminal joins with a dendrite of the cell body of another neuron.
Neurotransmitters are messengers that are carried across the neuromuscular junction.

Question 3

Functional types of Neurons; Sensory, Motor, Interneurons

Answer 3

Sensory => (afferent or receptor) Neurons carry messages from receptors in the sense organs, or in the skin, to the central nervous system (brain and spinal cord).
Motor => (efferent or effector) Neurons carry messages from the central nervous system to the effectors, the muscles and glands.
Interneurons/connector/relay => are located in the CNS and are the link between the sensory and motor neurons.

Question 4

Structural types of neurons; Multipolar, bipolar, unipolar and pseudounipolar neurons

Answer 4

Multipolar => 1 axon + multiple dendrites extending from the cell body. Most common and includes most of the interneurons in the brain and spinal cord as well as the motor neurons that carry messages to the skeletal muscles.
Bipolar => 1 axon and 1 dendrite. Both the axon and dendrite may have many branches at their ends. Bipolar neurons occur in the eye, ear and nose, where they take impulses from the receptor cells to other neurons.
Unipolar => Just 1 extension, an axon. Not found in humans but in insects.
Pseudounipolar => Properties of both unipolar and bipolar neurons. 1 axon from the cell body that separates into 2 extensions. Connects to dendrites, and axon terminals. Similar to most sensory neurons that carry messages to the spinal cord.

Question 5

Nerve Fibres

Answer 5

Nerve fibres = Axons and dendrites of nerve cells. Any long extension of cytoplasm of a nerve cell body.
Nerve = Bundles of nerve fibres held together by connective tissue.

Question 6

Nerve Impulses

Answer 6

The message that travels along a nerve fibre, an electrochemical change because of a change in electrical voltage and that is brought about by changes in chemicals (conc of ions inside and out of cell membrane)

Question 7

Electrical charge + Potential Difference

Answer 7

-> A ve+ and ve- charge attract each other by an electrical force.
-> The force that pulls unlike charges together is measured.
-> Strength ↑ as the charge gets closer or larger.
-> When ve+ and ve- charges come together they release energy.
-> When seperated they have the potential to come together and release energy.
-> Potential difference between 2 places is measured
-> Volts (V) or milivolts (mV)

Question 8

Potential difference across a cell membrane

Answer 8

• The fluid outside the cell (extracellular fluid), contains a high conc of sodium chloride (Na+ and Cl-)
• The fluid inside the cell (intracellular fluid) has a low conc of sodium ions and chloride ions (Na+ and Cl-). Main ve+ ions are Potassium (K+) and ve- from organic substances made by the cell
• Membrane potential is the differences in conc between in and out of cell.

Question 9

Resting Membrane potential

Answer 9

Membrane potential of unstimulated nerve cells, about 70mV less than outside (aprox -70mV due to the fluid inside the cell being more ve- charged than the fluid outside the cell)

Question 10

Protein channels

Answer 10

Ions are unable to diffuse through the phospholipid bilayers of the cell membrane directly. Instead, move through protein channels.

Question 11

Leakage channels

Answer 11

Open all the time.

Question 12

Voltage-Gated channels

Answer 12

Only open when the nerve is stimulated

Question 13

Sodium-Potassium Pump

Answer 13

Sodium and Potassium ions move across the cell membrane through a carrier protein - sodium-potassium pump - which it removes 2 K+ ions into the cell for every 3 Na+ ions that are removed.
∴ net reduction of ve+ ions inside the cell.
Moves against the conc gradient ∴ active transport and uses Adenosine Triphosphate (ATP)

Question 14

Polarisation

Answer 14

The location of ions, permeability, and sodium-potassium pump = net flow of ve+ ions OUT of the cell because more K+ ions are diffusing out than Na+ ions diffusing INTO the cell. + addition of ve- organic ions inside the cell making it more ve- than OUT.

This produces a negative resting membrane potential and the membrane is said to be polarised.

Question 15

Conc of Sodium ions (Na+)

Answer 15

Na+ is x10 higher outside than inside. Slightly permeable due to limited no. of sodium leakage channels. This limits Na+ diffusion.

Question 16

Conc of Potassium ions (K+)

Answer 16

Conc of K+ is x30 greater inside than out. Highly permeable to potassium due to large no. of potassium leakage channels. More K+ ions diffuse than Na+ ions.

Question 17

Conc of Chloride ions (Cl-)

Answer 17

Cl- is greater outside than inside. Highly permeable + diffusion through protein channels.

Question 18

Conc of large ve- charged organic ions

Answer 18

Greater inside than outside. Cell membrane is impermeable, ∴ stay inside the cell

Question 19

*Summary - S-P pump

Answer 19

The resting membrane potential is maintained by a difference in the no. of leakage channels for sodium and potassium ions, the membrane being impermeable to large organic negative ions and the sodium-potassium ions. This results in the intracellular fluid being less positively charged than the extracellular fluid.

Question 20

Action Potential

Answer 20

The rapid depolarisation and repolarisation of the membrane (where if the stimulus is sufficient, the signal will be passed along the neuron due to opening and closing of voltage-gated channels)