Question

Explain how leak channels and gated channels differ.

Discuss the role of calcium ions in the transmission of an action potential at the synapse.

Define continuous propagation and saltatory propagation

Identify and describe the three spinal meninges.

Graded potentials

		produce an effect that increases with distance from the point of stimulation.
		produce an effect that spreads actively across the membrane surface without diminishing.
		always cause repolarization.
		may be either a hyperpolarization or a depolarization.
		are often all-or-none.

please type it

Answer 1

1. Leak channels, also known as passive channels are always open, which allows the passage of sodium ions (Na) and potassium ions (K) across the membrane to maintain the resting membrane potential of –70 millivolts. Whereas the voltage-gated ion channels are opened and closed in response to different membrane potential changes. They can be chemically controlled, voltage controlled, or mechanically controlled. Most gated channels at the resting potentials are closed.

2. Action potentials open calcium channels in the synaptic knob membrane that allows an inward movement of calcium ions. Calcium ions activate the release of synaptic vesicles from the neurotransmitter into the synaptic cleft. During this exocytose cycle the synaptic vesicles fuse with the presynaptic membrane.

3. Continuous propagation mechanism is when an action potential in an axon spreads through a sequence of small steps into a neighbouring area of its membrane. Whereas, the mechanism of saltatory propagation is when it propagates by jumping along the axon from one site to another.

4. The three layers of meninges are; dura mater, arachnoid mater, and pia meter.

a. The dura mater is the outermost layer of meninges, which lies immediately below the skull and vertebral column bones. It is dense, rugged, and inextensible.

b. It is made of connective tissue layers, is avascular, and does not receive any innervation. The arachnoid material is the middle layer of meninges which lie directly below the dura mater.

c. The pia mater is located beneath the subarachnoid space. It is very small and closely adhered to the brain and spinal cord surface. It's the only covering that fits the brain contours (the gyri and the fissures).

5. Graded potential – may be either a depolarization or a hyperpolarization.