Nervous System

Neuroglia are nervous system cells that are not neurons. Choice D gives three types of these cells.

The dura mater is in contact with the skull.

When a graded potential exceeds the threshold for producing an action potential, the AP happens regardless of the strength of the graded potential. This is an all or none event. (Choice D is wrong as sodium ions should be moving IN.)

During the ~0.5 ms period of the action potential in which sodium ions are rushing into a nerve cell, the nerve cannot respond to any stimulus no matter how strong the stimulus is. Because of the impossibility of response, this period is called “absolutely” refractive (refractory = resisting ordinary methods).

The autonomic nervous system is comprised of the sympathetic and the parasympathetic divisions.

Schwann cells surround the axon to form the myelin sheath in peripheral neurones. Oligodendrocytes perform a similar function for neurones in the CNS.

The ciliary muscle is doughnut-shaped with the lens in the “hole” and attached to the muscle by ciliary fibres (zonules). When the ciliary muscle relaxes, it moves away from the lens (the diameter of the hole increases) which causes the ciliary fibres to pull on the lens. This tension in the fibres stretches and flattens the lens into a less convex shape.

The hypothalamus of the diencephalon

Tracts refer to axons which are encased in myelin which makes them look white. Descending refers to impulses that carry information from the brain to the body (motor commands) usually to muscle.

The resting potential has the inside of the cell at about −70 mV compared to the outside.