Nervous System

The sympathetic division “stirs you up” rather than promoting the conservation of energy.

Graded potentials that are above the threshold stimulate an action potential.

Spinal reflexes initiate and complete without the need for nerve impulses to be sent to or from the brain. In fact an active brain will exert some restraint on the muscle activity that is generated. Hence a dead brain does not exert any restraint so the spinal reflexes are more marked.

CSF is located in the subarachnoid space and within the brain.

“Most sensitive” means sounds loudest to us. Some people can hear sound with frequency as low as 20 Hz or as high as 20,000 Hz, but the sound will be very faint. Sounds with frequency between 500 and 6000 Hz seem to be loudest to the human ear.

The others refer to the optic chiasma, the cruciate ligament and the decussation of pyramids.

When Na⁺ ions move into the axon, it is called depolarisation as the resting potential changes from −70 mV to +30 mV. Movement out by K⁺ ions is called repolarisation as the potential returns to −70 mV. One followed by the other is the action potential.

The “barrier” is the wall of the capillary that allows some molecules/ ions to pass through into the cerebral spinal fluid but prevents the passage of many other molecules.

A decussation is a crossing over. Nerves from the left side of the brain cross over to the right side of the spinal cord to innervate the right-hand side of the body (and vice versa).

The precentral gyrus is the primary motor area of the brain.