IGCSE Coordinated Science: Nervous Control in Humans 1. Describe the human nervous system in terms of the central nervous system(brain and spinal cord as areas of coordination) and the peripheral nervoussystem which together serve to coordinate and regulate body functions. ● Nervous System ○ The point of the nervous system is to “detect” and “respond” tostimuli. Stimuli is basically a detectable change in ones internal orexternal environment. The Nervous System is split into twoessential systems, the Central nervous System and the PeripheralNervous System. ● Central Nervous System ○ We commonly abbreviate this as the CNS. The CNS consists mainlyof the brain and spinal cord. The Spinal cord is a long, thin ,tubular bundle of nervous tissue and support tissue that runsthrough a tunnel in the backbone, essentially protecting it. Theskull protects the brain. The CNS gives out instructions to theother parts of the body to perform certain jobs. If your centralnervous system is impaired, you might be paralyzed! ● Peripheral Nervous System ○ Key job of PNS is to detect stimuli and send impulses to the brainregarding the detected stimuli ○ PNS is made out of receptors and nerves which help carry theimpulses ● Receptor Cells: Cells that detect something about its environment. ○ There are many receptors in the body which are able to detect awide variety of things such as Temperature, Light, Touch, Soundand Chemicals. ■ Effectors are opposite of receptors. ■ Effectors respond to stimuli, whilst receptors detectit. Effectors are usually muscle and glands. 2. Describe the structure and function of the eye, including accommodationand pupil reﬂex.
Human eye is a Sensory OrganFeatures of Eye Section Feature Retina This is the most inner-most layer of the eye. It is verysensitive to light. Fovea is located here along with Rodsand Cons. Iris The Iris widens and narrows to control the amount of lightthat enters the eye depending on the light intensity. Suspensory Ligaments Loosens and tightens. This is to adjust the thickness of thelens. Choroid Middle layer that surrounds the eye that contains manyblood vessels.
Iris This widens and narrows to control amount of light thatenters the eye. This amount is dependent on lightintensity Scelera Outer most, protective layer of the eye. Retina This is the inner most section of the eye. It is verysensitive to light and is where the fovea is located. It alsocontains rods and cones. Fovea A light sensitive section. Accomodation ● The angle the light hits the eye depends on the distance of the objectfrom the light ● All light rays that hit the eye needs some amount of refraction to bedirected to the fovea. ● This why the lens can widen and narrow according to the distance of theobject being looked at. ● This widening and narrowing is to ensure that the light ray can hit theretina at the right spot. ● We call this accomodation ● This is the process that involves focusing light to achieve a sharp image ● 70% of light rays are refracted as they pass through cornea: ● The lens then makes ﬁnal adjustments by changing its shape so lightcoming from near or far objects can be focused on.
When lens focuses on near objects: ● Ciliary muscle contracts ● This is why if you force your eyes on close objects for a long period oftime, your eyes begin to feel sore. ● This causes suspensory ligaments to relax. ● Lens are allowed to be thickened and become more convex. ● Lens become more elastic and will thicken if allowed. ● Give’s lens more refractory power. On far objects: ● Ciliary muscles relax ● Suspensory Ligaments tense up ● Stretches the lens so makes it less thinner and convex. ● Decreases lens refractory power. Pupil Reﬂex ● Pupil increases in size in dim light and vice-versa: ● The increase in size (dilation) is to increase the amount of light collectedand to boost vision. ● The decrease in size (contraction) is to decrease the amount of lightcollected and hence protect ones retina’s. ● This is an automatic reﬂex rather than a conscious action and one doesnot need to consciously devote effort to allow this process to occur. 3 Identify motor (effector), relay (connector) and sensory neurones fromdiagrams Just focus on the three neurons you need to know. 4 Describe a simple reﬂex arc in terms of sensory, relay and motor neurones,and a reﬂex action as a means of automatically and rapidly integrating andcoordinating stimuli with responses. Reﬂex Actions ● Reﬂex are fast, automatic, and cannot be learned. ● These exist to ensure that animals have a good chance of survival Reﬂex Actions include:
● Blinking (stimulated by bright light) ● Knee jerk (stimulated by the force applied to the knee) ● Yawning (stimulated by high Carbon Dioxide levels) Reﬂex Arc: Process which controls the reﬂex actions. The path taken for a reﬂex arc: Sensory Cell –> Sensory Neurone –> Relayneurone –> Motor neurone –> Effector