The ner­vous sys­tem

Jamaica Gleaner - - SPORTS -

THE NER­VOUS sys­tem en­ables us to con­trol and co­or­di­nate all the body ac­tiv­i­ties. It en­ables per­form­ers to pro­duce high-pre­ci­sion move­ments re­peat­edly, mak­ing them ap­pear skil­ful, while other func­tions such as heart­beat carry on au­to­mat­i­cally. The ner­vous sys­tem con­sists of the brain, spinal cord, and the nerves which sup­ply all parts of the body. It is re­spon­si­ble for all our con­scious (or vol­un­tary) ac­tions and has two main parts.

THE CEN­TRAL NER­VOUS SYS­TEM

This con­sists of the brain and spinal cord. The brain is the cen­tral cen­tre of the en­tire sys­tem and is where all the in­com­ing (sen­sory) in­for­ma­tion are pro­cessed and from where the out­go­ing (motor) in­for­ma­tion orig­i­nates. The spinal cord goes down the in­side of the spinal col­umn from the brain. It car­ries all the nerve (sen­sory and motor) mes­sages (im­pulses) be­tween the body and the brain.

THE PE­RIPH­ERAL NER­VOUS

This con­sists of the nerve fi­bres that branch out from the spinal cord, and the var­i­ous or­gans to which they are at­tached. Sen­sory nerves de­tect stim­uli such as tem­per­a­ture, light, sound, touch, etc, and send ner­vous im­pulses to the brain. Once the in­for­ma­tion has been pro­cessed, the ner­vous im­pulses are sent out down the motor nerves to the mus­cles and glands, which carry out the nec­es­sary ac­tion

STRUC­TURE OF NERVE CELLS

Nerve cells or neu­rons carry in­for­ma­tion to or from the spinal cord and brain. They have three main sec­tions:

(a) Den­drites re­ceive mes­sages in the form of nerve im­pulses.

(b) The nu­cleus is the main body of the cell.

(c) The axon trans­mits the im­pulse away from the nu­cleus.

Neu­rons are not ac­tu­ally con­nected to each other but are sep­a­rated by a mi­cro­scopic gap called the synap­tic gap. Im­pulses are able to cross this gap via the re­lease of a chem­i­cal sub­stance called ace­lyl­choline, which al­lows an im­pulse to travel through the ner­vous sys­tem at great speed.

TYPES OF NEU­RONE

There are three types of neu­ron. Each have a dif­fer­ent func­tion and this de­ter­mines where the im­pulse is sent.

1. Sen­sory (af­fer­ent) neu­rons – These re­ceive in­for­ma­tion from the sense or­gans (eyes, ears, nose, tongue, skin) and from re­cep­tors in the body and send im­pulse to the cen­tral ner­vous sys­tem (CNS)

2. Re­lay neu­rons – These are in­side the brain or spinal cord and do the de­ci­sion-mak­ing af­ter the im­pulse from the sen­sory neu­rons reaches the brain. If a de­ci­sion for ac­tion is taken, the im­pulse is past to the motor nerve.

3. Motor (ef­fer­ent) neu­rons – These carry im­pulses from the CNS to mus­cles or or­gans. The cell body is in­side the CNS and the axon leads out of it.

IN­VOL­UN­TARY NER­VOUS SYS­TEM

This part of the ner­vous sys­tem is re­spon­si­ble for func­tions over which we have no con­trol, for e.g. our heart­beat and di­ges­tion. These ac­tions are con­trolled by the medulla ob­lon­gata, an area that forms the top of the spinal cord. This is di­vided into two sec­tions:

1. The sym­pa­thetic ner­vous sys­tem – Re­spon­si­ble for pre­par­ing the body for ac­tion. It stim­u­lates the adrenal gland and causes the heart rate and breath­ing rate to in­crease. It also slows down the func­tion­ing of or­gans not nec­es­sary for phys­i­cal ac­tiv­ity. This is known as the fight or flight re­sponse.

2. The parasym­pa­thetic ner­vous sys­tem – Re­spon­si­ble for slow­ing the body down and func­tions in op­po­si­tion to the sym­pa­thetic ner­vous sys­tem.

RE­CEP­TORS AND RE­FLEX AC­TIONS

The brain also re­ceives in­for­ma­tion from three main types of re­cep­tor or­gans:

1. Ex­te­ro­cep­tors – Out­side the body (eyes, ears etc.)

2. In­te­ro­cep­tors – In­side the body (chem­i­cal changes in blood or lungs)

3. Pro­pri­o­cep­tors – From within mus­cles, ten­dons and joints. These are:

a. Golgi ten­don or­gans – de­tects the amount of stretch in a ten­don

b. Mus­cle spin­dle – de­tects stretch in mus­cles.

c. Joint re­cep­tors – tell the brain at what an­gle the joints are po­si­tioned.

The in­for­ma­tion pick up by these or­gans en­ables us to move our limbs quickly with­out the need to watch them.

There are times when we are re­quired to act quickly, for in­stance, if we touch some­thing hot. This is where our re­flexes come into play. The im­pulse does not need to travel to the brain for in­ter­pre­ta­tion. The im­pulse travel in a fast arc from sen­sory, to re­lay to motor nerves. Mov­ing the hand from the hot ob­ject is the with­drawal re­flex which is sim­i­lar to sneez­ing or blink­ing as a re­sponse to a for­eign ob­ject in the nose or eye. An­other ex­am­ple is the knee-jerk re­flex known as stretch re­flex, wherein a bang on the knee re­sults in the leg ex­tend­ing.

Next topic: The ex­cre­tory and di­ges­tive sys­tems

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