Nervous system.

Extracts from this essay...


NERVOUS SYSTEM Nerve tissue of vertebrates consists of:- (a) Three types of cell:- (i) Neurons, many million, function transmit messages (impulses). (ii) Schwann cells, associate with neurons in PNS (iii) Neurological cells, found within CNS (b) Connective tissue and blood vessels. Neurons Described as unipolar, bipolar and multipolar, according to how many processes project from the cell body. Three types:- (i) Motor (ii) Sensory (iii) Connector (intermediate, relay or inter) 1 Motor (efferent) neurons Transmits impulses from CNS to effectors e.g. muscles. Cell body located CNS. Axon enters a peripheral nerve and terminates in a muscle. May be over a metre long. A peripheral nerve may contain several thousand axons. Axon enclosed within a fatty myelin sheath. At about 1mm intervals are constrictions called nodes of Ranvier. Function of sheath is protection, insulates axon and speeds up transmissions of impulses. Nodes allow exchange of materials between axoplasm and surrounding tissue. Some vertebrates have axons which are non-myelated, however majority are myelated. Both myelated and non myelated neurons associated with Schwann cells, which produces the myelin sheath in the case of myelinated neurons. Both types surrounded by a thin neurilemma which is part of the Schwann cell.


Mescaline and LSD produce their hallucinatory effect by interfering with nor-adrenaline. Reflexes A quick automatic response to a particular stimulus which do not require conscious control, e.g. knee jerk, blinking. Reflex arc - the pathway of a reflex impulse Minimum number of neurons is two, e.g. knee jerk, however usually three. Not as simple as they appear. Connector neurons also transmit impulses to brain which can override the reflex action, e.g. pick up a hot valuable object. Function Complete automation of all protective and avoiding reactions, also internal regulation mechanisms. Leaves higher centres of nervous system free to deal with more complex problems involved in coping successfully with the environment. These reflexes are not learned, i.e. unconditional reflexes. 1 Innate reflexes (born with) e.g., sucking reflex - baby will suck almost any object placed in its mouth. Vital reflex which activates expulsion of milk from mother's mammary glands during suckling. 2 Acquired reflexes - young infants acquire additional reflexes and later override them at certain stages of their growth and development, e.g. grasping reflex. Conditioned reflexes (learned reflexes). e.g. Pavlov experiment with dogs. (a) Primary stimulus: FOOD Response salivation - Innate reflex (b) Primary stimulus: FOOD secondary stimulus ringing bell Response salivation (c)


Impulses spread rapidly all over the muscle in a similar way as nerve impulses are transmitted. Causes contraction of the muscle. Using energy from ATP the bonds between actin and myosin break and reform near each Z line. The Z lines are thus pulled closer together as actin and myosin do not stretch. Bridges, seen connecting the thick and thin filaments. Bonds form between the bridges and the actin filament. On contraction the bridge swings through an arc, pulling the actin filament past the myosin filament. After is has completed its movement, each bridge detaches itself from the actin filament and re-attaches itself at another site further along. The cycle is repeated. Shortening of muscle thus brought about by the bridges going through a kind of ratchet mechanism. Just as the transmission of an action potential by a neuron is 'all or nothing' event, so are the contractions of the muscle cells they innervate. This means that an individual cell is either relaxed or fully contracted. However, muscles are capable of differing strengths of contraction. This is achieved by varying the number of muscle cells involved in the contraction, i.e. whereas as the muscle cells will be used in a strong contraction, only a few will be used in a weak one. ?? ?? ?? ?? Handout nervours system and muscles.doc

The above preview is unformatted text

Found what you're looking for?

  • Start learning 29% faster today
  • Over 150,000 essays available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Over 180,000 student essays
  • Every subject and level covered
  • Thousands of essays marked by teachers

Related AS and A Level Anatomy & Physiology

  1. Respiratory system

    This is the lower section of the muscles. External This is responsible for the evaluation of the rib, and expanding the top section of the ribs. Gaseous exchange This is the main function of the respiratory system. This means oxygen and carbon dioxide travelling between the lungs and the blood.

  2. A level Project, Personal Exercise Program on Netball.

    The principle of specificity also implies that to become better at a particular exercise or skill, you must perform that exercise or skill. Netball should be practiced on the netball court to be specific. Variation is the principle that adds an array of activities to the training process.

  1. The human bodys immune system

    with antibodies and complement proteins they will neutralize or partly neutralize the antigen. Next, they must elude a series of nonspecific defenses - cells and substances that attack all invaders regardless of the epitopes they carry. These include patrolling scavenger cells, complement, and various other enzymes and chemicals.

  2. Physiology Within Sport

    within the heart, because as more is required to become oxygenated more is also sent back which is deoxygenated. On average the cardiac output supplies approximately 5 litres of blood per minute however during exercise there are certain organ and working muscles which receive more blood than others to supply

  1. The Structure of Skeletal Muscle.

    They are: * Type I: slow twitch (ST), slow oxidative (also called red fibres) * Type IIA: fast twitch (FT), fast oxidative (also called white fibres) * Type IIB: fast-glycolytic (a kind of white FT fibres) FT fibres have more access to myosin ATPase than ST fibres.

  2. Free essay

    Body In Action

    Because the lower limbs have to bear the weight of the human body - reaction forces at the feet can be 5-10 times the body weight during sprinting and jumping - the bones of the pelvic girdle, the thigh, and the lower leg are massive and have a network of fibers and many strong muscles to maximize strength and stability.

  1. structure and function of the digestive system and nutrients

    The structure of water is very simple and consists of just Hydrogen and Oxygen. These combine to produce the well- known chemical formula- H2O There is an almost infinite source of water, it can be found in all food and drink.

  2. Skeletal System and Joints

    The condyles at the knee form a condylar joint. The medial and lateral condyles on the distal end, are bumps that fit into corresponding articular facets on the tibia. The gap between the two condyles is called the intercondylar fossa (or notch).

  • Over 180,000 essays
    written by students
  • Annotated by
    experienced teachers
  • Ideas and feedback to write
    your own great essays

Marked by a teacher

This essay has been marked by one of our great teachers. You can read the full teachers notes when you download the essay.

Peer reviewed

This essay has been reviewed by one of our specialist student essay reviewing squad. Read the full review on the essay page.

Peer reviewed

This essay has been reviewed by one of our specialist student essay reviewing squad. Read the full review under the essay preview on this page.