Notes on Skeletal muscle contraction, Neuron and kinds of Neuron and Importance of Spinal Cord


Skeletal muscle contraction:
Electron microscopy and biochemical analysis show that in muscle fibres cell bends are due to the placement of muscle protein action and myosin with myofibrils. Myosin occurs as thick filaments and actin as thin filaments. The lightest region of a myofibril contains only actin whereas the darkest region contains both.
The functional (contractile) unit of a myofibril is sarcomere each of which extends from one Z line to another z line. The actin filaments attach to the Z lines whereas myosin filaments do not.

When a sarcomere contracts the actin filament slide pas the myosin filaments as they approach one another. This process shortens the sarcomere. The combined decreases in length of the individual sarcomeres account for contraction of the whole muscle fibres and in turn, the whole muscle.
A ratchet mechanism between two filament types produces the actual contraction. Myosin contains globular projections that attach to actin as specific active binding sites, forming attachments called cross bridges. Once cross bridges form, they exert a force on thin actin filament and cause it to move.

Neuron and kinds of Neuron:
Neuron is functional unit of nervous system. Neurons are specialized to produce signals that can be communicated over short to long distances from one part of animals’ body to another. There are three neurons.

(1) Sensory neurons (receptor or afferent): Either act as receptors of stimuli themselves or are activated by receptors. Changes in the internal or external environments stimulate sensory nervous which respond by sending signals to the major integrating centers where information is processed.
(2) Inter neurons: It comprise the integrating centres and receive signals from sensory neurons and transmit them to motor neurons.
(3) Motor neurons (effector or efferent): It sends the processed information via a signal to the body’s effector muscles, causing them to contract or to glands causing them to secret.

Importance of Spinal Cord:
Spinal cord is the part of central nervous system that extends from the brain to near of into the tail. A cross section shows a neural canal that contains cerebro spinal fluid. The grey matter consists of cell bodies and dendrites and is concerned with reflex connections at various levels of spinal cord. Extending from spinal cord are ventral and dorsal roots of spinal nerves. These roots contain main motor and sensory fibres (axon or dendrites) that contribute to the major spinal nerves. White matter of spinal cord gets its name from the whitish myelin that covers it.

Function: Spinal cord is link between brain and most of body parts and is involved in reflex actions.
A reflex is predictable involuntary response to a stimulus. Thus both voluntary and involuntary limb movements, as well as certain organ functions depend on this link.

Comments

Post a Comment

Popular posts from this blog

What is the Dynamic Theory of Profit

Image
Clark's Dynamic Theory of Profit And Its Criticism The Dynamic Theory of Profit is associated with the name of an American Economist, J. B. Clark. In the world of reality, according to J. B. Clark, profit arises only in a dynamic economy. An economy is said to be dynamic when there is a change in population growth or change in the method of production or a change in the consumer’s wants, etc. A society which is without these changes is called a static society. In a static society, only monopoly profits continue to exist. All other economic profits are gradually eliminated by competition. In a dynamic society, an entrepreneur is always confronted with continuous unpredictable changes in demand for his product. The variation in demand may take place due to changes in fashions, tastes, the standard of living, distribution of income, population, new inventions, international repercussions, technological advances, etc. A prudent entrepreneur will always keep an eye on future demand
Read more

Compare the anatomy of Bifacial and Isobilateral leaves

BIFACIAL LEAF: It is also called dorsiventral leaf. This leaf is more strongly illuminated on upper surface than on lower surface. This unequal illumination induces a difference in the internal structure between upper and lower sides. Its internal structure shows: (1)        Upper Epidermis This is single layer of cells with thick cuticle which checks excessive evaporation of water from the surface. It does not contains chloroplasts, stomata are also absent. (2)        Lower Epidermis This is also single layer but with a thin cuticle. It bears many stomata, two guard cells of which contain some chloroplast, none are present in the epidermal cells. Internal to each stomata is large cavity called respiratory cavity. Lower epidermis of leaf is meant for exchange of gases (oxygen and carbon dioxide) between the atmosphere and the plant body. Excess water also evaporates from lower epidermis. (3)        Mesophyll The ground tissue lying between upper epidermis and th
Read more

osmoregulation in terrestrial and aquatic animals

Mechanism of osmoregulation is very important for all groups of animals whether inhibting land or water. Unlike plant cells, animal cells when placed in hypotonic solution burst due to the continuous absorption of water. On the contrary they would shrink and die if constantly placed in hypertonic solution. Normally uptake and loss of water are in balance for proper survival of cell. (1)        Osmoregulation in terrestrial animals: Terrestrial animals are more likely to loose water by evaporation through their permeable surfaces exposed to amsophere. Among various animal groups only Arthropods and vertebrates became the most successful land dwellers. They have developed number of strategies to maintain osmoregulation of their body fluid. (a) Water proof external coverings: To prevent water loss through external surfaces, vertebrates like reptiles, birds and mammals have water proof keratinized epidermis. Similarly the insects have developed external water proof layer called
Read more