Anatomy and Physiology of Muscle Contraction, Brain, Spinal Cord, Ear, and Skin

Posted on May 5, 2024 in Biology

Physiology of Muscle Contraction

Contraction and Relaxation of Skeletal Muscle Fibers: The contraction and relaxation of skeletal muscle fibers occurs in following steps.

Muscle contraction occurs because cross-bridges attach to and ‘walk along the thin on at both ends of a sarcomere, progressively pulling the thin filaments toward the of a sarcomere. As the thin filaments slide inward, the Z discs come closer together, sarcomere shortens.

Contraction cycle: The contraction cycle is the repeating sequence of events that adding of the filaments

  • Myosin ATPase hydrolyzes ATP and becomes energized,
  • The myosin head attaches to actin, forming a crossbridge,
  • The crossbridge generates force as it rotates toward the center of the sarcomere stroke
  • Binding of ATP to the myosin, head detaches it from actin. The myosin head again hydrolyzes the ATP, return to its original position, and binds to a new site on actin as the continues

An increase in Ca2+ concentration in the cytosol starts filament sliding, a decrease off the sliding process The muscle action potential propagating into the T tubule system causes opening of

release channels in the SR membrane. Calcium ions diffuse from the SR into the

dat combine with troponin. This binding causes tropomyosin to move away from the

binding sites on actin.

Structure of Brain

Brain and Its Parts

Brain is a very complex Organ, forming the centre of the nervous system. It is enclosed in a bony structure termed as cranium. The general structure, of human brain resembles that of other mammals, except in size. The human brain is three times larger in size than the brain of a typical mammal with a comparable body size. Cerebral cortex (the major portion of the brain) consists of neural tissue arranged in a convoluted layer, which covers the surface of the forebrain. The frontal lobes of the brain are specifically expanded and are responsible for carrying out functions like self-control, planning, reasoning, and abstract thought.
Cerebrum: Cerebrum forms the major Portion of the brain. It is divided into two hemispheres known as cerebral hemisphere, which repositioned over the brain stem.
The left and right cerebral hemispheres are separated from each other by a prominent longitudinal fissure Corpus callosum connects the two cerebral hemisphere internally. It is broad band, made up of white matter, and comprises of axons extending between the two hemispheres

Cerebral Cortex: Cerebral cortex is the outer layer of neural tissue that covers the cerebrum. It ranges in thickness from 1.5-5 mm. It is sometimes referred to as the grey matter, since the nerves in this area are not insulated as in most other parts of the brain that appear white.

Brain Stem

Brain stem is the part of brain lying between the spinal cord and diencephalon. It comprises of the following parts:

  • Medulla Oblongata
  • Pons
  • Midbrain

Medulla Oblongata: Medulla oblongata (2.5 cm long) is the lower half of the brain stem, which continues with the spinal cord. The upper part of the brain stem is continuous with the pons. Medulla oblongata us situated within the cranium, just above the foramen magnum. Central fissures mark the anterior and posterior surfaces of the medulla oblongata.

Pons: Pons is a part of brain stem located above the medulla and below the midbrain. The cerebellum lies posterior to the pons.

Structure and Reflexes of Spinal Cord

The spinal cord is made up of grey and white matter. The grey matter is arranged in the shape of H or a butterfly and is surrounded by the white matter. The grey matter is made up of dendrites, neuronal cell bodies, non-myelinated

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Physiology of the Ear

The ear is the organ of hearing and lance. The parts of the ear include :

External or Outer Ear, consisting of:

  • Pinna or Auricle: This is the outside part of the ear.
  • External Auditory Canal or Tube: This is the tube that connects the outer ear to the inside or middle ear.
  • Tympanic Membrane (Eardrum): The tympanic membrane divides the external ear from the middle ear.

Middle Ear (Tympanic cavity), consisting of

  • Ossicles: Three small bones that are connected and transmit the sound waves to the inner ear. The bones are called:
  • Malleus, Incus, Stapes
  • Eustachian Tube: A canal that links the middle ear with the back of the nose. The eustachian tube helps to equalize the pressure in the middle ear. Equalized pressure is needed for the proper transfer of sound waves. The eustachian tube is lined with mucous, just like the inside of the nose and throat.

Inner ear, consisting of:
Cochlea: This contains the nerves for hearing.

Vestibule: This contains receptors for balance.

Semicircular Canals: This contains receptors for balance.

How do We hear?

Hearing starts with the outer ear. When a sound is made outside the outer ear, the sound waves, or vibrations, travel down the external auditory canal and strike the eardrum (tympanic membrane). The eardrum vibrates. The vibrations are then passed to 3 tiny bones in the middle ear called the ossicles. The ossicles amplify the sound. They send the sound waves to the inner ear and into the fluid-filled hearing organ (cochlea). Once the sound waves reach the inner ear, they are converted into electrical impulses. The auditory nerve sends these impulses to the brain. The brain then translates these electrical impulses as sound.

Structure of Skin

Skin is the thick, protective covering of body which comprises of the following layers:

Epidermis: It is the outermost covering of stratified squamous epithelial tissue, lacking blood vessels. The major portion of epidermis is made up of keratinocytes cells, which synthesise a protein called keratin. Desmosomes are protein structures which act like bridges for keratinocytes. These keratinocytes constantly move towards the periphery of the skin. Thickness of epidermis varies from 0.05 mm. (at eyelids) to 0.8-1.5 mm (on soles of feet and palms of hands). The epidermis is further differentiated into four distinct layers made up of keratin and is distinguished by the various maturation stages. Starting from the lowest lying layer and moving towards the superficial layer, the layers of the epidermis are as follows:

  • Stratum Basale: It is the deepest layer of epidermis present just above the dermis, and consists of dividing and non-dividing keratinocytes. The inner basal surface of epidermal keratinocytes consists of small structures called hemidesmosomes. Gradually these keratinocytes undergo division followed by differentiation and move towards the upper surface. Basal cells consist of a pigment called melanin, produced by melanocytes.
  • Stratum Spinosum: As the cells from stratum basale mature, they move upwards to form the next layer, which is stratum spinosum. The cells in this layer are connected by intercellular bridges called desmosomes. At microscopic level, these desmosomes appear as ‘prickles’. Stratum spinosum contains Langerhans cells which are dendrites, and are formed in the bone Langerhan’s cells play a crucial role in immunological reactions to skin.
  • Stratum Granulosum: The cells now move upwards to reach stratum granulosum where become flat and anucleated. The cytoplasm of cells appears granular.
  • Stratum Corneum: This layer is composed of several layers of hexagonal shaped viable, cornified cells called corneocytes. These corneocytes are keratinocytes that are in heir last phase of maturation. The corneocytes arm around 10-30 layers in almost every part of skin; but, the thickest layers are found in the alms and soles.