Control and Coordination Part-2

6Human brain

  • Human brain is a highly complex organ, which is mainly composed of nervous tissue
  • It is present in a cavity called the skull.
  • It is surrounded by a bony box known as the cranium.
  • The tissues are highly folded to accommodate a large surface area in less space. 
  • It is covered with membranes called the meninges.
  • The human brain can be divided into three regions-forebrain, midbrain and hindbrain.

Fore brain

  • Cerebrum: It is the largest part of the brain that is roughly divided into two parts called the cerebral hemispheres. The cerebrum controls voluntary motor actions. It is the site of sensory perceptions, like tactile and auditory perceptions. It is the seat of learning and memory.
  • Frontal: It controls the facial muscular activities.
  • Temporal: It helps in hearing.
  • Occipital: It helps in vision.
  • Parietal: It controls the sensation of taste, touch, temperature etc.
  • Olfactory lobes: They are the prominent lobes and they help in producing sensation of smell.

Midbrain

  • It has no sub division and its function is to control involuntary actions such as change in pupil size and some reflex actions.

Hindbrain

  • Cerebellum: It is also like cerebrum and we can say it is the second largest part of the brain. Their major function is to control body movements and posture movements.
  • Pons: It is the small ovoid body located near the brain stem. It controls some aspects of respiration and involuntary actions.
  • Medulla oblongata: It is the stem of the brain. It controls involuntary activities like coughing, sneezing, heart beat etc.

Spinal cord

  • Spinal cord controls the reflex actions and conducts massages between different parts of the body and brain.

Reflex Action

  • It is a sudden, involuntary reaction of the body in response to stimuli.
  • For example, when your hand touches a very hot electric iron, you move away your hand in a jerk.
  • All of this happens in flash and your hand is saved from the imminent injury. This is an example of reflex action.

Reflex Arc

  • The path through which nerves signals, involved in a reflex action, travel is called the reflex arc.
  • The following flow chart shows the flow of signal in a reflex arc.
    Receptor → Sensory neuron → Relay neuron → Motor neuron → Effector (muscle)
  • The receptor is the organ which comes in the danger zone. The sensory neurons pick signals from the receptor and send them to the relay neuron.
  • The relay neuron is present in the spinal cord.  It is processed there, and the information is brought back to the concerned muscle to carry out the action.
  • The effector comes in action, moves the receptor away from the danger.