Central Nervous System: The Brain and Spinal Cord

Central Nervous System

• Central nervous system is the centre of all neural activities. It organizes all incoming sensory information, controls all cognitive activities and provides motor control over muscles and glands. It is assumed that human brain has developed periodically during millions of years from the brain of primitive animals and this development process is still continued. The weight of an adult human brain is approximately 1.36 kg and it contains 100 billon nerve cells. Brain has many structures which perform specific functions.

Brain

• Brain is located inside the skull. For the ease of study, brain can be divided into three parts.
• Forebrain: Itconsists of thalamus, hypothalamus and cerebrum.
• Midbrain: It is located between forebrain and hindbrain.
• Hindbrain: It consists of medulla, pons and cerebellum.
• Forebrain: Forebrain is considered the most important part of brain as it performs all cognitive, emotional and motor activity.Now, we will discuss some important parts of forebrain: hypothalamus, thalamus and cerebrum.

• Hypothalamus: It is one of the smallest parts of brain but it plays a major role in determining behavior. It regulates the physiological processes of emotional and motivational behavior such as eating, drinking, sleeping, regulation of body temperature and sexual arousal etc. It also regulates and controls internal environment of the body by controlling activities such as heart rate, blood pressure, levels of hormones (secretions of various endocrinal glands).
• Thalamus: It is an oval shaped structure located on the upper part of hypothalamus. It works as a ‘relay station’ which sends sensory signal received from sensory organs to appropriate part of the brain. It also sends the output motor signals received from brain to appropriate body parts.
• Cerebrum: This is also known as cerebral cortex. It performs all higher level cognitive activities such as attention, perception, learning, memory, language and problem solving etc. Cerebrum consists of two third of the total area of the brain. Its thickness varies from 1.5 mm to 4 mm which entirely covers the surface of brain. Cerebrum is divided into two equal halves which are called cerebral hemispheres. Although both hemispheres are similar in appearance but their functions are different. For e.g. left hemisphere controls language related behavior whereas right hemisphere controls activities related to images, spatial relations, pattern recognition etc. Both hemispheres are connected to each other by a bundle of nerve fibers known as corpus callosum. It communicates messages between both the hemispheres.
• Midbrain
  It is relatively smaller in size and connects both forebrain and hindbrain. It consists of visual and auditory sensory centers. An important part of midbrain is reticular activating system (RAS) which is responsible for emotional behavior. It makes us alert and active by regulating sensory information. It also helps us in selecting information from environment.
• Hindbrain
  Medulla oblongata: It is lowest part of brain which is attached to spinal cord. It regulates basic life saving activities such as breathing, heart rate and blood pressure. That is why medulla is called vital centre of the brain.
• Pons: Pons is attached to medulla on one side and to midbrain on the other side. Pons receives auditory signals transmitted by our ears. Pons is considered to be related with our sleep system specially with dream sleep. It contains nuclei that affect facial expressions and inhalation-exhalation process.
  Cerebellum: This is most developed part of the hindbrain. It can be easily identified due to its rough surface. It controls and maintains body postures and balance. It is cerebellum due to which we don’t need to focus too much on our postures while performing activities such as walking, riding a bicycle or dancing.

Spinal Cord

• It is a bundle of nerve fibre shaped like a long rope which is located inside vertebral column to its entire length. It is attached to medulla of brain on one side. The other side is freely extended like a tail. The inside structure is same in its entire length. The mid part of spinal cord is shaped like butterfly which is made up of grey matter. Circling this grey matter is white matter of spinal cord.
• Spinal cord performs two major functions: first it send sensory signals received from lower parts of body to brain and taking motor impulse received from brain to different body parts, second it also controls some reflex actions.
• Reflex Action: Reflex action is an involuntary action which happens immediately after a specific stimulation. Reflex action takes place without conscious decision of brain. For example blinking of eyes is a reflex action. When any object suddenly comes close to our eyes, our eyes blink. Our nervous system performs many reflex actions like contractions of pupils in the eye, immediately removing hands when touched by a very hot or very cold. These reflex actions are directly controlled by spinal cord in which brain does not play any role.

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Important Points of Human Behavior :- 

1. “Inthis chapter, the relation of human behavior and biology is described.”
2. The cell is the basic unit of human body. Many cells form tissue, many tissue to organ, many organs to organ systems are formed. These organ systems perform specific functions of our body. Nerve cell is the basic and smallest unit of nervous system. It is also called neuron.
3. Nerve cells are of three types on the basis of functions: Sensory, motor and association neurons.
4. Nerve cells perform the function of transmitting information in our body.
5. Nervous system is of two types: Central Nervous System and Peripheral Nervous System.
6. Central Nervous system consists of brain and spinal cord.
7. Peripheral nervous system is divided in two parts somatic nervous system and autonomic nervous system.

Human Behavior Questions and Answers

1. Which part of nerve cell contains nucleus?
A Axon
B. Soma
C. Myelin Sheath
D. Nodes of Ranvier

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2. Which part of nerve cell increases the speed of nerve conduction?
A Myelin Sheath
B. Dendrites
C. Thalamus
D. Pons

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“3. Which part of brain controls activities like eating, drinking, sleeping, temperature regulation and sexual arousal?”
A Pons
B. Cerebellum
C. Hypothalamus
D. Thalamus

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4. How many pairs of cranial nerves are there in human brain?
A. 6
B. 10
C. 12
D. 31

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