The Central Nervous System (CNS) controls the body and mind. It is made up of the brain and the spinal cord. The brain controls all our actions, thoughts and every activity we undergo. The brain interprets information from our eyes (sight), ears (sound), nose (smell), tongue (taste), and skin (touch), as well as from internal organs such as the stomach.
THE BRAIN AND ITS FUNCTION
The brain is composed of numerous brain cells or neurons, confined and protected by the cranium of the skull.
THE HIND BRAIN
This consists of the cerebellum, pous and medulla oblongata.
1. THE CEREBELLUM
i) It receives impulses from the ear.
ii) It is involved in balance and posture.
iii) It co-ordinates voluntary muscles.
2. THE POUS
i) It serves as the link station between the cerebellum, spinal cord and the rest of the brain.
ii) It carries information between the right and left side of the cerebellum and the cerebrum.
3. THE MEDULLA OBLONGATA
i) It controls breathing / respiration.
ii) It controls heartbeat.
iii) It controls digestion.
iv) It controls size of blood vessels / blood circulation.
v) It controls the secretion of saliva.
THE SPINAL CORD
The spinal cord is the pathway for communication between the body and the brain. The spinal cord communicates back to the body whatever information that is interpreted by the brain. When the spinal cord is injured, the exchange of information between the brain and other parts of the body is disrupted.
The spinal cord is composed of neurons. It extends from the brain to the tail and is protected by the vertebrae. A swelling or ganglion on the dorsal root is formed by the cell bodies of sensory neurons.
FUNCTIONS OF THE SPINAL CORD
i) It connects the nerves to the brain and conducts impulses from them to the brain.
ii) It coordinates simple reflex action.
THE PERIPHERAL NERVOUS SYSTEM
The peripheral nervous system consist of all the nerves connecting the brain and the spinal cord which links the Central Nervous System (CNS) to all the parts of the body.
i) The somatic nervous system: This receives information from sensory receptors and conducts same to the Central Nervous System (CNS).
ii) The autonomic nervous system: This consists of sensory and motor nerves which connect the brain or spinal cord to internal organs such as the liver, heart and alimentary canal. It is made up of two parts.
(a) Sympathetic system which prepares the body for action, and
(b) Parasympathetic system which often acts to return the body to normal state after stimulation by the sympathetic system.
A neurone is a specialized cell which receives information and transmits it in form of electrical impulses to muscles and glands.
CLASSIFICATION OF NEURONS
i) Afferentor sensory neurone: Conduct impulses from receptor or sensory organ to the Central Nervous System (CNS).
ii) Efferent of motor neurone: Relay impulses from the Central Nervous System (CNS) to effector organs i.e. muscles and glands.
iii) Intermediate or association neurone: Transmits impulses within the Central Nervous System (CNS).
TYPES OF NERVOUS ACTION
i) REFLEX ACTION: A reflex or involuntary action is a quick and automatic response by an organ or system of organs of the body to a stimulus e.g. sneezing.
ii) REFLEX ARC: A reflex arc is the nervous path-way taken by a reflex action. It consist of sensory cells which receive the stimulus, sensory or afferent neurone, intermediate neurons, motor or efferent neurone and the effector i.e. muscle or gland which takes action.
iii) VOLUNTARY ACTION: A voluntary action is an action consciously taken in response to stimulus.
CONDITIONED REFLEX AND ITS ROLE ON BEHAVIOUR
A conditioned reflex is an acquired behavior over a long period of time of exposure to a particular stimulus. Once learned and mastered it can be performed without think e.g. teaching, swimming, driving.
DIFFERENCES BETWEEN REFLEX ACTION AND VOLUNTARY ACTION
|SN||REFLEX ACTIONS||VOLUNTARY ACTIONS|
|1.||Its base is the spinal cord||Its base is the brain|
|2.||It involve a minimum number of nerve cells||It involve a large number of nerve cells|
|3.||It is inborn||It can be learnt|
|4.||Action is initiated by muscle receptor cells||Action is initiated by the brain|
|5.||The act takes a shorter distance||The act takes a longer distance|
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