The nervous system is the control and communication system of the body. It sends and receives messages. The nervous system controls all our body movements. It is made up of two parts, the central nervous system (CNS), and the peripheral nervous system (PNS). The central nervous system consists of the brain and the spinal cord, and the peripheral nervous system is made up of the nerves and neurons.
The central nervous system; consists of the brain and spinal cord.
Diagram showing the different structures of the brain.
The brain; it is a large soft mass of nerve tissue that is contained within a vault of bone called the cranium. It is made up of the neurons nerve cells, and other supporting cells. The brain is composed of grey and white matter. The grey matter is the nervous tissues that formed the ‘H’-Shaped structure, and it is surrounded by white matter. The human brains has more than 10 billion nerve cells and over 50 billion other cells, an average weighs 3 1/8 pounds. The brain monitors and regulates our bodily functions and co-ordinates almost all our voluntary movement. The brain is our area of thought, creativity and consciousness.
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The spinal cord; it is an ovoid of column of nervous tissue that average 44 cm in length when flattened. It expands from the medulla oblongata in the brain stem to the second lumbar vertebra in the spinal canal. The spinal cord is the centre of reflexive action. There is a reflex arc that goes from the peripheral nerve to the spinal cord, up to the brain and back down to relay (spread) the action. The spinal cord is contained in a vertebral vault, and it passes down through a hole in each vertebrate. It is surrounded by other tissues, pia mater, cerebrospinal fluid (CSF), arachnoid mater and dura mater. These three maters are called meninges, and they surround the brain. The anterior of the “H” is made up of motor cells from the fibers that make up the motor portion of the peripheral nerves. The sensory neurons enter the posterior of the “H”.
The peripheral nervous system; this is the nerves on the periphery of the body. The autonomic nervous system (ANS) is under the control of central nervous system (CNS) and also part of the peripheral nervous system, these nerves stay inside the body and effect organs and soft tissues. The autonomic nervous system is automatic, and in control of voluntary bodily functions. It is separated into two parts; the sympathetic and parasympathetic nervous system. It regulates the function of the glands, the adrenal medulla, smooth muscle tissue, organs and the heart.
1.2 Explain the functions of each part of the nervous system.
The nervous system is made up large numbers of units known as neurons. They send, receive and process the nerve impulses inside and outside the body. Sensory neurons convert physical stimuli, e.g. smell, light, or sound, into action possibilities, which are then transmitted to the spinal cord or brain. Afferent neurons bring information into the central nervous system. We also have the motor neurons which transmit nerve impulses (sudden urge) away from the brain and spinal cord to muscles or glands, and are known as efferent neurons.
Brain; the cerebral cortex is linked to three main varieties of activity:
Mental activities; this involved in memory, intelligence, sense of responsibility, thinking, reasoning, moral sense and learning. These are accredited to the higher centres.
Sensory perception; this includes the perception of pain, temperature, touch, sight, hearing, taste and smell.
Initiation and control; to initiate and control voluntary muscle contraction.
The nerve cells initiate the contraction of voluntary muscles. Nerve fibres from Betz’s cell move past descending through the internal capsule to the medulla oblongata, and crosses to the opposite side and descends in the spinal cord. The motor region of the right hemisphere of the cerebrum controls voluntary movement of the left side of the body. There is a group of nerve cells called the motor speech (broca’s); it controls the movement essential for speech. The postcentral (sensory) is the area that perceived sensations of pain, temperature, pressure and touch, knowledge of muscular movement and position of joints. The parietal is believed to be connected with obtaining and retaining accurate knowledge of objects. We perceive spoken word from the sensory speech, and the auditory (hearing) receive and interpret transmitted impulses from the inside ear by the auditory nerves. The olfactory (smell) receives impulses from the nose via olfactory nerves and interpret it. Taste is the area where impulses from special nerves endings in taste bud and tongue, and in the lining of the cheeks, palate and pharynx are perceived as taste. The visual is the area which receives and interprets impulses as impressions. There are groups of cells called known as nuclei, they act as relay stations. It passes one neurone to the other in chain. Some important masses of grey matter are:
Basal nuclei; it is thought to influence skeletal muscle tone
Thalamus; this is where sensory input from skin, viscera and special sense organs are transmitted to before redistribution to cerebrum
Hypothalamus; it controls the output of hormones from both lobes of the gland, and it also control the autonomic nervous system, such as thirst, body temperature, hunger, heart and blood vessels defensive reactions.
Spinal cord; it is the centre of reflexive action. The reflex arc is the pathway of nerves through spinal cord. The first step of reflex arc is stimulation of a receptor nerve. They sense heat, coolness, pressure or over-stretching of the muscle. The sensory neuron transmits impulse to spinal cord. The sensory nerves link directly with a motor or glandular nerve, or go through in-between nerve and then to the motor of the glandular nerve, depending on the reflex being stimulated. The nerve sends signals to the muscles or glands to react. Visceral reflexes control heart muscle, glands and organs, and the somatic reflexes control involuntary movement of the skeletal muscles. The spinal cord does the followings:
Support the body and the skull, helps us to stand upright and maintain body balance.
Flexible movement; it allows and helps the head and neck move, and permit the body to stretch, lean, rotate and lean.
It helps protect internal organs, such as heart and lungs.
It provides base for attachment of muscles, ligaments and tendons (tough band connecting muscle to bone).
It has bone marrow inside the bones of the spinal cord that produces red blood cells and also stores minerals.
It connects the upper body to the lower body.
Its intervertebral discs acts like a shock absorber.
Peripheral nervous system; it is the autonomic nervous system which is part of the peripheral nervous system, that control the internal organs; it consists of the motor neurons. It has two systems, the sympathetic nervous system and the parasympathetic system. The autonomic nervous system controls muscles in the heart, the smooth muscle of the intestine, bladder, and uterus. The sympathetic nervous system is involved in the fight or running away response. The parasympathetic is involved in relaxation. Each of the two functions in the reverse of the other (resentment). The two systems act in opposition to maintain homeostasis (state of equilibrium). The sympathetic nervous system promotes the following activities:
It allows blood flow to skeletal muscles and the lungs.
It diverts blood flow away from the gastro-intestinal tract and skin.
It dilates bronchioles of the lung.
Increases heart rate and the ability of cardiac cell (myocytes) to contract.
Dilate pupils (opening in eye) and relaxes the ciliary (surrounding lens of eye) muscle to the lens.
It narrows all intestinal sphincters and urinary sphincter.
It inhibits (adversely affect action of an organ) peristalsis.
Responsible for the stimulation of orgasm.
The parasympathetic nervous system promotes:
The expansion of blood vessels leading to the gastro-intestinal tract, increasing blood flow.
The constriction of bronchiolar diameter when the need for oxygen has diminished.
The constriction of the pupil (opening in the eye) and contraction of the ciliary (surrounding lens of eye) muscle to the lens.
The stimulation of salivary gland secretion, and speed up peristalsis (muscle contraction).
The erection of genitals.
The stimulation of sexual arousal.
The control of the myocardium (heart muscle).
3.2 Explain the transmission of an impulse across a synapse.
A synapse is the junction where communication between neurons and neurons between muscles takes place. Synaptic transmission starts when nerve impulse arrives at the pre-synaptic axon terminal. The depolarisation (less polarity) of the pre-synaptic membrane starts series of events leading to transmitter release, and the activation of receptors that is on the post-synaptic membrane. Synaptic vesicle lives in different pool; attached to the cytoskeleton in a reverse pool, or free in the cytoplasm. A number of the free vesicles make their way to the plasma membrane for docking, and sequence of primary reactions prepares the vesicular and plasma membranes for fusion. The membranes of the synaptic vesicles are drawn together passing through protein complexes that are articulated on the vesicle and pre-synaptic membranes. A depolarised axon terminal open voltage calcium channel and calcium ions run into the axon terminal and some of the calcium ions attach to a protein on the synaptic vesicle membrane known as synaptotagmin. The vesicles are drawn closer to the pre-synaptic membrane, when calcium attach to synaptotagmin on the synaptic vesicles adjacent to the active region. Transmitter cargo is release into the synaptic cleft when the vesicles combine with the axon membrane. Some transmitter molecules attach to receptor molecules in the post-synaptic membrane. Post-synaptic cell response depends on neurotransmitter and receptor combination. After attaching acetylcholine, the channel opens and sodium ions enter the post-synaptic cell, and generate an exciting post-synaptic response. The transmitters are removed or inactivated quickly from the synaptic cleft. Acetylcholine, an enzyme in the synaptic cleft, acetylcholinesterase (AChE), breaks down Ach into choline and acetate. The transmitter released from the receptor causes the channel to close. Some transmitters are not broken down by enzymes and many transmitters rapidly clear from the synaptic cleft and taken into the pre-synaptic terminal by special proteins known as transporters. This process is called reuptake, it not only cut off synaptic activity quickly, but also allow the terminal to recycle transmitter molecules. Membrane needed for the creation of synaptic vesicles, is also recycled passing through endocytosis of the pre-synaptic membrane. The recycled vesciles which are now filled with neurotransmitter molecules are ready for another circle of synaptic transmission.
4.1 Describe the main parts of the brain and explain their functions.
The brain; it is a large soft mass of nerve tissue that is contained within a vault of bone called the cranium. It is made up of the neurons nerve cells, supporting cells. The brain is composed of grey and white matter. The grey matter is the nervous tissues that formed the ‘H’-Shaped structure, and it is surrounded by white matter. The human brains has more than 10 billion nerve cells and over 50 billion other cells, an average weighs 3 1/8 pounds. The brain monitors and regulates our bodily functions and co-ordinates almost all our voluntary movement. The brain is our area of thought, creativity and consciousness.
Functions of the brain; the functions of the three main parts of the brain are the followings:
The cerebrum; this is the largest portion of the brain, it occupies about 2/3 fractions of the human brain. The cerebral hemisphere is separated into two by a longitudinal fissure. The two hemispheres are joined by a fibre called corpus callosum that consists of long bundles of closely packed nerve fibres of about 10cm long. The corpus callosum has about 200 million of nerve fibres.
The cerebral hemisphere is divided into four lobes by three deep grooves called fissures. From the front part of the brain to the back is known as the Frontal lobe, the Temporal lobe, Parietal lobe and Occipital. The right part of the brain controls the left part of the body while the left part of the brain controls the right.
Frontal lobe- It is involved in inner monitoring of complex thoughts, actions and creative ideas. The anterior (front) portion of the frontal lobe is called the prefrontal cortex. The posterior (back) of the frontal lobe consists of the motor and premotor areas. Nerve cells that produce movement are located in the motor areas.
Temporal lobe- it helps in the decoding and interpretation of sounds. It is the centre for memory and emotions. It also helps in language comprehension.
Occipital lobe – it decodes and interprets the visual information, such as shapes and colours.
Parietal lobe- it is the main area for feelings, touch, hot, cold and pain. It takes different bits of information from the surroundings, organises it and communicates it to other part of the brain.
The cerebral cortex; this is the outside surface of the cerebrum with a layer of 2-4mm thick. It has a greyish brown look, and it is referred to as the gray matter. The surface of cerebral cortex is divided into large number of folds, which increases the surface area of the brain.
The Diencephalon – it is made up of mainly subcortical nuclei, thalamus and hypothalamus. .
Thalamus – it lays crossway to the cerebrum. The thalamus plays an important part in the link between the sense organs and cerebral cortex. It receives bulk of incoming signal from the sense organs. It also determines the source of signals, evaluates their importance integrates them and passes them to the cerebrum.
Hypothalamus – it lies in the base of thalamus, weighs about 4 gm with a small vascularised structure. It is only about 1/300 of the total brain mass. It incorporates and manages visceral activities. It maintains homeostasis and the body’s internal equilibrium. The hypothalamus corrects the rate of heart beat and respiration whenever they go wrong. It is known as the control centre for fight and flight (Control Mind, 2010).
The mid brain; this component forms the middle part of the brain. It controls the activity of voluntary muscles. It is made up of four small lobes called the corpora quadrigemina. The upper part is colliculi which receives sensory informations from eyes and muscles of the head; it controls all the visual reflexes and coordinates the movements of the head and eyes. The lower part control part of colliculi and receives sensory impulses from the ears and muscles of the head. (Control Mind, 2010).
The hind brain; It is made up of the followings:
Cerebellum; it is the second largest part of the brain and it consists of two cerebral hemispheres. They are located at the cerebral hemisphere and the brain stem. The cerebellum assists in the maintenance posture and balance of the body. It plays an important role in controlling the fast muscular activities of the brain, e.g., running and talking.
Medulla Oblongata; this is the posterior part of the brain which links the other parts of the brain to the spinal cord. The medulla controls the subconscious activities, e.g., digestion and breathing.
Brain stem; it is part of the brain that controls basic functions that are necessary for maintaining blood pressure, eye movements, heartbeat, swallowing and breathing.
Pons Varoli; it is the base of the brain stem. It connects the cerebral cortex to the cerebellum. It relays the information between cerebrum and cerebellum. It is the part of the brain that controls arousal and control respiration (Quizlet, 2010).
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