The Nervous System PDF

The nervous system: Introduction and terminology: The nervous system is the body's control and communication centre and ensures that humans respond effectively and quickly to their environment. This ensures their survival. We live in an environment that is constantly changing and we are exposed to...

The nervous system: Introduction and terminology: The nervous system is the body's control and communication centre and ensures that humans respond effectively and quickly to their environment. This ensures their survival. We live in an environment that is constantly changing and we are exposed to external stimuli that are constantly changing, eg. changes in light or temperature, as well as internal stimuli eg. changes in muscle tension. The nervous system needs to detect these stimuli and enable to body to respond effectively to each stimulus. The terminology that will be used in this section includes the following: 1. Stimulus: A physical or chemical change in the environment that requires a response from the organism. 2. Meninges: The three protective membranes that surround the brain and spinal cord. 3. Reflex action: A quick, involuntary, automatic action that involves the spinal cord and does NOT involve the brain. 4. Reflex arc: The pathway a reflex action follows in order to bring about a reflex action. 5. Synapse: A gap between two consecutive neurons or between a neuron and an effector. 6. Neurotransmitter: A chemical substance that enable an electrical impulse to flow smoothly between consecutive neurons. (eg. Acetylcholine) 7. Receptor: an organ that detects the stimulus and converts it into an impulse 8. Effector: an organ or gland that receives the impulse from the CNS and carries out the appropriate response. How the nervous system is divided: How the nervous system is divided: 1. The central nervous system (CNS) 2. The peripheral nervous system (PNS) The central nervous system (CNS): The central nervous system is made up of two parts: The brain The spinal cord The brain: The brain is the enlarged upper part of the spinal cord, protected by a bony cranium, cerebrospinal fluid and three membranes called meninges. These meninges are: The dura mater – outermost membrane The arachnoid matter – middle membrane The pia mater – the membrane closest to the brain The four parts of the brain that you need to know the location and function of are: Cerebrum: Controls voluntary actions Receives and interprets sensations Responsible for higher mental functions. Memory, intelligence, judgement Corpus callosum: A white band of neurons that connect the two hemispheres of the cerebrum Cerebellum (Tree of life): Controls all voluntary actions to ensure smooth movement Control muscle tone to maintain balance and posture Medulla oblongata (part of the brain stem): Controls involuntary functions. E.g breathing, blood pressure, peristalsis The spinal cord: The spinal cord consists of: 1. Central canal: This canal runs through the centre of the spinal cord and is filled with a cerebrospinal fluid. 2. Grey matter and white matter: The grey matter forms a h-shaped structure inside the spinal cord, while the white matter surrounds it. The white matter contains myelinated nerve fibres that extend to and forms the brain. 3. Spinal nerves: A pair of spinal nerves enters and leaves the spinal cord between each successive vertebra. Each spinal nerve consists of two roots: The dorsal root: Composed of sensory neurons, it conducts impulses from the receptors to the grey matter of the spinal cord. The cell bodies of these neurons are located in a swelling called a ganglion. Ventral root: Composed of motor neurons, it conducts impulses from the grey matter of the spinal cord towards the effectors. 4. Protection: The spinal cord is protected by the same three meninges that protects the brain. The two functions of the spinal cord are: Carrying signals from the brain: The spinal cord receives signals from the brain that control movement and autonomic functions. Carrying information to the brain: The spinal cord nerves also transmit messages to the brain from the body, such as the sensations of touch, pressure, and pain. The peripheral nervous system (PNS): The PNS consists of all the nervous tissue outside the CNS. It is made up of the nervous tissue that links the CNS to the receptors or effectors of the body. Cranial nerves are connected to the brain and conducts impulses to and from the sensory receptors and muscles in the face. Spinal nerves enter and leave the spinal cord between the vertebrae. The functions of the PNS are therefore twofold: 1. Sensory functions: Conducts impulses from the receptor cells in the sense organs to the CNS. 2. Motor functions: Conducts impulses from the CNS to the effectors (muscles or glands) The motor division is then divided again into two different parts: a. Somatic nervous system: Motor neurons conduct impulses from the CNS to the skeletal muscles that control voluntary movements. b. Autonomic nervous system: Motor neurons conducts impulses from the CNS to cardiac and smooth muscles and glands, that control involuntary movements The autonomic nervous system is then divided into two different parts: a. Sympathetic nervous system: Prepares the body for ‘Fight or flight’ b. Parasympathetic nervous system: Return the body to normal after being stimulated by the sympathetic nervous system. The structure and functioning of a neuron: There are three types of neurons: 1. Sensory/afferent neuron 2. Motor/efferent neuron 3. Interneuron/connector neuron The parts of the neurons along with the specific functions that part controls, is shown below: The reflex arc: A reflex is a quick, automatic response that involves the spinal cord and not the brain. The reflex arc is therefore the pathway along which an impulse is transmitted in order to bring about a response to a stimulus during a reflex action. Reflexes are vital in order to protect the body from harm. Example of reflexes include blinking, coughing, sneezing, dilating and constricting of pupil of the eye ect. The diagram below shows the reflex arc. The synapse: A synapse is the minute gap between consecutive neurons or between a neuron and an effector. A neurotransmitter (Acetylcholine) is secreted by the synaptic knobs which facilitates the movement of the impulse over the gap. This ensures smooth communication of an impulse. Disorders of the nervous system: There are two disorders that need to be studied in this section: 1. Alzheimer’s disease 2. Multiple sclerosis Alzheimer’s disease: An irreversible brain disorder that gradually worsens, resulting in memory loss and decreased mental functioning. Can be caused by a number of factors: Amyloid plaque that develops between neurons Shortage of neurotransmitters at the synapse Symptoms of the disease begin with short-term memory loss. As the condition progresses, the patient experiences severe long-term memory loss, leading to an inability to recognize friends or family. Tasks involving multiple steps, such as getting dressed, become impossible. Additionally, the patient may suffer from mood swings, aggression, and irritability. In the advanced stages, the patient loses the ability to speak. Multiple sclerosis: This is an auto-immune disease that affects neurons of the CNS. The body’s own immune system attacks and destroys the myelin sheaths in the CNS. Myelin sheaths help to accelerate the conduction of nervous impulses. This attack therefore causes symptoms that include: Gradual loss of muscle control and co-ordination in most parts of the body An increased disability in function such as vision, memory and speech. Receptor organs: The eye Throughout the body, sensory receptors detect different stimuli and convert them into nerve impulses. These impulses travel through the central nervous system (CNS) to the brain, where they are interpreted and trigger an appropriate response. The eye is one such sensory organ Depth perception requires two eyes. When light hits the retina, it stimulates photoreceptor cells known a rods and cones. Rods are responsible for black-and-white vision, while cons handle colour vision. These photoreceptors generate nerve impulse that travel via the optic nerve to the cerebrum, where an image is formed. The fovea, or the yellow spot, on the retina contains only cones and is the area of clearest vision. The black spots lacks photoreceptor cells, so no images are formed there. The eye’s front is protected by a thin, transparent membrane called the conjunctiva, which is kept moist by fluid secreted by the tear gland. This fluid contains enzymes that kill bacteria. Functioning of the eye: There are three different functions that the eye performs. These three functions are only possible because the cornea and the lens are able to refract light rays. The pathway of light rays through the eye is as follows: Cornea - Aqueous Humour - Pupil - Lens - Vitreous Humour – Retina Accommodation: This term refers to the adjustment of the curvature of the lenses to cater for vision at various distances. Pupillary mechanisms: This term refers to the change in size of the pupil under different light intensities. Binocular vision: This term is used to describe the process involved in forming a 3D imagine, which allows the person to estimate size, distance and depth. Visual defects: There are many visual defects that affect the eye. Some of these can be corrected by wearing glasses or contact lenses. Other defects require surgery. Short-sightedness (Myopia): A person is able to focus clearly on close objects, but not on distant objects. This is due to the shape of the eyeball being too long – a concave lens is required to correct this condition. Long-sightedness (Hyperopia): A person who can see distant objects clearly but has difficulty focusing on near objects likely has a condition where the eyeball is too short. This condition is known as hyperopia or farsightedness. To correct it, a convex lens is needed to help focus light properly on the retina. Astigmatism: This condition, known as astigmatism, occurs when the cornea or lens has an unequal curvature, causing only part of the image to be clearly in focus. Astigmatism can be corrected by using a lens that compensates for the defective curvature of the eye. Cataracts: This condition, known as cataracts, results when the lens becomes cloudy, impairing vision. Cataracts typically occur in older individuals, as well as in diabetics and those with hypertension (high blood pressure). Cataracts can be corrected through surgery, where the defective lens is replaced with a synthetic lens. Receptor organs: The ear The structure of the ear: The ear is responsible for two primary functions: hearing and balance. To achieve these functions, the ear contains receptors that detect sound stimuli as well as mechanoreceptors that ensure balance and equilibrium. Understanding the structures of the ear and their respective functions is crucial. Function of the ear: Balance and Equilibrium When the head moves, fluid in the inner ear, specifically in the semicircular canals, is disturbed. This disturbance stimulates mechanoreceptors called maculae and cristae, which then send a nerve impulse to the cerebellum of the brain. In response, the cerebellum sends impulses to the effector muscles to restore balance and equilibrium. Head with respect to gravity: Speed and direction of movement: Hearing defects: There are two main types of hearing defects. Otitis media (Middle ear infection): The middle ear can become infected when a virus or bacteria enters it via the Eustachian tube, leading to fluid buildup and causing severe earache. If medication does not alleviate the condition, grommets (small tubes) may be surgically inserted into the eardrum. These grommets have tiny holes that allow moisture to drain from the eardrum and air to enter the Eustachian tube, helping to relieve the infection and restore normal function. Deafness and speech disorders: Deafness can be caused by several factors: 1. Damage to the Auditory Nerve: Impairment of the nerve responsible for transmitting sound signals from the inner ear to the brain. 2. Damage to the Brain's Auditory Processing Area: Damage to the part of the brain that interprets impulses from the auditory nerve. 3. Problems with the Outer or Middle Ear: Dysfunction in these parts of the ear, such as blockages or infections, can impair hearing. 4. Damage to the Inner Ear (Cochlea): Damage to the cochlea, which is crucial for converting sound vibrations into nerve impulses. Treatment options for hearing disorders include: a) Hearing Aids: Worn behind the ear, these devices amplify sound waves to improve hearing. b) Cochlear Implants: Used when the cochlea is damaged. An electronic device is surgically implanted into the bone behind the ear to stimulate the auditory nerve directly. Hearing-impaired individuals often use sign language to communicate, which involves facial expressions, hand gestures, and body movements. It's important to accord people with hearing impairments the same respect as those who can hear, ensuring they are not subjected to discrimination. Questions: Section A: Terminology and Definitions (20 marks) 1. Define the following terms: o Stimulus (2) o Meninges (2) o Reflex action (2) o Synapse (2) o Neurotransmitter (2) 2. Match the following terms with their correct descriptions: o A. Reflex arc o B. Receptor o C. Effector Descriptions: 4. An organ that detects the stimulus and converts it into an impulse. 5. The pathway a reflex action follows in order to bring about a reflex action. 6. An organ or gland that receives the impulse from the CNS and carries out the appropriate response. (3 marks) 3. Fill in the blanks: o The brain is protected by the bony cranium, cerebrospinal fluid, and three membranes called _____. (1) o The two main divisions of the nervous system are the _____ and the _____. (2) o The spinal cord is composed of grey matter and _____. (1) o The cerebellum controls voluntary actions to ensure smooth movement and maintains _____. (1) o The parasympathetic nervous system is responsible for _____ the body to normal after a 'fight or flight' response. (1) (10 marks) Section B: Structure and Function (30 marks) 4. Describe the structure and function of the following parts of the brain: o Cerebrum (3)  o Corpus callosum (2) o Cerebellum (3) o Medulla oblongata (2) (10 marks) 5. Explain the two main functions of the spinal cord. (5 marks) 6. Compare the central nervous system (CNS) and peripheral nervous system (PNS) in terms of structure and function. (5 marks) 7. Explain the difference between the somatic and autonomic nervous systems, including the two divisions of the autonomic nervous system. (10 marks) Section C: Neurons and Reflex Arcs (25 marks) 8. Draw and label a diagram of a motor neuron. (5 marks) 9. Explain the pathway of a reflex arc and its importance in the body. (5 marks) 10. Describe the role of a synapse in the transmission of nerve impulses. (5 marks) 11. Explain the impact of multiple sclerosis on the nervous system and the symptoms it causes. (5 marks) 12. Describe the symptoms and causes of Alzheimer's disease. (5 marks) Section D: Sensory Organs (25 marks) 13. Describe the structure and function of the eye, including the role of rods and cones. (10 marks) 14. Explain the three main functions of the eye (Accommodation, Pupillary mechanisms, Binocular vision). (10 marks) 15. List and describe two common visual defects and their corrections. (5 marks) Section E: The Ear and Hearing (25 marks) 16. Draw and label the structure of the ear. (5 marks) 17. Describe how the ear maintains balance and equilibrium. (5 marks) 18. Explain the causes and treatment options for otitis media (middle ear infection). (5 marks) 19. Describe the different types of deafness and how they are treated. (10 marks) Answers: Section A: Terminology and Definitions (20 marks) 1. Definitions: o Stimulus: A physical or chemical change in the environment that requires a response from the organism. (2) o Meninges: The three protective membranes that surround the brain and spinal cord. (2) o Reflex action: A quick, involuntary, automatic action that involves the spinal cord and does NOT involve the brain. (2) o Synapse: A gap between two consecutive neurons or between a neuron and an effector. (2) o Neurotransmitter: A chemical substance that enables an electrical impulse to flow smoothly between consecutive neurons (e.g., Acetylcholine). (2) 2. Matching: o A. Reflex arc - 2. The pathway a reflex action follows in order to bring about a reflex action. (1) o B. Receptor - 1. An organ that detects the stimulus and converts it into an impulse. (1) o C. Effector - 3. An organ or gland that receives the impulse from the CNS and carries out the appropriate response. (1) 3. Fill in the blanks: o The brain is protected by the bony cranium, cerebrospinal fluid, and three membranes called meninges. (1) o The two main divisions of the nervous system are the central nervous system (CNS) and the peripheral nervous system (PNS). (2) o The spinal cord is composed of grey matter and white matter. (1) o The cerebellum controls voluntary actions to ensure smooth movement and maintains balance and posture. (1) o The parasympathetic nervous system is responsible for returning the body to normal after a 'fight or flight' response. (1) Section B: Structure and Function (30 marks) 4. Brain Structures: o Cerebrum: Controls voluntary actions, receives and interprets sensations, and is responsible for higher mental functions such as memory, intelligence, and judgment. (3)  o Corpus callosum: A white band of neurons that connects the two hemispheres of the cerebrum, allowing communication between them. (2) o Cerebellum: Controls all voluntary actions to ensure smooth movement, and controls muscle tone to maintain balance and posture. (3) o Medulla oblongata: Controls involuntary functions such as breathing, blood pressure, and peristalsis. (2) 5. Functions of the Spinal Cord: o Carrying signals from the brain: The spinal cord receives signals from the brain that control movement and autonomic functions. (2.5) o Carrying information to the brain: The spinal cord nerves also transmit messages to the brain from the body, such as the sensations of touch, pressure, and pain. (2.5) 6. Comparison of CNS and PNS: o CNS (Central Nervous System): Consists of the brain and spinal cord; it is responsible for processing information and coordinating bodily functions. (2.5) o PNS (Peripheral Nervous System): Includes all nervous tissue outside the CNS; it links the CNS to receptors and effectors, conducting sensory and motor functions. (2.5) 7. Somatic vs. Autonomic Nervous Systems: o Somatic Nervous System: Conducts impulses from the CNS to skeletal muscles, controlling voluntary movements. (3) o Autonomic Nervous System: Conducts impulses from the CNS to cardiac and smooth muscles and glands, controlling involuntary movements. (3) o Sympathetic Nervous System: Prepares the body for 'fight or flight' responses. (2) o Parasympathetic Nervous System: Returns the body to normal after a sympathetic response. (2) Section C: Neurons and Reflex Arcs (25 marks) 8. Motor Neuron Diagram: (Drawing should include the following labels: Dendrites, Cell body, Axon, Myelin sheath, Node of Ranvier, Axon terminal) (5 marks) 9. Reflex Arc Pathway: o The reflex arc is the pathway along which an impulse travels to bring about a quick, automatic response to a stimulus. It involves the following steps: ▪ The receptor detects a stimulus and generates a nerve impulse.  ▪ The sensory neuron conducts the impulse to the spinal cord. ▪ The impulse is transmitted through an interneuron in the spinal cord. ▪ The motor neuron conducts the impulse to the effector. ▪ The effector produces the response (e.g., pulling a hand away from a hot object). (5) 10. Role of Synapse: o A synapse is a minute gap between consecutive neurons or between a neuron and an effector. The synapse allows nerve impulses to be transmitted from one neuron to another via neurotransmitters like acetylcholine. These neurotransmitters are released from the synaptic knobs and bind to receptors on the next neuron, facilitating the continuation of the nerve impulse. This process ensures smooth communication and coordination of nerve impulses within the nervous system. (5) 11. Multiple Sclerosis Impact: o Multiple sclerosis (MS) is an autoimmune disease where the immune system attacks and destroys the myelin sheaths in the CNS. Myelin sheaths help to accelerate the conduction of nerve impulses. The loss of myelin leads to symptoms such as: ▪ Gradual loss of muscle control and coordination ▪ Increased disability in functions like vision, memory, and speech (5) 12. Alzheimer’s Disease: o Alzheimer’s disease is an irreversible brain disorder characterized by memory loss and decreased mental functioning. It is caused by factors such as amyloid plaques that develop between neurons and a shortage of neurotransmitters at the synapse. Symptoms begin with short-term memory loss and progress to severe long-term memory loss, inability to recognize friends or family, mood swings, and loss of speech in advanced stages. (5) Section D: Sensory Organs (25 marks) 13. Structure and Function of the Eye: o Structure: The eye contains photoreceptor cells known as rods and cones, located on the retina. Rods are responsible for black-and-white vision, while cones handle color vision. The optic nerve transmits the generated nerve impulses to the cerebrum, where an image is formed. The fovea (yellow spot) contains only cones and is the area of clearest vision, while the black spot (blind spot) lacks photoreceptor cells, so no images are formed there. o Function: The eye’s main functions include accommodation (adjusting the lens curvature for near or far vision), pupillary mechanisms (changing pupil size  under different light intensities), and binocular vision (forming a 3D image to estimate size, distance, and depth). (10) 14. Eye Functions: o Accommodation: Adjustment of the lens's curvature to focus on objects at various distances. o Pupillary Mechanisms: Changes in pupil size in response to light intensity. o Binocular Vision: The process of forming a 3D image, allowing for the estimation of size, distance, and depth. (10) 15. Visual Defects: o Short-sightedness (Myopia): The person can focus clearly on close objects but not on distant objects due to an elongated eyeball. A concave lens corrects this condition. (2.5) o Long-sightedness (Hyperopia): The person can see distant objects clearly but has difficulty focusing on near objects due to a shortened eyeball. A convex lens corrects this condition. (2.5) Section E: The Ear and Hearing (25 marks) 16. Ear Diagram: (Drawing should include the following labels: Outer ear, Middle ear, Inner ear, Eardrum, Cochlea, Semicircular canals, Auditory nerve) (5 marks) 17. Balance and Equilibrium: o The ear maintains balance and equilibrium through the fluid in the semicircular canals of the inner ear. When the head moves, the fluid is disturbed, stimulating mechanoreceptors (maculae and cristae) that send nerve impulses to the cerebellum. The cerebellum then sends impulses to the effector muscles to restore balance. (5) 18. Otitis Media (Middle Ear Infection): o Otitis media is a middle ear infection caused by viruses or bacteria entering through the Eustachian tube, leading to fluid buildup and severe earache. If medication does not alleviate the condition, grommets (small tubes) may be surgically inserted into the eardrum to drain fluid and restore normal function. (5) 19. Types of Deafness and Treatment: o Types: ▪ Damage to the Auditory Nerve: Impairs sound signal transmission from the inner ear to the brain.  ▪ Damage to the Brain's Auditory Processing Area: Affects the brain's ability to interpret sound impulses. ▪ Outer/Middle Ear Problems: Includes blockages or infections that impair hearing. ▪ Damage to the Cochlea: Affects the conversion of sound vibrations into nerve impulses. o Treatment: ▪ Hearing Aids: Amplify sound waves to improve hearing. ▪ Cochlear Implants: Surgically implanted devices that stimulate the auditory nerve directly, used when the cochlea is damaged. (10)