The Nervous System


Published on

A slideshow for Grade 12 Life Sciences, focussing on the Nervous System. Info and diagrams on the central and peripheral nervous system etc.

Published in: Education, Technology
1 Comment
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

The Nervous System

  1. 1. Module 2: Life Processes Life Sciences Matric Syllabus Mind Action Series: Life Sciences Textbook and Workbook
  2. 2. 2.2a) The Nervous System
  3. 3. • Co-ordination is the way in which information is communicated between the receptors of the body, the central nervous system and the effectors to bring about appropriate responses to any change in the environment.• There are essentially two co-ordinating systems – the nervous system and the endocrine system, which work together to respond to external changes and to control conditions inside the body.• Co-ordination is brought about in two ways: – The fastest method is by means of impulses travelling along nerves and is called nervous co-ordination. – The slower method is by means of chemicals called hormones which are carried in the blood. This is known as chemical co-ordination. 2.2a) The Nervous System
  4. 4. • The nervous system is the body’s control and communication centre.• It provides a continuous flow of information between the brain and the parts of the body.• This enables the body to function in an orderly and effective way and to perform everyday tasks such as eating, writing, running, solving a problem and controlling emotions such as fear. 2.2a) The Nervous System
  5. 5. The nervous system has three overall functions: – Sensory function – sensory receptors detect the changes in the external environment and the environment within the organism. – Integrative function – the central nervous system integrates this information. – Motor function – effectors (muscles and glands) bring about a response.For example: you are riding a bicycle and see that the traffic lighthas turned red (sensory function). Your central nervous systemintegrates this information (red light means ‘stop’ – integrativefunction), and you use your muscles to apply your brakes to stopthe bicycle (motor function). 2.2a) The Nervous System
  6. 6. • We live in an environment where external factors are constantly changing. Inside our bodies, conditions are also changing, e.g. changes in blood pressure, tension in muscles, blood sugar levels etc.• These internal and external changes are called stimuli.• A stimulus is any physical or chemical change in our internal or external environment that is capable of causing a response in an organism. 2.2a) The Nervous System
  7. 7. stimulus Sensory Function Receptors respond to stimuli sensory CNS processes and integratesIntegrative Function the sensory input motor Effectors e.g. muscles and glands Motor Function make the correct response response 2.2a) The Nervous System
  8. 8. The nervous system is made up of millions of special cells calledneurons that form a continuous network all over the body.• Neurons can function for over a lifetime, given the correct conditions.• They cannot undergo mitosis, and thus cannot be replaced if destroyed.• They have a very high metabolic rate and need continuous supplies of oxygen and glucose to survive.In addition to neurons, there are supporting cells calledneuroglia which bind neurons together, giving them support andhelping them with their nutrition. 2.2a) The Nervous System
  9. 9. • A neuron has the same basic parts as most animal cells: they have a cell body, containing a cell membrane, cytoplasm, nucleus and cell organelles.• In addition, neurons have long, thin fibres of cytoplasm extending from the cell body which make it possible for nerve impulses to be carried long distances.• The fibres may be: – Dendrites, which carry impulses towards the cell body. – An axon, which carries impulses away from the cell body. 2.2a) The Nervous System
  10. 10. • Neurons can be classified according to their structure or functions.• Functionally, neurons are classified according to the direction in which nerve impulses travel: – Sensory neurons – Connector neurons – Motor neurons• Structurally, they are divided according to the number of fibres stretching out from the cell body: – Multipolar neurons – Bipolar neurons – Unipolar neurons 2.2a) The Nervous System
  11. 11. • These carry impulses from receptors towards the central nervous system (CNS), where the sensation is interpreted. They are afferent neurons, i.e. they take the sensation TOWARDS the CNS.• They are usually unipolar, i.e. they have one fibre attached to the cell body, which then divides. 2.2a) The Nervous System
  12. 12. • They are also known as relay neurons, association neurons or interneurons.• They are multipolar neurons with many dendrites.• They are found in the CNS and they make up 99% of the neurons in the body.• They receive impulses from sensory neurons and pass them on to other neurons. 2.2a) The Nervous System
  13. 13. • Motor neurons carry impulses away from the CNS to effectors (such as muscles) to bring about the appropriate response.• They are therefore efferent neurons. ‘Efferent’ means away from.• They are multipolar neurons, and are located in the grey matter in the CNS. 2.2a) The Nervous System
  14. 14. Functions of parts:Dendrites collect information from other cells and passit on to the cell body.The cell body controls the metabolism of the cell.The node of Ranvier allows rapid conduction ofimpulses by forcing them to ‘jump’ from one node tothe next.Schwann cells are wrapped around the axon severaltimes. Their inner layers of fatty tissue fuse to form themyelin sheath.The axon is extended to carry impulses away from thecell body over long distances.The myelin sheath forms electrical insulation aroundthe axon, preventing distortion of impulses fromactivity in neighbouring cells.Terminal branches carry impulses to the synapticknobs/end plates.Synaptic knobs form a synapse with another neuron, amuscle cell or a gland cell. 2.2a) The Nervous System
  15. 15. • Adjacent neurons do not touch each other, there is a small gap separating them. This gap or synaptic cleft plus the adjacent membranes, form a synapse.• A synapse is thus the junction across which a nerve impulse passes from an axon terminal to a neuron, a muscle cell or a gland cell.• In the cytoplasm of the synaptic knobs there are hundreds of small vesicles (sacs) filled with molecules of a neurotransmitter such as the chemical acetylcholine. 2.2a) The Nervous System
  16. 16. As neurons do not touch, impulses have to cross the gap (synapse)to continue their path through the nervous system.• When nerve impulses reach the terminal branches of axons, they cause vesicles in the synaptic knob to fuse with the presynaptic membrane, using energy from the mitochondria.• The membranes then burst, releasing neurotransmitters which diffuse across the synaptic cleft.• The neurotransmitters become attached to neuroreceptors in the post-synaptic membrane, which they either excite or inhibit. 2.2a) The Nervous System
  17. 17. • The receptors release the neurotransmitters back to the synaptic cleft which can then be inactivated by enzymes and reabsorbed by the pre-synaptic membrane. This is very important as, unless the transmitter is removed from the synaptic cleft, subsequent impulses would have no effect as the receptors on the postsynaptic membrane would all be bound.In this way, impulses are carried across the gap chemically, i.e. byway of a chemical neurotransmitter. An impulse carried along anerve fibre is an electric impulse.Synapses are important because: 1) they make sure that the flowof impulses travel in one direction only, 2) they allow the dispersalof impulses, 3) they allow unnecessary and continual stimuli to befiltered out. 2.2a) The Nervous System
  18. 18. 2.2a) The Nervous System
  19. 19. Nerve impulses reach Neurotransmitters Receptors release theterminal branches of excite or inhibit neurotransmitters back axons neuroreceptors into the synaptic cleft Neurotransmitters Neurotransmitters are Vesicles in synaptic attach to inactivated by enzymes knob fuse with neuroreceptors in post- and reabsorbed by pre-presynaptic membrane synaptic membrane synaptic membrane Membranes burst, Neurotransmitters Thus, impulses are releasing diffuse across synaptic carried across the gap neurotransmitters cleft chemically. 2.2a) The Nervous System
  20. 20. The human nervous system isdivide into the:• Central Nervous System • Brain • Spinal cord• Peripheral Nervous System • Cranial nerves • Spinal nerves 2.2a) The Nervous System
  21. 21. • The CNS is made up of a concentrated mass of interconnected neurons, grouped together to form the brain and spinal cord.• The CNS tissues are protected and nourished by three connective tissue membranes called meninges. The space between the 2nd and 3rd layer of membranes is filled with cerebro-spinal fluid which acts as a cushion, protecting the CNS against shock and damage. 2.2a) The Nervous System
  22. 22. • The whole CNS and its meninges are enclosed within a bony case made up of two separate structures. – The cranium is a strong, dome-shaped structure that protects the brain against mechanical injuries. It is made up of eight, curved skull bones, immovably dove-tailed together by fibrous joints called sutures. – The vertebral column is made up of thirty-three, irregular shaped vertebrae that surround the spinal cord and protect it against mechanical injury. 2.2a) The Nervous System
  23. 23. • The brain is the enlarged, upper part of the spinal cord. It is shaped like a large mushroom. The cap of the mushroom is the cerebrum, and the stalk is the brain stem. 2.2a) The Nervous System
  24. 24. 2.2a) The Nervous System
  25. 25. • The large cerebrum is divided into two cerebral hemispheres by a longitudinal fissure. The hemispheres are held together by a mass of white tissue called the corpus callosum that provides a communication link between the cerebral hemispheres.• Its surface is made up of a large number of folds and grooves that enlarge the surface area so that a large number of brain cells can fit into a small cranial cavity.• There are four cavities known as ventricles in the centre of the brain. They are filled with cerebro-spinal fluid.• The outer 3mm of the cerebrum forms the cerebral cortex, made up of grey matter. The grey matter is made up of a collection of cell bodies of neurons. Below the grey matter is an area of white matter, made up of a collection of myelinated nerve fibres. 2.2a) The Nervous System
  26. 26. Functions of the cerebrumThe cerebral cortex is divided into three functional areas:• The motor area in the frontal lobe is where all the voluntary movements of the body originate.• The sensory areas receive and interpret impulses from the sense organs, e.g: – Hearing, tasting and smelling in the temporal lobe – Sight in the occipital lobe – Skin sensations in the parietal lobe, e.g. touch, cold and hot temperatures and pain.• The association cortex is not involved with motor or sensory functions and is involved in higher mental activities such as intelligence, memory, perception, language and consciousness. 2.2a) The Nervous System
  27. 27. 2.2a) The Nervous System
  28. 28. The cerebellum forms the upper part of the brain stem. It is madeup of two hemispheres and has shallow surface folds.FunctionsThe cerebellum receives sensory input from the motor region of thecerebrum, the eyes, muscle spindles & organs of balance in innerears.• It processes this information and uses it to co-ordinate the actions of the voluntary muscles so that complicated physical actions can be performed in a smooth, controlled way.• It is partly responsible for controlling muscle tone (correct tension in the muscles).• Using information from the inner ear, it helps maintain posture and balance. 2.2a) The Nervous System
  29. 29. The hypothalamus is situated above the pituitary.Functions• Controls homeostasis, e.g. temperature, water levels, pH levels, food intake, etc.• Controls and drives certain behaviours, e.g. aggression, self- defence and reproductive behaviours.• Controls functioning of the pituitary gland. 2.2a) The Nervous System
  30. 30. Forms the lowest part of the brain stem.When it leaves through the foramen magnum at the base of thecranium, it is known as the spinal cord.Functions• Serves as the pathway for impulses to and from the brain.• Acts as a reflex centre, controlling important reflexes such as breathing, heartbeat, blood pressure, swallowing and peristalsis.• Also controls less important reflexes such as sneezing, coughing, hiccupping and salivating. 2.2a) The Nervous System
  31. 31. • The spinal cord is an elongated rod of nervous tissue that extends from the medulla oblongata through the foramen magnum.• It is situated in the vertebral canal of the vertebral column and is approximately 45cm long. 2.2a) The Nervous System
  32. 32. • A spinal cord has an H-shaped central area of grey matter made up of nerve cell bodies, dendrites and synapses.• White matter surrounds the grey matter and is made up of axons with myelin sheaths.• The central canal occurs in the centre of the grey matter. It is filled with cerebro-spinal fluid. The central canal runs down from the ventricles in the brain. 2.2a) The Nervous System
  33. 33. • The cord is partly divided into right and left sides by two grooves: dorsal groove and ventral groove.• A pair of spinal nerves enters and leaves the spinal cord between successive vertebrae. Each spinal nerve has a dorsal root that enters the grey matter, and a ventral root that leaves the grey matter.• A collection of neuron cell bodies forms a ganglion in the dorsal root. 2.2a) The Nervous System
  34. 34. The PNS consists of all the nervous tissue outside the CNS. It isdivided into two main divisions:• Somatic nervous system that controls all voluntary muscular movements.• Autonomic nervous system, that controls the functioning of involuntary muscles and glands.The PNS is made up of nerves that link the CNS to the receptors andeffectors of the body, i.e. 43 pairs of nerves that include:• 12 pairs of cranial nerves connected to the brain. These may be afferent (sensory) nerves or efferent (motor) nerves or mixed nerves made up of both sensory and motor nerves.• 31 pairs of spinal nerves which enter and leave spinal cord between the vertebrae (all mixed nerves). 2.2a) The Nervous System
  35. 35. Functions of the PNS:• The PNS collects information from receptors and transmits this information by way of impulses along sensory neurons to the CNS – sensory function.• It transmits impulses from the CNS by way of motor neurons to effectors to bring about an appropriate response – motor function. 2.2a) The Nervous System
  36. 36. This system involves receiving information from receptors andbringing about appropriate responses by voluntary, skeletalmuscles. 2.2a) The Nervous System
  37. 37. A reflex action is a fast, automatic response by an effector organ, i.e.a muscle (whether voluntary or involuntary) or a gland, to a stimulusreceived by a receptor organ.Reflex centres may be situated in the:• Brain – controlling reflexes such as sneezing, breathing, blinking etc.• Spinal cord – controlling primitive reflexes such as the knee jerk when tapped below the knee-cap.• A reflex arc is the pathway along which nerve impulses are carried from a receptor to an effector to bring about a reflex action.• A reflex arc is thus the functional unit of the nervous system, while a neuron is the structural unit of the nervous system. 2.2a) The Nervous System
  38. 38. Consider what happens when you prick your finger.• The stimulus of the pin prick generates impulses in sensory nerve endings of pain in the skin of your finger – the receptor.• These impulses are conducted along sensory neurons to the grey matter in the spinal cord. Here the impulses synapse with connector neurons which serve as reflex centres.• From the connector neurons, impulses make synaptic contact with the motor neurons in the grey matter and travel along these neurons to the effectors.• The effector, the flexor muscle in the finger, brings about a response by contracting very quickly to pull the finger away from the pin to protect the finger.• Impulses are also carried up the spinal cord to the cerebral cortex (parietal lobe) where the stimulus is interpreted as pain. 2.2a) The Nervous System
  39. 39. 2.2a) The Nervous System
  40. 40. • The ANS is involved in keeping a balanced internal environment i.e. maintaining homeostasis. It responds to sensory input from all body organs and makes the necessary adjustments.• The effectors in the ANS are smooth, involuntary muscle, cardiac muscles and glands.• There are two divisions in the ANS: – Sympathetic nervous system – gets you ‘ready for action’ – Parasympathetic nervous system – calms you down 2.2a) The Nervous System
  41. 41. Body part Sympathetic system Parasympathetic systemHeart beat Strengthens and accelerates Weakens, slows downBlood vessels of skin and Constricts arteries and raises Dilates arteries, lowersdigestive organs blood pressure blood pressureBlood vessels of heart, lungs, Dilates arteries, allowing the Constricts arteries, reducesskeletal muscles flow of more blood – can flow of blood run fasterDigestive tract Slows down peristalsis Speeds up peristalsisUrinary bladder Relaxes bladder wall Contracts bladder wallBladder and anal sphincters Contracts RelaxesMuscles in bronchial tubes Muscles relax, dilating air Muscles contract, causing air passages for easier passages to constrict breathing 2.2a) The Nervous System
  42. 42. Body part Sympathetic system Parasympathetic systemMuscles of iris Radial muscles contract, dilating Circular iris muscles contract, pupil – see better constricting pupilSweat glands Increases sweat to cool one down No effectLiver Stimulates the breakdown of No effect glycogen into glucose – use for energySalivary glands Decreases secretion of saliva Increases secretion of salivaTear glands Little effect Increases secretion of tearsAdrenal medulla Stimulates secretion of adrenalin No effectKidney Decreased excretion of urine increased excretion of urineBrain Increased concentration No effect 2.2a) The Nervous System
  43. 43. • The sympathetic nervous system works together with adrenalin in emergency situations that cause stress and require the ‘fight or flight’ state. Stimulation by these nerves results in more oxygen, glucose and blood being sent to the skeletal muscles, speeding up cellular respiration to release more energy for action.• The parasympathetic nervous system enables the body to ‘rest and digest’, i.e. to recover from sympathetic stimulation and return to normal.• Most organs are innervated by both the sympathetic and parasympathetic fibres (double innervation).• Effects produced by each system are generally antagonistic. 2.2a) The Nervous System
  44. 44. Alzheimer’s disease is a progressive and degenerative disease ofthe brain, which causes the deterioration of memory andthinking skills.CausesAlthough the cause is not fully understood, it is known thatAlzheimer’s disease develops because of a complex series ofevents that happen in the brain over a long period of time.Genetic, environmental and lifestyle factors may be at fault.PrevalenceAlzheimer’s is prevalent in older people and affects bothgenders. 15% of people over the age of 65, and 50% of peopleover the age of 85 develop Alzheimer’s. 2.2a) The Nervous System
  45. 45. SymptomsPeople with Alzheimer’s show symptoms of memory loss andchanges in their thinking skills. Problems may include: – Getting lost – Taking a long time to do daily tasks – Mood and personality changes – Poor judgement – In some cases, hallucinations.In severe cases, the people affected by Alzheimer’s cannotcommunicate properly and are dependent on others to care forthem. They may be in bed for most of the time as their bodystops functioning. 2.2a) The Nervous System
  46. 46. TreatmentThere is no cure for Alzheimer’s. Some medicines, however, canhelp maintain thinking skills and can control or improve certainkinds of behaviour for a short period of time. These medicines,however, cannot delay the progression of the disease.Certain factors may reduce the risk of developing Alzheimer’s: – Regular exercise – Healthy diet – Limiting alcohol consumption – Avoiding tobacco – Staying socially active – Engaging in intellectually stimulating activities 2.2a) The Nervous System
  47. 47. Co-ordination = the way in which information is communicated betweenthe receptors of the body, the central nervous system and the effectorsto bring about appropriate responses to any change in the environment.Nervous system = the body’s control and communication centre.Synapse = the junction across which a nerve impulse passes from anaxon terminal to a neuron, a muscle cell or a gland cell.Neurotransmitter = a chemical substance released from axon terminalsat a synapse to either stimulate or inhibit the post-synaptic membrane.Stimulus = any physical or chemical change in our internal or externalenvironment that is capable of causing a response in an organism. 2.2a) The Nervous System
  48. 48. Cerebro-spinal fluid = a fluid formed from blood plasma inspecial areas in the walls of the ventricles. It protects andnourishes the CNS and prevents cells from drying out. 2.2a) The Nervous System