.............UNIT 1: Nervous System....................

Human Nervous System

1. UNIT 1: THE NERVOUS SYSTEM (Campbell et.al, 2010)

2. 1. Introduction Two systems enables animals to respond to the environment: Nervous system Endocrine system What is the difference between the two systems?

3. Each unicellular organism can respond to stimuli in its environment. Animals are multicellular and most groups respond to stimuli using systems of neurons . The simplest animals with nervous systems, the cnidarians , have neurons arranged in nerve nets .

4. A nerve net is a series of interconnected nerve cells .

5. More complex animals have nerves Nerves are bundles that consist of the axons of multiple neurons . AXON

6. Bilaterally symmetrical animals exhibit cephalization . Cephalization is the clustering of sensory organs at the front end of the body.

7. Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS ). The CNS consists of a brain and longitudinal nerve cords .

8. Annelids and arthropods have segmentally arranged clusters of neurons called ganglia.

9. In vertebrates: The CNS is composed of the brain and spinal cord and the peripheral nervous system (PNS) is composed of nerves and ganglia .

10. In vertebrates: The spinal cord conveys information from the brain to the PNS. The spinal cord also produces reflexes independently of the brain. A reflex is the body’s automatic response to a stimulus . For example, a doctor uses a mallet to trigger a knee-jerk reflex .

11. Knee-jerk reflex

12. 2. The Human Nervous system The human nervous system has 3 specific functions: Receives sensory input It performs integration It generates motor output

13. The human nervous system CENTRAL NERVE SYSTEM (CNS) PERIPHERAL NERVE SYSTEM (PNS) Cranial and Spinal nerves)

14. The human nervous system CENTRAL NERVE SYSTEM (CNS) PERIPHERAL NERVE SYSTEM (PNS) Cranial and Spinal nerves) BRAIN SPINAL CORD

15. The human nervous system CENTRAL NERVE SYSTEM (CNS) PERIPHERAL NERVE SYSTEM (PNS) Cranial and Spinal nerves) BRAIN SPINAL CORD SOMATIC/MOTORNERVOUS SYSTEM (Skin, senses and skeletal muscles) AUTONOMIC NERVOUS SYSTEM (Cardic- , smooth muscles and glands)

16. The human nervous system CENTRAL NERVE SYSTEM (CNS) PERIPHERAL NERVE SYSTEM (PNS) Cranial and Spinal nerves) BRAIN SPINAL CORD SOMATIC/MOTORNERVOUS SYSTEM (Skin, senses and skeletal muscles) AUTONOMIC NERVOUS SYSTEM (Cardic- , smooth muscles and glands) SYMPATHETIC PARASYMPATHETIC

17. a. Human Brain and spinal cord Consist of 6 major parts : Cerebrum Cerebellum The Diencephalon Medulla Oblongata Pons Spinal cord

18. Structure of the Human Brain

19. Structure of the Human Brain

20. i . Cerebrum

21. The cerebrum has right and left cerebral hemispheres. Each cerebral hemisphere consists of a cerebral cortex ( gray matter ) overlying white matter and basal nuclei. Grey matter : cell bodies of neurons White matter : Myelin sheath around axons of neurons. The cerebral cortex consists of folds and grooves called sulci and gyri . The basal nuclei are important centres for planning and learning movement sequences

22. A thick band of axons called the corpus callosum provides communication between the right and left cerebral corticals The right half of the cerebral cortex controls the left side of the body, and vice versa. Each side of the cerebral cortex has four lobes: frontal, temporal, occipital, and parietal lobe. Protected by 3 meninges: Dura mater (outer), Pia mater(inner), Arachnoid (middle).

23. The human brain (Cerebrum) viewed from the rear

24. FOUR LOBES OF CEREBRAL CORTEX

25. FUNCTION S OF FOUR LOBES OF CEREBRAL CORTEX Frontal lobe - motor control, memory, reasoning, intelligence, imagination, thinking, judgment. Initiates voluntary muscle movement. Parietal lobe – Taste, speech, somatosensory integration Temporal lobe – Hearing and balance, smell Occipital lobe - Sight

26. ii. Cerebellum

27. The Cerebellum lies under the occipital lobe of cerebrum. Divided into 2 cerebellar hemispheres which is attached by a vermis. Consist of parallel grooves . Cross section show the white matter in a “tree-like” shape, with thin grey matter surrounding it. Functions: 1) Maintain posture and balance . 2) Ensures smooth, coordinated voluntary muscle movement.

28. iii. Diencephalon

29. The diencephalon develops into three regions: the epithalamus , thalamus, and hypothalamus. The epithalamus includes the pineal gland and generates cerebrospinal fluid from blood. Secrete melatonin – believed to be involved in jet lag and insomnia. Also starts puberty.

30. Thalamus has grey matter on inside and white matter on outside. Thalamus is located on side and roof of third ventricle. Functions of the thalamus : Receives info via nerves from various parts of body and sends it to the appropriate part of the cerebrum for integration. Involved in emotions and memory .

31. The hypothalamus : Forms the floor of the third ventricle. Functions of the HYPOTHALAMUS : Helps to maintain homeostasis by regulating hunger, sleep, thirst, body temperature and water balance. Controls the pituitary gland (link between nervous and endocrine gland)

32. iv. Medulla Oblongata

33. The medulla oblongata: Below Pons above spinal cord. Contains the reflex centres : 1. Cardiac reflex centre : regulate heartbeat 2. Respiratory - : regulate breathing 3. Vasomotor- : regulate blood pressure 4. Peristaltic - : regulate peristalsis 5. Regulate reflexes like vomiting, sneezing, coughing, hiccups

34. v. Pons

35. The Pons: Pons in Latin means bridge. Contains bundles of axons traveling between the cerebellum and the rest of CNS. Help Medulla Oblongata to regulate breathing – has Pneumotaxic - and Apneustic centers https://www.youtube.com/watch?v=44B0ms3XPKU

36. vi. Spinal cord

37. The Spinal Cord: The spinal cord is an elongated cylindrical structure, about 45 cm long. It extends from the medulla oblongata to the second lumbar vertebrae of the backbone. The terminal part of the spinal cord is called the conus medullaris .

38. The spinal cord consists of long tracts of myelinated nerve fibres (known as white matter ) arranged around a symmetrical butterfly-shaped cellular matrix of grey matter . The grey matter contains cell bodies of motor neuron fibres, and interneurons. Protected by the vertebral column. The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord.

39. The spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body. Also contains neural circuits that can independently control numerous reflexes and central pattern generators .

40. Cross section through spinal cord

41. REFLEX ARC REACTION OF SPINAL CORD

42. B. PERIPHERAL NERVE SYSTEM Lies outside the CNS. Contains nerves (bundles of axons) Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves. Cranial nerves originate in the brain and mostly terminate in organs of the head and upper body Spinal nerves originate in the spinal cord and extend to parts of the body below the head

43. It consist of two functional components: Somatic (MOTOR ) and autonomic nerve system . The motor system carries signals to skeletal muscles and is voluntary. The autonomic nervous system regulates the internal environment in an involuntary manner.

44. The autonomic nervous system has sympathetic , parasympathetic , and enteric divisions. The sympathetic and parasympathetic divisions have antagonistic effects on target organs. The sympathetic division correlates with the “fight-or-flight” response The parasympathetic division promotes a return to “rest and digest” The enteric division controls activity of the digestive tract, pancreas, and gallbladder.

45. C. NERVE TISSUE Consist of: Nerve cells called neurons (receives and conduct impulses to and from CNS And supporting cells called neuroglia (supply support and nourishment to neurons).

46. STRUCTURE OF A NEURON Vary in appearance depending on their function and location. A neuron consist of 3 major parts: 1. Cell body (Contains nucleus and several other organelles in neuroplasm e.g. Nissl bodies, Neurofibrils , ext.) 2. Axon (Nerve fiber that transports impulses away from cell body to another neuron. Always protected by a Myelin sheath) 3. Dendrite (Short nerve processes that transports impulses towards the cell body from other neurons or from the sensory receptors).

47. Neurons are classified according to structure or function. According to structure there are 3 types of neurons: a.UNIPOLAR NEURON (Neuron with one process extending from cell body) b. BIPOLAR NEURON (Neuron with 2 processes extending from the cell body) c. MULTIPOLAR NEURON (Neuron with many processes extending from the cell body)

48. TYPES OF NEURONS ACCORDING TO FUNCTION : SENSORY NEURON : Transport impulses from the sensory receptors to the central nervous system (CNS) INTERNEURON: Convey impulses between various parts of the CNS like between sensory and motor neurons. Integration of impulse. MOTOR NEURON : Transport impulses from the CNS to the effector organ (muscle or gland)

49. TYPES OF NEURONS ACCORDING TO FUNCTION : SENSORY NEURON : Transport impulses from the sensory receptors to the central nervous system (CNS) INTERNEURON: Convey impulses between various parts of the CNS like between sensory and motor neurons. Integration of impulse. MOTOR NEURON : Transport impulses from the CNS to the effector organ (muscle or gland)

50. 3. TRANSMISSION OF NERVE IMPULSES ACROSS AN AXON Nerve impulses are conducted along neurons by means of electrochemical transmission. There has to be a significant electrical potential difference across a membrane ( membrane potential) for an impulse to be conducted.

51. RESTING AND ACTION POTENTIAL OF THE AXONAL MEMBRANE RESTING POTENTIAL When an axon is not conducting an impulse the membrane potential is -65mV This indicates that the inside of the axon is more negative [ more K-ions and less Na+ ions] than the outside [less K-ions and more Na+ ions])

52. RESTING POTENTIAL

53. ACTION POTENTIAL BEGINS Is a rapid change in polarity across a part of the axon membrane as the nerve impulse occurs. It uses gated channel proteins in axon membrane to exchange Na+ and K- ions . When the Na+ gates open and Na+ moves inside the axon , depolarization take place. The action potential changes from - 65mV to +40mV. The Na+ gates close and K- gates open and K- leave the axon Action potential change from +40mV to -65mV , r epolarization occurred

54. ACTION POTENTIAL BEGINS (DEPOLIRIZATION)

55. ACTION POTENTIAL ENDS (REPOLIRIZATION)

56. Threshold Is the minimum change in polarity across the axon membrane that is required to generate an action potential.

57. Propagation of Action Potentials – In nonmyelinated axons the impulse travels at 1m/sec. In myelinated axons , the gated ion channels (producing an action potential) are concentrated at the nodes of Ranvier, therefore the action potential “jumps” from node to node – this is called saltatory conduction . Speed – 200m/sec.

58. 4. Chemical transmission across a synapse Synapse – Open space between the axon of one neuron and the dendrite of the following neuron. The membrane of the first neuron is the presynaptic membrane and the membrane of the other neuron is called the postsynaptic membrane. Gap between neurons is the synaptic cleft.

59. Synapse

60. Chemical transmission across a synaptic cleft It is carried out by means of neurotrans-mitters , found in synaptic vesicles. Nerve impulses reaches the axon terminal . Gated channels for Ca + open and Ca + enter the terminal. The rise in Ca + stimulates synaptic vesicles to merge with the presynaptic membrane . Neurotransmitter molecules are released into synaptic cleft.

61. They diffuse through to the postsynaptic membrane. Where they bind with specific receptor proteins. Taken up by vesicles of dendrite Change impulse to electrical transmission further.

62. 5. Neurotransmitters and Neuromodulators Neurotransmitters: Acetylcholine ( ACh ) - Excites skeletal muscles but inhibits cardiac muscles. Excitatory or inhibitory effect on smooth muscles and glands Norepinephrine (NE) - Important for dreaming, waking and mood Dopamine - Emotions, learning and attention Serotonin - Thermoregulation, sleeping, and perception

63. Neurotransmitters: Neurotransmitters are present in CNS and PNS. After the effect of neurotransmitters, they are digested by enzymes in the postsynaptic membrane or retaken up by presynaptic membrane . Neuromodulators : Block the release of neurotransmitters or modify a neuron’s response to a neurotransmitter. E.g. endorphins.

64. 5. Neurodisorders Disorders of the nervous system include schizophrenia, depression, Alzheimer’s disease, Parkinson’s disease and ADD. Genetic and environmental factors contribute to diseases of the nervous system.

65. Depression Two broad forms of depressive illness are known: major depressive disorder and bipolar disorder In major depressive disorder , patients have a persistent lack of interest or pleasure in most activities Bipolar disorder is characterized by manic (high-mood) and depressive (low-mood) phases Treatments for these types of depression include drugs such as Prozac and lithium

66. Drug Addiction and the Brain Reward System The brain’s reward system rewards motivation with pleasure Some drugs are addictive because they increase activity of the brain’s reward system These drugs include cocaine, amphetamine, heroin, alcohol, and tobacco Drug addiction is characterized by compulsive consumption and an inability to control intake

67. Drug Addiction and the Brain Reward System Addictive drugs enhance the activity of the dopamine pathway Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug.

68. Alzheimer disease Alzheimer’s disease is a mental deterioration characterized by confusion, memory loss , and other symptoms Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain A successful treatment in humans may hinge on early detection of amyloid plaques There is no cure for this disease though some drugs are effective at relieving symptoms

69. Alzheimer disease