The Nervous System

1. The Nervous System Health Science 1

2. Structure and Function of the Nervous System

3. Neuron • This is the nerve cell • Functions to transmit a message from one cell to the next • Contains a nucleus, cytoplasm and a cell membrane

4. Dendrite • Extension of the neuron • It is possible to have more than one dendrite on a nerve cell Is a path along which nerve impulses travel

5. Axon • Another extension of nerve cell • Only one axon per cell • Another path for nerve impulses to travel along a nerve cell • Covered by Neurilemma (also called Myelin sheath) that speeds up the nerve impulse as it travels along the axon

6. Axon cont… • This covering produces a fatty substance called myelin which protects the axon • Myelin is also called “white matter”

7. Axons carry messages AWAY from the cell body • Dendrites carry messages TO the cell body

8. Nervous Tissue • All neurons possess the characteristics of being able to react when stimulated and of being able to pass the nerve impulse generated on to other neurons

9. Nervous tissue • Irritability – The ability to react when stimulated • Conductivity – The ability to transmit a disturbance to distant points

10. Types of neurons • Sensory (afferent) – emerge from the skin or sense organs and carry messages or impulses toward the spinal cord and brain. • Motor (efferent) – carry messages from the brain and spinal cord to the muscles and glands. • Associative (interneurons) – carry impulses from the sensory neuron to the motor neuron.

11. Synapse • The area of the neuron where the message goes from one cell to the next. • Messages go from the axon of one cell to the dendrite of another. • They never touch. • Synaptic cleft – the space between the cells.

12. Synapse cont… • Conduction accomplished through neurotransmitters at the end of the axon • Special chemicals • Epinephrine • Norepinephrine • Acetylcholine

13. Central Nervous System

14. Brain • Complex, intricate mass of soft nervous tissue. • Weighs about 3 pounds • Contains over a billion nerve cells (neurons) • Protected by the cranial cavity in the skull, the meninges and the cerebrospinal fluid.

15. Brain cont… • Cerebral cortex (outer) made up of gray matter and is the highest center of reasoning and intellect. • Deeper part of cerebral cortex is made up of myelinated nerve tracts and is called white matter.

16. Required an adequate blood supply to supply it with oxygen • Without oxygen, brain damage will occur within 4-8 minutes.

17. Cerebrum • Largest part of the brain – occupies the whole upper part of the skull. • Covered by the cerebral cortex • Divided into right and left hemisphere • Deep groove known as longitudinal fissure.

18. Surface of cerebrum • Surface is covered by furrows and ridges. • Deep furrows or grooves = Fissures • Shallower ones = sulci • Elevated ridges between the sulci are the gyri (convolutions)

19. Convolutions increase the surface area of the brain, resulting in more gray matter. • Surface varies from one brain to another, however, certain fissures are constant and represent important demarcations, dividing the hemispheres into 4 lobes.

20. Cerebral functions • Each lobe of the hemispheres control different types of function.

21. Frontal Lobe • Controls the motor functions of humans. • This motor area controls the voluntary muscles. • Left side controls voluntary movement on the right side of the body. • Right side controls voluntary movement on the left side of the body.

22. Also 2 areas which control speech. • If damaged, one may know what to say, but could be unable to speak. • Allows us to recognize words and to interpret the meaning (spoken or read)

23. Parietal lobe • Comprises the sensory area. • Receives and interprets nerve impulses from the sensory receptors for pain, touch, heat and cold. • Further helps in the determination of distances, sizes and shapes

24. Occipital lobe Located over the cerebellum Houses the visual area, controlling eyesight.

25. Temporal Lobe • Upper part contains the auditory area (including specific tones) • Anterior part – olfactory area (smell)

26. Other cerebral functions • Controls conscious thought, judgment, memory, reasoning and willpower • WE ARE THE MOST INTELLIGENT OF ALL ANIMALS 

27. Diencephalon Located between cerebrum and midbrain Damage could result in increased sensitivity to pain, or total loss of consciousness. • Thalamus – spherical mass of gray matter • Acts as a relay station for incoming and outgoing nerve impulses from sensory organs and from areas of the brain.

28. Hypothalamus – below the thalamus. Connected to the pituitary gland, the thalamus and midbrain by a bundle of nerve fibers.

29. Limbic System • Part of the brain associated with emotional control. • Hyppocampalgyri helps to store and retain short-term memory • HYPOTHALAMUS is part of the limbic sytem and considered the “brain” of the brain.

30. Vital Functions of hypothalamus • Autonomic nervous control • Cardiovascular control (blood pressure) • Temperature control (maintain normal body temperature) • Appetite control • Water balance • Manufacture of oxytocin (contracts the uterus during labor)

31. Gastrointestinal control • Emotional state • Sleep control

32. Cerebellum • Behind pons and below the cerebrum • Divided into right and left cerebellar hemispheres, connected to a central portion called the vermis • Consist of gray matter on outside, and white matter on the inside

33. Cerebellum controls all body functions that have to do with skeletal muscles. • Maintenance of balance • Maintenance of muscle tone • Coordination of muscle movement • Damage or injury to cerebellum results in motor impairment.

34. Brain Stem • 3 parts • Midbrain • Pons • Medulla • Provides a pathway for messages going to and from the cerebrum • Gray matter

35. Pons • In front of the cerebellum, between the midbrain and medulla oblongata • Conductive pathway for nerve impulses between the cerebrum, cerebellum and other areas of the nervous system • Center that controls respiration (breathing)

36. midbrain • Contains the nuclei for reflex centers involved with vision and hearing

37. Medulla oblongata • Between pons and spinal cord • Inside the cranium, above the foramen magnum (opening) in occipital bone • Serves as passageway for nerve impulses between the brain and spinal cord

38. Contains the nuclei for vital functions such as the heart rate, the rate and depth of respiration and blood pressure control • Swallowing and vomiting

39. Coverings of the brain • Three layers called the Meninges • Dura mater – outer brain covering that lines the inside of the skull. Contains abundance of blood vessels. • Arachnoid – middle layer, resembles cobweb with fluid filled spaces • Pia mater – covers surface of the brain, consisting of blood vessels held together by connective tissue.

40. Space between the arachnoid and pia mater is filled with cerebrospinal fluid, produced within the ventricles of the brain. • CSF – acts as a shock absorber and source of nutrients for the brain

41. Spinal Cord • Continues down from the brain • Begins at the foramen magnum and continues to the second lumbar vertebrae • Lies within the vertebrae of the spinal column

42. Submerged in CSF and surrounded by three meninges (like the brain) • Gray matter within the internal section • White matter on external surface • Reflex center and conduction pathway to and from the brain

43. Peripheral Nervous System • All of the nerves and ganglia (groups of cell bodies) • Connects the CNS to the various body structures • Functions – Control the automatic (involuntary) activities of the body • Act as the reflex center of the body

44. Nerves • Nerve is bundle of nerve fibers enclosed by connective tissue. • If the nerve fibers carry impulses from the sense organs to the brain or spinal cord, they are called sensory (afferent) • If it’s fibers carry impulses from the brain or spinal cord to muscles or glands, they are called motor (efferent) Mixed nerves contain both sensory and motor.

45. Peripheral Nervous System • Cranial Nerves • 12 pairs • Designated by number and name • Name may give clue to its function • Functions are concerned mainly with activities of the head and neck • Spinal Nerves • 31 pairs • All are mixed nerves • Named in relation to their location on the spinal cord • Carry messages to and from the spinal cord and brain to all parts of the body

46. In a spinal cord injury, there is no sensation or movement • Spinal nerves divide and branch to form a plexus

47. Autonomic Nervous System • Includes nerves, ganglia, and plexuses which carry impulses to all smooth muscle, secretory glands and heart muscle. • Regulates the activities of the heart, blood vessels, respiratory organs, alimentary canal, kidneys, urinary bladder and reproductive organs. • Usually not under conscious control. They are automatic.

48. 2 divisions of ANS • Sympathetic • Referred to as the “fight or flight system” • When the body perceives it is in danger or under stress, it prepares to run away or stand and fight. • Parasympathetic • Helps to restore balance in the body afterwards.

49. ANS cont… • Strongly influenced by emotion. • During periods of fear, anger or stress, the sympathetic division acts to prepare the body for action. • The effects of the parasympathetic counteract the effects. • Operate as a pair, to keep the body balances and functioning properly.

50. Somatic Nervous System • The somatic nervous system is responsible for all voluntary muscle contractions and sensory information processing, while the other portions of the peripheral nervous system control involuntary processes of the body. • The somatic nervous system enervates all sensory organs, including the eyes, ears, tongue, and skin, as well as all the skeletal muscles, and the muscles attached to the bone and used for voluntary movement.