Chapter 10. The Nervous System

Transcription

1 Chapter 10 The Nervous System

2 Objectives List the organs and divisions of the nervous system and describe the generalized functions Identify the major types of cells in the nervous system and discuss the function of each Identify the major anatomical components of the brain and spinal cord and briefly comment on the function of each Identify and discuss the coverings and fluid spaces of the brain and spinal cord Compare and contrast spinal and cranial nerves Discuss the structure and function of the two divisions of the autonomic nervous system Describe major nervous system disorders 2

3 Nervous System 1. Central nervous system (CNS) - brain and spinal cord 2. Peripheral nervous system (PNS) - all nerves Autonomic nervous system (ANS) Somatic nervous system 3

4 Central Nervous System Contains: Brain Spinal cord Made of gray and white matter 4

5 Brainstem Made up of 3 parts: medulla oblongata, pons, and midbrain Medulla- regulates the vital functions of heart rate, breathing, and BP; regulates reflexes of coughing, sneezing, swallowing, and vomiting Pons- contains respiratory centers that work with those in medulla Midbrain- contains centers for visual reflexes, auditory reflexes, and righting (equilibrium) reflexes 5

6 Cerebellum Second largest part of the human brain Function Regulates coordination of voluntary movement, muscle tone, stopping movements, and equilibrium 6

7 Diencephalon Consist of hypothalamus, thalamus, and pineal gland Control the functioning of most internal organs Controls hormone secretion by anterior and posterior pituitary glands Contains centers for controlling appetite, wakefulness, pleasure, etc. 7

8 Hypothalamus Contributes to healthy survival

9 Thalamus Dumbbell-shaped mass of gray matter extending into each cerebral hemisphere Superior to the hypothalamus Inferior to the cerebrum Relays and integrates sensory impulses to cerebrum Produces emotions of pleasantness or unpleasantness associated with sensations 9

10 Cerebrum Largest part of the human brain Consists of two hemispheres separated by longitudinal fissure Outer layer of gray matter is the cerebral cortex Interior composed mainly of white matter Functions of the cerebrum: mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements 10

11 Central Nervous System Spinal Cord: Outer portion: Columns of white matter, composed of bundles of myelinated nerve fibers Interior portion: Gray matter made up mainly of neuron dendrites and cell bodies Spinal cord tracts provide two-way conduction paths - ascending and descending Spinal cord contains all spinal cord reflexes; sensory and motor tracts conduct impulses to and from the brain 11

12 Cross-section of spinal cord

13 Peripheral nervous system Also known as (PNS) - all nerves outside of brain and spinal cord Contains: 1. Autonomic nervous system (ANS) 2. Somatic nervous system 13

14 Autonomic Nervous System The ANS- consists of motor neurons that conduct impulses from the spinal cord or brainstem to the following tissues: 1. Cardiac muscle tissue 2. Smooth muscle tissue 3. Glandular epithelial tissue Consists of two main divisions: Sympathetic nervous system- Fight or Flight Parasympathetic nervous system 14

15 Autonomic Nervous System Sympathetic nervous system Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are elicited Group of changes induced by sympathetic control is called the fight-or-flight response 15

16 Autonomic Nervous System Parasympathetic nervous system Function - dominates control of many visceral effectors under normal, everyday conditions What are visceral effectors referring to? 16

17 Autonomic Nervous System Motor neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue Regulates body s automatic or involuntary functions 17

18 Autonomic Nervous System Autonomic neurotransmitters Cholinergic fibers pre-ganglionic axons of parasympathetic and sympathetic systems release acetylcholine Adrenergic fibers - axons of sympathetic postganglionic neurons release norepinephrine (noradrenaline) 18

19 Somatic Nervous System Also part of peripheral nervous system Voluntary action signaling of the nervous system to the voluntary muscles 19

20 Peripheral Nervous System Cranial nerves 12 pairs - attached to undersurface of the brain Connect brain with the neck and structures in the thorax and abdomen 20

21 The Cranial Nerves I Olfactory II Optic III Oculomotor IV Trochlear V Trigeminal VI Abducens VII Facial VIII Acoustic IX Glossopharyngeal X Vagus XI Spinal accessory XII Hypoglossal On Old Olympus Tiny Tops, A Finn And German Viewed Some Hops

22 The Cranial Nerves NERVE FUNCTION I Olfactory Sense of smell II Optic Vision III Oculomotor Eye movements IV Trochlear Eye movements V Trigeminal Sensation of face, scalp, teeth VI Abducens Eye movements VII Facial Sense of taste VIII Acoustic Hearing, sense of balance IX Glossopharyngeal Swallowing X Vagus Sensations of throat, slowing of HR XI Spinal accessory Shoulder shrug XII Hypoglossal Tongue movements

23 Peripheral Nervous System Spinal nerves: contain dendrites of sensory neurons and axons of motor neurons Conduct impulses necessary for sensations and voluntary movements Skin surface area supplied by a single nerve is called a dermatome 23

24 Transmission How do the signals get around? video 24

25 Neurons (nerve fibers) 1. Cell body: contains the nucleus, essential for the life of the neuron 2. Dendrites processes that transmit impulses toward the cell body 3. Axon - elongated projection that conducts impulses away from the cell 4. Protected by the myelin sheath: made of Schwann cells 25

26 Nerves Bundle of peripheral axons Tract bundle of central axons White matter- brain or cord tissue composed primarily of myelinated axons (tracts) Gray matter- brain or center of spinal cord tissue composed primarily of cell bodies and unmyelinated fibers 26

27 Neurons Neurons classified according to function or direction of impulse Sensory neurons (afferent neurons): conduct impulses to the spinal cord and brain Motor neurons (efferent neurons): conduct impulses away from brain and spinal cord to muscles and glands Interneurons: conduct impulses from sensory neurons to motor neurons; also called central or connecting neurons 27

28 Glia (neuroglia) Support cells: bring cells of nervous tissue together structurally and functionally Three main types of connective tissue cells of the CNS: 1. Astrocytes 2. Microglia 3. Oligodendrocytes 28

29 Neuron signaling 1. Reception the information is received 2. Transmission an electrical process send information from the afferent (sensory) neurons to the interneurons in the CNS 3. Integration the information is processed 4. Transmission interneurons transmit information to efferent (motor) neurons then to muscles or glands 5. Actual response 29

30 The Synapse Definition - the place where impulses are transmitted from one neuron to another Synapse made of three structures - synaptic knob, synaptic cleft, and plasma membrane Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron 30

31 The Synapse Names of neurotransmitters - acetylcholine, (catecholamines; norepinephrine, dopamine, and serotonin), endorphins, enkephalins, nitric oxide (NO), and other compounds Parkinson disease (PD) - characterized by abnormally low levels of dopamine in motor control areas of the brain; patients usually exhibit involuntary trembling and muscle rigidity 31

32 Parkinsonism

33 Reflex A reflex is an involuntary or automatic, one way action that your body does in response to something - without you even having to think about it Nerve impulses are conducted from afferent receptors to effector receptors over neuron pathways or reflex arcs Five essential parts: 1. Receptors- detect a change and generate impulses 2. Sensory neurons- transmit impulses from receptors to the CNS 3. CNS- contains one or more synapses 4. Motor neurons- transmit impulses from the CNS to the effector 5. Effector- performs its characteristic action 33

34 Patellar reflex

35 Disorders of nervous tissue Multiple sclerosis Characterized by myelin loss in central nerve fibers and resulting conduction impairments Tumors General name for nervous system tumors is neuroma Most neuromas are gliomas, glial tumors Multiple neurofibromatosis - characterized by numerous benign tumors 35

36 Brain disorders Destruction of brain tissue Cerebrovascular accident (CVA) 2 types hemorrhage from or cessation of blood flow through cerebral blood vessels; a stroke Cerebral palsy (CP) - condition in which damage to motor control areas of the brain before, during, or shortly after birth causes paralysis (usually spastic) of one or more limbs 36

37 Brain disorders Dementia - progressive loss of memory, shortened attention span, personality changes, reduced intellectual capacity, motor control deficit Alzheimer disease (AD) - brain disorder of the middle and late adult years characterized by dementia Huntington disease (HD) - inherited disorder characterized by chorea (purposeless movement) progressing to severe dementia HIV (also causes AIDS) can infect neurons and thus cause dementia 37

38 Brain disorders Seizure disorders Seizure - sudden burst of abnormal neuron activity that results in temporary changes in brain function Epilepsy - many forms, all characterized by recurring seizures Electroencephalogram - graphic representation of voltage changes in the brain used to evaluate brain activity 38

39 Peripheral Nerve disorders Neuritis - general term referring to nerve inflammation Sciatica is inflammation of the sciatic nerve that innervates the legs Neuralgia, or muscle pain, often accompanies neuritis 39

40 Peripheral Nerve disorders Trigeminal neuralgia - recurring episodes of stabbing pain along one or more branches of the trigeminal (fifth cranial) nerve in the head Bell palsy - paralysis of facial features resulting from damage to the facial (seventh cranial) nerve 40

41 Peripheral Nerve disorders Herpes zoster or shingles Viral infection caused by chickenpox virus that has invaded the dorsal root ganglion and remained dormant until an episode of shingles Usually affects a single dermatome, producing characteristic painful plaques or vesicles 41

42 Disorders of the Autonomic Nervous System Stress-induced disease Prolonged or excessive response to stress can disrupt normal functioning throughout the body Examples of stress-induced conditions include heart disease, digestive problems, and reduced resistance to disease 42