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CHAPTER 7

CHAPTER 7. THE NERVOUS SYSTEM. Introduction. The Nervous System (NS) is the master controlling and communicating system of the body. Functions of the NS:. It uses sensory receptors to monitor changes occurring inside and outside the body.

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CHAPTER 7

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  1. CHAPTER 7 THE NERVOUS SYSTEM

  2. Introduction • The Nervous System (NS) is the master controlling and communicating system of the body.

  3. Functions of the NS: • It uses sensory receptors to monitor changes occurring inside and outside the body. • It processes and interprets the sensory input and makes decisions about what should be done. • It activates muscles or glands.

  4. Organization of the Nervous System • Structural Classification – Includes ALL nervous system organs • Central NS (CNS) – consists of the brain and spinal cord • Peripheral NS (PNS) – consists of the nerves that extend from the brain or spinal cord

  5. Organization of the Nervous System • Functional Classification • Sensory (Afferent) Division – consist of nerve fibers that carry impulses to the CNS from sensory receptors; helps keep the CNS constantly informed of events going on both inside and outside the body. • Motor (Efferent) Division – carries impulses from the CNS to the organs, muscles, and glands to activate them; has 2 smaller subdivisions: • Somatic NS – allows us to consciously control our skeletal muscles (voluntary) • Autonomic NS – regulates events that are involuntary

  6. Nervous Tissue: Structure & Function • The NS is made up of 2 types of cells – supporting cells and neurons • Supporting Cells - Lumped together in the CNS as NEUROGLIA, which means “nerve glue.” Each different type of neuroglia is called GLIA. The CNS glia include: • Astrocytes – star shaped cells that help make exchanges between the neurons and the capillaries; MAKES UP NEARLY ½ OF THE NERUAL TISSUE • Microglia – spider shaped cells that dispose of debris, including bacteria and dead brain cells • Ependymal Cells – line the cavities of the brain and spinal cord; have cilia to circulate cerebrospinal fluid • Oligodendrocytes – provide insulation to the nerve fibers

  7. Nervous Tissue: Structure & Function • Neurons – Anatomy: • Also called NERVE CELLS – specialized to transmit messages from one part of the body to another. • All neurons have a cell body and one or more slender processes extending from the cell body. • Parts of the Neuron: • Cell Body – the metabolic center of the neuron; contains organelles • Nucleus – center of the cell • Mitochondrion – gives the cell its energy • Nissl Substance – the rough ER that maintains the shape of the cell • Dendrites – convey incoming messages TOWARD the cell body • Axons – convey incoming messages AWAY from the cell body • Axonal Terminals – where the axons end • Schwann Cells – cells that wrap around the axon • Nodes of Ranvier – the gaps or indentions between the Schwann Cells

  8. Nervous Tissue: Structure & Function • Neurons – Classification: • Functional Classification – groups neurons according to the direction the nerve impulse is traveling; 3groups: • Sensory – carry impulses from sensory receptors to the CNS • Motor – carry impulses from the CNS to the muscles and glands • Association – they connect the motor and sensory neurons in a pathway • Structural – groups neurons according to the number of processes extending from the cell body; 3 groups: • Multipolar – has several processes; includes all motor and association neurons • Bipolar – has 2 processes (axon and dendrite); found only in the eye and ear • Unipolar – have one process; includes sensory neurons in the PNS

  9. Nervous Tissue: Structure & Function • Physiology • Nerve Impulse – an electrochemical event, initiated by stimuli, that transmits to other neurons, muscle, or glands. • Reflexes – rapid, predictable, and involuntary responses to stimuli; 2 types: • Autonomic Reflex – secretion of saliva and changes in the size of the pupil • Somatic Reflex – pulling your hand away from a hot object

  10. Reflex Arc

  11. Central Nervous System • Functional Anatomy of the Brain: • Size = about 2 good fistfuls of pinkish gray matter • Weight = a little over 3 pounds • 4 major parts of the brain: • Cerebrum – largest part • Cerebellum • Brain stem • Diencephalon

  12. Parts of the Brain

  13. Cerebrum • Structure: • Consists of 2 large masses called CEREBRAL HEMISPHERES – mirror images of each other • 4 lobes of the cerebral hemispheres: • Frontal Lobe = anterior portion of each cerebral hemisphere • Parietal Lobe = posterior to the frontal lobe • Temporal Lobe = lies below the frontal and parietal lobes • Occipital Lobe = posterior portion of each cerebral hemisphere • Cerebral Cortex – outermost portion of the cerebrum

  14. Structure of the Cerebrum

  15. Cerebrum • Functions • The cerebrum is concerned with higher brain functions. • Three Functional Regions • Motor Areas – the motor area of the right cerebral hemisphere controls skeletal muscles on the left side of the body and vice versa • Frontal Lobe = PRIMARY MOTOR AREA – controls speech, movement of the eyes, and writing • Sensory Areas – involves several lobes • Parietal Lobe = sensations from all parts of the skin • Occipital Lobe = vision • Temporal Lobe = hearing

  16. Cerebrum • Functions • Three Functional Regions continued… • Association Areas – function in the analysis and interpretation of sensory experiences and are involved with memory, reasoning, verbalizing, judgement, and emotional feelings • Frontal Lobe = concentrating, planning, problem solving • Parietal Lobe = understanding speech and choosing the words needed to express thoughts and feelings • Temporal Lobe = understanding speech and reading printed words, memory of visual scenes and music • Occipital Lobe = analyzing visual patterns and recognizing another person or an object • Both cerebral hemispheres participate in basic functions. However, in most persons one side acts as a dominant hemisphere for certain functions. • In 90% of the population, the left hemisphere is dominant for speech, writing, and reading.

  17. Cerebellum • The cerebellum is a large mass of tissue located below the occipital lobes of the cerebrum and posterior to the pons and medulla oblongata of the brainstem. • Functions: • It communicates with other parts of the CNS • It transmits sensory information concerning the position of the limbs and joints • It stimulates skeletal muscles to cause the desired body movement • It helps maintain posture • Damage to the cerebellum can result in tremors, inaccurate movements of voluntary muscles, the loss of muscle tone, and the loss of equilibrium

  18. Brainstem • Brain Stem – a bundle of nervous tissue that connects the cerebrum to the spinal cord • 3 parts: • Midbrain • A short section of the brain stem located between the diencephalons and pons • Serves as a reflex center • Responsible for moving the eyes to view something as the head is turned • It contains the auditory reflex centers that operate when a person needs to move his/her head in order to hear sounds more distinctly

  19. Brainstem • 3 Parts Continued: • Pons • Appears as a rounded bulge on the underside of the brain stem • Relays impulses to and from the medulla oblongata to the cerebrum • Medulla Oblongata • An enlarged continuation of the spinal cord extending from the pons to the skull • The nerve fibers that connect the brain and spinal cord MUST pass through the medulla olongata

  20. Brain Stem

  21. Diencephalon • Located between the cerebral hemispheres and above the midbrain • Contains the thalamus – central relay station for sensory impulses ascending from other parts of the NS to the cerebral cortex • Contains the hypothalamus – plays a key role in maintaining homeostasis by regulating a variety of activities such as blood pressure, body temperature, body weight, sleep, and hunger

  22. Protection of the CNS • Nervous tissue is very soft and delicate • Meninges - 3 connective tissue membranes covering and protecting the CNS structures • Dura Mater – outermost layer; very tough and leathery • Arachnoid Mater – the middle layer; weblike • Pia Mater – innermost layer; clings tightly to the surface of the brain and spinal cord • Cerebrospinal Fluid • Provides a watery cushion around the brain and spinal cord • Any significant change in CSF may be a sign of meningitis

  23. Brain Dysfunctions • Traumatic Brain Injuries • Concussion – occurs when brain injury is slight; The victim may be dizzy, “see stars,” or lose consciousness briefly; no permanent brain damage • Contusion – the result of marked tissue destruction; can result in coma lasting from hours to a lifetime • Cerebral Edema – swelling of the brain due to inflammatory response to injury; can result in death

  24. Spinal Cord • Structure – a cylindrical shaped structure which is a continuation of the brain stem • 31 pairs of spinal nerves arise from the cord and exit from the vertebral column to serve the body area close by • Function – provides a 2-way conduction pathway to and from the brain

  25. Peripheral Nervous System • Consist of nerves found outside the CNS • Structure of a Nerve • Nerve – a bundle of neuron fibers found outside the CNS. • Nerves are classified according to the direction in which they transmit impulses: • Mixed Nerves – nerves carrying both sensory and motor fibers • Sensory Nerves – nerves carrying impulses toward the CNS • Motor Nerves – nerves carrying impulses away from the CNS • Cranial Nerves - 12 pairs that arise from the brain and serve the head and neck • Spinal Nerves – 31 pairs that arise from the spinal cord and serve the limbs

  26. Peripheral Nervous System • Autonomic Nervous System • Structure: • The motor subdivision of the PNS that controls body activities automatically • Also known as the INVOLUNTARY NERVOUS SYSTEM • Autonomic Functioning – 2 divisions: • Sympathetic Division • Referred to as the “fight-or-flight”system • Its activity is evident when we are excited or find ourselves in emergency or threatening situations • Signs of Activity = pounding heart, deepbreathing, sweaty skin • It allows the body to cope rapidly with situations that threaten homeostasis • Parasympathetic Division • Most active when the body is at rest and not threatened in any way. • Concerned with normal digestion and elimination of wastes and conserving body energy • Example: Relaxing after a meal

  27. Developmental Aspects of the Nervous System • Because the NS is formed during the first month of embryonic development, any maternal infection early in pregnancy can have harmful effects on the fetal NS. • One of the last areas of the CNS to mature is the hypothalamus, which regulates body temperature. This is why premature babies usually have to be monitored closely and put under a heating element. • The brain reaches its maximum weight in the young adult • Neurons die throughout life and are not replaced – brain mass declines with age

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