Nervous System

1. Nervous System Anatomy and Physiology

2. What are the major functions of the nervous system? • The master controlling and communicating system of the body • Functions: • Sensory input – monitoring stimuli occurring inside and outside the body • Integration – interpretation of sensory input • Motor output – response to stimuli by activating effector organs

4. How is the nervous system organized? • Central nervous system (CNS) • Brain and spinal cord • Integration and command center • Peripheral nervous system (PNS) • Paired spinal and cranial nerves • Carries messages to and from the spinal cord and brain

6. What are the divisions of the peripheral nervous system? • Sensory (afferent) division • Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain • Visceral afferent fibers – transmit impulses from visceral organs to the brain • Motor (efferent) division • Transmits impulses from the CNS to effector organs

7. What are the parts of the motor division? • Somatic nervous system • Conscious control of skeletal muscles • Autonomic nervous system (ANS) • Regulate smooth muscle, cardiac muscle, and glands • Divisions – sympathetic and parasympathetic

8. What are the functions of the sympathetic and parasympathetic divisions? • Parasympathetic- “resting and digesting system” • Most active in nonstressful situations • Keeps energy use low and maintains vital housekeeping activities running. • Sympathetic division- “fight or flight” division • Exercise, excitement, emergency, and embarrassment division • Prepares the body for action

10. What types of supporting cellsmake up central nervous tissue? Known as neuroglia or glial cells • Astrocytes-star shaped cells that connect neurons together and to their blood supply. • Microglia- function as phagocytes by engulfing foreign invaders. • Ependymal- (epithelial-like) provide a barrier between brain and spinal fluid. • Oligodendrocytes- connect thick neuronal fibers and produce an important insulating material called the myelin sheath.

12. What are neurons? • Conduct messages in the form of nerve impulses • They number in the billions (much higher in anatomy teachers) • Have extreme longevity • Most cannot divide (hippocampus is a rare exception; it is involved in memory). • Have a high metabolic rate; require mucho oxygen and glucose • 3 basic regions: dendrites, cell body, and axons • Impulses travel from dendrites to cell body to axons

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15. How is a nerve impulse transmitted across a neuron? • The sodium-potassium pump creates a resting potential across the membrane of a neuron. • When a threshold stimulus is applied to the neuron, an action potential travels down the neuron. (action potential=nerve impulse) • The nerve impulse will jump from the axon to the dendrite of another neuron across a synapse by the use of neurotransmitters

16. What is the all-or-none phenomenon? • An action potential either happens completely or not at all. • Many sub-threshold stimuli can cause an action potential. Neurons can have different thresholds (pain) • It is similar to the flash point of a burning twig. As a match is placed under a twig, the twig must get hot enough to produce a flame on the twig.

17. What is saltatory conduction? • Myelin sheath found on the axon insulates and doesn’t allow the depolarization of the membrane. • The action potential must jump from one node of Ranvier to the next. This makes the action potential move faster down the axon. • Some can reach speeds of 100 m/s. • Unmyelinated neurons propagate slow action potentials that must move from one site to the next. This is called continuous conduction.

18. Saltatory conduction

19. What is a synapse? • Synapses are gaps between neurons • Exists between the axon of one neuron and the dendrite of another. • Neurons can have a large number connecting to numerous other neurons. (This accounts for the complexity of the nervous system) • When an action potential reaches the end of an axon, neurotransmitters are stimulated to flood the gap and bond to ion channels on the post synaptic neuron. • This causes an action potential to be produced.

20. Vesicles with neurotransmitters Synapse

22. Page 409

23. What are neurotransmitters? • Molecules that bridge the synapse • Over 50 different types have been discovered • Some can be excitatory or inhibitory • See page 416-417 for types

24. What are reflexes? • Rapid, automatic responses to stimuli, in which a particular stimulus always causes the same motor response. • Produces the simplest behaviors. Ex. Removing hand from a hot object. • Occur over neural pathways called reflex arcs. • 5 basic components: receptor, sensory neuron, integration center, motor neuron, and effector.

27. What are the major parts of the brain? • Cerebral hemispheres, diencephalon, Brain stem, and cerebellum • Cerebrum and cerebellum have a gray matter nuclei surrounded by white matter and a gray matter cortex. • Gray matter- unmyelinated neurons • White matter- myelinated neurons

29. What are the functions of the cerebral cortex? • Interprets sensory impulses (including auditory,visual, and olfactory), controls voluntary and skilled skeletal muscle, functions in intellectual and emotional processing. • Shows lateralization of function • Most people the left hemisphere is dominant and is specialized for language and mathematical skills • The right hemisphere is more concerned with visual-spatial skills and creative endeavors. • Right hemisphere controls the left side of the body (motor control) and vice versa.

30. See page 436

31. What are the functions of the diencephalon? • Consists of the thalamus, hypothalamus and epithalamus and encloses the third ventricle. • Thalamus-Relay station for sensory and motor impulses to and from the cerebrum. Functions in memory. • Hypothalamus-Regulates hormonal output of the pituitary gland, regulates body temp., food intake, water balance, thirst, and biological rhythms and drives. (limbic system) • Limbic System- functional system involving cerebral structures and the diencephalon that mediates emotional responses and is also involved in memory.

33. What are the parts and functions of the brain stem? • Medulla oblongata- respiratory rhythm, heart rate, and blood pressure • Pons- regulation of respiration • Midbrain- visual and auditory reflex centers and fear response

34. What is the function of the cerebellum? • Cerebellum processes and interprets impulses from the motor cortex making movements smooth and well timed. (coordination)

35. What protects the brain? • The brain is protected by bone, meninges, cerebrospinal fluid, and the blood-brain barrier. • Meninges have 3 layers: • Dura mater- tough layer of fibrous connective tissue • Arachnoid mater- filled with large blood vessels and CSF • Pia mater- delicate connective tissue with capillaries • Blood-brain barrier- keep blood products separate from neurons. Formed from tight capillary walls and ependymal cells that form a tight membrane around capillaries. • CSF- liquid cushion produced by the choroid plexus and fills the cranial cavity.

37. Blood-brain barrier

39. What is the spinal cord? • Two-way impulse conduction pathway and a reflex center. • Lies within the vertebral column • Protected by meninges and CSF • 31 pairs of spinal nerve roots extend from the cord.