The Nervous System

1. The Nervous System Kimberly Colon Karina Jimenez Cassidy Marrero Elizabeth Francisco

2. Three Specific Functions • Sensory Input: Sensory receptors in the body respond to external and internal stimuli by generating nerve signals that travel to the brain and spinal cord. Example: Temperature sensors in the skin may signal to the brain that the air surrounding the body is cold.

3. Three Specific Functions • Integration: Brain and spinal cord interpret the data received from sensory receptors and signal the appropriate nerve response. • Example: The sensory information from temperature receptors is sent to the hypothalamus, the brain center that controls body temperature.

4. Three Specific Functions • Motor Output: Nerve impulses from the brain and spinal cord go to the effectors, which are muscles, glands, and organs. • Example, the hypothalamus triggers shivering

5. Divisions of the Nervous System • The central nervous system (CNS): Brain and spinal cord, which have a central location. • Peripheral nervous system (PNS): Includes the cranial and spinal nerves and is divided into afferent (sensory) and efferent (motor) divisions.

6. Nerve Tissue Made up of two principle types of cells. • Neurons: Nerve cells, which transmit nerve impulses. • Neuroglia: Which support and nourish neurons

7. Cell Body: Nucleus and other organelles Dendrites: Shorter, branched extensions that receive signals from sensory receptors Axon: Conducts nerve signals -Nerve: Parallel axons in PNS -Tract: Axon bundle in CNS Neurons

8. Types of Neurons • Motor neurons: Take nerve impulses from the CNS to muscles, organs, or glands. • Sensor neurons: Take nerve impulses from sensory receptors to the CNS. • Interneurons: Convey nerve impulses between various parts of the CNS.

9. Resting Potential: exists because the cell membrane is polarized • Action Potential: conducting nerve signals, depolarization/repolarization.

10. Transmission Across Synapse • Each axon branches into many fine endings, each tipped by a small swelling called an axon terminal. • The synaptic cleft is the small gap between the presynaptic membrane and the postsynaptic membrane • Transmission across a synapse is carried out by molecules called neurotransmitters.

11. The Central Nervous System

12. Central nervous system • Containing the brain and spinal cord • Gray matter: gray because it contains cell bodies and short, nonmyelinated fibers • White matter: white because it contains myelinated axons that run together in bundles called tracts. The myelin covering on these axons gives them a shiny, white experience

13. Central nervous system • Both the spinal cord and brain are wrapped in protective membranes known as meninges • Dura Mater: Tough, white, fibrous connective tissue that lies next to the skull and vertebrae • Arachnoid mater: deep to the dura mater, consists of spider-web-like connective tissue • Pia mater: Deepest meninx and follows the contours of the brain and spinal cord

15. Structure of the Spinal Cord • The spinal nerves extend from the cord between the vertebrae. • A cross section of the spinal cord shows: • The central canal which has cerebrospinal fluid, like meninges that protect the spinal cord. • The dorsal root of a spinal nerve contains sensory fibers entering the gray matter and the anterior root of a spinal nerve contains motor fibers exiting the gray matter. The posterior and anterior roots join, forming a spinal nerve that leaves the vertebral canal.

16. Functions of the spinal cord • Provides a means of communication between the brain and the peripheral nerves that leave the cord • Reflex arcs: A stimulus causes sensory receptors to generate action potentials that travel in sensory neurons to the spinal cord • Interneurons integrate the incoming data and relay signals to motor neurons • A response to the stimulus occurs when motor axons cause skeletal muscles to contract

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18. The Cerebrum • Largest portion of the brain in humans • Last center to receive sensory input and carry out integration before commanding voluntary motor responses • Communicates with and coordinates the activities of the other parts of the brain • Cerebral hemispheres: frontal, parietal, occipital, and temporal lobes • Cerebral cortex: outer layer of gray matter that covers the cerebral hemispheres

19. Motor & sensory areas of the cortex • Primary motor area: the frontal lobe just anterior to the central sulcus. • Where voluntary commands to skeletal muscles begin and each part of the body is controlled by a certain section • Primary somatosensory area: posterior to the central sulcus in the parietal lobe. • Where sensory information from the skin and skeletal muscles arrive, and each part of the body is sequentially represented

20. Association areas: places where integration occurs and where memories are stored • Anterior to the primary motor is area is a premotor area • Premotor area organizes motor functions for skilled motor activities, and then the primary motor area sends signals to the cerebellum and the basal nuclei, which integrate them • Cerebral Palsy: A condition characterized by a spastic weakness of the arms and legs

23. Processing centers • Prefrontal area: In the frontal lobe, receives information from the other association area and uses the information to reason and plan our actions • Broca’s area: (motor speech area) In the left frontal lobe. Ability to speak is dependent on this area. Damage to this can interfere with a person’s ability to control the muscles of the face and neck that allow speech. • Wernicke’s areas: (general interpretive area) Receives information from all of the other sensory association areas. Damage to this areas hinders a person’s ability to interpret written and spoken messages.

24. Limbic system • A collection of structures that lies just inferior to the cerebral cortex and contains neural pathways that connect portions of the cerebral cortex and the temporal lobes with the thalamus and the hypothalamus. • The limbic system guides individuals into behavior the is likely to increase the chance of survival and is involved in learning and memory. • Hippocampus: most inferior structure of the limbic system, vital in processing of short-term memory to become long-term memory.

25. Diencephalon • Region that encircles the third ventricle • Hypothalamus: forms the floor of the ventricle. Is an integrating center that helps maintain homeostasis by regulating hunger, sleep, thirst, body temperature, and water balance. • Thalamus: consists of two masses of gray matter located in the sides and roof of the third ventricle. It functions as a sensory “relay center” Visual, auditory, and somatosensory information arrive at the thalamus

26. The Cerebellum • Separated from the brain stem by the fourth ventricle. • Receives sensory input from the eyes, ears, joints and muscles about the present position of body parts • It receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum send motor impulses by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance.

27. The Brain Stem • Midbrain: Acts a a relay station for tracts passing between the cerebrum and the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. • Pons: Functions with the medulla oblongata to regulate breathing rate and has reflex centers concerned with head movements in response to visual and auditory stimuli. • Medulla oblongata: Contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction. Also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. • Reticular formation: assists the cerebellum in maintaining muscle tone; it also assists the pons and medulla in regulating respiration, heart rate, and blood pressure. The sensory component of it processes sensory stimuli and uses the signals to keep us mentally smart.

28. The Peripheral Nervous System

29. The Peripheral Nervous System • The Peripheral Nervous System (PNS) lies outside the Central Nervous System and is made of nerves and ganglia. • Nerves: bundles of axons (with and without myelin sheaths) that travel together. • Ganglia: swellings that contain groups of cell bodies.

30. Divisions of the PNS • The Peripheral Nervous System is divided into: • Afferent, or sensory system • Efferent, or nervous system

31. Afferent Sensory System • The somatic sensory system serves the skin, skeletal muscles, joints, and tendons. • The visceral ensory system supplies the internal organs of the body. • Nerves from both of these systems take information to the central nervous system.

32. Efferent Motor System • The somatic motor system carries commands from the central nervous system to skeletal muscles. • The autonomic motor system regulates the activity of cardiac and smooth muscles and glands.

33. Types of Nerves • Cranial Nerves: • 12 pairs (referred to by Roman numerals) • Located in the head, neck, and facial regions • Some cranial nerves are sensory (containing sensory fibers), motor (containing motor fibers), and mixed (containing both sensory and motor nerves) • However, the vagus nerve (cranial nerve X) has sensory and motor branches to the face and most of the internal organs. It contains somatic and visceral sensory nerves and efferent, or motor, nerves.

34. Types of Nerves • Spinal Nerves: • 31 pairs (one of each pair on either side of the spinal cord) • Group in the cervical, thoracic, lumbar, and sacral regions of the vertebral column. • Spinal nerves are mixed nerves because they contain sensory fibers and motor fibers. -Sensory fibers conduct impulses from sensory receptors to the spinal cord. - Motor fibers conduct impulses from spinal cord to effectors. • Each spinal nerve serves the particular region of the body in which it is located.

35. Cranial nerves

36. Spinal nerves

37. Somatic Motor Nervous System and Reflexes • Most actions are voluntary and originate in the motor cortex of the brain. • Reflexes, automatic involuntary responses, also occur in the somatic motor nervous system. These reflexes are protective mechanisms that are essential to homeostasis. • Cranial reflexes, such as blinking the eyes, involve the brain. • A spinal reflex causes pain sensory receptors to generate action potentials that move along a sensory fiber through the posterior root ganglia of the spinal cord.

38. How reflexes happen: • Sensory neurons enter the cord posteriorly and pass signals to interneurons. • Interneurons synapse with motor neurons whose short dendrites and cell bodies are in the spinal cord. • Nerve action potentials travel along a motor fiber to an effector. • Responses occur because certain interneurons carry nerve impulses to the brain via tracts in spinal cord and brain. • Reflexes, such as the knee-jerk reflex or the ankle-jerk reflex can be used to determine if the nervous system is acting properly.

39. Autonomic Motor Nervous System and Visceral Reflexes • The autonomic motor nervous system is composed of the sympathetic and parasympathetic divisions. • They both: • Function automatically and involuntarily • Innervate all internal organs • Utilize two motor neurons and one ganglion to transmit an action potential In contrast, a somatic motor neuron travels directly to its effector, without synapsing at a ganglion.

40. Visceral Reflexes • Visceral reflex actions include those that regulate blood pressure and breathing rate, and are especially important to maintenance of homeostasis. • These actions begin when sensory neurons send messages via spinal nerves to the central nervous system and are completed when motor neurons stimulate smooth muscle, cardiac muscle, or a gland.

41. Sympathetic Division: “Fight or Flight” • The fibers of this division arise from the middle portion of the spinal cord and almost immediately terminate in ganglia that lie near the cord. Therefore, the preganglionic fiber is short, but the postganglionic fiber that makes contact with an organ is long, as seen in the picture below. • The sympathetic division is important in emergency situations when a person may be required to fight or take flight. It accelerates the heartbeat, dilates the bronchi, and inhibits the digestive tract. • The neurotransmitter released by the postganglionic axon in this kind of situation is norepinephrine, which increases heart rate and contractility.

42. Parasympathetic Division: “Rest and Digest” • The parasympathetic division includes several cranial nerves as well as fibers that arise from the bottom portion of the spinal cord. • This division is referred to as the craniosacral portion of the autonomic system. • In this division, the preganglionic fiber is long and the postganglionic fiber is short because the ganglia lie near or within the organ.

43. The parasympathetic division promotes all of the internal responses associated with a relaxed state. • Parasympathetic nerves cause the pupil to contract, promote digestion of food, slow heart rate, and decrease the strength of cardiac contraction. • The neurotransmitter utilized by the parasympathetic division is acetylcholine.

44. Effects of Aging • After age 60, the brain begins to lose thousands of neurons a day. • By age 80, the brain weighs about 10% less than when the person was a young adult. • The cerebral cortex loses as much as 45% of its cells. • Therefore, such mental activities as learning, memory, and reasoning decline. • Neurotransmitter production also decreases, resulting in slower synaptic transmission. • As a person ages, processing and translating a thought into action take longer.

45. Mental impairment is NOT an automatic consequence of getting older. • Maintaining the health of the cardiovascular system is fundamental to retaining mental function. • Older individuals can stay mentally alert by challenging the brain. • Taking courses, reading, solving puzzles, exercise, etc. • Neurological disorders are more apt to occur in the elderly. • Alzheimer disease and Parkinson disease

46. Homeostasis • The nervous system detects, interprets, and responds to changes in internal and external conditions to keep the internal environment relatively constant. • Together with the endocrine system, it coordinates and regulates the functioning of the other systems in the body to maintain homeostasis. • The everyday regulation of internal organs usually takes place below the level of consciousness. • Composed of blood and tissue fluids.

47. Subconscious control is dependent on reflex actions that involve the hypothalamus and the medulla oblongata. • Heart rate, the constriction of blood vessels, and the breathing rate. • The hypothalamus works closely with the endocrine system and produces the hormone ADH, which causes the kidneys to reabsorb water. • The nervous system stimulates skeletal muscles to contract, it controls the major movements of the body which helps us take precautions or stay in a moderate environment.