Structure of the Nervous System

1. Chapter 9

2. Applied Learning Outcomes • Use the terminology associated with the nervous system • Learn about the following: • Nerve structure • Types of nerve pathways • Nervous system components • Central nervous system structure and function • Peripheral nervous system structure and function • Understand the aging and pathology of the nervous system Chapter 9 – Structure of the Nervous System

3. Overview Nervous system composed of neurons and neuroglia. Bundled into two major components: Central Nervous System (CNS): Major division of the nervous system composed of the brain and spinal cord; works as a controlling network for the entire body Peripheral Nervous System (PNS): The part of the nervous system made up of neurons and neuroglia outside of the brain and spinal cord; provides motor and sensory communication between the CNS and the body

4. Overview Chapter 9 – Structure of the Nervous System

5. Nerve Structure A typical nerve is covered by a continuous protective sheet of connective tissue called the epineurium. Within that are neurofascicles surrounded by a covering called the perineurium. Chapter 9 – Structure of the Nervous System

6. Nerve Structure Nerve: is defined as an enclosed bundle of neurons and associated neuroglia running to various structures throughout the body. Nerves primarily constitute the PNS. Nerve tracts are found in the brain and spinal cord (CNS) Nerve tracts are neurons bunched together in pathways that are not indistinct bundles. Afferent nerves: carry sensory information from the body to brain. Efferent nerves: carry information from the CNS to muscles and glands

7. Nerve Structure Nerve is covered by epineurium-it forms a protective sheath around the nerve and is an entryway for blood vessels that assist the nerve. Within the epineurium are numerous Neurofascicles: a tight bundle of axons and associated neuroglia It generally contains a mix of myelinated and unmylinated axons. Each neurofascicle is covered by the perineurium. Each neuron and its associated neuroglia within a neurofascicle are surrounded by an endoneurium.

8. Nerve Structure • Ganglia are collections of nerve cell bodies covered by the • epineurium. • They are an accumulation of nerve cell bodies • located outside the CNS. • Ganglia of the PNS are: • Composed of unipolar neurons • Are usually associated with sensory function

9. Nervous System Components Central Nervous System (CNS) Composed of the Brain and Spinal Cord Three layers of tissues separate the brain and spinal cord from their bony covering. These three layers called meninges are made of the dura mater arachnoid mater pia mater

10. The Meninges • Dura mater • Outmost layer • Pressed tightly against the interior of the cranium and • the vertebral column • Acts as a barrier against trauma to the CNS • Prevents CNS from rubbing against skull or vertebral • column • Arachnoid mater • Located below the dura mater • Like a spider web • Cushions the CNS from rapid movements and blunt hits • to the skull and vertebral column. • Under it is subarachnoid space-a cavity filled with cerebro- • spinal fluid and blood vessels.

11. The Meninges • Pia mater • Directly makes contact with the brain and spinal cord • Adheres to brain and spinal cord • Carries blood vessels to CNS • Forms sheaths over nerves passing through the outer • meninges layers • Assists with the production of cerebrospinal fluid • Associated with pia mater is the choroid plexus--it is a mass • of blood vessels and glial cells (ependymal cells) that secrete • cerebrospinal fluid

12. The Central Nervous System The central nervous system is composed of the brain and the spinal cord. Afferent peripheral nerves act as trunks that feed sensory information to the brain through their entry into the spinal cord. Chapter 9 – Structure of the Nervous System

13. Central Nervous System • The Brain: • Three Major parts: • Forebrain, Midbrain, and Hindbrain • Forebrain: composed of the cerebrum and diencephalon • responsible for emotions, memory, • motor movement, and thought. • Cerebrum is divided into the left and right cerebral hemispheres • Cerebrum is separated by midsagittal crease called longitudinal • cerebral fissure. • Left Hemisphere: are specialized for language and speech • Right Hemisphere: said to be the site of more “creative side.” • Corpus callosum: band of white matter that connects the left • and right brain.

14. Cerebrum • The hemispheres are divided into four lobes: • Frontal lobe- processes intellectual information that helps • with organization of thoughts. also posterior region has voluntary control over skeletal muscles. • Parietal lobe- involved with emotions and sensory interpretation.-interprets sensory info from the lips, skin, and tongue. • Temporal lobe- organizes and stores memories of • sounds and vision. • Occipital lobe- interprets vision and assists with eye • function. • Insula is a small region near the temporal lobe that plays • And important role in processing memories.

15. Forebrain • Diencephalon contains the thalamus and hypothalamus. • Ventricles are also found in the forebrain. • Consists of four connected cavities that contain • cerebrospinal fluid • They are associated with the choroid plexus and • continue into the spinal cord • They protect the brain from trauma by acting as a • cushion when head is hit or violently moved. Hydrocephalus is a disease in children where they produce too Much cerebrospinal fluid.

16. Midbrain Small strip of neurons that connects cerebrum to the hindbrain Possesses the auditory and visual reflex areas Controls the ability of the eyes to adjust to changes in light Intensity or sound.

17. Hindbrain • Pons: first part of the hindbrain. It is connected to midbrain • Organizes and transmits sensory information received • from the body. • Medulla oblongata lies just below the pons • Regulates involuntary body functions such as blood pressure, • breathing, heart rate, and swallowing. • Cerebellum lies posterior to the pons • Plays a role in balance, posture, and coordination of body • movement Brain Stem: refers to the midbrain and hindbrain by many people

18. Spinal Cord Is a cylinder of nervous tissue enclosed in the spinal canal of the Vertebral column. Meninges covers its surface Central canal contains cerebral spinal fluid is continuous with ventricles of the brain Surface of spinal cord is covered with white matter. Ascending tract found along the dorsal portion of the spinal cord They carries sensory information up to the brain. Descending tract run along the ventral and lateral portions of the spinal cord. They carry motor information directly to the PNS and our effectors.

19. The Peripheral Nervous System The peripheral nervous system is composed of somatic nerves, autonomic nerves, and ganglia. It is divided into the sympathetic and parasympathetic nervous systems. Chapter 9 – Structure of the Nervous System

20. Peripheral Nervous System • PNS: • composed of nerves that branch out from the brain and • spinal cord • not covered with meninges • do not have a cavity containing cerebrospinal fluid • Divided into the • Somatic nervous branch • Autonomic nervous branch

21. Peripheral Nervous System • Two nervous branches • Somatic nerves • Enable the voluntary control of body movements • through their communication with skeletal muscles. • Composed of: • afferent neurons which collect sensory • information • efferent neurons which relay commands • for muscle action. • Autonomic nervous system • Controls involuntary body functions • Its primary purpose is to maintain a stable internal • environment for the body.

22. 12 Cranial Nerves

23. Spinal Nerves Nerves that originate from the spinal cord and pass out of The vertebral column. Spinal nerves carry motor and sensory information for reflex control and two way communication to the brain. Each spinal nerve exits the spinal cord from two short, lateral Branches. The sensory branch called the dorsal root. The motor branch is called the ventral root.

24. Autonomic Nervous System • Uses the cranial and spinal nerves to carry out a wide array of tasks. • It performs these tasks by sending out regulatory information from • the brain. • This information controls the glands, cardiac muscle, and • smooth muscles necessary for maintaining homeostasis. • It does not require conscious thought • It is integrated with the endocrine system to • assist body with digestion, sexual functions, and • stress responses. • Autonomic Nervous System has two regions: • Parasympathetic nerve division • Sympathetic nerve division

25. Autonomic Nervous System Parasympathetic nerve division emerges from the cranial nerves and the sacral spinal nerves. Sympathetic nerve division arises from the thoracic and lumbar spinal cord. These two components typically counteract each other’s actions to fine tune the body’s responses to internal changes and environmental stimuli.

26. Autonomic Nervous System Sometimes called the “fight or flight and rest to digest” system. Sympathetic system prepares the body to react to stress. Parasympathetic system promotes relaxation and digestion.

27. Human Senses • Gustation—Chemoreceptors on the tongue sense taste • Olfaction—Chemoreceptors in the nose sense smell • Vision—Photoreceptors in the retina of the eye sense light • Hearing—Neurons in the cochlea sense sound vibrations • Equilibrium—Neurons in the semicircular canals and vestibule of the ear sense position • Taction or Tactility—Sensory receptors in the skin perceive touch Chapter 9 – Structure of the Nervous System

28. Human Senses The human head contains a concentration of sensory structures.

29. Human Senses Sense of smell -- olfaction Sense of taste-- gustation Sense of vision-- photoreceptors Sense of hearing-- audition Sense of balance--equilibrium Both smell and taste rely on chemoreceptors to detect chemicals dissolved in the air or water. Vision uses photoreceptors to convert light into a neural signal. Hearing uses a series of receptors that are sensitive to different types of sounds and vibrations. Equilibrium uses a combination of receptors to detect the body’s position as it Is moving and standing still.

30. Taste Taste buds are distributed throughout the upper surface of the tongue. Saliva is to ensure wet environment for taste to occur. Taste is detected by chemoreceptors. Five taste sensations: bitter, salt, sour, sweet, and umani Umani the taste that occurs when food ingredient monosodium Glutamate (MSG) dissolves in mouth. Umani receptors are distributed throughout the tongue. Thought to stimulate appetite.

31. Smell Olfaction serves two purposes: detect potentially harmful or valuable chemicals in the air an important supplement to taste. Chemoreceptors for smell are within the olfactory bulb These are located in upper region of nasal cavity Olfactory bulb is an extension of olfactory nerve.

32. Vision Eyes are specialized organs used to see objects and perceive movement. Eyelids and eyelashes are used to protect eyes. Conjunctiva-thin transparent layer that tightly covers anterior surface of the eye Lacrimal gland- produces tears that lubricate and protect eye from infection Lacrimal duct-tube that connects with nasal cavity, tears usually drain off surface of the eye Retina-inside layer located at back of eye, contains photoreceptors Sclera-tough outermost layer of the eye, white in color Cornea-clear covering at the front surface of the eye

33. Parts of the Eye Extrinsic muscles- the six muscles that move the eye Choroid- layer of blood vessels lining the inner surface of the sclera Ciliary body-a ring of muscles and connective tissue attached to the lens, adjusts lens of the eye Lens-transparent structure inside the eye that focuses the light rays for clear vision Iris-colored part of the eye, ring of muscles that adjusts the pupil Pupil-opening in the eye that lets the light enter

34. Parts of the Eye Aqueous humor-a clear watery fluid in the anterior chamber of the eyeball, helps maintain shape of cornea for properly focused vision Vitreous humor-gel-like fluid that fills the cavity behind the eye lens, maintains the spherical shape of the eye Cones-a photoreceptor sensitive to bright light and color. Rods-a photoreceptor sensitive to dim light. Fovea-central point at back of the eye that contains only the densest concentration of cones.

35. Diagram of the eye

36. The Ear

37. The Ear Human Ear converts sounds and body orientations into neuron Signals for the brain The ear is composed of three regions: external ear middle ear inner ear The external ear is composed of the: auricle or pinna-fleshy part of the ear that catches sound waves and funnels them into the ear canal external auditory meatusor auditory canal- ear canal

38. The Ear The Middle ear: tympanic membrane or eardrum-vibrates in response to sounds transmitted by the auditory canal. ossicles are the three ear bones that the eardrum vibrates against. These vibrations are transmitted to the inner ear. Three ossicles are the malleus -hammer incus- anvil stapes-stirrup Eustachian tube connects the middle ear to the throat. It prevents damage to the middle ear by adapting to changes in air pressure.

39. The Ear The Inner ear: is housed in a cavity in the temporal bone it is composed of the cochlea-is a coiled, fluid filled organ that converts vibrations into neuron impulses that are sent to the brain. semicircular canals-are fluid filled chambers that respond to body position. The vibrations are transferred from the stapes to part of the cochlea called the oval window. Organ of Corti: is the part of the inner ear that contains the neurons that respond to different sounds. Sound waves then vibrate again the round window of the cochlea. This permits pressure from sound waves to be released so they don’t echo.

40. The Ear The Inner Ear continued: Semicircular canals- respond to body position Changes in the direction of flow stimulates neurons, which the brain interprets as movement. Three canals superior canal detects forward and backward motion lateral canal detects forward and side to side motion posterior canal also detects side to side motion Vestibule-is the base of the semicircular canals detects body position.

41. Wellness and Illness over the Life Span • Most brain aging is due to loss of myelinization and decreased blood flow. • Most people show a decrease in complex brain functions as they age. • Aging is accompanied by some neuron loss in the brain. Chapter 9 – Structure of the Nervous System

42. Pathology of the Nervous System Common categories are trauma cerebrovascular and neurovascular diseases nervous system tumors developmental disorders metabolic and toxic diseases CNS infections neurogenerative diseases

43. Trauma categorized by its location Peripheral neuropathy It causes numbness, pain, tingling, or weakness in the PNS. Traumatic neuropathies of the CNS Whiplash-nerve damage in the neck caused by an abrupt, forced movement of the head. Shaken baby syndrome is severe injuries that result when a young child is violently shaken.

44. Cerebrovascular and neurovascular diseases are blood vessel disorders that impair the nervous system function Aneurysms-bulges in blood vessels caused by stretching and thinning of the vessels. Ateriovenous malformations is an unusual tangling of blood vessels in the CNS or PNS that disrupt blood flow occur after birth but may not cause problems until adulthood. Ischemic attacks a condition caused by insufficient flood flow to a body part. (Stroke) Transient ischemic attack (mini stroke) caused by temporary loss of blood flow

45. Nervous system tumors Abnormal growths that develop from neuroglia (glioma) cells of the meninges (meningioma) Immune cells in the nervous system (lymphoma) Neurons (neuroblastoma and neuroma)

46. Developmental disorders of the nervous system Caused by some factor that interferes with the DNA’s ability to form Or carry out normal functions of a body component. Can produce four characteristic problems with nerve function: athetosis causes slow, involuntary movements of the hands and feet. repetitive, involuntary twisting movements chorea causes muscular twitching of the arms, legs, and face. short, irregular, nonrepetitive muscle contractions palsy causes paralysis of a muscle or group of muscles. muscle paralysis caused by nerve loss tremor causes uncontrollable, rhythmic shaking movements

47. Metabolic or toxic nervous system diseases Caused by poisons that impede the functions of neuroglia or neurons. Large amounts of calcium sodium, and potassium affect the action potential of the neurons. Many types of metals interfere with the metabolism of nervous system cells. Bacterial, fungal, and protistan infections of the nervous system damage cells due to the toxins they produce.

48. Aging of the Nervous System Nerve cell mass of the brain and spinal cord decreases after the Age of 40. The average person loses 5 to 10% of his or her brain’s weight between ages 20 and 90 years. Decreased blood flow may account for brain shrinkage and weight loss. People in older age groups have diminished and slower memory capabilities. PNS degeneration also occurs. This causes a reduction or loss of reflexes. This produces a problem in balance and mobility. Sensory loss is also seen with age. It is most likely due to degradation Of the sensory structure. Hearing loss affects men more than women in the age range of 70-79. Vision loss occurs equally in each gender.

49. Summary • The human nervous system is formed of two components that work together to coordinate body functions: the central and peripheral nervous systems. • Information from the environment is transmitted to the CNS by nerves of the PNS. • Sensory information is used by the brain to formulate a response. Responses of the brain are channeled to the body via the somatic or autonomic nervous system. • Nervous system structure is subject to damage resulting from a variety of diseases. Chapter 9 – Structure of the Nervous System