Nervous System

1. Nervous System MR OGUNDELE

2. Nervous system • The nervous system has two divisions. The central nervous system (CNS) consists of the brain and spinal cord. The peripheral nervous system (PNS) consists of cranial nerves and spinal nerves. • The peripheral nervous system relays information to and from the central nervous system, and the brain is the center of activity that integrates this information, initiates responses.

3. Nervous system • The PNS is further subdivided into afferent and efferentdivisions. • The afferent divisioncarries information to the CNS while Instructions from the CNS are transmitted via the efferent divisionto effector organs

4. Nervous system • The efferent nervous system is divided into: • The somatic nervous system, which consists of the fibers of themotor neurons that supply the skeletal muscles; and • The autonomic nervous system, which consists of fibers that innervatesmooth muscle, cardiac muscle, and glands. ANS is further subdivided into the sympathetic nervous system and the parasympathetic nervous system.

5. Neurons • Neurons are the fundamental structural and functional units of the nervous system. They are specialized for the reception, integration and transmission of information. • Neuroglial cells are the supporting cells of the nervous system, occupying the spaces between the neurons.

6. Neurons • A neuron consists of: • A cell body or soma: This contains the nucleus, cytosol and organelles including the rough and smooth endoplasmic reticulum. • Dendritic processes(afferent or receptive zone), which are responsible for synaptic contacts with other nerve cells.

7. Neuron • Axon (transmission zone), involved in signal conduction. This consists of an initial segment, the axon proper and the terminal synaptic bouton • The cytoplasm of the axons, or axoplasm, contains mitochondria, microtubules, neurofilaments and smooth endoplasmic reticulum. There are nofreeribosomesand no rough endoplasmic reticulum, hence no protein synthesis is possible.

8. Neuroglial cells

9. The brain • The major parts are the medulla, pons, and midbrain (collectively called the brain stem), the cerebellum, the hypothalamus, the thalamus, and the cerebrum.

10. The brain

12. Brain stem • The brain stem controls many of the life-sustaining processes, such as respiration, circulation, and digestion that are common to all vertebrates. These processes are often referred to as vegetative functions, meaning functions performed unconsciously or involuntarily.

14. MEDULLA The medulla extends from the spinal cord to the pons and is anterior to the cerebellum. The medulla contains cardiac centers that regulate heart rate, vasomotor centers that regulate the diameter of blood vessels, and respiratory centers that regulate breathing. Medulla has reflex centers for coughing, sneezing, swallowing, and vomiting.

15. PONS • The pons bulges anteriorly from the upper part of the medulla. Within the pons are tworespiratory centers that work with those in the medulla to produce a normal breathing rhythm. The many other neurons in the pons connect the medulla with other parts of the brain.

16. MIDBRAIN • The midbrain extends from the pons to the hypothalamus and encloses the cerebral aqueduct, a tunnel that connects the third and fourth ventricles. Several different kinds of reflexes are integrated in the midbrain, including visual and auditory reflexes.

17. CEREBELLUM • The cerebellum is separated from the medulla and pons by the fourth ventricle. Function of the cerebellum include coordination, regulation of muscle tone, the appropriate trajectory and endpoint of movements, and the maintenance of posture and equilibrium.

18. HYPOTHALAMUS Located superior to the pituitary gland and inferior to the thalamus, the hypothalamus is a small area of the brain with many diverse functions: 1. Production of antidiuretic hormone (ADH) and oxytocin; these hormones are then stored in the posterior pituitary gland

19. Functions of hypothalamus 2. Regulation of body temperature by promoting responses such as sweating in a warm environment or shivering in a cold environment. 3. Regulation of body rhythms such as secretion of hormones, sleep cycles, changes in mood, or mental Alertness

20. THALAMUS The thalamus is superior to the hypothalamus and inferior to the cerebrum. The third ventricle is a narrow cavity that passes through both the thalamus and hypothalamus. Many of the functions of the thalamus are concerned with sensation. 

21. The amygdala is an almond-shaped structure in the brain and is responsible for the response and memory of emotions, especially fear . • The hippocampus is a small organ located within the brain's medial temporal lobe and is responsible for processing of long term memory and emotional responses.

22. CEREBRUM • The largest part of the human brain is the cerebrum, which consists of two hemispheres separated by the longitudinal fissure. At the base of this deep groove is the corpus callosum, and it connects the right and left hemispheres. Within each hemisphere is a lateral ventricle.

23. Cerebrum • The surface of the cerebrum is gray matter called the cerebral cortex. Gray matter consists of cell bodies of neurons. Internal to the gray matter is white matter, made of myelinated axons and dendrites that connect the lobes of the cerebrum to one another and to all other parts of the brain.

24. Cerebrum • In the human brain the cerebral cortex is folded extensively. The folds are called convolutions or gyri and the grooves between them are fissures or sulci • The cerebral cortex is divided into lobes that have the same names as the cranial bones

25. Cerebral lobes

26. Frontal Lobes • Within the frontal lobes are the motor areas that generate the impulses for voluntary movement Anterior to the motor areas are the premotor areas, which are concerned with learned motor skills that require a sequence of movements • Also in the frontal lobe, usually only the left lobe for most right-handed people, is Broca’s motorspeech area, which controls the movements of the mouth involved in speaking.

27. Parietal Lobes • The general sensory areas in the parietal lobes receive impulses from receptors in the skin and feel and interpret the cutaneous sensations. • The taste areas, which overlap the parietal and temporal lobes,receive impulses from taste buds on the tongue andelsewhere in the oral cavity.

28. Temporal Lobes • The olfactory areas in the temporal lobes receive impulses from receptors in the nasal cavities for the sense of smell. • The auditory areas, as their name suggests, receive impulses from receptors in the inner ear for hearing.

29. Occipital Lobes • Impulses from the retinas of the eyes travel along the optic nerves to the visual areas in the occipital lobes

30. MENINGES ANDCEREBROSPINAL FLUID • The connective tissue membranes that cover the brain and spinal cord are called meninges; The three layers are : Dura layer Arachnoid layer Pia Layer

31. Meninges • The thick outermost layer, made of fibrous connective tissue, is the dura mater (Latin for “tough mother”), which lines the skull and vertebral canal. is the strongest meninx • The middle arachnoid membrane (arachnids are spiders) is made of web-like strands of connective tissue.

32. Meninges • The innermost pia mater (Latin for “gentle mother”) is a very thin membrane on the surface of the spinal cord and brain. Between the arachnoid and the pia mater is the subarachnoid space, which contains cerebrospinal fluid (CSF), the tissue fluid of the central nervous system.

33. CEREBROSPINAL FLUID • The ventricles (cavities) of the brain: two lateral ventricles, the third ventricle, and the fourth ventricle. Each contains a choroid plexus, a capillary network that forms cerebrospinal fluid from blood plasma.

34. CEREBROSPINAL FLUID • This is a continuous process, and the cerebrospinal fluid then circulates from the lateral and third ventricles, cerebrospinal fluid flows through the fourth ventricle, then to the central canal of the spinal cord, and to the cranial and spinal subarachnoid spaces.

35. CSF • The total volume of cerebrospinal fluid is approximately 150ml and it is produced at a rate of450mlperday (thus replacing itself three times a day). • 50% to 70% of the CSF is secreted by cells of the choroid plexus and ependyma cells in the ventricle while the rest is secreted by ultrafiltration of blood plasma through choroid capillaries.

36. CSF • CSF circulates from lateral ventricles through foramina of monro into the third ventricle and flows from the third ventricle to the fourth through aqueduct of Sylvius and flows into subarachnoid space by means of three foramina: A single medial aperture (foramen of Magendie) and a pair of lateral aperture (foramen of Luschka) • .

37. CSF • This then drains into the subarachnoid space which surrounds the entire brain and spinal cord. The resorption of CSF takes place in the arachnoid granulation (arachnoid villi: these are protrusion of the arachnoid through the dura mater projecting into the intracranial venous sinus) and is emptied into the several venous sinuses of the cerebrum. It is then returned into the venous circulation.

38. CEREBRAL CIRCULATION • The cerebral circulation receives approximately 15% of the cardiac output, or 750 mL per minute. • The brain does not store nutrients and has a high metabolic demand that requires the high blood flow.

40. Blood flow • There are 5 main components to the Circle of Willis: the anterior cerebral artery, the anterior communicating artery, the internal carotid arteries, the posterior cerebral artery, and the posterior communicating artery. It’s important to note the middle cerebral arteries arise from the Circle also.

41. Blood flow in the brain • The vertebral arteries arise from the subclavian arteries, and the internal carotid arteries are branches of the common carotid arteries • The internal carotid arteries branch to form two major cerebral arteries, the anterior and middle cerebral arteries. The right and left vertebral arteries come together at the level of the pons on the ventral surface of the brainstem to form the midline basilar artery.

42. Blood flow in the brain • The basilar artery joins the blood supply from the internal carotids in an arterial ring at the base of the brain called the circle of Willis • The posterior cerebral arteries arise at this confluence, and supplies blood to the occipital lobe and part of the temporal lobe. The posterior communicating arteries provides communication between the carotid and vertebral arteries

43. Blood flow in the brain • The anterior and posterior communicating arteries conjoined the two major sources of cerebral vascular supply and improves the chances of any region of the brain to receive blood if one of the major arteries becomes occluded

44. Spinal Cord • The spinal cord transmits impulses to and from the brain and is the integrating center for the spinal cord reflexes. • It extends from the foramen magnum of the occipital bone to the intervertebral disk between the first and • second lumbar vertebrae. The spinal nerves emerge from the intervertebral foramina.

45. spinal nerves • There are 31 pairs of spinal nerves, named according to their respective vertebrae: • 8 cervical pairs, • 12 thoracic pairs, • 5 lumbar pairs, • 5 sacral pairs, • 1 very small coccygeal pair

46. REFLEX ARC • A reflex arc is the pathway nerve impulses travel when a reflex is elicited. There are five parts: • 1. Receptors detect a change (the stimulus) and generate impulses. • 2. Sensory neurons transmit impulses from receptors to the central nervous system (CNS).

47. REFLEX ARC • 3. The CNS contains one or more synapses and the interneurons that may be part of the pathway. • 4. Motor neurons transmit impulses from the CNS to an effector. • 5. The effector performs its characteristic action. • The spinal cord reflexes include stretch reflexes and flexor reflexes

48. Cranial Nerves • The 12 cranial nerves control both sensory and motor activities within various part of the body

50. Lumbar Puncture • Cerebrospinal fluid may be obtained via lumbar puncture and evaluated for glucose and protein levels, presence of bacteria and white blood cells, levels of immunoglobulin, antibodies, and culture and sensitivity.