Nervous System PDF

CHAPTER 5: NERVOUS SYSTEM \- The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts. The brain and spinal c...

CHAPTER 5: NERVOUS SYSTEM \- The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts. The brain and spinal cord form the control center known as the central nervous system (CNS), where information is evaluated and decisions made. The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the body and send this information to the CNS. Efferent nerves in the PNS carry signals from the control center to the muscles, glands, and organs to regulate their functions. Screenshot (23) TWO SUBIVISIONS - Central Nervous System (CNS) -- consist of the Brain and Spinal Cord - - FOUR LOBES OF THE BRAIN 1. **Temporal Lobe** - important for processing sensory input and assigning it emotional meaning. It is also involved in laying down long-term memories. Some aspects of language perception are also housed here. 2. **Frontal Lobe** - positioned at the front of the brain, the frontal lobe contains the majority of dopamine- sensitive neurons and is involved in attention, reward, short-term memory, motivation, and planning. 3. **Occipital Lobe** - visual processing region of the brain, housing the visual cortex. 4. **Parietal Lobe** - the parietal lobe integrates sensory information including touch, spatial awareness, and navigation.  CENTRAL NERVOUS SYSTEM - The spinal cord is the highway for communication between the body and the brain. When the spinal cord is injured, the exchange of information between the brain and other parts of the body is disrupted. - The spinal cord contains circuits that control certain reflexive responses. TWO SUBIVISIONS - Peripheral Nervous System (PNS) -- consist of Nerves - - The PNS can be said to consist of 12 pairs of cranial nerves and 31 pairs of spinal nerves. Cranial nerves emerge in pairs on either side of the base of the skull, through small openings called foramina. Screenshot (25) Cranial Nerves -- carry impulses to and from the Brain Spinal Nerves -- carry impulses to and from the Spinal Cord  ANATOMY OF THE PNS - The peripheral nervous system is made of nerves, ganglia and plexuses. A nerve contains the axons of multiple neurons bound together byconnective tissue. The axon itself is often myelinated, containing phospholipid secreted by a glial cell called the Schwann cell. The thin coveringof Schwann cell cytoplasm forms the innermost layer protecting an axon and is called the neurilemma or neurolemma. IMG\_256 PERIPHERAL NERVOUS SYSTEM FUNCTIONAL CLASSIFICATION \- The functional classification is concerned only in PNS structure. 2 DIVISION OF PERIPHERAL NERVOUS SYSTEM 1\. **Sensory** - carry signals from the outer parts of your body (periphery) into the central nervous system. 2\. **Motor** - carry signals from the central nervous system to the outer parts (muscles, skin, glands) of your body. MOTOR HAS TWO DIVISIONS - Somatic Division - the somatic nervous system (SNS) is a division of the PNS that includes all of the voluntary efferent neurons. The SNS is the only consciously controlled part of the PNS and is responsible for stimulating skeletal muscles in the body. - Autonomic Division (Visceral) - the autonomic nervous system (ANS) is a division of the PNS that includes all of the involuntary efferent neurons. The ANS controls subconscious effectors such as visceral muscle tissue, cardiac muscle tissue, and glandular tissue. AUTONOMIC HAS TWO PARTS - Sympathetic -Also called the \'fight or flight\' division. It response to stress, danger, excitement, exercise, emotions, and embarrassment. The sympathetic division increases respiration and heart rate, releases adrenaline and other stress hormones, and decreases digestion to cope with these situations. - Parasympathetic - Important for control of \'normal\' body functions and the "rest and digest" response when the body is relaxed, resting, or feeding. The parasympathetic works to undo the work of the sympathetic division after a stressful situation. Among other functions, the parasympathetic division works to decrease respiration and heart rate, increase digestion, and permit the elimination of wastes. NERVOUS TISSUE \- The nervous system is responsible for the control of the body and the communication among its parts. Nervous tissue contains two categories of cells---neurons and supporting cell or also called neuroglia. NEURONS - Neurons are highly specialized nerve cells that generate and conduct nerve impulses. A typical neuron consists of dendrites, the cell body, and an axon.  PARTS OF A NEURON 1. Cell Body (Soma) -- Spherical part of the nucleus that contains the nucleus. To control all of the function of the cell 2. Dendrites -- brings information to the neuron and also responsible for responding to stimuli; they receive incoming signals towards the cell body. 3. Axon -- Sends information to the other neuron. The axon is surrounded by a whitish, fatty layer called the myelin sheath. Outside the myelin sheath there is a cellular layer called the neurilemma. 4. Synapse - In the central nervous system, a synapse is a small gap at the end of a neuron that allows a signal to pass from one neuron to the next. Synapses are found where nerve cells connect with other nerve cells. 5. Axon Terminal - is the very end of a branch of a nerve\'s axon, a long slender nerve fiber that conducts electrical signals to a nerve synapse (the gap between nerve cells). The signal then moves across the synapse to another axon by means of a neurotransmitter (an electrochemical substance). 6. Myelin Sheath -The myelin sheath is a protective covering that surrounds fibres called axons, the long thin projections that extend from the main body of a nerve cell or neuron. This sheath is composed of protein and lipids. 7. Nodes of Ranvier - are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. About one micrometer in length, these gaps expose the axonal membrane to the extracellular fluid. Screenshot (27) **CLASSIFICATION OF NEURONS ACCORDING TO FUNCTION AND STRUCTURE** FUNCTIONAL CLASSIFICATION - Groups neurons according to the direction of the nerve impulse is travelling relative to the CNS. a. SENSORY Neurons -- carry impulses from sensory receptors to CNS b. MOTOR Neurons -- carry impulses from to CNS to the viscera and/or muscles and glands c. ASSOCIATION Neurons -- connect the sensory and motor neurons in neural pathways  STRUCTURAL CLASSIFICATION - Based on the number of processes extending from the cell body. a. MULTIPOLAR Neurons -- Several processes b. BIPOLAR Neurons -- Two processes (Dendrites and Axon) c. UNIPOLAR Neurons -- Single process Screenshot (29) SUPPORTING CELLS - Supporting cells in the CNS are grouped as neuroglia (a.k.a. glia), meaning "nerve glue". - Neuroglia -- do not transmit nerve impulses \- never lose their ability to divide \- most brain tumors are gliomas or tumors formed by glial cells. SUPPORTING CELLS IN THE CNS a. ASTROCYTES -- brace and anchor neurons to blood capillaries b. MICROGLIA -- dispose off debris (brain cells, bacteria, etc.) c. EPENDYMAL CELLS -- circulate cerebrospinal fluid and form protective cushion around the CNS d. OLIGODENDROCYTES -- produce myelin sheath SUPPORTING CELLS IN THE PNS a. SCHWANN Cells -- form myelin sheaths around nerve fibers that are found in the PNS b. SATELLITE Cells -- act as protective, cushioning cells  **PHYSIOLOGY** NERVE IMPULSES Two major functional properties of Neurons a. IRRITABILITY -- ability to respond to stimulus and convert it into a nerve impulse. b. CONDUCTIVITY -- ability to transmit the impulse to other neurons, muscles, or glands. Screenshot (31) NERVE IMPULSE SALTATORY CONDUCTION - conduction occurring in fibers with myelin sheaths. - faster because nerve impulse literally jumps or leaps from node to node along the length of the fiber - occurs because no current can flow across the axonal membrane where there is fatty myelin insulation. FACTORS THAT IMPAIR THE CONDUCTION OF IMPULSES - Alcohol, sedatives, anesthetics - Cold - Continuous pressure  REFLEX ARC - REFLEX -- predictable involuntary response to a stimulus - SOMATIC REFLEX -- involves skeletal muscles - VISCERAL REFLEX -- involves smooth muscles, cardiac muscles, or gland - SPINAL REFLEX -- carried out by neurons in the spinal chord and not immediately involving the brain is called Reflex Arc. - - **CENTRAL NERVOUS SYSTEM** THE SPINAL CORD Screenshot (33) - It is consists of 31 pairs of spinal nerves. - Two Main Function: 1\. It is the connecting link between the brain and most of the body 2\. It is involved in spinal reflex actions, both somatic and visceral. - The Somatic spinal reflexes, involve a series of responses to the - stimulation of sensory receptors in the skin and skeletal muscles. - Visceral spinal reflexes, occur in the certain organs. ANATOMY OF THE SPINAL CORD - It is part of the central nervous system that extends from the foramen magnum of the skull caudally for about 47 cm to the level of first lumbar vertebra in adults. - The superior end is continuous with the medulla oblangata. It's inferior end tapers off as the cone shape conus terminalis. Extending caudally from the conus is a nonneural fibers called fillum terminale.  - The cylindrical spinal cord is slightly thicker than a pencil, slightly flattened dorsally and ventrally with the two prominent enlargements : Cervical enlargement and Lumbosacral enlargement. **SPINAL MENINGES** THREE LAYERS 1. Dura mater, the outermost layer is a tough fibrous membrane that merges with the fillum terminale. 2. Arachnoids , middle layer runs caudally to the S2 vertebral level where it joins the fillum terminate. 3. Pia mater , innermost layer is the highly vascular and is spinal. Screenshot (35) 4. Epidural space is between in the Dura matter and Periosteum of the vertebrae containing many blood vessels and some fats. 5. Subdural space is between Dura matter and the Arachinoid, which is merely a slit and contaning no cerebrospinal fluid. 6. Subarachnoid space, separates the arachnoid and pia matter, contains cerebrospinal fluid, blood vessels, and spinal roots.  **CEREBROSPINAL FLUID** - Clear watery ultra filtrates solutions formed primarily from blood in the choroid plexus of the brain. Screenshot (37) **Internal Structure of the Spinal Cord**  - Central canal -- it contains cerebrospinal fluid - Anterior median fissure -- divided the spinal cord into more or less symmetrical left and right halves. - Posterior median septum -- median septum - Gray matter -- dark portion of H- shaped or butterfly shaped. Two Posterior Projections and Two Anterior Projections: Dorsal or posterior horns Ventral or anterior horns Screenshot (38) - Dorsal root ganglion -- the fibers that enter the cord by the dorsal root will found in an enlarge area. - White matter - compost of myelinated fiber tracts Three Regions - Posterior column - ascending tracts that carry sensory input in the brain. - Anterior and lateral columns -- responsible for motor tracts. - Quadriplegic -- four limbs are affected. - Paraplegic - only the legs are paralyzed. **THE BRAIN** BRAIN: Lateral View  BRAIN: Sagittal Section Screenshot (40) - Weighs only 1,400 grams (3lb), yet contains more than 100 billion neurons. - Has 4 major divisions: 1\. Brainstem - Composed of Midbrain Pons Medulla Oblongata - About the size of a thumb in diameter, approx. 3 inches long that provides pathway for ascending and descending tracts. - Reticular Formation - a diffuse mass of gray matter that extends the entire length of the brain stem. - Reticular Activating System (RAS) - the special group of reticular formation neurons that plays a role in consciousness, and the awake sleep cycles. **Brainstem** a. Midbrain -- relatively small part of the brain stem. Located from mammillary bodies to the pons inferiorly. Cerebral Aqueduct -- tiny canal that travels through midbrain Corpora Quadrigemina -- four dorsal rounded protrusion, involves vision and hearing. b\. Pons -- means "Bridge". Fiber tract that has rounded structure that protrudes below the midbrain. Involves the control of breathing. c\. Medulla Oblongata -- is a fiber tract as well and is the most inferior part of the brainstem. Regulate vital & visceral activities, control heart rate, blood pressure, breathing, swallowing and vomiting. **Cerebellum** 2\. Cerebrum - Is the pair of cerebral hemispheres; most obvious physical feature of the brain. Cerebral Cortex -- outer portion of cerebrum with many folds. Speech, memory, logical and emotional response, as well as consciousness interpretation of sensation, and voluntary moment -- are all function of cerebral cortex neurons. Basal Ganglia -- white matter and deep, large masses of gray matter. Lying below the gray matter of the cerebral cortex. Corpus Callosum -- a bundle of fibers that connect the two cerebral hemispheres. 3\. Diencephalon - Composed of the thalamus, hypothalamus, epithalamus, & ventral thalamus. Thalamus -- encloses the shallow third ventricle of the brain, for sensory impulses. Hypothalamus -- makes up the floor of the diencephalon. Plays a role in the regulation of body temperature, water balance, and metabolism. Epithalamus -- forms the roof of the third ventricle. contains Pineal Body & Choroid Plexus. Choroid Plexus -- form the cerebrospinal fluid (colorless body fluid that protects brain, spinal cord from trauma, supplies nutrients to nervous system tissue, and removes waste from cerebral metabolism.) [Brain is surrounded by the same 3 meninges that protect the spinal cord.] **THE CEREBRAL HEMISPHERES**  - Gyri -- (Gyrus) the elevated ridges of tissue - Sulci -- shallow grooves (The sulci and fissures are both grooves in the cortex, but they are differentiated by size. A sulcus is a shallower groove that surrounds a gyrus. A fissure is a large furrow that divides the brain into lobes and also into the two hemispheres as the longitudinal fissure.) - Somatic Sensory Area -- allows you to recognize pain, coldness or a light touch. Located posterior to the central fissure in the parietal lobe. - Primary Motor Area -- allow us to consciously move our skeletal muscles. Located anterior to the central fissure in the frontal lobe. - Pyramidal or Corticospinal Tract -- is a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk. - Broca's area -- involves the ability to speak. 4\. Midbrain or Mesencephalon - It is the topmost part of the of the brain stem. - It extends from the mammillary bodies to the pons inferiorly. - Serves important functions in motor movement, particularly movements of the eye, and in auditory and visual processing. **3 Structures MIDBRAIN:** 1. Cerebral Aqueduct - (aqueductus mesencephali, mesencephalic duct, sylvian aqueduct, or aqueduct of Sylvius) -- tiny canals that travel through the midbrain and connects the third ventricle of the diencephalon to the 2. Cerebral Peduncles -- conveys ascending and descending impulses.fourth ventricle below. 3. Corpora Quadrigemina - the reflex centers involved with vision and hearing. STRUCTURE OF THE MIDBRAIN Screenshot (42) 5\. Pons (Bridge) rounded structure that protrudes just below the midbrain. It is the area of brain stem is fiber tracts. It has the important nuclei involved in the control of breathing 6\. Medulla Oblongata most inferior part of brain stem. It is also important fiber tract area. It contains many nuclei that regulate vital visceral activities. Contains of centers that control heart rate, blood pressure , breathing , swallowing and vomiting. 7\. Cerebellum receives information from the sensory systems, the spinal cord, and other parts of the brain and then regulates motor movements. The cerebellum coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity. If the cerebellum is damaged movements become clumsy and disorganized , a condition called ataxia. 8\. The Blood-Brain in Barrier Brain is the only organ that is absolutely dependent on a constant internal environment. Is a highly selective semipermeable border that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). **BRAIN DYSFUNCTIONS** - Caused by disorders that occur in a specific area of brain 1. Senile Dementia - it is characterized by progressive mental deterioration, including anxiety, irritability, difficulty with speech and irrationality. 2. Alzheimer's Disease - it is a neurodegenerative disease characterized by a progressive loss of memory, intellectual functions and speech. 3. Cerebral Palsy - it involves an impairment of skeletal motor activities to some degree, ranging from muscular weakness to complete paralysis. 4. Cerebrovascular Accident ( also called STROKE) - is a sudden withdrawal or sufficient blood supply to the brain caused by the impairment of incoming blood vessels. The major causes of CVA are: Thrombosis -- clotting of blood in a blood vessel. Embolism -- a blockage in a blood vessel. Hemorrhage -- rupture of a cerebral artery as the result of an aneurysm. 5. Epilepsy -- nervous disorder characterized by recurring attacks of motor, sensory or psychological malfunction. 6. Headache -- brain itself is not sensitive to brain, but the veins on the surface of brain, the cerebral arteries the cranial nerves and parts of dura mater are. If one of these areas is disturbed a headache may result. **PERIPHERAL NERVOUS SYSTEM** - consists of nerves and scattered groups of neuronal cell bodies (ganglia) found outside the CNS. STRUCTURE OF A NERVE Nerve is a bundle of neuron fibers found outside the CNS. Within a nerve, neuron fibers, or processes, are wrapped in protective connective tissue coverings. Each fiber is surrounded by a delicate connective tissue sheath, or endoneurium. Groups of fibers are bound by a coarser connective tissue wrapping, the perineurium, to form fiber bundles or fascicles. All the fascicles are bound together by a though fibrous sheath, the epineurium, to form the cordlike nerve.  - Mixed nerves - nerves carrying both sensory and motor fibers - Afferent or sensory nerves - nerves that carry impulses toward the CNS only - Efferent or motor nerves - nerves that carry only motor fibers CRANIAL NERVES - 12 pairs of cranial nerves that primarily serve the head and neck. SPINAL NERVES AND NERVE PLEXUSES - there are 31 pairs of human spinal nerves that are formed by the combination of the ventral and dorsal roots of the spinal cord. Screenshot (44) SPINAL NERVES AND NERVE PLEXUSES - Almost immediately after being formed, each spinal nerve divides into dorsal and ventral rami. - The rami, like the spinal nerves, contain both motor and sensory fibers. - The smaller dorsal rami, serve the skin and muscles of the posterior body trunk - The ventral rami of spinal nerves T1 through T12 form the intercostal nerves, which supply the muscles between the ribs and the skin and muscles of the anterior and lateral trunk. - The ventral rami of all spinal nerves form complex network of nerves called plexuses, which serve the motor and sensory needs of the limbs THE AUTONOMIC NERVOUS SYSTEM - is the motor subdivision of the PNS that controls body activities automatically. - composed of a special group if neurons that regulate cardiac muscle, smooth muscle, and glands - Responsible for control of the bodily functions not consciously directed such as breathing, the heartbeat, and digestive processes **ANS has a chain of two motor neurons.** \- First motor neuron is found in the brain or spinal cord and it's axon s called preganglionic axon. \- Second motor neuron is in the ganglion and it's axon is called postganglionic axon. - The ANS has two arms, both serve the same organs but cause essentially opposite effects, counterbalancing each other\'s activities to keep body systems running smoothly. - The first arm is the sympathetic part, mobilizes the body during extreme situations such as fear, exercise or rage. - The second arm is the parasympathetic division allows us to \"unwind\" and to conserve energy.  ANATOMY OF THE SYMPATHETIC AND PARASYMPATHETIC DIVISION - The sympathetic division also called the "Thoracolumbar Division" Screenshot (46) - Preganglionic axon enter sympathetic chain ganglion via white ramus communicans. Some axons synapse with post ganglionic neurons in the sympathetic chain ganglia. Post ganglionic axons leave sympathetic chain ganglia via gray ramus communicans and enter the spinal nerve to travel to the skin. And the axon leaves sympathetic chain ganglion without synapsing and forms a splanchnic nerves and travel to collateral ganglia.  - The first neuron of parasympathetic division are located in brain nuclei of several cranial nerve and in the S2 and S4 level of the spinal cord. Screenshot (48) - The parasympathetic division send preanglionic neurons from the cranial and sacral area. This is why it is also known as the CRANIOSACRAL DIVISION. - The neurons of the cranial region send their axons out in cranial nerves to serve the head and neck organs. They synapse with second motor neuron in a terminal ganglion. - In the sacral region, the preanglionic axons leave the spinal cord and form pelvic nerves, also called the pelvic splanchnic nerve which travel to the pelvic cavity. AUTONOMIC FUNCTIONING Body organs serve by the ANS receive fibers from both divisions. When both division serve the same organ they cause antagonistic effects, mainly because their post ganglionic axons release different neurotransmitter. The parasympathetic fibers called "Cholinergic fibers" release acetylcholine.  The sympathetic postganglionic fibers called "Adrenergic fibers" release norepinephrine or also called noradrenalin. The preanglionic axons of both divisions release acetylcholine. The sympathetic division is often referred to as the fight or flight system. The parasympathetic division is most active when the body is rest and not threatened in any way. This division also sometimes called the "Resting and Digesting System"