Anatomy & Physiology - Nervous System PDF

ANATOMY & PHYSIOLOGY Chapter 8: Nervous System Nervous System Functions 1. Receiving sensory input 2. Integrating information 3. Controlling muscles and glands 4. Maintaining homeostasis 5. Establishing and maintaining mental activity Main Divisions of Nervous System Central nervous syst...

ANATOMY & PHYSIOLOGY Chapter 8: Nervous System Nervous System Functions 1. Receiving sensory input 2. Integrating information 3. Controlling muscles and glands 4. Maintaining homeostasis 5. Establishing and maintaining mental activity Main Divisions of Nervous System Central nervous system (CNS) brain and spinal cord Peripheral nervous system (PNS) All the nervous tissue outside the CNS Sensory division Conducts action potentials from sensory receptors to the CNS Motor division Cells of the Nervous System Conducts action potentials to effector organs, such Neurons as muscles and glands receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs. Somatic nervous system Glial cells Transmits action potentials from the CNS to skeletal supportive cells of the CNS and PNS, meaning muscles. these cells do not conduct action potentials. Instead, Autonomic nervous system glial cells carry out different functions that enhance Transmits action potentials from the CNS to cardiac neuron function and maintain normal conditions muscle, smooth muscle, and glands within nervous tissue. Enteric nervous system A special nervous system found only in the Neurons digestive tract. A neuron (nerve cell) has a: Cell body – which contains a single nucleus Dendrite – which is a cytoplasmic extension from the cell body, that usually receives information from DELGADO BSN 1C  other neurons and transmits the information to the Myelin is an excellent insulator that prevents almost cell body all ion movement across the cell membrane. Axon – which is a single long cell process that Gaps in the myelin sheath, called nodes of leaves the cell body at the axon hillock and conducts Ranvier, occur about every millimeter. sensory signals to the CNS and motor signals away Ion movement can occur at the nodes of Ranvier. from the CNS Myelination of an axon increases the speed and efficiency of action potential generation along the Structural Types of Neurons axon. Multipolar neurons have many dendrites and a Multiple sclerosis is a disease of the myelin sheath single axon. that causes loss of muscle function. Most of the neurons within the CNS and nearly all motor neurons are multipolar. Unmyelinated Neurons Bipolar neurons have two processes: one dendrite Unmyelinated axons lack the myelin sheaths. and one axon. These axons rest in indentations of the Bipolar neurons are located in some sensory oligodendrocytes in the CNS and the Schwann cells organs, such as in the retina of the eye and in the in the PNS. nasal cavity. A typical small nerve, which consists of axons of Pseudo-unipolar neurons have a single process multiple neurons, usually contains more extending from the cell body, which divides into two unmyelinated axons than myelinated axons. processes as short distance from the cell body. One process extends to the periphery, and the Organization of Nervous Tissue other extends to the CNS. Nervous tissue varies in color due to the The two extensions function as a single axon with abundance or absence of myelinated axons. small, dendrite-like sensory receptors at the Nervous tissue exists as gray matter and white periphery. matter. Gray matter consists of groups of neuron cell Glial Cells bodies and their dendrites, where there is very little Glial cells are the supportive cells of the CNS and myelin. PNS. White matter consists of bundles of parallel axons Astrocytes serve as the major supporting cells in with their myelin sheaths, which are whitish in color. the CNS. Astrocytes can stimulate or inhibit the signaling The Nervous System activity of nearby neurons and form the blood-brain The nervous system can be divided into the central barrier. nervous system and the peripheral nervous system. Ependymal cells line the cavities in the brain that The central nervous system (CNS), consists of contains cerebrospinal fluid. the brain and spinal cord. Microglial cells act in an immune function in the The peripheral nervous system (PNS) consists of CNS by removing bacteria and cell debris. all the nerves and ganglia outside the brain and Oligodendrocytes provide myelin to axons of spinal cord. neurons in the CNS. Schwann cells provide myelin to axons of neurons Spinal Cord in the PNS. Extends from the foramen magnum to the 2nd lumbar vertebra Myelin Sheath Protected by vertebral column Myelin sheaths are specialized layers that wrap Spinal nerves allow movement around the axons of some neurons, those neurons If damaged paralysis can occur are termed, myelinated. The sheaths are formed by oligodendrocytes in the CNS and Schwann cells in the PNS. DELGADO BSN 1C  Central canal: fluid filled space in center of cord Reflexes A reflex is an involuntary reaction in response to a stimulus applied to the periphery and transmitted to the CNS. Reflexes allow a person to react to stimuli more quickly than is possible if conscious thought is involved. Most reflexes occur in the spinal cord or brainstem rather than in the higher brain centers. A reflex arc is the neuronal pathway by which a reflex occurs and has five basic components. Reflex Arc Components 1. A sensory receptor 2. A sensory neuron 3. Interneurons, which are neurons located between and communicating with two other neurons 4. A motor neuron 5. An effector organ (muscles or glands). Gray Matter and White Matter Note: The simplest reflex arcs do not involve Gray Matter: interneurons. center of spinal cord looks like letter H or a butterfly Reflexes White Matter: The simplest reflex is the stretch reflex. outer layer of spinal cord A stretch reflex occurs when muscles contract in contains myelinated fibers response to a stretching force applied to them. The knee-jerk reflex, or patellar reflex is a classic White Matter in Spinal Cord example of a stretch reflex. Located in the white matter of the CNS are three The withdrawal reflex, or flexor reflex, is to columns: dorsal, ventral, and lateral. remove a limb or another body part from a painful Columns contain ascending and descending tracts. stimulus. Ascending tracts: The sensory receptors are pain receptors, and axons that conduct action potentials toward the stimulation of these receptors initiates the reflex. brain Descending tracts: Spinal Nerves axons that conduct action potentials away from the Arise along spinal cord from union of dorsal roots brain and ventral roots. Contain axons of sensory and somatic motor Gray Matter in Spinal Cord neurons. The gray matter has a letter H shape with horns. Located between vertebra. Posterior horns: Categorized by region of vertebral column from contain axons which synapse with interneurons which it emerges (C for cervical). Anterior horns: 31 pairs organized in 3 plexuses. contain somatic neurons Lateral horns: contain autonomic neurons DELGADO BSN 1C  Cervical Plexus Brainstem Spinal nerves C1-4 Components: Innervates muscles attached to hyoid bone and Medulla oblongata skin of neck and back of head. Pons Contains the phrenic nerve which innervates Midbrain diaphragm. Brainstem Components Brachial Plexus 1. Medulla oblongata Originates from spinal nerves C5-T1. Location: Supply nerves to the upper limbs, shoulders, hand. continuous with spinal cord Function: Lumbosacral Plexus regulates heart rate, blood vessel diameter, Originates from spinal nerves L1 to S4. breathing, swallowing, vomiting, hiccupping, Supplies nerves lower limbs. coughing, sneezing, balance Other: pyramids: involved in conscious control of skeletal muscle 2. Pons Location: above medulla, bridge between cerebrum and cerebellum Function: breathing, chewing, salivation, swallowing, relay station between cerebrum and cerebellum 3. Midbrain Location: above pons Function: coordinated eye movement, pupil diameter, turning head toward noise Other: the dorsal part has the four colliculi which are involved in visual and auditory reflexes 4. Reticular Formation Location: scattered throughout brainstem Function: regulates cyclical motor function, respiration, walking, chewing, arousing and maintaining consciousness, regulates The Brain sleep-wake cycle The four major regions of the brain are: the brainstem the cerebellum the diencephalon the cerebrum DELGADO BSN 1C  Cerebellum Cerebrum Characteristics Location: Largest portion of brain attached to the brainstem by the cerebellar Divisions: peduncles Right hemisphere Characteristics: Left hemisphere means “little brain” separated by longitudinal fissure cortex is composed of gyri, sulci, gray matter Lobes: frontal, parietal, occipital, temporal, insula Functions: (fifth lobe) controls balance muscle tone Cerebrum Components coordination of fine motor function 1. Cerebral Cortex Location: Diencephalon surface of cerebrum, composed of gray matter Located between the brainstem and cerebrum Function: Components: controls thinking, communicating Thalamus remembering, understanding, and initiates Hypothalamus voluntary movements Epithalamus Cerebrum Surface Features Diencephalon Components Longitudinal fissure: 1. Thalamus divides cerebrum into left and right hemispheres Characteristics: Gyri: folds on cerebral cortex that increase surface largest portion of diencephalon area Function: Sulci: shallow indentations regulates sensory input traveling from the spinal Fissure: deep indentations cord and brainstem to the cerebral cortex influences moods and detects pain Cerebral Hemispheres Left hemisphere: 2. Epithalamus: controls right side of body Location: responsible for math, analytic, and speech above thalamus Right hemisphere: Function: controls left side of body emotional and visceral response to odors responsible for music, art, abstract ideas contains the pineal gland which is an endocrine Corpus callosum: gland that plays a role in controlling some long-term connection between the two hemispheres cycles that are influenced by the light-dark cycle Lobes of the Brain 3. Hypothalamus 1. Frontal lobe Location: Location: anterior below thalamus Function: controls voluntary motor functions, Characteristics: aggression, moods, smell controls pituitary gland and is connected to it by 2. Parietal lobe infundibulum Location: top Function: Function: evaluates sensory input such as touch, controls homeostasis, body temp, thirst, hunger, pain, pressure, temperature, taste fear, rage, sexual emotions 3. Occipital lobe Location: posterior Function: vision DELGADO BSN 1C  4. Temporal lobe Location: lateral Between the arachnoid mater and the pia mater is the Function: hearing, smell, memory subarachnoid space, which is filled with cerebrospinal fluid and contains blood vessels. Sensory Functions CNS constantly receives sensory input Cerebrospinal Fluid We are unaware of most sensory input Cerebrospinal Fluid Cerebrospinal fluid (CSF) bathes Sensory input is vital of our survival and normal the brain and spinal cord, providing a protective functions cushion around the CNS. The ependymal cells located in the choroid plexuses Memory of the ventricles produce the CSF. Working memory occurs when the brain briefly CSF fills the brain ventricles, the central canal of the stores information required for an immediate spinal cord, and the subarachnoid space. performance of a task. It lasts only a few seconds to minutes. Cranial Nerves Short-term memory lasts longer than working 12 pair of cranial nerves memory and can be retained for a few minutes to a few Named by roman numerals days. 2 categories of functions: sensory and motor Short-term memory is transferred to long-term memory, where it may be stored for only a few Cranial Nerve I (Olfactory) is a pure sensory nerve for minutes or become permanent, by consolidation. smell Consolidation is a gradual process involving the Cranial Nerve II (Optic) is a pure sensory nerve for formation of new and stronger synaptic connections. vision The length of time memory is stored may depend on Cranial Nerve III (Occulomotor) is a pure motor nerve how often it is retrieved and used. for eye movement Declarative memory, or explicit memory, involves the Cranial Nerve IV (Trochlear) is a pure motor nerve for retention of facts, such as names, dates, and places, eye movement as well as related emotional undertones. Cranial Nerve V (Trigeminal) is both a motor and Procedural memory, or reflexive memory, involves sensory nerve. It is sensory for pain, touch, and the development of motor skills, such as riding a temperature for the eye and lower and upper jaws. It is bicycle. motor for muscles of chewing. Cranial Nerve VI (Abducens) is a pure motor nerve for Meninges eye movement The meninges are three connective tissue layers that Cranial Nerve VII (Facial) is both a sensory and motor surround the brain and spinal cord. nerve. It is sensory for taste and motor for facial The outermost (most superficial) meningeal layer is expression. the dura mater, which is the toughest of all the Cranial Nerve VIII (Vestibulocochlear) is a pure meninges. sensory nerve for hearing and equilibrium The dura mater forms two layers around the brain Cranial Nerve IX (Glossopharyngeal) is both a motor and only one layer around the spinal cord. and sensory nerve. It is sensory for taste and motor for The second meningeal membrane is the very thin, swallowing. wispy arachnoid mater. Cranial Nerve X (Vagus) is both a motor and sensory The space between the dura mater and the arachnoid nerve. It is sensory and motor for organs in the thoracic mater is the subdural space, which is normally only a and abdominal cavities. potential space containing a very small amount of Cranial Nerve XI (Accessory) is a pure motor nerve serous fluid. for the trapezius, sternocleidomastoid, and muscles of The third meningeal membrane, the pia mater, is the larynx. very tightly bound to the surface of the brain and spinal Cranial Nerve XII (Hypoglossal) is a pure motor nerve cord. for the tongue DELGADO BSN 1C Autonomic Nervous System The autonomic neurons innervate smooth muscle, cardiac muscle, and glands. Autonomic functions are largely controlled unconsciously. The autonomic nervous system is composed of the sympathetic division and the parasympathetic division. Increased activity in sympathetic neurons generally prepares the individual for physical activity, whereas parasympathetic stimulation generally activates involuntary functions, such as digestion, that are normally associated with the body at rest. Enteric Nervous System The enteric nervous system (ENS) consists of plexuses within the wall of the digestive tract. The plexuses include: Sensory neurons that connect the digestive tract to the CNS. Sympathetic and parasympathetic neurons that connect the CNS to the digestive tract. Enteric neurons, located entirely within the enteric plexuses. Enteric neurons are capable of monitoring and controlling the digestive tract independently of the CNS through local reflexes. For example, stretching of the digestive tract is detected by enteric sensory neurons, which stimulate enteric interneurons. The enteric interneurons stimulate enteric motor neurons, which stimulate glands to secrete. DELGADO BSN 1C