Anatomy & Physiology. Chapter 7 Notes Nervous System. Monitor/collecting stimuli occurring inside and outside the body

Transcription

1 Anatomy & Physiology Chapter 7 Notes Nervous System Functions of the Nervous System 1) Sensory input 2) Integration Monitor/collecting stimuli occurring inside and outside the body To process and interpret sensory input and decide if action is needed 3) Motor output A response to integrated stimuli The response activates muscles or glands Structural Classification of the Nervous System Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerves outside the brain and spinal cord Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Somatic nervous system = voluntary Autonomic nervous system = involuntary Organization of the Nervous System Nervous Tissue: Neuroglia of CNS 1) Astrocytes Abundant, star-shaped cells in CNS Brace neurons Form barrier between capillaries and neurons

2 Control the chemical environment of the brain 2) Oligodendrocytes Produce myelin sheath around nerve fibers in the central nervous system (CNS) Nervous Tissue: Neuroglia of PNS 1) Satellite cells Protect neuron cell bodies 2) Schwann cells Form myelin sheath in the peripheral nervous system Neuroglia vs. Neurons Neuroglia Do not transmit electrical impulses Undergo mitosis (brain tumors) Neurons (nerve cells) Neuron Anatomy 1) Cell body Cells specialized to transmit messages Major regions of neurons Nissl substance is specialized rough endoplasmic reticulum Neurofibrils are intermediate cytoskeleton that maintains cell shape Nucleus Large nucleolus 2) Dendrites are extensions that conduct impulses toward the cell body 3) Axons are extensions that conduct impulses away from the cell body Axons and Nerve Impulses Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap Synaptic cleft is the gap between adjacent neurons Synapse is the junction between nerves

3 Nerve Fiber Coverings Schwann cells produce myelin sheaths (insulation) in jelly-roll like fashion Nodes of Ranvier are gaps in myelin sheath along the axon caused by separation of different schwann cells Multiple sclerosis is an autoimmune disease where myelin sheaths are destroyed causing an electrical short-circuits Functional Classification of Neurons Sensory (afferent) neurons carry impulses towards the CNS Cutaneous sense organs (pain/temperature, touch, pressure) Proprioceptors detect stretch or tension Motor (efferent) neurons Carry impulses from the central nervous system Functional Properties of Neurons 1) Irritability is the ability to respond to stimuli 2) Conductivity is the ability to transmit an impulse Nerve Impulse Propagation 1) The plasma membrane at rest is polarized 2) Depolarization a stimulus allows sodium (Na + ) to flow inside the membrane 3) The exchange of ions initiates an action potential in the neuron 4) Repolarization - potassium ions rush out of the neuron after sodium ions rush 5) The sodium-potassium pump restores the original configuration (3 Na out/2 K in) requiring ATP Continuation of the Nerve Impulse between Neurons Transmission of a nerve impulse is an electrochemical event Impulses are able to cross the synapse to another nerve (can be disrupted by analgesics or decreased blood flow) Neurotransmitter is released from a nerve s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite The Reflex Arc Reflexes are rapid, predictable, and involuntary responses to stimuli A reflex arc is direct route from a sensory neuron, to an interneuron, to an effector involving both PNS and CNS Reflexes contain 4-5 components

4 Types of Reflexes and Regulation Autonomic reflexes 1) Smooth muscle regulation 2) Pupillary response to light 3) Heart and blood pressure regulation 4) Regulation of glands 5) Digestive system regulation Somatic reflexes 1) Activation of skeletal muscles Central Nervous System (CNS) CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord Four ventricles chambers within the brain filled with cerebrospinal fluid form Regions of the Brain 1) Cerebral hemispheres 2) Diencephalon 3) Brain stem 4) Cerebellum Cerebral Hemispheres (Cerebrum) Paired left and right superior parts of the brain Include more than half of the brain mass The surface is made of gyri (ridges) and sulci (grooves) Lobes of the Cerebrum Fissures (deep grooves) divide the cerebrum into lobes Frontal lobe Parietal lobe Occipital lobe Temporal lobe Specialized Areas of the Cerebrum Somatic sensory area receives impulses from the body s sensory receptors Primary motor area sends impulses to skeletal muscles

5 Broca s area involved in our ability to speak Cerebral areas involved in special senses Gustatory area (taste) Visual area (sight) in occipital lobe Auditory area (hearing) Olfactory area (smell) Layers of the Cerebrum Gray matter is the outer layer composed mostly of neuron cell bodies White matter is myelinated fiber tracts inside the gray matter Corpus callosum connects hemispheres Diencephalon Sits in the center of the brain enclosed by the cerebral hemispheres Three parts: 1) Thalamus 2) Hypothalamus 3) Epithalamus Thalamus Surrounds the third ventricle The relay station for sensory impulses Transfers impulses to the correct part of the cortex for localization and interpretation Hypothalamus Sits under the thalamus Important autonomic nervous system center Helps regulate body temperature Controls water balance Regulates metabolism An important part of the limbic system (emotions) regulating thirst, appetite, sex, pain, and pleasure The pituitary gland is attached to the hypothalamus Epithalamus Forms the roof of the third ventricle Houses the pineal body (endocrine gland)

6 Includes the choroid plexus (knots of capillaries) which functions to form cerebrospinal fluid Brain Stem Attaches to the spinal cord Parts of the brain stem Midbrain 1) Midbrain 2) Pons 3) Medulla oblongata Has two bulging fiber tracts called the cerebral peduncles for ascending and descending impulses Has four rounded protrusions called the corpora quadrigemina Pons Reflex centers for vision and hearing The bulging center part of the brain stem mostly composed of fiber tracts Includes nuclei involved in the control of breathing Medulla Oblongata The lowest part of the brain stem Merges into the spinal cord Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting Reticular Formation Diffuse mass of gray matter along the brain stem Involved in motor control of visceral organs Reticular activating system plays a role in awake/sleep cycles and consciousness Cerebellum Two hemispheres with convoluted surfaces (cauliflower) Located under occipital lobe of cerebrum

7 Provides involuntary coordination of body movements (balance and equilibrium) from proprioceptors and special sense organs in the ear Ataxia is a condition of clumsy, disorganized movements caused by damage to the cerebellum Protection of the Central Nervous System 1) Scalp and skin 2) Skull and vertebral column 3) Meninges 4) Cerebrospinal fluid 5) Blood brain barrier Meninges 1) Dura mater Periosteum attached to surface of the skull Meningeal layer outer covering of the brain 2) Arachnoid layer 3) Pia mater Middle layer web-like layer with CSF circulating beneath it Internal layer that clings to the surface of the brain Meningitis is inflammation of the meninges that may spread to the nervous tissue Cerebrospinal Fluid (CSF) Similar to blood plasma composition Formed by the choroid plexus (capillaries) Forms a watery cushion to protect the brain Circulated in arachnoid space, ventricles, and central canal of the spinal cord May be uses to diagnose medical conditions via spinal taps Hydrocephalus is swelling of the brain due to a blockage of CSF Blood Brain Barrier Brain is susceptible to fluctuations of hormones, ions, nutrients, and temperature Includes the least permeable capillaries of the body Blocks many potentially harmful substances but allows: Fats and fat soluble molecules Respiratory gases Alcohol

8 Nicotine Anesthesia Traumatic Brain Injuries Concussion Slight brain injury and no permanent brain damage Contusion Nervous tissue destruction occurs and does not regenerate Cerebral edema Swelling from an inflammatory response that compresses brain tissue causing death Cerebrovascular Accident (CVA) Stroke Occurs when blood flow to the brain is disrupted Loss of some functions or death may result May cause hemiplegia (partial paralysis) or aphasias (inability to speak or understand language) Transient ischemic attack (TIA) is a mini-stroke caused by a temporary block of blood flow (not permanent) Alzheimer s Disease Progressive degenerative brain disease (dementia) affecting 5-15% of people over the age of 65 Unknown cause but structural changes is seen Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death Over half of nursing home patients have Alzheimer s Parkinson s Disease Caused by degeneration of basal nuclei (located in the white matter of the cerebral hemispheres) Resting tremor, forward-bent walking posture, shuffling gait, and stiff facial expression Drugs, electrical stimulation, and fetal tissue are all methods of management no cure! Huntington s Disease Massive degeneration of basal nuclei and cerebral cortex (later stages) Wild, jerky continuous flapping movements Late stage mental deterioration The Nervous System

9 Spinal Cord Extends from the medulla oblongata to the region of T12 Below T12 is the cauda equina (a collection of spinal nerves) Enlargements occur in the cervical and lumbar regions Spinal Cord Anatomy Exterior white mater are conduction tracts (ascending and descending tracts) Internal gray matter is mostly cell bodies Dorsal (posterior) horns receive sensory info Anterior (ventral) horns sends motor info Central canal filled with cerebrospinal fluid Peripheral Nervous System Nerves and ganglia outside the central nervous system A nerve is a bundle of neuron fibers Neuron fibers are bundled by connective tissue Structure of a Nerve Endoneurium surrounds each fiber Groups of fibers are bound into fascicles by perineurium Fascicles are bound together by epineurium Classification of Nerves Mixed nerves carry both sensory and motor fibers Afferent (sensory) nerves carry impulses toward the CNS Efferent (motor) nerves carry impulses away from the CNS Cranial Nerves 12 pairs of nerves that mostly serve the head and neck Numbered in order, front to back Most are mixed nerves, but three are sensory only I Olfactory nerve sensory for smell II Optic nerve sensory for vision III Oculomotor nerve motor fibers to eye muscles IV Trochlear motor fiber to eye muscles V Trigeminal nerve sensory for the face; motor fibers to chewing muscles

10 VI Abducens nerve motor fibers to eye muscles VII Facial nerve sensory for taste; motor fibers to the face VIII Vestibulocochlear nerve sensory for balance and hearin IX Glossopharyngeal nerve sensory for taste; motor fibers to the pharynx X Vagus nerves sensory and motor fibers for pharynx, larynx, and viscera XI Accessory nerve motor fibers to neck and upper back XII Hypoglossal nerve motor fibers to tongue