Nervous System PDF

HUMAN ANATOMY & PHYSIOLOGY NERVOUS SYSTEM Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning Nerve Anatomy Myelin Sheath and Neurilemma: Formation Action Potentials An action potential (AP) or impulse is a sequence of ra...

HUMAN ANATOMY & PHYSIOLOGY NERVOUS SYSTEM Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning Nerve Anatomy Myelin Sheath and Neurilemma: Formation Action Potentials An action potential (AP) or impulse is a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization) and then restore it to the resting state (repolarization).  During an AP, voltage-gated Na+ and K+ channels open in sequence  According to the all-or-none principle, if a stimulus reaches threshold, the action potential is always the same.  A stronger stimulus will not cause a larger impulse. Action Potentials Neurotransmission Chemical (99%) Electrical (1%) SYNAPSE 1. Action potential reaches axon terminal of presynaptic neuron. 2. Ca2+ enters synaptic knob. 3. Neurotransmitter is released by exocytosis into synaptic cleft. 4. Neurotransmitter binds to receptors that are integral part of chemically gated channels on subsynaptic membrane of postsynaptic neuron. 5. Binding of neurotransmitter to receptor opens that specific channel. Synapse: Information Transmission Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning Spinal Cord Spinal Nerves Spinal Cord Structure: Protection and Coverings Vertebrae Spinal meninges  Three layers of connective tissue Dura mater Arachnoid mater Pia mater  Continuous with cranial meninges Cerebrospinal fluid (CSF) Spinal Meninges and Spaces Epidural space: between vertebrae and dura mater Dura mater- tough ,dense connective tissue  Extends to vertebra S2 (well beyond spinal cord) Arachnoid mater: resembles spider’s web  Extends into subarachnoid space Subarachnoid space  CSF circulates in this space Pia mater: thin, delicate layer  Adheres to surface spinal cord (and brain)  Contains blood vessels Spinal Meninges and Spaces  Spinal Cord Functions Reflexes  fast, involuntary sequences of actions in response to stimuli  Simple (withdrawal) Spinal (reflex arc): simple  Complex (learned sequence such as driving car) Cranial: more complex REFLEX ARC 1. Sensory receptor: responds to stimulus 2. Sensory neuron: through dorsal root ganglion and root  posterior horn 3. Integrating center: single synapse between sensory and motor neurons 4. Motor neuron: from anterior horn  ventral root  spinal nerve 5. Effector: muscle responds Example of Reflex Arc: Patellar Reflex 1. Sensory receptor is stimulated by tap on patellar tendon 2. Sensory neuron: through dorsal root  spinal cord 3. Integrating center: single synapse in spinal cord 4. Motor neuron: through ventral root  spinal nerve  femoral nerve 5. Effector: quads contract, extend leg Brain Anatomy Brain components  Cerebrum  Cerebellum  Brain stem  Hypothalamus  Thalamus Brain: Major Parts Brain stem: continuous with spinal cord  Medulla oblongata, pons, midbrain Diencephalon: superior to brain stem  Thalamus, hypothalamus, and pineal gland Cerebrum: largest part and most superior  Surface covered with gray matter: cortex  Deep to cortex is cerebral white matter Cerebellum: posterior and inferior  Means “little brain” Cranial meninges: dura mater, arachnoid mater, and pia mater Brain: Major Parts Brain: Major Parts Meninges Brain: Blood Supply and Protection Requires 20% of the body’s O2 supply 4 min lack  permanent damage Requires continuous glucose supply Blood-brain Barrier (BBB)  Allows passage of lipid soluble materials: O2, CO2, alcohol, anesthetic agents  Controls entry of most harmful materials  Created by tight capillaries and astrocytes Cerebrospinal Fluid (CSF)  Cushions brain and provides nutrients  Formed in choroid plexuses  Blood-Brain Barrier (BBB) Protects brain from chemical fluctuations in blood  Strictly limits exchange between blood and brain Minimizes harmful blood-borne substances Limits use of drugs for treatment of brain and spinal cord disorder Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning Cerebrospinal Fluid (CSF) Brain Stem: Medulla Oblongata Most inferior part of brainstem  White matter connects spinal cord and other parts of brain Contains vital nuclei  Cardiovascular center Regulates heart rate, blood pressure  Medullary rhythmicity area Adjusts respiratory rhythm Other sensory and reflex motor areas Cranial nerves VIII-XII attached here Brain Stem: Pons Serves as a “bridge”  Connects medulla to midbrain and above  Contains ascending and descending tracts  Connects left and right sides of cerebellum Contains nuclei  Motor relays from cerebrum to cerebellum  Helps control breathing  Cranial nerves V-VIII attached here Brain Stem Reticular Formation Netlike arrangement of gray and white matter Contains ascending and descending tracts Ascending part = reticular activating system (RAS)  Carries sensory pathways to cerebral cortex  Helps maintain consciousness  Helps induce sleep Cerebellum Maintenance of balance Enhancement of muscle tone Coordination and planning of skilled voluntary muscle activity Diencephalon Diencephalon Thalamus: major sensory relay center  Also motor, autonomic, and consciousness functions Hypothalamus: lies inferior to thalamus  Control of pituitary and hormone production  Works with ANS regulating many viscera  Involved with feelings and behavior patterns  Regulation of eating, drinking, fluid levels  Control of body temperature  Regulation of circadian rhythms, sleep, waking Pineal gland: secretes melatonin  Controls sleep, biological clock Hypothalamus Controls many homeostatic functions:  body temperature  thirst  urine output  food intake  hormone secretion Plays role in:  Emotional and behavioral patterns  Sleep-wake cycle Important link between nervous and endocrine system  Cerebrum Largest portion of brain (80%) Divided into:  Right and Left Cerebral Hemispheres Outer surface is highly convoluted cerebral cortex  Highest, most complex integrating area of the brain  Plays key role in most sophisticated neural functions Chapter 5 The Central Nervous System Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning Cerebrum Cerebrum Cerebral Cortex Sensory perception Voluntary control of movement Language Sophisticated mental events (thinking, memory, decision making, creativity) Consist of 4 major lobes:  Occipital  Temporal  Parietal  Frontal Limbic System Emotion Basic, inborn behavioral patterns related to survival and perpetuation of the species Role in motivation and learning Limbic System Sensory Areas Primary somatosensory area: postcentral gyrus  Input includes: touch, proprioception, pain, itching, tickle, temperature Primary visual area: occipital lobe Primary auditory area: temporal lobe Primary gustatory (taste) area: base of postcentral gyrus Primary olfactory (smell) area: medial aspect of temporal lobe Cerebrum: Functional Areas Lateralization Brain controls opposite side of the body: all sensory and motor pathways cross in CNS  Left side of the brain controls right side of body  Right side of brain controls left side of body Left hemisphere important for spoken and written language, numerical and scientific skills, and reasoning Right side more involved with spatial and pattern recognition and emotional content Memory Process for storing and retrieving information Involves structural and functional changes Involves association areas, parts of limbic system, and diencephalon Skill memory also involves cerebellum and basal ganglia Cranial Nerves  Cranial Nerves I. Olfactory: special sensory  smell II. Optic: special sensory  vision III. Oculomotor: motor  control of eye movements IV. Trochlear: motor  control of eye movements V. Trigeminal: mixed  General sensory: touch, pain, pressure, hot, cold in face  Motor: to muscles used for chewing VI. Abducens: motor  control of eye movements VII. Facial: mixed  Special sensory (taste) from anterior of tongue  Motor to muscles of facial expression, tear glands, and some salivary glands VIII. Vestibulocochlear: special sensory  ear  Cranial Nerves IX. Glossopharyngeal: mixed  Sensory for posterior of tongue, pharynx, and palate; blood pressure  Motor to pharyngeal muscles (swallowing), salivary gland (parotid) X. Vagus: mixed (the major parasympathetic nerve)  Sensory from pharynx, ear, diaphragm, visceral organs in thoracic and abdominal cavities  Motor to palatal and pharyngeal muscles (swallowing and voice); to viscera in thoracic and abdominal cavities XI. Accessory: motor to voluntary muscles including sternocleidomastoid and trapezius (move head, shoulders) XII. Hypoglossal: motor to tongue (swallowing and speech) Freeman 45-20 Aging Rapid brain growth during first few years of life  Due to increase in size of neurons and proliferation of neuroglia  Increase in development of dendritic branches and synaptic contacts From early adulthood through old age:  Decline in brain mass  Fewer synaptic contacts brain function  Some decrease in brain function