Nervous System PDF

NERVOUS SYSTEM What?  the master control and communication system of the body  3 Functions:  uses its millions of sensory receptors to monitor changes occurring both inside and outside the body  stimuli – changes; sensory input – gathered information  it processes and interprets the sensor...

NERVOUS SYSTEM What?  the master control and communication system of the body  3 Functions:  uses its millions of sensory receptors to monitor changes occurring both inside and outside the body  stimuli – changes; sensory input – gathered information  it processes and interprets the sensory input and decides what should be done at each moment – a process called integration  it then causes a response, or effect, by activating Organization of the Nervous System  Structural Classification: Central nervous system  consists of the brain and spinal cord, which occupy the dorsal body cavity and act as the integrating and command centers of the nervous system  interpret incoming sensory information and issue instructions based on past experience and current conditions Organization of the Nervous System  Structural Classification: Peripheral nervous system  includes all parts of the nervous system outside the CNS  consists mainly of the nerves that extend from the spinal cord and brain  spinal nerves – carry impulses to and from the spinal cord  cranial nerves – carry impulses to and from the brain Organization of the Nervous System  Functional Classification: Sensory division or Afferent division  consists of nerves that convey impulses to the CNS from sensory receptors located in various parts of the body  keeps the CNS constantly informed of events going on both inside and outside the body  somatic sensory fibers – sensory fibers delivering impulses from the skin, skeletal muscles and joints  visceral sensory fibers – transmitting impulses from the visceral organs Organization of the Nervous System  Functional Classification: Motor division or Efferent division  carries impulses from the CNS to effector organs, the muscles and glands  these impulses activate muscles and glands – that is – they effect a motor response 2 Subdivisions: Somatic nervous system Autonomic nervous system Organization of the Nervous System  Functional Classification: Motor division or Efferent division 2 Subdivisions: Somatic nervous system  allows us to consciously or voluntarily control our skeletal muscles  often referred to as the voluntary nervous system Organization of the Nervous System  Functional Classification: Motor division or Efferent division 2 Subdivisions: Autonomic nervous system (ANS)  regulates events that are automatic, or involuntary, such as the activity of smooth muscle, cardiac muscle, and glands  commonly called the involuntary nervous system  has 2 parts: sympathetic and parasympathetic Nervous Tissue: Structure & Function  Supporting Cells  in the CNS – glia or glial cells or neuroglia – “nerve glue” – support, insulate and protect the delicate neurons CNS Neuroglia include the ff: Astrocytes  abundant star-shaped cells that account for nearly half of neural tissue  form a living barrier between capillaries and neurons, help determine capillary permeability, and play a role in making exchanges between the two Nervous Tissue: Structure & Function CNS Neuroglia include the ff: Astrocytes  they help protect the neurons from harmful substances that might be in the blood  also help control the chemical environment in the brain by mopping up leaked potassium ions, which are involved in generating a nerve impulse, and recapturing chemicals released for communication purposes Nervous Tissue: Structure & Function CNS Neuroglia include the ff: Microglia  spiderlike phagocytes that monitor the health of nearby neurons and dispose of debris, such as dead brain cells and bacteria Ependymal cells  neuroglia that line the central cavities of the brain and the spinal cord  the beating of their cilia helps to circulate the cerebrospinal fluid that fills those cavities and forms a protective watery cushion around the CNS Nervous Tissue: Structure & Function CNS Neuroglia include the ff: Oligodendrocytes  neuroglia that wrap their flat extensions tightly around the nerve fibers, producing fatty insulating coverings called myelin sheaths Neuroglia somewhat resemble neurons structurally but they are not able to transmit nerve impulses Most brain tumors are gliomas, or tumors formed by neuroglia Nervous Tissue: Structure & Function PNS Supporting Cells include the ff: Schwann cells  form the myelin sheaths around nerve fibers in the PNS Satellite cells  act as protective, cushioning cells for peripheral neuron cell bodies Neurons: Anatomy  also called nerve cells – highly specialized to transmit messages (nerve impulses) from one part of the body to another  they have a cell body, which contains the nucleus  one or more slender processes extending from the cell body Cell body  the metabolic center of the neuron Neurons: Anatomy Processes or Fibers  armlike which vary in length from microscopic to about 7 feet in the tallest humans  dendrites – neuron processes that convey incoming messages (electrical signals) toward the cell body  axons – generate nerve impulses and typically conduct them away from the cell body Each neuron has only one axon and may have hundreds of branching dendrites, depending on the neuron type Neurons: Anatomy Processes or Fibers  axon terminals – branches of axon that contain hundreds of tiny vesicles, or membranous sacs that contain chemicals – Neurotransmitters  synaptic cleft – a tiny gap that separates each axon terminal from the next neuron  synapse – an impulse is transmitted from one neuron to another Neurons: Anatomy Processes or Fibers  myelin sheaths – a whitish, fatty material which has a waxy appearance that covers most of the long nerve fibers  protects and insulates the fibers and increases the transmission rate of nerve impulses  nodes of Ranvier – gaps or indentations between myelin sheaths Neurons: Anatomy Multiple sclerosis  gradually destroys the myelin sheaths around CNS fibers by converting them to hardened sheaths called sclerosis  the electrical current is short-circuited and may jump to another demyelinated neuron causing the nerve signals to not reach the intended target  the affected person may have visual and speech disturbances, lose the ability to control his or her muscles, and become increasingly disabled Neurons: Classification Functional Classification: Sensory neurons or Afferent neurons  neurons carrying impulses from sensory receptors to the CNS  keep us informed about what is happening both inside and outside the body  its cell bodies are always found in a ganglion outside the CNS  at the dendrite endings of the sensory neurons are specialized receptors that are activated by specific changes occurring nearby Neurons: Classification Functional Classification: Sensory neurons or Afferent neurons  cutaneous sense organs – the simpler types of sensory receptors in the skin  proprioceptors – sensory receptors in the muscles and tendons  detect the amount of stretch, or tension in skeletal muscles, their tendons and joints  pain receptors – the least specialized of the cutaneous receptors and are also the most numerous, because pain warns us that some type of body damage Neurons: Classification Functional Classification: Motor neurons or Efferent neurons  neurons carrying impulses from the CNS to the viscera and/or muscles and glands  its cell bodies are usually located in the CNS Interneurons or Association neurons  they connect the motor and sensory neurons in neural pathways  cell bodies are typically located in the CNS Neurons: Classification Structural Classification  based on the number of processes, including both dendrites and axons, extending from the cell body  multipolar neuron – the most common structural type  have several dendrites and axons  bipolar neuron – neurons with 2 processes – 1 axon and 1 dendrite  rare in adults, found only in some special sense organs (eye, nose), where they act in sensory processing as receptor cells Neurons: Classification Structural Classification:  unipolar neurons – have a single process emerging from the cell body as if the cell body were on a “cul-de-sac” off the “main road” that is the axon  unique in that only the small branches at the end of the peripheral process are dendrites  remainder of the peripheral process and the central process function as the axon  the axon conducts nerve impulses both toward and away from the cell body  sensory neurons found in PNS ganglia Physiology: Nerve Impulses 2 Major Functional Properties of Neurons: Irritability  the ability to respond to a stimulus and convert it into a nerve impulse Conductivity  the ability to transmit the impulse to other neurons, muscles or glands Physiology: Reflexes Reflexes  are rapid, predictable, and involuntary responses to stimuli  either somatic or autonomic  somatic reflexes – include all reflexes that stimulate the skeletal muscles  autonomic reflexes – regulate the activity of smooth muscles, the heart, and glands  regulate digestion, elimination, blood pressure and sweating Physiology: Reflexes Reflex Arc 5 Elements:  receptor  sensory  interneuron  motor neuron  effector Physiology: Reflexes Reflex Arc 5 Elements:  simple patellar or knee-jerk reflex – a two-neuron reflex arc, the simplest type in humans  flexor or withdrawal reflex – a three-neuron reflex arc in which the limb is withdrawn from a painful stimulus Reflex testing is an important tool in evaluating the condition of the nervous system Reflexes that are exaggerated, distorted, or absent indicate damage or disease in the nervous system CNS: Functional Anatomy of the Brain Cerebral Hemispheres  collectively called cerebrum  the most superior part of the brain  gyri – elevated ridges of tissue  sulci – shallow grooves that separates the gyri  fissures – deeper grooves which separate large regions of the brain CNS: Functional Anatomy of the Brain 3 Basic Regions:  Superficial cortex of gray matter – looks gray in fresh brain tissue  Internal area of white matter  Basal nuclei CNS: Functional Anatomy of the Brain Cerebral Cortex  functions in the speech, memory, logical and emotional responses, consciousness, the interpretation of sensation, and voluntary movement  primary somatic sensory area – located in the parietal lobe posterior to the central sulcus  allows you to recognize pain, differences in temperature or a light touch  Primary motor area Gustatory area (taste) Working Speech/language memory & judgment Problem solving Language comprehensi on Broca’s area (motor Visual area speech) Olfactory area Auditory area CNS: Functional Anatomy of the Brain Cerebral Cortex  primary motor area – allows us to consciously move our skeletal muscles, is anterior to the central sulcus in the frontal lobe  the axons of these motor neurons form the major voluntary motor tract – pyramid tract or corticospinal tract  most of the neurons in this area control body areas having the finest motor control – the face, mouth and hands CNS: Functional Anatomy of the Brain Cerebral Cortex  broca’s area – motor speech area  a specialized cortical area that is very involved in our ability to speak  found at the base of the precentral gyrus  damage to this area, which is located in only one cerebral hemisphere (usually the left), causes the inability to say words properly  Primary motor area Gustatory area (taste) Working Speech/language memory & judgment Problem solving Language comprehensi on Broca’s area (motor Visual area speech) Olfactory area Auditory area CNS: Functional Anatomy of the Brain Cerebral Cortex  anterior association area – areas involved in higher intellectual reasoning and socially acceptable behavior  frontal lobe – house areas involved with language comprehension  complex memories are stored in the temporal and frontal lobes CNS: Functional Anatomy of the Brain Cerebral Cortex  posterior association area – plays a role in recognizing patterns and faces, and blending several different inputs into an understanding of the whole situation  speech area – located at the junction of the temporal, parietal and occipital lobes  allows you to sound out words and just like the Broca’s area, is only found in one cerebral hemisphere  Primary motor area Gustatory area (taste) Working Speech/language memory & judgment Problem solving Language comprehensi on Broca’s area (motor Visual area speech) Olfactory area Auditory area CNS: Functional Anatomy of the Brain Cerebral White Matter  deeper and is the most of the remaining cerebral hemisphere tissue  composed of fiber tracts carrying impulses to, from or within the cortex  corpus callosum – one very large fiber tract that connects the cerebral hemispheres  allows the cerebral hemispheres to communicate with one another CNS: Functional Anatomy of the Brain Cerebral White Matter  association fiber tracts – connects areas within a hemisphere  projection fiber tracts – connect the cerebrum with lower CNS centers such as the brain stem Basal Nuclei  islands of gray matter, buried deep within the white matter  help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex CNS: Functional Anatomy of the Brain Basal Nuclei  Parkinson’s disease – individuals who have problems with their basal nuclei  often unable to walk normally or carry out other voluntary movements in a normal way CNS: Functional Anatomy of the Brain Diencephalon  or interbrain – sits atop the brain stem and is enclosed by the cerebral hemispheres  major structures: thalamus, hypothalamus and epithalamus CNS: Functional Anatomy of the Brain Thalamus  encloses the shallow third ventricle of the brain, is a relay station for sensory impulses passing upward to the sensory cortex Hypothalamus  makes up the floor of the diencephalon  plays a role in regulating body temperature, water balance and metabolism  the center for many drives and emotions CNS: Functional Anatomy of the Brain Hypothalamus  regulates the pituitary gland and produces 2 hormones of its own Epithalamus  forms the roof of the third ventricle  choroid plexus – knots of capillaries which form the cerebrospinal fluid CNS: Functional Anatomy of the Brain Brain Stem  about the size of a thumb in diameter and approximately 3 inches long  structures: midbrain, pons, medulla oblongata  providing pathway for ascending and descending tracts  produce the rigidly programmed autonomic behaviors necessary for survival  some are associated with the cranial nerves and control vital activities such as breathing and blood pressure CNS: Functional Anatomy of the Brain Midbrain  extends from the mammillary bodies to the pons inferiorly  cerebral aqueduct – a tiny canal that travels through the midbrain, connects the third ventricle of the diencephalon to the fourth ventricle below  cerebral peduncles – little feet of the cerebrum and convey ascending and descending impulses  corpora quadrigemina – 4 rounded protrusions that involved with vision and hearing CNS: Functional Anatomy of the Brain Pons  rounded structure that protrudes just below the midbrain  involved in the control of breathing Medulla Oblongata  most inferior part of the brain stem  important fiber tract area  contains centers that control heart rate, blood pressure, breathing, swallowing, and vomiting CNS: Functional Anatomy of the Brain Reticular formation  a diffuse mass of gray matter extending the entire length of the brain stem  reticular activating system (RAS) – a special group of reticular formation neurons that plays a role in consciousness and the awake/sleep cycle  damage to this area can result in prolonged unconsciousness (coma) CNS: Functional Anatomy of the Brain Cerebellum  large, cauliflower-like that projects dorsally from under the occipital lobe of the cerebrum  has an outer cortex made up of gray matter and inner region of white matter  provides the precise timing for skeletal muscle activity and controls our balance  it plays its role less well when it is sedated by alcohol CNS: Functional Anatomy of the Brain Cerebellum  if damaged, movements become clumsy and disorganized – a condition called ataxia  victims cannot keep their balance and may appear drunk because of the loss of muscle coordination Protection of the CNS Meninges  3 connective tissue membranes covering and protecting the CNS structures  dura mater – “hard mother” – the outermost layer, a double-layered membrane where it surrounds the brain  periosteal layer – attached to the inner surface of the skull  meningeal layer – forms the outermost covering of the brain and continues as dura mater of the spinal cord Protection of the CNS Meninges  falx cerebri & tentorium cerebelli – separate the cerebellum from the cerebrum  a fold that attaches the brain to the cranial cavity  arachnoid mater – the weblike middle meningeal layer Protection of the CNS Meninges  arachnoid mater – a weblike middle meningeal layer  subarachnoid space – space where the threadlike extensions of the arachnoid span to attach it to the innermost membrane and it is filled with cerebrospinal fluid  pia mater – “gentle mother” – delicate, clings tightly to the surface of the brain and spinal cord, following every fold Protection of the CNS Cerebrospinal Fluid (CSF)  a watery “broth” with components similar to blood plasma  it contains less protein and more vitamin C  forms a watery cushion that protects the fragile nervous tissue from blows and other trauma and helps the brain “float” so it is not damaged by the pressure of its own weight Protection of the CNS The Blood-Brain Barrier  composed of least permeable capillaries in the whole body  seamlessly bound together by tight junctions all around thus water-soluble substances, only water, glucose and essential amino acids can pass though the walls of these capillaries  useless against fats, respiratory gases, and other fat-soluble molecules that’s why alcohol, nicotine and anesthetics can affect the brain Spinal Cord  approximately 17 inches long, a glistening white continuation of the brain stem  provides two-way conduction pathway to and from the brain  a major reflex center  cushioned and protected by meninges  cauda equina – collection of spinal nerves at the inferior end of the vertebral canal and it looks so much like a horse’s tail Spinal Cord & Spinal Roots: Gray Matter  looks like a butterfly or the letter H in cross section  surrounds the central canal which contains CSF  dorsal or posterior horns – 2 posterior projections  contain interneurons  dorsal root ganglion – enlarged area where the cell bodies of the sensory neurons are found – its fibers enter the cord by the dorsal root  Dorsal posterior Central horn of gray Dorsal root canal matter ganglion Lateral horn of gray matter Spinal nerve Ventral horn of Dorsal root of spinal nerve gray matter Ventral root of Pia mater spinal nerve Arachnoid mater Dura mater Spinal Cord & Spinal Roots: Gray Matter  damaged to the dorsal root or its ganglion will cause loss of sensation from the body area it served  ventral or anterior horns – 2 anterior projections  contain cell bodies of motor neurons of the somatic nervous system, which send their axons out the ventral root of the cord The dorsal and ventral roots fuse to form the spinal nerves Spinal Cord: White Matter  composed of myelinated fiber tracts – some running to higher centers, some traveling from the brain to the cord, and some conducting impulses from one side of the spinal cord to the other 3 regions: Dorsal columns – ascending tracts that carry sensory input to the brain Lateral and Ventral columns – contain both ascending and descending (motor) tracts Spinal Cord: White Matter sensory or afferent tracts  tracts conducting sensory impulses to the brain motor or efferent tracts  carrying impulses from the brain to skeletal muscles Spastic paralysis – results when the spinal cord is transected or crushed  a loss of feeling or sensory input occurs in the body areas below the point of cord destruction Spinal Cord: White Matter Quadriplegic  if the spinal cord injury occurs high in the cord, that all four limbs are affected Paraplegic  if only the legs are paralyzed Peripheral Nervous System  consists of nerves and scattered ganglia Structure of a Nerve:  nerve – a bundle of neuron fibers found outside the CNS  endoneurium – a delicate connective tissue sheath that surrounds the neuron fibers  perineurium – a coarser connective tissue wrapping that bounds groups of tissues – to form fiber bundles - fascicles  epineurium – a tough fibrous sheath that bound together all the fascicles to form the Peripheral Nervous System Cranial Nerves:  12 pairs – primarily serve the head and neck  one pair – vagus nerves – extends to the thoracic and abdominal cavities Peripheral Nervous System Spinal Nerves:  dorsal ramus/rami – serve the skin and muscles of the posterior body trunk  ventral ramus/rami – from T1 to T12 form the intercostal nerves, which supply the muscles between the ribs and the skin and muscles of the anterior and lateral trunk  form complex networks of nerves called plexuses – serves the motor and sensory needs of the limbs Autonomic Nervous System  the motor subdivision of the PNS that controls body activities automatically  composed of a specialized group of neurons that regulate cardiac muscle, smooth muscle and glands  at every moment, signals flood from the visceral organs into the CNS, and the ANS system makes adjustments as necessary to best support body activities Autonomic Nervous System Sympathetic Division  also called the thoracolumbar division because its preganglionic neurons are in the gray matter of the spinal cord from T1 through L1  often referred to as the “fight-or-flight” system  mobilizes the body during extreme situations such as fear, exercise or rage  a pounding heart; rapid, deep breathing; cold, sweaty skin; a prickly scalp; and dilated eye pupils are sure signs of SNS Autonomic Nervous System Sympathetic Division  the widespread and prolonged effects of sympathetic activation help explain why we need time to calm down after an extremely stressful situation  its function is to provide the best conditions for responding to some threat, whether the best response is to run, to see better, or to think more clearly Autonomic Nervous System Parasympathetic Division  sometimes called the “rest-and-digest” system – allows us to “unwind” and conserve energy, particularly by decreasing demands on the cardiovascular system  most active when the body is at rest and not threatened in any way  chiefly concerned with promoting normal digestion, with elimination of feces and urine Autonomic Nervous System Parasympathetic Sympathetic Division Division  exercise  digestion  excitement  defecation  emergency  diuresis  embarrassment