Central Nervous System. Chapter 11. Nervous System II. Nervous System Review. Brain and spinal cord

Transcription

1 Chapter 11 Nervous System II Nervous System Review Central Nervous System brain & spinal cord Peripheral Nervous System contains nerves connecting CNS to all other body parts Cranial nerves arising from the brain Spinal nerves arising from the spinal cord into somatic & autonomic nervous systems Somatic fibers connect to skin & skeletal muscles & control conscious activities; voluntary Autonomic fibers connect to viscera, glands & control subconscious activities; involuntary Central Nervous System Brain and spinal cord 1

2 Central Nervous System Brain & spinal cord connected by brainstem Brain Largest, most complex part of nervous system Consist of 2 hemispheres, diencephalon, cerebellum & brainstem Protected by cranium Spinal Cord 2 way communication between CNS & PNS Protected by vertebral column Meninges Membranes surrounding & protecting CNS 3 layers dura mater tough, outer CT attached to periosteum. Contain many blood vessels & nerves. arachnoid mater middle, web-like membrane w/out blood vessels pia mater inner, delicate membrane w/ many nerves & blood vessels to nourish cells of CNS; a band of pia mater called the denticulate ligament attaches dura mater to spinal cord subarachnoid space between arachnoid & pia contains cerebrospinal fluid (CSF) 2

3 Ventricles interconnected cavities within cerebral hemispheres & brain stem continuous with central canal of spinal cord filled with cerebrospinal fluid (CSF) lateral ventricles largest; ventricles 1 & 2 third ventricle w/in midline of brain fourth ventricle w/in brainstem, in front of cerebellum cerebral aqueduct connects 3 rd & 4 th ventricles interventricular foramen connects laterals & 3 rd ventricle 3

4 Cerebrospinal Fluid secreted by choroid plexus located in pia mater circulates in ventricles, central canal of spinal cord, & subarachnoid space completely surrounds brain and spinal cord clear nutritive liquid mechanical protection (cushions) helps maintain stable ion conc. in CNS reabsorbed into blood stream by arachnoid granulations ventricles lined w/ cilia from ependymal cells; cilia aids in movement of CSF; ependymal cells regulate composition of CSF (selective) FYI Meningitis inflammation of meninges; (pia & arachnoid are most common) Subdural hematoma accumulation of blood between dura mater & arachnoid space Spinal tap measures CSF pressure Hydrocephalus - CSF pressure w/in brain; developing cranial sutures allow excess swelling. Shunt drains excess fluid away Spinal Cord Structure Continuous nerve tissue from brain thru vertebral column 31 segments starting w/ foramen magnum Cervical enlargement nerves to upper limbs Lumbar enlargement nerves to lower limbs Conus medullaris tapered area below lumbar E. Filum terminale distal portion of tail; thin cord of CT Cauda equina area below conus medullaris; consist of spinal nerves & filum terminale 4

5 Spinal Cord Structure foramen magnum to 2 nd lumbar vertebra Spinal Cord Structure Cross section resembles butterfly (gray mater) surrounded by white mater Cross section shows spinal cord by 2 grooves Anterior median fissure Posterior median sulcus Gray matter Posterior horns upper wing Anterior horns lower wing Lateral horns side protrusion Gray commissure area surrounding central canal; connects R & L wings Central canal lined w/ependymal cells; contains CSF Cross Section of Spinal Cord 5

6 Spinal Cord Structure White matter 3 areas surrounding gray matter Anterior funiculi (ventral) Posterior funiculi (dorsal) Lateral funiculi Ventral root Dorsal root Dorsal root ganglion a bundle of cell bodies outside CNS Fusion of dorsal & ventral root forms spinal nerve that passes thru intervertebral foramen Cross Section of Spinal Cord Spinal Cord Functions Center for spinal reflexes Carries nerve impulses to & from brain 6

7 Reflex Arcs Reflexes automatic, subconscious responses to stimuli. Helps maintain homeostasis Consist of receptors, sensory neurons, interneurons, motor neurons & effectors Examples sneezing, blinking, knee jerk, withdrawal Protective Withdrawal Reflex 7

8 Tracts of the Spinal Cord Ascending tracts conduct sensory impulses (afferent) to brain Descending tracts conduct motor impulses (efferent) from brain to motor neurons reaching muscles & glands Provides a 2-way communication Located in white matter Brain Functions interprets sensations determines perception stores memory reasoning makes decisions coordinates muscular movements regulates visceral activities determines personality controls emotions Major Parts cerebrum 2 hemispheres diencephalon brain stem cerebellum Cerebrum Largest part of brain Develops from forebrain Consist of 2 hemispheres 8

9 Structure of Cerebrum corpus callosum nerve fibers connecting hemispheres convolutions or gyri ridges caused by infolding sulci -shallow grooves fissure deep grooves longitudinal fissure separates hemispheres transverse fissure separates cerebrum from cerebellum Lobes of Cerebrum Each hemisphere is into lobes named after bones covering them Frontal Parietal Temporal Occipital Insula lobe located w/in lateral sulcus; covered by frontal, parietal & temporal lobes Functions of Cerebrum interpretation initiating voluntary movements storing & retrieving memory reasoning intelligence personality 9

10 Functional Regions of Cerebral Cortex Cerebral Cortex thin layer of gray matter on surface of cerebrum; Divided into motor, sensory & association areas Motor Areas Primary Motor Areas frontal lobes;anterior to central sulcus controls voluntary muscles; skeletal Broca s Area anterior to motor area left hemisphere controls muscles needed for speech Frontal Eye Field above Broca s area controls voluntary movements of eyes & eyelids Sensory Areas Sensory fibers cross over; R hemisphere interprets info from L hemisphere Sensory Area parietal lobe; posterior to central sulcus interprets sensations on skin Visual Area occipital lobe interprets vision Auditory Area temporal lobe interprets hearing 10

11 Association Areas regions of cortex that are not primary motor or sensory areas analyze & interpret sensory experiences provide memory, reasoning, verbalization, judgment, emotions Frontal Lobe Association Areas concentrating planning problem solving consequences of behavior Parietal Lobe understanding speech word expression feelings Association Areas Temporal Lobe remember visual scenes, music & complex patterns Occipital Lobe analyze visual patterns & recognition Hemisphere Dominance both analyze impulses & send impulses to opposite side of body in over 90% of population, left hemisphere is dominant in right handed people In most Left hemisphere controls speech writing reading verbal skills computational skills Nondominant hemisphere controls nonverbal tasks motor tasks provides emotions 11

12 Memory Consequences of learning & being able to access it later Short Term working memory closed circuit circuit is stimulated over and over when impulse flow stops, memory disappears Long Term repeated stimulation changes neuron structure strengthens synaptic transmission basal ganglia masses of gray matter deep within cerebral hemispheres forms from forebrain known as caudate nucleus, putamen, & globus pallidus produce dopamine control certain motor activities Basal Nuclei Diencephalon between cerebral hemispheres & brainstem surrounds 3rd ventricle mostly gray matter contains the following thalamus hypothalamus optic tracts optic chiasm infundibulum posterior pituitary mammillary bodies pineal gland 12

13 Diencephalon Thalamus receives & directs sensory impulses to appropriate part of cerebral cortex for interpretation Hypothalamus maintains homeostasis by regulating visceral activities links nervous & endocrine systems Limbic System Located in diencephalon Functions controls emotions produces feelings recognizes life threating condition Brainstem Consist of midbrain, pons, medulla oblongata Attaches brain to spinal cord 13

14 Midbrain between diencephalon & pons contains bundles of fibers that join brainstem & spinal cord w/ higher brain contains gray matter that acts as reflex centers cerebral aqueduct connects 3 rd & 4 th ventricles cerebral peduncles bundles of nerve fibers corpora quadrigemina 4 dome protrusions that are centers for visual & auditory reflexes Brainstem Pons rounded bulge on underside of brainstem between medulla oblongata & midbrain regulate rate & depth of breathing 14

15 Medulla Oblongata enlarged continuation of spinal cord conducts ascending & descending impulses between brain and spinal cord contains cardiac, vasomotor, & respiratory control centers contains various nonvital reflex control centers (coughing, sneezing, swallowing & vomiting) Reticular Formation network of nerve fibers w/in brain stem connects to hypothalamus, basal nuclei, cerebellum, & cerebrum filters incoming sensory information arouses cerebral cortex into state of wakefulness injury causes unconsciousness Types of Sleep Slow Wave person is tired decreasing activity of reticular formation restful dreamless reduced blood pressure & respiratory rate ranges from light to heavy alternates with REM sleep between minutes Rapid Eye Movement (REM) some areas of brain active heart and respiratory rates irregular dreaming occurs 5-15 minutes 15

16 Sleep Disorders Insomnia inability to sleep Narcolepsy extreme daytime sleepiness Sleep apnea upper airway collapses during sleep; blocks breathing; snoring Parasomnias sleep walking & sleep talking Restless leg syndrome repetitive leg jerks; leg pain at night Sleep paralysis inability to move a few minutes after waking Cerebellum 2 hemispheres inferior to occipital lobes posterior to pons & medulla oblongata vermis connects hemispheres cerebellar cortex gray matter arbor vitae white matter cerebellar peduncles allows communication between other parts of CNS coordinates skeletal muscle activity maintains posture Peripheral Nervous System Nerves that branch from CNS and connect to other body parts 16

17 Structure of Peripheral Nerve CT surrounding bundles of nerve fibers Epineurium outer most layer Perineurium surrounds each fascicle Endoneurium surrounds each axon Blood vessels located in epineurium & perineurium Nerve Fiber Classification Sensory Nerves conduct impulses to CNS Motor Nerves conduct impulses from CNS to muscles & glands Mixed Nerves contain both sensory & motor nerve fibers; most nerves Review terms Afferent towards Efferent - away Nerve Fiber Classification Nerve fibers into 4 general groups General somatic efferent fibers carry motor impulses from CNS to skeletal muscles General visceral efferent fibers carry motor impulses away from CNS to smooth muscles & glands General somatic afferent fibers carry sensory impulses to CNS from skin & skeletal muscles General visceral afferent fibers carry sensory impulses to CNS from blood vessels & internal organs 17

18 Nerve Fiber Classification Nerve fibers into 3 specialized groups Special somatic efferent fibers carry motor impulses from brain to muscles used in chewing, swallowing, speaking, & facial expressions Special visceral afferent fibers carry sensory impulses to brain from olfactory & taste receptors Special somatic afferent fibers carry sensory impulses to brain from receptors of sight, hearing, & equilibrium receptors Cranial Nerves 12 pairs 1 st & 2 nd pair originate w/in cerebrum others form from brainstem Oh Oh Oh To Touch And Feel Very Good Velvet AH Cranial Nerves Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulocochlear Glossopharyngeal Vagus Accessory & Hypoglossal 18

19 Cranial Nerves I and II Olfactory (I) sensory only impulses associated w/smell receptors located in upper nasal cavity Optic (II) sensory only impulses associated w/vision Cranial Nerves III and IV Oculomotor (III) motor impulses to eye muscles that raise eyelids move the eyes focus lens adjust pupil Trochlear (IV) smallest cranial nerves motor impulses to superior oblique muscles that moves the eye downward Cranial Nerve V Trigeminal (V) largest cranial nerve mixed nerves; sensory to face & motor to chewing muscles opthalmic division sensory from surface of eyes, tear glands, scalp, forehead, & upper eyelids maxillary division sensory from upper jaw, teeth, lip, palate, & skin of face mandibular division sensory from scalp, skin of jaw, lower teeth, gum, & lip motor to muscles of mastication 19

20 Cranial Nerves VI and VII Abducens (VI) motor impulses to lateral rectus muscles that move eyes to outside Facial (VII) mixed sensory from taste receptors motor to muscles of facial expression, tear glands, & salivary glands Cranial Nerves VIII and IX Vestibulocochlear (VIII) sensory forms 2 branches Vestibular - sensory from equilibrium receptors of ear Cochlear - sensory from hearing receptors of inner ear Glossopharyngeal (IX) mixed sensory from pharynx, tonsils, tongue, & carotid arteries motor to salivary glands & muscles of pharynx Vagus (X) mixed somatic motor to muscles of speech & swallowing autonomic motor to viscera sensory from pharynx, larynx, & esophagus, Cranial Nerve X 20

21 Cranial Nerves XI and XII Accessory (XI) 2 branches cranial- motor to muscles of soft palate, pharynx, larynx spinal motor to muscles in neck & back Hypoglossal (XII) motor to muscles of the tongue controls speaking, chewing, & swallowing Spinal Nerves mixed nerves provides 2-way communication between brain & limbs 31 pairs 8 cervical (C1 to C8) 12 thoracic (T1 to T12) 5 lumbar (L1 to L5) 5 sacral (S1 to S5) 1 coccygeal (Co) Adult spinal cord ends between L1-L2 vertebrae lumbar, sacral & coccygeal nerves form cauda equina & are called descending nerves each spinal nerve forms from fusion of 2 roots Dorsal root posterior branch of axons of sensory neurons Dorsal root ganglion lateral enlargement cell bodies of sensory neurons Ventral root anterior branch of axons of motor neurons;cell bodies are in spinal cord Spinal Nerves 21

22 Nerve Plexus Nerve plexus branching networks formed by spinal nerves; not in T2-T12 Cervical Plexus C1-C4 supply muscles & skin of the neck contributes to phrenic nerve associated w/diaphragm Brachial plexuses C5-T1 supply impulses to upper limbs Lumbosacral plexuses T12-S5 supply impulses from lumbar region to pelvic cavity Brachial Plexus Lumbosacral Plexus 22

23 Autonomic Nervous System functions w/out conscious effort controls visceral activities regulates smooth & cardiac muscles, & glands efferent fibers typically lead to ganglia outside CNS 2 Divisions sympathetic prepares body for fight or flight situations; stress parasympathetic functions under normal restful conditions; maintains homeostasis Autonomic Nerve Fibers all are motor (efferent) includes 2 neurons preganglionic fibers axons of preganglionic neurons leave CNS to synapse with postganglionic fibers axons of postganglionic neurons synapse w/viscera effector Control of Autonomic Activity Controlled largely by CNS Medulla oblongata regulates cardiac, vasomotor & respiratory activities Hypothalamus regulates visceral functions; renal & digestive Limbic system & cerebral cortex control emotions 23

24 Life-Span Changes Brain cells begin to die before birth Over average lifetime, brain shrinks 10% Most cell death occurs in temporal lobes By age 90, frontal lobe has lost half its neurons Number of dendrites Decreased levels of neurotransmitters Fading memory Slowed responses and reflexes Changes increase risk of falling Sleep problems common; decrease in REM sleep Diseases or Disorders Lou Gehrig s disease amyotrophic lateral sclerosis (ALS) Motor neurons degenerate & replaced w/ fibrous tissue; decline of muscle function Genetic; abnormal enzyme doesn t break down O 2 free radicals Anencephaly fetus w/brainstem but lacks upper brain structures Lissencephaly smooth brain; lack of convolutions causes retardation & seizures Diseases or Disorders Cerebral palsy motor impairment caused by blocked cerebral blood vessels Parkinson disease dopamine producing neurons degenerate; leads to tremors; muscle rigidity Dementia Alzheimer 24

25 Cerebral Injuries Concussion brain jarred against cranium loss of consciousness temporary loss of memory headache recovery usually complete Cerebrovascular Accident stroke sudden interruption in blood flow brain tissues die 25