Divisions of the Nervous System

Transcription

1 Marieb s Human Anatomy and Physiology Marieb Hoehn Chapter 12 The Central Nervous System Lecture 19 1 Divisions of the Nervous System You are here CNS PNS 3 Brain Embryology & Overview Table & Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson,

2 Overview of the Brain Functions regulates visceral activities coordinates muscular movements interprets sensations determines perception stores memory carries out reasoning makes decisions determines personality Major Parts diencephalon thalamus hypothalamus brain stem midbrain (mesencephalon) pons medulla oblongata cerebellum cerebrum (two hemispheres) 5 Protection of the Brain The brain is protected Mechanically by The skull bones The meninges The cerebrospinal (CSF) fluid Biochemically by the blood-brain barrier Capillaries interconnected by tight junctions Astrocytes/ependymal cells control permeability of general capillaries/choroid capillaries May be obstacle to delivery of drugs May become more permeable during stress 6 Meninges of the Brain - dura mater outer, tough (anchoring dural folds) - Subdural space like interstitial fluid - arachnoid mater web-like - Subarachnoid space CSF - pia mater inner, delicate *Singular of meninges is meninx Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson,

3 Dural Folds Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 Falx Cerebri within longitudinal fissure; separates cerebral hemispheres Tentorium Cerebelli above cerebellum; separates occipital lobe from cerebellum 8 Ventricles of the Brain interconnected cavities within cerebral hemispheres and brain stem continuous with central canal of spinal cord filled with cerebrospinal fluid (CSF) lateral ventricles (1, 2) third ventricle (3) fourth ventricle (4) cerebral aqueduct 9 secreted by choroid plexus of ventricles (~500 ml/day) circulates in ventricles, central canal of spinal cord, and subarachnoid space completely surrounds brain and spinal cord clear liquid (more Na + and Cl -, but less K +, Ca 2+, glucose, and protein than plasma) nutritive and protective helps maintain stable ion concentrations in CNS Cerebrospinal Fluid 10 3

4 Flow of CSF (Monro) (Luscka) (Magendie) Know Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, Overview of the Cerebrum of the Brain Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, Over 85% of brain mass, with about 14 billion multipolar neurons in cortex - Lobes named for overlying bones. (See sulci above for divisions) 12 Functions of Cerebrum interpretation initiating voluntary movements storing memory retrieving memory reasoning center for intelligence and personality The cerebrum can be divided into several functional areas: - Motor (frontal cortex) - Sensory (parietal, occipital, and temporal cortex) - Association (all lobes) Points to keep in mind: - Each cerebral hemisphere receives information from, and sends information to, the opposite side of the body - Although symmetrical, the cerebral hemispheres are not entirely equal in function 14 4

5 Functions of Parts of Brain Part of Brain Motor areas Primary motor cortex (Precentral gyrus) Broca s area (motor speech area) Voluntary control of skeletal muscles Controls muscles needed for speech Major Function Frontal eye field Controls muscles needed for eye movement Sensory areas Cutaneous Sensory Area (postcentral gyrus) Receives somatic sensations Visual area (occipital lobe) Auditory area (temporal lobe) Association areas (all lobes) Basal nuclei Limbic system Diencephalon Thalamus Hypothalamus Brainstem Midbrain Pons Medulla Oblongata Reticular formation (system) Cerebellum Receives visual sensations Receives auditory sensations Analyze and interpret sensory experiences; coordinate motor responses memory, reasoning, verbalization, judgment, emotions Subconscious control certain muscular activities, e.g., learned movement patterns (a nucleus is a collection of neuron cell bodies in the CNS); putamen, globus pallidus, caudate controls emotions, produces feelings, interprets sensory impulses, facilitates memory storage and retrieval (learning!) gateway for sensory impulses heading to cerebral cortex, receives all sensory impulses (except smell) Vital functions associated with homeostasis Major connecting center between spinal cord and brain and parts of brainstem; contains corpora quadrigemina (visual and auditory reflexes) Helps regulate rate and depth of breathing, relays nerve impulses to and from medulla oblongata and cerebellum Contains cardiac, vasomotor, and respiratory control centers, contains various nonvital reflex control centers (coughing, sneezing, vomiting) Filters incoming sensory information; habituation, modulates pain, arouses cerebral cortex into state of wakefulness (reticular activating system) Subconscious coordination of skeletal muscle activity, maintains posture 15 Brain Sensory and Motor Areas * (Gnostic) Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 *Somatosensory = Somesthetic 16 Cerebral Cortex Motor/Sensory Homunculi Notice the relative amount of cortical tissue devoted to each sensory function. 17 5

6 Hemispheric (Cerebral) Lateralization Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Categorical hemisphere Representational hemisphere 18 Basal Nuclei (formerly basal ganglia) nuclei are masses of gray matter in CNS deep within cerebral hemispheres three nuclei: caudate nucleus and putamen, (together called the striatum), and the globus pallidus subconscious control certain muscular activities, e.g., learned movement patterns 1. Receive input from entire cerebral cortex. 2. Relay motor impulses originating in the substantia nigra, along with their own output, through the thalamus to the motor cortex to influence muscle movement. 19 Brain Cerebral White Matter Three types of myelinated tracts form cerebral white matter: 1. Association same hemisphere 2. Commisural between corresponding gyri in opposite hemispheres 3. Projection Ascending and descending tracts Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson,

7 Consists of portions of frontal lobe portions of temporal lobe hypothalamus thalamus basal nuclei other deep nuclei associated with sense of smell (less significant) Functions controls emotions produces feelings interprets sensory impulses facilitates memory storage and retrieval (learning!) The motivational system Limbic System Figure from: Saladin, Anatomy & Physiology, McGraw Hill, Memory A Memory is the persistence of knowledge that can be accessed (we hope!) at a later time. Memories are not stored in individual memory cells or neurons; they are stored as pathways called engrams, or memory traces that use strengthened or altered synapses. Immediate memory lasts a few seconds, e.g., remembering the earliest part of a sentence to make sense of it. Short-term memory (STM) lasts a few seconds to a few hours Working memory is a form of this (repeating a phone number over to yourself just long enough to dial it and then forget it!) Limited to a few bits of information (about 7-9). So, chunk up! Long-term memory (LTM) can last a lifetime Can hold much more information that STM Declarative (events and facts) Procedural (motor skills) 22 Diencephalon between cerebral hemispheres and brainstem surrounds third ventricle thalamus hypothalamus epithalamus optic tracts optic chiasm infundibulum posterior pituitary mammillary bodies pineal gland (Tectum) 23 7

8 Diencephalon - Thalamus Ventral nuclei - Posterior; relay for taste - Anterior and Lateral; voluntary motor - Forms wall of third ventricle - Crude interpretation center for pain, touch, pressure, temperature Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 Relay for hearing Relay for vision The gateway to the cerebral cortex. Major relay for sensory information coming into the cerebral cortex, roles in cortical arousal, learning, and memory 24 Diencephalon - Hypothalamus Hypothalamus - maintains homeostasis by regulating visceral activities (see list below for examples ) - Heart rate and blood pressure - Body temperature - Stimulation of the pituitary (links nervous and endocrine) - Water balance (ADH) - SM contraction (OT) - Feeding/satiety centers - Movement/secretions of glands and intestines - Sleep and wakefulness - Rage/aggression - Psychosomatic illness Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, Brain Stem Three Parts 1. Midbrain 2. Pons 3. Medulla Oblongata (Tectum) 26 8

9 Midbrain between diencephalon and pons contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain Major connecting center between spinal cord and brain and parts of brainstem (Tectum) cerebral aqueduct cerebral peduncles bundles of nerve fibers contains red nucleus (rubro-) and substantia nigra corpora quadrigemina centers for visual and auditory reflexes Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Origins of: CN III, IV 27 Pons rounded bulge on underside of brainstem between medulla oblongata and midbrain helps regulate rate and depth of breathing relays nerve impulses to and from 1. medulla oblongata and brainstem via longitudinal tracts 2. cerebellum via transverse tracts Origins of CN V, VI, VII, VIII 28 enlarged continuation of spinal cord running through foramen magnum of skull conducts all ascending (olive) and descending (pyramids - decussation) impulses between brain and spinal cord contains cardiac, vasomotor, and respiratory control centers Medulla Oblongata nucleus gracilis and nucleus cunneatus on dorsal side; sensory info, cross over, then send to thalamus Origins (nuclei) of: CN IX, X, XI, and XII 29 9

10 complex network of nerve fibers scattered throughout the brain stem extends into the diencephalon connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum filters incoming sensory information; habituation Reticular Formation modulates pain arouses cerebral cortex into state of wakefulness Ascending portion is called the reticular activating system (prefix = reticulo-) 30 integrates sensory information concerning position of body parts coordinates skeletal muscle activity helps to maintain posture May also be involved in several sensory, linguistic, emotional and non-motor functions virtually all fibers entering and leaving are ispsilateral Cerebellum Figure from: Saladin, Anatomy & Physiology, McGraw Hill, extends from the foramen magnum to 2 nd lumbar vertebra cervical and lumbar enlargements Spinal Cord Structure Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 cauda equina (horse s tail) thin nerve fibers that exit at different level than they arise (note that spinal cord does not extend into this area of the lumbar spine). Begins around L2 and extends to S5. Good area for lumbar puncture and collection of CSF

11 Meninges of the Spinal Cord Figures from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Denticulate ligaments branches of pia mater connecting to the arachnoid Space between the dura mater and the vertebral body is called the epidural space 35 Cross Section of Spinal Cord The spinal cord is a center for spinal reflexes aids in locomotion is a conduit for nerve impulses to and from the brain 36 Organization of Spinal Gray Matter You should know the major areas of gray matter of within the spinal cord: Posterior = sensory Lateral = visceral motor Anterior = somatic motor Figure from: Martini, Anatomy & Physiology, Prentice Hall,

12 Spinal Cord and Nerve Roots Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9 th ed., Pearson, 2013 Ventral root - axons of motor neurons whose cell bodies are in spinal cord Dorsal root - axons of sensory neurons in the dorsal root ganglion Dorsal root ganglion - cell bodies of sensory neurons 38 Organization of Spinal White Matter Figure from: Martini, Anatomy & Physiology, Prentice Hall, Tracts of the Spinal Cord Ascending tracts conduct sensory impulses to the brain Descending tracts conduct motor impulses from the brain to motor neurons reaching muscles and glands All the axons in a tract share a common origin and destination Tracts are usually named for their place of origin (1 st ) and termination (2 nd ) Most axons cross over during their travel. What will this mean clinically? 40 12

13 fasciculus cuneatus/gracilis - fine touch, pressure, body movement - cross (decussate) in medulla spinothalamic - crude pain, temperature, pressure, and touch - cross in spinal cord Ascending Tracts 3 spinocerebellar - subconscious coordination of muscle movements (1 st and 2 nd order neurons) - ipsilateral Decussation (crossing over) st, 2 nd, and 3 rd Order Sensory Neurons 1 st order neuron from receptor to the spinal cord (cell bodies are located in the dorsal root ganglion) 3 2 nd order neuron from spinal cord to thalamus 3 rd order neuron from thalamus to sensory cerebral cortex - terminate in the cerebral cortex Decussation corticospinal (direct, pyramidal) - voluntary movement of skeletal muscles - lateral cross in medulla - contralateral reticulospinal (indirect, extrapyramidal) - subconscious muscle tone, sweat glands - some lateral cross, anterior do not cross Descending Tracts Upper motor begin in precentral gyrus of cortex Decussation rubrospinal (indirect, extrapyramidal) - subconscious regulation of upper limb tone/movement - cross in brain (less important in humans) Upper MN Cerebral cortex to spinal cord Lower MN Spinal cord to effector Lower 43 13

14 Review The brain is protected by the Skull bones Meninges CSF Blood-brain barrier The meninges of the brain and spinal cord consist of the Dura mater Arachnoid (membrane) Pia mater 44 Review Important motor areas of cerebral cortex Precentral gyrus (Primary motor area) Broca s area Frontal eye field Important sensory areas of cerebral cortex Postcentral gyrus (Primary cutaneous sensory) Visual area (occipital lobe) Auditory area (temporal lobe) The spinal cord is a Center for spinal reflexes Conduit for nerve impulses to and from the brain 45 Review 46 14

15 Review Spinal cord contains nerve tracts Ascending = sensory Descending = motor 47 15