Anatomy and Physiology The Central Nervous System Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 12 The Central Nervous System Lecture 19 94 min, 51 slides

Lecture Overview The brain The spinal cord Overview Protection Meninges Ventricles and the CSF The structure of the major parts of the brain Functional areas of the brain The spinal cord Spinal meninges, and spinal reflexes Ascending and descending spinal tracts

Divisions of the Nervous System You are here CNS PNS

Brain – Embryology & Overview Table & Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013

Overview of the Brain Functions Major Parts regulates visceral activities coordinates muscular movements interprets sensations determines perception stores memory carries out reasoning makes decisions determines personality Major Parts cerebrum (two hemispheres) diencephalon thalamus hypothalamus brain stem midbrain (mesencephalon) pons medulla oblongata cerebellum

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 Two points of entry to brain: general capillaries and capillaries of the choroid plexuses.

Meninges of the Brain *Singular of meninges is meninx Dura mater – thick, collagenous membrane (about thickness of rubber kitchen glove) Arachnoid mater – simple squamous epithelium; loose meshwork of collagenous and elastic fibers spanning the gap (subarachnoid space) Pia mater – delicate membrane, close follows contours of nervous tissue that it covers. - dura mater – outer, tough (anchoring dural folds) - arachnoid mater – web-like - pia mater – inner, delicate *Singular of meninges is meninx - Subdural space – like interstitial fluid - Subarachnoid space – CSF Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013

Dural Folds Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013 Falx Cerebri – within longitudinal fissure; separates cerebral hemispheres Tentorium Cerebelli – above cerebellum; separates occipital lobe from cerebellum

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

Cerebrospinal Fluid 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+, Ca2+, glucose, and protein than plasma) nutritive and protective helps maintain stable ion concentrations in CNS About 500 ml of CSF produced per day; about 100-160 ml present at any time.

Flow of CSF Know (Luscka) (Magendie) (Monro) Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013

Overview of the Cerebrum of the Brain Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013 Over 85% of brain mass, with about 14 billion multipolar neurons in cortex Lobes named for overlying bones. (See sulci above for divisions)

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

Brain – Sensory and Motor Areas * 4 6 1 5 8 7 2 3 9 40 (Gnostic) 44 39 22 10 42 18 43 41 19 17 Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson, 2013 *Somatosensory = Somesthetic

Cerebral Cortex Motor/Sensory Homunculi Notice the relative amount of cortical tissue devoted to each sensory function.

Hemispheric (Cerebral) Lateralization Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Categorical hemisphere Representational hemisphere

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 Receive input from cerebral cortex, other subcortical nuclei, and each other. Output is through thalamus and (along with output from substantia nigra of midbrain) goes to the premotor and prefrontal cortex to influence muscle movement directed by primary motor cortex. Also seem to filter out incorrect or inappropriate responses of cognition and emotion. Receive input from entire cerebral cortex. Relay motor impulses originating in the substantia nigra (where is this?), along with their own output, through the thalamus to the motor cortex to influence muscle movement.

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, 9th ed., Pearson, 2013

Basal Nuclei nuclei are masses of gray matter in CNS deep within cerebral hemispheres caudate nucleus, putamen, globus pallidus (together called the corpus striatum) subconscious control certain muscular activities, e.g., learned movement patterns Relay motor impulses originating in the cerebral cortex and substantia nigra of the midbrain.

Limbic System The motivational system 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!) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 The motivational system

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)

Diencephalon between cerebral hemispheres and brainstem surrounds third ventricle thalamus hypothalamus epithalamus optic tracts optic chiasm infundibulum posterior pituitary mammillary bodies pineal gland (Tectum)

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, 9th 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

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, 9th ed., Pearson, 2013

Brain Stem Three Parts Midbrain Pons Medulla Oblongata (Tectum)

Brain Stem Three Parts Midbrain Pons Medulla Oblongata (Tectum)

Midbrain between diencephalon and pons contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain cerebral aqueduct cerebral peduncles – bundles of nerve fibers contains red nucleus (rubro-) and substantia nigra corpora quadrigemina – centers for visual and auditory reflexes Major connecting center between spinal cord and brain and parts of brainstem (Tectum) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Origins of: CN III, IV

Pons Origins of CN V, VI, VII, VIII rounded bulge on underside of brainstem between medulla oblongata and midbrain helps regulate rate and depth of breathing relays nerve impulses to and from medulla oblongata and brainstem via longitudinal tracts cerebellum via transverse tracts Origins of CN V, VI, VII, VIII

Medulla Oblongata 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 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

Reticular Formation 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 modulates pain arouses cerebral cortex into state of wakefulness Ascending portion is called the ‘reticular activating system’ (prefix = reticulo-)

Cerebellum 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 controls ipsilateral muscles (on the Cerebellum is connected to the brainstem by three pairs of peduncles: Superior peduncles connect to midbrain (output to midbrain and thalamus) Middle peduncles connect to pons (input from cerebrum about muscle movements and hearing/equilibrium from inner ear) Inferior peduncles connect to medulla (input from spinocerebellar tracts with proprioceptive information) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

Functions of Parts of Brain Part of Brain Major Function Motor areas Primary motor cortex (Precentral gyrus) Voluntary control of skeletal muscles Broca’s area (motor speech area) Controls muscles needed for speech Frontal eye field Controls muscles needed for eye movement Sensory areas Cutaneous Sensory Area (postcentral gyrus) Receives somatic sensations Visual area (occipital lobe) Receives visual sensations Auditory area (temporal lobe) Receives auditory sensations Association areas (all lobes) Analyze and interpret sensory experiences; coordinate motor responses memory, reasoning, verbalization, judgment, emotions Basal nuclei 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 Limbic system controls emotions , produces feelings, interprets sensory impulses, facilitates memory storage and retrieval (learning!) Diencephalon Thalamus gateway for sensory impulses heading to cerebral cortex, receives all sensory impulses (except smell) Hypothalamus Vital functions associated with homeostasis Brainstem Midbrain Major connecting center between spinal cord and brain and parts of brainstem; contains corpora quadrigemina (visual and auditory reflexes) Pons Helps regulate rate and depth of breathing, relays nerve impulses to and from medulla oblongata and cerebellum Medulla Oblongata Contains cardiac, vasomotor, and respiratory control centers, contains various nonvital reflex control centers (coughing, sneezing, vomiting) Reticular formation (system) Filters incoming sensory information; habituation , modulates pain, arouses cerebral cortex into state of wakefulness (reticular activating system) Cerebellum Subconscious coordination of skeletal muscle activity, maintains posture

Review of Major Brain Areas 12 1 2 3 11 4 5 6 10 (White part) 7 8 9

Summary from Last Lecture Part of Brain Major Function Brainstem   Medulla Oblongata (Embryology?) (Ventricles nearby?) Contains cardiac, vasomotor, and respiratory control centers Nucleus gracilis/cunneatus Origin of CN 9, 10, 11, 12 Pons Bridge between medulla and midbrain via transverse tracts (to cerebellum) and longitudinal tracts(to medulla/midbrain) Helps regulate rate and depth of breathing Origin of CN 5, 6, 7, 8 Midbrain Major connecting center between spinal cord and brain and parts of brainstem Contains corpora quadrigemina (visual and auditory reflexes) Origin of CN 3 and 4 Location of red nucleus (rubrospinal tract) Origin of substantia nigra Cerebellum Subconscious coordination of skeletal muscle activity, maintains posture Hemispheres separated by falx cerebelli and vermis Cerebellar peduncles (sup, middle, inf) attach to rest of brainstem Diencephalon (Embryology?) Thalamus Gateway (relay) for sensory impulses heading to cerebral cortex; hearing, vision, taste Crude interpretation for pain, touch, pressure, and temperature relay for motor information (voluntary) Forms walls of third ventricle Hypothalamus Vital functions associated with homeostasis, ANS, psychosomatic illness, feeding/satiety Connected to pituitary by infundibulum (pituitary stalk)

Spinal Cord Structure extends from the foramen magnum to 2nd lumbar vertebra cervical and lumbar enlargements 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. Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Spinal cord extends entire length of vertebral column early in fetal development, to L3 at birth, and to L1 in an adult. Thus, it occupies only the upper two thirds of the vertebral column in an adult. The lower third of the vertebral column is occupied by the cauda equina.

Meninges of the Spinal Cord Figures from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Space between the dura mater and the vertebral body is called the epidural space

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

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, 2001

Organization of Spinal White Matter Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

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 (1st) and termination (2nd) Most axons cross over during their travel. What will this mean clinically?

Ascending Tracts fasciculus cuneatus/gracilis - fine touch, pressure, body movement - cross (decussate) in medulla spinothalamic - crude pain, temperature, pressure, and touch - cross in spinal cord spinocerebellar - subconscious coordination of muscle movements (1st and 2nd order neurons) - ipsilateral 3 2 1 Decussation (crossing over)

1st, 2nd, and 3rd Order Sensory Neurons 1st order neuron – from receptor to the spinal cord (cell bodies are located in the dorsal root ganglion) 2nd order neuron – from spinal cord to thalamus 3rd order neuron – from thalamus to sensory cerebral cortex - terminate in the cerebral cortex 3 2 1 Decussation

Descending Tracts 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 rubrospinal (indirect, extrapyramidal) - subconscious regulation of upper limb tone/movement - cross in brain (less important in humans) Upper motor – begin in precentral gyrus of cortex Decussation Lower Upper MN – Cerebral cortex to spinal cord Lower MN – Spinal cord to effector

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

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

Review

Review Spinal cord contains nerve tracts Ascending = sensory Descending = motor 95 min, 47 slides