Central nervous system

brain stem major functions

-acts as a passageway for all ascending and descending tracts between cerebrum and spinal cord -contains nuclei of cranial nerves III to XII -regulates automatic behaviours required for survival such as respiration

cerebral hemispheres are composed of

-an outer cerebral cortex, inner region of cerebral white matter, and some nuclei embedded deep within white matter - these hemispheres in a superior view are separated by a longitudinal fissure

white matter midbrain

-ascending tracts occupy the white matter of midbrain behind the cerebral peduncles -several nuclei embedded within white matter, some of which are associated with cranial nerves III, IV, V -other major nuclei include red nucleus and substantia nigra.

CNS: brain consists

-brain consists of cerebral hemispheres, diencephalon, cerebellum, brain stem

CNS: brain stem includes

-brain stem includes midbrain, pons, medulla oblongata

medulla oblongata in terms of gray and white matter

-composed of gray and white matters the arrangement of which is the same as the spinal cord in the inferior half of the medulla. - in superior half of medulla, gray matter is embedded within the white matter as clusters of nuclei. -most of these nuclei are associated with cranial nerve V, VIII, IX, X, XI, XII. - inferior olivary nucleus: relay center for properioceptive information to the cerebellum, and the nucleus gracilis and nucleus cuneatus both of which are associated with the medial lemniscus tract

cerebellum

-contained within the posterior cranial fossa, underneath the tentorium cerebelli, behind the medulla and pons from which is separated by the 4th ventricle -consists of 2 cerebellar hemispheres connected by a worm like structure, vermis. -attached to the brain stem by 3 pairs of cerebellar peduncles. -superior cerebellar peduncles carry axons that connect the cerebellum to the red nucleus of the midbrain and thalamus. -middle cerebellar peduncles connect the pontine muclei of pons to the cerebrum -inferior cerebellar peduncles carry bundles of axons travelling between medulla and cerebellum such as spinocerebellar tracts

classification of nervous system: CNS

-includes the brain and spinal cord -brain stem in turn includes midbrain, pons, medulla oblongata

diencephalon

-located between cerebral hemispheres and midbrain -includes thalami and other structures surround third ventricle such as hypothalamus and epithalamus.

medulla oblongata

-pyramidal in shape, separated from pons by transverse sulcus, ponto-medullary sulcus, superiorly and continuous with the spinal cord inferiorly. -viewing anteriorly, there is an elevation, pyramid on either side of median anterior fissure formed by pyramidal tracts. -lateral to the pyramid is second elevation, olive, overlies the inferior olivary nucleus. -cranial nerves IX, X, XI, XII emerge from anterolateral surface of medulla

spinal cord starts from where and ends where? in newborn infants? why?

-starts from medulla oblongata at the level of foramen magnum and ends at the levels of LI-LII intervertebral disc -in newborn infants, it extends low as the level of LIII. B/C elongation of the spinal cord stops at the age of 4-5 but growth of the vertebral column continues.

spinal cord length?

-terminal cord like part of CNS located in vertebral canal -43 to 45 cm, occupying the upper two-thirds of the vertebral canal

archanoid mater

-thin layer of loose connective tissue attached to inner surface of dura mater. -separated from pia mater by subarchnoid space that mainly contains CSF. -subarchnoid space surrounding the spinal cord continues inferiorly and ends at the level of vertebra SII. space between end point of spinal cord (vertebrae LI-LII) and vertebra SII is called lumbar cistern and contains roots of spinal nerves and CSF -arachnoid granulations (villi) are small finger like projectiosn of arachnoid mater mostly on superior part of the brain that drain the CSF into the dural sinuses

1)lateral horns of T1 TO L2= 2) lateral horns of S2 to S4=

1) carry cell bodies of sympathetic neurons 2) house the cell bodies of parasympathetic neurons

4 ventricles in the brain:

1) lateral ventricles: each lateral venticles is connected to the 3rd venticle thru interventircular foramen of Monro. 2)third ventricle: irregular and narrow space located within diencephalon between left and right thalami. ventricle is connected to the 4th ventricle through the cerebral aqueduct that passes through the midbrain 3)fourth ventricle: diamond shaped space, bounded by pons and upper part of medulla anteriorly and cerebellum posteriorly. 4th ventricle is connected to the central canal of spinal cord (inferiorly) to third ventricle (superiorly) and through two lateral apertures (foramina of luschka) and a median aperture (foramen of Magendi) to subarchnoid space

3 main sulci on each cerebral hemisphere

1)central sulcus: separates frontal lobe from the parietal lobe 2)lateral sulcus: superior boundary of the temporal lobe and mainly separates it from the frontal lobe 3)parieto-occipital: sulcus separates the parietal lobe from the occipital lobe

pyramidal and extrapyramidal tracts consist of ___ sets of neurons

2

Central nervous system division and subdivision

Brain= i)forebrain (prosencephalon)= telencephalon (cerebrum; lateral ventricles) and diencephalon (structures surrounding the 3rd cerebral ventricle) ii)midbrain (mesencephalon)= N/A; cerebral aqueduct iii)hindbrain (rhombencephalon)= metencephalon (pons and cerebellum; fourth ventricle) and myelencephalon (medulla oblongata; fourth ventricle) Spinal cord= ...central canal

meninges

CNS is surrounded and protected by 3 membranes of connective tissue known as meninges: dura mater, arachnoid mater, pia mater from outside to inside.

upper motor neurons (UMNs) of the pyramidal tracts reside

in the motor cortex of the cerebral hemispheres.

peripheral nervous system

includes the spinal and cranial nerves and associated ganglia

CNS processes the _____ _____ and ____ ____ messages and is also involved in higher mental activities such as ____, _____, and ____.

incoming sensory outgoing motor learning, memory, and reasoning

in some segments of spinal cord there is a third horn between the ventral and dorsal horns known as what and example

lateral horn T1 TO L2 S2 TO S4

denticulate ligaments

lateral triangular extensions of the pia mater that anchor spinal cord to the deep surface of the arachnoid and dura maters.

cerebrum

left and right cerebral hemispheres, diencephalon contained within the anterior and middle cranial fossae

hypothalamus

located inferior and medial to the thalamus and functions as the center of autonomic nervous system thus controlling emotion, body temp, eating, drinking, etc. regulates the function of major components of endocrine system through pituitary gland

What nerve fibres carry signals away from CNS?

motor or efferent

the three columns contain bundles of ____ nerve fibers, ___, that travel along the length of the spinal cord.

myelinated tracts

white matter is located deep to the cortex and is formed by the ____ ______ ____. nerve bundles can be classified into 3 groups: 1) 2) 3)

myelinated nerve bundles 1) association fibers : join diff parts of the same cerebral hemispheres 2) commissural fibers: connect different gyri of one hemisphere to the corresponding gyri of the other hempisphere. corpus callosum is the largest commissural fiber bundle located at bottom of longitudinal fissure 3) projectional fibers : ascending (sensory) and descending (motor) fibers connecting cortex to the lower centers of CNS. ex. internal capsule, thick band of white matter located between the caudate nucleus and putamen anteriorly, thalamus and globus pallidus posteriorly.

a cluster of nerve cell bodies embedded within the CNS

nucleus

gray matter of pons

organized as nuclei embedded in the white matter

rubrospinal tract

part of extrapyramidal pathways the UMNs of which reside in the red nucleus of midbrain and their axons decussate at the level of pons and then descend through the medulla oblongata and lateral column of the spinal cord. axons synapse with the LMNs of the ipsilateral ventral horn of the spinal cord

cortiscospinal tract

part of pyramidal pathways the UMNs of which resise in the motor cortex of the cerebrum and their axons descend through the brain stem. majority of these axons decussate at the level of caudal medulla oblongata and continue in the lateral column of the spinal cord as the lateral corticospinal tract. these axons synapse with LMNs of ipsilateral ventral horn of the spinal cord. rest of the axons of the corticospinal tract continue to descend in the ventral column of the spinal cord as the ventral corticospinal tract that decussate before synapsing with the LMNs of the contralateral ventral horn of the spinal cord.

other major nuclei include but not limited to the ____ _____ that act as a relay center for motor pathways between the cerebrum and cerebellum that coordinates voluntary movements

pontine nuclei

nervous system

receiving and processing impulses from the external or internal environments and initiating an appropriate response

pineal gland

regulates the circadian rhythm and distribution of pigment melanin in the skin.

pons

related to cerebellum (posteriorly), medulla oblongata (inferiorly) and midbrain (superiorly). anterior surface is convex and carries a longitudinal sulcus, basilar sulcus, occupied by the basilar artery. cranial nerves VI, VII, VIII emerge from the ponto-medullary sulcus, whereas cranial nerve V appears at the anterolateral surface of the pons

major motor tracts of spinal cord

relay motor instruction from cerebral cortex to the spinal cord. tracts classified as pyramidal and extrapyramidal tracts

What nerve fibres carry information towards CNS?

sensory or afferent

major sensory tracts (pathways) of the spinal cord:

sensory tracts of the spinal cord relay the sensory information from sensory receptors to the sensory areas of the brain. these tracts consist of three sets of neurons (with exception of dorsal spinocerebellar tract). 1st order neuron reisdes in the dorsal root ganglion of spinal nerve and conducts impulses from sensory receptors to the spinal cord or medulla oblongata. 2nd order neuron is located either in dorsal horn of spinal cord or within the medulla oblongata and relays impulses to the thalamus. 3rd order neuron residing in the thalamus conveys impulses to the sensory areas of the cerebral cortex

gray matter of spinal cord

shaped like H with a ventral (anterior ) horn and a dorsal (posterior) horn on each side

epithlamus

small region posterior and superior to the thalamus and mainly consists of the pineal gland

from functional point of view, nervous system is composed of the ___ and ____ (____) ____ ____.

somatic and visceral (autonomic) nervous systems

caudal part of the neural tube forms the ___ ____ whereas the cephalic part forms the _____ ____. Lumen of neural tube in brain is ____ and develops into ___ ____. This lumen in spinal cord remains narrow and forms ____ ____

spinal cord cerebral vesicles larger cerebral ventricles central canal

internal features of the spinal cord

spinal cord consists of the gray and white matters

section of the spinal cord that gives rise to a pair of a spinal nerve is known as a ____ ____ _____ thus there are ____ spinal cord segments including: ___ _____ segments, C_-C_ ___ _____ segments, T_-T_ ___ _____ segments, L_-L_ ___ _____ segments, S_-S_ ___ _____ segment, C_

spinal cord segment 31 8 cervical segments, C1-C8 12 thoracic segments, T1-T12 5 lumbar segments, L1-L5 5 sacral segments, S1-S5 1 coccygeal segment, Co

external features of the spinal cord

spinal cord when viewed externally looks like cylinder with two enlargements in the cervical and lumbar regions

lumbar enlargement

supply the lower limbs

dorsal horns contain

the cell bodies of the sensory neurons. neurons receive information from the sensory neurons residing the dorsal root ganglia whose axons form the dorsal root of the spinal nerves

dorsal rootlets merge to form what

the dorsal (sensory) root of the spinal nerve

ventral rootlets join to form what

the ventral (motor) root of the spinal nerve

dura mater

thick layer of dense connective tissue that attached to the inner surface of neurocranium in the skull, but separate from walls of vertebral canal by epidural space. dura mater surrounding the spinal cord ends at the level of vertebra SII. dura mater within the skull is composed of an outer periostal layer and an inner menigneal layer. Periosteal layer is attached to inner surface of cranial cavities. Meningeal layer separates from the periosteal layer in several locations to form two distinct structures. 1)dural relfections: form incomplete partitions to divide the cranial cavity into some compartments i) falx cerebri: sagittal sickle shape reflection of dura mater that occupies longitudinal fissure of cerebrum and partially separates cerebral hemispheres ii) tentorium cerebelli: tent like horizontal sheet intervenes between cerebellum and occipital lobe of the cerebral hemispheres. notched anteriorly to provide a passage for midbrain iii) falx cerebelli : less prominent vertical reflection of the dura in sagittal plane along the vermis that partially separates cerebellar hemispheres 2)dural sinuses: drain venous blood of the brain to circulatory system

cerebellar cortex

thrown into folds that appear like leaf like ridges, folia, on the surface of the cerebellum. main function of the cerebellum includes coordination of voluntary movements and maintenance of posture and balance

2 main groups of ____ in the white matter of the spinal cord: 1)____ (____) ______: 2) _____ (____) _____:

tracts 1) ascending (sensory) tracts: convey messages from the periphery to the upper centers of the nervous system. e.g. dorsal (posterior) spinocerebellar tract, dorsal column (medial lemiscus) tract, and lateral spinothalamic tract. 2) descending (motor) tracts: convey messages from the upper centers of the nervous system to the periphery, e.g. lateral and ventral corticospinal tracts

on the surface of the spinal cord two main longitudinal grooves can be identified:

ventral (anterior) median fissure and dorsal (posterior) median sulcus

either side of the ventral median fissure the ____ (___) ____ of the spinal nerves emerges.

ventral (motor) rootlets

each spinal nerve is formed by the union of the _____ and ____ roots.

ventral and dorsal roots

axons of the LMNs exit the spinal cord as the ___ ____ of the spinal nerve and target skeletal muscles

ventral root

upper motor neurons of the extrapyramidal tract are housed

within the brain stem and cerebellar cortex

describe gray and white matter in the brain

a thin outer shell of gray matter, cortex, covers the core of white matter

anterior spinothalamic tract

another ascending tract with similar neuronal design, origin, course and termination that conveys the impulses of non discriminative touch

lower motor neurons (LMNs) of both pyramidal and extrapyramidal tracts are located in the

anterior horn of the spinal cord

red nucleus

associated with rubrospinal tract as part of the extrapyramidal pathways

white matter

bundles of myelinated nerve fibers known as tracts

components of the CNS: brain and spinal cord, are enclosed and protected by what?

by bony cavities, the cranial cavity and the vertebral cavity

main components of basal ganglia

caudate nucleus putamen globus pallidus =nuclei involved in coordination of motor function

ventral horns contain

cell bodies of the motor neurons that their axons form the motor (ventral) roots of the spinal nerves

from structural point of view, nervous system divided into the ___ ____ ___ (__) and the ___ ____ ____ (__).

central nervous system (CNS) peripheral nervous system (PNS)

gray matter of cerebellum forms

cerebellar cortex that surrounds the white matter in which deep cerebellar nuclei are located.

gray matter forms the ____ ____ and clusters of nuclei within the white matter that are collectively known as ___ ____ (nuclei)

cerebral cortex basal ganglia

choroid plexus is responsible for secretion of _____ ______ (___) that circulates in all __ ventricles, central canal of the spinal cord, subarchnoid space.

cerebrospinal fluid (CSF) 4

cerebral ventricles house a specialized vascular plexus known as the

choroid plexus

brain stem

composed of medulla oblongata, pons, midbrain from inferior to superior

gray matter

composed of nerve cell bodies, bundles of unmyelinated nerve fibers and non-neuronal supportive cells called neuroglia

extrapyramidal tracts

conduct signals that regulate those body movements that are subconscious or postural in nature. includes the rubrospinal, tectospinal, vestibulospinal, and reticulospinal tracts

dorsal spinocerebellar tract

conducts impulses concerned with unconscious proprioception (sense of position) collected from joints and muscles of the lower limb and trunk to the cerebellar cortex. 1st order neuron of this tract located in the dorsal root ganglion of spinal nerve synapses with 2nd order neuron that resides in the dorsal horn of spinal cord. axons of 2nd order neurons form dorsal spinocerebellar tract that travels in the lateral column (funiculus) of the spinal cord. this tract ascends through the medulla oblongata and ends to the ipsilateral cerebellar cortex after passing through the inferior cerebellar peduncle. Upper limb is conveyed by a different tract to the cerebellar.

dorsal column (medial lemniscus) tract)

conducts the nerve impulses for conscious properioception, collected from joints and muscles except temporomandibular joint and discrimnative (fine) touch from the entire body (except most of the head region) to cerebral cortex. 1st order neuron of this tract is located in dorsal root ganglion of spinal nerve. axon of this neuron ascends in the dorsal column of the spinal cord and synapses with second order neuron in the nucleus gracilis and nucleus cuneatus within the medulla oblongata. axon of the second order neuron decussates (crosses the midline) and ascends through the brain stem as the medial lemniscus. medial lemniscus synapses with 3 order neuron in the thalamus. axon of the 3rd order neuron projects to the sensory area of the cerebral cortex for conscious sensation

midbrain

connects to the pons inferiorly and diencephalon superiorly. anterior aspect of midbrains presents 2 columns: cerebral peduncles between which cranial nerve III emerges and these columns contain descending tracts such as corticospinal and corticobulbar tract collectively known as crus cerebri on posterior aspect of midbrain, 4 elevators known as superior and inferior colliculi that are relay center for visual and auditory reflexes

spinal cord tapers down inferior to the lumbar enlargement forming the ___ _____

conus medullaris

pyramidal tracts

convey impulses for the control of skeletal muscles of the limbs and trunk and include lateral and ventral corticospinal tracts

lateral spinothalamic tract

conveys the impulses concerned with pain and temperature collected from the entire body except head region. 1st order neuron of this tract is located in the dorsal root ganglion of the spinal nerve. axon of this neuron synapses with 2nd order neuron in the dorsal horn of the spinal cord. axon of the 2nd order neuron decussates (crosses the midline) and ascends through the lateral column of the spinal cord as the lateral spinothalamic tract. this tract synapses with the 3rd order neuron in the thalamus. axon of the 3rd order neuron projects to the sensory area of the cerebral cortex where the information is processed into conscious sensation

Peripheral nervous system division and subdivision

cranial nerves: 12 pairs spinal nerves: 31 pairs

pia mater

delicate, thin layer of connective tissue that is intimately in touch with the surface of the brain and spinal cord. carries blood vessels to the depth of the nervous tissues of CNS

what is each lobe responsible for

different aspects of brain functions, main role is to initiate motor impulse (frontal lobe), to receive general sensory stimuli (parietal lobe), auditory impulses (temporal lobe) and visual impulses (occipital lobe)

either side of the dorsal median sulcus the ____ (____) _____ of the spinal nerves emerge.

dorsal (sensory) rootlets

each dorsal root of the spinal nerve is associated with a ganglion, the ____ _____ ______

dorsal root ganglion

thalamus

egg shaped structure consisting of a group of nuclei most of which are sensory. thalamus relays all senses except smell to certain sensory areas of the cerebral hemisphere

nervous system is developed from

embryonic neural tube

filum terminale:

extension of the pia mater arising from the conus medualris that extends inferiorly and fuses with arachnoid and dura maters to anchor the spinal cord to coccyx.

white matter of pons

formed by the ascending and descending tracts.

4 main lobes of cerebral hemisphere

frontal parietal occipital temporal

substantia nigra

functionally linked to the basal ganglia regulating the voluntary movements.

aggregation of nerve cell bodies outside the CNS

ganglion

cervical enlargements

give rise to the nerves innervating the upper limbs

nervous tissue in the CNS is organized as ___ and ____ matters.

gray and white

right and left halves of the gray matter are connected by a narrow strip, ___ _____, containing the central ____

gray commissure central canal

white matter of the spinal cord surrounds ____ _____ and is organized as ___, ___, and ____ ____ (_____) on each half of the spinal cord.

gray matter ventral, lateral and dorsal columns (funiculi)

describe gray and white matter in spinal cord

gray matter forms an H shaped inner core surrounded by white matter

outer surface of the cerebral hemispheres represents folds, ____, separated by furrows,____.

gyri sulci

dorsal root ganglion

housing the cell bodies of the sensory neurons