Anatomy - Nervous System

Front 1

Nervous System

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Regulatory system
-CNS
-PNS
-mostly composed of the nervous tissue organized with connective tissue wrappings
-infiltrated by blood vessels

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Nervous Tissue

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-neurons
-supporting cells(glial cells)

Front 3

Supporting cells

Back 3

-4 types in CNS
--astrocytes
--microglia
--ependymal cells
--oligodendrocytes
-2 types in PNS
--satellite cells
--schwann cells

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Astrocytes

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-form the blood-brain barrier - excludes harmful substances(toxins) from getting to neurons in the brain - acts as a selective barrier - lipid soluble substances(nonpolar) can cross the BBB - some drugs can if nonpolar
-in parkinsons the dopaminergic neurons are destroyed - dopamine is not released - dopamine can't be given for treatment b/c it cant cross BBB - so a nonpolar precursor to dopamine is given

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Microglia

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specialized macrophages that act as phagocytes to engulf and digest pathogens and cell debris
-only immune cells to fight pathogens

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Ependymal cells

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squamous-columnar shaped cells with cilia on their apical surfaces
-like ventricles- spaces within brain that contain cerebrospinal fluid
-involved in filtration of blood to produce csf
-cilia beat to circulate csf

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Oligodendrocytes

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-use their extensions to wrap around segments of axons to form myelin sheaths

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Satellite cells

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-surround neuronal cell bodies in PNS
-function is unknown but believed to maintain chemical environment of cell bodies

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Schwann cells

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-each wraps around a segment of an axon in PNS to produce myelin sheaths

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Neuron General Characteristics

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-amitiotic b/c lack centrioles
-most exhibiy longevity - they last a lifetime - exception = bipolar neurons in olfactory epithelium are replaced every 30-60 days
-high metabolic rate - depend on glucose and oxygen for energy production

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Parts of a neuron

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-cell body = soma = perikaryon
-dendrites
-axon

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Cell Body

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-biosynthetic center of a neuron - contains all cytoplasmic organelles except centrioles - prominent rough ER called Nissl Bodies
-protein synthesis occurs in cell body - referred to as biosynthetic center of a neuron

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Dendrites

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-processes that extend from neuronal cell body
-can be 1 or more per neuron
-do not have uniform diameters - appear tapered
-they receive signals called graded potentials that are converged toward the cell body
-referred to as receptive region of a neuron

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Axon

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-each neruon has only one axon extended from axon hilloc
-an axon may give off side branches called axon collaterals
-each axon gives off end branches called telodendria - end in bulbous structures called boutons, synaptic knobs, or axon terminals
-lacks nissl bodies + golgi apparatus
-cannot produce proteins especially those proteins exported to cell membrane or exterior - synth'd in cell body and transported to axon

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Axon

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Transport of substances from cell body down the axon is called anterograde transport
-transport of substances from axon to cell body is referred to as retrograde transport
-have uniform diameter - not tapered
-only region capable of generating and transmitting action potentials
--do not decrease in intensity over distance(graded potentials do)

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Tract or Nerve

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-In an unmyelinated axon the endoneurium surrounds the axon exterior to the axolemma
-in a myelinated axon the endoneurium is exterior to the myelin sheath

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Myelination of Axons in PNS

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-each schwann cells wraps around a segment of the axon
-concentric rings of the plasma membrane of the schwann cell are squeezed around that segment of axon w/ the nucleus and cytoplasm of schwann cells on the outer ring - called the neurilemma
-uses saltatory

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Myelination of axons in CNS

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-by oligodendrocytes
-each oligodendrocyte uses its cytoplasmic extensions to wrap around segemnts of axon leaving gaps
-the nucleus of oligodendrocytes is located far awya from myelinated axons - neurilemma is not formed
-uses saltatory

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Myelin Sheaths

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-whitish due to lipids + proteins in them
-poor conductors of electrical signals - during action potential transmission signals develop at nodes of ranvier
-signal 'jumps' from node to node - called saltatory conduction - faster than continuous conduction where every region of axolemma must be depolarized and action potential developed

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Phases of an Action Potential

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1 - resting membrane potential
2 - depolarization phase
3 - repolarization phase

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Resting Membrane Potential

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-established by the partial nature of the plasma membrane(axolemma in axon) to K+ ions - membrane is more permeable to K+ than Na+ - so K+ moves down the concentration gradient
-more K+ leaves cell than Na+ entering cell - negative inside charge

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Depolarization Phase

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-when neuron is stimulated, Na+ channels open - sodium influx
-when threshold potential is reached expolsive entry of Na+ into cells, once threshold potential reaches certain level action potential is generated and depolarization ends

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Repolarization Phase

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-closing of the Na+ channels and opening of K+ channels - Na+ influx stops and potassium efflux starts
-membrane potential goes below the RMP because channels are slow to close - called hyperpolarization/ undershoot
-Na+/K+ pump works to maintain the RMP

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Nerve Grouping Criteria(PNS)

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1 diameter - larger the diameter -> lower resistance to current flow - larger axons conduct nerve impulses faster than smaller axons(increase in resistance)
2 - degree of myelination - heavily myelinated axons employ saltatory conduction which is faster than continuous conduction of unmyelinated axons

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Cerebrum

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83% of brain mass
shallow grooves = sulci
deeper grooves = fissures
longitudinal fissure divides into 2 hemispheres - left and right - held together by corpus callosum

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Hemisphere Division

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5 lobes
-frontal lobe
-pparietal lobe
-temporal lobe
-occipital lobe
--all visible externally
-insule
--cannot be viewed externally - buried deep into hemisphere covered by fronal, parietal, and temporal lobes
---located inferior to lateral fissure - separates frontal lobe/parietal lobe from temporal lobe below

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Cerebral Hemisphere

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3 Divisions
-outer cerebral cortex
-inner white cerebral matter
-basale nuclei
3 major functional areas
-motor areas
-sensory areas
-association areas

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Cerebral Cortex

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-outermost region of cerebral hemisphere including all of the convolutions seen on the cerebrum
--because of convolutions the surface area or cerebral cortex is increased
--40% of total brain mass
-composed of gray matter - consists of unmyelinated parts of neurons - cell body & dendrites

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Motor Areas

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All in frontal lobe
-primary motor cortex
-premotor cortex
-Broca's area
-frontal eye field

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Primary Motor Cortex

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-located in precentral gyrus - in front of central sulcus(separates frontal & parietal lobe)
-contains large neurons called Pyramidal cells - form thick tracts called Pyramidal tracts that descend toward the spinal cord and the tracts decussate(cross over) before they enter the spinal cord
--pyramidal tracts control voluntary movement of skeletal muscle
---the decussation explains the contralateral control of voluntary skeletal muscle movements by the cerebral hemisphere
----the precentral gyrus in left cerebral hemisphere contains the pyyamidal cells that give off pyramidal tracts that cross over to control the voluntary movement on the right side of the body and vice versa - damage to left precentral gyrus = loss of voluntary movement on right side of body - right side paralysis(paralysis on one side of body = hemiparalysis)

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Premotor Cortex

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-'memory bank' for skilled skeletal muscle movement that is repetitious or patterned in nature ex. playing an instrument

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Broca's Area

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'motor speech area' - controls skeletal muscle involved in speech production - exists in only one cerebral hemisphere - left in most people

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Frontal eye field

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in frontal lobe
-controls the extrinsic eye muscles which control voluntary movement of the eye

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Sensory Areas

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Where sensory inputs via sensory pathways are delivered to the cerebral cortex for 'interpretation'
-each sensory area is associated with its own association area
-primary somatosensory cortex
-primary visual cortex
-primary auditory cortex
-primary olfactory focrtex
-primary gustatory cortex

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Association Area

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sensory input are integrated and interpreted into fine tune the sensory input

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Primary Somatosensory Cortex

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located in the postcentral gryus(gyrus posterior to central sulcus)
-neurons in postcentral gyrus allow for spatial discrimination - which part of the body is being stimulated(touch)
-the tracts from these neruons also decussate - hence touching on the right side of the body is processed in postcentral gyrus in the left hemisphere
-postcentral gyrus located in parietal lobe of each hemisphere - the primary somatosensory cortex is in parietal lobe - somatosensory association area is in parietal lobe next to primary somatosensory area

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Primary visual Cortex

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along with its visual association area - located in occipital lobe of each hemisphere
-damage to occipital lobes in the 2 hemispheres will lead to blindness

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Primary Auditory Cortex

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along with its association area are located in the temporal lobe of each hemisphere

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Primary Olfactory Cortex

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Along with its association area is located in both frontal and temporal lobes of each hemisphere

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Primary Gustatory Cortex

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Along with its association area is located in the insula

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Cerebral White Matter

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-composed of tracts of myelinated axons - whitish
-3 types of tracts based on direction tracts travel
--commissural tracts
--projection tracts
--association tracts

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Commissural Tracts

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connect areas between the 2 cerebral hemispheres - corpus callosum

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Projection Tracts

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2 types
-descendant tracts - motor tracts that descend from areas in the cerebral cortex to lower brain areas or the spinal cord ex. pyramidal tracts
-ascendant tracts - sensory tracts that send info from spinal cord to lower brain areas or to the cerebral cortex ex. spinothalamic tract - all sensory input must make a stop in the thalamus before being sent to cerebral cortex for processing - thalamus = 'gateway to cerebral cortex'

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Association tracts

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connect areas within the same cerebral hemisphere
ex. arcuate fasciculate - connects Broca's area and Wernicke's area in the left hemisphere

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Wernicke's Area

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invloved in language production by using words produced by the Broca's area
-Wernicke's encephalopathy - results in word salad - nonsensical words which do not produce language

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Basale Nuclei

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composed of clusters of neuronal cell bodies which are never myelinated - 'gray matter'
-located deep in the cerebral white matter - the descending pyramidal tracts run through the Basale Nuclei giving them a striated or striped appearance
-consist of caudate, putamen, globus pallidus

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2 Ventricles Located in the Cerebrum

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-lateral ventricles
-1 lateral ventricle in left hemisphere and one in right hemisphere
-separated by the Septum Pellucidum
-connected by the interventricular foramen(foramen of monro) to the 3rd ventricle below

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Diencephalon

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made of 3 paired structures made up of gray matter
-thalamus - 80% of total diencephalon mass
-hypothalamus
-epithalamus

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Hypothalamus

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below the thalamus
-connected to the pituitary gland below via the infradibulum(= pituitary stalk)
-damage may result in emotional imbalance, sleep disturbance, dehydration, or water intoxication, anorexia, or obesity
--generalized endocrine dysfunction - hypofunction/hyperfunction - diseased state - homeostatic imbalances

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Thalamus

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all aparent sensory impulses to cererbal cortex make a stop and synapse w/ nuclei in the thalamus before being relayed to the sensory areas of the cerebral cortex - 'gateway to cerebral cortex'

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Epithalamus

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dorsal to the thalamus
-attached to epithalamus = pineal gland - releases hormone melatonin - acts in sleep center in hypothalamus to induce sleep
-melatonin has been shown to act as an antioxidant - will prevent certain diseases and slow down aging process

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3rd Ventricle

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surrounded by the thalamus, hypothalamus, and epithalamus - located in diencephalon

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Brain Stem

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Consists of an outer white matter embedded with islands of gray matter - inner gray matter(opposite to arrangement in cerebrum - similar to spinal cord)
-located between diencephalon and spinal cord
-ends at foramen magnum
-midbrain, pons, medulla oblongata

Front 54

Midbrain

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superior area of brain stem
-contains cerebral aqueduct - connects 3rd ventricle to the 4th ventricle which is surrounded by the pons and medulla oblongata
-on ventral side - superior cerebellar peduncles that connect motor tracts to the cerebellum
-also present are cerebral peduncles - contain descending pyramidal tracts
-embedded in white matter of midbrain are the 4 grouped nuclei called corpora quadragemina
--2 superior nuclei - superior colliculi - visual reflex centers - controls tracking/movement of head to follow a moving object close to the eyes
--2 inferior nuclei - inferior colliculi - auditory reflex centers - control the startle reflex - movement of head towards direction of unexpected sound
-and the 2 colored nuclei

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2 colored nuclei

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present in midbrain
-substantia nigra - appears black due to increase in melanin required for the synthesis of neurotransmitter dopamine which is released fromthe axonal terminal of neuron located in substantia nigra - initiaing movements + intensity of movements
--damage results in slow to initaite movements, mask-like face, slurred speech, resting tremors, shuffling gait -> parkinsons disease
-red nucleus - invloved in regulating limb flexion

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Pons

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means bridge
-located b/w midbrain and medulla oblongata
-composed of tracts
--horizontal tracts - travel through the middle cerebellar peduncle to the cerebellum
--vertical tracts - descend into the medulla oblongata - part includes the descending pyramidal tracts
-contains the respiratory centers
--apneustic center - regulates the rate of breathing
--pneumotaxic center - regulates the depth of each breath

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Medulla Oblongata

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Most inferior part of the brain stem that blends in with the spinal cord at the level of the foramen magnum
-the descendant pyramidal tracts from the precentral gyri decussate on the ventral side of the medulla - the point where the pyramidal tracts decussate = Decussation of the Pyramids
---explains the contralateral control of the voluntary skeletal muscle movements of the body by the cerebral cortex
-contains centers that automatically regulate body activities necessary for survival - such as cardiovascular center - the 2 respiratory centers - apneustic and pneumotaxic are also in medulla and work together with the ones in the pons

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Cerebellum structure

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11% of the total brain mass
-separated from the cerebrum by the transverse fissure
-divided into 2 cerebellar hemispheres held together medially by the worm-like structure called the vermis
-each cerebellar hemisphere is divided into 3 lobes - anterior lobe, posterior lobe(these two viewed externally), and the floculonadular lobe(buried deep to the vermis
-each hemisphere has 2 regions - the outer gray matter and the inner white matter - called the arbor vitae = 'tree of life'

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Cerebellum functions

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Acts to produce smooth coordinated skeletal muscle movement
-also involved in posture and balance(equilibrium)
-alcohol intoxication affects the function of the cerebellum - loss of balance, uncoordinated muscle movements

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Spinal Cord

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Extends from level of the foramen magnum to the 1st or 2nd lumbar vertebrae ~17 inches long
-has 3 protective structures
--bony structure
--meninges
---outer duramatter - single layered called 'dural spinal sheath'
---middle arachnoid matter
---inner pia matter
Dural spinal sheath doesn't make contact with the internal surface of the vertebral column - space is the epidural space

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Epidural space

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contains fat and veins
-anesthesia is introduced here to block pain pathways to the lower region of the body

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Spinal Matter Arrangement

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spinal sheath is separated from arachnoid matter by the subdural space - contains veins

The arachnoid matter is separated from the inner pia matter by the subarachnoid sapce - contains csf, similar to subarachnoid space around brain
-running through core of spinal cord is the central canal - continuous w/ the 4th ventricle and medulla oblongata - hence contains csf

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cerebral spinal fluid

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acts as fluid cushion, provides buoyancy, provides nutrients and oxygen to neurons in spinal cord

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Spinal Cord Cross Section

Back 64

2 regions
-outer white matter
-inner gray matter - shaped like the letter 'H'
--the 2 sides are connected by a thin layer of gray matter called the Gray Commisure
--composed of neuron cell bodies, dendrites, unmyelinated axons
--divided into 3 areas
---posterior(dorsal) horn - contains interneurons
-anterior(ventral) horn - contains cell bodies of motor neurons
-lateral horn - present only in thoracic and lumbar regions of spinal cord - houses the autonomic fibers especially the sympathetic fibers

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White Matter Spinal Cord

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composed of mainly myelinated tracts
-descendant tracts
-ascendant tracts
-transverse tracts
these tracts travel through 3 funiculi
-posterior funiculus
-anterior funiculus
-lateral funiculus

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Spinal Cord Structure

Back 66

tapered structure
-the tapered end of the spinal cord is called the COnus Medullaris
--attached to the posterior surface of the cocyx by the pia matter
---part is called the Filum terminale - anchors the spinal cord vertebrae to the coccyx
-the pia matter also forms tooth-like structures called Denticulate ligaments - anchor the spinal cord laterally to the internal surface of the vertebral column

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Cauda Equina

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since the spinal cord ends at the level of L1 or L2, spinal nerves of the lumbar and sacral regions form a bundle below the conus medullaris = cauda equina - 31 pairs of spinal nerves

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Paralysis

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loss of motor function

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Paresthesia

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sensory loss

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Spinal cord transection

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can result in loss of motor function and sensation
transection above the cervical enlargement(enlarged area around cervical vertebrae - spinal nerves from cervical enlargement innervate the upper limbs to allow for voluntary skelmus movement and for sensory appreciation - somatosensory input) will result in quadriplegia - all 4 limbs lose motor function and appreciation of sensory input
-Lumbar enlargement - around lower thoracic and upper lumbar areas - spinal nerves from lumbar enlargement innervate the lower limbs, but transection above cervical enlargement relieves both cervical and lumbar enlargement from cerebral control
-transection b/w cervical and lumbar enlargement pesults in paraplegia - loss of motor function and sensation in lower limbs

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Special Senses

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mediated by specialized cells called sensory receptor cells
-3 types
--photoreceptors - respond to changes in light energy - account for 70% of sensory receptors in human body - located in eye
--mechanoreceptors - respond to changes in pressure, vibration, or stretch - touch receptors - corpuscles, - hair cells located in ears - mediate sense of hearing
--chemoreceptors - respond to changes in concentration of chemicals dissolved in liquid

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Structure of an Eye

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3 parts
-eye wall
-humors(fluids)
-lens

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Eye Wall

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3 layers or tunics
-fibrous layer - outer layer
-vascular layer - middle layer
-retina - inner layer

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Fibrous Layer

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posterior 5/6 called the sclera
anterior 1/6 called the cornea
-composed of tough dense regular CT

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Sclera

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maintains shape of the eyeball
-acts as attachment site for extrinsic eye muscles
-protects eye from trauma
-continuous w/ dura matter surrounding the brain - severe untreated eye infection can lead to meningitis - inflammation of the meninges + encephalitis - inflammation of brain tissue

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Cornea

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-most anterior part of the eye
-avascular and transparent - allows light to enter the lens w/o interference

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Middle Vascular Layer

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Also called Uvea
-3 parts
--posterior choroid
--middle cilliary body
--anterior iris

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Iris

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central opening is the pupil
-light passes through the pupil to the lens
-the size of the pupil is influenced by the autonomic nervous system - divided into sympathetic and parasympathetic
--activation of sympathetic nervous system causes pupil to dilate - fibers contract - objects placed at a distance will cause pupillary dilation
--activation of parasympathetic nervous system causes pupillary constriction - viewing of close objects causes pupillary constriction

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Inner Layer - Retina

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confined to posterior of eye
2 main layers
-pigmented layer - abuts the choroid
-neural layer - abuts the pigmented layer + projects into the vitreous humor

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pigmented layer of retina

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cells are pigmented - melanin - prevents light from scattering
-cells receive nutrients & oxygen from the underlying choroid
-nutrients and oxygen are passed on to neurons in the neural layer

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neural layer of retina

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3 types of neurons
-photoreceptors
-bipolar neurons
-ganglion cells

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Photoreceptors

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in contact with cells of the pigmented layer
-these cells act as the nutrient source for the photoreceptors
-detachment of the pigmented layer from the neural layer results in death of photoreceptors - blindness -> retinal detachment

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Ganglion cells

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axons of ganglion cells bundle to form optic nerve

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Humors in the Eye

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2 types
-aqueous humor - anterior segment of eye
-vitreous humor - posterior segment of eye

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Aqueous humor

Back 85

formed and drained
-formed by filtering blood in the capillaries located in the cilliary processes
-drained by the canal of Schlemm
-the rate of filtration = rate of drainage - if the rate of filtration > rate of drainage - glaucoma which compresses lens and optic nerve - can lead to blindness

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Vitreous humor

Back 86

formed during embryonic development - lasts a lifetime

Front 87

Visual Input

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input to the occipital lobe is integrated and interpreted using the visual association area - "definition" to the object being viewed
--from right eye to left occipital lobe and vice versa

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Ear Structure

Back 88

-External - Auricle, external auditory canal
-middle
-inner

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External Ear

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Auricle - composed of elastic cartilage covered with skin
external auditory canal - carved through temporal bone - lined w/ skin w/ ceruminous glands - secrete cerumen which prevents objects from getting to middle ear - keeps tympanic membrane pliable so it can vibrate freely
tympanic membrane - cone shaped membrane that separates outer and middle ear

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Middle Ear

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-air filled region containing smallest bones in human body - ossicles
--malleus - abuts the apex of tympanic membrane
--incus
--stapes - sits atop the oval window
-separated from inner ear by bony wall - has round window and oval window

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Inner Ear

Back 91

Labyrinth - 2 sections
-bony labyrinth - filled with fluid called perilymph
-membranous labyrinth - filled with fluid called endolymph - located inside bony labyrinth surrounded by perilymph

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Bony Labyrinth

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3 areas
-vestibule - contains 2 membranous sacs - utricle, saccule - these contains equilibrium receptors called maculae
-semicircular canals
-cochlea

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Semicircular Canals

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- contains membranous labyrinth called semicircular ducts
-end in large structures called ampullae - house equilibrium receptors called cristae ampullare

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Cochlea

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2 1/2 turn around bony pillar called modiolus
-inside is membranous labyrinth called cochlear duct - contains structure called organ of corti - consists of 2 membrane, supporting cells, hair cells - act as mechanoreceptorrs for hearing

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Organ of Corti

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lower membrane called basilar membrane - surrounded by endolymph inside cochlear duct(surrounded by perilymph)
-sitting atop basilar membrane are the supporting cells which support the hair cells - apical surface have stiffened cilia called stereocilia
---trapped in viscous overlying membrane called tectorial membrane wrapped around the bse of the hair cells are the afferent(sensory) fibers of the cochlear nerve(division of the vestibulocochlear nerve)

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Route of Soundwaves in Ear

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Pinna directs soundwaves into external auditory canal -> sound waves hit tympanic membrane which vibrates -> vibrations cause the malleus to oscillate -> oscillation is transferred from malleus to incus and then stapes -> stapes sits atop oval window, which opens into the inner ear(labyrinth) -> the fluids in the inner ear move which results in the movement/oscillation of the basilar membrane in the organ of corti - > the supporting cells and then the hair cells above the basilar membrane also oscillate -> the stereocilia trapped in the gel-like tectorial membrane bend -> sends off electrical signals that are transferred to the afferent fibers wrapped around the bases of the hair cells -> strong electrical signals result in generation and transmission of action potentials by the afferent fibers of the cochlear nerve -> travel to the vestibulocochlear nerve -> travels to the auditory relay center in the thalamus -> then to the primary auditory cortex in the temporal lobes - if reflexes are involved in processing of the sound input, some of the impulse is delivered to the inferior colliculi in the midbrain

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Chemoreceptors

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-olfactory cells
-gustatory cells

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Olfaction

Back 98

sense of smell
-The olfactory cells which are bipolar neurons act as chemoreceptors for olfaction
-located in the root of the nasal cavity is the olfactory epithelium
--consists of 3 types of cells - olfactory cells(bipolar neurons), supporting cells, basal cells

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Olfactory epithelium

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bipolar neuron - 1 dendrite 1 axon
-the dendrites end in cilia called olfactory hairs
--cilia are trapped in a thin layer of mucus(mucin + water) coating the olfactory epithelium
-the axons form a bundle - olfactory nerve
-supporting cells protect the olfactory cells - also secrete mucus which coats surface of olfactory epithelium
-basal cells - undergo mitosis to produce new olfactory cells because they are replaced every 30-60 days they do NOT exhibit longevity

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Odorant criteria

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-has to be gaseous to be inhaled
-chemical must dissolve in the mucus coating the surface of the olfactory epithelium

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Route of Olfaction

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dissolved chemical in mucus binds to cilia trapped in the mucus - > results in generation of electrical signals -> transferred to olfactory nerve - > strong electrical signals result in generation/transmission of action potentials -> impulse travels mitrals cells(motor neurons) - a bundle of mitral cell axons form the olfactory tract -> carries impulse to relay center in the thalamus -> carried to the primary olfactory cortex in the frontal lobe - if there is an emotional connection to the smell, impulse is carried to the mamillary bodies(part of limbic system of brain responsible for emotion)

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Gustation

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Sense of taste
-detected by the chemoreceptors called gustatory cells
--specialized epithelial cells w/ microvilli on the apical surface

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Taste Buds

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housed in peg-like projections called papillae - located on the dorsum of the tongue, inner surface of the cheeks, and in the pharynx(oro pharynx - part of the throat)
-gustatory cells, supporting cells, and basal cells

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Gustatory cells

Back 104

replaced every 7 days
are NOT neurons - specialized epithelial cells located in taste buds housed in papillae

Front 105

Basal Cells

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undergo mitosis to produce new gustatory cells which are destroyed by the chemicals

Front 106

Microvilli of gustatory cells

Back 106

called gustatory hairs
-extend through taste pores(opening of the taste buds) where the gustatory hairs are bathed in saliva - chemicals to be tasted(=tasteants) must be dissolved in saliva

Front 107

Gustatory impulse travel

Back 107

3 cranial nerves
-facial cranial nerve
-glossopharyngeal cranial nerve
-vagus cranial nerve

gustatory impulses are delivered to gustatory relay center in thalamus ventral posterior medial nucleus -> primary gustatory cortex in the insula