Nervous System

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nervous system development:

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from ectoderm of embryo in recponse to signaling molecules from notochord

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Cells of nervous system:

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- neurons (receptive, integrative, motor functions)

- neuroglial cells (support and protect neurons)

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neuron composition:

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- cell body

- dendrites

- axon

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Neuronal cell body:

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the region of neuron containing the large pale-staining nucleus and perinuclear cytoplasm

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Inclusions :

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- located in neuronal cell bodies encompass nonliving substances: melanin, lipofuscin pigment, lipid droplets

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types of neurons:

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unipolar (pseudounipolar) - dorsal root ganglia, cranial nerve ganglia

multipolar (motor)- most common

bipolar - retina, vestibular and cochlear ganglia, olfactory epithelium of nasal cavity

pyramidal - hippocampus

Purkinje - cerebellum

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Dendrites:

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- receive stimuli from other nerve cells

*Spines - permit synapse of dendrites with other neurons

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Axons:

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- transmit impulses to other neurons or effector cells, namely cell of muscle, glands

* axon hillock - pyramid shaped region of the soma, devoid of ribosomes, usually on opposite site to dendrites, initial segment- beginning of myelin sheath

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Spike trigger zone-

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where excitatory and inhibitory are summed to determine whether propagation of action potential is to occur

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presence of myelin permits subdivision of CNS to:

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- white matter- AXONES

- gray matter- BODIES

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Astrocytes:

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- provide structural and metaboilc support to neurons, act as scavengers of ions and neurotransmiters relesed into extracellular space

- the lagrest of neuroglial cells

- two types:

*protoplasmic astrocytes in the gray matter of CNS

*fibrous astrocytes in white matter of CNS

- composed of glial fibrillar acidic protein

- assist in blood-brain barrier

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Oligodendrocytes:

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- function in eletrical insulation in myelin production in CNS

- in both white and gay matter

*interfascicular oligodendrocytes <3 myelin

*satellite oligodendrocytes ?

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Microglial cells:

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-members of mononuclear phagocyte system

- orginate not from the neural tube but from the bone marrow

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Ependymal cells:

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- from limiting membrane and also may function in the transportation of cerebrospinal fluid

-ependymocytes low columnar to cuboidal epithelial cells

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Shwann cells:

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- form both myelinated and unmyelinated coverings over axons of the PNS

- node of Rindver between two different Schwann cells

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Synapse:

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- are sites of impulse transmission between presynaptic and postsynaptic cells

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Neurotransmiters:

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- signaling molecules that are released at presynaptic membranes and activate receptors on postsynaptic membranes

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Huntington's chorea -

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loose of cells producing GABA- inhibitory neurotransmiter

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Parkinson's disease -

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related to absence of dopamine ( bradykinesia- slow movement)

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Peripheral nervous system:

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- peripheral nerves and cell bodies outside CNS

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Connective tissue investment of peripheral nerves:

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epineurium --> perineurium --> endoneurium

* underlying Schwann cells

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Functional classification of nerves:

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* sensory- afferent

* motor- efferent

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motor innervation to skeletal muscles is provided by...

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somatic nerves

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Autonomic Nervous System:

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- provide motor innervation to smooth muscle and cardiac muscle, supply secretomotor innervation of glands

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Sympathetic nervous system:

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- prepare body for "flight or fight"

*thoracolumbar outflow

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Parasympathetic Nervous system:

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- prepare body to "rest or digest"

*craniosacral outflow

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Ganglia:

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- sensory - house cell bodies of sensory neurons (gorsal root ganglia ,,, capsule cells, satelite cells)

- autonomic ganglia - house cell bodies of postganglionic autonomic nerves (terminal ganglia V, X)

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Blood- brain barrier:

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*endothelial cells of CNS capillaries prevent the free passage of selective blood-bore substances into the neural tissue

*continuous capillaries

*receptor-mediated transport

* numerous astrocytes --> perivascular glia limitans

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Choroid plexus-

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- composed of folds of pia matter within the ventricles of the brain, produces CSF

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Cerebrospinal Fluid

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bathes, nourishes and protects the brain and spinal cord

stability of CSF in maintained by blood-CSF barrier composed of zonulae occludentes between cells of simple cuboidal epithelium

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Cerebral cortex:

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- responsible for learning, memory, sensory intergation, information analysis, initiation of motor responses

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Layers of cerebral cortex:

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1. molecular layer (horizontal cells, neuroglia)

2. external granular layer (granule- stellate cells, neuroglial cells)

3. external pyramidal layer (neuroglial cells, large pyramidal cells)

4. internal granular layer (granule cells, pyramidal cells, neuroglia- the greatest density)

5. internal pyramidal layer ( the largest pyramidal cells and neuroglia, the lowest density)

6. multiform layer (Martinotti cells, neuroglia)

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Cerebellar cortex:

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RESPONSIBLE FOR BALANCE, EQUILIBRIUM, MUSCLE TONE, MUSCLE COORDINATION

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Cerebellar cortex- layers:

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1. molecular layer (below pia matter, satellate cells, dendrites of Purkinje fibers, basket cells, unmyelinated axons from granular layer)

2. Purkinje cell layer (Purkinjr cells only in cerebellum, their axons project to white matter, receives maaaany excitatory and inhibitory synapses, form proper response, the only cell in cerebellar cortex that sends information outside--> always inhibitory output using GABA

3. granular layer (the deepest) consists of small granule cells- glomeruli- cerebellar islands

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nerve regeneration :

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nerve cells unlike neuroglial cells can not proliferate but can regenerate thir axons located in PNS

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Anterograde reaction process-

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the portion of the axon distal undergoes degeneration and it is phagocytosed

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Retrograde reaction and regeneration

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- the proximal portion of injured axon undergoes degradation followed by sprouting of new axon whose growth is directed by Schwann cells