Nervous System Introduction
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- 1. Astrocyte
- 2. Oligodendrocyte
- 3. Microglial
- 4. Ependymal
- 5.Schwann Cells
- 6.Satellite Cells
Outnumber neurons by about 10 to 1.
6 types of supporting cells
4 are found in the CNS:
Blood/Brain Barrier, Housekeeping, Etc.
Star-shaped, abundant, and versatile
Guide the migration of developing neurons
Act as K+ and NT buffers
Involved in the formation of the blood brain barrier
Function in nutrient transfer
Production Of Myelin In CNS
- the myelin sheath which provides the electrical insulation for certain neurons
- in the CNS
Specialized immune cells that act as the macrophages of the CNS
Cell Production Of CSF & Tight Junction Boundaries
Low columnar epithelial-esque cells that line the ventricles of the brain and some of the central canal of the spinal cord
- Some are ciliated which facilitates the movement of cerebrospinal fluid
Production Of Myelin In PNS
Surrounding PNS Neurons
Reticular Formation: medulla + pons + midbrain
– contains more than 100 clusters of neurons
• dispersed gray matter (sometimes called the “central gray”
Functions of Reticular Formation: medulla + pons + midbrain
1. Somatic motor control (primarily of extensor muscles)
2. Cardiovascular control
3. Pain modulation
4. Sleep and consciousness
Brain Anatomy- Medulla Oblongata (MYELENCEPHALON)
3 cm long (1 inch)
forms inferior part of brain stem
- lateral side - Olive
- – contains inferior olivary nuclei (relay nuclei)
- – communicates with the cerebellum
three groups of nuclei (we will consider 2)
1. autonomic nuclei controlling visceral activities
• cardiac center
• vasomotor center
• two respiratory centers
2. relay stations along sensory or motor pathways nucleus gracilis and nucleus cuneatus
– sensory information crosses over to other side decussation of pyramids
– descending motor tracts
– majority of fibers cross over throughout the brain stem
3. Mesencephalon (Midbrain)
– surface gray -cerebrum cortex
– deep gray - basal nuclei
– white matter
– corpora quadrigemina
– cerebral peduncles
– substantia nigra
– red nucleus
– medulla oblongata
- water, glucose
- lipid soluble substances - oxygen, carbon dioxide, caffeine, nicotine, heroin, and anesthetics
sodium, potassium, chloride, creatinine, and urea
do not pass
proteins, most antibiotics neurotransmitters, formed elements
Normal capillary bed in the human body is very permeable
Two different barriers
- 1. blood brain barrier
- 2. Blood-CSF barrier
blood brain barrier
capillary bed has tight junctions protoplasmic pseudopodia of astrocytes cover capillary and release chemicals that control the permeability of the endothelium
ependymal cells in choroid plexus have tight junctions
Blood brain barrier not found in..
– portions of the hypothalamus
– posterior pituitary gland
– pineal gland
– choroid plexus
Things that by-pass bbb
nasal sprays can travel up the olfactory nerve fibers
Anatomy-Cerebrospinal Fluid components
– very different from plasma
– lower pH, proteins, K, Ca, HCO3 and glucose
– Na is about the same
Anatomy-Cerebrospinal Fluid FUNCTIONS..
• human brain weighs about 1500 g in air but 50 g when suspended in CSF
• protects brain from striking the cranium
c. Chemical Stability
- • Helps provide means of rinsing metabolic
- wastes from
Anatomy-Cerebrospinal Fluid and the CNS and regulating its chemical environment
- – formed in the choroid plexus
- • in roofs of the ventricles
- – volume = 100 - 160 ml
- • produce about 500 ml per day
- – 160 mm pressure
– between L3 and L4
– CSF from subarachnoid space
– spinal tap: 3-9 ml
epidural and spinal blocks
– into the epidural space
– steroids and anastethetics
Anatomy-Ventricles & Cerebrospinal Fluid
1. lateral ventricles
2. 3rd ventricle
3. 4th ventricle
– in each cerebral hemisphere
– 1st two ventricles fuse to form the lateral ventricles
– connected to third ventricle by interventricular foramen
– between left and right thalamic clusters
-the floor is the hypothalamus
– connected to 4th ventricle by mesencephalic (cerebral) aquaduct
– between inferior brain stem and the cerebellum
– connects to the spinal canal in the spinal cord
– double layer over most of brain
• outer periosteal layer
• inner meningeal layer
• separated by dural sinus which empty into the internal jugular veins
– single layer over spinal cord
• epidural space between dural sheath and bone
– middle cob-web layer
– separated from dura mater by subdural space some feel this my be an artifact
- – separated from pia mater by
- subarachnoid space
• 2 spaces contain cerebrospinal fluid
• subarachnoid space is much larger
– arachnoid villi
–inner most delicate areolar connective tissue
2 types of glia in the PNS
-Surround clusters of neuronal cell bodies in the PNS
-Probably serve as “replacement” cells for damaged neurons
-Form myelin sheaths around the larger nerve fibers in the PNS.
- Vital to neuronal regeneration
Axons and Myelination
Axolemma = axon plasma membrane.
Surrounded by a myelin sheath, a wrapping of lipid which:
– Protects the axon and electrically isolates it
– Increases the rate of AP transmission
The myelin sheath is made by ________ in the CNS and by _________ in the PNS.
This wrapping is never complete. Interspersed along the axon are gaps where there is no myelin – these are nodes of Ranvier.
In the PNS, the exterior of the Schwann cell surrounding an axon is the neurilemma
2 cell types
- -Functional, signal conducting cells
- -Supporting cells
The functional and structural unit of the nervous system
- Specialized to conduct information from one part of the body
- to anotherThere are many, many different types of
- neurons but most have certain structura and
- functional characteristics in common:
Cell body (soma)
- or more specialized, slender processes (axons/dendrites)
- input region (dendrites/soma)
- conducting component (axon)
- -A secretory
- (output) region (axon terminal)
Clusters of somata in the CNS are known as nuclei.
Clusters of somata in the PNS are known as ganglia
Armlike extensions emanating from every neuron.
- The CNS consists of both somata and processes
- whereas the bulk of the PNS consists of processes.
Tracts = Bundles of processes in the CNS
Nerves = Bundles of processes in the PNS
2 types of processes that differ in structure and function:
•Dendrites are thin, branched processes whose main function is to receive incoming signals.
•They effectively increase the surface area of a neuron to increase its ability to communicate with other neurons.
•Small, mushroom-shaped dendritic spines further increase the SA
•Convey info towards the soma thru the use of graded potentials – which are somewhat similar to action potentials.
Most neurons have a single axon – a long (up to 1m) process designed to convey info away from the cell body.
Originates from a special region of the cell body called the axon hillock.
Transmit APs from the soma toward the end of the axon where they cause NT release.
Often branch sparsely, forming collaterals.
Each collateral may split into telodendria which end in a synaptic knob, which contains synaptic vesicles – membranous bags of NTs.
- Nervous system has
- two branches, CNS and PNS.
- CNS contains the
- brain and spinal cord.
- PNS contains, Sensory
- afferent and a Motor efferent sub region.
- The sensory PNS has
- visceral and somatic divisions
- The motor PNS has a
- somatic and visceral sub division but the visceral subregion has an autonomic
- branch with both parasympathetic and sympathetic divisions.
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