Nervous System

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Nervous System

Neuron Structure

Schwann cell - type of neuroglia(only found in PNS - Peripheral Nervous System)

axon - connects cell body to axon terminals(with synaptic vesicles inside); carries impulses away from cell body to axon terminals

cell body - has typical cell structures

dendrites - recieving portion(impulses from other neurons) are seen as projections off of cell body

Functional Classification of Neurons

motor(efferent) - outward, away; exciting; ventral, comes out front of spinal cord

interneuron - between sensory & motor neurons; totally enclosed in CNS; routes impulses where they need to go

sensory(afferent) - approaching, entering; goes into back of spinal cord(dorsal)

Meninges

Spinal Cord: meninges are in the same order except there is an epidural space between the bone & Dura Mater with blood vessels running through it(where epidurals are administered)

transverse & sagittal sinus that are flattened blood vessels

innermost layer of meninges is Pia Mater; covers brain like shrink wrap in all sulcus & sulci; contains blood capillaries known as choroid plexus that make cerebrospinal fluid that circulates above the Pia Mater; closest to brain

Arachnoid Mater - 2nd, mid layer; web-like, thin like a spider web, beneath is subarachnoid space with CSF circulating

outside part of meninges is called Dura Mater(outermost layer of meninges under subdural space); closest to skull

looks like a sac that covers brain & ic connected to bone & christa galli

meningitis - inflamation of meninges

meninges - protective covering for brain and spinal cord

Spinal Cord

ganglion - clusters of cell bodies(neurons) forms swollen area on dorsal in PNS vs. nuclei - clusters of cell bodies in CNS

nerves - only in PNS, not in brain or spinal cord vs. tracts - only in CNS

2 functions: spinal reflexes; conduct ascending(sensory) -posterior entry is also sensory; descending tracts(motor) - anterior exit is also motor

from foramen magnum to vertebral foramen

Ventricles & Location of Cerebro Spinal Fluid

location: ventricles, central canal(SC), & subarachnoid space

4 ventricles(fluid-filled sacs with CSF) in brain

Reflex Arc

ex: step on a tac, lifts foot immediately

ex: feel something burning, pulls hand away asap

example: hitting the patellar ligament on knee; simplest of all reflexes, same thing happens everytime, same action that cannot be controlled

direct route from sensory nueron to effectors(always travels the same path); rapid, predictable, involuntary response

Cerebrospinal Fluid

hydrocephaly - "water on the brain"; fontanel membrane has not ossified * so it keeps stretching to fit the liquid and head is very large; fluid must be removed by channeling the fluid out and into a tube in the neck

spinal tap/lumbar puncture - between L3 and L4 vertebrae(below spinal cord); goes into subarachnoid space and examines fluid for infection

secretes 500 ml; only 140 ml present in a day, rest of it goes to sinuses

functions: maintain stable ionic concentrations for CNS; protective cushion

clear, viscous(thick) fluid secreted by choroid plexus into subarachnoid space

5 Types of Neuroglia

5. Schwann - PNS; only cell of Perioheral Nervous System

4. Ependymal - CNS; in fluid-filled cavities of brain are ventricles, in spinal cord is central canal; controls composition of this fluid & circulate the cerebrospinal fluid

3. Astrocytes - CNS; star-shaped, large cells with processes that come in contact with blood capillaries & neuron; handle exchange/transport of substances between blood & neuron

2. Oligodendrocytes - CNS; form myelin in CNS; wherever they are, there is also white matter; without them, there is gray matter in CNS

1. Microglial - CNS; phagocytize(eat) cell bacteria & cell debris; numbers of these will increase when infection arises

Nerve Structure

wrapping around the entire structure is the epineurium

surrounding the perineuium is many fasicles

wrapping around endoneurium is the perineuium

connected to axon is the endoneurium

nerve cell connected to nerve by axon

2 Divisions

Peripheral Nervous System (PNS)

motor division - somatic and autonomic nervous systems

sensory division - input of receptors

spinal nerves

12 pairs of cranial nerves

all other nerves

Central Nervous System (CNS)

spinal cord

brain

Nervous Tissue

located in spinal cord, brain, and nerves (these are made up of nervous tissue)

neuroglia - netted support tissue for neuron

neuron - entire (single) cell

Myelin Formation

node of Ranvier (ron-vee-ay) - important when transmitting & conducting impulses along the axon

all Schwann cells together form myelin

myelinated axons - white matter unmyelinated axons - grey matter

made up of phospholipids(fat) - protein and cholesterol

5 Characteristics of Neurons

Also study:

12 Cranial Nerves

nerve impulse physiology

nerve impulse/action potential

events leading to the release of a neurotransmitter

comparison of somatic & autonomic nervous systems

special senses

conductivity - transmits impulses from one nerve to another

excitable - sensitive to changes in environment and pH is relevant(acidosis depresses, alkalosis excites)

high metabolic rate - chemical reations are happening very quickly

amniotic - do not divide; won't be replaced

extreme longevity - lives a long time(your life span)