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Nervous System 2

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Absolute refractory period
a. Time during which a second stimulus cannot produce an action potential
b. Voltage-gated Na+ channels already open or are inactivated
WHAT DO THE MENINGES COVER?
THE ENTIRE CNS.
Axons
long thin process, send impulse
1. Originates on axon hillock of soma, initial segment contains trigger zone, with neurofilaments for transport
2. Axon collaterals - side branches
3. Terminates in many fine filaments or axon terminals with synaptic knobs containing synaptic vesicles
WHERE DOES THE SPINAL CORD END?
L2
Schwann cells
produce myelin sheath around axons of PNS neurons.

Schwann cell membrane wraps around the axon many times; nucleus & cytoplasm form outermost layer or neurolemma which provides regeneration tube.

Nodes are uncovered areas between Schwann cells.
A SKULL FRACTURE MAY LACERATE WHICH ARTERY?
THE MIDDLE MENINGEAL ARTERY, LOCATED IN THE EPIDURAL SPACE.

THIS IS A LIFE THREATENING PROBLEM.
Continuous propagation
Continuous propagation - action potential moves in series of small steps along the unmyelinated axon
PERIPHERAL NERVOUS SYSTEM IS COMPRISED OF
PERIPHERAL RECEPTOR ORGANS

SPINAL NERVES

PERIPHERAL NERVES

GANGLIA
WHAT ARE THE LAYERS OF THE MENINGES?
DURA
ARACHNOID
PIA
Saltatory propagation
action potential jumps from node to node along the myelinated axon, 5-7X faster, uses less ATP energy
WHERE IS THE EPIDURAL SPACE?
BETWEEN THE SKULL AND THE DURA MATTER.
Neurons
converts stimuli into nerve impulses (excitability), limited mitosis
WHAT IS THE TENTORIUM CEREBELLI?
A HORIZONTAL REFLECTION OF THE DURA BETWEEN THE OCCIPITAL LOBE OF THE CEREBRUM AND THE CEREBELLUM.
Relative refractory period
a. Time during which only a second very strong stimulus produces an action potential
b. Voltage-gated Na+ channels are closed but no longer inactivated
T0 = resting membrane pot
T1 = depolarized
T2 = reverse polarity
T3 = repolarized
T4 = hyperpolarized
Red = absolute refractory period (see physiology text)
Green = relative refractory period (see physiology text)
HOW MUCH DOES THE BRAIN AND SPINAL CORD WEIGH?
1400 GRAMS

MALE BRAIN IS HEAVIER THAN FEMALE.
Soma
cell body with typical plasma membrane & cell organelles.
WHAT IS THE FALX CEREBELLI?
INCOMPLETELY SEPARATES THE CEREBELLAR HEMISPHERES.
Dendrites
highly branched generally short cytoplasmic processes, receive input
WHAT ARE THE TWO LAYERS OF THE DURA.
PERIOSTEAL LAYER -ALONG THE SKULL.

INNER MENINGEAL LAYER.
Neurons classified by number of processes:
1. Unipolar - one bifurcated process, dendrites & axon are continuous, sensory neurons
2. Bipolar - two processes, one dendritic & one axonic, special senses neurons
3. Multipolar - more than two processes, one axon & several dendrites, motor neurons

WHAT ARE THE PARTS OF THE DIENCEPHALON?
THALAMUS
HYPOTHALAMUS
EPITHALAMUS
SUBTHALAMUS
Axon diameter
larger diameter axons conduct faster than smaller diameter axons
Type A fibers: 4-20 mm axon diameter, myelinated, 12-140 m/ sec
Type B fibers: 2-4 mm axon diameter, myelinated, 12-18 m/sec
Type C fibers: less than 2 mm axon diameter, unmyelinated, 0.5-2 m/sec

WHAT DO YOU CALL A BUNDLE OF AXONS IN THE CNS?
TRACT
FASCICULUS
PEDUNCLE
LEMNISCUS
Myelinated axons
have a thick myelin sheath composed of lipid & protein (myelin), acts as insulating layer.

myelinated axons conduct faster than unmyelinated axons
WHAT IS THE FALX CEREBRI?
IT'S A VERTICAL REFLECTION OF THE DURA BETWEEN THE CEREBRAL HEMISPHERES.
Unmyelinated axons
covered by a thin layer of glial plasma membrane
BRAINSTEM
MESCENCEPHALON (MIDBRAIN)

PONS & MEDULLA
Satellite cells
Neuroglial cell that surround & support ganglionic cells in PNS
WHICH SPINAL NERVES HAVE NO CORRESPONDING VERTEBRAE.
C8
Microglia
form from monocytes, phagocytic cells (microbes & debris) in CNS
HOW DOES THE DURA PROVIDE SUPPORT AND COVERAGE FOR THE BRAIN?
FALIX CEREBRI

TENTORIUM CEREBELLI

FALIX CEREBELLI
Ependyma
Neuroglia cell - line CSF-filled cavities of CNS & filter CSF.
FOUR LOBES OF THE CEREBRUM
FRONTAL
PARIETAL
TEMPORAL
OCCIPITAL
oligodendrocytes
most common neuroglial cell, produce myelin sheath around axons in CNS
WHERE IS THE CIRCLE OF WILLIS LOCATED?
VENTRAL ASPECT OF THE BRAIN
ARACHNOID LAYER
AVASCULAR, EXTERNAL MESOTHELIUM.
CENTRAL NERVOUS SYSTEM IS COMPRISED OF
BRAIN

SPINAL CORD
Astrocytes
star shaped, in CNS, maintain K+ balance, link neurons & vessels forming blood-brain barrier.
THE CAUDA EQUINA IS WHAT PART OF THE SPINAL CORD?
L2-L5
WHERE IS THE SUBARACHNOID SPACE?
SPACE BETWEEN THE ARACHNOID PIA LAYER.
CONTAIN CSF, CEREBRAL VESSELS,ARACHNOID GRANULATION.
SITE OF HEMORRHAGE - ANEURYSM,CIRCLE OF WILLIS.
AUTOMONIC NERVOUS SYSTEM
REGULATION OF VISCERAL FUNCTION.

PART OF CNS AND PNS
WHERE DO THE 2 MOST COMMON ANEURYSMS IN THE CIRCLE OF WILLIS OCCUR?
ANTERIOR COMMUNICATING ARTERY.

POSTERIOR COMMUNICATING ARTERY.
WHAT IS LOCATED BETWEEN THE TWO LAYERS OF THE DURA?
VENOUS CHANNELS CALLED SINUSES.
Neuroglial cells.
do not generate or conduct impulses; support, nurture & protect neurons, smaller, more numerous, mitotic.
WHAT ARE THE PARTS OF THE BASAL GANGLIA?
CAUDATE NUCLEUS
GLOBUS PALLIDUS
CLAUSTRUM
PUTAMEN
AMYGLADA
WHERE IS THE SUBDURAL SPACE?
SPACE BETWEEN THE DURA AND ARACHNOID.

TRAUMA TO THE BRIDGING VEINS CAN CAUSE TRAUMA AND HEMATOMA.
WHAT IS THE FUNCTIONAL UNIT OF THE CNS?
NEURON- CELL BODY
AXON
DENDRITE

SYNAPSE- DENDRITE-AFFERRENT
AXON-EFFERENT
PIA LAYER
THIN AND VASCULAR

HUGS THE BRAIN.
WHAT ARE THE TWO TYPES OF GOLGI NEURONS IN THE CNS?
GOLGI TYPE I - EXCITATORY

GOLGI TYPE II - INHIBATORY
HOW MANY PAIRS OF SPINAL NERVES?
31
WHAT IS BETWEEN THE CEREBRUM & BRAINSTEM?
DIENCEPHALON AND BASAL GANGLIA.
WHAT DO YOU CALL A CHAIN OF COMMUNICATING NEURONS IN THE CNS.
PATHWAY
WHAT PROTECTS THE CNS?
SKULL
VERTEBRAE
MENINGES
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