Topic 19: Nervous System Flashcards
What are the 2 divisions of the Nervous system?
Central nervous system
peripheral nervous system
Central Nervous System (CNS)
“command centre”
brain + spinal cord
processes + integrates info
Peripheral Nervous System (PNS)
a) cranial nerves
to/from brain
b) spinal nerves
to/from spinal cord
What are the 2 divisions of the PNS?
a) sensory/afferent division
has sensory receptors that detect stimuli (change in internal or external environments)
b) motor/efferent division
nerves convey impulses away from CNS
innervates (supplies nerves to) effectors = muscles + glands
(endocrine or exocrine)
Describe the relationship between the CNS and PNS
receptors; detect stimuli
PNS (sensory neurons); afferent
CNS: integrate
PNS (efferent); motor neurons
Effector; executes response, muscle and glands
Neurons
conduct impulses
make up CNS + PNS
mostly amitotic (irreplaceable)
o exceptions = taste, olfaction, memory
Describe the structure of a neuron
a. cell body
b. dendrites
c. axon
d. axon hillock
e. axon terminal
cell body
typical organelles
RER called - Nissl Bodies
groups/clusters in CNS = nuclei (gray matter)
groups/clusters in PNS = ganglia
dendrites
receive incoming messages + relay to cell body
axon
carry impulses away from cell body
axon hillock
where axon meets cell body
axon terminal
typically branched with synaptic end
bulbs (enlarged tips)
Nodes of Ranvier
gaps in myelin sheath
axon may be…
myelinated - – wrapped in many layers of cell membrane from Schwann cells (PNS) or oligodendrocytes (CNS)
electrical insulation
unmyelinated – no myelin
myelinated axon bundles in:
o CNS = tracts (white matter) o PNS = nerves
Neuroglia (glial cells)
support neuron cells = can undergo mitosis (prone to cancer – brain tumor)
List the cell types of the nervous system
neurons
neuroglia glial cells)
List the CNS neuroglia
i. oligodendrocytes
ii. microglia
iii. astrocytes
iv. ependymal – neural epithelia
i. oligodendrocytes
produce myelin around axon
microglia
protective – become phagocytic if detect infected, dead, or damaged neurons (because immune cells can’t enter CNS)
astrocytes
surround blood capillaries to form part of blood brain
barrier (BBB)
help control capillary permeability
ependymal – neural epithelia
line brain ventricles + central canal of the spinal cord
secrete cerebrospinal fluid (CSF) + circulate it (cilia)
PNS neuroglia
i. Schwann cells
form myelin around axons in PNS
ii. Satellite cells
surround neuron cell bodies in ganglia – protection + support
How can neurons be classified?
1) Structural/Anatomical types:
based on # of cell processes off of cell body
2) Functional types:
based on direction of impulse conduction
Unipolar
1 process that divides into two: central + peripheral
peripheral end has dendrites = sensory receptors (pain, touch
etc) - remainder is axon
always sensory
Bipolar
2 processes: 1 axon, 1 process with dendrites
sensory – retina, nose (olfaction)
Multipolar
3 or more processes: 1 axon, many dendrites
all interneurons + motor neurons
Describe the functional types of neurons
a) Sensory/Afferent Neurons mostly unipolar
from sensory receptors to CNS
b) Interneurons
within CNS (between sensory + motor)
99% of neurons (mostly multipolar)
c) Motor/Efferent Neurons
CNS to effectors (all multipolar)
Neuron Junctions (Synapses):
1) Neuronal junction:
neuron to neuron
can be chemical (use neurotransmitters) or electrical (ions)
2) Neuromuscular junction:
motor neuron to skeletal muscle
3) Neuroglandular junction:
motor neuron to gland
Chemical Neuronal Synapses:
most common
Describe the structure of a Chemical Neuronal Synapses:
1) Presynaptic Neuron:
neuron bringing impulse
2) Axon Terminal: within synaptic end bulbs o inside the end bulb (presynaptic membrane) = synaptic vesicles containing neurotransmitter (nt) 3) Synaptic Cleft: space between neurons
4) Postsynaptic Neuron: receives the impulse has postsynaptic membrane o = cell membrane of dendrites or cell body with receptor sites for nt
Bone
skull + vertebral column
Meninges
connective tissue around brain + spinal cord
What are the layers of the meninges?
a) dura mater (outer)
b) arachnoidmater(middle)
c) pia mater (inner)
dura mater
(outer)
brain = 2 fused layers
o separated in some places to form spaces = venous (dural) sinuses – contain blood
spinal cord = 1 layer
subdural space
deep to dura mater
filled with ISF
epidural space
(spinal cord only)
o filled with fat, blood vessels, CT, etc.
superficial to dura mater
arachnoid mater
(middle)
avascular
subarachnoid space
o contains cerebrospinal fluid
o web-like strands of CT secure it to pia mater below
has arachnoid granulations (brain only)
o project into dural sinuses
o CSF enters granulations to return to blood
pia mater
(inner)
on surface of CNS (brain + spinal cord)
vascular
meningitis
inflammation of meninges
List the protective features of the CNS
Bone Meninges CSF Blood Brain Barrier (BBB): 5) Cerebral Arterial Circle:
Cerebrospinal Fluid (CSF)
surrounds brain + spinal cord
in brain ventricles + central canal of spinal cord
cushions CNS – brain buoyant
formed from blood plasma (similar composition)
produced by choroid plexuses (blood capillaries) found in each ventricle
ventricles:
- spaces inside brain (filled with CSF)
- 2 lateral ventricles (1st + 2nd) – in cerebrum
- 3rd ventricle = in diencephalon
- 4th ventricle = surrounded by pons, medulla oblongata, cerebrum
central canal:
• space in spinal cord
Blood Brain Barrier (BBB):
2 cell types:
a) endothelial cells (of capillaries) with tight junctions
b) astrocytes – foot processes wrap around endothelial cells
selectively permeable
o allows: glucose, fat soluble material o not toxins, antibiotics, etc.
Cerebral Arterial Circle:
cerebral arteries form circle at base of forebrain
o circles pituitary gland + optic chiasma (where optic nerves cross)
o unites the two major blood supplies to the brain (anterior + posterior)
o provides an alternate route for blood if vessels blocked
Forebrain:
a) cerebrum
(= right + left cerebral hemispheres)
lobes (named after overlying bones):
i. frontal
ii. temporal
iii. parietal
iv. occipital
v. insula – deep to temporal lobe
What surface features does the forebrain have?
i. fissures = deep grooves
ii. gyri = ridges
iii. sulci = shallow grooves (separate gyri)
fissures
deep grooves
longitudinal fissure
separates right + left cerebral hemispheres
transverse fissure
separates cerebellum + cerebrum
lateral fissure
separates temporal lobe from rest of cerebrum
gyri
ridges
examples:
o postcentral gyrus in parietal lobe o precentral gyrus in frontal lobe
sulci
shallow grooves (separate gyri)
example:
o central sulcus – between frontal + parietal lobes
What are the 3 layers of the forebrain?
i. cerebral cortex
ii. tracts (white matter)
iii. basal nuclei
cerebral cortex
2 – 4 mm thick, gray matter has functional areas: motor areas sensory areas association areas others:
motor areas
all in frontal lobe
control skeletal muscle movement
3 regions:
a primary motor area (precentral gyrus)
b premotor area
c Broca’s area (motor speech)
sensory area
a general sensory area (pain, touch, temp,
pressure)
postcentral gyrus in parietal
lobe
vision
occipital lobe
auditory + olfaction
temporal lobe
taste + visceral sensation
(e.g. full bladder) insula
association areas
recognize info from memories
o parietal, occipital, temporal lobes
others:
memory o temporal lobes concious intellect (personality, learning, ideas, judgement, etc.) o prefrontal cortex
list the types of tracts
association tracts
from gyrus to gyrus in same hemisphere
commissural tracts
from gyrus to gyrus in opposite hemispheres e.g. corpus callosum
projection tracts
run vertically (brain to spinal cord / spinal cord to brain
TRACTS= WHITE MATTER
basal nuclei
control skeletal muscle movement
paired masses of grey matter with white matter
Diencephalon
all gray matter
a) thalamus
b) hypothalamus
thalamus
2 lobes connected by intermediate mass (bridge through 3rd ventricle)
relay station for impulses coming to cortex (from spinal cord)
hypothalamus
inferior to thalamus, above pituitary
major regulator of the internal environment (visceral control)
o e.g. blood pressure, heart rate
Midbrain:
connects pons + diencephalon
contains cerebral aqueduct
anterior portion = cerebral peduncles (projection tracts)
posterior portion = 4 nuclei = corpora quadrigemina
o 2 superior colliculi
• visual reflexes
o 2 inferior colliculi • hearing
Hindbrain
Pons
Medulla
Cerebellum
Pons
anterior to cerebellum
tracts between brain + spinal cord, + tracts to/from cerebellum
pontine respiratory centres
Medulla
inferior to pons
ends at foramen magnum
2 bulges (called pyramids) = large motor tracts (= part of corticospinal tracts)
o just above spinal cord = decussation (crossover) of pyramids
3 vital centres in medulla:
i. cardiac
ii. vasomotor (blood vessels)
iii. respiratory
several non-vital centres for swallowing, sneezing, vomiting
Brain Stem
= midbrain, pons, medulla
Cerebellum
posterior to pons/medulla
has folds similar to gyri = folia
cortex = gray matter
arbor vitae (deep to cortex) = white matter
coordinates skeletal muscle contraction
o balance, posture
a) Limbic System
nuclei in cerebrum + diencephalon
regulates emotions (laughing, crying, etc.)
contains areas involved in memory (memories evoke emotional responses)
Reticular Formation
nuclei in brain stem
cortex, thalamus, + hypothalamus involved
o (together form RAS = Reticular Activating System)
regulates alertness + attention
o filters stimuli + only sends new/unusual signals to other brain areas
sleep results when inhibited if damaged = coma
2 pairs
= only sensory neurons o I and II
1 pair
mainly sensory neurons o VIII
9 pairs
mixed nerves
o carry both sensory + motor neurons
▪ motor neurons have cell bodies in brainstem nuclei 12
▪ sensory neurons have cell bodies in ganglia of PNS o e.g. trigeminal nerve (V)
▪ motor function = chewing
▪ sensory fxn = conveys general sensations (touch, pressure, pain,
temperature) from face to CNS
Cranial Nerves
12 pairs total
