nervous systems Flashcards
2 divisions
central nervous system CNS
peripheral nervous system PCS
CNS
- command centre
- brain and spinal cord
- processes and integrates info
PNS consists of
cranial nerves to/from brain
spinal nerves to/from spinal cord
2 divisions of PNS
sensory/afferent division
motor/efferent division
sensory/afferent division
has sensory receptors that detect stimuli (changes in the internal or external environments)
-nerves convey impulses toward CNS
motor/efferent division
- nerves convey impulses away from CNS
- innervates (supplies nerves to) effectors = muscles and glands (endocrine or exocrine)
relationship b/w cns and pns
page 1 of notes
nervous system organization
page 2 of notes
histology cell types:
neurons
neuroglia (glial cells)
neurons
conduct impulses
make up CNS and PNS
mostly amitotic (irreplaceable)
exceptions = taste, olfaction, memory
neuron structure
cell body
and processes from cell body: dendrites and axon
cell body
typical organelles
RER called Nissl bodies
groups/clusters in CNS=nuclei (gray matter)
groups/clusters in PNS=ganglia
dendrites
receive incoming messages and relay to cell body
axon
- carries impulses away from cell body
- axon hillock-where axon meets cell body
- axon terminal->typically branched with synaptic end bulbs (enlarged tips). may be: myelinated or unmyelinated
myelinated
wrapped in many layers of cell membrane from Schwann cells (PNS) or oligodendrocytes CNS
- electrical insulation
- gaps in myelin sheath are called nodes of Ranvier
myelinated axon bundles in
cns=tracts (white matter)
pns=nerves
unmyelinated
no myelin
neuroglia (glial cells)
support neurons = can undergo mitosis (prone to cancer -brain tumour)
types of neuroglia (glial cells) in CNA
oligodendrocytes
microglia
astrocytes
ependymal cells
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)
ependymal cells
- neural epithelium
- line brain ventricles and central canal of spinal cord
- secrete cerebrospinal fluid (CSF) and circulate it (cilia)
types of PNS neuroglia
schwann cells
satellite cells
schwann cells
form myelin around axons in PNS
Satellite cells
surround neuron cells bodies in ganglia
-protection and support
structural/anatomical types:
based on number of processes coming off cell body
a) unipolar
b) bipolar
c) mutlipolar
neuron classification
structural/anatomical types and functional types
unipolar
1 process that divides into 2 central and 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 and motor neurons
functinoal types
based on direction of impulse conduction
a) sensory/afferent neurons
b) interneurons
c) motor/efferent neurons
sensory/ afferent neurons
mostly unipolar
from sensory receptors to CNS
interneurons
w/in CNS (b/w sensory and motor)
99% of neurons (mostly multipolar)
motor/ efferent neurons
CNS to effectors (all multipolar)
neuronal junctions (synapses)
neuron to neuron
neuromuscular junction
neuroglandular junction
neuron to neuron
can be chemical (use neurotransmitters) or electrical (ions)
neuromuscular junction
motor neuron to skeletal muscle cell
neuroglandular junction
motor neuron to smooth or cardiac muscle, or a gland
chemical neuronal synapses more common structure:
presynaptic neuron
synaptic cleft
postsynaptic neuron
presynaptic neuron
neuron bringing impulse
has axon terminal with synaptic end bulbs
inside end bulb = synaptic vesicles containing neurotransmitter (nt)
presynaptic membrane (cell membrane facing space)
synaptic celft
space b/w neurons
postsynaptic neuron
receives the signal
has postsynaptic membrane
=cell membrane of dendrites or cell body with receptors for nt
CNS protective features
bone meninges cerebrospinal fluis CSF blood-brain barrier BBB cerebral arterial circle
CNS bone
skull and vertebral column
meninges
CT around brain and spinal cord
meninges layers
dura mater (outer) arachnoid mater (middle) pia mater (Inner)
dura mater
outer
- brain-2 fused layers (separated in some places to from spaces = venous (dural), sinuses - contain blood)
- spinal cord - 1 layer
- deep to dura mater = subdural space (filled with ISF)
- superficial to dura mater= epidural space (spinal cord only) (filled with fat, blood vessels, CT etc)
arachnoid mater
middle
- avascular
- subarachanoid space
- contains cerebrospinal fluid (CSF)
- web-like strands of CT secure it to pia mater
- has arachnoid villi (brain only)
- project into dural sinuses
- CSF enters villi to return to blood
pia mater
inner
- on surface of CNS (brain and spinal cord)
- vascular
meningitis is..
inflammation of meninges
cerebrospinal fluid CSF
surrounds brain and spinal cord
in brain ventricles and central canal of spinal cord
cerebrospinal fluid ventricals
- spaces inside brain (filled with CSF)
- 2 lateral ventricles (1st and 2nd) in cerebrum)
- 3rd ventricle-in diencephalon
- 4th ventricle- surround by pons, medulla oblongata, cerebellum
cerebrospinal fluid ventricles central canal
space in spinal cord
- cushion CNS -brain buoyant
- formed from blood plasma (similar composition)
- produced by choroid plexuses (blood capillaries) found in each ventricle
- circulation diagram on page 6
Blood-brain barrier BBB 2 cell types
- endothelial cells ( of capillaries ) with tight junctions
- astrocytes - foot processes wrap around endothelial cells
BBB
selectively permeable
- allows: glucose, fat soluble material to cross
- not toxins, antibiotics etc
- in most parts of brain except: posterior pituitary, hypothalamus vomiting centre
cerebral arterial circle
cerebral arteries form circle at base of forebrain
-circles pituitary gland and optic chiasma (where optic nerves cross)
-unites the 2 major blood supplies to the brain (anterior and posterior)
-provides an alternate route for blood if vessels blocked
(go to page 7 and 8)
