BIOL125 Lecture Notes - Lecture 7: Schwann Cell, Synovial Membrane, Antibody
BIOL week 7 LC nervous system and musculoskeletal system through lifespan
- CNS = brain and spinal cord
- PNS = afferent neurons and efferent neurons
Development of the nervous system
- Adult brain:
o100 billion neurons, 20 billion within the cerebral cortex
oOne neuron can make up 10,000 synaptic connections
oOver 100 trillion synaptic connections
- Characterised by three phases
1. Neurogenesis, neural proliferation and migration, folding the brain develops
through proliferation of neural progenitor cells (neurogenesis – generation of the
neural tissue itself); these cells undergo mitosis and they migrate; folding
2. Neuronal connectivity creation of synapses
3. Synaptogenesis and synaptic pruning vital in hippocampus to allow us to put
new short-term memories into long-term memory
Neurogenesis, neural proliferation and migration, folding
- Neurulation starts week 3 of gestation (neuronal progenitor cells divide and migrate)
- Neural plate neural groove neural tube (allows development of brain in anterior
section; develops into spinal cord in posterior/caudal section) primary brain
vesicles secondary brain vesicles
Neuronal Connectivity
- Around week 12 gradual thickening of the cortex and formation of cortical layers
- Around mid-gestation:
oDirect contact between cortex and rest of CNS
oGyrification (starting to form gyri)
oFirst primary sulci begin to form (allows greater volume of neural tissue
within the brain)
Synaptogenesis and Pruning
- Synaptogenesis – creating of synapses (starts around 6 months of development)
- 3 phases:
1. Immature synapses form between axons and dendrites
2. Then, synapses undergo maturation and convert from a silent to an active state
(able to actually function)
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3. Finally, the synaptic number is reduced to refine the neuronal connections within
the circuit (through process of synaptic pruning)
- Synaptic pruning = process of synapse elimination, starts near the time of birth and is
completed by the time of sexual maturation
oContinues on through childhood and puberty – stops at the end of puberty;
still do this on a regular basis in the hippocampus though
oSynaptic pruning is thought to be very important for adult learning too
many brain connections has been linked to the inability to learn new things
oDisrupted in some illnesses:
Schizophrenia – too much synaptic pruning
Autism – not enough synaptic pruning
oInfluenced by environmental factors
oAssociated with learning processes
Myelination in the CNS and PNS
- All developing neurons are unmyelinated in the first instance
- Myelination occurs at different times in different structures
- Peripheral nerve myelination commences first, then spinal cord and then brain
- Premature oligodendrocytes around 10 weeks
- Oligodendrocytes (cells in CNS that produce myelin) don’t mature until around week
30 whereas Schwann cells that produce myelin in PNS mature (are active) earlier
- Mature oligodendrocytes around week 30
- Lipid layer of myelin insulates the nerves
- Peripheral nerve myelination
oCommences from the end of the third month
oDifferent timings for each nerve
- Spinal cord myelination
oCommences in the fourth month
oSensory fibres myelinate first
oMyelination commences in the neck (cervical) region and extends caudally
oMotor fibres do not begin to myelinate until after birth and continue to
myelinate for at least the first two years
- Brainstem and cerebellum are myelinated before birth
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Biol week 7 lc nervous system and musculoskeletal system through lifespan. Adult brain: 100 billion neurons, 20 billion within the cerebral cortex, one neuron can make up 10,000 synaptic connections, over 100 trillion synaptic connections. Neurulation starts week 3 of gestation (neuronal progenitor cells divide and migrate) Neural plate neural groove neural tube (allows development of brain in anterior section; develops into spinal cord in posterior/caudal section) primary brain vesicles secondary brain vesicles. Around week 12 gradual thickening of the cortex and formation of cortical layers. Around mid-gestation: direct contact between cortex and rest of cns, gyrification (starting to form gyri, first primary sulci begin to form (allows greater volume of neural tissue within the brain) Synaptogenesis creating of synapses (starts around 6 months of development) 1: then, synapses undergo maturation and convert from a silent to an active state.
