PSL300H1 Lecture Notes - Lecture 7: Peripheral Nervous System, Somatic Nervous System, Autonomic Nervous System
PSL300
Lecture 7: Overview of Neuroanatomy
The Central Nervous System
• Includes the brain and the spinal cord
• The brain is housed inside the skull
o Protected by layers of membranes, CSF and the skull
• Spinal cord is made up of vertebrae
o Stacks of bones
o Cervical → thoracic → lumbar → sacral
• The brain has ~86 billion neurons, and the spinal cord ~1 billion neurons
The Peripheral Nervous System
• The PNS includes all neurons, and some parts of neurons, outside the
CNS
• The PNS comprises:
o Somatic nervous system → for controlling voluntary action via
skeletal muscle
o Autonomic nervous system → for visceral functions such as
heart rate and breathing
• PNS has approx. 100-600 million neurons
Ventricles are filled with cerebrospinal fluid
• In the brain there are ventricles that are full of CSF
o Hollow spaces that produce the CSF
• Third ventricle is connected to the 4th ventricle through the cerebral
aqueduct
• The CSF provides a physical and a chemical barrier
o Can cushion blows to the area
o Only certain materials can enter the CSF from the blood
(blood brain barrier)
The CNS includes gray and white matter
• Gray matter consists of nerve cell bodies, unmyelinated axons, and
dendrites
o The cell bodies are arranged either in layers (in parts of the brain) or in clusters called nuclei (singular:
nucleus)
• White matter consists of myelinated axons running in bundles called tracts
• In the peripheral nervous system, clusters of neurons are called ganglia (singular: ganglion), and bundles of
axons are nerves
CNS and Energy
• The brain has just ~2% of the body’s mass, but gets 15% of the blood pumped by the heart
• The brain also consumes half the body’s glucose – uses up a lot of energy
• The CNS saves energy by limiting communication between neurons
o Neurons communicate with each other by sending action potentials (spikes) down their axons, but those
action potentials take a lot of energy
o The energy supply to the CNS can support only a low rate of firing, e.g. in cortex it permits an average
rate per cell of just one spike every 6 s
o At any moment, only ~4% of your neurons are firing
o That is, communication is expensive, and so the CNS has to use it sparingly
Document Summary
The peripheral nervous system: the pns includes all neurons, and some parts of neurons, outside the. Cns: the pns comprises, somatic nervous system for controlling voluntary action via skeletal muscle, autonomic nervous system for visceral functions such as heart rate and breathing, pns has approx. In the peripheral nervous system, clusters of neurons are called ganglia (singular: ganglion), and bundles of axons are nerves. Important for reflexes that are involving multiple limbs: signals that stay within the spinal cord. Information from the nose: cranial nerve 2 optic nerve. Information from the retina about the visuals that you are seeing. Interface between the cerebrum and the brain stem: thalamus. Important for cerebral lateralization: allows for communication between the 2 hemispheres, types of skill in the left and right hemisphere are not symmetrically distributed, different parts of the brain are in charge of different functions.
