Anatomy and Physiology

The nervous system consists of the brain and spinal cord (central nervous system, CNS) and the peripheral nerves (peripheral nervous system, PNS). 

The PNS includes the autonomic nervous system, responsible for control of involuntary functions.

The neurone is the functional unit of the nervous system. 

• Each neurone has a cell body and axon terminating at a synapse, supported by astrocytes and microglial cells. 

  • Astrocytes provide the structural framework for the neurones, control their biochemical environment and form the blood–brain barrier. 

  • Microglial cells are blood-derived mononuclear macrophages with immune and scavenging functions. 

  • In the CNS, oligodendrocytes produce and maintain a myelin sheath around the axons. 

  • In the PNS, myelin is produced by Schwann cells.

The brain consists of two cerebral hemispheres, each with four lobes (frontal, parietal, temporal and occipital), the brainstem and the cerebellum. 

The brainstem comprises the midbrain, pons and medulla. 

The cerebellum lies in the posterior fossa, with two hemispheres and a central vermis attached to the brainstem by three pairs of cerebellar peduncles. 

Between the brain and the skull are three membranous layers called the meninges: dura mater next to the bone, arachnoid and pia mater next to the nervous tissue. 

The subarachnoid space between the arachnoid and pia is filled with cerebrospinal fluid (CSF) produced by the choroid plexuses. 

• The total volume of CSF is between 140 and 270 mL and there is a turnover of the entire volume 3–4 times a day; thus CSF is produced at a rate of approximately 700 mL per day.

The spinal cord contains afferent and efferent fibres arranged in discrete bundles (pathways running to and from the brain), which are responsible for the transmission of motor and sensory information. 

• Peripheral nerves have myelinated and unmyelinated axons. 

• The sensory cell bodies of peripheral nerves are situated in the dorsal root ganglia. 

• The motor cell bodies are in the anterior horns of the spinal cord