SPINAL CORD AND PNS

• Spaces in the brain continuous with the central canal of the spinal cord

• Filled with CSF

VENTRICLES OF THE BRAIN

• Specialized capillaries in the pia mater called choroid plexus secrete CSF

• Clear liquid, similar to blood plasma• More Na+ and less of other dissolved ions• Nutritive and protective, provides a pathway

to the blood for waste

CSF

• 31 segments, each gives rise to a spinal nerve

• Connects PNS to CNS• 2 enlargements give

rise to many nerves in those areas– Cervical enlargement– Lumbar enlargement

SPINAL CORD

• White matter surrounding a core of gray matter• Resembles a butterfly with wings outstretched• Posterior and Anterior Horns• Gray commissure• Central canal• 3 parts to the white matter – compose tracts– Anterior funiculus– Posterior funiculus– Lateral funiculi

INTERNAL ANATOMY

• Reflex – a series of action potentials coming from a sensory receptor to the brain, then to an effector in response.

• For example, stepping on a tack:– Pain receptors send action potential up nerves in leg and

spinal cord to brain– Brain sends action potentials down spinal cord and nerves of

leg to muscles of the leg– Effectors move the leg

• Receptor -> Sensory Neuron -> Interneuron -> Motor Neuron -> Effector

REFLEX ARC

• Spinal cord like a 2 way street• Ascending Tracts – sensory impulses to the

brain• Descending Tracts – motor impulses to

effectors• Action potentials can only travel in one

direction, therefore spinal cord has neurons oriented in both directions

TRACTS

• Plexus – a network of nerves• Fibers of various spinal nerves are sorted and

recombined in a way that enables fibers associated with a particular peripheral body part to reach it

PLEXUS