Nervous System: General Principles Comparative Anatomy Tony Serino. Ph.D. Biology Dept. Misericordia Univ.

Nervous System Controls and/or modifies all other systems Rapid response time Usually short duration Reflex arc illustrates functional control

Divisions of the Nervous System

Nervous Tissue Non-excitable Tissue (Supportive cells) Neuroglia –present in CNS Schwann and Satellite cells –present in PNS Neurons (excitable tissue) Initiate and conduct electrical signals (action potentials)

Neuroglia (glial cells) Phagocytic,protective Form BBB Regulate microenvironment Pass on nutrients; get rid of waste

Neuroglia Line cavities Create CSF Secrete myelin in CNS

PNS Supportive Cells Schwann cells –secrete myelin in PNS Satellite cells –surround neuron cell bodies in PNS

Neuron Anatomy Axonal terminal Nerve ending Synaptic boutons Synaptic knobs

Functional Zones of a Neuron Receptor Zone Initial segment of Axon (trigger zone) Nerve endings Axon

Internal Cell Body Structures

Myelination In PNS, a Schwann cell wraps and individual segment of a single axon In the CNS, an oligodendrocyte performs the same function but can attach to more than one axon

Node of Ranvier: gaps in myelin sheath

Types of Neurons Anatomical classification Functional Classification Based on number of process projecting from cell body Functional Classification Based on location of neuron and direction of information flow

Functional Classes

General Terms Ganglia vs. Nuclei Nerve vs. nerve fiber Areas of densely packed nerve cell bodies Ganglia are usually found in PNS Nuclei are found in CNS Nerve vs. nerve fiber A nerve is a dissectible structure containing hundreds of axons A nerve fiber is a single axon CT sheaths covering peripheral nerves:

Nerve CT sheaths

Synapses Areas where neurons communicate with other cells Can be chemical (with neurotransmitters) or electrical (gap junctions)

Anatomy of Synapse (chemical) Neurotransmission ends when NT diffuses away, re-absorbed by presynaptic neuron, or NT metabolized (degraded) by enzymes in cleft

Neurotransmission Electrical signal (action potential (AP)) descends axon to synaptic knob (nerve end) Depolarization opens Ca++ channels to open in presynaptic membrane Triggers a number of synaptic vesicles to fuse with outer membrane Dumps neurotransmitter (NT) into synaptic cleft NT diffuses across cleft and binds to receptor on postsynaptic membrane This leads to channels opening on postsynaptic membrane changing the membrane’s potential