Overview
This lecture introduces the basics of nervous tissue and the organization of the nervous system, focusing on its structure, function, and fundamental cell types.
Introduction to the Nervous System
- The nervous system is one of the body's main communication systems, fundamental to personality, behavior, and consciousness.
- It controls the body with electrical signals and neurotransmitters, while the endocrine system uses hormones.
- Nervous system functions in three steps: receiving information (stimuli), processing/integration, and issuing commands.
Organization of the Nervous System
- The nervous system has two main anatomical divisions: central nervous system (CNS—brain and spinal cord) and peripheral nervous system (PNS—all nerves and ganglia outside CNS).
- The PNS is divided into sensory (afferent) and motor (efferent) divisions.
- Sensory fibers: Somatic (from skin, muscles, joints) and visceral (from internal organs).
- Motor fibers: Somatic (to skeletal muscles, voluntary), Autonomic (to smooth/cardiac muscles and glands, involuntary).
Autonomic Nervous System
- The autonomic system has sympathetic (arouses body for action, "fight or flight") and parasympathetic (calms, "rest and digest" or SLUDD: salivation, lacrimation, urination, digestion, defecation) divisions.
- Sympathetic neurons originate from thoracic/lumbar spinal cord; parasympathetic from brain and sacral spinal cord.
Structure and Functions of Neurons
- Two cell types: neurons (transmit electrical signals) and neuroglia/glial cells (support).
- Neuron properties: excitability (response to stimuli), conductivity (signal transmission), secretion (release neurotransmitters).
- Three functional classes: sensory/afferent neurons (detect stimuli), interneurons (process information, memory), motor/efferent neurons (send commands to effectors).
- Neurons cannot switch functional class.
Neuron Anatomy
- Soma (cell body): contains nucleus, nucleolus, mitochondria, lysosomes, Golgi, rough ER (Nissl bodies); lacks centrioles (no mitosis in adults).
- Dendrites: receive signals; axon: transmits signals away from soma; axon hillock/trigger zone initiates the signal.
- Axons are insulated by myelin sheath for faster signal transmission.
- Axon terminals (synaptic knobs): store neurotransmitters produced in the soma.
Types of Neurons and Synapses
- Neuron shapes: multipolar (one axon, multiple dendrites), bipolar (one dendrite stalk, one axon), unipolar (axon and dendrite joined), anaxonic (no axon).
- Collections of neuron cell bodies: ganglion (PNS), nucleus (CNS).
- Collections of axons: nerve (PNS), tract (CNS).
- Synapse: gap between neurons where neurotransmitters cross from presynaptic to postsynaptic neuron.
Axonal Transport
- Proteins and neurotransmitters are produced in the soma and transported down the axon via microtubules using motor proteins.
- Anterograde transport: soma to axon terminal; retrograde transport: axon terminal to soma.
Key Terms & Definitions
- Neuron — Nerve cell transmitting electrical signals.
- Neurotransmitter — Chemical messenger released by neurons.
- Afferent (Sensory) Neuron — Transfers stimuli to CNS.
- Efferent (Motor) Neuron — Sends commands from CNS to effectors.
- Interneuron — Processes information within CNS.
- Ganglion — Cluster of neuron cell bodies in PNS.
- Nucleus (CNS) — Cluster of neuron cell bodies in CNS.
- Nerve — Bundle of axons in PNS.
- Tract — Bundle of axons in CNS.
- Myelin Sheath — Insulation around axon for faster signal transmission.
- Synapse — Junction between neurons for signal transfer.
Action Items / Next Steps
- Review the structures and functions of neurons and nervous system divisions.
- Prepare for next video covering neural support cells (neuroglia).