Study Guide: Nervous Tissue (Anatomy & Physiology Chapter 11)

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Chapter 11: Nervous Tissue

Overview of Nervous Tissue

The nervous tissue is a fundamental component of the nervous system, responsible for transmitting electrical and chemical signals throughout the body. It consists of specialized cells that detect stimuli, process information, and coordinate responses.

Sensory Input and Motor Output: Motor neurons transmit impulses away from the CNS to effectors (muscles and glands). Sensory neurons transmit impulses towards the CNS from receptors in the skin or internal organs.
Central Nervous System (CNS): Includes the brain and spinal cord, responsible for processing and integrating information.
Peripheral Nervous System (PNS): Consists of nerves outside the CNS, connecting it to limbs and organs.
Somatic vs. Autonomic Nervous System: Somatic controls voluntary movements; autonomic regulates involuntary functions (sympathetic and parasympathetic branches).

Types of Glial Cells

Glial cells support and protect neurons. They are essential for maintaining homeostasis, forming myelin, and providing support and protection for neurons.

Oligodendrocytes: Found in the CNS, form myelin sheaths around axons.
Schwann Cells: Found in the PNS, form myelin sheaths and aid in nerve regeneration.
Astrocytes: Connect blood vessels to neurons, form the blood-brain barrier, and secrete growth factors.
Ependymal Cells: Form membranes around tissues in the cerebrospinal fluid (CSF).

Myelin Sheath and Nodes of Ranvier

The myelin sheath is a fatty layer that insulates axons, increasing the speed of nerve impulse transmission. The nodes of Ranvier are gaps in the myelin sheath that facilitate rapid signal conduction.

Function: Myelination allows for saltatory conduction, where impulses jump from node to node, increasing speed and efficiency.
Unmyelinated fibers: Conduct impulses more slowly.

Resting Membrane Potential

The resting membrane potential is the electrical charge difference across the neuron's membrane when the cell is not transmitting a signal.

Typical Value:
Sodium (Na+) and Potassium (K+) Distribution: More Na+ outside, more K+ inside.
Channels: When a signal depolarizes the neuron, sodium channels open, allowing Na+ to enter.

Action Potential

An action potential is a rapid change in membrane voltage that travels along the axon of a neuron, enabling communication.

Phases: Resting, depolarization, repolarization, and threshold.
Threshold: Minimum stimulus required to trigger an action potential.
Refractory Period: Time during which a neuron cannot fire another action potential.
All-or-None Principle: Action potentials are not graded; they either occur fully or not at all.

Equation:

Myelination and Saltatory Conduction

Myelination increases the speed and efficiency of nerve impulse transmission. Saltatory conduction allows impulses to jump between nodes of Ranvier, saving energy and increasing speed.

Benefits: Faster impulse transmission, less energy used.

Neurotransmitters and Synaptic Transmission

Neurotransmitters are chemical messengers that transmit signals across synapses from one neuron to another.

Process: Electrical signal reaches the presynaptic terminal, neurotransmitters are released into the synaptic cleft, and bind to receptors on the postsynaptic neuron.
Examples:
- Acetylcholine: Stimulates muscle contraction.
- Dopamine: Mood, happiness.
- Serotonin: Sleepiness and mood.
- Endorphins: Pain reduction.
- GABA: Inhibitory neurotransmitter.
- Histamine: Involved in wakefulness and appetite control.
- Glutamate: Learning and memory.

Diseases of the Nervous System

Several diseases affect the nervous system, each with distinct causes, symptoms, and treatments.

Disorder	Cause	Symptoms	Treatment/Prognosis
Amyotrophic lateral sclerosis (ALS)	Neurodegenerative disease, scarring and progressive damage of nerve cells in the spinal cord and brain.	Loss of ability to speak, swallow, breathe.	No cure; treatments slow progression, manage symptoms.
Epilepsy	Excessive firing of neurons in short period of time in brain.	Seizures, loss of consciousness, uncontrollable jerking.	Anticonvulsive drugs, nerve stimulators, deep brain stimulators.
Multiple sclerosis (MS)	Myelin around nerve fibers is lost and forms scar tissue.	Affects ability to walk, talk, swallow, vision problems.	Corticosteroids, beta interferons, glatiramer acetate.

Key Vocabulary Terms

Term	Definition	Example/Application
Sensory Neuron	Neuron that detects stimuli and transmits signals to the CNS.	Feeling hot or cold on skin.
Motor Neuron	Neuron that transmits signals from CNS to muscles or glands.	Muscle contraction.
Action Potential	Electrical signal traveling down the axon.	Nerve impulse.
Threshold	Minimum stimulus required to trigger an action potential.	Bowling ball must hit pins with enough force.
Refractory Period	Time after an action potential when a neuron cannot fire again.	Recovery time after running a marathon.
Reuptake	Process of recycling neurotransmitters in the synapse.	Antidepressant drugs block serotonin reuptake.
Saltatory Conduction	Jumping of action potential from node to node along myelinated axon.	Sound of a train starting out, clinking and clacking.

Summary

Nervous tissue is essential for communication within the body, enabling rapid and efficient transmission of signals. Understanding the structure and function of neurons, glial cells, myelination, and synaptic transmission is crucial for comprehending how the nervous system operates and how diseases can disrupt its function.