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Nervous Tissue: Structures, Functions, and Action Potentials, Exams of Biology

Howard Community CollegeBiology

A comprehensive overview of nervous tissue, covering its structures, functions, and the mechanisms of action potentials. It explores the organization of the nervous system, including the central and peripheral nervous systems, and delves into the different types of neurons and neuroglia cells. The document also explains the process of myelination and the generation of action potentials, highlighting key concepts like resting membrane potential, graded potentials, and the refractory period.

Typology: Exams

2024/2025

Available from 12/22/2024

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Chapter 12 - Nervous Tissue
questions and answers 2025-
2026(latest update with
verified solutions)
Structures of the Nervous System - answer Brain, Cranial Nerves,
Nerves, Spinal Cord, Spinal Nerves, Ganglia and Sensory Receptors.
Together they contribute approx 3% of overall body weight.
Cranial Nerves - answer Nerves that come off the base of the base
of the brain. There are 12 pairs (left & right sided).
Nerve - answer A bundle of hundreds to thousands of axons. Each
nerve follows a specific path to its part of the body.
Spinal Nerves - answer Nerves that exit off of the cord. There are
31 pairs (left and right sided).
Ganglia - answer A mass of nervous tissue that is located outside
of the brain and cord.
Sensory Receptors - answer Dendrites of sensory neurons that
monitor our internal and external environment.
Functions of the Nervous System (3) - answer 1) Sensory Function -
receptors in our tissues that detect internal signals (e.g.
temperature, blood sugar) and external signals (e.g. car coming at
you). These tell our brain what's going on and then the brain sends
other signals in response. Neurons called sensory (afferent) neurons
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Chapter 12 - Nervous Tissue

questions and answers 2025-

2026(latest update with

verified solutions)

Structures of the Nervous System - answer Brain, Cranial Nerves, Nerves, Spinal Cord, Spinal Nerves, Ganglia and Sensory Receptors. Together they contribute approx 3% of overall body weight. Cranial Nerves - answer Nerves that come off the base of the base of the brain. There are 12 pairs (left & right sided). Nerve - answer A bundle of hundreds to thousands of axons. Each nerve follows a specific path to its part of the body. Spinal Nerves - answer Nerves that exit off of the cord. There are 31 pairs (left and right sided). Ganglia - answer A mass of nervous tissue that is located outside of the brain and cord. Sensory Receptors - answer Dendrites of sensory neurons that monitor our internal and external environment. Functions of the Nervous System (3) - answer 1) Sensory Function - receptors in our tissues that detect internal signals (e.g. temperature, blood sugar) and external signals (e.g. car coming at you). These tell our brain what's going on and then the brain sends other signals in response. Neurons called sensory (afferent) neurons

carry sensory information from the body into the spinal cord and brain.

  1. Integrative Function - the brain and spinal cord process the sensory information and make decisions based on this information. This is perception and is done by interneurons.
  2. Motor Function - motor neurons (efferent) carry out the response that has been processed or decided. It travels to skeletal muscles, smooth muscles or glands for the response. Organization of the Nervous System (2 systems) - answer 1) Central Nervous System (CNS) - consists of the brain and spinal cord
  3. Peripheral Nervous System (PNS) - all other nervous tissue that is not the brain or cord Somatic Nervous System - answer The body nervous system which consist of two types:
  4. Sensory neurons that send sensory information from the head, body, limbs, eyes, ears, mouth and nose to the CNS
  5. Motor neurons that send signals from the brain and cord to only SKELETAL muscle. These actions are voluntary. Skeletal = Somatic Autonomic Nervous System - answer Body actions that are involuntarily controlled which consists of two types:
  6. Sensory neurons that send their sensory information from autonomic receptors in our organs and blood vessels to the brain

Neuron Structure and Function Variations (3) - answer 1) Multipolar Neurons - contains several dendrites and one axon. They're the most common and are typically found in the brain and spinal cord.

  1. Bipolar Neurons - contains one main dendrite and one axon. They're typically found in the retina of the eye, inner ear and smell region in the brain.
  2. Unipolar Neurons - these begin as bipolar in an embryo but the axon and dendrite fuse into a single process. They're typically found in skin for sensations of touch and stretching. CNS Neuroglia Cells (4 types) - answer 1) Astrocytes - star shaped cells with many branching processes. They're the largest and most numerous neuroglia cells. Their processes make contact with blood capillaries, neurons and pia mater. Their functions are to support the neurons by creating a barrier to prevent harmful substances in the blood from affecting the neurons (blood-brain barrier). They regulate the growth of neurons and maintain the appropriate chemical environment (ion regulation).
  3. Oligodendrocytes - smaller than astrocytes with very few processes. Their job is to form and maintain the myelin sheath around axons.
  4. Microglia - small with spine like projections. Their function is phagocytosis, engulfing cellular debris, microbes and damaged tissue.
  5. Ependymal Cells - cuboidal or columnar shaped cells that form a single layer that line the ventricles of the brain and spinal cord. Their function is to produce, monitor and circulate cerebrospinal fluid.

PNS Neuroglia Cells (2 types) - answer 1) Schwann Cells - encircle the axons in the PNS. They function to form myelin sheaths around axons and aid in axon regeneration.

  1. Satellite Cells - flat cells that surround the cell body of a neuron. Their job is to regulate the exchange of materials (CO2, O2, Glucose, etc.) between the cell body and interstitial fluid. Myelination - answer A lipid and protein covering of the axon called the myelin sheath. The purpose of the myelin sheath is to electrically insulate the axon which increases the speed of the nerve impulse. The Nodes of Ranvier are gaps in the myelination that participates in the speeding up of the nerve impulse. Neurolemma - answer The outer nucleated layer of the Schwann cell which aids in regeneration of the axon when injured. Gray Matter - answer Gray matter is composed of neuron cell bodies, dendrites, unmyelinated axons and neuroglia cells. Exists in both spinal cord and brain. White Matter - answer White matter is composed of myelinated axons. Exists in both spinal cord and brain. Action Potential Genesis - answer The Action Potential begins, when stimulated, in the cell body and dendrites. Once initiated, the axon serves as the conductor of the impulse and is the conduit of the signal to its destination. Electrochemical Gradient - answer Is the chemical concentration difference plus the electrical charge difference. Ions will move from high concentration to low as well as from a positive charge moving to a negative charge.

Generation of Action Potentials - answer An AP is a sequence of events in which voltage-gated channels open in the axon and the axon terminal. It requires enough stimulation to change the RMP from -70 to -55 mV for an AP to occur. The first channels that open allow Na+ to enter the cell. When enough Na+ enters the cell, K+ channels open. As K+ leaves the cell, it causes repolarization to occur. Depolarization occurs when enough graded potentials cause the RMP to reach the threshold of -55 mV. When -55 mV is reach, Na+ channels open and the AP is conducted down the axon. Depolarization Phase - answer When a graded potential causes the membrane to depolarize to -55 mV. This causes Na+ to rush into the cell. Repolarization Phase - answer When the threshold level reaches +30 mV, K+ are opened to return the membrane back to the -70 mV level. Refractory Period - answer The period of time after an action potential in which the cell can not generate another action potential. Relative Refractory Period - answer The period of time in which a second AP can occur if a large enough stimulus acts upon it. Axon Diameter - answer The larger the axon's diameter, the faster the action potential will travel. Schwann cells and myelination increase the diameter of axons and thus speed up the signal transmission. Axon Fibers (3 types) - answer 1) A Fibers - largest in diameter, heavily myelinated and their conduction speed is 12-130 m/s. They're found in our sensory neurons for touch, pressure, temperature, joint position; and our motor neurons to skeletal muscle

  1. B Fibers - have less myelination than A fibers so they're smaller and have a conduction speed of up to 15 m/s. They're found in sensory neurons of organs to our spinal cord and brain. The motor neurons are autonomic that go from our brain and cord to all autonomic nervous systems glands and smooth muscle.
  2. C Fibers - the smallest unmyelinated fibers. They have a conduction speed of 0.5-2 m/s. They're found in sensory neurons for pain and some temperature (hot and cold). Motor neurons are autonomic that go to cardiac muscle, smooth muscles and glands. Presynaptic Neuron - answer The neuron that is sending the signal. Postsynaptic Neuron - answer The neuron that is receiving the signal. Synapses can occur either axon-dendrite, axon-cell body or axon-axon. Electrical Synapse - answer Where an action potential conducts directly between two neurons at a gap junction. Not the most common but can be seen in smooth muscle and cardiac muscle. It has two advantages:
  3. Faster communication - signal goes faster through the gap junction than across the synaptic cleft
  4. Synchronization - where a group of neurons synchronize to contract at the same time. Very important in heart or organs with smooth muscle. Chemical Synapse - answer Where the action potential causes release of a neurotransmitter that crosses the synaptic cleft to the postsynaptic neuron. The release of the chemical causes a delay, making the chemical synapse slower. The neurotransmitter causes gated channels to release ions on the postsynaptic side creating an action potential. These are primarily seen in skeletal muscle, spinal cord and brain.

Neural Circuits (5 types) - answer 1) Simple circuit - where the presynaptic neuron stimulates one postsynaptic neuron (one-on- one)

  1. Diverging circuit - where the AP from the presynaptic neuron causes an AP in many other postsynaptic neurons. Areas found include sensory receptors in the skin.
  2. Converging circuit - where a postsynaptic neuron receives AP's from several presynaptic neurons. This is common in motor neurons in skeletal muscle.
  3. Reverberating circuit - where the incoming impulse stimulates a series of AP's that may travel to and from the original presynaptic neuron. Examples are breathing, waking up and short term memory.
  4. Parallel after-discharge circuit - where the presynaptic neuron stimulates a group of neurons which all synapse with one postsynaptic neuron. An example is when performing math calculations.