Nervous System Fundamentals: Anatomy and Physiology Chapter 11

Binghamton University BIOL 251

What are the functions of the nervous system?

Sensory input, integration, and motor output

Sensory input

Monitors changes that occur inside and outside the body

Integration

Processing and interpretation of input information → the nervous system “decides” what response to make

Motor output (motor response)

Response is carried out

The Central Nervous System (CNS)

Composed of the brain and spinal cord and is responsible for interpreting sensory input and deciding motor output

The Peripheral Nervous System (PNS)

Composed of nerves that extend from the CNS to the rest of the body and allows information to be sent between the CNS and the rest of the body

What are the general cell types in the nervous system?

Neurons and neuroglia

Neurons

nerve cells that can respond to stimuli and specialize to generate or transmit electrical signals (nerve impulses)

Neuroglia

provide support and maintenance to neurons

What are the types of neuroglia?

Astrocytes, microglial cells, ependymal cells, satellite cells, oligodendrocytes, and Schwann cells

Astrocytes

Projections from membrane surface connect to and wrap around neurons, nerve endings, and surrounding blood capillaries that are found in the CNS

What are the main functions of astrocytes?

They provide nutrient supply for neuron cells, allow migration of young neurons, and “clean up” area surrounding neurons (leaked K+ ions, neurotransimtter)

Microglial cells

Cells in the CNS that contact nearby neuron cells to monitor neuron health and migrate toward injured neurons and transform into a macrophage and phagocytize the neuron

Ependymal cells

Cells that commonly have cilia that line central cavity of the CNS to circulate cerebrospinal fluid within cavities

Satellite cells

cells that support and protect neuron cell in the PNS

Oligodendrocytes

Cell that wraps around nerve fibers in the CNS to create an insulating covering called a myelin sheath for neurons

Schwann cells

Cell that wraps around nerve fibers in the PNS to create an insulating covering called a myelin sheath for neurons

What are some other characteristics of neurons?

Longevity, amitotic, metabolism

What is the general structure of a neuron?

Cell body, nuclei/ganglia, dendrites, axon

Cell body

portion of cell containing the nucleus that synthesizes proteins and neurontransmitters

Nuclei

clusters of cell bodies in the CNS

Ganglia

Clusters of cell bodies in the PNS

Dendrites

The receptive region of the neuron that provides increased surface area for incoming signals and conveys incoming messages toward the cell body

Axon

single, long “nerve fiber” extending from the cell body that is the conducting region of the neuron

What is the function of a neuron being conductive?

It generates and transmits nerve impulses away from the the cell body

Tracts

bundles of axons in the CNS

Nerves

bundles of axons in the PNS

Axon branches at the end to form terminal branches and _____ _______.

axon terminals

Axon terminals

the secretory region of the neuron where neurotransmitter is released to pass the impulse to the next neuron

Myelin sheaths

protects and electrically insulates long and/or large nerve fibers to increase speed at which impulse are transmitted

they are found only on axon portion of the neuron and not all axons are myleniated

Myelination in the PNS

Schwann cells on the axon form the myelin sheath, but none of the Schwann cells contact each other (myelin sheath gaps)

Myelin sheath gaps

region of axon that is “exposed” due to absence of Schwann cell covering

Functional Classification of Neurons

Afferent (sensory) neurons and Efferent (motor) neurons

Functional classification groups neurons according to direction in which nerve impulse travel relative to the CNS

Afferent neuron

Sensory → neurons transmit signals to the CNS

Efferent neuron

Motor → neurons transmit motor signals away from the CNS

Impulses travel to effector organs (muscle or glands)

Interneuron

found in between sensory and motor neurons and passes signals through CNS pathways where integration occurs

Why is communication between interneurons necessary or helpful?

Interneurons can connect to other interneurons which is helpful for information integration and processing

Membrane potential

a difference in electrical charge across the plasma membrane

Resting membrane potentional

approximately -70 mV

What is the purpose of changing the membrane potential of neurons?

To change the permeability of the plasma membrane to one or more ions which requires the use of ion channels in the plasma membrane

What are the types of electrical signals that can be produced by a change in resting membrane potential?

Graded potential and action potential

Ion channels

proteins in plasma membrane that form “channels” to allow passage of ions into/out of cell

Types of ion channels

Leakage channels and gated channels (which can be chemically, voltage, or mechanically gated)

Leakage channels

always open and allow free flow of ions across plasma membrane

Gated channels

Have a “gate” that must open before ions can move

Chemically gated

open when a certain chemical (neurotransmitter) binds to a protein

Voltage-gated

open and close in response to changing membrane potentials

Mechanically gated

open in response to physical deformation of receptor

What can changes in membrane potential voltage due to opening or closing of ion channels result in?

Depolarization or hyperpolarization

Depolarization

excitation of a neuron; when the inside of the cell becomes more positively charged compared to the resting membrane potential

Does excitation/depolarization of a neuron make it more or less likely to send a message?

It is more likely to send a message because it increases the membrane potential towards to threshold voltage needed trigger an action potential

Hyperpolarization

inhibits a neuron; when the inside of the cell becomes more negatively charged compared to the resting membrane potential

Does hyperpolarization of a neuron make it more or less likely to send a message?

It is less likely because decreasing the membrane potential moves the voltage further from the threshold needed to trigger an action potential

Graded

magnitude varies directly with stimulus strength

Graded potentials

Necessary to initiate a nerve impulse

Only occur over short distances

Can be depolarizing or hyperpolarizing

Action potentials (nerve impulses)

Necessary to send information from one neuron to another

Have a consistent strength

Occur over long distances

are only depolarizing; membrane potential changes from -70 mV to +30 mV every time

Generating Action Potentials (AP)

changing the permeability of the plasma membrane to ions via opening of voltage-gated ion channels in membrane in response to changing membrane potential