Anatomy & Physiology I: Chapter 11 (Unfinished)

Nervous tissues

What are the basic functions of the nervous system

1. It is the master control & communication system

2. Communication is rapid and specific

What are the three steps of information flow through the nervous system?

1. Sensory input

2. Integration

3. Motor output

What is sensory input?

Input gathered by sensory receptors about internal and external enviornments

What is inegration?

The processing of the sensory input (planning how to respond)

What is motor output?

The activation of effector organs tp produce a response

What are the two major divisions of the nervous system?

1. The Central Nervous System (CNS)

2. The Peripheral Nervous System (PNS)

What makes up the central nervous system?

It consists of the brain & spinal cord.

What is the function of the central nervous system?

It serves as the control center and is responsible for integration.

What makes up the peripheral nervous system?

Nerves outside of the central nervous system (spinal & cranial nerves)

What is the function of the peripheral nervous system?

It transmits sensory inputs and motor outputs.

What are the two subdivisions of the peripheral nervous system?

1. Sensory (afferent) division

2. Motor (efferent) division

What makes up the sensory (afferent) division?

1. Somatic sensory fibers

2. Visceral sensory fibers

What is the function of somatic sensory fibers?

They send signals from the skin, skeletal muscles, and joints to the CNS

What is the function of visceral sensory fibers?

They send signals from the visceral organs to the CNS

What is the function of the sensory (afferent) division?

It conducts impulses from receptors to the central nervous system

What are the two subdivisions of the motor (efferent) system?

1. Somatic (voluntary) nervous system

2. Autonomic (involuntary) nervous system

What is the somatic (voluntary) nervous system?

It consists of somatic (voluntary) motor nerve fibers.

What is the function of the somatic (voluntary) nervous system?

It sends signals from the CNS to skeletal muscles.

What is the autonomic (involuntary) nervous system?

It consists of visceral (involuntary) motor nerve fibers

What is the function of the autonomic (involuntary) nervous system?

It conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands.

What are the two subdivisions of the autonomic nervous system?

1. Sympathetic Nervous System

2. Parasympathetic Nervous System

What is the function of the sympathetic nervous system?

It mobilizes the body for activity

What is the function of the parasympathetic nervous system?

It prepares the body for rest

How are the two subdivisions of the autonomic nervous system related to each other?

Which four glial cells are found in the central nervous system?

1. Astrocytes

2. Microglia

3. Ependymal cells

4. Oligodendrocytes

What are astrocytes?

They are highly branched cells (star-shaped) and are the most abundant glial cells in the CNS.

What is the function of astrocytes?

1. They support neurons

2. Connect neurons to capillaries

3. Control the chemical environment of neurons 

What are microglia?

They are small with thorny processes and are the primary immune cells of the CNS

What is the function of microglia?

They remove harmful microorganisms, dead cells, and neuronal debris

What are ependymal cells?

They are ciliated cells that line the cavities of the brain and spinal column.

What is the function of ependymal cells?

1. The cilia on the cells help circulate cerebrospinal fluid

2. They form a semipermeable barrier between CSF and interstitial fluid

What are oligodendrocytes?

They are branched cells in the CNS that form the myelin sheaths around nerve fibers.

What is the function of oligodendrocytes?

They wrap around nerve fibers in the CNS to form myelin sheaths

Which two glial cells are found in the peripheral nervous system?

1. Satellite cells

2. Schwann cells

What are satellite cells?

They are found in the peripheral nervous system

What is the function of satellite cells?

Similar to astrocytes

1. They support neurons

2. Connect neurons to capillaries

3. Control the chemical environment of neurons 

What are Schwann cells?

They are found in the peripheral nervous system.

What is the function of Schwann cells?

Similar to oligodendrocytes:

They wrap around nerve fibers in the PNS to form myelin sheaths.

What is a neuron?

A large amitotic cell with a cell body and one or more processes.

What are the structural components of a neuron

Cell body (soma), dendrites, axon, axon terminals, myelin sheath, and myelin sheath gap.

What is the cell body (soma) of a neuron?

It contains the nucleus and organelles

What is the function of the cell body (soma) of a neuron?

It controls the cells activities and integrates incoming signals

What are the dendrites of a neuron?

They are branching extensions closest to the cell body.

What is the function of dendrites?

It receives signals from other neurons and carries them towards the cell body.

What is the axon hillock of a neuron?

A cone-shaped region of the lower cell bod where the axon begins.

What is the function of the axon hillock?

It’s the trigger zone where nerve impulses (action potentials) begin

What is the axon of a neuron?

A long fiber expanding from the axon hillock.

What is the function of the axon?

It carries impulses away from the cell body to other neurons, muscles, or glands.

What is the myelin sheath of a neuron?

An insulating covering around some axons, formed by glial cells.

What is the function of the myelin sheath?

It increases the speed of nerve impulse transmission.

What is the myelin gap (nodes of ranvier) in a neuron?

They are gaps between myelin sheath segments along the axon

What is the function of the myelin gap (nodes of ranvier)?

It releases neurotransmitters to communicate with other neurons, muscles, or glands.

What are 4 characteristics of a neuron?

1. They have an extreme longevity (up to a full lifetime)

2. Amitotic (don’t divide)

3. They have a high metabolic rate (brain= 2.5% body weight) (brain= 20% metabolic use)

4. They respond to stimuli (excitable) and generate electrical impulses (action potentials)

What are the roles of dendrites and axons in neuronal function?

Dendrites receive signals from other neurons and send them toward the cell body

Axons carry signals away from the cell body to the axon terminals, which then transmit the signal to the dendrites of other neurons or to effector cells

What is the name given to clusters of neuronal cell bodies in the CNS?

Nuclei

What is the name given to clusters of neuronal cell bodies in the PNS?

Ganglia

What is the name given to bundles of neuron processes in the CNS?

Tracts

What is the name given to bundles of neuron processes in the PNS?

Fibers

What is current?

The flow of electircal charge (ions) across a membrane

What is a gated channel?

A membrane protein that opens or closes an ion channel when it changes shape

What is a leak channel?

A membrane protein that includes a non-gated channel that is always open

What is the difference between a gated ion channel and a leak channel?

A gated channel is able to open and close in response to stimuli, while a leak channel is always open

What triggers the opening of a ligand-gated channel?

it is triggered when a membrane receptor binds to a neurotransmitter

What is an example of a ligand-gated channel being triggered & opened?

The acetylcholine receptor at the neuromuscular junction when acetylcholine binds to it

What triggers the opening & closing of a voltage-gated channel?

Changes in membrane potential

What are examples of a voltage-gated channel being triggered to open & close?

1. voltage-gated calcium channels on the axon terminal

2. voltage-gated sodium channels responsible for action potential depolarization of sarcolemma

What is chemical gradient? 

Ions move from higher concentration to lower concetration

What is electrical gradient?

Ions move toward opposite electrical charge.

What is an electrochemical gradient?

The combined effect of an ion’s concentration difference and the membrane’s electrical charge difference, allowing the ion move.

How does an electrochemical gradient contribute to the flow of ions across a membrane?

It moves ions across the membrane by combining concentration and electrical differences, determining the direction and rate of ion flow.

What is a membrane potential?

The difference in ionic charge on either side of the cell membrane, measured in millivolts.

How is a membrane potential formed?

It occurs when unequal ion distribution and selective ion permeability creates a voltage difference between the inside and outside of the cell

How is a positive membrane potential (> 0 mV ) formed?

When the inside of the cell has more positive charges than the outside, the membrane potential is > 0 mV

How is a negative membrane potential (< 0 mV ) formed

When the outside of the cell has more positive charges than the inside, the membrane potential is < 0 mV

What is a resting membrane potential?

The difference in ionic charge on either side of the cell membrane when a neuron is at rest, measured in millivolts.

What is the normal resting membrane potential of a neuron?

-70mV

Are there more positive ions inside the neuron or outside the neuron when it is at rest?

There are more positive ions outside the neuron than inside

What is the major cation outside the neuron when it is resting?

High sodium (Na+)

What is the major cation inside the neuron when it is resting?

High potassium (K+)

What is depolarization?

When the inside of the membrane becomes less negative

What is repolarization?

When the inside of the membrane returns toward the resting potential

What is hyperpolarization?

When the membrane becomes more negative than the resting potential

What is grade potential?

A brief, localized change in membrane potential that usually occurs in dendrites or cell body

Does the size of a graded potential change with stimulus strength?

The size varies with stimulus strength

What protein restores the resting membrane ion distribution after a graded potential?

The sodium-potassium pump (Na+/K+-ATPase)

Which two ions are moved by the sodium-potassium pump (Na+/K+-ATPase)?

1. Sodium ions (Na⁺) are pumped out of the cell

2. Potassium ions (K⁺) are pumped into the cell

How does the distance traveled by a graded potential differ from the distance traveled by an action potential?

1. Graded potentials weaken as they move away from the site of stimulation because ions leak out and the signal spreads passively without being regenerated.

2. Action potentials don’t weaken as they travel because they are all-or-none signals.

How does the size of a graded potential differ from the size of an action potential?

1. In a graded potential, the size varies with stimulus strength

2. In an action potential, the size doesn’t vary with stimulus strength

How does the stimulus for a graded potential differ from the stimulus for an action potential?

1. Graded potentials are stimulated by the opening of a gated ion channel 

2. Action potentials are stimulated by the opening of a voltage-gated ion channel

Can graded potentials summate?

They can summate, combining to reach threshold and trigger an action potential

Can action potentials summate?

They can’t summate because each one is an all-or-none event and is followed by a refractory period.

Can action potential be depolarizing, repolarizing, & hyperpolarizing?

They can be depolarizing, repolarizing, or briefly hyperpolarizing, depending on the phase of the action potential.

Can graded potentials be depolarizing, repolarizing, & hyperpolarizing?

They can be depolarizing or hyperpolarizing, depending on the ions moving across the membrane, but they do not actively repolarize.

What is an action potential?

A brief large reversal of the membrane potential from -70mV to +30mV

What triggers an action potential?

The opening of a voltage-gated ion channel

What are the three phases of an action potential?

1. Depolarization

2. Repolarization

3. Hyperpolarization

What change in membrane potential happens during depolarization?

The membrane potential rises from -70mV to +30mV

What change in membrane potential happens during repolarization?

The membrane potential falls from +30mV back to -70mV

What change in membrane potential happens during hyperpolarization?

The membrane potential continues to fall below the -70mV resting potential

Which voltage-gated ion channels are opened during depolarization?

Voltage-gated sodium (Na+) channels open