Nervous system chapter 12

Sensory input, integration, and motor output What is the overall function of the nervous system?

Sensory input, integration, and motor output

To sense and respond to external or internal changes in the body through voluntary or involuntary responses

Central nervous system (CNS) and peripheral nervous system (PNS)

The brain and spinal cord

To receive, interpret, integrate, and respond to signals from the PNS

Cranial nerves and spinal nerves

To carry sensory information to the CNS and motor commands from the CNS to effectors

PNS → CNS → PNS

The afferent division

To carry sensory information from receptors toward the CNS

The efferent division

To carry motor commands from the CNS to effectors

Afferent arrives at the CNS

Efferent exits the CNS

Sensory input → CNS integration → Motor output

Afferent division brings information to the CNS; the CNS integrates the signals; the CNS sends commands to the efferent division; the efferent division carries commands to effectors

A neuron located entirely within the CNS that receives, integrates, and relays information between neurons

Exclusively in the CNS

To process and relay information between sensory and motor neurons

Sensory neurons carry information toward the CNS, while motor neurons carry commands away from the CNS

From the brain; many originate from the brainstem

Relating to the body, particularly the skin, skeletal muscles, and bones

Skin, skeletal muscles, and bones

Relating to internal organs and structures

Digestive organs, spleen, bladder, heart, and lungs

Somatic information comes from the body wall and musculoskeletal system, while visceral information comes from internal organs

Regulating involuntary functions of internal organs, glands, cardiac muscle, and smooth muscle

Sympathetic and parasympathetic divisions

Prepares the body for fight-or-flight responses

Promotes rest-and-digest activities

A muscle, gland, or other target that carries out a response to a motor command

Skeletal muscles, smooth muscles, cardiac muscle, and glands

To detect stimuli from the internal or external environment

Sensory receptors detect stimuli, and afferent nerves carry the information to the brain or spinal cord

Relay it to the brain or integrate it locally to produce a spinal reflex

Specialized brain regions process and integrate sensory information and help determine an appropriate response

Through efferent nerves, often via the spinal cord or directly through cranial nerves

A rapid, automatic response integrated in the spinal cord

By receptor location and by the type of stimulus detected

A receptor that detects stimuli from outside the body

In the skin and special sense organs

Touch, pressure, pain, temperature, smell, hearing, taste, and vision

A receptor that detects stimuli from internal organs and the body's internal environment

Visceroceptors

Changes in internal chemistry, organ stretch, and other conditions within the viscera

A receptor that detects the position and movement of the body by sensing stretch in muscles, tendons, ligaments, and joints

Information about body position and movement

A receptor that detects mechanical forces such as touch, pressure, stretch, or vibration

A mechanoreceptor that detects changes in pressure, such as blood pressure

A mechanoreceptor

A receptor that detects temperature changes

A receptor that detects chemical changes

Changes in blood oxygen, carbon dioxide, or pH

A receptor that detects light

A receptor that detects potentially damaging stimuli associated with pain

Functional classification describes what stimuli receptors detect or where they are located; structural classification describes their physical structure

A sensory receptor formed by exposed nerve endings embedded in tissues

In many tissues, particularly epithelia and connective tissue beneath epithelia

Pain and temperature; some also detect light touch

A sensory nerve ending surrounded by connective tissue that helps modify or enhance its sensitivity to stimuli

It can increase sensitivity to particular signals and filter mechanical stimuli

Primarily in the papillary dermis

Light touch

In deeper connective tissues, including the deep dermis and subcutaneous tissues

Deep pressure and vibration

Stretch of the skin or other tissues

Muscle spindles and other receptors in muscles, tendons, and joints

A specialized cell with structures that detect a particular stimulus and communicate the information to neurons

A photoreceptor cell in the retina

Light

Changes in blood chemistry, including oxygen, carbon dioxide, and pH

To cardiorespiratory control centers in the medulla

Chemoreceptors stimulate signals to the medulla that can increase breathing rate

An exteroceptor and a thermoreceptor

An interoceptor and a chemoreceptor

A proprioceptor and a mechanoreceptor

Exteroceptors and photoreceptors

The two classifications describe different features and together provide a fuller description of a receptor

Neurons and neuroglia

To receive and transmit electrical signals and communicate with other cells

To support, protect, nourish, and insulate neurons and help maintain the nervous system environment

An electrical signal transmitted along a neuron's plasma membrane, usually through an action potential

A rapid change in membrane voltage that propagates along an excitable cell membrane

About 86 billion

They have high metabolic demands to maintain their functions and signaling

Most mature neurons do not divide

Some neurons can survive for many decades, potentially for a person's entire lifetime

The cell body containing the nucleus and much of the cell's machinery

To receive signals and generally carry them toward the cell body

The region where the cell body connects to the axon and where action potentials are commonly initiated

To conduct electrical signals away from the cell body toward the axon terminals

The ends of an axon that communicate with another neuron, muscle, or gland

Swollen endings of axon terminals that contain synaptic vesicles

Neurotransmitters

Clusters of rough endoplasmic reticulum and associated ribosomes involved in protein synthesis in neurons

Dendrites → cell body → axon → axon terminals → target cell

A type of neuroglial cell in the PNS that wraps around axons and can form myelin

To insulate axons and increase the speed of nerve impulse propagation

A gap between adjacent myelin segments along an axon

Action potentials are regenerated, allowing impulses to travel rapidly by saltatory conduction

CNS neuroglia that form myelin sheaths around axons

Schwann cells myelinate axons in the PNS, while oligodendrocytes myelinate axons in the CNS

By the number of processes extending from the cell body

Multipolar, bipolar, and unipolar neurons

A neuron with one axon and multiple dendrites

A neuron with one dendrite and one axon

A neuron with a single process extending from the cell body; sensory neurons are commonly pseudounipolar

By the direction in which they transmit information and their role in the nervous system

Pseudounipolar

Multipolar

Multipolar

A site where a neuron communicates with another neuron or a target cell

The cell that sends a signal into a synapse

The cell that receives a signal across a synapse

Yes, a neuron can receive signals at some synapses and send signals at others

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

Astrocytes, microglia, ependymal cells, and oligodendrocytes

Satellite cells and Schwann cells

Star-shaped CNS neuroglia that support neurons and help regulate the chemical environment

Helping maintain the blood-brain barrier

A selective barrier that restricts the movement of many substances from the blood into brain tissue

It helps maintain a stable chemical environment for neurons and protects brain tissue from many harmful substances

Substances such as glucose, water, ions, and amino acids can cross through regulated pathways

They help regulate extracellular ion concentrations and take up and recycle neurotransmitters

They communicate with blood vessels and help coordinate local blood flow with neural activity

Immune-related neuroglia in the CNS that defend nervous tissue and remove debris

Phagocytosis and immune defense

Macrophages

Cells that line the ventricles of the brain and the central canal of the spinal cord

They help form the boundary between cerebrospinal fluid and nervous tissue and are involved in CSF production and circulation

Fluid that surrounds the brain and spinal cord and helps protect and support the CNS

Within the brain

Within the spinal cord

Forming myelin sheaths around CNS axons

PNS neuroglia that surround neuronal cell bodies in ganglia

To support neuronal cell bodies and regulate their local chemical environment

Supporting PNS axons and forming myelin sheaths around them

Layers of glial cell plasma membrane rich in lipids and proteins

It reduces current leakage and allows action potentials to be regenerated at nodes of Ranvier

A bundle of axons located in the PNS

A bundle of axons located in the CNS

A collection of neuronal cell bodies located in the PNS

Ganglia

A collection of neuronal cell bodies located in the CNS

Nuclei

A nerve is a bundle of axons in the PNS, while a tract is a bundle of axons in the CNS

A ganglion is a collection of neuronal cell bodies in the PNS, while a nucleus is a collection of neuronal cell bodies in the CNS

CNS tissue composed primarily of myelinated axons and neuroglia

Tracts

CNS tissue containing neuronal cell bodies, dendrites, synapses, neuroglia, and some unmyelinated axons

Nuclei and other regions containing neuronal cell bodies and synapses

In gray matter

CNS pathways that carry information upward, typically from the spinal cord toward the brain

CNS pathways that carry commands from the brain toward lower CNS regions, including the spinal cord

Receptors detect stimuli; sensory nerves carry signals through the PNS; CNS pathways carry the information through tracts to the brain

Commands travel through descending CNS pathways, synapse with motor neurons, and reach effectors through PNS nerves

The processing and integration of nervous system information to help convert sensory input into an appropriate response

A rapid, automatic response to a stimulus

The neural pathway that produces a reflex response

A reflex arc

In the spinal cord

A reflex involving one synapse between a sensory neuron and a motor neuron

No

The knee-jerk stretch reflex

A reflex involving two or more synapses and at least one interneuron

The withdrawal reflex

Polysynaptic reflexes

A rapid, automatic response that moves a body part away from a potentially harmful stimulus

A sequence of neural processing steps that produces a rapid reflex response

A sensory neuron carries information to the spinal cord, interneurons process it, and motor neurons activate muscles to withdraw the hand

No, the spinal cord can integrate the reflex and initiate the motor response

The simultaneous processing of information by different neural pathways

The spinal cord initiates a rapid withdrawal reflex while ascending pathways carry sensory information to the brain for pain perception

It carries pain and temperature information toward the brain, including the thalamus

The brain processes the sensation and can generate additional motor commands

The brain processes the pain and sends motor commands through descending tracts to motor neurons that activate muscles

The withdrawal reflex is rapid and integrated in the spinal cord, while the later voluntary response involves processing and decision-making by the brain

To carry sensory information toward the brain

To carry motor commands from the brain toward lower CNS regions

Sensory input carries information from receptors to the CNS, while motor output carries commands from the CNS to effectors

Stimulus → sensory receptor → afferent neuron → CNS integration → efferent neuron → effector → response

Voluntary responses involve conscious control, while involuntary responses occur automatically without requiring conscious control

Structural classification describes the number of processes, while functional classification describes the neuron's role and direction of information flow