233 Chapter 12 Neural Tissue
An Introduction to the Nervous System
The Nervous System
Includes all neural tissue in the body
Neural tissue contains two kinds of cells
Neurons - Cells that send and receive signals
Neuroglia (glial cells) - Cells that support and protect neurons
Organs of the Nervous System
Brain and spinal cord
Sensory receptors of sense organs (eyes, ears, etc.)
Nerves connect nervous system with other systems
Divisions of the Nervous System
Anatomical Divisions
Central nervous system (CNS) – Brain and Spinal Cord
Peripheral nervous system (PNS)
31 pair of spinal nerves
12 pair of cranial nerves
4 plexuses – Cervical, Brachial, Lumbar, Sacral
The Central Nervous System (CNS)
Functions of the CNS are to process and coordinate:
Sensory data from inside and outside body
Motor commands control activities of peripheral organs (e.g., skeletal muscles)
Higher functions of brain: intelligence, memory, learning, emotion
The Peripheral Nervous System (PNS)
Functions of the PNS
Deliver sensory information to the CNS
Carry motor commands to peripheral tissues and systems
Nerves (also called peripheral nerves)
- Bundles of axons with connective tissues and blood vessels
- Carry sensory information and motor commands in PNS
- Cranial nerves – connect to brain
- Spinal nerves – attach to spinal cord
Functional Divisions of the PNS
Afferent division - Carries sensory information from PNS sensory receptors to CNS
Efferent division - Carries motor commands from CNS motor neurons to PNS muscles and glands
Receptors and effectors of Afferent division
Receptors - Detect changes or respond to stimuli
Neurons and specialized cells
Complex sensory organs (e.g., eyes, ears)
Effectors - Respond to efferent signals
Cells and organs
The Efferent Division
Somatic nervous system (SNS) - Controls voluntary and involuntary (reflexes) skeletal
,muscle contractions
Autonomic nervous system (ANS)
Controls subconscious actions, contractions of smooth muscle and cardiac muscle, and
glandular secretions (ANS subdivisions)
Sympathetic division has a stimulating effect
Parasympathetic division has a relaxing effect
Neurons
Neurons - The basic functional units of the nervous system
The structure of neurons
The multipolar neuron
Common in the CNS
Cell body (soma)
Short, branched dendrites
Long, single axon
The Cell Body
Large nucleus and nucleolus
Perikaryon (cytoplasm)
Mitochondria (produce energy)
RER and ribosomes (produce neurotransmitters)
Cytoskeleton - Neurofilaments and neurotubules in place of microfilaments and
microtubules Neurofibrils: bundles of neurofilaments that provide support for dendrites and
axon
Nissl bodies - Dense areas of RER and ribosomes, Make neural tissue appear gray (gray
matter)
Dendrites - Highly branched, Dendritic spines - Receive information from other neurons
The axon - Is long and carries electrical signal (action potential) to target. Axon structure is
critical to function
Structures of the Axon
Axoplasm - Cytoplasm of axon, Contains neurofibrils, neurotubules, enzymes, organelles
Axolemma - Specialized cell membrane, Covers the axoplasm
Axon hillock - Thick section of cell body, Attaches to initial segment
Initial segment - Attaches to axon hillock
Collaterals - Branches of a single axon – communication with multiple other neurons
Telodendria - Fine extensions of distal axon
Axon terminals - Tips of telodendria
The Structure of Neurons
The synapse - Area where a neuron communicates with another cell
Presynaptic cell - Neuron that sends message
Postsynaptic cell - Cell that receives message
The synaptic cleft - The small gap that separates the presynaptic membrane and the
postsynaptic membrane
The synaptic terminal - Is expanded area of axon of presynaptic neuron which contains
synaptic vesicles of neurotransmitters
Neurotransmitters - Are chemical messengers
- Released at presynaptic membrane
, - Affect receptors of postsynaptic membrane
- Are broken down by enzymes
- Are reassembled at axon terminal
Recycling Neurotransmitters
Axoplasmic transport
Neurotubules within the axon
Transport raw materials
Between cell body and axon terminal
Powered by mitochondria, kinesin, and dynein
Types of Synapses
Neuromuscular junction - Synapse between neuron and muscle
Neuroglandular junction - Synapse between neuron and gland
Structural Classification of Neurons
Anaxonic neurons - Found in brain and sense organs
Bipolar neurons - Found in special sensory organs (sight, smell, hearing)
Unipolar neurons - Found in sensory neurons of PNS
Multipolar neurons - Common in the CNS, Include all skeletal muscle motor neurons
Anaxonic Neurons – Small, All cell processes look alike
Bipolar Neurons - Are small, One dendrite, one axon
Unipolar Neurons - Also called pseudounipolar neurons, Have very long axons, Fused
dendrites and axon, Cell body to one side
Multipolar Neurons - Have very long axons, Multiple dendrites, one axon
Three Functional Classifications of Neurons
Sensory neurons - Afferent neurons of PNS
Motor neurons - Efferent neurons of PNS
Interneurons - Association neurons
Sensory Neurons
Monitor internal environment (visceral sensory neurons)
Monitor effects of external environment (somatic sensory neurons)
Structures of Sensory Neurons
Unipolar
Cell bodies grouped in sensory ganglia
Processes (afferent fibers) extend from sensory receptors to CNS
Three Types of Sensory Receptors
Interoceptors
Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive)
Internal senses (taste, deep pressure, pain)
Exteroceptors
External senses (touch, temperature, pressure)
Distance senses (sight, smell, hearing)
Proprioceptors
Monitor position and movement (skeletal muscles and joints)
An Introduction to the Nervous System
The Nervous System
Includes all neural tissue in the body
Neural tissue contains two kinds of cells
Neurons - Cells that send and receive signals
Neuroglia (glial cells) - Cells that support and protect neurons
Organs of the Nervous System
Brain and spinal cord
Sensory receptors of sense organs (eyes, ears, etc.)
Nerves connect nervous system with other systems
Divisions of the Nervous System
Anatomical Divisions
Central nervous system (CNS) – Brain and Spinal Cord
Peripheral nervous system (PNS)
31 pair of spinal nerves
12 pair of cranial nerves
4 plexuses – Cervical, Brachial, Lumbar, Sacral
The Central Nervous System (CNS)
Functions of the CNS are to process and coordinate:
Sensory data from inside and outside body
Motor commands control activities of peripheral organs (e.g., skeletal muscles)
Higher functions of brain: intelligence, memory, learning, emotion
The Peripheral Nervous System (PNS)
Functions of the PNS
Deliver sensory information to the CNS
Carry motor commands to peripheral tissues and systems
Nerves (also called peripheral nerves)
- Bundles of axons with connective tissues and blood vessels
- Carry sensory information and motor commands in PNS
- Cranial nerves – connect to brain
- Spinal nerves – attach to spinal cord
Functional Divisions of the PNS
Afferent division - Carries sensory information from PNS sensory receptors to CNS
Efferent division - Carries motor commands from CNS motor neurons to PNS muscles and glands
Receptors and effectors of Afferent division
Receptors - Detect changes or respond to stimuli
Neurons and specialized cells
Complex sensory organs (e.g., eyes, ears)
Effectors - Respond to efferent signals
Cells and organs
The Efferent Division
Somatic nervous system (SNS) - Controls voluntary and involuntary (reflexes) skeletal
,muscle contractions
Autonomic nervous system (ANS)
Controls subconscious actions, contractions of smooth muscle and cardiac muscle, and
glandular secretions (ANS subdivisions)
Sympathetic division has a stimulating effect
Parasympathetic division has a relaxing effect
Neurons
Neurons - The basic functional units of the nervous system
The structure of neurons
The multipolar neuron
Common in the CNS
Cell body (soma)
Short, branched dendrites
Long, single axon
The Cell Body
Large nucleus and nucleolus
Perikaryon (cytoplasm)
Mitochondria (produce energy)
RER and ribosomes (produce neurotransmitters)
Cytoskeleton - Neurofilaments and neurotubules in place of microfilaments and
microtubules Neurofibrils: bundles of neurofilaments that provide support for dendrites and
axon
Nissl bodies - Dense areas of RER and ribosomes, Make neural tissue appear gray (gray
matter)
Dendrites - Highly branched, Dendritic spines - Receive information from other neurons
The axon - Is long and carries electrical signal (action potential) to target. Axon structure is
critical to function
Structures of the Axon
Axoplasm - Cytoplasm of axon, Contains neurofibrils, neurotubules, enzymes, organelles
Axolemma - Specialized cell membrane, Covers the axoplasm
Axon hillock - Thick section of cell body, Attaches to initial segment
Initial segment - Attaches to axon hillock
Collaterals - Branches of a single axon – communication with multiple other neurons
Telodendria - Fine extensions of distal axon
Axon terminals - Tips of telodendria
The Structure of Neurons
The synapse - Area where a neuron communicates with another cell
Presynaptic cell - Neuron that sends message
Postsynaptic cell - Cell that receives message
The synaptic cleft - The small gap that separates the presynaptic membrane and the
postsynaptic membrane
The synaptic terminal - Is expanded area of axon of presynaptic neuron which contains
synaptic vesicles of neurotransmitters
Neurotransmitters - Are chemical messengers
- Released at presynaptic membrane
, - Affect receptors of postsynaptic membrane
- Are broken down by enzymes
- Are reassembled at axon terminal
Recycling Neurotransmitters
Axoplasmic transport
Neurotubules within the axon
Transport raw materials
Between cell body and axon terminal
Powered by mitochondria, kinesin, and dynein
Types of Synapses
Neuromuscular junction - Synapse between neuron and muscle
Neuroglandular junction - Synapse between neuron and gland
Structural Classification of Neurons
Anaxonic neurons - Found in brain and sense organs
Bipolar neurons - Found in special sensory organs (sight, smell, hearing)
Unipolar neurons - Found in sensory neurons of PNS
Multipolar neurons - Common in the CNS, Include all skeletal muscle motor neurons
Anaxonic Neurons – Small, All cell processes look alike
Bipolar Neurons - Are small, One dendrite, one axon
Unipolar Neurons - Also called pseudounipolar neurons, Have very long axons, Fused
dendrites and axon, Cell body to one side
Multipolar Neurons - Have very long axons, Multiple dendrites, one axon
Three Functional Classifications of Neurons
Sensory neurons - Afferent neurons of PNS
Motor neurons - Efferent neurons of PNS
Interneurons - Association neurons
Sensory Neurons
Monitor internal environment (visceral sensory neurons)
Monitor effects of external environment (somatic sensory neurons)
Structures of Sensory Neurons
Unipolar
Cell bodies grouped in sensory ganglia
Processes (afferent fibers) extend from sensory receptors to CNS
Three Types of Sensory Receptors
Interoceptors
Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive)
Internal senses (taste, deep pressure, pain)
Exteroceptors
External senses (touch, temperature, pressure)
Distance senses (sight, smell, hearing)
Proprioceptors
Monitor position and movement (skeletal muscles and joints)
