Nervous System: Neural Tissue 1 - PHYL 301

Nervous System

• Controls and regulates the activity of the body

• Provides swift but brief responses

Endocrine System

• Controls and regulates the activity of the body

• Slower, but longer-lasting and multi-organ responses

Overview of Nervous System

• Includes all nervous (neural) tissue

  • Central Nervous System (CNS)

    • Brain

    • Spinal cord

  • Peripheral Nervous System (PNS): all nervous tissue outside the CNS

    • Cranial nerves

    • Spinal nerves

Central Nervous System (CNS)

• Brain

• Spinal Cord

Peripheral Nervous System (PNS)

All nervous tissue outside the CNS

• Cranial Nerves

• Spinal Nerves

What are the 3 Nervous System Functions

1. Sensation (input)

2. Integration (processing)

3. Response (output)

Pathway: Stimulus → Receptor → interneurons → effector → response

What is sensation & sensation?

Detects stimuli (changes inside/outside body)

• Receptors detect stimuli

Stimuli

Changes/events in the internal or external environment

What is integration?

• Interneurons recieve sensory signals

  • Processes

• Interprets and compares stimuli with current and past situations

• May send signals (if needed) to cause a response/effect

What is Response (Motor Activity)?

• Sensory or integrative signals can activate effectors (e.g., muscles, glands)

• Produce a response that has an effect on the internal or external environment

What is the Central Nervous System (CNS)’s Functions?

• Integrates, processes, and coordinates input & output

  • Sensory input: stimuli → CNS

  • Motor output: CNS → organs & tissues

• Origin of intelligence, memory, learning, and emotion

• Main sources of interneurons

  
  

What is the Peripheral Nervous System(PNS)’s Functions?

• Provides sensory information to the CNS and carries motor commands away from the CNS

• Divided into:

  • Afferent division

    • Brings sensory information to the CNS

    • Receptors detect stimuli

  • Efferent division

    • Carries motor commands to muscles and glands

    • Effectors respond to CNS commands

Afferent division

• Brings sensory information to the CNS

  • Towards brain/spinal cord

• Receptors detect stimuli

A = Arrives; Afferent → Axial Skeleton

Efferent division

• Carries motor commands to muscles and glands

  • Away from brain/spinal cord

• Effectors respond to CNS commands

  • Efferent causes Effects

E = Exits; Exit CNS → effectors

What are the two branches of the PNS’s efferent division, and what does each control?

• Somatic nervous system (SoNS*)

  • skeletal muscle

• Autonomic nervous system (ANS)

  • Sympathetic division/nervous system (SyNS*)

  • Parasympathetic division/nervous system (PSNS*)

  • smooth muscle, cardiac muscle, glands, and adipose tissue

What are the three branches of the PNS’s afferent division, and what does each control?

• Somatic sensory receptors

  • skin, muscles, joints

• Visceral sensory receptors

  • internal organs

• Special sensory receptors

  • vision, hearing, etc.

Describe the nervous system as a control system with the following
components: sensory receptors, afferent pathways, control (integrating)
center, efferent pathways, and effector (target) organs

1. Sensory receptor: A receptor in your skin detects potentially damaging heat.

2. Afferent pathway: A sensory neuron carries the signal to the spinal cord.

3. Integrating center: Interneurons in the spinal cord process the signal and activate motor neurons.

4. Efferent pathway: Motor neurons carry commands to your arm muscles.

5. Effector (target organ): Your arm muscles contract, pulling your hand away.

Neurons

• Transfer and process information via action potentials

• Consist of a soma (cell body), axon, dendrites, perikaryon, dendritic spines, and axon terminals

Neuroglia

• Support nervous system function

• Protect the neuron

• Cells with specialized support roles

• Do NOT send action potenials

• ~50% brain mass

Order the signal travels through a neuron

DCBA
Dendrites → Cell Body → Axon → Axon Terminals

Axon

(typically) long neuron extension; carries impulses from cell body

Dendrites

Recieves input, branches

Cell Body

Contains the nucleus and organelles

Axon terminals

Output; Affects another neuron, or muscle

• Ends of telodendria

Axon hillock

Where the axon initial segment connects to cell body; where cell body and axon attaches

Axolemma

plasma membrane of axon

Axoplasm

Cytoplasm of axon

• Axoplasmic transport: movement of material between the cell body and the axons

Collaterals

side branches of main axon

• “-lat” = middle

Telodendria

End branches of axon & collaterals

• “-endria” = Later

Ependymal Cells

• Form ependyma: a cellular lining

• Line Central Nervous System (CNS) cavities

  • Lines brain & spinal cord

• Produce cerebrospinal fluid (CSF)

• Cilia circulate CSF

Microglia

• Specialized phagocytes (eats stuff)

• Protect against pathogens

• Dispose of pathogens, debris, & waste

Immune defense and waste removal

Astrocytes

• Largest & most abundant glial cells

• Form the blood-brain barrier (BBB) around blood vessels

Oligodendrocytes

Form myelin sheaths in CNS

• Can myeliante segments on mulitple axons

White matter

Areas rich in myelinated axons

White = “wrapped”, fatty creamy/yellow phospholipids

Gray matter

• Areas lacking myelinated axons

• Mostly neuronal cell bodies and dendrites

Ganglion

Cluster of neuronal cell bodies in Peripherial Nervous System (PNS)

What forms Peripheral nerves

PNS neuronal axons bundled together

Satellite Cells: PNS Neuroglia (glial cells)

Surround & protect cell bodies

Schwann Cells: PNS Neuroglia (glial cells)

Surround & myelinate axons

• Covers one segment of axon

• Schwann cells are also called neurolemmocytes

• Consists of: Axolemma/neurolemma

What is a myelin sheath made of?

• Made of multiple phospholipid membrane layers

• Contains proteins embedded in myelin

  • PLPs - proteolipid proteins

  • MBPs - myelin basic proteins

What is myelin, what does it do?

• Lipid-rich, insulating sheath made of tightly wrapped layers of glial cell membrane around an axon

• Speeds up action potential conduction; The action potential is regenerated at gaps called nodes of Ranvier, so it appears to jump from node to node

  • Saltatory conduction

How does myelination differ in the CNS and PNS?

• Both: Wraps around repeated and packed

• CNS: An oligodendrocyte sends out several extensions; Each extension wraps an axon segment, so one cell can myelinate segments on multiple axons

• PNS: A Schwann cell encloses an axon segment in a groove, then wraps its membrane around that segment; nucleus and most of its cytoplasm stay outside the compact myelin; One myelinating Schwann cell covers one segment of one axon.

COPS Myelin Mnemonic

CO = CNS & Oligodendrocytes
PS = PNS & Schwann Cells

Officer Maya Lin and pet Swan

Strucural classification: Neuron classification

Based on the number of processes extending from the cell body

Functional classification: Neuron classification

• Sensory

• Interneuron (connects sensory & motor; processes sensory information)

• Motor

Anaxonic: Strucural classification of Neuron

• Many processes, but difficult to differentiate axons and dendrites

• Rare in humans; found only in the CNS

• “ana” = without; without axon

Bipolar: Strucural classification of Neuron

• Cell body between dendrite and axon

• Unmyelinated axons

Pseudounipolar: Strucural classification of Neuron

• Cell body off to one side of the axon

• “Pseudo” – starts as bipolar, becomes “unipolar”

• Most common sensory neuron type

  • Fast detection (Signal doesn’t have to go through cell body)

Multipolar: Strucural classification of Neuron

• Single axon and multiple dendrites (typically)

• Most common type in the CNS

• Most common motor neuron type

What is a stimulus, and how does it reach the CNS as a signal?

• Change in the internal or external environment by a receptor

• Receptor detects the stimulus

• Sensory neuron carries the signal from the PNS toward the CNS

  • An afferent fiber is the axon of that sensory neuron

Somatic sensory neurons: Sensory (Afferent) Neurons

Detect external stimuli in skin, muscles, & other organs

• Interoceptors: monitor internal organ activity

Visceral sensory neurons: Sensory (Afferent) Neurons

Detect internal stimuli from organs

• Exteroceptors: provide information about the external environment •

• Proprioceptors: monitor position and movement

Interoceptors

monitor internal organ activity

Exteroceptors

provide information about the external environment

Proprioceptors

monitor position and movement

Motor neurons

• Send information from CNS → PNS

• Efferent fibers: Axons of motor neurons

What are the two motor divisions?

• Somatic nervous system (SoNS): somatic motor neurons innervating skeletal muscle

• Autonomic nervous system (ANS): visceral motor neurons innervating organs and glands

Somatic nervous system (SoNS)

Somatic motor neurons innervating (controlling) skeletal muscle

Autonomic nervous system (ANS)

visceral motor neurons innervating (controlling) organs and glands

• Preganglionic & (post)ganglionic fibers: axons carry impulses (autonomic motor commands) from CNS → ANS tissues & organs

Interneurons

• Located entirely in the CNS

• Connect sensory & motor neurons

• Analyze sensory input

• Coordinate motor outputs

• Can be excitatory or inhibitory

Synapse

Junction between a neuron and another cell

Two major types of synapses

• Chemical synapse (vesicular): release of neurotransmitters

• Electrical synapse (nonvesicular): ion movement via gap junctions

Electrical synapse

• Membranes of both cells connected with gap junctions

  • Allows ions to flow from one cell to the next

  • Diffusion of ions changes membrane potential; may push postsynaptic cells to threshold

• Less common than chemical synapses

• Faster impulses; can travel in either direction

Chemical Synapses

• Utilize neurotransmitters

• Slower than electrical synapses

• More regulation & control than electrical synapses

• Make up vast majority of synapses (vs. electrical)

Which is more common in the nervous system?

Chemical Synapses

What is a synapse, and how do chemical and electrical synapses differ?

A synapse is a junction where a neuron communicates with another neuron or a target cell, such as a muscle or gland.

• At a chemical synapse, the sending cell releases a neurotransmitter that crosses a gap and binds to receptors on the receiving cell. Transmission is typically one-way.

• At an electrical synapse, ions flow directly between cells through gap junctions. Transmission is very fast and often goes both ways

What structures make up a chemical synapse?

Structure	Location and role
Axon terminal (synaptic knob)	The end of the presynaptic neuron where neurotransmitter is released.
Voltage-gated calcium channels	In the terminal membrane. They open when an action potential arrives, letting Ca²⁺ enter.
Synaptic vesicles	Small sacs in the presynaptic terminal that store neurotransmitter.
Synaptic cleft	The narrow gap between the cells that the neurotransmitter crosses.
Neurotransmitter receptors	On the postsynaptic cell. They bind the neurotransmitter and trigger a response.

What's the order of chemical synaptic transmission?

1. Calcium channels open in the presynaptic axon terminal

2. Exocytosis of neurotransmitters into synapic cleft

3. Neurotransmitters bind to receprots on the postsnyaptic membrane

4. Ion channels open in the postsynaptic membrane