MCB 244 UIUC Final Exam - Part I

What is the nervous system?

The communication and control system

What are the three main functions of the nervous system?

Collect Information

Process and Evaluate information

Initiate a response to information

How does the Nervous system collect information?

Receptors detect stimuli and send sensory signals to spinal cord and brain

How does the nervous system process and evaluate information?

brain and spinal cord determine response to sensory input

How does the nervous system initiate response to information?

brain and spinal send motor output via nerves to effectors (muscles or glands)

Definition of effectors

Muscles or glands that respond to motor neuron signals and carry out the nervous system's commands

Structural Organization of nervous system is split into what two parts with what main structures?

Central Nervous System (CNS) - Brain and Spinal Cord

Peripheral Nervous System (PNS) - Nerves and Ganglia

Central Nervous System split into what two functional organizations

Sensory

Motor

Afferent Vs Efferent

Afferent = Arriving

-Sensory

-Carries information toward the CNS

-From receptors → to brain/spinal cord

-Example: Touch, pain, temperature signals going to the brain

Efferent = Exiting

- Motor

- Carries information away from the CNS

-From brain/spinal cord → to effectors (muscles or glands)

-Example: Brain telling muscles to move

Sensory vs. Motor - which is afferent/efferent?

Sensory - afferent

Motor - efferent

What is the function of the sensory nervous system?

afferent nervous system; receives sensory information from receptors and transmits it to CNS

Sensory Nervous System subsections

Somatic & Visceral Sensory System

Somatic sensory system

detects stimuli we consciously perceive

Visceral sensory system

detects stimuli we typically do not perceive, for example, signals from the heart or kidneys

What is the function of the motor nervous system?

Initiates motor output and transmits it from CNS to effectors

Somatic motor system

sends voluntary signals from CNS to skeletal muscles

Autonomic motor system

(visceral motor) sends involuntary commands to heart,smooth muscle, and glands; has sympathetic and parasympathetic divisions

sympathetic

part of the autonomic nervous system responsible for the "fight-or-flight" response

parasympathetic

Promotes relaxation, recovery, and energy storage. "rest & Digest"

Is a nerve a neuron?

NO

A nerve

a bundle of parallel axons in the PNS

What nervous system is a nerve found in?

PNS

3 connective tissue wrappings of a nerve

Epineurium, Perineurium, Endoneurium

Epineurium

a thick layer of dense irregular connective tissue; encloses entire nerve

Perineurium

a layer of dense irregular connective tissue; wraps fascicle (bundle of axons in nerve)

Endoneurium

Delicate layer of areolar connective tissue; separates and electrically insulates each axon; wraps an individual axon

How are nerves vascularized? What two tissue parts are involved, and what is exchanged?

blood vessels branch through epineurium and perineurium to become capillaries; allow for exchange between axons and blood

Cranial nerves

extend from brain

Spinal Nerves

extend from spinal cord

Sensory nerves

contain sensory neurons sending signals to CNS

Motor nerves

contain motor neurons sending signals from CNS

Mixed nerves

contain both sensory and motor neurons, Individual axons in these nerves transmit only one type of information

Most named nerves are in what category?

Mixed Nerves

Ganglion

a cluster of neuron cell bodies in the PNS

The structural unit of nervous system

Neuron

Neuron characteristics

Excitability, Conductivity, Secretion, Extreme longevity, Amitotic

Excitability

responsiveness to a stimulus, which causes change in cell's membrane potential

Conductivity

ability to propagate electrical signal; voltage-gated channels along membrane open sequentially

Secretion

release of neurotransmitter in response to conductive activity; messenger is released from vesicle to influence target cell

Extreme longevity

cell can live throughout person's lifetime

Amitotic

After fetal development, mitotic activity is lost in most neurons

Parts of a neuron

Cell body (soma), Dendrites, Axon, Cytoskeleton

Cell body (soma)

- Contains nucleus; plasma membrane encloses cytoplasm (perikaryon)

- Initiates some graded potentials, receives others from dendrites; conducts these potentials to axon

- Contains chromatophilic substance (Nissl bodies) made of ribosomes (free and bound)

chromatophilic substance (Nissl bodies)

Within Cell Body

made of ribosomes (free and bound)

Dendrites

short, unmyelinated processes branching off cell body; receive input and transfer it to cell body

True or False:

Dendrites take messages from cell body and send them out

False

Axon

long process emanating from cell body; makes contact with other neurons, muscle cells, or glands

Axon Function

conduct action potentials and then release neurotransmitter at synaptic knobs

Parts of the Axon

axon hillock, axoplasm, axolemma, axon collaterals, telodendria, synaptic knobs, synaptic vesicles

Axon Hillock

Part where axon attaches to cell body

Cytoplasm within axon

axoplasm

Membrane within axon

axolemma

Branches of an axon

axon collaterals

Where are synaptic vesicles housed?

tips of telodendria; synaptic knobs (terminal boutons)

What do synaptic vesicles carry

Neurotransmitters

Cytoskeleton

Composed of microfilaments, intermediate filaments, microtubules

Intermediate filaments (aka Neurofilaments) functions

aggregate to form bundles, neurofibrils; provide tensile strength

Interneurons vs Mixed Nerves

Interneurons = neurons inside the CNS that connect other neurons.

Mixed Nerves = nerves with both sensory + motor axons

Neuron Transport

Axons move material to and from the cell body. Can be through fast axonal transport or slow axonal transport

2 types of Neuron transport

Anterograde transport, Retrograde transport

Anterograde transport

from cell body; moves newly synthesized material toward synaptic knobs

Retrograde transport

cell body; moves used materials from axon for breakdown and recycling in soma

Fast axonal transport (speed & fxn)

- Occurs at about 400 mm per day

- Involves movement along microtubules

- Powered by motor proteins that split ATP

- Anterograde or retrograde motion possible

Slow axonal transport (speed & fxn)

- Occurs at about 0.1 to 3 mm per day

- Results from flow of axoplasm

- Substances only moved from cell body toward knob

How are neurons classified

by number of processes coming off soma

Structural Classification of Neurons

Multipolar, Bipolar, Unipolar (pseudounipolar), Anaxonic

Most common neuron type

Multipolar

Multipolar neurons

many dendrites, one axon: most common type

Neuron type that is limited

Bipolar

Bipolar neurons

one dendrite and one axon; limited number; e.g.,: retina of the eye

Neuron that splits into two processes

Unipolar neurons (pseudounipolar)

Unipolar neurons (pseudounipolar)

one process extends from cell body; splits into two processes- peripheral process splits into several receptive dendrites, and central process leads to synaptic knobs in CNS

Neuron that has dendrites but no axons

Anaxonic

Functional Classification of Neurons

classified by the direction they propagate action potentials

Sensory, Motor, and Interneurons

What neuron conducts input from somatic and visceral receptors to CNS; and of which most are unipolar (a few bipolar) & are afferent

Sensory Neurons

What neuron conducts output from CNS to somatic and visceral effectors; all which are multipolar & are efferent

Motor Neurons

What neuron receives, processes, and integrates information from many other neurons; communicate between sensory and motor neurons; is located within CNS; makes up 99% of our neurons; generally are multipolar & are association neurons?

Interneurons

Synapse

Place where a neuron connects to another neuron or an effector

Either Electrical or Chemical

Electrical Synapse

presynaptic and postsynaptic neurons bound together by gap junctions; fast: no synaptic delay in passing electrical signal

Chemical Synapse

- Presynaptic Neuron - axon terminal produces signal

- Postsynaptic Neuron - receives signal; most commonly with one of its dendrites

Synaptic Cleft - small fluid-filled gap between the two neurons

Synaptic Delay - time it takes for all of these events

Events of Synaptic Communication

1. Neurotransmitter molecules released from vesicles of synaptic knob into cleft

2. Neurotransmitter diffuses across cleft and binds to postsynaptic receptors

3. Binding of neurotransmitter to receptor initiates postsynaptic potential (a graded potential)

Which synapse is most common? Which is faster?

Most common: Chemical

Faster: Electrical

Glial Cells (Neuroglia)

- Non-excitable, support cells found in CNS and PNS

- Approximately same number of glial cells as there are neurons; glial cells account for about half the volume of nervous system

- General characteristics: capable of mitosis; protect and nourish neurons; provide physical scaffolding for nervous tissue; guide migrating neurons during development; critical for normal function at neural synapses

Types of Glial Cells

(CNS) -> Astrocytes, Ependymal Cells, Microglia, Oligodendrocytes

(PNS) -> Satellite Cells, Neurolemmocytes (Schwann Cells)

Most abundant Glial Cell in CNS

Astrocytes

What Glial Cells form structural support, assist in neuronal development, regulate tissue fluid composition, occupy the space of dying neurons, and alter synaptic activity

Astrocytes

What Glial Cell helps form the blood-brain barrier by wrapping feet around brain capillaries (BBB controls which substances have access to brain)

Astrocytes

What Glial Cell lines cavities in the brain and spinal cord

Ependymal Cells

Where is cerebrospinal fluid (CSF) produced, and what glial cell aids this production?

Choroid Plexus, Ependymal Cells

What glial cell is small, wanders the CNS and replicate in infection, similar to the phagocytic cells of immune system; engulf infectious agents and remove debris

Microglia

What glial cell has large cells with slender extensions which wrap around axons of neurons forming myelin sheath

Oligodendrocytes

What glial cells are arranged around neuronal cell bodies in a ganglion; electrically insulate and regulate the exchange of nutrients and wastes

Satellite Cells

What glial cells are elongated, flat cells that ensheath PNS axons with myelin, which allows for faster AP propagation

Neurolemmocytes (Schwann cells)

Which glial cells are found in the CNS vs PNS?

(CNS) -> Astrocytes, Ependymal Cells, Microglia, Oligodendrocytes

(PNS) -> Satellite Cells, Neurolemmocytes (Schwann Cells)

Myelination

process of wrapping an axon with myelin

Myelin

several layers of membrane of glial cells (neurolemmocytes in PNS; oligodendrocytes in CNS); high lipid content gives it glossy-white appearance and insulates axon

Myelin in the PNS

neurolemmocyte encircles the axon and wraps it in layers forming myelin sheath; neurolemmocyte's cytoplasm and nucleus are pushed to periphery forming neurilemma

How much can a neurolemmocyte myelinate of an axon? Does this occur in PNS or CNS?

only 1 mm, thus several are needed for one axon.

PNS

neurofibril nodes (nodes of Ranvier)

gaps between neurolemmocytes

How much can an oligodendrocyte myelinate axon? Does this occur in PNS or CNS?

1 mm of multiple axons, each at multiple spots

CNS